"Chemistry. Grade 10". O.S. Gabrielyan (gdz)

Qualitative analysis of organic compounds | Detection of carbon, hydrogen and halogens

Experience 1. Detection of carbon and hydrogen in an organic compound.
Work conditions:
The device was assembled as shown in Fig. 44 textbooks. Pour a pinch of sugar and a little copper oxide (II) CuO into the test tube. They put a small cotton swab in a test tube, somewhere at the level of two-thirds of it, then poured a little anhydrous copper sulphate CuSO 4 . The test tube was closed with a cork with a gas outlet tube, so that its lower end was lowered into another test tube with calcium hydroxide Ca(OH) 2 previously poured into it. Heated the test tube in the flame of a burner. We observe the release of gas bubbles from the tube, the turbidity of the lime water and the blueness of the white CuSO 4 powder.
C 12 H 22 O 11 + 24CuO → 12CO 2 + 11H 2 O + 24Cu
Ca(OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O
CuSO 4 + 5H 2 O → CuSO 4 . 5H2O
Conclusion: The initial substance contains carbon and hydrogen, since carbon dioxide and water were obtained as a result of oxidation, and they were not contained in the CuO oxidizer.

Experience 2. Detection of halogens
Work conditions:
They took a copper wire, bent at the end with a loop with tongs, calcined it in a flame until a black coating of copper oxide (II) CuO formed. Then the cooled wire was dipped into a solution of chloroform and again brought into the flame of the burner. We observe the coloring of the flame in a bluish-green color, since copper salts color the flame.
5CuO + 2CHCl 3 \u003d 3CuCl 2 + 2CO 2 + H 2 O + 2Cu

Features of the analysis of organic compounds:

• - Reactions with organic substances proceed slowly with the formation of intermediate products.
• - Organic substances are thermolabile, charring when heated.

Pharmaceutical analysis of organic medicinal substances is based on the principles of functional and elemental analysis.

Functional analysis - analysis by functional groups, i.e. atoms, groups of atoms or reaction centers that determine the physical, chemical or pharmacological properties of drugs.

Elemental analysis is used to test the authenticity of organic medicinal substances containing sulfur, nitrogen, phosphorus, halogens, arsenic, and metals in the molecule. The atoms of these elements are found in organoelement medicinal compounds in a non-ionized state; a necessary condition for testing their authenticity is preliminary mineralization.

It can be liquid, solid and gaseous substances. Gaseous and liquid compounds mainly have a narcotic effect. The effect decreases from F - Cl - Br - I. Iodine derivatives mainly have an antiseptic effect. Communication C-F; C-I; C-Br; C-Cl is covalent, therefore, for pharmaceutical analysis, ionic reactions are used after mineralization of the substance.

The authenticity of preparations of liquid halogen derivatives of hydrocarbons is established by physical constants (boiling point, density, solubility) and by the presence of halogen. The most objective is the method of establishing the authenticity of the identity of the IR spectra of the drug and standard samples.

To prove the presence of halogens in the molecule, the Beilstein test and various mineralization methods are used.

Table 1. Properties of halogenated compounds

Chloroethyl Aethylii cloridum (INN Ethylchloride)	Fluorotan 1,1,1-trifluoro-2chloro-2-bromoethane (INN Halothane)	Bromocamphor 3-bromo-1,7,7,trimethylbicycloheptanone-2
The liquid is transparent, colorless, easily volatile, with a peculiar smell, hardly soluble in water, miscible with alcohol and ether in any ratio.	Colorless liquid, transparent, heavy, volatile, with a characteristic odor, slightly soluble in water, miscible with alcohol, ether, chloroform.	White crystalline powder or colorless crystals, odor and taste, very poorly soluble in water, easily soluble in alcohol and chloroform.
Bilignostum pro injectionibus Bilignost Bis-(2,4,6-triiodo-3-carboxyanilide) adipic acid	Bromisoval 2-bromoisovalerianil-urea
White crystalline powder, slightly bitter taste, practically insoluble in water, alcohol, chloroform.	White crystalline powder or colorless crystals with a slight specific odor, slightly soluble in water, soluble in alcohol.

Beilstein test

The presence of a halogen is proved by calcining the substance in the solid state on a copper wire. In the presence of halogens, copper halides are formed, coloring the flame green or blue-green.

The halogens in an organic molecule are bound by a covalent bond, the degree of strength of which depends on the chemical structure of the halogen derivative, therefore, different conditions are necessary for the elimination of a halogen to transfer it to an ionized state. The resulting halide ions are detected by conventional analytical reactions.

Chloroethyl

· Mineralization method - boiling with an alcohol solution of alkali (given the low boiling point, the determination is carried out with a reflux condenser).

CH 3 CH 2 Cl + KOH c KCl + C 2 H 5 OH

The resulting chloride ion is detected with a solution of silver nitrate by the formation of a white curdled precipitate.

Cl- + AgNO 3 > AgCl + NO 3 -

Fluorotan

Mineralization method - fusion with metallic sodium

F 3 C-CHClBr + 5Na + 4H 2 O> 3NaF + NaCl + 2NaBr + 2CO 2

The resulting chloride and bromide ions are detected with a solution of silver nitrate by the formation of white cheesy and yellowish precipitates.

Fluoride ion is proved by the reactions:

• - reaction with a solution of alizarin red and a solution of zirconium nitrate, in the presence of F- red color turns into light yellow;
• - interaction with soluble calcium salts (a white precipitate of calcium fluoride precipitates);
• - decolorization reaction of iron thiocyanate (red).
• When added to ftorotane conc. H 2 SO 4 , the drug is in the bottom layer.

Bromisoval

Mineralization method - boiling with alkali (alkaline hydrolysis in aqueous solution), the smell of ammonia appears:

· Heating with conc. sulfuric acid - the smell of isovaleric acid

Bromocamphor

Mineralization method by reducing mineralization method (with metallic zinc in an alkaline medium)

Bromide ion is determined by reaction with chloramine B.

Bilignost

• · Method of mineralization - heating with concentrated sulfuric acid: the appearance of violet vapors of molecular iodine is noted.
• · IR spectroscopy - 0.001% solution of the drug in 0.1 N sodium hydroxide solution in the range from 220 to 300 nm has an absorption maximum at l=236 nm.

Iodoform

• Mineralization methods:
  • 1) pyrolysis in a dry test tube, violet vapors of iodine are released
  • 4CHI 3 + 5O 2 > 6I 2 + 4CO 2 + 2H 2 O
  • 2) heating with conc. sulfuric acid
  • 2CHI 3 + H 2 SO 4 > 3I 2 + 2CO 2 + 2H 2 O + SO 3

Good quality (purity of halogenated hydrocarbons).

The good quality of chlorethyl and halothane is checked by establishing acidity or alkalinity, the absence or acceptable content of stabilizers (thymol in halothane - 0.01%), extraneous organic impurities, impurities of free chlorine (bromine in halothane), chlorides, bromides, non-volatile residue.

• 1) Chloroethyl: 1. Determine the boiling point and density,
• 2. Inadmissible admixture of ethyl alcohol (reaction of formation of iodoform)
• 2) Bilignost: 1. Heating with kH 2 SO 4 and the formation of violet vapors I 2
• 2. IR spectroscopy
• 3) Fluorotan: 1. IR spectroscopy
• 2. t boiling; density; refractive index
• 3. there should be no impurities Cl- and Br-

Quantitative determination of chlorethyl GF is not provided, but it can be performed by the method of argentometry or mercurymetry.

Method of quantitative determination - reverse argentometric titration according to Folhard after mineralization (see the reaction in the definition of authenticity).

1. Reaction before titration:

pharmaceutical drug chloroethyl titration

NaBr + AgNO 3 > AgBrv+ NaNO 3

2. Titration reaction:

AgNO 3 + NH 4 SCN > AgSCN v + NH 4 NO 3

• 3. At the equivalence point:
• 3NH 4 SCN + Fe (NH 4) (SO 4) 2>

Quantitative method - argentometric Kolthoff titration after mineralization (reactions see identification).

