If the starting acid is polybasic, then the formation of either full esters is possible - all HO groups are replaced, or acid esters - partial substitution. For monobasic acids, only full esters are possible (Fig. 1).
Rice. 1. EXAMPLES OF ESTERS based on inorganic and carboxylic acid
Nomenclature of esters.
The name is created as follows: first, the group R attached to the acid is indicated, then the name of the acid with the suffix “at” (as in the names of inorganic salts: carbon at sodium, nitrate at chromium). Examples in Fig. 2
Rice. 2. NAMES OF ESTERS. Fragments of molecules and corresponding fragments of names are highlighted in the same color. Esters are usually thought of as reaction products between an acid and an alcohol; for example, butyl propionate can be thought of as the result of the reaction between propionic acid and butanol.
If you use trivial ( cm. TRIVIAL NAMES OF SUBSTANCES) the name of the starting acid, then the name of the compound includes the word “ester”, for example, C 3 H 7 COOC 5 H 11 - amyl ester of butyric acid.
Classification and composition of esters.
Among the studied and widely used esters, the majority are compounds derived from carboxylic acids. Esters based on mineral (inorganic) acids are not so diverse, because the class of mineral acids is less numerous than carboxylic acids (the variety of compounds is one of the hallmarks of organic chemistry).
When the number of C atoms in the original carboxylic acid and alcohol does not exceed 6–8, the corresponding esters are colorless oily liquids, most often with a fruity odor. They form a group of fruit esters. If an aromatic alcohol (containing an aromatic nucleus) is involved in the formation of an ester, then such compounds, as a rule, have a floral rather than a fruity odor. All compounds in this group are practically insoluble in water, but easily soluble in most organic solvents. These compounds are interesting because of their wide range of pleasant aromas (Table 1); some of them were first isolated from plants and later synthesized artificially.
| Table 1. SOME ESTERS, having a fruity or floral aroma (fragments of the original alcohols in the compound formula and in the name are highlighted in bold) | ||
| Ester Formula | Name | Aroma |
| CH 3 COO C 4 H 9 | Butyl acetate | pear |
| C 3 H 7 COO CH 3 | Methyl Butyric acid ester | apple |
| C 3 H 7 COO C 2 H 5 | Ethyl Butyric acid ester | pineapple |
| C 4 H 9 COO C 2 H 5 | Ethyl | crimson |
| C 4 H 9 COO C 5 H 11 | Isoamil isovaleric acid ester | banana |
| CH 3 COO CH 2 C 6 H 5 | Benzyl acetate | jasmine |
| C 6 H 5 COO CH 2 C 6 H 5 | Benzyl benzoate | floral |
When the size of the organic groups included in the esters increases to C 15–30, the compounds acquire the consistency of plastic, easily softened substances. This group is called waxes; they are usually odorless. Beeswax contains a mixture of various esters; one of the components of the wax, which was isolated and its composition determined, is the myricyl ester of palmitic acid C 15 H 31 COOC 31 H 63. Chinese wax (a product of cochineal excretion - insects of East Asia) contains ceryl ester of cerotic acid C 25 H 51 COOC 26 H 53. In addition, waxes also contain free carboxylic acids and alcohols, which include large organic groups. Waxes are not wetted by water and are soluble in gasoline, chloroform, and benzene.
The third group is fats. Unlike the previous two groups based on monohydric alcohols ROH, all fats are esters formed from the trihydric alcohol glycerol HOCH 2 – CH (OH) – CH 2 OH. Carboxylic acids that make up fats usually have a hydrocarbon chain with 9–19 carbon atoms. Animal fats (cow butter, lamb, lard) are plastic, fusible substances. Vegetable fats (olive, cottonseed, sunflower oil) are viscous liquids. Animal fats mainly consist of a mixture of glycerides of stearic and palmitic acid (Fig. 3A, B). Vegetable oils contain glycerides of acids with a slightly shorter carbon chain length: lauric C 11 H 23 COOH and myristic C 13 H 27 COOH. (like stearic and palmitic acids, these are saturated acids). Such oils can be stored in air for a long time without changing their consistency, and therefore are called non-drying. In contrast, flaxseed oil contains unsaturated linoleic acid glyceride (Figure 3B). When applied in a thin layer to the surface, such oil dries under the influence of atmospheric oxygen during polymerization along double bonds, and an elastic film is formed that is insoluble in water and organic solvents. Natural drying oil is made from linseed oil.
