When carboxylic acids react with alcohols (esterification reaction), esters:
R 1 -COOH (acid) + R 2 -OH (alcohol) ↔ R 1 -COOR 2 (ester) + H 2 O
This reaction is reversible. The reaction products can interact with each other to form the initial substances - alcohol and acid. Thus, the reaction of esters with water - hydrolysis of the ester - is the reverse of the esterification reaction. Chemical equilibrium, which is established when the rates of direct (esterification) and reverse (hydrolysis) reactions are equal, can be shifted towards the formation of ether by the presence of dehydrating substances.
Esters in nature and technology
Esters are widespread in nature, find application in technology and various industries. They are good solvents for organic substances, their density is less than that of water, and they practically do not dissolve in it. Thus, esters with a relatively low molecular weight are flammable liquids with low boiling points and smells of various fruits. They are used as solvents for varnishes and paints, flavoring products in the food industry. For example, methyl ester of butyric acid has the smell of apples, ethyl alcohol of this acid has the smell of pineapples, isobutyl ester of acetic acid has the smell of bananas:
C 3 H 7 —COO — CH 3 (butyric acid methyl ester);
C 3 H 7 —COO — C 2 H 5 (butyric acid ethyl ester);
CH 3 -COO-CH 2 -CH 2 (acetic acid isobutyl ester)
Esters of higher carboxylic acids and higher monobasic alcohols are called waxes... Thus, beeswax consists mainly of palmitic acid ester of myricyl alcohol C 15 H 31 COOC 31 H 63; sperm whale wax - spermaceti - an ester of the same palmitic acid and cetyl alcohol C 15 H 31 COOC 16 H 33
Now let's talk about complex ones. Esters are widespread in nature. To say that esters play a big role in human life is to say nothing. We encounter them when we smell a flower that owes its scent to the simplest esters. Sunflower or olive oil is also a complex ester, but it has a high molecular weight - just like animal fats. We wash, wash and wash with means that are obtained by the chemical reaction of processing fats, that is, esters. They are also used in various areas of production: they are used to make medicines, paints and varnishes, perfumes, lubricants, polymers, synthetic fibers and much, much more.
Esters are organic compounds based on oxygen-containing organic carboxylic or inorganic acids. The structure of a substance can be represented as an acid molecule, in which the H atom in the OH- hydroxyl is replaced by a hydrocarbon radical.
Esters are obtained by the reaction of an acid and an alcohol (esterification reaction).
Classification
- Fruit esters - liquids with a fruity smell, the molecule contains no more than eight carbon atoms. Obtained from monohydric alcohols and carboxylic acids. Floral-scented esters are produced using aromatic alcohols.
- Waxes are solids containing from 15 to 45 C atoms in a molecule.
- Fats - contain 9-19 carbon atoms in a molecule. Obtained from glycerin a (trihydric alcohol) and higher carboxylic acids. Fats can be liquid (vegetable fats called oils) and solid (animal fats).
- Esters of mineral acids in their physical properties can also be both oily liquids (up to 8 carbon atoms) and solids (from nine C atoms).
Properties
Under normal conditions, esters can be liquid, colorless, with a fruity or floral odor, or solid, plastic; usually odorless. The longer the chain of the hydrocarbon radical, the harder the substance. Almost insoluble in water. They dissolve well in organic solvents. Combustible.
React with ammonia to form amides; with hydrogen (it is this reaction that turns liquid vegetable oils into solid margarines).
As a result of the hydrolysis reaction, they decompose into alcohol and acid. Hydrolysis of fats in an alkaline medium leads to the formation of not acid, but its salt - soap.
Esters of organic acids are low-toxic, have a narcotic effect on humans, mainly belong to the 2nd and 3rd class of hazard. Some reagents in production require the use of special eye and respiratory protection. The longer the ether molecule is, the more toxic it is. Esters of inorganic phosphoric acids are poisonous.
Substances can enter the body through the respiratory system and skin. Symptoms of acute poisoning are excitement and impaired coordination of movements, followed by depression of the central nervous system. Regular exposure can lead to diseases of the liver, kidneys, cardiovascular system, violations of the blood count.
Application
In organic synthesis.