• 1. Reaction before titration:
• 3NH 4 SCN + Fe (NH 4) (SO 4) 2 > Fe (SCN) 3 + 2 (NH 4) 2 SO 4

exact amount brownish red

2. Titration reaction:

NaBr + AgNO 3 > AgBrv+ NaNO 3

3. At the equivalence point:

AgNO 3 + NH 4 SCN > AgSCNv + NH 4 NO 3

bleaching

Bilignost

The method of quantitative determination is indirect iodometry after oxidative cleavage of bilignost to iodate when heated with a solution of potassium permanganate in an acidic medium, excess potassium permanganate is removed with sodium nitrate, and a solution of urea is added to the mixture to remove excess nitrous acid.

The titrant is 0.1 mol/l sodium titsulphate solution, the indicator is starch, at the equivalence point, the disappearance of the blue color of starch is observed.

Reaction scheme:

t; KMnO 4 + H 2 SO 4

RI 6 > 12 IO 3 -

Substituent isolation reaction:

KIO 3 + 5KI + 3H 2 SO 4 > 3I 2 + 3K 2 SO 4 + 3H 2 O

Titration reaction:

I 2 + 2Na 2 S 2 O 3 > 2NaI + Na 2 S 4 O 6

Iodoform

The method of quantitative determination is reverse argentometric titration according to Folgard after mineralization.

Mineralization:

CHI 3 + 3AgNO 3 + H 2 O> 3AgI + 3HNO 3 + CO 2

Titration reaction:

AgNO 3 + NH 4 SCN > AgSCN v + NH 4 NO 3

At the equivalence point:

3NH 4 SCN + Fe (NH 4) (SO 4) 2 > Fe (SCN) 3 v + 2 (NH 4) 2 SO 4

Storage

Chloroethyl in ampoules in a cool, dark place, halothane and biggnost in orange glass bottles in a dry, cool, dark place. Bromocamphor is stored in orange glass bottles in a cool, dry place.

Chloroethyl is used for local anesthesia, halothane for anesthesia. Bromocamphor is used as a sedative (sometimes to stop lactation). Bromisoval is a hypnotic drug, bilignost is used as a radiopaque substance in the form of a mixture of salts in solution.

Literature

• 1. USSR State Pharmacopoeia / USSR Ministry of Health. - X ed. - M.: Medicine, 1968. - S. 78, 134, 141, 143, 186, 373.537
• 2. State Pharmacopoeia of the USSR Issue. 1. General methods of analysis. Medicinal plant materials / Ministry of Health of the USSR. - 11th ed., add. - M.: Medicine, 1989. - S. 165-180, 194-199
• 3. Lecture material.
• 4. Pharmaceutical chemistry. At 2 o'clock: textbook / V. G. Belikov - 4th ed., revised. and additional - M.: MEDpress-inform, 2007. - S. 178-179, 329-332
• 5. Guide to laboratory studies in pharmaceutical chemistry. Edited by A.P. Arzamastsev, pp. 152-156.

Appendix 1

Pharmacopoeial articles

Bilignost

Bis-(2,4,6-triiodo-3-carboxyanilide) adipic acid

C 20 H 14 I 6 N 2 O 6 M. c. 1139.8

Description. White or almost white fine crystalline powder with slightly bitter taste.

Solubility. Practically insoluble in water, 95% alcohol, ether and chloroform, easily soluble in solutions of caustic alkalis and ammonia.

Authenticity. 0.001% solution of the drug in 0.1 N. sodium hydroxide solution in the range from 220 to 300 nm has an absorption maximum at a wavelength of about 236 nm.

When 0.1 g of the drug is heated with 1 ml of concentrated sulfuric acid, violet vapors of iodine are released.

The color of the solution. 2 g of the drug is dissolved in 4 ml of 1 N. sodium hydroxide solution, filter and wash the filter with water to obtain 10 ml of the filtrate. The color of the resulting solution should not be more intense than the standard No. 4b or No. 4c.

Hydrogen peroxide test. To 1 ml of the resulting solution is added 1 ml of hydrogen peroxide; turbidity should not appear within 10-15 minutes.

Compounds with an open amino group. 1 g of the drug is shaken with 10 ml of glacial acetic acid and filtered. To 5 ml of a clear filtrate add 3 drops of 0.1 mol sodium nitrite solution. After 5 minutes, the color that appears should not be more intense than the standard No. 2g.

Acidity. 0.2 g of the drug is shaken for 1 minute with boiling water (4 times 2 ml) and filtered until a clear filtrate is obtained. Titrate the combined filtrates! 0.05 n. sodium hydroxide solution (indicator - phenolphthalein). For titration, no more than 0.1 ml of 0.05 N should be spent. sodium hydroxide solution.

Chlorides. 2 g of the drug is shaken with 20 ml of water and filtered until a clear filtrate is obtained. 5 ml of the filtrate, made up to 10 ml with water, must pass the chloride test (no more than 0.004% in the preparation).

Phosphorus. 1 g of the drug is placed in a crucible and ashed until a white residue is obtained. To the residue is added 5 ml of diluted nitric acid and evaporated to dryness, after which the residue in the crucible is mixed well with 2 ml of hot water and filtered into a test tube through a small filter. The crucible and filter are washed with 1 ml of hot water, collecting the filtrate in the same test tube, then 3 ml of ammonium molybdate solution are added and left for 15 minutes in a bath at a temperature of 38--40 °. The test solution may have a yellowish color, but should remain transparent (not more than 0.0001% in the preparation).

Iodine monochloride. 0.2 g of the drug is shaken with 20 ml of water and filtered until a clear filtrate is obtained. To 10 ml of the filtrate add 0.5 g of potassium iodide, 2 ml of hydrochloric acid and 1 ml of chloroform. The chloroform layer should remain colorless.

Iron. 0.5 g of the drug must pass the iron test (no more than 0.02% in the drug). The comparison is made with a standard prepared from 3.5 ml of standard solution B and 6.5 ml of water.

Sulphated ash from 1 g of the drug should not exceed 0.1%.

Heavy metals. Sulphated ash from 0.5 g of the preparation must pass the test for heavy metals (not more than 0.001% in the preparation).

Arsenic. 0.5 g of the preparation must pass the test for arsenic (not more than 0.0001% in the preparation).

Quantitation. About 0.3 g of the drug (accurately weighed) is placed in a 100 ml volumetric flask, dissolved in 5 ml of sodium hydroxide solution, topped up with water to the mark and mixed. 10 ml of the resulting solution is placed in a flask with a capacity of 250 ml, 5 ml of a 5% potassium permanganate solution is added and 10 ml of concentrated sulfuric acid, 0.5--1 ml, are carefully added along the walls of the flask, with stirring, and left for 10 minutes. Then add slowly, 1 drop every 2-3 seconds, with vigorous stirring. sodium nitrite solution until the liquid becomes colorless and the manganese dioxide dissolves. After that, immediately add 10 ml of a 10% urea solution and stir until the bubbles completely disappear, while washing off sodium nitrite from the walls of the flask. Then 100 ml of water, 10 ml of a freshly prepared potassium iodide solution are added to the solution, and the released iodine is titrated with 0.1 N. sodium thiosulfate solution (indicator - starch).

1 ml 0.1 n. sodium thiosulfate solution corresponds to 0.003166 g C 20 H 14 l 6 N 2 0 6 , which should be at least 99.0% in the preparation.

Storage. List B. In orange glass jars, protected from light.

Radiopaque agent.

Iodoform

Triiodomethane

CHI 3 M.v. 393.73

Description. Small lamellar shiny crystals or fine-crystalline powder of lemon-yellow color, sharp characteristic persistent odor. Volatile already at ordinary temperature, distilled with water vapor. Solutions of the drug quickly decompose from the action of light and air with the release of iodine.

Solubility. Practically insoluble in water, sparingly soluble in alcohol, soluble in ether and chloroform, slightly soluble in glycerin. fatty and essential oils.

Authenticity, 0.1 g of the drug is heated in a test tube on a burner flame; purple vapors of iodine are released.

Melting point 116--120° (with decomposition).

Coloring substances. 5 g of the drug is vigorously shaken for 1 minute with 50 ml of water and filtered. The filtrate should be colorless.

acidity or alkalinity. To 10 ml of the filtrate add 2 drops of bromthymol blue solution. The yellow-green color that appears should turn blue from the addition of no more than 0.1 ml of 0.1 N. sodium hydroxide solution or yellow from the addition of not more than 0.05 ml of 0.1 n. hydrochloric acid solution.

