Physical and chemical properties of fats. Obtaining fats and their chemical properties

A group of important organic substances - lipids - along with steroids and waxes are fats. Their content in living cells varies from 5 to 10% of the dry cell mass. These substances are studied, based on the characteristics of their molecular structure, which determine the chemical properties of fats. The chemistry of organic compounds considers these substances as the product of an esterification reaction between trihydric alcohol glycerin and higher limiting or unsaturated carboxylic acids.

In this article, we will study not only their use in industry and the importance, but also the production of fats and the chemical properties characteristic of this class of compounds.

History of the discovery

The structure was studied in the middle of the 19th century. The French chemist E. Shevrel heated them with water in the presence of alkali and found in the reaction products molecules of fatty carboxylic acids and glycerol. M. Bertlo conducted a reverse reaction: when glycerin was heated with a mixture of stearic and palmitic acids, he received triglyceride-fat. Based on these experiments, it was concluded that the substances studied belong to the class of esters. The chemical properties of fats have confirmed this conclusion.

Fats - esters

As it was proved by the experiments of M. Bertlo and E. Chevrel, triglycerides are esters of the triatomic alcohol of glycerin and higher monobasic carboxylic acids. Fat containing steroinic or palmitic acid is solid, for example, beef, pork, lamb. These are animal fats. If the composition of triglycerides includes unsaturated fatty acids - oleic, linoleic, linolenic - such fats are liquid and are called oils (sunflower, peanut, linseed).

The chemical properties of fats differ from other esters by the fact that several different carboxylic acids can enter the composition of their molecules .

Physical properties

Both natural and synthetic, for example, margarine, triglycerides have common characteristics. The main one is hydrophobicity, low melting point and low specific gravity. They are readily soluble in organic solvents, for example, in benzene, carbon tetrachloride. All fats are easily absorbed by porous or fibrous materials. According to the theory of the chemical structure of organic substances M. Butlerova, the physical and chemical properties of fats are interrelated. Confirmation of this fact will be given below.

Chemical reactions of triglycerides

The quantitative and qualitative composition of the fat molecule, as well as its spatial configuration, confirms the fact that triglycerides belong to the class of esters. Their main chemical property is the reaction with water (hydrolysis). It easily occurs in the presence of catalysts - alkalis, magnesium oxides, zinc or calcium. A mixture of carboxylic acids and glycerol is found in reaction products. Since the reaction of fats with water is reversible, the conditions under which it passes through to the end - towards the formation of glycerol and higher monobasic carboxylic acids - are created in industry. For this purpose, a solution of alkali is continuously supplied to the reaction mixture, and the products are immediately withdrawn from the reaction sphere. These techniques prevent the possibility of a reverse process, leading to the formation of fat. Hydrolysis is widely used in the chemistry of organic synthesis to produce the above substances.

Reaction of alkaline saponification

Continue to study organic substances - esters. Fats, whose chemical properties are represented by the hydrolysis reaction, are also able to react with alkalis. This reaction is called saponification and it is the opposite of the esterification process. Glycerol and fatty acids obtained as a result of alkaline saponification are treated with soda or a caustic soda. As a result, a soap is formed.

It is solid, has the formula C ₁₇ H ₃₅ COONa and is called economic. If you add dyes to it, glycerin, cosmetic fragrances, we get toilet soap. Liquid soap, in contrast to solid species, is obtained if the fat in the saponification reaction is mixed not with sodium hydroxide, but with caustic potassium. For example, potassium palmitate C ₁₅ H ₃₁ COOK - liquid potassium soap. The starting raw materials for the reaction of saponification are cheap fats of animal or vegetable origin.

Liquid Fats - Oils

They include molecules of unsaturated carboxylic acids having double bonds. Vegetable fats are synthesized in the channels of the endoplasmic reticulum under the action of enzymes from glycerin and fatty acids. And they, in turn, are formed in the reactions of the Calvin cycle, resulting from photosynthesis. Oil droplets accumulate in seeds, fruits, less often in the vegetative parts of plants and serve as a supply of nutrients. The physicochemical properties of fats produced by plants are due to the presence of a double pi bond in their molecules. At the place of its rupture, there are reactions of addition, for example, of hydrogen atoms. This leads to the formation of solid hydrogenated triglycerides.