- For the production of insecticides, herbicides, lubricants, impregnations for leather and paper, detergents, glycerin, nitroglycerin, drying oils, oil paints, synthetic fibers and resins, polymers, plexiglas, plasticizers, ore dressing reagents.
- As an additive to engine oils. 
- In the synthesis of perfumery fragrances, food fruit essences and cosmetic flavors; medicines, for example, vitamins A, E, B1, validol, ointments.
- As solvents for paints, varnishes, resins, fats, oils, cellulose, polymers.
In the assortment of the PrimeChemicalsGroup store you can buy demanded esters, including butyl acetate and Tween-80.
Butyl acetate
It is used as a solvent; in the perfumery industry for the manufacture of fragrances; for tanning leather; in pharmaceuticals - during the manufacture of certain drugs.
Twin-80
It is also polysorbate-80, polyoxyethylene sorbitan monooleate (based on olive oil sorbitol). Emulsifier, solvent, technical lubricant, viscosity modifier, essential oil stabilizer, nonionic surfactant, moisturizer. Part of solvents and cutting fluids. It is used for the production of cosmetic, food, household, agricultural and technical products. It has the unique property of transforming a mixture of water and oil into an emulsion.
5 march 2018Compounds obtained by the esterification reaction from carboxylic acids are commonly referred to as esters. In this case, OH- is replaced from the carboxyl group by the alkoxy radical. As a result, esters are formed, the formula of which is generally written as R-COO-R ".
The structure of the ester group
The polarity of chemical bonds in ester molecules is similar to the polarity of bonds in carboxylic acids. The main difference is the absence of a mobile hydrogen atom, in the place of which a hydrocarbon residue is located. At the same time, the electrophilic center is located on the carbon atom of the ester group. But the carbon atom of the alkyl group connected to it is also positively polarized.
Electrophilicity, and hence the chemical properties of esters, are determined by the structure of the hydrocarbon residue that took the place of the H atom in the carboxyl group. If the hydrocarbon radical forms a conjugated system with the oxygen atom, then the reactivity increases markedly. This happens, for example, in acrylic and vinyl esters.
Physical properties
Most esters are liquid or crystalline with a pleasant aroma. Their boiling points are usually lower than those of carboxylic acids with close molecular weights. This confirms the decrease in intermolecular interactions, and this, in turn, is explained by the absence of hydrogen bonds between neighboring molecules.
However, just like the chemical properties of esters, the physical ones depend on the structural features of the molecule. More precisely, on the type of alcohol and carboxylic acid from which it is formed. On this basis, esters are divided into three main groups:
- Fruit esters. They are formed from lower carboxylic acids and the same monohydric alcohols. Liquids with characteristic pleasant floral-fruity aromas.
- Waxes. They are derivatives of higher (the number of carbon atoms from 15 to 30) acids and alcohols, each having one functional group. These are plastic substances that soften easily in the hands. The main component of beeswax is myricyl palmitate С 15 Н 31 СООС 31 Н 63, and the Chinese one is ceryl ester of cerotinic acid С 25 Н 51 СООС 26 Н 53. They do not dissolve in water, but they are soluble in chloroform and benzene.
- Fats. Formed from glycerin and medium and higher carboxylic acids. Animal fats, as a rule, are solid under normal conditions, but melt easily when the temperature rises (butter, pork fat, etc.). Vegetable fats are characterized by a liquid state (flaxseed, olive, soybean oil). The fundamental difference in the structure of these two groups, which affects the differences in the physical and chemical properties of esters, is the presence or absence of multiple bonds in the acid residue. Animal fats are glycerides of unsaturated carboxylic acids, and vegetable fats are saturated acids.
Chemical properties
Esters react with nucleophiles, resulting in alkoxy substitution and acylation (or alkylation) of the nucleophilic agent. If there is an α-hydrogen atom in the structural formula of an ester, then ester condensation is possible.