Halogens. 5 ml of the same filtrate, diluted with water to 10 ml, must pass the chloride test (no more than 0.004% in the preparation).

sulfates. 10 ml of the same filtrate must pass the sulfate test (not more than 0.01% in the preparation).

Ash from 0.5 g of the drug should not exceed 0.1%.

Quantitation. About 0.2 g of the drug (accurately weighed) is placed in a conical flask with a capacity of 250--300 ml, dissolved in 25 or 95% alcohol, 25 ml of 0.1 n. silver nitrate solution, 10 ml of nitric acid and heated under reflux on a water bath for 30 minutes, protecting the reaction flask from light. The refrigerator is washed with water, 100 ml of water is added to the flask and the excess of silver nitrate is titrated with 0.1 N. ammonium thiocyanate solution (indicator - iron ammonium alum).

In parallel, conduct a control experiment.

1 ml 0.1 n. silver nitrate solution corresponds to 0.01312 g of CHI 3 , which should be at least 99.0% in the preparation.

Storage. In a well-closed container, protected from light, in a cool place.

Qualitative analysis. Purpose, possible methods. Qualitative chemical analysis of inorganic and organic substances

Qualitative analysis has its own purpose detection of certain substances or their components in the analyzed object. Detection is carried out by identification substances, that is, establishing the identity (sameness) of the AS of the analyzed object and the known AS of the determined substances under the conditions of the applied method of analysis. To do this, this method preliminarily examines reference substances (Section 2.1), in which the presence of the substances to be determined is known. For example, it was found that the presence of a spectral line with a wavelength of 350.11 nm in the emission spectrum of the alloy, when the spectrum is excited by an electric arc, indicates the presence of barium in the alloy; the blueness of an aqueous solution when starch is added to it is an AC for the presence of I 2 in it and vice versa.

Qualitative analysis always precedes quantitative.

At present, qualitative analysis is performed by instrumental methods: spectral, chromatographic, electrochemical, etc. Chemical methods are used at certain instrumental stages (sample opening, separation and concentration, etc.), but sometimes using chemical analysis, you can get results more simply and quickly, for example, to establish the presence of double and triple bonds in unsaturated hydrocarbons by passing them through bromine water or an aqueous solution of KMnO 4 . In this case, the solutions lose their color.

A detailed qualitative chemical analysis makes it possible to determine the elemental (atomic), ionic, molecular (material), functional, structural and phase compositions of inorganic and organic substances.

In the analysis of inorganic substances, elemental and ionic analyzes are of primary importance, since knowledge of the elemental and ionic composition is sufficient to establish the material composition of inorganic substances. The properties of organic substances are determined by their elemental composition, but also by their structure, the presence of various functional groups. Therefore, the analysis of organic substances has its own specifics.

Qualitative chemical analysis is based on a system of chemical reactions characteristic of a given substance - separation, separation and detection.

The following requirements apply to chemical reactions in qualitative analysis.

1. The reaction should proceed almost instantly.

2. The reaction must be irreversible.

3. The reaction must be accompanied by an external effect (AS):

a) a change in the color of the solution;

b) the formation or dissolution of a precipitate;

c) release of gaseous substances;

d) flame coloring, etc.

4. The reaction should be sensitive and, if possible, specific.

Reactions that make it possible to obtain an external effect with an analyte are called analytical , and the substance added for this - reagent . Analytical reactions carried out between solids are referred to as " dry way ", and in solutions -" wet way ».

The “dry route” reactions include reactions carried out by grinding a solid test substance with a solid reagent, as well as by obtaining colored glasses (pearls) by fusing certain elements with borax.

Much more often, the analysis is carried out "wet way", for which the analyte is transferred into solution. Reactions with solutions can be performed test tube, drip and microcrystalline methods. In test-tube semi-microanalysis, it is performed in test tubes with a capacity of 2-5 cm 3 . To separate the precipitates, centrifugation is used, and evaporation is carried out in porcelain cups or crucibles. Drop analysis (N.A. Tananaev, 1920) is carried out on porcelain plates or strips of filtered paper, obtaining color reactions by adding one drop of a reagent solution to one drop of a solution of a substance. Microcrystalline analysis is based on the detection of components through reactions that form compounds with a characteristic color and shape of crystals observed under a microscope.

For qualitative chemical analysis, all known types of reactions are used: acid-base, redox, precipitation, complex formation, and others.

Qualitative analysis of solutions of inorganic substances is reduced to the detection of cations and anions. For this use general and private reactions. General reactions give a similar external effect (AC) with many ions (for example, the formation of precipitates of sulfates, carbonates, phosphates, etc. by cations), and private reactions with 2-5 ions. The fewer ions give a similar AS, the more selective (selective) the reaction is considered. The reaction is called specific when it allows one ion to be detected in the presence of all the others. Specific, for example, to the ammonium ion is the reaction:

NH 4 Cl + KOH  NH 3  + KCl + H 2 O

Ammonia is detected by smell or by the blue color of a red litmus paper soaked in water and placed over a test tube.

The selectivity of reactions can be increased by changing their conditions (pH) or by applying masking. masking is to reduce the concentration of interfering ions in the solution below the limit of their detection, for example, by binding them into colorless complexes.

If the composition of the analyzed solution is simple, then it is analyzed after masking fractional way. It consists in the detection of one ion in any sequence in the presence of all the others with the help of specific reactions that are carried out in separate portions of the analyzed solution. Since there are few specific reactions, when analyzing a complex ionic mixture, one uses systematic way. This method is based on separating a mixture into groups of ions with similar chemical properties by converting them into precipitates using group reagents, and the group reagents act on the same portion of the analyzed solution according to a certain system, in a strictly defined sequence. Precipitates are separated from each other (for example, by centrifugation), then dissolved in a certain way and a series of solutions is obtained, which makes it possible to detect an individual ion in each by a specific reaction to it.

There are several systematic methods of analysis, named after the group reagents used: hydrogen sulfide, acid-base, ammonia-phosphate other. The classical hydrogen sulfide method is based on the separation of cations into 5 groups by obtaining their sulfides or sulfur compounds when exposed to H 2 S, (NH 4) 2 S, NaS under various conditions.

More widely used, accessible and safe is the acid-base method, in which cations are divided into 6 groups (Table 1.3.1.). The group number indicates the sequence of exposure to the reagent.

Table 1.3.1

Classification of cations according to the acid-base method

Group number		Group reagent	Solubility of compounds
	Ag + , Pb 2+ , Hg 2 2+		Chlorides are insoluble in water
	Ca2+, Sr2+, Ba2+		Sulfates are insoluble in water
	Zn 2+ , Al 3+ , Cr 3+ , Sn 2+ , Si 4+ , ​​As		Hydroxides are amphoteric, soluble in excess alkali
	Mg 2+ , Mn 2+ , Fe 2+ , Fe 3+ , Bi 3+ , Sb 3+ , Sb 5+		Hydroxides are insoluble in excess NaOH or NH 3
Group number		Group reagent	Solubility of compounds
	Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Hg 2+		Hydroxides dissolve in excess NH 3 with the formation of complex compounds
	Na + , K + , NH 4 +		Chlorides, sulfates, hydroxides are soluble in water

Anions in the analysis basically do not interfere with each other, therefore, group reagents are used not for separation, but to check the presence or absence of a particular group of anions. There is no consistent classification of anions into groups.

In the simplest way, they can be divided into two groups with respect to the Ba 2+ ion:

a) giving highly soluble compounds in water: Cl - , Br - , I - , CN - , SCN - , S 2- , NO 2 2- , NO 3 3- , MnO 4- , CH 3 COO - , ClO 4 - , ClO 3 - , ClO - ;

b) giving poorly soluble compounds in water: F -, CO 3 2-, CsO 4 2-, SO 3 2-, S 2 O 3 2-, SO 4 2-, S 2 O 8 2-, SiO 3 2-, CrO 4 2-, PO 4 3-, AsO 4 3-, AsO 3 3-.

Qualitative chemical analysis of organic substances is divided into elemental , functional , structural and molecular .

