Dihydric fatty alcohol of the general formula. Alcohols

Derivatives of hydrocarbons, the molecules of which contain one or more hydroxyl groups OH.

All alcohols are divided into monatomic And polyatomic

Monohydric alcohols

Monohydric alcohols- alcohols that have one hydroxyl group.
There are primary, secondary and tertiary alcohols:

U primary alcohols the hydroxyl group is located at the first carbon atom, the secondary carbon atom is at the second, etc.

Properties of alcohols, which are isomeric, are similar in many ways, but they behave differently in some reactions.

Comparing the relative molecular weight of alcohols (Mr) with relative atomic masses hydrocarbons, it can be noted that alcohols have more high temperature boiling. This is explained by the presence of a hydrogen bond between the H atom in the OH group of one molecule and the O atom in the -OH group of another molecule.

When alcohol is dissolved in water, hydrogen bonds are formed between the alcohol and water molecules. This explains the decrease in the volume of the solution (it will always be less than the sum of the volumes of water and alcohol separately).

The most prominent representative of chemical compounds of this class is ethanol. His chemical formula C 2 H 5 -OH. Concentrated ethanol(aka - wine spirit or ethanol) is obtained from diluted solutions by distillation; It has an intoxicating effect, and in large doses it is a strong poison that destroys living liver tissue and brain cells.

It should be noted that ethanol useful as a solvent, preservative, and a means of lowering the freezing point of any drug. One more no less famous representative this class - methyl alcohol (it is also called - woody or methanol). Unlike ethanol methanol deadly even in the smallest doses! First it causes blindness, then it simply “kills”!

Polyhydric alcohols

Polyhydric alcohols- alcohols having several OH hydroxyl groups.
Dihydric alcohols are called alcohols containing two hydroxyl groups (OH group); alcohols containing three hydroxyl groups - trihydric alcohols. In their molecules, two or three hydroxyl groups are never attached to the same carbon atom.

Dihydric alcohols also called glycols, since they have a sweet taste - this is typical for all polyhydric alcohols

Polyhydric alcohols with a small number of carbon atoms - these are viscous liquids, higher alcohols - solids. Polyhydric alcohols can be obtained by the same synthetic methods as saturated polyhydric alcohols.

Preparation of alcohols

1. Receipt ethyl alcohol (or wine alcohol) by fermentation of carbohydrates:

C 2 H 12 O 6 => C 2 H 5 -OH + CO 2

The essence of fermentation is that one of the simplest sugars - glucose, produced technically from starch, under the influence of yeast fungi, breaks down into ethyl alcohol and carbon dioxide. It has been established that the fermentation process is caused not by the microorganisms themselves, but by the substances they secrete - zymases. To obtain ethyl alcohol, vegetable raw materials rich in starch are usually used: potato tubers, bread grains, rice grains, etc.

2. Hydration of ethylene in the presence of sulfuric or phosphoric acid

CH 2 =CH 2 + KOH => C 2 H 5 -OH

3. When haloalkanes react with alkali:

4. During the oxidation of alkenes

5. Hydrolysis of fats: in this reaction the well-known alcohol is obtained - glycerol

By the way, glycerol It is included in many cosmetic products as a preservative and as a means to prevent freezing and drying!

Properties of alcohols

1) Combustion: Like most organic matter alcohols burn to form carbon dioxide and water:

C 2 H 5 -OH + 3O 2 -->2CO 2 + 3H 2 O

When they burn, a lot of heat is released, which is often used in laboratories (laboratory burners). Lower alcohols burn with an almost colorless flame, while higher alcohols have a yellowish flame due to incomplete combustion of carbon.

2) Reaction with alkali metals

C 2 H 5 -OH + 2Na --> 2C 2 H 5 -ONa + H 2

This reaction releases hydrogen and produces alcoholate sodium Alcoholates very similar to salt weak acid, and they are easily hydrolyzed. Alcoholates are extremely unstable and when exposed to water, they decompose into alcohol and alkali. From this it follows that monohydric alcohols do not react with alkalis!

3) Reaction with hydrogen halide
C 2 H 5 -OH + HBr --> CH 3 -CH 2 -Br + H 2 O
This reaction produces a haloalkane (bromoethane and water). This chemical reaction of alcohols is caused not only by the hydrogen atom in the hydroxyl group, but by the entire hydroxyl group! But this reaction is reversible: for it to occur, you need to use a water-removing agent, such as sulfuric acid.

