Ethyl acetate ester. Where are esters used? Fats as esters. Classification of fats

When carboxylic acids react with alcohols (esterification reaction), they form 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 starting materials - 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 ester by the presence of water-removing substances.

Esters in nature and technology

Esters They are widely distributed in nature and are used in technology and various industries. They are good solvents organic matter, their density is less than the density of water, and they practically do not dissolve in it. Thus, esters with a relatively small molecular weight are flammable liquids with low boiling points and have the odors of various fruits. They are used as solvents for varnishes and paints, fragrances for products in food industry. For example, methyl ester of butyric acid has the smell of apples, ethanol this acid - the smell of pineapples, isobutyl ester of acetic acid - the smell of bananas:
C 3 H 7 -COO-CH 3 (butyric acid methyl ester);
C 3 H 7 -COO-C 2 H 5 (ethyl butyrate);
CH 3 -COO-CH 2 -CH 2 (isobutyl acetate)
Esters of higher carboxylic acids and higher monobasic alcohols are called waxes. Thus, beeswax consists mainly of the palmitic acid ester of myricyl alcohol C 15 H 31 COOC 31 H 63; sperm whale wax – spermaceti – ester of the same palmitic acid and cetyl alcohol C 15 H 31 COOC 16 H 33

Fats and oils are natural esters that are formed by triatomic alcohol - glycerol and higher fatty acids with a straight carbon chain containing even number carbon atoms. In turn, sodium or potassium salts of higher fatty acids are called soaps.

When carboxylic acids interact with alcohols ( esterification reaction) esters are formed:

This reaction is reversible. The reaction products can interact with each other to form the starting materials - alcohol and acid. Thus, the reaction of esters with water - ester hydrolysis - is the reverse of the esterification reaction. The chemical equilibrium established when the rates of forward (esterification) and reverse (hydrolysis) reactions are equal can be shifted towards the formation of ester by the presence of water-removing agents.

Esters in nature and technology

Esters are widespread in nature and are used 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 small molecular weight are highly flammable liquids with low boiling points and have the odors of various fruits. They are used as solvents for varnishes and paints, and as flavoring agents for food industry products. For example, the methyl ester of butyric acid has the smell of apples, the ethyl ester of this acid has the smell of pineapples, and the isobutyl ester of acetic acid has the smell of bananas:

Esters of higher carboxylic acids and higher monobasic alcohols are called waxes. Thus, beeswax consists mainly of
at once from the 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 that 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 from three carboxylic acids: oleic, palmitic and stearic. Obviously, two of them are saturated (saturated), and oleic acid contains a double bond between the carbon atoms in the molecule. Thus, the composition of fats may 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 fats of vegetable origin - flaxseed, hemp, sunflower and other oils. 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. Thus, palm oil is a fat that is solid under normal conditions.

The composition of fats determines their physical and chemical properties. 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:

hydrolysis:

Soap

All fats, like other esters, are subject to hydrolysis. Hydrolysis of esters - reversible reaction. To shift the equilibrium towards the formation of hydrolysis products, it is carried out in alkaline environment(in the presence of alkalis or Na 2 CO 3). Under these conditions, the hydrolysis of fats occurs irreversibly and leads to the formation of salts of carboxylic acids, which are called soaps. Hydrolysis of fats in an alkaline environment is called saponification of fats.

When fats are saponified, glycerin and soaps are formed - sodium or potassium salts of higher carboxylic acids:

Crib

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 the products we receive chemical reaction processing of 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 - organic compounds based on oxygen-containing organic carbon 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. Possesses unique property turn a mixture of water and oil into an emulsion.

Esters. Among functional derivatives of acids, esters occupy a special place - derivatives of acids in which the hydrogen atom in the carboxyl group is replaced by a hydrocarbon radical. General formula of esters

where R and R" are hydrocarbon radicals (in formic acid esters R is a hydrogen atom).

Nomenclature and isomerism. The names of esters are derived from the name of the hydrocarbon radical and the name of the acid, in which the suffix -am is used instead of the ending -ova, for example:

Esters are characterized by three types of isomerism:

• 1. Isomerism of the carbon chain begins at acid residue from butanoic acid, by the alcohol residue - from propyl alcohol, for example, ethyl isobutyrate, propyl acetate and isopropyl acetate are isomeric.
• 2. Isomerism of the position of the ester group --CO--O--. This type of isomerism begins with esters whose molecules contain at least 4 carbon atoms, such as ethyl acetate and methyl propionate.
• 3. Interclass isomerism, for example, propanoic acid is isomeric to methyl acetate.

