Grade 11. Lesson #

Topic: Fats as esters.

Purpose: To form the concept of fats as esters. To acquaint students with the distribution, composition and physical properties of fats, saturated and unsaturated fats, to find out their importance as food and participants in metabolism.

Basic concepts and terms: Higher carboxylic acids, polyhydric alcohols, glycerol, esters, hydrolysis, saponification.

Lesson type: Combined.

DURING THE CLASSES

1. ORGANIZATIONAL STAGE

1) What compounds are called alcohols?

2) What are polyhydric alcohols?

3) What compounds are called carboxylic acids?

4) What are higher carboxylic acids?

5) What functional groups contain carboxylic acid

you and esters?

IV. STUDY NEW MATERIAL

1) THE CONCEPT OF FATS.

Fats can be characterized as esters formed by a trihydric alcohol - glycerol - and three molecules of higher carboxylic acids. The most common carboxylic acids are stearic acid C H COOH and oleic acid C COOH.

It should be noted that fats are a certain class of organic compounds, since very often students understand all oily substances as fats, including machine (mineral) oils, which consist mainly of aliphatic and aromatic hydrocarbons.

Fats are named based on their composition: listing the residues of carboxylic acids that make up their composition: tristearic fat, or tristearate (includes three stearic acid residues), trioleic fat, or trioleate (includes three oleic acid residues). Having characterized fats as esters, they find out their chemical structure.

Exercise.

Make a formula of tristearic and trioleic fats, based on the fact that they are esters of stearic and oleic acids with glycerol.

2) CLASSIFICATION OF FATS.

All fats are divided into two main groups: solid and liquid.

One pattern can be deduced: solid fats are predominantly formed by higher saturated carboxylic acids, and liquid fats are predominantly unsaturated, although the classification according to the state of aggregation is more biological than chemical.

3) PHYSICAL PROPERTIES OF FAT AND THEIR DISTRIBUTION IN NATURE.

Animal fats are more often solid (beef, mutton), but there are also liquid ones (fish oil). At the same time, vegetable fats are more often liquid substances (linseed, sunflower oil), but there are also solid ones (coconut oil).

Fats are widely distributed in nature. Along with carbohydrates and proteins, they are part of all plant and animal organisms and constitute one of the main parts of human food.

All fats are lighter than water. They are insoluble in water, but readily soluble in many organic solvents (dichloroethane, gasoline).

V. GENERALIZATION AND SYSTEMATION OF STUDENTS' KNOWLEDGE

1) Make a formula for fat, which is formed by:

a) three oleic acid residues;

b) two residues of oleic and one residue of stearic acids;

c) one residue of oleic and two residues of stearic acids.

2) Write two possible formulas for a fat that has 57 carbon atoms and two double bonds in the molecule if the fat contains acid residues with an even number of carbon atoms.

VI. HOMEWORK

Prepare brief reports on the use of fats and their role in the life of organisms.

Grade 11. Lesson #

Topic: Chemical properties of fats. The importance of fats in the life of organisms.

Purpose: To acquaint students with the chemical properties of fats, the biological role of fats in the life of animals and plant organisms. To form the ability to draw up equations for the reactions of fat hydrolysis, to give an idea of ​​the hydrogenation of fats, to teach how to write equations for the corresponding reactions.

Equipment and materials: Periodic system of chemical elements of D. I. Mendeleev.

Basic concepts and terms: Higher carboxylic acids, polyhydric alcohols, glycerol, esters, hydrolysis, saponification.

Lesson type: Learning new material.

DURING THE CLASSES

I. ORGANIZATIONAL STAGE

II. CHECK HOMEWORK

III. UPDATING STUDENTS' BASIC KNOWLEDGE

Conversation.

1) What compounds are called fats?

2) How are fats classified?

C) What acids are present in fats?

4) How do saturated carboxylic acids differ from unsaturated ones?

IV. STUDY NEW MATERIAL

1) CHEMICAL PROPERTIES OF FAT.

1. Hydrolysis of fats.

Hydrolysis of fats is carried out in the presence of alkali (or soda), which converts the resulting carboxylic acids into salts. Moreover, salts of higher carboxylic acids are soaps (we will get to know these compounds in more detail in the next lesson), and as a result, the hydrolysis reaction (and not only fats, but also esters) is often also called saponification.