4) Intramolecular dehydration (in the presence of catalyst H 2 SO 4)

In this reaction, under the action of concentrated sulfuric acid and heating occurs. During the reaction, it is formed unsaturated hydrocarbon and water.
The abstraction of a hydrogen atom from an alcohol can occur in its own molecule (that is, a redistribution of atoms in the molecule occurs). This reaction is intermolecular dehydration reaction. For example, like this:

During the reaction, ether and water are formed.

If added to alcohol carboxylic acid, for example acetic acid, then the formation of an ether will occur. But esters are less stable than ethers. If the reaction of the formation of an ether is almost irreversible, then the formation of an ester is reversible process. Esters easily undergo hydrolysis, breaking down into alcohol and carboxylic acid.

6) Oxidation of alcohols.

Alcohols are not oxidized by atmospheric oxygen at ordinary temperatures, but when heated in the presence of catalysts, oxidation occurs. An example is copper oxide (CuO), potassium permanganate (KMnO 4), chromium mixture. The action of oxidizing agents produces various products and depend on the structure of the original alcohol. Thus, primary alcohols are converted into aldehydes (reaction A), secondary alcohols are converted into ketones (reaction B), and tertiary alcohols are resistant to oxidizing agents.

Regarding polyhydric alcohols, they have a sweetish taste, but some of them are poisonous. Properties of polyhydric alcohols similar to monohydric alcohols, while the difference is that the reaction does not proceed one at a time to the hydroxyl group, but several at once.
One of the main differences is polyhydric alcohols easily react with copper hydroxide. This produces a transparent solution of a bright blue-violet color. It is this reaction that can detect the presence of a polyhydric alcohol in any solution.

Interact with nitric acid:

From the point of view practical application The reaction with nitric acid is of greatest interest. Emerging nitroglycerine And dinitroethylene glycol used as explosives and trinitroglycerin- also in medicine, as a vasodilator.

Ethylene glycol

Ethylene glycol- typical representative polyhydric alcohols. Its chemical formula is CH 2 OH - CH 2 OH. - dihydric alcohol. This is a sweet liquid that can dissolve perfectly in water in any proportions. Chemical reactions can involve either one hydroxyl group (-OH) or two simultaneously.

Ethylene glycol- its solutions are widely used as an anti-icing agent ( antifreeze). Ethylene glycol solution freezes at a temperature of -34 0 C, which in the cold season can replace water, for example, for cooling cars.

With all the benefits ethylene glycol It must be taken into account that this is a very strong poison!

We've all seen glycerol. It is sold in pharmacies in dark vials and is a viscous, colorless liquid with a sweetish taste. - This trihydric alcohol. It is very soluble in water and boils at a temperature of 220 0 C.

Chemical properties glycerol are in many ways similar to the properties monohydric alcohols, but glycerin can react with metal hydroxides (for example, copper hydroxide Cu(OH) 2), resulting in the formation of metal glycerates - chemical compounds similar to salts.

The reaction with copper hydroxide is typical for glycerin. The chemical reaction produces a bright blue solution copper glycerate

Emulsifiers

Emulsifiers- This higher alcohols, esters and other complex chemicals, which when mixed with other substances, such as fats, form stable emulsions. By the way, all cosmetics are also emulsions! Substances that are artificial waxes (pentol, sorbitan oleate), as well as triethanolamine and lecithin are often used as emulsifiers.

Solvents

Solvents- These are substances used mainly for the preparation of hair and nail varnishes. They are presented in a small range, since most of these substances are highly flammable and harmful to the human body. The most common representative solvents is acetone, as well as amyl acetate, butyl acetate, isobutylate.

There are also substances called thinners. They are mainly used together with solvents for the preparation of various varnishes..

The most well-known and used in human life and in industry substances belonging to the category of polyhydric alcohols are ethylene glycol and glycerin. Their research and use began several centuries ago, but their properties are largely inimitable and unique, which makes them indispensable to this day. Polyhydric alcohols are used in many chemical syntheses, industries and spheres of human activity.