The analysis begins with preliminary tests of organic matter. For solids, measure t melt. , for liquid - t kip or , refractive index. The molar mass is determined by lowering t frozen or increasing t bale, that is, by cryoscopic or ebullioscopic methods. An important characteristic is solubility, on the basis of which there are classification schemes for organic substances. For example, if a substance does not dissolve in H 2 O, but dissolves in a 5% NaOH or NaHCO 3 solution, then it belongs to a group of substances that includes strong organic acids, carboxylic acids with more than six carbon atoms, phenols with substituents in ortho and para positions, -diketones.

Table 1.3.2

Reactions for the identification of organic compounds

Connection type	Functional group involved in the reaction
Aldehyde		a) 2,4 - dinitrophenylhydrozide b) hydroxylamine hydrochloride c) sodium hydrogen sulfate
		a) nitrous acid b) benzenesulfonyl chloride
aromatic hydrocarbon		Azoxybenzene and aluminum chloride
		See aldehyde
unsaturated hydrocarbon	C \u003d C - - C ≡ C -	a) KMnO 4 solution b) Br 2 solution in CCL 4
Nitro compound		a) Fe (OH) 2 (Mohr's salt + KOH) b) zinc dust + NH 4 Cl c) 20% NaOH solution
		a) (NH 4) 2 b) ZnCl 2 solution in HCl c) iodic acid
		a) FeCl 3 in pyridine b) bromine water
Ether is simple		a) hydroiodic acid b) bromine water
Ether complex		a) NaOH (or KOH) solution b) hydroxylamine hydrochloride

Elemental analysis detects elements included in the molecules of organic substances (C, H, O, N, S, P, Cl, etc.). In most cases, the organic matter is decomposed, the decomposition products are dissolved, and the elements in the resulting solution are determined as in inorganic substances. For example, when nitrogen is detected, the sample is fused with potassium metal to form KCN, which is treated with FeSO 4 and converted to K 4 . By adding to the latter a solution of Fe 3+ ions, Prussian blue Fe 4 3 - (AC for the presence of N) is obtained.

Functional analysis determines the type of functional group. For example, a reaction with (NH 4) 2 can detect alcohol, and with a KMnO 4 solution, primary, secondary and tertiary alcohols can be distinguished. Primary KMnO 4 oxidizes to aldehydes, discoloring, secondary oxidizes to ketones, forming MnO 2, and does not react with tertiary ones (Table 1.3.2).

Structural analysis establishes the structural formula of an organic substance or its individual structural elements (double and triple bonds, cycles, and so on).

Molecular analysis establishes the entire substance. For example, phenol can be detected by reaction with FeCl 3 in pyridine. More often, molecular analysis is reduced to establishing the complete composition of a compound on the basis of data on the elemental, functional, and structural composition of the substance. At present, molecular analysis is carried out mainly by instrumental methods.

When calculating the results of the analysis, it is necessary to perform the calculations very carefully. A mathematical error made in numerical values ​​is tantamount to an error in analysis.

Numerical values ​​are divided into exact and approximate. Accurate, for example, can include the number of analyzes performed, the serial number of the element in the periodic table, approximate - the measured values ​​of mass or volume.

Significant digits of an approximate number are all its digits, except for zeros to the left of the decimal point and zeros to the right after the decimal point. Zeros in the middle of a number are significant. For example, in the number 427.205 - 6 significant digits; 0.00365 - 3 significant figures; 244.00 - 3 significant figures.

The accuracy of calculations is determined by GOST, OST or TU for analysis. If the calculation error is not specified in advance, then it should be borne in mind that that the concentration is calculated up to the 4th significant figure after the decimal point, the mass - up to the 4th decimal place after the decimal point, the mass fraction (percentage) - up to hundredths.

Each analysis result cannot be more accurate than the measuring instruments allow (therefore, in the mass expressed in grams, there cannot be more than 4-5 decimal places, i.e. more than the accuracy of the analytical balance 10 -4 -10 -5 g) .

Extra numbers are rounded off according to the following rules.

1. The last digit, if it is  4, is discarded, if  5, add one to the previous one, if it is 5, and there is an even number in front of it, then add one to the previous one, and if odd, then subtract (for example, 12.465  12, 46; 12.475  12.48).

2. In sums and differences of approximate numbers, as many decimal places are retained as there were in the number with the smallest number of them, and when dividing and multiplying, as much as is required for a given measurand (for example, when calculating mass using the formula

Although V is measured to hundredths, the result should be calculated to 10 -4 -10 -5 g).

3. When raising to a power, as a result, take as many significant digits as there were in the number being raised to a power.

4. In intermediate results, take one decimal digit more than according to the rounding rules, and to evaluate the order of calculations, round all numbers to the first digit.

Mathematical processing of analysis results

At any of the listed stages of quantitative analysis, errors can be made and, as a rule, errors are allowed, therefore, the fewer stages the analysis has, the more accurate its results.

error measurement refers to the deviation of the measurement result x i from the true value of the measured quantity .

Difference х i -  =∆х i called absolute error , and attitude (∆х i /)100% called relative error .

The errors of the results of quantitative analysis are divided into gross (misses), systematic and random . Based on them, the quality of the obtained analysis results is assessed. Quality parameters are their right, accuracy, reproducibility and reliability.

The result of the analysis is considered right , if it has no gross and systematic error, and if, in addition, the random error is minimized, then accurate, corresponding to the truth. To obtain accurate measurement results, quantitative determinations are repeated several times (usually odd).

Gross errors ( misses) are those that lead to a sharp difference in the result of a repeated measurement from the rest. The causes of misses are gross operational errors of the analyst (for example, the loss of part of the sediment during its filtering or weighing, incorrect calculation or recording of the result). Misses are identified among a series of repeated measurements, usually using Q-criteria. To calculate it, the results are arranged in a row in ascending order: x 1, x 2, x 3,…x n-1, x n. Doubtful is usually the first or last result in this series.

The Q-criterion is calculated as the ratio of the absolute value of the difference between the questionable result and the one closest to it in the series to the difference between the last and the first in the series. Difference x n- x 1 called range of variation.

For example, if the last result in a row is doubtful, then

To identify a miss, the Q calculated for it is compared with the tabular critical value Q table given in analytical reference books. If Q  Q table, then the questionable result is excluded from consideration, considering it a miss. Mistakes must be identified and corrected.

Systematic errors are those that lead to a deviation of the results of repeated measurements by the same positive or negative value from the true value. They can be caused by incorrect calibration of measuring devices and instruments, impurities in the reagents used, incorrect actions (for example, choosing an indicator) or the individual characteristics of the analyst (for example, vision). Systematic errors can and should be eliminated. For this use:

1) obtaining the results of quantitative analysis by several methods different in nature;

2) development of the analysis methodology on standard samples, i.e. materials, the content of analytes, in which is known with high accuracy;

3) the method of additions (the "introduced-found" method).

Random errors - these are those that lead to insignificant deviations of the results of repeated measurements from the true value for reasons whose occurrence cannot be clarified and taken into account (for example, voltage fluctuations in the mains, the analyst's mood, etc.). Random errors cause scatter in the results of repeated determinations carried out under identical conditions. Scatter determines reproducibility results, i.e. obtaining the same or similar results with repeated determinations. The quantitative characteristic of reproducibility is standard deviation S, which is found by methods of mathematical statistics. For a small number of measurements (small sample) with n=1-10

elective call the set of results of repeated measurements. The results themselves are called sampling options . The totality of the results of an infinitely large number of measurements (in titration n30) called the general sample , and the standard deviation calculated from it is denoted by . The standard deviation S() shows by what average value the results of n measurements deviate from the average result x or true.

Practical work No. 1

Reagents : paraffin (C 14 H 30

Equipment :

Note:

2. The halogen in organic matter can be detected by the flame color reaction.

Work algorithm:

Pour lime water into the receiver tube.

Connect the test tube with the mixture to the test tube with a gas outlet tube with a stopper.

Heat the test tube with the mixture in the flame of an alcohol lamp.

Ignite the copper wire in the flame of an alcohol lamp until a black coating appears on it.

Bring the cooled wire into the test substance and again bring the spirit lamp into the flame.

Conclusion:

pay attention to: changes occurring with lime water, copper sulfate (2).

What color does the flame of the spirit lamp turn into when the test solution is added?

Practical work No. 1

"Qualitative analysis of organic compounds".