To substantiate the subsequent approach to establishing the structure of carbohydrates and proteins, it is important to emphasize that it was the study of hydrolysis reactions, the detection of glycerol and carboxylic acids as fat decomposition products, that allowed scientists to establish their structure in due time.

2. Hydrogenation of fats.

The composition of liquid fats includes residues of unsaturated carboxylic acids, therefore, they are able to attach hydrogen molecules. Thus, liquid fats are converted into solid ones. Very often this process is used to obtain combined

fats and margarines.

Exercise.

Write the reaction equation for the hydrogenation of trioleic fat.

Like any hydrogenation process, hydrogenation of fats takes place in the presence of a catalyst - platinum or nickel - at high hydrogen pressure. One of the most significant disadvantages of this reaction is the use of expensive catalysts, small amounts of which can then be included in the resulting fat mixtures. The search for cheap and non-toxic catalysts is one of the main problems in the production of fat mixtures.

3. Partial oxidation of fats.

Liquid fats (containing residues of unsaturated acids), interacting with atmospheric oxygen, are able to form solid films - “cross-linked polymers”.

When stored for a long time under the influence of moisture, oxygen, air, light and heat, fats acquire an unpleasant odor and taste. This process is called "rancidity". Unpleasant smell and taste are caused by the appearance in fats of their transformation products: free fatty acids, hydroxy acids, aldehydes and ketones.

2) USE OF FATS AND THEIR SIGNIFICANCE IN THE LIFE OF ORGANISMS

Work with the textbook.

Short messages from students.

V. GENERALIZATION AND SYSTEMATIZATION OF STUDENTS' KNOWLEDGE

1) Write the structural formulas of triglycerides of margarine, lauric

and linoleic acids, which are constituents of some fats.

2) Write the reaction equations: a) hydrolysis of formic acid propyl ester; b) synthesis of butyric acid methyl ester; c) hydrolysis of fat based on palmitic acid, in the presence of sodium hydroxide. For one of the esters, write the formula and indicate the name of the carboxylic acid isomeric to it.

3) As a result of the interaction of 23 g of formic acid with methyl alcohol, 24 g of an ester were obtained. Calculate the mass fraction of the ether yield.

4) What volume of hydrogen (n.a.) is spent on the transformation of fat (trioleate) weighing 5 kg into solid fat, if the volume fraction of production losses of hydrogen is 8%.

5) What mass of fat is required to obtain 36.8 g of glycerol (by alkaline saponification), if we assume that the fat is pure tristearate and the mass fraction of fat saponification is 80%.

Fat classification

Animal fats contain mainly glycerides of saturated acids and are solids. Vegetable fats, often referred to as oils, contain glycerides of unsaturated carboxylic acids. These are, for example, liquid sunflower, hemp and linseed oils.

Natural fats contain the following fatty acids

Physical properties of fats

• Animal fats (mutton, pork, beef, etc.) are usually solids with a low melting point (fish oil is an exception). Saturated acids predominate in solid fats.
• Vegetable fats - oils (sunflower, soybean, cottonseed, etc.) - liquids (exception - coconut oil, cocoa bean oil). Oils contain mainly residues of unsaturated (unsaturated) acids.

Chemical properties of fats

1. Hydrolysis, or saponification, of fats occurs under the action of water, with the participation of enzymes or acid catalysts (reversibly), while alcohol is formed - glycerol and a mixture of carboxylic acids:

Alkaline hydrolysis produces salts of higher fatty acids called soaps. Soaps are obtained by hydrolysis of fats in the presence of alkalis:

Soaps are potassium and sodium salts of higher carboxylic acids.

2. Hydrogenation of fats - the conversion of liquid vegetable oils into solid fats - is of great importance for food purposes. The product of the hydrogenation of oils is solid fat (artificial lard, salomas). Margarine- edible fat, consists of a mixture of hydrogenated oils (sunflower, corn, cottonseed, etc.), animal fats, milk and flavorings (salt, sugar, vitamins, etc.).

This is how margarine is obtained in industry:

Under the conditions of the oil hydrogenation process (high temperature, metal catalyst), some of the acidic residues containing C=C cis bonds are isomerized into more stable trans isomers. The increased content of trans-unsaturated acid residues in margarine (especially in cheap varieties) increases the risk of atherosclerosis, cardiovascular and other diseases.