First “acquaintance” with ethylene glycol and glycerin: history of production

In 1859, through a two-step process of reacting dibromoethane with silver acetate and subsequent treatment of ethylene glycol diacetate obtained in the first reaction with potassium hydroxide, Charles Wurtz synthesized ethylene glycol for the first time. Some time later, a method of direct hydrolysis of dibromoethane was developed, but on an industrial scale at the beginning of the twentieth century, dihydric alcohol 1,2-dioxyethane, also known as monoethylene glycol, or simply glycol, was obtained in the USA by hydrolysis of ethylene chlorohydrin.

Today, both in industry and in the laboratory, a number of other methods are used, new, more economical from a raw material and energy point of view, and environmentally friendly, since the use of reagents containing or releasing chlorine, toxins, carcinogens and other hazardous substances environment and human substances, is decreasing as “green” chemistry develops.

Glycerin was discovered by pharmacist Karl Wilhelm Scheele in 1779, and the composition of the compound was studied by Théophile Jules Pelouz in 1836. Two decades later, the structure of the molecule of this trihydric alcohol was established and substantiated in the works of Pierre Eugene Marcel Verthelot and Charles Wurtz. Finally, another twenty years later, Charles Friedel carried out the complete synthesis of glycerol. Currently, the industry uses two methods for its production: through allyl chloride from propylene, and also through acrolein. The chemical properties of ethylene glycol, like glycerin, are widely used in various fields chemical production.

Structure and structure of the connection

The molecule is based on the unsaturated hydrocarbon skeleton of ethylene, consisting of two carbon atoms, in which the double bond has been broken. Two hydroxyl groups were added to the vacated valence sites on the carbon atoms. The formula of ethylene is C 2 H 4, after breaking the tap bond and adding hydroxyl groups (through several stages) it looks like C 2 H 4 (OH) 2. This is ethylene glycol.

The ethylene molecule has linear structure, while a dihydric alcohol has something of a trans configuration in the placement of hydroxyl groups relative to the carbon backbone and to each other (this term fully applies to the position of the relative multiple bond). Such a dislocation corresponds to the most distant location of hydrogens from the functional groups, lower energy, and therefore maximum stability of the system. Simply put, one OH group “looks” up and the other looks down. At the same time, compounds with two hydroxyls are unstable: with one carbon atom, when formed in the reaction mixture, they immediately dehydrate, turning into aldehydes.

Classification

The chemical properties of ethylene glycol are determined by its origin from the group of polyhydric alcohols, namely the subgroup of diols, that is, compounds with two hydroxyl fragments at adjacent carbon atoms. A substance that also contains several OH substituents is glycerol. It has three alcohol functional groups and is the most common representative of its subclass.

Many compounds of this class are also obtained and used in chemical production for various syntheses and other purposes, but the use of ethylene glycol is more widespread and is involved in almost all industries. This issue will be discussed in more detail below.

Physical characteristics

The use of ethylene glycol is explained by the presence of a number of properties that are inherent in polyhydric alcohols. This distinctive features, characteristic only for of this class organic compounds.

The most important of the properties is the unlimited ability to mix with H 2 O. Water + ethylene glycol gives a solution with a unique characteristic: its freezing point, depending on the concentration of the diol, is 70 degrees lower than that of the pure distillate. It is important to note that this dependence is nonlinear, and upon reaching a certain quantitative glycol content, reverse effect- The freezing point increases as the percentage of solute increases. This feature has found application in the production of various antifreezes, “anti-freeze” liquids, which crystallize at extremely low thermal characteristics of the environment.

Except in water, the dissolution process proceeds well in alcohol and acetone, but is not observed in paraffins, benzenes, ethers and carbon tetrachloride. Unlike its aliphatic ancestor - such gaseous substance Like ethylene, ethylene glycol is a syrup-like, transparent liquid with a slight yellow tint, sweetish in taste, with an uncharacteristic odor, practically non-volatile. Freezing of one hundred percent ethylene glycol occurs at - 12.6 degrees Celsius, and boiling at +197.8. IN normal conditions the density is 1.11 g/cm 3 .

Receipt methods

Ethylene glycol can be obtained in several ways, some of them today have only historical or preparative significance, while others are actively used by humans on an industrial scale and beyond. Following in chronological order, let's look at the most important ones.

