abstract
Synthesis of amines from alcohols
Introduction 3
1. Characterization of alkylation processes 4
2. Chemistry and theoretical foundations of the process 10
3. Process Technology 13
References 16
Introduction
Alkylation is the process of introducing alkyl groups into the molecules of organic and some inorganic substances. These reactions are of great practical importance for the synthesis of aromatic compounds alkylated to the nucleus, isoparaffins, many mercaptans and sulfides, amines, substances with ether bonds, elemental and organometallic compounds, processed products of α-oxides and acetylene. Alkylation processes are often intermediate steps in the production of monomers, detergents, etc.
Many of the alkylation products are produced on a very large scale. Thus, about 4 million tons of ethylbenzene, 1.6 million tons of isopropylbenzene, 0.4 million tons of higher alkylbenzenes, over 4 million tons of glycols and other products of processing of alkylene oxides, about 30 million tons of isoparaffin alkylate, about 1 million tons of tert-butyl methyl ether, etc.
1. Characterization of alkylation processes
1. Classification of alkylation reactions
The most rational classification of alkylation processes is based on the type of newly formed bond.
Alkylation at a carbon atom (C-alkylation) consists in replacing the hydrogen atom located at the carbon atom with an alkyl group. Paraffins are capable of this substitution, but alkylation is most characteristic for aromatic compounds (the Friedel-Crafts reaction):
https://pandia.ru/text/78/129/images/image003_92.gif" width="221" height="23 src=">
Alkylation at oxygen and sulfur atoms (O - and S-alkylation) is a reaction in which an alkyl group binds to an oxygen or sulfur atom:
ArOH + RCI ArOH + NaCl + H2O
NaSH + RCI → RSH + NaCI
In this case, processes such as the hydrolysis of chlorine derivatives or the hydration of olefins also fall under the too general definition of alkylation, and this shows that only such reactions of introducing an alkyl group that do not have other, more significant and defining classification features should be called alkylation.
Alkylation at the nitrogen atom (N-alkylation) consists in replacing hydrogen atoms in ammonia or amines with alkyl groups. This is the most important of the methods for the synthesis of amines:
ROH + NH3 → RNH2 + H2O
As in the case of hydrolysis and hydration reactions, N-alkylation is often classified as ammonolysis (or aminolysis) of organic compounds).
Alkylation at atoms of other elements (Si-, Pb-, AI-alkylation) is the most important way to obtain element - and organometallic compounds, when the alkyl group is directly bonded to the heteroatom:
2RCI + Si R2SiCI2
4C2H5CI + 4PbNa → Pb(C2H5)4 + 4NaCI + 3Pb
3C3H6 + AI + 1.5H2 → Al(C3H7)3
Another classification of alkylation reactions is based on differences in the structure of the alkyl group introduced into an organic or inorganic compound. It can be saturated aliphatic (ethyl and isopropyl) or cyclic. In the latter case, the reaction is sometimes called cycloalkylation:
https://pandia.ru/text/78/129/images/image007_43.gif" width="61" height="26">ROCH=CH2
CH3-COOH + CH≡CH CH3-COO-CH=CH2
Finally, alkyl groups may contain various substituents, such as chlorine atoms, hydroxy, carboxy, sulfonic acid groups:
C6H5ONa + CICH2-COONa → C6H5O-CH2-COONa + NaCI
ROH + HOCH2-CH2SO2ONa → ROCH2–CH2SO2ONa + H2O
The most important of the reactions of introducing substituted alkyl groups is the process
2. Alkylating agents and catalysts
All alkylating agents according to the type of bond that breaks in them during alkylation, it is advisable to divide into the following groups:
1..gif" width="260" height="38 src=">
This means that the elongation and branching of the carbon atom chain in the olefin significantly increases its alkylation ability:
CH2=CH2< CH3-CH=CH2 < CH3-CH2-CH=CH2 < (CH3)2C=CH2
In some cases, alkylation with olefins proceeds under the influence of initiators of radical chain reactions, illumination, or high temperature. Here intermediate active particles are free radicals. The reactivity of different olefins in such reactions converges significantly.
Chlorine derivatives are alkylating agents of the widest range of action. They are suitable for C-, O-, S- and N-alkylation and for the synthesis of most elemento- and organometallic compounds. The use of chlorine derivatives is rational for those processes in which they cannot be replaced by olefins or when chlorine derivatives are cheaper and more accessible than olefins.