Rice. 3. GLYCERIDES OF STEARIC AND PALMITIC ACID (A AND B)– components of animal fat. Linoleic acid glyceride (B) is a component of flaxseed oil.
Esters of mineral acids (alkyl sulfates, alkyl borates containing fragments of lower alcohols C 1–8) are oily liquids, esters of higher alcohols (starting from C 9) are solid compounds.
Chemical properties of esters.
Most characteristic of esters of carboxylic acids is the hydrolytic (under the influence of water) cleavage of the ester bond; in a neutral environment it proceeds slowly and noticeably accelerates in the presence of acids or bases, because H + and HO – ions catalyze this process (Fig. 4A), with hydroxyl ions acting more efficiently. Hydrolysis in the presence of alkalis is called saponification. If you take an amount of alkali sufficient to neutralize all the acid formed, then complete saponification of the ester occurs. This process is carried out on an industrial scale, and glycerol and higher carboxylic acids (C 15–19) are obtained in the form of alkali metal salts, which are soap (Fig. 4B). Fragments of unsaturated acids contained in vegetable oils, like any unsaturated compounds, can be hydrogenated, hydrogen attaches to double bonds and compounds similar to animal fats are formed (Fig. 4B). Using this method, solid fats are produced industrially based on sunflower, soybean or corn oil. Margarine is made from hydrogenation products of vegetable oils mixed with natural animal fats and various food additives.
The main method of synthesis is the interaction of a carboxylic acid and an alcohol, catalyzed by the acid and accompanied by the release of water. This reaction is the opposite of that shown in Fig. 3A. In order for the process to proceed in the desired direction (ester synthesis), water is distilled (distilled) from the reaction mixture. Through special studies using labeled atoms, it was possible to establish that during the synthesis process, the O atom, which is part of the resulting water, is detached from the acid (marked with a red dotted frame), and not from the alcohol (the unrealized option is highlighted with a blue dotted frame).
Using the same scheme, esters of inorganic acids, for example, nitroglycerin, are obtained (Fig. 5B). Instead of acids, acid chlorides can be used; the method is applicable for both carboxylic (Fig. 5C) and inorganic acids (Fig. 5D).
The interaction of carboxylic acid salts with RCl halides also leads to esters (Fig. 5D); the reaction is convenient in that it is irreversible - the released inorganic salt is immediately removed from the organic reaction medium in the form of a precipitate.
Use of esters.
Ethyl formate HCOOC 2 H 5 and ethyl acetate H 3 COOC 2 H 5 are used as solvents for cellulose varnishes (based on nitrocellulose and cellulose acetate).
Esters based on lower alcohols and acids (Table 1) are used in the food industry to create fruit essences, and esters based on aromatic alcohols in the perfume industry.
Polishes, lubricants, impregnating compositions for paper (waxed paper) and leather are made from waxes; they are also included in cosmetic creams and medicinal ointments.
Fats, together with carbohydrates and proteins, make up a set of foods necessary for nutrition; they are part of all plant and animal cells; in addition, when they accumulate in the body, they play the role of an energy reserve. Due to its low thermal conductivity, the fat layer well protects animals (especially marine animals - whales or walruses) from hypothermia.
Animal and vegetable fats are raw materials for the production of higher carboxylic acids, detergents and glycerol (Fig. 4), used in the cosmetics industry and as a component of various lubricants.
Nitroglycerin (Fig. 4) is a well-known drug and explosive, the basis of dynamite.
Drying oils are made from vegetable oils (Fig. 3), which form the basis of oil paints.
Esters of sulfuric acid (Fig. 2) are used in organic synthesis as alkylating (introducing an alkyl group into a compound) reagents, and esters of phosphoric acid (Fig. 5) are used as insecticides, as well as additives to lubricating oils.
Mikhail Levitsky
Esters are derivatives of oxoacids (both carboxylic and mineral) RkE(=O)l(OH)m, (l ≠ 0), formally being the products of the replacement of hydrogen atoms of hydroxyls -OH acidic function with a hydrocarbon residue (aliphatic, alkenyl, aromatic or heteroaromatic); are also considered as acyl derivatives of alcohols. In the IUPAC nomenclature, esters also include acyl derivatives of chalcogenide analogues of alcohols (thiols, selenols and tellurenes).
They differ from ethers, in which two hydrocarbon radicals are connected by an oxygen atom (R1-O-R2).
General formula of esters:
Nomenclature of esters.