The first method for producing ethylene glycol from dibromoethane has already been described above. Ethylene formula, double bond which is broken, and the free valences are occupied by halogens, the main starting material in this reaction, in addition to carbon and hydrogen, contains two bromine atoms. The formation of an intermediate compound at the first stage of the process is possible precisely due to their elimination, i.e., replacement by acetate groups, which upon further hydrolysis are converted into alcohol groups.

In progress further development science, it has become possible to obtain ethylene glycol by direct hydrolysis of any ethanes substituted by two halogens at neighboring carbon atoms, using aqueous solutions of metal carbonates from alkaline group or (less environmentally friendly reagent) H 2 O and lead dioxide. The reaction is quite “labor-intensive” and occurs only at significantly elevated temperatures and pressure, but this did not stop the Germans from using this method during the world wars to produce ethylene glycol on an industrial scale.

Your role in the formation organic chemistry The method of obtaining ethylene glycol from ethylene chlorohydrin by hydrolysis with carbon salts of alkaline metals also played a role. When the reaction temperature increased to 170 degrees, the yield of the target product reached 90%. But there was a significant drawback - the glycol had to be somehow extracted from the salt solution, which directly involved a number of difficulties. Scientists have solved this issue by developing a method with the same starting material, but breaking the process into two stages.

Hydrolysis of ethylene glycol acetates, previously the final stage of the Wurtz method, has become in a separate way, when they managed to obtain the initial reagent by oxidizing ethylene in acetic acid with oxygen, that is, without the use of expensive and completely unenvironmentally friendly halogen compounds.

There are also many known methods for producing ethylene glycol by oxidizing ethylene with hydroperoxides, peroxides, organic peracids in the presence of catalysts (osmium compounds), etc. There are also electrochemical and radiation-chemical methods.

Characteristics of general chemical properties

The chemical properties of ethylene glycol are determined by its functional groups. The reactions may involve one hydroxyl substituent or both, depending on the process conditions. The main difference is reactivity is that due to the presence of several hydroxyls in a polyhydric alcohol and their mutual influence appear stronger than those of their monatomic “brothers”. Therefore, in reactions with alkalis, the products are salts (for glycol - glycolates, for glycerol - glycerates).

The chemical properties of ethylene glycol, as well as glycerin, include all reactions of monohydric alcohols. Glycol gives complete and partial esters in reactions with monobasic acids; glycolates, respectively, are formed with alkali metals, and in a chemical process with strong acids or their salts release aldehyde acetic acid- due to the detachment of a hydrogen atom from the molecule.

Reactions with active metals

Interaction of ethylene glycol with active metals(standing after hydrogen in the chemical tension series) at elevated temperatures gives ethylene glycolate of the corresponding metal, plus hydrogen is released.

C 2 H 4 (OH) 2 + X → C 2 H 4 O 2 X, where X is an active divalent metal.

for ethylene glycol

You can distinguish a polyhydric alcohol from any other liquid using a visual reaction that is characteristic only of this class of compounds. To do this, freshly precipitated alcohol (2), which has a characteristic blue tint, is poured into a colorless solution of alcohol. When mixed components interact, the precipitate dissolves and the solution turns saturated blue- as a result of the formation of copper glycolate (2).

Polymerization

The chemical properties of ethylene glycol are great value for the production of solvents. Intermolecular dehydration of the mentioned substance, that is, the elimination of water from each of the two glycol molecules and their subsequent association (one hydroxyl group is completely eliminated, and only hydrogen leaves the other), makes it possible to obtain a unique organic solvent - dioxane, which is often used in organic chemistry, despite its high toxicity.

Exchange of hydroxyl for halogen

When ethylene glycol reacts with hydrohalic acids, replacement of hydroxyl groups with the corresponding halogen is observed. The degree of substitution depends on the molar concentration of hydrogen halide in the reaction mixture:

HO-CH 2 -CH 2 -OH + 2HX → X-CH 2 -CH 2 -X, where X is chlorine or bromine.

Obtaining ethers

In the reactions of ethylene glycol with nitric acid (of a certain concentration) and monobasic organic acids(formic, acetic, propionic, oleaginous, valerian, etc.) formation of complex and, accordingly, simple monoesters occurs. At other concentrations nitric acid- glycol di- and trinitroesters. Used as a catalyst sulfuric acid given concentration.