The alkylating action of chlorine derivatives manifests itself in three different types of interactions: in electrophilic reactions, in nucleophilic substitution, and in free radical processes. The mechanism of electrophilic substitution is characteristic of alkylation at the carbon atom, but, unlike olefins, reactions are catalyzed only by aprotic acids (aluminum chloride, iron chloride). In the limiting case, the process proceeds with the intermediate formation of a carbocation:
https://pandia.ru/text/78/129/images/image014_29.gif" width="318" height="26 src=">
In another type of reaction, characteristic of alkylation at oxygen, sulfur and nitrogen atoms, the process consists in the nucleophilic substitution of the chlorine atom. The mechanism is similar to the hydrolysis of chlorine derivatives, and the reaction proceeds in the absence of catalysts:
https://pandia.ru/text/78/129/images/image016_28.gif" height="25"> → 4NaCI + Pb(C2H5)4 + 3Pb
Alcohols and ethers are capable of C-, O-, N- and S-alkylation reactions. Olefin oxides, which are internal ethers of glycols, can also be classified as ethers, and of all ethers, only olefin oxides are practically used as alkylating agents. Alcohols are used for O - and N-alkylation in cases where they are cheaper and more accessible than chlorine derivatives. To break their alkyl-oxygen bond, acid-type catalysts are required:
R-OH + H+ ↔ R-OH2 ↔ R+ + H2O
3. Energy characteristics of the main alkylation reactions
Depending on the alkylating agent and the type of bond breaking in the alkylated substance, alkylation processes have very different energy characteristics. The values of thermal effects for the gaseous state of all substances in some important processes of alkylation at C-, O- and N-bonds are given in Table 1. Since they significantly depend on the structure of alkylating substances, the table lists the most common ranges of changes in thermal effects.
Table 1
Thermal effect of the most important alkylation reactions
Alkylating agent | A broken bond |
|
It can be seen from a comparison of the given data that when using the same alkylating agent, the heat of reaction during alkylation at different atoms decreases in the following order Car > Salif > N > O, and for different alkylating agents it changes as follows:
https://pandia.ru/text/78/129/images/image020_18.gif" width="161" height="28 src=">, which gives a high value of the equilibrium constant at all admissible temperatures. In contrast, the interaction phenols with ammonia and amines reversibly:
ArOH + NH3 ↔ ArNH2 + H2O 
In the overwhelming majority of cases, alcohols react with ammonia and amines only in the presence of catalysts. Sulfuric acid is used to produce methylanilines from aniline and methanol:
Ammonium "href="/text/category/ammonij/" rel="bookmark"> ammonium. The action of heterogeneous catalysts is to activate the C - O-bond in alcohol due to chemisorption on their acid sites:
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https://pandia.ru/text/78/129/images/image026_14.gif" width="390" height="53 src=">
In this case, the ratio of the rate constants of successive reaction steps is unfavorable for obtaining the primary amine, since ammonia is a weaker base and a nucleophilic reagent. The same acid-type catalysts cause intermolecular migration of alkyl groups, similar to the previously encountered reaction of transalkylation of aromatic compounds under the influence of AICI3. Thus, reversible reactions of transalkylation of amines occur:
2RNH2 ↔ R2NH + NH3
2R2NH ↔ RNH2 + R3N
strongly influencing the composition of alkylation products. In this case, the equilibrium ratios are much more than kinetic ones and are beneficial for obtaining the primary amine.
Although equilibrium is not completely achieved in practice, a relatively small excess of ammonia can still be used, which reduces the cost of its recovery. If the target product of the process is a secondary amine, then by returning primary and tertiary amines to the reaction, their formation can be completely excluded, directing the process only in the desired direction. In this case, stationary concentrations of by-products are established in the reaction mass, corresponding to the conditions of equality of the rates of their formation and consumption.
Dehydrogenating catalysts (copper, nickel, cobalt deposited on alumina) can also be used to carry out the reaction between ammonia and alcohols. In this case, the reaction mechanism is completely different - first, the alcohol is dehydrogenated to aldehyde, and then the aldehyde is condensed with ammonia and the resulting imine is hydrogenated:
Mixers "href="/text/category/smesiteli/" rel="bookmark">mixer 1 and fed into heat exchanger 2, where they are evaporated and heated by hot reaction gases. In reactor 3, the reactions described above proceed and amines are formed with almost complete conversion methanol Hot gases give off their heat to the initial mixture in heat exchanger 2 and are sent for further processing.