Reagents: paraffin (C 14 H 30 ), lime water, copper oxide (2), dichloroethane, copper sulfate (2).

Equipment : metal stand with foot, spirit lamp, 2 test tubes, cork with gas tube, copper wire.

Note:

carbon and hydrogen can be detected in organic matter by its oxidation with copper oxide (2).

halogen in organic matter can be detected using a flame color reaction.

Work algorithm:

1st stage of work: Melting of paraffin with copper oxide

1. Assemble the device according to fig. 44 on page 284, for this, place 1-2 g of copper oxide and paraffin in the bottom of the test tube, heat it up.

2nd stage of work: Qualitative determination of carbon.

1. Pour lime water into the receiver tube.

2. Connect the test tube with the mixture to the test tube with a gas outlet tube with a stopper.

3.Heat the test tube with the mixture in the flame of an alcohol lamp.

3rd stage of work: Qualitative determination of hydrogen.

1. In the upper part of the test tube with the mixture, place a piece of cotton wool, putting copper sulfate (2) on it.

4th stage of work: Qualitative determination of chlorine.

1. Ignite the copper wire in the flame of an alcohol lamp until a black coating appears on it.

2. Insert the cooled wire into the test substance and again bring the spirit lamp into the flame.

Conclusion:

1. pay attention to: changes occurring with lime water, copper sulfate (2).

2. What color is the flame of the spirit lamp colored when the test solution is added.

The study of organic matter begins with its isolation and purification.

1. Precipitation

precipitation- separation of one of the compounds of a gas or liquid mixture of substances into a precipitate, crystalline or amorphous. The method is based on changing the solvation conditions. The effect of solvation can be greatly reduced and a solid can be isolated in its pure form by several methods.

One of them is that the final (often said - target) product is converted into a salt-like compound (simple or complex salt), if only it is capable of acid-base interaction or complex formation. So, for example, amines can be converted into substituted ammonium salts:

(CH 3) 2 NH + HCl -> [(CH 3) 2 NH 2] + Cl -,

and carboxylic, sulfonic, phosphonic and other acids - in salt by the action of the corresponding alkalis:

CH 3 COOH + NaOH -> CH 3 COO - Na + + H 2 O;

2CH 3 SO 2 OH + Ba (OH) 2 -> Ba 2+ (CH 3 SO 2 O) 2 - + H 2 O;

CH 3 P (OH) 2 O + 2AgOH -> Ag (CH 3 PO 3) 2– + 2H 2 O.

Salts as ionic compounds dissolve only in polar solvents (H 2 O, ROH, RCOOH, etc.). The better such solvents enter into donor-acceptor interactions with salt cations and anions, the greater the energy released during solvation, and the higher solubility. In non-polar solvents, such as hydrocarbons, petroleum ether (light gasoline), CHCl 3 , CCl 4 , etc., salts do not dissolve and crystallize (salt out) when these or similar solvents are added to a solution of salt-like compounds. From salts, the corresponding bases or acids can be easily isolated in pure form.

Aldehydes and ketones of non-aromatic nature, by adding sodium hydrosulfite, crystallize from aqueous solutions in the form of sparingly soluble compounds.

For example, acetone (CH 3) 2 CO crystallizes from aqueous solutions with sodium hydrosulfite NaHSO 3 in the form of a sparingly soluble hydrosulfite derivative:

Aldehydes easily condense with hydroxylamine to release a water molecule:

The resulting products are called oximes They are liquids or solids. Oximes are weakly acidic in nature, manifested in the fact that the hydrogen of the hydroxyl group can be replaced by a metal, and at the same time - weakly basic in nature, because oximes combine with acids, forming salts such as ammonium salts.

When boiled with dilute acids, hydrolysis occurs, while the aldehyde is released and the hydroxylamine salt is formed:

Thus, hydroxylamine is an important reagent that makes it possible to isolate aldehydes in the form of oximes from mixtures with other substances with which hydroxylamine does not react. Oximes can also be used to purify aldehydes.

Like hydroxylamine, hydrazine H 2 N–NH 2 reacts with aldehydes; but since there are two NH 2 groups in the hydrazine molecule, it can react with two aldehyde molecules. the product of substitution of one hydrogen atom in a hydrazine molecule by a phenyl group C 6 H 5:

The reaction products of aldehydes with phenylhydrazine are called phenylhydrazones.Phenylhydrazones are liquid and solid, they crystallize well. When boiled with dilute acids, like oximes, they undergo hydrolysis, as a result of which a free aldehyde and a phenylhydrazine salt are formed:

Thus, phenylhydrazine, like hydroxylamine, can serve to isolate and purify aldehydes.

Sometimes another hydrazine derivative is used for this purpose, in which the hydrogen atom is replaced not by a phenyl group, but by an H 2 N–CO group. Such a hydrazine derivative is called NH 2 –NH–CO–NH 2 semicarbazide. The condensation products of aldehydes with semicarbazide are called semicarbazones:

Ketones also readily condense with hydroxylamine to form ketoximes:

With phenylhydrazine, ketones give phenylhydrazones:

and with semicarbazide - semicarbazones:

Therefore, hydroxylamine, phenylhydrazine, and semicarbazide are used for the isolation of ketones from mixtures and for their purification to the same extent as for the isolation and purification of aldehydes. Of course, it is impossible to separate aldehydes from ketones by this method.

Alkynes with a terminal triple bond interact with an ammonia solution of Ag 2 O and are isolated in the form of silver alkynides, for example:

2(OH) - + HC=CH -> Ag–C=C–Ag + 4NH 3 + 2H 2 O.

The starting aldehydes, ketones, and alkynes can be easily isolated from poorly soluble substitution products in pure form.

2. Crystallization

Crystallization methods separation of mixtures and deep purification of substances are based on the difference in the composition of the phases formed during the partial crystallization of the melt, solution, gas phase. An important characteristic of these methods is the equilibrium, or thermodynamic, separation factor, equal to the ratio of the concentrations of the components in the equilibrium phases - solid and liquid (or gas):

where x and y are the mole fractions of the component in the solid and liquid (or gas) phases, respectively. If a x<< 1, т.е. разделяемый компонент является примесью, k 0 = x / y. In real conditions, equilibrium is usually not reached; the degree of separation in a single crystallization is called the effective separation factor k, which is always less k 0 .

There are several crystallization methods.

When separating mixtures by the method directional crystallization the container with the initial solution slowly moves from the heating zone to the cooling zone. Crystallization occurs at the boundary of the zones, the front of which moves at the speed of the container.

To separate components with similar properties, it is used zone melting ingots cleaned of impurities in an elongated container, slowly moving along one or more heaters. The section of the ingot in the heating zone melts, and crystallizes again at the exit from it. materials (Ge, Si, etc.).

Countercurrent column crystallization is produced in a column, in the upper part of which there is a cooling zone, where crystals form, and in the lower part there is a heating zone, where the crystals melt. The crystals in the column are moved by gravity or using, for example, a screw in the direction opposite to the movement of the liquid It is characterized by high productivity and high yield of purified products. It is used in the production of pure naphthalene, benzoic acid, caprolactam, fatty acid fractions, etc.

To separate mixtures, dry and purify substances in the solid-gas system, sublimation (sublimation) and desublimation.

Sublimation is characterized by a large difference in equilibrium conditions for different substances, which makes it possible to separate multicomponent systems, in particular, when obtaining substances of high purity.

3. Extraction

Extraction- a separation method based on the selective extraction of one or more components of the analyzed mixture using organic solvents - extractants. As a rule, extraction is understood as the process of distributing a solute between two immiscible liquid phases, although in the general case one of the phases can be solid (extraction from solids) or gaseous. Therefore, the more accurate name of the method is liquid-liquid extraction, or simply liquid extraction.Usually in analytical chemistry, the extraction of substances from an aqueous solution using organic solvents is used.

The distribution of substance X between the aqueous and organic phases under equilibrium conditions obeys the distribution equilibrium law. The constant of this equilibrium, expressed as the ratio between the concentrations of substances in two phases:

K= [X] org / [X] water,

at a given temperature there is a constant value, depending only on the nature of the substance and both solvents. This value is called distribution constant.Approximately, it can be estimated from the ratio of the solubility of the substance in each of the solvents.