For esters containing an unsaturated acid or an unsaturated alcohol, two more types of isomerism are possible: isomerism of the position of the multiple bond and cis-, trans-isomerism.

Physical properties of esters. Esters of lower carboxylic acids and alcohols are volatile, water-insoluble liquids. Many of them have a pleasant smell. For example, butyl butyrate smells like pineapple, isoamyl acetate smells like pear, etc.

Esters of higher fatty acids and alcohols are waxy substances, odorless, and insoluble in water.

Chemical properties of esters. 1. Hydrolysis or saponification reaction. 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 and alkali form a salt:

• 2. Addition reaction. Esters containing an unsaturated acid or alcohol are capable of addition reactions.
• 3. Recovery reaction. Reduction of esters with hydrogen results in the formation of two alcohols:

4. Reaction of formation of amides. Under the influence of ammonia, esters are converted into acid amides and alcohols:

17. Structure, classification, isomerism, nomenclature, methods of preparation, physical properties, chemical properties amino acids

Amino acids (aminocarboxylic acids) are organic compounds whose molecule simultaneously contains carboxyl and amine groups.

Amino acids can be considered as derivatives of carboxylic acids in which one or more hydrogen atoms are replaced by amine groups.

Amino acids are colorless crystalline substances, highly soluble in water. Many of them have a sweet taste. All amino acids are amphoteric compounds; they can exhibit both acid properties, due to the presence of the carboxyl group --COOH in their molecules, and the basic properties due to the amino group --NH2. Amino acids interact with acids and alkalis:

NH2 --CH2 --COOH + HCl > HCl * NH2 --CH2 --COOH (glycine hydrochloride salt)

NH 2 --CH 2 --COOH + NaOH > H 2 O + NH 2 --CH 2 --COONa ( sodium salt glycine)

Due to this, solutions of amino acids in water have the properties of buffer solutions, i.e. are in a state of internal salts.

NH 2 --CH 2 COOH N + H 3 --CH 2 COO -

Amino acids can usually undergo all the reactions characteristic of carboxylic acids and amines.

Esterification:

NH 2 --CH 2 --COOH + CH 3 OH > H 2 O + NH 2 --CH 2 --COOCH 3 (glycine methyl ester)

An important feature of amino acids is their ability to polycondensate, leading to the formation of polyamides, including peptides, proteins, nylon, and nylon.

Peptide formation reaction:

HOOC --CH2 --NH --H + HOOC --CH2 --NH2 > HOOC --CH2 --NH --CO --CH2 --NH2 + H2O

The isoelectric point of an amino acid is the pH value at which the maximum proportion of amino acid molecules has zero charge. At this pH, the amino acid is least mobile in the electric field, and this property can be used to separate amino acids as well as proteins and peptides.

A zwitterion is an amino acid molecule in which the amino group is represented as -NH 3 + and the carboxy group is represented as -COO? . Such a molecule has a significant dipole moment with zero net charge. It is from such molecules that the crystals of most amino acids are built.

Some amino acids have multiple amino groups and carboxyl groups. For these amino acids it is difficult to talk about any specific zwitterion.

Most amino acids can be obtained through the hydrolysis of proteins or as a result of chemical reactions:

CH 3 COOH + Cl 2 + (catalyst) > CH 2 ClCOOH + HCl; CH 2 ClCOOH + 2NH 3 > NH 2 --CH 2 COOH + NH 4 Cl

Esters are most often prepared by acylation of hydroxy derivatives with carboxylic acids, their acid chlorides and anhydrides, as well as ketenes (see below); The interaction of salts of carboxylic acids with halides and tosylates according to the S^-mechanism is quite widely used (p. 112). Other methods include the addition of carboxylic acids to acetylene (p. 142, part 1), the Bayer-Villiger rearrangement (p. 35), and the Tishchenko reaction (p. 41). To obtain methyl esters, the reaction of carboxylic acids with diazomethane is used (to be discussed later).

The names of esters R-CO-OR 1 are usually composed of the name of the radical R 1 and the name of the acid followed by the ending am: ethyl acetic acid - ethyl acetate; benzoic acid propyl ester - propyl benzoate; oxalic acid dimethyl ester - dimethyl oxalate.

Chemical properties

The properties of esters reveal, on the one hand, a certain similarity with the properties of the previously discussed derivatives - acid chlorides and anhydrides, on the other - a noticeable originality; in particular, new types of reactions appear, such as acyloin condensation, pyrolysis and others.