The resulting products are separated by multi-stage distillation; at each stage, pressure is created to obtain reflux by cooling with water. First of all, the most volatile ammonia is distilled off in column 4, which is recycled. The bottom liquid enters the extractive distillation column 5 with water (in the presence of water, the relative volatility of trimethylamine becomes the highest compared to others) methylamines. The trimethylamine (TMA) distilled off in this case can be partially taken in the form of a commercial product, but its main amount is sent for recycling. For the other two amines, the boiling points differ more (6.8 and 7.40C), and they can be separated by conventional distillation in columns 6 (monomethylamine, MMA) and 7 (dimethylamine, DMA). Each of them can be taken from the top of the column as a marketable product or partially (or completely) sent for recycling.
Finally, in column 8, unconverted methanol is distilled off from the wastewater and returned to the reaction. The total yield of amines, taking into account all losses, reaches 95%.
In the synthesis of ethylamines, the stage of preparation of the initial mixture and the reaction unit are performed similarly to those shown in Fig. 1. The separation of amines is facilitated by a greater difference in boiling points (16.5, 55.9 and 89.50) and is achieved by conventional distillation with sequential distillation of ammonia, mono-, di- and triethylamines. In this case, the by-product is ethylene, which is removed from the system by condensing the mixture to still strip off the ammonia.
Petrochemicals" href="/text/category/neftehimiya/" rel="bookmark">petrochemical
synthesis. M., Chemistry. 1988. - 592 p.;
4., Vishnyakova petrochemical synthesis. M., 1973. - 448 p.;
5. Yukelson basic organic synthesis. M., "Chemistry", 1968.
Amines.
Amines- derivatives of ammonia, in which one, two or all three hydrogen atoms are replaced by radicals.
Amine classification: Amines are classified according to two criteria:
1) according to the number of radicals that replace the hydrogen atom in ammonia, amines are divided into:
-primary :
-secondary :
-tertiary:
2) according to the nature of the radicals associated with the nitrogen atom, amines are divided into:
- aliphatic . Aliphatic amines are those amines in which the radicals are the residues of alkanes, alkenes, alkadienes, but not arenes:
propylamine 2-propenylamine 2-propynylamine
Aliphatic also include amines that have aromatic fragments in their structure if they are separated from the nitrogen atom by at least one group - CH 2 -, for example, benzylamine:
- aromatic . Only those amines are considered aromatic, in which the nitrogen atom is directly bonded to the aromatic nucleus, for example:
- fatty aromatic : in these amines, if they are tertiary, the nitrogen atom is connected to one aliphatic and two aromatic radicals or, conversely, to one aromatic and two aliphatic radicals, for example:
If a fatty aromatic amine is secondary, then it has one aliphatic radical and the other aromatic, for example:
Isomerism and nomenclature of aliphatic amines
To name an aliphatic amine according to the IUPAC nomenclature, you need to choose the longest chain of carbon atoms in contact with the amino group. Number the chain from the side closest to the amino group. Then indicate the number of the atom associated with the nitrogen atom, and write “amino” through a hyphen. After that, indicate the numbers of atoms of the main chain and the names of the hydrocarbon radicals associated with them. At the end, together with the name of the last of the radicals, give the name of the alkane corresponding to the main chain.
According to rational nomenclature, first, as they become more complex, the radicals associated with nitrogen are named, and then the word "amine" is attributed together. The table below shows examples of names for amines with the formula C 5 H 13 N
| IUPAC | Rational | |
 | 1-aminopentane | amylamine |
 | 2-aminopentane | 1-methylbutylamine |
 | 3-aminopentane | 1-ethylpropylamine |
 | 1-amino-2-methylbutane | 2-methylbutylamine |
 | 2-amino-2methylbutane | Tret-amylamine |
 | 2-amino-3-methylbutane | 1,2-dimethylpropylamine |
 | 1-amino-3-methylbutane | Isoamylamine |
 | 1-amino-2,2-dimethylpropane | Neopentylamine |
 | 1-(N-methyl)aminobutane | Methylbutylamine |
 | 2-(N-methyl)aminobutane | Methyl- second-butylamine |
 | 1-(N-methyl)amino-2-methylpropane | Methylisobutylamine |
| 2-(N-methyl)amino-2-methylpropane | Methyl tert.-butylamine | |
 | 1-(N-methyl-N-ethyl)aminoethane | Methyldiethylamine |
 | 1-(N,N-dimethyl)aminopropane | Dimethylpropylamine |
 | 2-(N,N-dimethyl)aminopropane | Dimethylisopropylamine |
Methods for obtaining amines.