The phase into which the extractable component passes after liquid extraction is called extract; the phase depleted of this component, raffinate.

In industry, countercurrent multistage extraction is most common. The required number of separation stages is usually 5–10, and for difficult-to-separate compounds, up to 50–60. The process includes a number of typical and special operations. impurities and removal of the mechanically entrapped stock solution) and re-extraction, i.e., the return of the extracted compound to the aqueous phase for the purpose of its further processing in an aqueous solution or re-extraction purification. Special operations are associated, for example, with a change in the oxidation state of the separated components.

Single-stage liquid extraction, effective only at a very high value of the distribution constant K are used primarily for analytical purposes.

Apparatus for liquid extraction - extractors- can be with continuous (columns) or stepped (mixer-settlers) phase contact.

Since during the extraction it is necessary to intensively mix two immiscible liquids, the following types of columns are mainly used: pulsating (with reciprocating motion of liquid), vibrating (with a vibrating plate pack), rotary disk (with a pack of disks rotating on a common shaft), etc. d.

Each stage of the mixer-settler has a mixing and settling chamber. Mixing can be mechanical (mixers) or pulsating; multistage is achieved by connecting the required number of sections into a cascade. Sections can be assembled in a common housing (box extractors). Mixer-settlers have an advantage over columns in processes with a small number of stages or with very large liquid flows. Centrifugal apparatuses are promising for processing large flows.

The advantages of liquid extraction are low energy costs (there are no phase transitions that require energy supply from outside); the possibility of obtaining highly pure substances; full automation of the process.

Liquid extraction is used, for example, to isolate light aromatic hydrocarbons from petroleum feedstocks.

Extraction of a substance with a solvent from the solid phase often used in organic chemistry to extract natural compounds from biological objects: chlorophyll from a green leaf, caffeine from coffee or tea mass, alkaloids from plant materials, etc.

4. Distillation and rectification

Distillation and rectification are the most important methods for separating and purifying liquid mixtures, based on the difference in the composition of the liquid and the vapor formed from it.

The distribution of mixture components between liquid and vapor is determined by the relative volatility α:

aik= (yi/ xi) : (yk / xk),

where xi and xk,yi and yk are the mole fractions of the components i and k respectively in the liquid and the vapor formed from it.

For a solution consisting of two components,

where x and y are the mole fractions of the volatile component in liquid and vapor, respectively.

Distillation(distillation) is carried out by partial evaporation of the liquid and subsequent condensation of the vapor. As a result of distillation, the distilled fraction is distillate- is enriched in a more volatile (low-boiling) component, and the non-distilled liquid - VAT residue- less volatile (high-boiling). Distillation is called simple if one fraction is distilled off from the initial mixture, and fractional (fractional) if several fractions are distilled off.

Distinguish between conventional and molecular distillation. conventional distillation are carried out at such pressures when the mean free path of molecules is many times less than the distance between the surfaces of liquid evaporation and vapor condensation. Molecular distillation carried out at very low pressure (10 -3 - 10 -4 mm Hg), when the distance between the surfaces of liquid evaporation and vapor condensation is commensurate with the free path of molecules.

Conventional distillation is used to purify liquids from low-volatile impurities and to separate mixtures of components that differ significantly in relative volatility. Molecular distillation is used to separate and purify mixtures of low-volatile and thermally unstable substances, for example, when isolating vitamins from fish oil, vegetable oils.

If the relative volatility α is low (low-boiling components), then the separation of mixtures is carried out by the rectification method. Rectification- separation of liquid mixtures into practically pure components or fractions that differ in boiling points. For rectification, column apparatuses are usually used, in which part of the condensate (phlegm) is returned for irrigation to the upper part of the column. In this case, multiple contact is made between the flows of the liquid and vapor phases. The driving force of rectification is the difference between the actual and equilibrium concentrations of the components in the vapor phase, corresponding to given composition of the liquid phase. The vapor-liquid system strives to achieve an equilibrium state, as a result of which the vapor upon contact with the liquid is enriched with volatile (low-boiling) components, and the liquid is enriched with low-volatile (high-boiling) components. Since the liquid and vapor move towards each other (countercurrent), with sufficient the height of the column in its upper part, almost pure volatile component can be obtained.

Rectification can be carried out at atmospheric or elevated pressure, as well as under vacuum conditions. At reduced pressure, the boiling point decreases and the relative volatility of the components increases, which reduces the height of the distillation column and makes it possible to separate mixtures of thermally unstable substances.

According to their design, distillation apparatuses are subdivided into packed, dish-shaped and rotary film.

Rectification is widely used in industry for the production of gasoline, kerosene (oil rectification), oxygen and nitrogen (low-temperature air rectification), for the isolation and deep purification of individual substances (ethanol, benzene, etc.).

Since organic substances are mainly thermally unstable, as a rule, they are used for deep purification. packed distillation columns, operating in vacuum. Sometimes, to obtain highly pure organic substances, rotary-film columns are used, which have very low hydraulic resistance and a short residence time of the product in them. As a rule, rectification in this case is carried out in a vacuum.

Rectification is widely used in laboratory practice for deep purification of substances. Note that distillation and rectification serve at the same time to determine the boiling point of the substance under study, and, therefore, make it possible to verify the degree of purity of the latter (constancy of the boiling point). For this purpose, they use also special devices - ebulliometers.

5. Chromatography

Chromatography is a method of separation, analysis and physico-chemical study of substances. It is based on the difference in the speeds of movement of the concentration zones of the studied components, which move in the flow of the mobile phase (eluent) along the stationary layer, and the studied compounds are distributed between both phases.

At the heart of all the diverse methods of chromatography, which were initiated by M.S. Tsvet in 1903, is adsorption from the gas or liquid phase on a solid or liquid interface.

In organic chemistry, the following types of chromatography are widely used for the purpose of separation, purification and identification of substances: column (adsorption); paper (distribution), thin-layer (on a special plate), gas, liquid and gas-liquid.

In these varieties of chromatography, two phases come into contact - one is immobile, adsorbing and desorbing the analyte, and the other is mobile, acting as a carrier of this substance.

Usually the stationary phase is a sorbent with a developed surface; mobile phase - gas (gas chromatography) or liquid (liquid chromatography).The flow of the mobile phase is filtered through the sorbent layer or moves along this layer. gas liquid chromatography the mobile phase is a gas, and the stationary phase is a liquid deposited usually on a solid carrier.

Gel permeation chromatography is a variant of liquid chromatography in which the stationary phase is a gel. (The method allows the separation of macromolecular compounds and biopolymers in a wide range of molecular weights.) The difference in the equilibrium or kinetic distribution of components between the mobile and stationary phases is a necessary condition for their chromatographic separation.

Depending on the purpose of the chromatographic process, analytical and preparative chromatography are distinguished. Analytical is designed to determine the qualitative and quantitative composition of the mixture under study.

Chromatography is usually carried out using special instruments - chromatographs, the main parts of which are the chromatographic column and the detector. At the moment of sample injection, the analyzed mixture is located at the beginning of the chromatographic column. Under the action of the mobile phase flow, the components of the mixture begin to move along the column at different speeds, and the well-sorbed components move more slowly along the sorbent layer. Detector at the exit from the column automatically continuously determines the concentrations of the separated compounds in the mobile phase. The detector signal is usually recorded by a chart recorder. The resulting diagram is called chromatogram.

Preparative chromatography includes the development and application of chromatographic methods and equipment for obtaining highly pure substances containing no more than 0.1% impurities.

A feature of preparative chromatography is the use of chromatographic columns with a large internal diameter and special devices for the isolation and collection of components. kilograms. Unique industrial devices with columns 0.5 m in diameter have been created to produce several tons of the substance annually.

Substance losses in preparative columns are low, which allows preparative chromatography to be widely used to separate small amounts of complex synthetic and natural mixtures. Gas preparative chromatography used to produce highly pure hydrocarbons, alcohols, carboxylic acids and other organic compounds, including chlorine compounds; liquid- for the production of drugs, polymers with a narrow molecular weight distribution, amino acids, proteins, etc.

Some studies state that the cost of high-purity products obtained by chromatography is lower than those purified by distillation. Therefore, it is advisable to use chromatography for fine purification of substances previously separated by distillation.