Chemical reactions of esters can be divided into the following groups: I. Nucleophilic reactions of the carbonyl group; II. O-alkyl bond cleavage reactions; III. Recovery reactions; IV. Pyrolytic elimination reactions. Very important a-position reactions are not considered separately; part of the material (ester condensation) will be discussed in the section “Nucleophilic reactions of the carbonyl group”, and part - in a special section devoted to methylene active compounds.

I. Nucleophilic reactions of the carbonyl group.

The most characteristic reactions of this group are the interaction of esters with O- and N-nucleophiles and organometallic compounds, as well as condensation reactions with carbanions.

Esters, like previous types of derivatives, undergo hydrolysis and acylate O- and N-nucleophiles according to the general scheme:

For the -OR"* group, the donor +M effect is noticeably superior to the acceptor; it is low-active towards nucleophiles (approximately at the level of activity of the carbonyl group of carboxylic acids themselves). Esters are not active acylating reagents; when interacting with weak nucleophiles (water, alcohols ) requires catalysis.

Hydrolysis of esters occurs under the influence of aqueous solutions acids or bases (usually alkalis). Hydrolysis with acidic catalysis leads to the formation of the corresponding carboxylic acid and alcohol; the mechanisms of hydrolysis are the opposite of those of acid-catalyzed esterification; depending on the structure of esters and conditions, these may be Ade2 mechanisms or A ac 1 (see page HO, 111). Hydrolysis under the influence of alkalis naturally leads to the formation of salts of carboxylic acids: R"CO-OR 2 + Na + OH -> R"-CO-CTNa + + R 2 -OH The mechanism here is different: this is a typical mechanism of interaction of carboxylic acid derivatives with anionic nucleophiles (discussed above using the example of acyl halides). In this case it looks like this:

First, the anionic nucleophile, the hydroxide anion, is added, then the alkoxide anion is expelled, which naturally deprotonates the resulting acid to form an alcohol and a more stable carboxylate anion. Because the speed-determining stage is here bimolecular, the mechanism is designated as Vds2, i.e. bimolecular reaction of acyl derivatives catalyzed by bases (B - Base). Unlike acid hydrolysis, alkaline hydrolysis practically irreversible., because salts of carboxylic acids are passive towards nucleophiles.

Hydrolysis of cyclic esters - lactones - leads to the formation of hydroxy acids (in acid hydrolysis) or their salts (in alkaline hydrolysis):

Acylation of alcohols with esters leads to the formation of new esters with reagent alcohols, displacing the “original” alcohols:

This reaction is also called re-ethrification(sometimes, especially in biochemistry, the term "transesterification" is used) or alcoholism esters (similar to hydrolysis). The reaction usually occurs under acid catalysis according to the AL c2 mechanism:

The mechanism is completely similar to the esterification mechanism (p. 110). The reaction is microscopically reversible and can be shifted to one or the other.

the other side, using excess alcohol is used as a solvent.

r 2 -oh

or R OH: usually redundant

Transesterification also occurs when esters of alcoholates of other alcohols are exposed to:

The reaction proceeds according to the Bds2 mechanism, similar to alkaline hydrolysis, with the difference that an acid salt is not formed here, and the reaction is reversible.

Transesterification reactions are used for both the synthesis and cleavage of esters. In particular, methyl esters of natural fatty acids (convenient forms for chromatography-mass spectrometric analysis) can be obtained from natural esters of these acids by treatment with excess methanol in the presence of H2SO4. Alcoholysis is used in the synthesis of polyesters (to be discussed later). Some biochemical reactions are also related to transesterification; in particular, this is how cholesterol esters are formed in the body.

Alcoholysis of lactones leads to hydroxy acid esters:

In addition to alcoholism, there is another option for transesterification - acidolysis; This - exchange reaction with a carboxylic acid molecule, and an ester of this new acid is formed, and the “old” acid is displaced:

Acylation of N-nucleophiles with esters leads to the formation amides(during the acylation of ammonia, primary and secondary amines), hydrazides(during the acylation of hydrazine and its substitutes), hydroxamic acids(for acylation of hydroxylamine):

The N-nucleophiles used (especially hydrazine and hydroxylamine) are more active than O-nucleophiles, so their reaction with esters can occur without catalysis, although in some cases basic or acid catalysis is used. The mechanism of non-catalytic interaction is a special case of the mechanisms of reactions of acid derivatives with H-Y type reagents:

To obtain alx*)0b_acylation with esters is used less frequently than acylation with acid chlorides and anhydrides, but quite a lot of examples of such syntheses are still known. To receive hydrazides And hydroxamic acids acylation with esters is best method , because hydrazine and hydroxylamine are strong nucleophiles, and when they interact with energetic acylating reagents - acyl halides and anhydrides - the reactions can proceed too violently and lead to diacylation products, and for hydrazine - also tri- and tetraacylation.