The most important derivatives of ethylene glycol

Valuable substances that can be obtained from polyhydric alcohols using simple ones (described above) are ethylene glycol ethers. Namely: monomethyl and monoethyl, the formulas of which are HO-CH 2 -CH 2 -O-CH 3 and HO-CH 2 -CH 2 -O-C 2 H 5, respectively. Their chemical properties are in many ways similar to glycols, but, just like any other class of compounds, they have unique reaction features that are unique to them:

• Monomethylethylene glycol is a colorless liquid, but with a characteristic disgusting odor, boiling at 124.6 degrees Celsius, highly soluble in ethanol, other organic solvents and water, much more volatile than glycol, and with a density lower than that of water (about 0.965 g/cm 3).
• Dimethylethylene glycol is also a liquid, but with a less characteristic odor, a density of 0.935 g/cm 3, a boiling point of 134 degrees above zero and a solubility comparable to the previous homologue.

The use of cellosolves, as ethylene glycol monoesters are generally called, is quite common. They are used as reagents and solvents in organic synthesis. They are also used for anti-corrosion and anti-crystallization additives in antifreeze and motor oils.

Areas of application and pricing policy of the product range

The cost at factories and enterprises involved in the production and sale of such reagents fluctuates on average about 100 rubles per kilogram of such chemical compound, like ethylene glycol. The price depends on the purity of the substance and the maximum percentage of the target product.

The use of ethylene glycol is not limited to any one area. Thus, it is used as a raw material in the production of organic solvents, artificial resins and fibers, and liquids that freeze at subzero temperatures. It is involved in many industrial sectors such as automobile, aviation, pharmaceutical, electrical, leather, tobacco. Its importance for organic synthesis is undeniably significant.

It is important to remember that glycol is a toxic compound that can cause irreparable harm to human health. Therefore, it is stored in sealed containers made of aluminum or steel with mandatory inner layer, protecting the container from corrosion, only in vertical positions and rooms not equipped with heating systems, but with good ventilation. The term is no more than five years.

Definition and nomenclature of dihydric alcohols

Organic compounds containing two hydroxyl groups ($-OH-$) are called dihydric alcohols or diols.

The general formula of dihydric alcohols is $CnH_(2n)(OH)_2$.

When designating dihydric alcohols, according to the IUPAC nomenclature, the prefix di- is added to the ending -ol, that is, a dihydric alcohol has the ending “diol”. The numbers indicate which carbon atoms the hydroxyl groups are attached to, for example:

Figure 1.

1,2-propanediol trans-1,2-cyclohexanediol 1-cyclohexyl-1,4-pentadiol

IN systematic nomenclature there is a differentiation between 1,2-, 1,3-, 1,4-, etc. diols.

If a compound contains hydroxyl groups on adjacent (vicial) carbon atoms, then dihydric alcohols called glycols.

The names of glycols reflect the method of their preparation by hydroxylation of alkenes, for example:

Figure 2.

The existence of stable dihydric alcohols is possible, starting with ethane, which corresponds to one diol - ethylene glycol. For propane, two alcohols are possible: 1,2- and 1,3-propanediols.

Of the alcohols corresponding to normal butane, the following compounds may exist:

• both hydroxo groups are nearby - one in the $CH_3$ group, the other in the $CH_2$ group;
• both hydroxyls are located in adjacent $CH_2$ groups;
• hydroxo groups are adjacent to non-adjacent carbon atoms, in the $CH_3$ and $CH_2$ groups;
• both hydroxyls are located in $CH_3$ groups.

The following diols correspond to isobutane:

• hydroxo groups are located nearby - in the $CH_3$ and $CH$ groups;
• both hydroxyls are located in $CH_3$ groups:

Figure 3.

Dihydric alcohols can be classified based on which alcohol groups are included in their particle composition:

1. Diprimary glycols. Ethylene glycol contains two primary alcohol groups.
2. Disecondary glycols. Contains two secondary alcohol groups.
3. Two-tertiary glycols. Contain three secondary alcohol groups.
4. Mixed glycols: primary - secondary, primary - tertiary, secondary - tertiary.

For example: isopentane corresponds to secondary-tertiary glycol

Figure 4.

Hexane (tetramethylethane) corresponds to two-tertiary glycol:

Figure 5.

