1) Esters – _________________________________________________________________.
Esters – __________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________:
Where R and R / - _____________________________, which can be either the same or different.
The functional group of esters is called __________________________:
The molecular composition of esters is expressed by the general formula C - H - O -- .
2) Ethyl ether acetic acid as a representative of esters.
3) Nomenclature and isomerism of esters
* When named esters, according to the rules of the IUPAC substitutive nomenclature, first indicate the name of the alkyl group of the alcohol, and then the name of the acid residue, replacing the suffix –ova in the name of the acid with the suffix –oat.
Ethyl ethanoate
2- residue 1-alkyl group
acid alcohol
* Structural isomerism
Within a class – chain isomerism:
The following isomers correspond to the molecular formula C 4 H 8 O 2:
Ethyl ethanoate Propyl methanoate Methyl propanoate
Interclass isomerism:
Ethyl ethanoate Butanoic acid
4) Hydrolysis of esters
o Acidic:
H 2 O + CH 3 -CH 2 -OH
_______________ _____________ ________
o Alkaline:
NaOH + CH 3 -CH 2 -OH
______________ ______________ _________ ______________
5) Esters in nature.
Many esters are naturally found in the cell sap of flowers and fruits of plants.
Fats.
1) Composition and structure of triglycerides.
Fats – ____________________________________________________________________________.
The main components of fats are _________________ –______________________
____________________________________________________________________________________.
Scheme reflecting the general structure of triglycerides:
Where R 1, R 2, R 3 are carboxylic acid residues (____________ CH 3 CH 2 CH 2 COOH, ________________ C 15 H 31 COOH, _____________ C 17 H 35 COOH, ________________ C 17 H 33 COOH, ___________________ C 17 H 31 COOH, ________________________ C 17 H 29 COOH.
2) Physical properties.
3) Fats as nutrients.
Fats are an important part of human and animal food. In the body, during the process of hydrolysis, fats are broken down into glycerol and higher carboxylic acids. Then, inside the cells, fats specific to a given organism are synthesized from hydrolysis products.
Fats are the most important source of energy: their oxidation produces twice as much energy as the oxidation of carbohydrates.
Homework: §§39-40, 42.
1. Create reaction equations that can be used to carry out the following transformations: C 2 H 6 ® C 2 H 6 ® C 2 H 5 OH ® CH 3 COOH ® CH 3 COO C 2 H 5
2. Make up the structural formulas of all possible isomers of the composition C 5 H 10 O 2 and give them names according to the rules of IUPAC substitutive nomenclature.
Lectures 20, 21 Hydrocarbons: alkanes, alkenes, alkenes, arenes.
| Names of homologous series Characteristics | Alkanes | Alkenes | Alkynes | Arenas | ||
| 1. Definition | Acyclic saturated hydrocarbons, in the molecules of which carbon atoms are connected to each other only by single (simple) bonds | Acyclic unsaturated hydrocarbons, in the molecules of which 2 carbon atoms are connected by a double bond | Acyclic unsaturated hydrocarbons, in the molecules of which 2 carbon atoms are linked by a triple bond | Cyclic unsaturated hydrocarbons, the molecules of which contain one or more benzene rings | ||
| 2. General formula | C n H 2n+2 | CnH2n | CnH2n-2 | CnH2n-6 | ||
| 3. The simplest representative | methane | ethene | ethin | benzene | ||
| A) Molecular formula | CH 4 | C2H4 | C2H2 | C6H6 | ||
| b) Structural formula | H ½ H¾C¾H ½ H | H H\/C═C/\H H | H¾CºC¾H | |||
| c) Electronic formula | ||||||
| 4. Spatial structure of the molecule: a) Shape | Methane - tetrahedral Homologues of methane, starting with butane - zigzag | In the double bond region - flat | In the triple bond area – cylindrical (linear) | Flat | ||
| b) Connection angle | ||||||
| c) Nature of connection | single | double | triple | Aromatic | ||
| d) Bond length | 0.154 nm | 0.133 nm | 0.120 nm | 0.140 nm | ||