The interaction of esters with organometallic compounds, as for acyl halides, can lead to ketones or go further to the formation of tertiary alcohols. When interacting with lithium alkyls, the reaction can be stopped under certain conditions at the stage of ketone formation:

When interacting with Grignard reagents, the reaction, as a rule, does not stop at the stage of ketone formation and goes further until the formation of a tertiary alcohol:

Condensation reactions involving the carbonyl group of esters are of great preparative importance. One of them is condensation of esters with ketones(acting as the methylene component):

The reaction was discussed earlier (p. 27); As a result, 1,3-diketones are formed, widely used in organic synthesis.

Another extremely important reaction is condensation of two ester molecules in the presence of a strong base ( ester condensation or Claisen condensation):

The reaction is similar to the previous one, with the difference that the role of the methylene component is not a ketone, but a second ester molecule. The reaction products are esters of p-oxocarboxylic acids. The option of condensing two identical ester molecules (R i= CH2R R 2 =R 4), i.e. self-condensation of esters under the action of strong bases. The simplest and most famous example is the condensation of two molecules of ethyl acetate to form acetoacetic ester(622) - one of the most widely used substances in organic synthesis:

In some cases, condensation is used different broadcasts(cross condensation); in these cases, it is necessary that one of the ethers (carbonyl component) does not contain an α-methylene group and that its carbonyl group has increased activity (to suppress the self-condensation of the methylene component). Such an ester, in particular, is oxalic acid diethyl ester (diethyl oxalate) (623), one of the typical partners in cross-condensation reactions:

An important special case of ester condensation is intramolecular condensation of dicarboxylic acid esters; in this case, the carbocyclic structure is closed; a 2-alkoxycarbonyl derivative of the cyclic ketone is formed:

This option is often called Dieckmann condensation it occurs most successfully with the formation of 5- and 6-membered cycles (n = 3, 4). Dieckmann condensation is one of the classical carbocyclization methods.

To carry out ester condensation it is necessary to use strong foundation, because only with its help it is possible to generate a carbanion from the a-position of an ester (the a-position of esters has lower CH-acidity than the a-position of carbonyl compounds, since the COOR group is less electron-withdrawing than the carbonyl group of aldehydes and ketones ). Most often used as a base alcoholate of the alcohol that forms the parent ester[if using alcohol another alcohol, the reaction will be complicated by transesterification (see above)]. Sometimes metal amides are used, and in some cases a superbase such as phenyllithium. The mechanism of ester condensation is quite similar to the previously discussed mechanism of condensation of esters with ketones:

This combines a mechanism similar to aldol condensation (formation of a carbanion and its attack on the carbonyl group) and a B ac -2 type mechanism (intramolecular displacement of an alkoxide anion).

II. O-alkyl bond cleavage reactions.

In the reactions described in the previous section, the bond is cleaved O-acyl. At the same time, a number of reactions leading to similar results occur with bond cleavage O-alkyl. These are reactions nucleophilic substitution at the alkyl carbon atom, where the nucleofuge is displaced as a carboxylic acid or carboxylate anion.

A typical example of such reactions is the acid hydrolysis of esters of tertiary, benzyl and allylic alcohols:

The key step in the reaction is the dissociation of the protonated ester (624) containing the “good” leaving group; dissociation is facilitated by the stability of tertiary, allylic, and benzyl cations (625). This is a typical S N 1 reaction, denoted here as A al 1; it is the reverse of esterification by the A al 1 mechanism (p. 111).

A peculiar option for the cleavage of the O-alkyl bond is the transformation of phenolphthalein (620) in an alkaline medium:

Under the influence of alkali, the phenolate dianion (626) is first formed; what happens next intramolecular 8^-reaction with displacement of carboxylatanion and with the formation of compound (627), containing a quinoid structure and therefore intensely colored. Upon acidification, the lactone cycle closes and is regenerated colorless connection (620). Both the forward and reverse reactions occur very quickly at room temperature, which allows the use of phenolphthalein as an acid-base indicator.

III. Reduction of esters.

The most common reactions in this group are the reduction of esters to primary alcohols and aldehydes, as well as their reductive combination called acyloin condensation.