The name is created as follows: first, the group R attached to the acid is indicated, then the name of the acid with the suffix “at” (as in the names of inorganic salts: carbon at sodium, nitrate at chromium). Examples in Fig. 2
Rice. 2. NAMES OF ESTERS. Fragments of molecules and corresponding fragments of names are highlighted in the same color. Esters are usually thought of as reaction products between an acid and an alcohol; for example, butyl propionate can be thought of as the result of the reaction between propionic acid and butanol.
If the trivial name of the starting acid is used, then the word “ester” is included in the name of the compound, for example, C 3 H 7 COOC 5 H 11 - amyl ester of butyric acid.
Homologous series of esters.
The general formula of esters is R1--CO---R2, where R1 and R2 are carbohydrate radicals. Esters are derivatives of acids in which the H in the hydroxyl is replaced by a radical. Esters are named after their acids and alcohols. who participate in education
H-CO-O-CH3-- methyl formate or methyl formic acid ester or methyl formic ester.
CH3-CO-O-C2H5 - ethyl acetate or ethyl ester of acetic acids or acetic ethyl ether..
C3H7-CO-O-CH3 - butyric acid methyl ester or methyl butyrate
C3H7-CO-O-C2H5 - ethyl ester of butyric acid or ethyl butyrate
In short, you need to write down the table of carboxylic acids. and to them the name of the salt (formic - formate, acetic - acetate, propionic - propinate, butyrate, valeric - valeriat, capronic - capronate, enanthic - enantonate, oxalic - oxalate, malonic - malonate, succinic - succinate .... Look How are the names of ethers formed?
CH3-CO-O (this is acetic acid without H) --C5H11- (this is a monovalent pentyl(amyl) radical - table) this is the name of this ester.
Amyl acetate ester, acetic acid amine ester, amyl acetate. Look again.
CH3CH2CH2CH2-CO-O (pentane or valeric acid) ---C4H9 (this is butyl) - butyl valerate, valerian butyl ether, butyl ester of valeric acid.
Isomerism.
Esters are characterized by isomerism of the hydrocarbon skeleton. For example, isomers are propyl acetate and isopropyl acetate. Since the ester molecule contains two hydrocarbon radicals - an acid residue and an alcohol residue - isomerism of each of the radicals is possible. For example, isomers are propyl acetate and isopropyl acetate (isomerism in the alcohol radical) or ethyl butyrate and ethyl isobutyrate (isomerism in the acid radical).
Physical properties. Esters are colorless liquids, slightly soluble or insoluble in water, and have a specific odor (in low concentrations - pleasant, often fruity or floral). Esters of higher alcohols and higher acids are solids.
Chemical properties . The most characteristic reaction for esters is hydrolysis. Hydrolysis occurs in the presence of acids or alkalis. When an ester is hydrolyzed in the presence of acids, a carboxylic acid and an alcohol are formed:
When an ester is hydrolyzed in the presence of alkalis, a carboxylic acid salt and an alcohol are formed:
Methods of obtaining.
Methods for producing esters. Main products and their areas of application. Conditions for the esterification reaction of organic acids with alcohols. Process catalysts. Features of the technological design of the esterification reaction unit.
1. Interaction of acids with alcohols:
This is the most common method for producing esters.
2. Synthesis of esters by aldehyde condensation:
The synthesis of esters from aldehydes (Tishchenko reaction) is carried out in the presence of aluminum alkoxide activated with ferric chloride or, better, aluminum chloride and zinc oxide. This method is of industrial importance.
3. Addition of organic acids to alkenes:
4. Synthesis of esters by dehydrogenation of alcohols:
5. Obtaining esters by transesterification.
This reaction has two varieties: the exchange reaction between ether and alcohol with alcohol radicals (alcoholysis reaction):
and the exchange reaction of acid radicals at the alcohol group of the ester:
6. Synthesis of esters from acid anhydrides and alcohols:
7. Interaction of ketones with alcohols:
8. Interaction between acid halides and alcohols:
9. Reaction between silver or potassium salts of acids and aliphatic halide derivatives:
10. Interaction of acids with aliphatic diazo compounds
Application.
Some esters are used as solvents (ethyl acetate is of greatest practical importance). Many esters, due to their pleasant smell, are used in the food and perfume and cosmetic industries. Esters of unsaturated acids are used to produce plexiglass; methyl methacrylate is most widely used for this purpose.
On the topic
"Esters and esters"
Completed by: Manzhieva A.A.