If in a dihydric alcohol both hydroxyls are located at adjacent carbon atoms, then these are $\alpha$-glycols. $\beta$-glycols appear when hydroxo groups are separated by one carbon atom. In $\gamma$-series diols, hydroxyls are located across two carbon atoms. With greater distance between hydroxyls, diols of the $\delta$- and $\varepsilon$-series appear.

Geminal diols

In the free state, only diols can exist that originate from hydrocarbons as a result of the replacement of two hydrogen atoms located at two different carbon atoms with hydroxyl groups. When hydroxo groups replace two hydrogen atoms at the same carbon atom, unstable compounds are formed - geminal diols or gem-diols.

Geminal diols are dihydric alcohols containing both hydroxyl groups on one carbon atom. These are unstable compounds that easily decompose with the elimination of water and the formation of a carbonyl compound:

Figure 6.

The equilibrium is shifted towards the formation of the ketone, so geminal diols are also called aldehyde or ketone hydrates.

The simplest representative of geminal diols is methylene glycol. This compound is relatively stable in aqueous solutions. However, attempts to isolate it lead to the appearance of a dehydration product - formaldehyde:

$HO-CH_2-OH \leftrightarrow H_2C=O + H_2O$

For example: A dihydric alcohol corresponding to ethane cannot exist in a free state if both hydroxyl groups are located at the same carbon atom. Water is immediately released and acetaldehyde is formed:

Figure 7.

Two dihydric alcohols corresponding to propane are also not capable of independent existence, since they will release water due to hydroxyls located at one carbon atom. In this case, propionaldehyde will be formed in one case, and acetone in the other:

Figure 8.

A small amount of heme-diols may not exist in a dissolved state. These are compounds that contain strong electron-withdrawing substituents, such as chloral hydrate and hexaphotracetone hydrate

Figure 9.

Physical properties of glycols

Glycols have the following physical properties:

• lower glycols are colorless transparent liquids with a sweetish taste;
• high boiling and melting points (boiling point of ethylene glycol 197$^\circ$С);
• high density and viscosity;
• good solubility in water, ethyl alcohol;
• poor solubility in non-polar solvents (for example, ethers and hydrocarbons).

General pattern: with increasing molecular weight of dihydric alcohols, the boiling point increases. At the same time, solubility in water decreases. Lower alcohols are mixed with water in any ratio. Higher diols have greater solubility in ether and less solubility in water.

For many substances, dihydric alcohols act as good solvents (the exception is aromatic and higher saturated hydrocarbons).

Alcohols whose molecules contain two hydroxyl groups are called dihydric or glycols. The general formula of dihydric alcohols is C n H 2n (OH) 2. Dihydric alcohols form homologous series, which can be easily written using the homologous series of saturated hydrocarbons, replacing two hydrogen atoms in their molecule with hydroxyl groups.

The first and most important representative of dihydric alcohols is ethylene glycol HOCH 2 -CH 2 OH (bp. = 197 o C). Antifreeze is made from it.

Glycols are stable in whose molecules the hydroxyl groups are located near different carbon atoms. If two hydroxyl groups are located near one carbon atom, then such dihydric alcohols are unstable, easily decompose, eliminating water due to hydroxyl groups and turning into aldehydes or ketones:

NOMENCLATURE

Depending on mutual position hydroxyl groups, α-glycols are distinguished (their hydroxyl groups are located near neighboring carbon atoms, which are located nearby, in position 1,2), β-glycols (their OH groups are located in position 1,3), γ-glycols (OH -groups – at position 1,4), δ-glycols (OH-groups – at position 1,5), etc.

For example: α-glycol - CH 2 OH-CHOH-CH 2 -CH 3

β-glycol - CH 2 OH-CH 2 -CHOH-CH 3

γ-glycol - CH 2 OH-CH 2 -CH 2 -CH 2 OH

According to rational nomenclature, the name α-glycols is formed from the name of the corresponding ethylene hydrocarbon, to which the word glycol is added. For example, ethylene glycol, propylene glycol, etc.

According to systematic nomenclature, the name of glycols is formed from the name of a saturated hydrocarbon, to which the suffix –diol is added, indicating the numbers of carbon atoms. Near which there are hydroxyl groups. For example, ethylene glycol CH 2 -OH-CH 2 OH according to the IUPAC nomenclature is ethanediol-1,2, and propylene glycol CH 3 -CHOH-CH 2 OH is propanediol-1,2.