2.Elemental qualitative analysis

Qualitative elemental analysis is a set of methods that allow you to establish what elements an organic compound consists of. To determine the elemental composition, organic matter is first converted into inorganic compounds by oxidation or mineralization (fusion with alkali metals), which are then examined by conventional analytical methods.

The great achievement of A. L. Lavoisier as an analytical chemist was the creation elemental analysis of organic substances(the so-called CH-analysis). By this time, there were already numerous methods for the gravimetric analysis of inorganic substances (metals, minerals, etc.), but they still did not know how to analyze organic substances in this way. The analytical chemistry of that time was clearly "limping on one leg"; Unfortunately, the relative lag behind the analysis of organic compounds, and especially the lag behind the theory of such an analysis, is felt even today.

Dealing with the problems of organic analysis, A. L. Lavoisier, first of all, showed that all organic substances contain oxygen and hydrogen, many contain nitrogen, and some contain sulfur, phosphorus or other elements. Now it was necessary to create universal methods quantitative determination of these elements, primarily methods for the accurate determination of carbon and hydrogen. To achieve this goal, A. L. Lavoisier proposed burning weighed portions of the test substance and determining the amount of carbon dioxide released (Fig. 1). At the same time, he was based on two of his observations: 1) carbon dioxide is formed during the combustion of any organic matter; 2) carbon dioxide is not contained in the initial substances, it is formed from carbon, which is part of any organic substance. The first objects of analysis were volatile organic substances - individual compounds such as ethanol.

Rice. 1. A. L. Lavoisier’s first device for the analysis of organic

substances by incineration

To guarantee the purity of the experiment, the high temperature was provided not by any fuel, but by the sun's rays focused on the sample by a huge lens. The sample was burned in a hermetically sealed installation (under a glass bell) in a known amount of oxygen, the carbon dioxide released was absorbed and weighed. The mass of water was determined indirect method.

For the elemental analysis of low-volatile compounds, A. L. Lavoisier later proposed more sophisticated methods. In these methods, one of the sources of oxygen necessary for sample oxidation was metal oxides, with which the combusted sample was premixed (for example, lead(IV) oxide). This approach was later used in many methods of elemental analysis of organic substances, usually it gave good results. However, the Lavoisier CH-analysis methods were too long, and, moreover, they did not allow a sufficiently accurate determination of the hydrogen content: direct weighing of the formed water was not carried out.

The CH-analysis technique was improved in 1814 by the great Swedish chemist Jens Jakob Berzelius. Now the sample was burned not under a glass cap, but in a horizontal tube heated from the outside, through which air or oxygen was passed. Salts were added to the sample to facilitate the combustion process. absorbed with solid calcium chloride and weighed. The French researcher J. Dumas supplemented this technique with the volumetric determination of released nitrogen (CHN analysis). The Lavoisier-Berzelius method was once again improved by J. Liebig, who achieved quantitative and selective absorption of carbon dioxide in the ball absorber he invented (Fig. 2.).

Rice. 2. Apparatus J. Liebig for burning organic substances

This made it possible to drastically reduce the complexity and laboriousness of CH-analysis, and most importantly, to increase its accuracy. Thus, Yu. Liebig, half a century after A.L. Lavoisier, completed the development of the gravimetric analysis of organic substances begun by the great French scientist. By the 1840s, Liebig found out the exact composition of many organic compounds (for example, alkaloids) and proved (together with F. Wöhler) the fact of the existence of isomers. These methods remained virtually unchanged for many years, their accuracy and versatility ensured the rapid development of organic chemistry in the second half of the 19th century. Further improvements in the field of elemental analysis of organic substances (microanalysis) appeared only at the beginning of the 20th century. The corresponding studies of F. Pregl were awarded the Nobel Prize (1923).

Interestingly, both A. L. Lavoisier and J. Liebig sought to confirm the results of a quantitative analysis of any individual substance by counter-synthesis of the same substance, paying attention to the quantitative ratios of the reagents during the synthesis. A. L. Lavoisier noted that chemistry generally has two ways to determine the composition of a substance: synthesis and analysis, and one should not consider oneself satisfied until both of these methods can be used for verification. This remark is especially important for researchers of complex organic substances. Their reliable identification, revealing the structure of compounds today, as in the days of Lavoisier, requires a correct combination of analytical and synthetic methods.

Detection of carbon and hydrogen.

The method is based on the reaction of organic matter oxidation with copper (II) oxide powder.

As a result of oxidation, carbon, which is part of the analyzed substance, forms carbon (IV) oxide, and hydrogen forms water. Qualitatively, carbon is determined by the formation of a white precipitate of barium carbonate during the interaction of carbon (IV) oxide with barite water. Hydrogen is detected by the formation of blue crystalline Cu804-5H20.

Execution technique.

In test tube 1 (Fig. 2.1), copper (II) oxide powder is placed to a height of 10 mm, an equal amount of organic matter is added and thoroughly mixed. A small lump of cotton wool is placed in the upper part of test tube 1, on which white powder without aqueous copper (II) sulfate is poured in a thin layer. The test tube 1 is closed with a stopper with a gas outlet tube 2 so that one of its ends almost touches the cotton wool, and the other end is immersed in a test tube 3 with 1 ml of barite water. Carefully heated in the flame of the burner, first the top layer of the mixture of the substance with copper (II) oxide, then the bottom

Rice. 3 Discovery of carbon and hydrogen

In the presence of carbon, turbidity of barite water is observed due to the formation of a precipitate of barium carbonate. After the appearance of a precipitate, tube 3 is removed, and tube 1 continues to be heated until water vapor is reached without aqueous copper (II) sulfate. In the presence of water, a change in the color of copper (II) sulfate crystals is observed due to the formation of crystalline hydrate CuSO4 * 5H2O

detection of halogens. Beilitein's test.

The method for detecting chlorine, bromine and iodine atoms in organic compounds is based on the ability of copper (II) oxide to decompose halogen-containing organic compounds at high temperatures to form copper (II) halides.

The analyzed sample is applied to the end of a pre-calcined copper wire and heated in a non-luminous burner flame. If halogens are present in the sample, the resulting copper (II) halides are reduced to copper (I) halides, which, evaporating, color the flame blue-green (CuCl, CuBr) or green (OD) color. Organofluorine compounds do not color the flame of copper (I) fluoride is non-volatile. The reaction is non-selective due to the fact that nitriles, urea, thiourea, individual pyridine derivatives, carboxylic acids, acetylacetone, etc. interfere with the determination. alkali and alkaline earth metal flames are viewed through a blue light filter.

Nitrogen detection, sulfur and halogens. "Test of Lassen"

The method is based on the fusion of organic matter with metallic sodium. During fusion, nitrogen passes into sodium cyanide, sulfur into sodium sulfide, chlorine, bromine, iodine into the corresponding sodium halides.

Fusion technique.

A. Solids.

Several grains of the test substance (5-10 mg) are placed in a dry (attention!) refractory test tube and a small piece (the size of a grain of rice) of metallic sodium is added. The mixture is carefully heated in a burner flame, heating the test tube evenly, until a homogeneous alloy is formed. It is necessary to ensure that sodium melts with the substance. During fusion, the decomposition of the substance occurs. Fusion is often accompanied by a small flash of sodium and blackening of the contents of the test tube from the resulting particles of coal. The test tube is cooled to room temperature and 5-6 drops of ethyl alcohol are added to eliminate residual metallic sodium. After making sure that the sodium residue has reacted (hissing stops when a drop of alcohol is added), 1-1.5 ml of water is poured into the test tube and the solution is heated to a boil. The water-alcohol solution is filtered and used to detect sulfur, nitrogen and halogens.

B. Liquid substances.

A refractory test tube is vertically fixed on an asbestos mesh. Metallic sodium is placed in the test tube and heated until melted. When sodium vapor appears, the test substance is introduced dropwise. Heating is increased after the substance is charred.

B. Highly volatile and sublimating substances.

A mixture of sodium and the test substance is covered with a layer of soda lime about 1 cm thick and then subjected to the above analysis.

Nitrogen detection. Nitrogen is qualitatively detected by the formation of Prussian blue (blue coloration).