Derivatives of carboxylic or inorganic acids in which the hydrogen atom in the hydroxyl group is replaced by a radical are called esters. Typically, the general formula of esters is denoted as two hydrocarbon radicals attached to a carboxyl group - C n H 2n+1 -COO-C n H 2n+1 or R-COOR’.
Nomenclature
The names of esters are composed of the names of the radical and the acid with the suffix “-at”. For example:
- CH3COOH- methyl formate;
- HCOOCH 3- ethyl formate;
- CH 3 COOC 4 H 9- butyl acetate;
- CH 3 -CH 2 -COO-C 4 H 9- butyl propionate;
- CH 3 -SO 4 -CH 3- dimethyl sulfate.
Trivial names for the acid contained in the compound are also used:
- C 3 H 7 SOOS 5 H 11- amyl ester of butyric acid;
- HCOOCH 3- methyl ester of formic acid;
- CH 3 -COO-CH 2 -CH(CH 3) 2- isobutyl ester of acetic acid.
Rice. 1. Structural formulas of esters with names.
Classification
Depending on their origin, esters are divided into two groups:
- carboxylic acid esters- contain hydrocarbon radicals;
- esters of inorganic acids- include the remainder of mineral salts (C 2 H 5 OSO 2 OH, (CH 3 O)P(O)(OH) 2, C 2 H 5 ONO).
The most diverse are esters of carboxylic acids. Their physical properties depend on the complexity of their structure. Esters of lower carboxylic acids are volatile liquids with a pleasant aroma, while esters of higher carboxylic acids are solids. These are poorly soluble compounds that float on the surface of the water.
The types of carboxylic acid esters are given in the table.
|
View |
Description |
Examples |
|
Fruity esters |
Liquids whose molecules contain no more than eight carbon atoms. They have a fruity aroma. Consist of monohydric alcohols and carboxylic acids |
|
|
Liquid (oils) and solids containing from nine to 19 carbon atoms. Consist of glycerol and carboxylic (fatty) acid residues |
Olive oil is a mixture of glycerin with residues of palmitic, stearic, oleic, linoleic acids |
|
|
Solids with 15-45 carbon atoms |
CH 3 (CH 2) 14 -CO-O-(CH 2) 29 CH 3-myricyl palmitate |
Rice. 2. Wax.
Esters of carboxylic acids are the main component of aromatic essential oils, which are found in fruits, flowers, and berries. Also included in beeswax.
Rice. 3. Essential oils.
Receipt
Esters are prepared in several ways:
- esterification reaction of carboxylic acids with alcohols:
CH 3 COOH + C 2 H 5 OH → CH 3 COOC 2 H 5 + H 2 O;
- reaction of carboxylic acid anhydrides with alcohols:
(CH 3 CO) 2 O + 2C 2 H 5 OH → 2CH 3 COOC 2 H 5 + H 2 O;
- reaction of salts of carboxylic acids with halogenated hydrocarbons:
CH 3 (CH 2) 10 COONa + CH 3 Cl → CH 3 (CH 2) 10 COOCH 3 + NaCl;
- reaction of addition of carboxylic acids to alkenes:
CH 3 COOH + CH 2 =CH 2 → CH 3 COOCH 2 CH 3 + H 2 O.
Properties
The chemical properties of esters are due to the -COOH functional group. The main properties of esters are described in the table.
Esters are used in cosmetology, medicine, and the food industry as flavoring agents, solvents, and fillers.
What have we learned?
From the topic of the 10th grade chemistry lesson we learned what esters are. These are compounds containing two radicals and a carboxyl group. Depending on the origin, they may contain residues of mineral or carboxylic acids. Esters of carboxylic acids are divided into three groups: fats, waxes, fruit esters. These are poorly soluble substances in water with low density and a pleasant aroma. Esters react with alkalis, water, halogens, alcohols and ammonia.
Test on the topic
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Esters– functional derivatives of carboxylic acids,
in molecules in which the hydroxyl group (-OH) is replaced by an alcohol residue (-OR)
Esters of carboxylic acids – compounds with the general formula
R-COOR",where R and R" are hydrocarbon radicals.
Esters of saturated monobasic carboxylic acids have a general formula:
Physical properties:
Volatile, colorless liquids
· Poorly soluble in water
· Most often with a pleasant smell
Lighter than water
Esters are found in flowers, fruits, and berries. They determine their specific smell.
They are a component of essential oils (about 3000 e.m. are known - orange, lavender, rose, etc.)