Obtaining amines from other nitrogen-containing compounds.
From nitro compounds Amines can be obtained by their hydrogenation with hydrogen on a Raney nickel catalyst. This catalyst is obtained by leaching aluminum from its alloy with nickel according to the reaction:
1-nitropropane 1-aminopropane
Similarly, primary amines can be obtained from nitroso compounds:
2-nitrosobutane 2-aminobutane
Amines can also be obtained from oximes. The oximes themselves are easily obtained from aldehydes or ketones by reacting them with hydroxylamine:
propanal hydroxylamine propanal oxime
When oximes are hydrogenated, the N-O bond is broken and an amine (always primary) and water are obtained:
propanal oxime propylamine
Primary amines can also be obtained from hydrazones, which in turn are obtained by the action of hydrazine on aldehydes or ketones
butanone hydrazine butanone hydrazone
When hydrogenating hydrazones the N-N bond is broken and an amine (always primary) and ammonia are obtained:
2-aminobutane
From amides of carboxylic acids also available amines, and not only primary, but from alkylamides - secondary and from dialkylamides - tertiary amines.
First, from carboxylic acids, the action of ammonia is obtained ammonium salts,for example:
propionic acid ammonium propionate
When the ammonium salt is heated above 100 ° C, water is released in the form of steam and an amide is formed:
ammonium propionate propionic acid amide
Hydrogenation of amides on platinum group catalysts results in primary amines and water:
propioamide propylamine
If instead of ammonia in the first of the above reactions we take primary amine, then after amide hydrogenation succeed secondary amine:
acetic acid 1-aminopropane propylammonium acetate
acetic acid propylamide
Ethylpropylamine - secondary amine
If instead of ammonia in the first of these three reactions we take secondary amine, then after amide hydrogenation succeed tertiary amine:
3-methylbutanoic acid methylisobutylamine
To obtain amines, a huge number of various methods have been discovered today. The most important of them will be discussed in separate chapters:
- Direct alkylation of ammonia and amines;
- indirect alkylation;
- Recovery methods;
- Preparation of primary amines from carboxylic acids. Rearrangements of Hoffmann, Curtius and Schmidt.
The above methods for the preparation of amines differ in their areas of application, in their availability, and in the number of by-products. In the same chapter, the general patterns of obtaining amines and some other specific ways of obtaining them will be briefly considered.
General methods for the preparation of amines
They occur during cleavage reactions: amides (Hoffmann rearrangement), hydroxamic acids and their derivatives (Lossen rearrangement), azides (Curtius, Schmidt rearrangement), oximes, ketones (Beckmann rearrangement). The driving force behind these rearrangements is the formation of an electron-deficient nitrogen atom.
Lossen rearrangement
This reaction has fundamentally the same intermediate product as in the Hoffmann and Curtius rearrangements. To carry out such a rearrangement, hydroxamic acids and their derivatives are used, which, under the action of dehydrating agents ($P_2O_5$, $SOCl_2$, polyphosphoric acid, etc.), sequentially form acylnitrene, then isocyanate, and then amine.
Amines- these are organic compounds in which the hydrogen atom (maybe more than one) is replaced by a hydrocarbon radical. All amines are divided into:
- primary amines;
- secondary amines;
- tertiary amines.
There are also analogues of ammonium salts - quaternary salts of the type [ R 4 N] + Cl - .
Depending on the type of radical amines can be:
- aliphatic amines;
- aromatic (mixed) amines.
Aliphatic limiting amines.
General formula C n H 2 n +3 N.
The structure of amines.
The nitrogen atom is in sp 3 hybridization. On the 4th non-hybrid orbital is a lone pair of electrons, which determines the main properties of amines:
Electron donor substituents increase the electron density on the nitrogen atom and enhance the basic properties of amines, for this reason, secondary amines are stronger bases than primary ones, because 2 radicals at the nitrogen atom create a greater electron density than 1.
In tertiary atoms, the spatial factor plays an important role: since 3 radicals obscure the lone pair of nitrogen, which is difficult to "approach" to other reagents, the basicity of such amines is less than primary or secondary ones.
Isomerism of amines.
Amines are characterized by isomerism of the carbon skeleton, isomerism of the position of the amino group:
What is the name of the amines?
The name usually lists hydrocarbon radicals (in alphabetical order) and adds the ending -amine:
Physical properties of amines.
