The group of important organic substances - lipids - contains fats along with steroids and waxes. Their content in living cells ranges from 5 to 10% of the dry weight of the cell. These substances are studied on the basis of their molecular structure, which determine the chemical properties of fats. The chemistry of organic compounds views these substances as the product of an esterification reaction between trihydric alcohol glycerol and higher saturated or unsaturated carboxylic acids.
In this article, we will study not only their application in industry and importance, but also the production of fats and chemical properties characteristic of this class of compounds.
Discovery story
The structure was studied in the mid-19th century. The French chemist E. Chevrel heated them with water in the presence of alkali and found molecules of fatty carboxylic acids and glycerol in the reaction products. M. Berthelot conducted the opposite reaction: when glycerol was heated with a mixture of storic and palmetic acids, he received triglyceride - fat. Based on these experiments, it was concluded that the studied substances belong to the class of esters. The chemical properties of fats confirmed this conclusion.
Fats - esters
As was proved by the experiments of M. Berthelot and E. Chevrel, triglycerides are esters of the trihydric alcohol glycerol and higher monobasic carboxylic acids. Fat containing storic or palmetic acid is solid, for example, beef, pork, and mutton. These are animal fats. If triglycerides contain unsaturated fatty acids - oleic, linoleic, linolenic - such fats are liquid and are called oils (sunflower, peanut, flaxseed).
The chemical properties of fats differ from other esters in that their molecules may include several different carboxylic acids.
Physical properties
Both natural and synthetic, for example, margarine, triglycerides have common features. The main ones are hydrophobicity, low melting point and low specific gravity. They dissolve well 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. Butlerov, the physical and chemical properties of fats are interconnected. 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 ester class. Their main chemical property is the reaction with water (hydrolysis). It easily occurs in the presence of catalysts - alkalis, oxides of magnesium, zinc or calcium. A mixture of carboxylic acids and glycerol is found in the reaction products. Since the reaction of fats with water is reversible, industry creates the conditions under which it passes to the end - towards the formation of glycerol and higher monobasic carboxylic acids. For this, an alkali solution is constantly fed into the reactive mixture, and the products are immediately removed from the reaction sphere. These techniques prevent the possibility of a reverse process leading to fat formation. Hydrolysis is widely used in chemistry of organic synthesis to obtain the above substances.
Alkaline saponification reaction
We continue to study organic matter - esters. Fats, whose chemical properties are represented by hydrolysis, are also able to interact with alkalis. This reaction is called saponification and it is the opposite of the esterification process. Glycerol and fatty acids obtained from alkaline saponification are treated with soda or sodium hydroxide. The result is soap.
It is solid, has the formula C 17 H 35 COONa and is called economic. If you add dyes, glycerin, cosmetic fragrances to it, we get a toilet soap. Liquid soap, unlike solid types, is obtained if fats in the saponification reaction are mixed not with sodium hydroxide, but with caustic potassium. For example, potassium palmitate C 15 H 31 COOK - liquid potassium soap. The feedstock for the saponification reaction 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 glycerol and fatty acids. And they, in turn, are formed in the reactions of the Calvin cycle, occurring as a result of photosynthesis. Drops of oil accumulate in seeds, fruits, less often in the vegetative parts of plants and serve as a supply of nutrients. The physicochemical properties of the fats formed by plants are due to the presence of a double pi bond in their molecules. At the point of its rupture, addition reactions, for example, of hydrogen atoms, take place. This leads to the formation of solid hydrogenated triglycerides.
Chemical properties of vegetable fats
As mentioned earlier, plant triglycerides contain higher unsaturated carboxylic acids. Oils can be processed through hydrogenation. This process is carried out with heating and in the presence of a catalyst - powdered nickel.
The reaction product is solid fat (salomas). It is used in the production of steorin, glycerol and soap making. If sugar, salt, milk and food coloring are added to salomas, then they get edible fat - margarine. When vitamins and natural butter are added to it, they get the so-called light oil - spread.
Synthetic fats
They are cheaper than natural ones and differ from natural triglycerides in their composition. One of the main sources of synthetic fats is natural and associated petroleum gases, as well as the oil itself. Higher paraffins contained in these natural resources are oxidized. The result is synthetic fatty acids. Their interaction with ethylene glycol produces synthetic fat. It is used in the leather industry (for the fatliquoring of fur skins and leathers). In the cosmetics industry, synthetic triglycerides are used in the manufacture of toilet soap, creams, lotions. In the building materials industry, artificial fats go into the production of varnishes, mastics, paints.
The chemical properties of fats obtained artificially do not differ from natural ones. They also enter into a hydrolysis reaction in the presence of acid and are exposed to alkalis (saponification reaction).
How triglycerides are formed in the human body
Due to metabolic reactions, fats in body cells can be synthesized from excess carbohydrates. This explains the fact that uncontrolled consumption of foods rich in starch and sucrose (flour products, rice, potatoes, sweets) leads to overweight. During digestion, foods containing fats are broken down in the duodenum to glycerol and fatty acids. Their hydrolysis occurs with the obligatory participation of lipase, an enzyme of the pancreas and bile secreted by the liver. Being a detergent, bile emulsifies fats, that is, it breaks down large molecules into finely divided droplets, which are easily split by lipase.
In the villi of the small intestine, fat molecules characteristic of the human body are synthesized from them, and then they are absorbed into the lymph. Fats enter the cells through the lymphatic vessels, and their excess is deposited in the subcutaneous fatty tissue or omentum.
The biological role of lipids
Studying the chemical properties of fats, we dwell on their ability to release a large amount of energy: one gram of fat gives 37.8 kJ of energy when completely oxidized. Therefore, triglycerides are its universal suppliers. Thus, fats are valuable foods. It is known that when stored improperly and for a long time, triglycerides “age” and rancid, becoming an unpleasant odor. This is due to the contact of fat with oxygen in the air. Oil that starts to deteriorate is easy to determine by adding potassium iodide to it. Peroxides contained in the product oxidize this compound to free iodine, which causes a blue color upon contact with starch-containing substances.
Fats are also the most important building material and are part of cell membranes and organoids. Their role is also great in the heat regulation of organisms. For example, animals that live at great depths, where the water temperature 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 the steppes, deserts and semi-deserts also accumulate a sufficient amount of fat in their bodies. 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 a well-developed omentum that protects the stomach, digestive glands from internal damage. Vital organs like the kidneys must always be in the layer of fat. With a sharp loss of weight in a person due to thinning of this layer, prolapse of the kidneys can be observed, which is a serious pathology that disrupts the excretory system.
The importance of lipids in the formation of cell membranes. Along with carbohydrates and proteins, they form two layers with a mosaic structure. Fat compounds with proteins are called lipoproteins. They determine the selective permeability of cell membranes.
This article examined the chemical composition and properties of fats, as well as their use in industry.