1. Hydrolysis. Acid and alkaline hydrolysis is possible, which is a reaction opposite to esterification. In the first case, hydrolysis is reversible, and the acid acts as a catalyst:
R-СОО-R "+ Н 2 О<―>R-COO-H + R "-OH
Basic hydrolysis is irreversible and is usually called saponification, and sodium and potassium salts of fatty carboxylic acids are called soaps:
R-COO-R "+ NaOH -> R-COO-Na + R" -OΗ
2. Ammonolysis. Ammonia can act as a nucleophilic agent:
R-СОО-R "+ NH 3 -> R-СО-NH 2 + R" -OH
3. Transesterification. This chemical property of esters can also be attributed to the methods of their preparation. Under the action of alcohols in the presence of H + or OH -, it is possible to replace the hydrocarbon radical combined with oxygen:
R-COO-R "+ R" "- OH -> R-COO-R" "+ R" -OH
4. Reduction with hydrogen leads to the formation of molecules of two different alcohols:
R-CO-OR "+ LiAlH 4 -> R-СΗ 2 -ОΗ + R" OH
5. Combustion is another reaction typical of esters:
2CΗ 3 -COO-CΗ 3 + 7O 2 = 6CO 2 + 6H 2 O
6. Hydrogenation. If there are multiple bonds in the hydrocarbon chain of the ether molecule, then hydrogen molecules can be added along them, which occurs in the presence of platinum or other catalysts. So, for example, from oils it is possible to obtain solid hydrogenated fats (margarine).
The use of esters
Esters and their derivatives are used in various industries. Many of them dissolve various organic compounds well, are used in perfumery and the food industry, to obtain polymers and polyester fibers.
Ethyl acetate. It is used as a solvent for nitrocellulose, cellulose acetate and other polymers, for making and dissolving varnishes. Due to its pleasant aroma, it is used in the food and perfume industries.
Butyl acetate. Also used as a solvent, but already for polyester resins.
Vinyl acetate (CH 3 -COO-CH = CH 2). It is used as a base for the polymer required in the preparation of adhesives, varnishes, synthetic fibers and films.
Malonic ether. Due to its special chemical properties, this ester is widely used in chemical synthesis to obtain carboxylic acids, heterocyclic compounds, aminocarboxylic acids.
Phthalates. Phthalic acid esters are used as plasticizers for polymers and synthetic rubbers, and dioctyl phthalate is also used as a repellent.
Methyl acrylate and methyl methacrylate. They easily polymerize to form sheets of organic glass resistant to various influences.
Introduction -3-
1. Structure -4-
2. Nomenclature and isomerism -6-
3. Physical properties and being in nature -7-
4. Chemical properties -8-
5. Getting -9-
6. Application -10-
6.1 Use of inorganic acid esters -10-
6.2 Use of organic acid esters -12-
Conclusion -14-
Used sources of information -15-
Appendix -16-
Introduction
Among the functional derivatives of acids, esters, derivatives of acids, in which the acidic hydrogen is replaced by alkyl (or generally hydrocarbon) radicals, occupy a special place.
Esters are classified according to which acid they are derived from (inorganic or carboxylic).
Among the esters, a special place is occupied by natural esters - fats and oils, which are formed by the trihydric alcohol glycerol and higher fatty acids containing an even number of carbon atoms. Fats are part of plant and animal organisms and serve as one of the energy sources of living organisms, which is released during the oxidation of fats.
The purpose of my work is to familiarize yourself in detail with such a class of organic compounds as esters and in-depth consideration of the field of application of individual representatives of this class.
1. Structure
General formula of carboxylic acid esters:
where R and R "are hydrocarbon radicals (in esters of formic acid, R is a hydrogen atom).
General fat formula:
where R ", R", R "" are carbon radicals.
Fats can be “simple” and “mixed”. The composition of simple fats contains the remains of the same acids (ie, R '= R "= R" "), the composition of mixed fats contains different ones.