The first 3 amines are gases, the middle members of the aliphatic series are liquids, and the higher ones are solids. The boiling point of amines is higher than that of the corresponding hydrocarbons, because in the liquid phase, hydrogen bonds are formed in the molecule.
Amines are highly soluble in water; as the hydrocarbon radical grows, the solubility decreases.
Getting amines.
1. Alkylation of ammonia (the main method), which occurs when an alkyl halide is heated with ammonia:
If the alkyl halide is in excess, then the primary amine can enter into an alkylation reaction, turning into a secondary or tertiary amine:
2. Recovery of nitro compounds:
Ammonium sulfide is used Zinin reaction), zinc or iron in an acidic environment, aluminum in an alkaline environment, or hydrogen in the gas phase.
3. Recovery of nitriles. use LiAlH 4:
4. Enzymatic decarboxylation of amino acids:
Chemical properties of amines.
All amines- strong bases, and aliphatic ones are stronger than ammonia.
Aqueous solutions are alkaline in nature.
Amines entered our lives quite unexpectedly. Until recently, these were poisonous substances, a collision with which could lead to death. And now, after a century and a half, we are actively using synthetic fibers, fabrics, building materials, dyes, which are based on amines. No, they did not become safer, people were simply able to "tame" them and subdue them, deriving certain benefits for themselves. About which one, and we'll talk further.
Definition
For the qualitative and quantitative determination of aniline in solutions or compounds, a reaction with is used at the end of which a white precipitate in the form of 2,4,6-tribromaniline falls on the bottom of the test tube.
Amines in nature
Amines are found in nature everywhere in the form of vitamins, hormones, metabolic intermediates, they are also found in animals and plants. In addition, when living organisms rot, medium amines are also obtained, which, in a liquid state, spread an unpleasant smell of herring brine. The "cadaveric poison" widely described in the literature appeared precisely due to the specific ambergris of amines.
For a long time, the substances we are considering were confused with ammonia due to a similar smell. But in the mid-nineteenth century, the French chemist Wurtz was able to synthesize methylamine and ethylamine and prove that they release hydrocarbons when burned. This was the fundamental difference between the mentioned compounds and ammonia.
Obtaining amines in industrial conditions
Since the nitrogen atom in amines is in the lowest oxidation state, the reduction of nitrogen-containing compounds is the simplest and most affordable way to obtain them. It is he who is widely used in industrial practice because of its cheapness.
The first method is the reduction of nitro compounds. The reaction during which aniline is formed is named by the scientist Zinin and was carried out for the first time in the middle of the nineteenth century. The second method is to reduce amides with lithium aluminum hydride. Primary amines can also be reduced from nitriles. The third option is alkylation reactions, that is, the introduction of alkyl groups into ammonia molecules.
Application of amines
By themselves, in the form of pure substances, amines are used little. One rare example is polyethylenepolyamine (PEPA), which makes epoxy resin easier to cure in the home. Basically a primary, tertiary or secondary amine is an intermediate in the production of various organics. The most popular is aniline. It is the basis of a large palette of aniline dyes. The color that will turn out at the end depends directly on the selected raw material. Pure aniline gives a blue color, while a mixture of aniline, ortho- and para-toluidine will be red.
Aliphatic amines are needed to obtain polyamides such as nylon and others. They are used in mechanical engineering, as well as in the production of ropes, fabrics and films. In addition, aliphatic diisocyanates are used in the manufacture of polyurethanes. Due to their exceptional properties (lightness, strength, elasticity and the ability to attach to any surface), they are in demand in construction (mounting foam, glue) and in the shoe industry (anti-slip soles).
Medicine is another area where amines are used. Chemistry helps to synthesize antibiotics of the sulfonamide group from them, which are successfully used as second-line drugs, that is, reserve ones. In case bacteria develop resistance to essential drugs.
Harmful effects on the human body
It is known that amines are very toxic substances. Any interaction with them can cause harm to health: inhalation of vapors, contact with open skin or ingestion of compounds into the body. Death occurs from a lack of oxygen, since amines (in particular, aniline) bind to blood hemoglobin and prevent it from capturing oxygen molecules. Alarming symptoms are shortness of breath, blue nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.
In case of contact with these substances on bare areas of the body, it is necessary to quickly remove them with cotton wool previously moistened with alcohol. This must be done as carefully as possible so as not to increase the area of \u200b\u200bcontamination. If symptoms of poisoning appear, you should definitely consult a doctor.
Aliphatic amines are a poison for the nervous and cardiovascular systems. They can cause depression of liver function, its degeneration and even oncological diseases of the bladder.