| 5. Possibility of rotation of carbon atoms relative to each other depending on the nature of the bond | Relatively free | Regarding a double bond it is difficult (impossible without breaking the double bond) | Regarding a triple bond it is difficult (impossible without breaking the triple bond) | Between the carbon atoms of the benzene ring is hindered (impossible without breaking the benzene ring) | ||
| 6. Trivial names | C 1 methane, C 2 ethane, C 3 propane, C 4 butane (ending –an, classified as semi-systematic) | CH 2 = CH 2 ethylene, CH 2 = CH – CH 3 propylene CH 2 = CH – CH 2 – CH 3 butylene | CHºCH acetylene | C 6 C 6 benzene | ||
| 7. Isomerism – | the phenomenon of the existence of compounds having the same qualitative and quantitative composition, but different chemical structure (different order connections of atoms in a molecule); for hydrocarbons it can be structural (chains; positions of multiple bonds) and spatial. | |||||
| Structural | Chain isomerism | CH 3 – CH 2 – CH 2 – CH 3 t boil = - 0.5°C CH 3 – CH– CH 3 ï CH 3 t boil = -1 0.2°C | CH 2 = CH – CH 2 – CH 3 butene-1 CH 2 = C – CH 3 ï CH 3 2-methylpropene | CHºС– CH 2 –CH 2 – CH 3 pentine-1 CHºС – CH–– CH 3 ï CH 3 3-methylbugin-1 | - | |
| Multiple bond position isomerism | - | CH 2 =CH– CH 2 – CH 3 butene-1 CH 3 –CH= CH– CH 3 butene-2 | CHºС – CH 2 – CH 3 butine-1 CH 3 –Сº С– CH 3 butine-2 | - | ||
| Spatial – cis-trans isomerism | - | Н 3 С Н\ ¤ С=С ¤ \ Н 3 С Н cis-isomer | H CH 3 \ ¤ C=C ¤ \ H 3 CH trans isomer | - | - | |
| Physical properties | ||||||
| 1. physical state: | C 1 -C 4 –_____, C 5 -C 15 – ________, C 16 – ________________________; | C 2 -C 4 –______, C 5 -C 17 –______, C 18 – ___________________; | C 2 -C 4 – _____, C 5 -C 16 –_______, C 17 – ___________________; | liquid (colorless, highly refractive, with a characteristic odor) | ||
| 2. t boil. and t float. | with increasing M r, t bp increases. and t float. | with increasing M r, t kip increases | t kip. = 80.1°С, t melt. =5.5°C | |||
| 3. water solubility | practically insoluble | practically insoluble | practically insoluble | insoluble | ||
| 4. physiological effect on the body | - | - | - | highly toxic compound | ||
| Chemical properties | ||||||
| Oxidation reactions: - complete oxidation (combustion) - incomplete oxidation | CH 4 +2O 2 →______+____+Q Mixtures of methane with oxygen (1:2 by volume) and air (1:10) are explosive 2CH 4 +3O 2 → | C 2 H 4 +_O 2 → C 2 H 4 +(O)+ H 2 O ® ethylene glycol | _C 2 H 2 +_O 2 → | _C 6 H 6 +__O 2 → | ||
| Substitution reactions (under illumination with chlorine and bromine) | 1) CH 4 +Cl 2 CH 3 ―CH 3 + Cl 2 → 2) During the halogenation of methane, all hydrogen atoms are successively replaced and a mixture of products is formed: CH 4 CH 3 Cl methane chloromethane → CH 2 Cl 2 CHCl 3 dichloromethane trichloromethane ( chloro- → CCl 4 roform) carbon tetrachloride (carbon tetrachloride) Solvent, heavy non-flammable liquid - fire extinguishing, obtained by complete chlorination of methane: CH 4 +4Cl 2 3) the interaction of other alkanes leads to the formation of a mixture of isomers: CH 3 - CH 2 -CH 3 + 2Cl 2 →CH 3 ― CH 2 ― CH 2 Cl + + CH 3 ―CHCl― CH 3 + 2HCl | - | - | H +Br 2 halogenation H +HONO 2 ® nitration | ||
| Pyrolysis | C 2 H 6 CH 2 = CH 2 + H 2 | - | - | - | ||
| Isomerization | CH 3 – CH 2 – CH 2 – CH 3 ® | - | - | - | ||
| Addition reactions: -halogens | - | CH 2 =CH 2 +Br 2 ® decolorization of bromine water (or a solution of bromine in tetrachloroethane) - a qualitative reaction to hydrocarbons with a double bond | СНºСН +Br 2 ® BrСН= СНBr +Br 2 ® | - | ||
| - hydrogen (hydrogenation) | - | CH 2 =CH 2 +H 2 ® | СНºСН ________® | +3H 2 benzene cyclohexane | ||
| - water (hydration) | - | CH 2 =CH 2 +H 2 O ® | CHºCH + H 2 O ® | - | ||
| - halogenated hydrocarbons | - | CH 2 = CH 2 + HCl ® | СНºСН + 2НCl ® | - | ||
| Polymcrization reaction (synthesis of BMC from low molecular weight compounds; NMC - monomer, BMC - polymer) | - | nCH 2 =CH 2 ® | trimerization 3 CHºCH | - | ||
The names of hydrocarbons are based onsystematic substitution nomenclature are the principles reflected in the diagram:
|
|
|
Not for UV
alkanes alkanes alkenes alkynes
2. The name of saturated hydrocarbons, which are taken as the basis for the names of all other organic compounds ( roots Greek numerals are highlighted):
Table 1.