The use of fats

o food industry

o pharmaceuticals

o Manufacture of soap and cosmetic products

o Lubricant production

Fats are esters of the trihydric alcohol glycerol and higher carboxylic acids, the general formula of which is shown on the slide.

Fats, as it is not surprising, belong to esters. Stearic acid C 17 H 35 COOH (or other fatty acids close to it in composition and structure) and trihydric alcohol glycerol C 3 H 5 (OH) 3 participate in their formation. Here's what the molecule diagram of such an ether looks like:

H 2 C-O -C (O) C 17 H 35

HC-O-C(O)C 17 H 35

H 2 C-O -C (O) C 17 H 35 tristearin, ester of glycerol and stearic acid, glycerol tristearate.

Fats have a complex structure - this is confirmed by the model of the tristearate molecule.

Chemical properties of fats: hydrolysis and hydrogenation of liquid fats.

For fats containing residues of unsaturated carboxylic acids, all reactions of unsaturated compounds are characteristic. The most important addition reaction of practical importance is hydrogenation of liquid fats . This reaction underlies the production of margarine (solid fat) from vegetable oil.

All fats, like other esters, undergo hydrolysis .

Hydrolysis of fats also occurs in our body: when fats enter the digestive organs, they are hydrolyzed under the influence of enzymes to form glycerol and carboxylic acids. Hydrolysis products are absorbed by the intestinal villi, and then fat is synthesized, but already characteristic of this organism. Subsequently, they are hydrolyzed and gradually oxidized to carbon dioxide and water. When fats are oxidized in the body, a large amount of energy is released. For people engaged in heavy physical labor, the energy expended is most easily compensated by fatty foods. Fats supply fat-soluble vitamins and other biologically active substances to body tissues.

Depending on the conditions, hydrolysis happens:

¾ Water(without catalyst, at high temperature and pressure).

¾ Acid(in the presence of an acid as a catalyst).

¾ Enzymatic(occurs in living organisms).

¾ Alkaline (under the action of alkalis).

The hydrolysis of esters is a reversible reaction. To shift the equilibrium towards the reaction products, it is carried out in an alkaline medium (in the presence of alkalis or alkali metal carbonates, for example, sodium carbonate).

The most important representatives of esters are fats.

Fats, oils

Fats- these are esters of glycerol and higher monoatomic. The common name for such compounds is triglycerides or triacylglycerols, where acyl is a carboxylic acid residue -C(O)R. The composition of natural triglycerides includes residues of saturated acids (palmitic C 15 H 31 COOH, stearic C 17 H 35 COOH) and unsaturated acids (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH). Higher carboxylic acids, which are part of fats, always have an even number of carbon atoms (C 8 - C 18) and an unbranched hydrocarbon residue. Natural fats and oils are mixtures of glycerides of higher carboxylic acids.

The composition and structure of fats can be reflected by the general formula:

Esterification- the reaction of the formation of esters.

The composition of fats can include residues of both saturated and unsaturated carboxylic acids in various combinations.

Under normal conditions, fats containing residues of unsaturated acids in their composition are most often liquid. They are called oils. Basically, these are fats of vegetable origin - linseed, hemp, sunflower and other oils (with the exception of palm and coconut oils - solid under normal conditions). Less common are liquid fats of animal origin, such as fish oil. Most natural fats of animal origin under normal conditions are solid (fusible) substances and contain mainly residues of saturated carboxylic acids, such as mutton fat.
The composition of fats determines their physical and chemical properties.

Physical properties of fats

Fats are insoluble in water, do not have a clear melting point, and expand significantly when melted.

The aggregate state of fats is solid, this is due to the fact that fats contain residues of saturated acids and fat molecules are capable of dense packing. The composition of oils includes residues of unsaturated acids in cis - configuration, therefore, dense packing of molecules is impossible, and the state of aggregation is liquid.

Chemical properties of fats

Fats (oils) are esters and are characterized by ester reactions.

It is clear that for fats containing residues of unsaturated carboxylic acids, all reactions of unsaturated compounds are characteristic. They decolorize bromine water, enter into other addition reactions. The most important reaction in practical terms is the hydrogenation of fats. Solid esters are obtained by hydrogenation of liquid fats. It is this reaction that underlies the production of margarine, a solid fat from vegetable oils. Conventionally, this process can be described by the reaction equation:

All fats, like other esters, undergo hydrolysis:

Hydrolysis of esters is a reversible reaction. In order to form hydrolysis products, it is carried out in an alkaline environment (in the presence of alkalis or Na 2 CO 3). Under these conditions, the hydrolysis of fats proceeds reversibly, and leads to the formation of salts of carboxylic acids, which are called. fats in an alkaline environment are called saponification of fats.