Chemical properties of vegetable fats

As mentioned earlier, triglycerides of plant origin contain higher unsaturated carboxylic acids. Oils can be processed by hydrogenation. This process is carried out with heating and in the presence of a catalyst - powdered nickel.

The reaction product is a solid fat (salomas). It is used in the production of steroin, glycerol and in soap making. If you add sugar, salt, milk and food colors to the salomas, you get edible fat - margarine. When you add vitamins and natural butter to it, you get a so-called light oil-spread.

Synthetic fats

They are cheaper than natural, and differ from natural triglycerides by their composition. One of the main sources of synthetic fat production is natural and associated petroleum gases, as well as oil itself. The higher paraffins contained in these minerals are oxidized. As a result, synthetic fatty acids are obtained. Their interaction with ethylene glycol leads to the production of synthetic fat. It is used in the leather industry (for fattening furskins and skins). In the cosmetic industry, synthetic triglycerides are used in the production of toilet soaps, creams, lotions. In the building materials industry, artificial fats are used for the production of varnishes, mastics, paints.

The chemical properties of fats obtained by artificial means do not differ from natural ones. They also enter into the hydrolysis reaction in the presence of acid and are exposed to the action of alkalis (saponification reaction).

How Triglycerides Are Formed in the Human Body

Due to metabolic reactions, fats in the body cells can be synthesized from an excess of carbohydrates. This explains the fact that uncontrolled consumption of food rich in starch and sucrose (flour products, rice, potatoes, sweets) leads to overweight. In the process of digestion, foods containing fats are split in the duodenum to glycerol and fatty acids. Their hydrolysis occurs with the obligatory participation of lipase, the enzyme of the pancreas and bile secreted by the liver. Being a detergent, bile emulsifies fats, that is, breaks up large molecules into finely dispersed drops, easily broken by a lipase.

In villi small intestine of them are synthesized fat molecules, characteristic of the human body, and then they are absorbed into the lymph. On the lymphatic vessels, fats enter the cells, and their excess is deposited in the subcutaneous fatty tissue or omentum.

The biological role of lipids

Studying the chemical properties of fats, let us dwell on their ability to allocate a large amount of energy: one gram of fat gives 37.8 kJ energy at full oxidation. Therefore, triglycerides are its universal suppliers. Thus, fats are valuable food products. It is known that if their storage is incorrect and prolonged, the triglycerides "grow old" and rancid, gaining an unpleasant odor. This is due to the contact of fat with oxygen in the air. The oil that starts to deteriorate is easy to determine if you add potassium iodide to it. The peroxides contained in the product oxidize this compound to free iodine, causing a blue staining when in contact with starch-containing substances.

Fats are also the most important building material and are part of the cell membranes and organoids. Great is their role in the heat regulation of organisms. For example, animals living in great depths where the temperature of the water is very low have a well-developed layer of subcutaneous fat, for example, in whales, it can reach a thickness of 1.5 m. Animals of steppes, deserts and semi-deserts also accumulate in their bodies a sufficient amount of fat. It is necessary for them as a source of endogenous water, since during the oxidation of fat, in addition to energy, a large amount of liquid is released. These animals include camels, jerboas, shrews.

Lipids play an important role in protecting internal organs. A person has well developed omentum, which protects the stomach, digestive glands from internal injuries. Such vital organs as the kidneys must necessarily be in a layer of fat. With a sharp loss of weight in humans due to thinning of this layer, there may be omission of the kidneys, which is a serious pathology that disrupts the excretory system.

The importance of lipids in the formation of cell membranes is great. Along with carbohydrates and proteins, they form two layers that have a mosaic structure. The connections of fats with proteins are called lipoproteins. They determine the selective permeability of cell membranes.

In this article, the chemical composition and properties of fats, as well as their application in industry, were considered.