The following fatty acids are most commonly found in fats:
Alkanoic acids
1. Butyric acid CH 3 - (CH 2) 2 - COOH
3. Palmitic acid CH 3 - (CH 2) 14 - COOH
4. Stearic acid CH 3 - (CH 2) 16 - COOH
Alkenic acids
5. Oleic acid C 17 H 33 COOH
CH 3 - (CH 2) 7 -CH === CH- (CH 2) 7 -COOH
Alkadienic acids
6. Linoleic acid C 17 H 31 COOH
CH 3 - (CH 2) 4 -CH = CH-CH 2 -CH = CH-COOH
Alkatrienoic acids
7. Linolenic acid C 17 H 29 COOH
CH 3 CH 2 CH = CHCH 2 CH == CHCH 2 CH = CH (CH 2) 4 COOH
2. Nomenclature and isomerism
Ester names are derived from the name of the hydrocarbon radical and the name of the acid, in which the suffix is used instead of the ending -ova - at , for example:
The following types of isomerism are characteristic of esters:
1. The isomerism of the carbon chain begins at the acid residue with butanoic acid, and at the alcohol residue with propyl alcohol, for example, ethyl butyrate is isomeric with ethyl isobutyrate, propyl acetate and isopropyl acetate.
2. Isomerism of the position of the ester group -CO-O-. This type of isomerism begins with esters that contain at least 4 carbon atoms, such as ethyl acetate and methyl propionate.
3. Interclass isomerism, e.g. isomeric propanoic acid methyl acetate.
For esters containing unsaturated acid or unsaturated alcohol, two more types of isomerism are possible: isomerism of the position of the multiple bond and cis-, trans-isomerism.
3. Physical properties and being in nature
Esters of lower carboxylic acids and alcohols are volatile, water-insoluble liquids. Many of them have a pleasant smell. So, for example, butyl butyrate has a pineapple smell, isoamyl acetate - pears, etc.
Esters of higher fatty acids and alcohols are waxy substances, odorless, insoluble in water.
The pleasant aroma of flowers, fruits, berries is largely due to the presence of certain esters in them.
Fats are widespread in nature. Along with hydrocarbons and proteins, they are part of all plant and animal organisms and constitute one of the main parts of our food.
According to the state of aggregation at room temperature, fats are divided into liquid and solid. Hard fats, as a rule, are formed by saturated acids, liquid fats (they are often called oils) - unsaturated ones. Fats are soluble in organic solvents and insoluble in water.
4. Chemical properties
1. Reaction of hydrolysis, or saponification. Since the esterification reaction is reversible, therefore, in the presence of acids, the reverse hydrolysis reaction occurs:
The hydrolysis reaction is also catalyzed by alkalis; in this case, hydrolysis is irreversible, since the resulting acid forms a salt with alkali:
2. Reaction of addition. Esters containing unsaturated acid or alcohol are capable of addition reactions.
3. Recovery reaction. The reduction of esters with hydrogen leads to the formation of two alcohols:
4. Reaction of amide formation. Under the action of ammonia, esters are converted to acid amides and alcohols:
5. Receiving
1. The reaction of esterification:
Alcohols react with mineral and organic acids to form esters. The reaction is reversible (reverse process - hydrolysis of esters).
The reactivity of monohydric alcohols in these reactions decreases from primary to tertiary.
2. Interaction of acid anhydrides with alcohols:
3. Interaction of acid halides with alcohols:
6. Application
6.1 Use of inorganic acid esters
Boric acid esters - trialkylborates- easily obtained by heating alcohol and boric acid with the addition of concentrated sulfuric acid. Boronomethyl ether (trimethyl borate) boils at 65 ° C, boron ethyl (triethyl borate) - at 119 ° C. Esters of boric acid are easily hydrolyzed with water.
The reaction with boric acid serves to establish the configuration of polyhydric alcohols and has been repeatedly used in the study of sugars.
Orthosilicon ethers- liquids. Methyl ether boils at 122 ° С, ethyl ether at 156 ° С.Hydrolysis with water proceeds easily even in the cold, but it proceeds gradually and with a lack of water leads to the formation of high molecular weight anhydride forms in which silicon atoms are connected to each other through oxygen (siloxane groups) :
These high molecular weight substances (polyalkoxysiloxanes) are used as binders that can withstand rather high temperatures, in particular for coating the surface of molds for precision metal casting.Dialkyl dichlorosilanes react similarly to SiCl 4, for example ((CH 3) 2 SiCl 2, forming dialkoxy derivatives:
Their hydrolysis with a lack of water gives the so-called polyalkylsiloxanes:
They have different (but very significant) molecular weights and are viscous liquids used as heat-resistant lubricants, and with even longer siloxane skeletons - heat-resistant electrical insulating resins and rubbers.
