Fats: structure, properties and examples. Polyhydric alcohols

Esters. Fats.

Previously we looked at a class of substances called ethers. Now let's consider esters.

There are similarities between ethers and esters.

Ethers

Both of them are organic compounds, whose molecules consist of hydrocarbon radicals linked by oxygen atoms.

For ethers the correct formula is: R-O-R or R1-O-R2.

In ethers as hydrocarbon radicals ( R, R1, R2) alcohol residues always appear.

An example of an ether is diethyl ether C 2 H 5 -O-C 2 H 5, consists of two residues ethyl alcohol, connected by an oxygen atom.

Esters

In the case of esters, one of the radicals is also alcohol residue(or phenol). And the second radical is the remainder of some acids.

The acid can be either organic or mineral. Alcohols and phenols react with acids, forming:

esters Educational response ester made from acid and alcohol (or phenol) is called.

esterification reaction

Esters of carboxylic acids If any of the carboxylic acids participates in the esterification reaction as an acid, the result is.

carboxylic acid esters Or in:

general view

Reactions to the formation of esters are extremely important for living nature, because all natural fats, oils and waxes are esters of carboxylic acids and alcohols.

Fats Fats represent .

esters of higher carboxylic (fatty) acids and trihydric alcohol glycerol

Here is a diagram of the formation of an ester of glycerol and stearic acid:

In naturally occurring fats, the same glycerol molecule is usually esterified with two or three different fatty acids. Only a few fatty acids take part in the formation of all natural fats. Natural fats are always mixtures. Fats are solid, if the acids forming them are

saturated

(marginal), such as stearic, palmitic or myristic acid.

The more residues of unsaturated (unsaturated) acids a fat contains, such as oleic, linoleic, lenolenic, the lower its melting point and the more liquid its consistency will be., i.e. esters of fatty acids and glycerol. But they contain relatively more quantity leftovers unsaturated fatty acids.

There are, of course, plenty of exceptions to this rule. For example, cocoa butter, shea butter, coconut oil have a rather solid consistency, but they are still traditionally called oils. Moreover, their hardness indicates that, as a rule, their composition is rich in saturated fatty acid residues. However, this is not without exceptions. For example, in liquid vegetable palm oil (“copra”), saturated acid residues predominate.

Hydrogenation of fats

Unsaturated fatty acids contain double bonds between carbon atoms; they react more easily, oxidize, and therefore deteriorate faster.

In order for vegetable oils and liquid animal fats to have greater chemical resistance and a longer shelf life, they are subjected to hydrogenation.

Hydrogenation of fats is the catalytic addition of hydrogen to esters of glycerol and unsaturated fatty acids.

Liquid fats turn into solid fats due to the addition of hydrogen at the site of the double bond between carbon atoms in esterified unsaturated acid molecules. Unsaturated acids after this procedure become saturated (saturated).

Thus, solid food margarine is obtained from liquid vegetable oil.

Preparation of soap from fats (saponification of fats).

Esters are insoluble (or almost insoluble) in water. They dissolve in organic solvents.

In water, esters can be hydrolyzed, i.e. disintegration into ions, followed by the formation of acid and alcohol from these ions.

The rate of this reaction will increase decisively if there is a sufficient amount of hydroxyl ions in the water ( HE).

When fats are heated with alkalis, esters split to form an alcohol and an acid salt:

The reaction of alkaline hydrolysis of esters is called saponification reaction. And the resulting sodium and potassium salts of higher fatty acids are called soaps.

For example: C 17 H 35 COONa– sodium stearate, S 15 N 31 SOOK– potassium palmitate.

Sodium soaps are solid, potassium soaps are liquid.

DEFINITION

Fats– esters of higher carboxylic acids and glycerol.

Fats and oils (liquid fats) are important natural compounds. All fats and oils plant origin consist 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 hydroxyl groups of glycerol can be esterified either with only one acid, such as palmitic or oleic, or with two or three different acids:

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

Physical properties of fats

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

Obtaining fats

Fats are obtained by an esterification reaction that occurs 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

Oils (liquid fats) are characterized by addition reactions:

- hydrogenation (hydrogenation reaction is the basis for the production of margarine)

- bromination

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

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

Application of fats

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

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

The most important representatives of esters are fats.

Fats, oils

Fats- these are esters of glycerol and higher monoatomic . Common name such compounds are 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 (oleic C 17 H 33 COOH, linoleic C 17 H 31 COOH). Higher carboxylic acids, which are part of fats, always have even number 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- reaction of formation of esters.

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

IN normal conditions fats containing residues of unsaturated acids are most often liquid. They are called oils. Basically, these are fats of vegetable origin - flaxseed, 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 (low-melting) substances and contain mainly residues of saturated carboxylic acids, for example, lamb 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 increase significantly in volume 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 the cis configuration, therefore dense packing of molecules is impossible, and the state of aggregation is liquid.

Chemical properties fat

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 and 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. To ensure the formation of 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 occurs 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, glycerin and soaps are formed - sodium and potassium salts of higher carboxylic acids:

Saponification– alkaline hydrolysis of fats, production of soap.

Soap– mixtures of sodium (potassium) salts of higher saturated carboxylic acids (sodium soap - solid, potassium soap - liquid).

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

The lipophilic part of the soap molecule dissolves in the contaminant, and the hydrophilic part ends up on the surface of the micelle. The micelles are charged in the same way, therefore they repel, and the pollutant and water turn into an emulsion (practically, it is dirty water).

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

Soaps should not be used in harsh or sea ​​water, since the resulting calcium (magnesium) stearates are insoluble in water.

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

Fats, not surprisingly, are esters. Their formation involves stearic acid C 17 H 35 COOH (or other fatty acids similar in composition and structure) and trihydric alcohol glycerol C 3 H 5 (OH) 3. This is what the diagram of the molecule of such an ether looks like:

H 2 C-O –C(O)C 17 H 35

NS-O –C(O)C 17 N 35

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

Fats have complex structure– this confirms 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, are subject to hydrolysis .

Hydrolysis of fats also occurs in our body: when fats enter the digestive organs, under the influence of enzymes they are hydrolyzed to form glycerol and carboxylic acids. The products of hydrolysis are absorbed by the intestinal villi, and then fat is synthesized, but already characteristic of a given organism. Subsequently, they hydrolyze and gradually oxidize to carbon dioxide and water. When fats are oxidized in the body, they release a large number of energy. For people who are busy physical labor The easiest way to compensate for the energy expended is with fatty foods. Fats supply fat-soluble vitamins and other biologically active substances to the body tissues.

Depending on the conditions, hydrolysis occurs:

¾ Water(without catalyst, with high temperatures and pressure).

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

¾ Enzymatic(occurs in living organisms).

¾ Alkaline (under the influence of alkalis).

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