Method of determination. 5 drops of the filtrate obtained after fusion of the substance with sodium are placed in a test tube, and 1 drop of an alcohol solution of phenolphthalein is added. The appearance of a crimson-red color indicates an alkaline environment (if the color does not appear, add 1-2 drops of a 5% aqueous solution of sodium hydroxide to the test tube). With the subsequent addition of 1-2 drops of a 10% aqueous solution of iron (II) sulfate , usually containing an admixture of iron (III) sulfate, a dirty green precipitate forms. Pipette 1 drop of a cloudy liquid from a test tube onto a piece of filter paper. As soon as the drop is absorbed by the paper, 1 drop of a 5% solution of hydrochloric acid is applied to it. nitrogen, a blue patch of Prussian blue appears.

Sulfur detection.

Sulfur is qualitatively detected by the formation of a dark brown precipitate of lead (II) sulfide, as well as a red-violet complex with a solution of sodium nitroprusside.

Method of determination. Opposite corners of a piece of filter paper measuring 3x3 cm are moistened with a filtrate obtained by fusing the substance with metallic sodium (Fig. 4).

Rice. 4. Carrying out a test for seu on a square piece of paper.

On one of the wet spots, retreating 3-4 mm from its border, a drop of 1% solution of lead (II) acetate is applied.

A dark brown coloration appears at the contact boundary due to the formation of lead (II) sulfide.

A drop of sodium nitroprusside solution is applied to the border of another spot. An intense red-violet color appears on the border of the "leaks", gradually changing color.

Detection of sulfur and nitrogen in the joint presence.

In a number of organic compounds containing nitrogen and sulfur, the presence of sulfur interferes with the opening of nitrogen. In this case, a slightly modified method for determining nitrogen and sulfur is used, based on the fact that when an aqueous solution containing sodium sulfide and sodium cyanide is applied to filter paper, the latter is distributed along the periphery of the wet spot. This technique requires certain skills, which makes it difficult to use.

Method of determination. The filtrate is applied dropwise to the center of the filter paper measuring 3x3 cm until a colorless wet spot with a diameter of about 2 cm is formed.

Rice. 5. Detection of sulfur and nitrogen in the joint presence. 1 - a drop of a solution of iron (II) sulfate; 2 - a drop of a solution of lead acetate; 3 - drop of sodium nitroprusside solution

1 drop of a 5% solution of iron (II) sulfate is applied to the center of the spot (Fig. 5). After the drop is absorbed, 1 drop of a 5% solution of hydrochloric acid is applied to the center. In the presence of nitrogen, a blue spot of Prussian blue appears. Then, 1 drop of a 1% solution of lead (II) acetate is applied along the periphery of the wet spot, and 1 drop of sodium nitroprusside solution is applied on the opposite side of the spot. in the second case, a spot of red-violet color. The reaction equations are given above.

The fluorine ion is detected by discoloration or yellow coloration of alizarinzirconium indicator paper after acidifying the Lassen test with acetic acid.

Detection of halogens with silver nitrate. Halogens are found in the form of halide ions by the formation of flaky precipitates of silver halides of various colors: silver chloride is a white precipitate that darkens in the light; silver bromide - pale yellow; silver iodide - a precipitate of intense yellow color.

Method of determination. To 5-6 drops of the filtrate obtained after fusing the organic substance with sodium, add 2-3 drops of dilute nitric acid. If the substance contains sulfur and nitrogen, the solution is boiled for 1-2 minutes to remove hydrogen sulfide and hydrocyanic acid, which interfere with the determination of halogens .Then add 1-2 drops of a 1% solution of silver nitrate. The appearance of a white precipitate indicates the presence of chlorine, pale yellow - bromine, yellow - iodine.

If it is necessary to clarify whether bromine or iodine is present, the following reactions must be carried out:

1. To 3-5 drops of the filtrate obtained after fusion of the substance with sodium, add 1-2 drops of dilute sulfuric acid, 1 drop of a 5% solution of sodium nitrite or a 1% solution of iron (III) chloride and 1 ml of chloroform.

When shaken in the presence of iodine, the chloroform layer turns purple.

2. To 3-5 drops of the filtrate obtained after fusion of the substance with sodium, add 2-3 drops of diluted hydrochloric acid, 1-2 drops of a 5% solution of chloramine and 1 ml of chloroform.

In the presence of bromine, the chloroform layer turns yellow-brown.

B. Discovery of halogens by Stepanov's method. It is based on the conversion of a covalently bound halogen in an organic compound into an ionic state by the action of metallic sodium in an alcoholic solution.

Phosphorus detection. One of the methods for detecting phosphorus is based on the oxidation of organic matter with magnesium oxide. Organically bound phosphorus is converted into a phosphate ion, which is then detected by reaction with molybdenum liquid.

Method of determination. Several grains of the substance (5-10 mg) are mixed with a double amount of magnesium oxide and ashed in a porcelain crucible, first with moderate and then with strong heating. After cooling, the ash is dissolved in concentrated nitric acid, 0.5 ml of the resulting solution is transferred into a test tube, added 0.5 ml of molybdenum liquid and heated.

The appearance of a yellow precipitate of ammonium phosphomolybdate indicates the presence of phosphorus in the organic matter.

3. Qualitative analysis by functional groups

Based on selective reactions of functional groups (See the presentation on the topic).

In this case, selective reactions of precipitation, complex formation, decomposition with the release of characteristic reaction products, and others are used. Examples of such reactions are presented in the presentation.

Interestingly, the formation of organic compounds, known as organic analytical reagents, can be used for bulk detection and identification. For example, analogs of dimethylglyoxime interact with nickel and palladium, and nitroso-naphthols and nitrosophenols with cobalt, iron and palladium. These reactions can be used for detection and identification (See the presentation on the topic).

4. Identification.

Determination of the degree of purity of organic substances

The most common method for determining the purity of a substance is to measure boiling point during distillation and rectification, most often used to purify organic substances. To do this, the liquid is placed in a distillation flask (a round-bottom flask with a drain tube soldered to the neck), which is closed with a stopper with a thermometer inserted into it and connected to a refrigerator. The thermometer ball should be slightly higher holes in the side tube through which steam escapes. The thermometer ball, being immersed in the vapor of a boiling liquid, takes on the temperature of this vapor, which can be read on the thermometer scale. using an aneroid barometer, fix atmospheric pressure and, if necessary, make a correction. If a chemically pure product is distilled, the boiling point remains constant throughout the distillation time. If a contaminated substance is distilled, the temperature during distillation rises as more is removed low-boiling at mess.

Another commonly used method for determining the degree of purity of a substance is to determine melting point.For this purpose, a small amount of the test substance is placed in a capillary tube sealed at one end, which is attached to the thermometer so that the substance is at the same level as the thermometer ball. The thermometer with the tube attached to it with the substance is immersed in some high-boiling liquid, for example glycerin, and slowly heated over low heat, observing the substance and the rise in temperature. If the substance is pure, the moment of melting is easy to notice, because the substance melts sharply and the contents of the tube immediately become transparent. At this moment, note the thermometer reading. Contaminated substances are usually melt at a lower temperature and over a wide range.

To control the degree of purity of a substance, you can measure density.To determine the density of liquids or solids, they are most often used pycnometer.The latter in its simplest form is a flask equipped with a ground glass stopper with a thin internal capillary, the presence of which contributes to a more accurate observance of the constancy of volume when filling the pycnometer. The volume of the latter, including the capillary, is found by weighing it with water.

The pycnometric determination of the density of a liquid is reduced to simply weighing it in a pycnometer. Knowing the mass and volume, it is easy to find the desired density of the liquid. - or another liquid with a known density and not interacting with the substance under study) and weighed again. The difference between both weighings allows you to determine the volume of the part of the pycnometer not filled with the substance, and then the volume of the substance taken for research. Knowing the mass and volume, it is easy to find the desired density of the substance.

Very often, to assess the degree of purity of organic matter, measure refractive index. The refractive index value is usually given for the yellow line in the spectrum of sodium with a wavelength D= 589.3 nm (line D).

The refractive index is usually determined using refractometer.The advantage of this method for determining the degree of purity of organic matter is that only a few drops of the test compound are required to measure the refractive index. This manual presents the considered physical properties of the most important organic substances. We also note that the universal method for determining the degree of purity of organic matter is chromatography.This method allows not only to show how pure a given substance is, but also to indicate what specific impurities and in what quantity it contains.