Esters of orthotitanic acid. Their get similarly to orthosilicon ethers by the reaction:
These liquids, easily hydrolyzed to methyl alcohol and TiO 2, are used to impregnate fabrics in order to make them waterproof.
Esters of nitric acid. They are obtained by the action of a mixture of nitric and concentrated sulfuric acids on alcohols. Methyl nitrate CH 3 ONO 2 (bp 60 ° C) and ethyl nitrate C 2 H 5 ONO 2 (bp 87 ° C) can be distilled with careful work, but when heated above the boiling point or during detonation they are very strong blow up.
Ethylene glycol and glycerin nitrates, incorrectly called nitroglycol and nitroglycerin, are used as explosives. Nitroglycerin itself (a heavy liquid) is inconvenient and dangerous to handle.
Pentrite - tetranitrate of pentaerythritol C (CH 2 ONO 2) 4, obtained by treating pentaerythritol with a mixture of nitric and sulfuric acids, is also a strong explosive with blasting action.
Glycerin nitrate and pentaerythritol nitrate have a vasodilating effect and are used as symptomatic agents for angina pectoris.
Fats and oils are natural esters that are formed by a trihydric alcohol - glycerol and higher fatty acids with an unbranched carbon chain containing an even number of carbon atoms. In turn, sodium or potassium salts of higher fatty acids are called soaps.
When carboxylic acids react with alcohols ( esterification reaction) esters are formed:
This reaction is reversible. The reaction products can interact with each other to form the initial substances - alcohol and acid. Thus, the reaction of esters with water — ester hydrolysis — is the reverse of the esterification reaction. Chemical equilibrium, which is established when the rates of direct (esterification) and reverse (hydrolysis) reactions are equal, can be shifted towards the formation of ether by the presence of dehydrating agents.
Esters in nature and technology
Esters are widespread in nature, find application in technology and various industries. They are good solvents organic substances, their density is less than the density of water, and they practically do not dissolve in it. Thus, esters with a relatively low molecular weight are highly flammable liquids with low boiling points and smells of various fruits. They are used as solvents for varnishes and paints, flavorings for food products. For example, methyl ester of butyric acid has the smell of apples, ethyl ester of this acid has the smell of pineapples, isobutyl ester of acetic acid has the smell of bananas:
Esters of higher carboxylic acids and higher monobasic alcohols are called waxes... So, beeswax is mainly about
at once from an ester of palmitic acid and myricyl alcohol C 15 H 31 COOC 31 H 63; sperm whale wax - spermaceti - an ester of the same palmitic acid and cetyl alcohol C 15 H 31 COOC 16 H 33.
Fats
The most important representatives of esters are fats.
Fats- natural compounds, which are esters of glycerol and higher carboxylic acids.
The composition and structure of fats can be reflected by the general formula:
Most fats are formed by three carboxylic acids: oleic, palmitic, and stearic. Obviously, two of them are saturated (saturated), and oleic acid contains a double bond between carbon atoms in the molecule. Thus, 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 are most often liquid. They are called oils. These are mainly vegetable fats - flaxseed, hemp, sunflower and other oils. Less common are liquid animal fats 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, mutton fat. So, palm oil is a solid fat under normal conditions.
The composition of fats determines their physical and chemical properties. It is clear that all reactions of unsaturated compounds are characteristic of fats containing residues of unsaturated carboxylic acids. They discolor 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 - solid fat from vegetable oils. Conventionally, this process can be described by the reaction equation:
hydrolysis:
Soap
All fats, like other esters, are exposed to hydrolysis... Ester hydrolysis is a reversible reaction. To shift the equilibrium towards the formation of hydrolysis products, it is carried out in an alkaline medium (in the presence of alkalis or Na 2 CO 3). Under these conditions, the hydrolysis of fats is irreversible and leads to the formation of carboxylic acid salts, which are called soaps. Hydrolysis of fats in an alkaline environment is called fat saponification.
When fats are saponified, glycerin and soaps are formed - sodium or potassium salts of higher carboxylic acids:
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