ISOMERIA

The isomerism of dihydric alcohols depends on the structure of the carbon chain:

the positions of hydroxyl groups in the alcohol molecule, for example, propanediol-1,2 and propanediol-1,3.

OBTAINING METHODS

Glycols can be obtained using the following methods:

1. Hydrolysis of dihalogen derivatives of saturated hydrocarbons:

2.Hydrolysis of halogen alcohols:

3. Oxidation of ethylene hydrocarbons with potassium permanganate or performic acid:

4.Hydration of α-oxides:

5.Bimolecular reduction of carbonyl compounds:

CHEMICAL PROPERTIES

The chemical properties of glycols are similar to the properties of monohydric alcohols and are determined by the presence of two hydroxyl groups in their molecules. Moreover, one or both hydroxyl groups can take part in the reactions. However, due to the mutual influence of one hydroxyl group on another (especially in α-glycols), the acid-base properties of glycols are somewhat different from the similar properties of monohydric alcohols. Due to the fact that hydroxyl exhibits a negative inductive effect, one hydroxyl group withdraws electron density from another in a similar way to how the halogen atom does in the molecules of substituted monohydric alcohols. As a result of this influence acid properties dihydric alcohols increase compared to monohydric ones:

H-O CH 2 CH 2 O N

Therefore, glycols, unlike monohydric alcohols, easily react not only with alkali metals, but also with alkalis and even hydroxides heavy metals. With alkali metals and alkalis, glycols form complete and incomplete alcoholates (glycolates):

With hydroxides of some heavy metals, for example copper hydroxide, glycols form complex glycolates. In this case, Cu(OH) 2, which is insoluble in water, easily dissolves in glycol:

Copper in this complex forms two covalent bonds and two – coordination. The reaction is qualitative for dihydric alcohols.

Glycols can form complete and partial ethers and esters. Thus, during the interaction of incomplete glycolate alkali metal partial ethers are obtained with alkyl halides, and a complete ether is obtained from a complete glycolate:

Methyl and ethyl cellosolves are used as a solvent in the production of varnishes, smokeless powder(pyroxylin), acetate silk, etc.

With organic and mineral acids dihydric alcohols form two rows esters:

Ethylene glycol mononitrate Ethylene glycol dinitrate

Ethylene glycol dinitrate – strong explosive, which is used instead of nitroglycerin.

The oxidation of glycols is carried out stepwise, with the participation of one or both hydroxyl groups simultaneously with the formation of the following products:

Dihydric alcohols undergo a dehydration reaction. Moreover, α-, β- and γ-glycols, depending on the reaction conditions, remove water in different ways. The elimination of water from glycols can be carried out intra- and intermolecularly. For example:

Intramolecular elimination of water:

Intermolecular elimination of water.

In 1906, A.E. Favorsky, distilling ethylene glycol with sulfuric acid, obtained a cyclic ether-dioxane:

Dioxane is a liquid that boils at 101 o C, mixes with water in any ratio, is used as a solvent and as an intermediate in some syntheses.

During the intermolecular elimination of water from glycols, hydroxy esters (alcohol esters) can be formed, such as diethylene glycol:

Diethylene glycol

Diethylene glycol is also obtained by reacting ethylene glycol with ethylene oxide:

Diethylene glycol is a liquid with a boiling point of 245.5 o C; used as a solvent, for filling hydraulic devices, and also in the textile industry.

Dimethyl ether of diethylene glycol (diglyme) H 3 C-O-CH 2 -CH 2 -O-CH 2 -CH 2 -O-CH 3 has found wide application as a good solvent.

Polyethylene glycol

Polyglycols are used as components of various synthetic detergents.

Polyesters of ethylene glycol with dibasic acids are widely used, which are used in the production of synthetic fibers, for example lavsan (the name “lavsan” is derived from initial letters the following words – laboratory high molecular weight compounds Academy of Sciences):

With methanol, terephthalic acid forms dimethyl ether (dimethyl terephthalate, boiling point = 140 o C), which is then converted into ethylene glycol terephthalate by transesterification. Polycondensation of ethylene glycol terephthalate produces polyethylene terephthalate with molecular weight 15000-20000. Dacron fiber does not wrinkle and is resistant to different weather conditions.