Esters of lower carboxylic acids and lower monohydric alcohols have a pleasant smell of flowers, berries and fruits. Esters of higher monobasic acids and higher monohydric alcohols are the basis of natural waxes. For example, beeswax contains an ester of palmitic acid and myricyl alcohol (myricyl palmitate):
CH 3 (CH 2) 14 –CO–O–(CH 2) 29 CH 3
|
Aroma. Structural formula. |
Ester name |
|
Apple
|
Ethyl ether 2-methylbutanoic acid |
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Cherry
|
Amyl formic acid ester |
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Pear
|
Isoamyl ester of acetic acid |
|
A pineapple |
Butyric acid ethyl ester (ethyl butyrate) |
|
Banana
|
Isobutyl ester of acetic acid (y isoamyl acetate also resembles the smell of banana) |
|
Jasmine
|
Benzyl ether acetate (benzyl acetate) |
The short names of esters are based on the name of the radical (R") in the alcohol residue and the name of the RCOO group in the acid residue. For example, ethyl acetic acid CH 3 COO C 2 H 5 called ethyl acetate.
Application
· As fragrances and odor enhancers in the food and perfumery (production of soap, perfume, creams) industries;
· In the production of plastics and rubber as plasticizers.
Plasticizers – substances that are introduced into the composition of polymer materials to impart (or increase) elasticity and (or) plasticity during processing and operation.
Application in medicine
At the end of the 19th and beginning of the 20th centuries, when organic synthesis took its first steps, many esters were synthesized and tested by pharmacologists. They became the basis of such medicines as salol, validol, etc. Methyl salicylate was widely used as a local irritant and analgesic, which has now been practically replaced by more effective drugs.
Preparation of esters
Esters can be obtained by reacting carboxylic acids with alcohols ( esterification reaction). The catalysts are mineral acids.
Video “Preparation of ethyl acetyl ether”
Video “Preparation of boronethyl ether”
The esterification reaction under acid catalysis is reversible. The reverse process - the cleavage of an ester under the action of water to form a carboxylic acid and alcohol - is called ester hydrolysis.
RCOOR" + H2O (H+)↔ RCOOH + R"OH
Hydrolysis in the presence of alkali is irreversible (since the resulting negatively charged carboxylate anion RCOO does not react with the nucleophilic reagent - alcohol).
This reaction is called saponification of esters(by analogy with alkaline hydrolysis of ester bonds in fats when producing soap).
Now let's talk about the difficult ones. Esters are widely distributed 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 whose aroma is due to the simplest esters. Sunflower or olive oil is also an ester, but of high molecular weight - just like animal fats. We wash, wash and wash with products that are obtained by the chemical reaction of processing fats, that is, esters. They are also used in a variety of 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 the substance can be represented as an acid molecule in which the H atom in the hydroxyl OH- is replaced by a hydrocarbon radical.
Esters are obtained by the reaction of an acid and an alcohol (esterification reaction).
Classification
- Fruit esters are liquids with a fruity odor, the molecule contains no more than eight carbon atoms. Obtained from monohydric alcohols and carboxylic acids. Esters with a floral scent are obtained using aromatic alcohols.
- Waxes are solid substances containing from 15 to 45 C atoms per molecule.
- Fats - contain 9-19 carbon atoms per molecule. Obtained from glycerin a (trihydric alcohol) and higher carboxylic acids. Fats can be liquid (vegetable fats called oils) or solid (animal fats).
- Esters of mineral acids, in their physical properties, can also be either oily liquids (up to 8 carbon atoms) or 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. They dissolve well in organic solvents. Flammable.
React with ammonia to form amides; with hydrogen (it is this reaction that turns liquid vegetable oils into solid margarines).
As a result of hydrolysis reactions, they decompose into alcohol and acid. Hydrolysis of fats in an alkaline environment leads to the formation not of acid, but of its salt - soap.
Esters of organic acids are low-toxic, have a narcotic effect on humans, and mainly belong to the 2nd and 3rd hazard classes. Some reagents in production require the use of special eye and breathing 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 include agitation 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, and blood disorders.
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, plexiglass, plasticizers, reagents for ore dressing.
- As an additive to motor 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 Prime Chemicals Group store you can buy popular esters, including butyl acetate and Tween-80.
Butyl acetate
Used as a solvent; in the perfumery industry for the production of fragrances; for tanning leather; in pharmaceuticals - in the process of manufacturing 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, humectant. Included in solvents and cutting fluids. Used for the production of cosmetic, food, household, agricultural, and technical products. It has the unique property of turning a mixture of water and oil into an emulsion.