| Number of C atoms | Name | Number of C atoms | Name | Number of C atoms | Name |
| C 1 | Meth en | C 7 | Hept en | From 13 | Tridek en |
| C 2 | This en | From 8 | Oct en | From 20 | Eicosis en |
| C 3 | Prop en | From 9 | Non en | From 21 | Geneicosis en |
| C 4 | Booth en | From 1 0 | Dec en | From 22 | Dokoz en |
| C 5 | Pent en | From 11 | Undek en | From 30 | Triacontan |
| C 6 | Hex en | From 12 | Dodek en | From 40 | Tetracontan |
Table 2.Names of Greek numerals
with which it is indicated
number of identical substituents Table 3. Names of alternates
| Number of substituents | Greek numeral | Number of substituents | Greek numeral | Deputy | Name |
| 2 | di- | 7 | hepta- | CH 3 - | Cl- |
| 3 | three- | 8 | octa- | C 2 H 5 - | Br- |
| 4 | tetra- | 9 | nona- | C 3 H 7 - | I - |
| 5 | penta- | 10 | deca- | F- | NH 2 - |
| 6 | hexa- |
3) The sequence of actions when compiling the names of organic hydrocarbons and their derivatives.
A. Names of straight chain hydrocarbons.
1. The names of alkanes are given in Table 1.
2. The names of alkenes and alkynes are based on the names of alkanes, in which the suffix –ane is replaced, respectively, by the suffix –ene or the suffix –ine. At the end we indicate the position of the multiple bond with an Arabic numeral.
B. Names of branched chain hydrocarbons.
1. Find the main circuit:
2) Includes double, triple bond,
3) Includes such substituents as F -, Cl -, Br -, I -.
2. We number from the end to which it is closest
1) Deputy
2) Double bond priority increases
3) Triple connection from top to bottom
4) In alphabetical order, we indicate the position of the substituents using Arabic numerals (for names, see Table 3).
5) We give preference to the option in which the first different digit is the smallest.
6) Using a prefix (see Table 2) we indicate the number of identical substituents.
7) Add the name of the main chain in accordance with the number of carbon atoms contained in it (see highlighted roots in Table 1)
8) In the case of alkenes and alkynes, add the appropriate suffix –ene or –ine at the end of the name.
9) We indicate the position of the multiple connection with an Arabic numeral (we give preference to the option in which the digit is the smallest).
C. Place a hyphen between numbers and letters, and a comma between numbers. The name of aromatic hydrocarbons is based on the name of its simplest representative - benzene.