When fats are saponified, glycerol and soaps are formed - sodium and potassium salts of higher carboxylic acids:

Saponification- alkaline hydrolysis of fats, obtaining soap.

Soaps- mixtures of sodium (potassium) salts of higher limiting carboxylic acids (sodium soap - solid, potassium - liquid).

Soaps are surfactants (abbreviated as surfactants, detergents). The detergent effect of soaps is due to the fact that soaps emulsify fats. Soaps form micelles with pollutants (conditionally, these are fats with various inclusions).

The lipophilic part of the soap molecule dissolves in the pollutant, while the hydrophilic part is on the surface of the micelle. Micelles are charged with the same name, therefore they repel each other, while the pollutant and water turn into an emulsion (practically, this is dirty water).

Soap also occurs in water, which creates an alkaline environment.

Soaps cannot be used in hard and sea water, as the resulting calcium (magnesium) stearates are insoluble in water.

DEFINITION

Fats- esters of higher carboxylic acids and glycerol.

Fats and oils (liquid fats) are important natural compounds. All vegetable fats and oils are composed almost entirely of glycerol esters (triglycerides). In these compounds, glycerol is esterified with higher carboxylic acids.

Fats have a general formula:

Here R, R', R'' are hydrocarbon radicals.

The three hydroxo groups of glycerol can be esterified either with just one acid, such as palmitic or oleic, or with two or three different acids:

The main limiting acids that form fats are palmitic C 15 H 31 COOH and stearic C 17 H 35 COOH; the main unsaturated acids are oleic C 17 H 33 COOH and linoleic C 17 H 31 COOH.

Physical properties of fats

Fats formed by saturated acids are solids, and unsaturated fats are liquid. All fats are very poorly soluble in water.

Getting fat

Fats are obtained by the esterification reaction between the trihydric alcohol glycerol and higher carboxylic acids:

Chemical properties of fats

Among the reactions of fats, a special place is occupied by hydrolysis, which can be carried out by the action of both acids and bases:

a) acid hydrolysis

b) alkaline hydrolysis

For oils (liquid fats), addition reactions are characteristic:

- hydrogenation (hydrogenation (hydrogenation) reaction underlies the production of margarine)

- bromination

The measure of unsaturation of acid residues that are part of fats is the iodine number, expressed by the mass of iodine (in grams), which can be added via double bonds to 100 g of fat. The iodine number is important when evaluating drying oils.

Oils (liquid fats) also undergo oxidation and polymerization reactions.

The use of fats

Fats are widely used in the food industry, pharmaceuticals, in the production of oils and various cosmetics, in the production of lubricants.

Examples of problem solving

EXAMPLE 1

Exercise	Vegetable oil weighing 17.56 g was heated with 3.36 g of potassium hydroxide until the oil layer completely disappeared. Under the action of an excess of bromine water on the solution obtained after hydrolysis, only one tetrabromo derivative is formed. Set the possible formula for fat.
Decision	Let us write in general form the equation of fat hydrolysis: For 1 mol of fat during hydrolysis, there are 3 mol of potassium hydroxide. Let's find the amount of potassium hydroxide substance and fat, moreover, the amount of fat is three times less: Knowing the amount and mass of fat, you can find its molar mass: Three hydrocarbon radicals R of acids account for 705 g/mol: Knowing that only one tetrabromo derivative was obtained, we can conclude that all acid residues are the same and contain 2 double bonds each. Then we get that each radical contains 17 carbon atoms, this is the radical of linoleic acid: Possible formula for fat:
Answer	The target fat is tilinolene

EXAMPLE 2

Exercise	Write two possible formulas for a fat that has 57 carbon atoms in a molecule and reacts with iodine in a ratio of 1:2. The composition of fat contains residues of acids with an even number of carbon atoms.
Answer	where R, R’, R” are hydrocarbon radicals containing an odd number of carbon atoms (another atom from the acid residue is part of the -CO- group). Three hydrocarbon radicals account for 57-6 = 51 carbon atoms. It can be assumed that each of the radicals contains 17 carbon atoms.