Now let's talk about the difficult ones. Esters are widely distributed in nature. Say that esters are playing big role in a person's life - 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 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 according to 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 special means 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 oil, 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 sorbitol olive oil). Emulsifier, solvent, technical lubricant, viscosity modifier, stabilizer essential oils, nonionic surfactant, humectant. Included in solvents and cutting fluids. Used for the production of cosmetic, food, household, agricultural, technical purpose. Possesses unique property turn a mixture of water and oil into an emulsion.
a class of compounds based on mineral (inorganic) or organic carboxylic acids, in which the hydrogen atom in the HO group is replaced by an organic group R . The adjective “complex” in the name of esters helps to distinguish them from compounds called ethers.If the starting acid is polybasic, then the formation of either full esters all HO groups are substituted, or acid esters partial substitution is possible. 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 is indicated R , attached to the acid, 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
If you use trivial ( cm. TRIVIAL NAMES OF SUBSTANCES) is 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 distinctive features organic chemistry).When the number of C atoms in the original carboxylic acid and alcohol does not exceed 68, 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 connections are interesting wide range 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 |
The third group is fats. Unlike the previous two groups based on monohydric alcohols
ROH , all fats are esters of glycerol alcohol HOCH 2 CH(OH)CH 2 OH. Carboxylic acids that make up fats usually have a hydrocarbon chain with 919 carbon atoms. Animal fats (cow butter, lamb, lard) plastic, low-melting substances. Vegetable fats (olive, cottonseed, sunflower oil) 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 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 thin layer On the surface, such oil dries under the influence of atmospheric oxygen during polymerization along double bonds, which forms an elastic film that is insoluble in water and organic solvents. Based on linseed oil produce natural drying oil.
Rice. 3. GLYCERIDES OF STEARIC AND PALMITIC ACID (A AND B) components of animal fat. Linoleic acid glyceride (B) component of linseed oil.
Esters of mineral acids (alkyl sulfates, alkyl borates containing fragments of lower alcohols C 18) oily liquids, esters of higher alcohols (starting from C 9) 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 in industrial scale, in this case glycerol and higher carboxylic acids (C 1519) are obtained in the form of alkali metal salts, which are soap (Fig. 4B). Fragments contained in vegetable oils unsaturated acids, 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. From hydrogenation products vegetable oils, mixed with natural animal fats and various food additives, margarine is made.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).
Interaction of carboxylic acid salts with alkyl halides
RCl 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 cellulose varnishes(based on nitrocellulose and cellulose acetate).Esters based on lower alcohols and acids (Table 1) are used in food industry when creating 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 protects animals (especially sea whales or walruses) well 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) known medicinal product 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 reagents (introducing an alkyl group into a compound), and esters of phosphoric acid (Fig. 5) are used as insecticides, as well as additives to lubricating oils.
Mikhail Levitsky
LITERATURE Kartsova A.A. Conquest of matter. Organic chemistry . Khimizdat Publishing House, 1999Pustovalova L.M. Organic chemistry. Phoenix, 2003
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) is 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
Among the functional derivatives of carboxylic acids special place occupy esters - compoundsions representing carboxylic acids with a water atomkind in the carboxyl group is replaced hydrocarbon radical. General formula of esters
Esters are often named after their acid residues andalcohols of which they are composed. So, discussed above esters may be called: ethanoethyl ether, crotonovomethyl ether.
Esters are characterized by three types of isomerism:
1. Isomerism of the carbon chain, begins at the acidic position the residue from butanoic acid, the alcohol residue from propyl alcohol, for example:
2. Isomerism of the position of the ester group /> -SO-O-. This type of isomerism begins with esters, inmolecules containing at least 4 carbon atoms, example: />
3. Interclass isomerism, for example:
For esters containing unsaturated acid orunsaturated alcohol, two more types of isomerism are possible: isomerismmultiple bond positions; cis-trans isomerism.
Physical properties esters. Esters /> lower carboxylic acids and alcohols are volatile, sparingly soluble or practically insoluble in waterliquids. Many of them have a pleasant smell. For example, butyl butyrate smells like pineapple, isoamyl acetate smells like pear, etc.
Esters tend to have a lower temperatureboiling point than their corresponding acids. For example, stearic acid boils at 232 °C (P = 15 mm Hg), and metilstearate - at 215 °C (P = 15 mm Hg). This is explained bythat there are no hydrogen bonds between the molecules of esters communications.
Esters of higher fatty acids and alcohols - waxesfigurative substances, odorless, insoluble in water, althoughhighly soluble in organic solvents. For example, bee the wax is mainly myricyl palmitate(C 15 H 31 COOC 31 H 63 ).
