Alcohols(or alkanols) are organic substances whose molecules contain one or more hydroxyl groups (-OH groups) connected to a hydrocarbon radical.
Classification of alcohols
According to the number of hydroxyl groups(atomicity) alcohols are divided into:
Monatomic, For example: 
Diatomic(glycols), for example:
Triatomic, For example: 
According to the nature of the hydrocarbon radical The following alcohols are released:
Limit containing only saturated hydrocarbon radicals in the molecule, for example: 
Unlimited containing multiple (double and triple) bonds between carbon atoms in the molecule, for example:
Aromatic, i.e. alcohols containing a benzene ring and a hydroxyl group in the molecule, connected to each other not directly, but through carbon atoms, for example:
Organic substances containing hydroxyl groups in the molecule, connected directly to the carbon atom of the benzene ring, differ significantly in chemical properties from alcohols and therefore are classified as an independent class of organic compounds - phenols.
For example:
There are also polyhydric (polyhydric alcohols) containing more than three hydroxyl groups in the molecule. For example, the simplest hexahydric alcohol hexaol (sorbitol)
Nomenclature and isomerism of alcohols
When forming the names of alcohols, a (generic) suffix is added to the name of the hydrocarbon corresponding to the alcohol. ol.
The numbers after the suffix indicate the position of the hydroxyl group in the main chain, and the prefixes di-, tri-, tetra- etc. - their number:
In the numbering of carbon atoms in the main chain, the position of the hydroxyl group takes precedence over the position of multiple bonds:
Starting from the third member of the homologous series, alcohols exhibit isomerism of the position of the functional group (propanol-1 and propanol-2), and from the fourth, isomerism of the carbon skeleton (butanol-1, 2-methylpropanol-1). They are also characterized by interclass isomerism - alcohols are isomeric to ethers:
Let's give a name to the alcohol, the formula of which is given below:
Name construction order:
1. The carbon chain is numbered from the end closest to the –OH group.
2. The main chain contains 7 C atoms, which means the corresponding hydrocarbon is heptane.
3. The number of –OH groups is 2, the prefix is “di”.
4. Hydroxyl groups are located at 2 and 3 carbon atoms, n = 2 and 4.
Alcohol name: heptanediol-2,4
Physical properties of alcohols
Alcohols can form hydrogen bonds both between alcohol molecules and between alcohol and water molecules. Hydrogen bonds arise from the interaction of a partially positively charged hydrogen atom of one alcohol molecule and a partially negatively charged oxygen atom of another molecule. It is thanks to hydrogen bonds between molecules that alcohols have abnormally high boiling points for their molecular weight. Thus, propane with a relative molecular weight of 44 under normal conditions is a gas, and the simplest of alcohols is methanol, having a relative molecular weight of 32, under normal conditions it is a liquid.
The lower and middle members of a series of saturated monohydric alcohols containing from 1 to 11 carbon atoms are liquids. Higher alcohols (starting from C12H25OH) at room temperature - solids. Lower alcohols have an alcoholic odor and a pungent taste; they are highly soluble in water. As the carbon radical increases, the solubility of alcohols in water decreases, and octanol no longer mixes with water.
Chemical properties of alcohols
The properties of organic substances are determined by their composition and structure. Alcohols confirm the general rule. Their molecules include hydrocarbon and hydroxyl groups, so the chemical properties of alcohols are determined by the interaction of these groups with each other.
The properties characteristic of this class of compounds are due to the presence of a hydroxyl group.
- Interaction of alcohols with alkali and alkaline earth metals. To identify the effect of a hydrocarbon radical on a hydroxyl group, it is necessary to compare the properties of a substance containing a hydroxyl group and a hydrocarbon radical, on the one hand, and a substance containing a hydroxyl group and not containing a hydrocarbon radical, on the other. Such substances can be, for example, ethanol (or other alcohol) and water. The hydrogen of the hydroxyl group of alcohol molecules and water molecules is capable of being reduced by alkali and alkaline earth metals (replaced by them)
- Interaction of alcohols with hydrogen halides. Substitution of a hydroxyl group with a halogen leads to the formation of haloalkanes. For example:
This reaction is reversible. - Intermolecular dehydrationalcohols- splitting off a water molecule from two alcohol molecules when heated in the presence of water-removing agents:
As a result of intermolecular dehydration of alcohols, ethers. Thus, when ethyl alcohol is heated with sulfuric acid to a temperature of 100 to 140°C, diethyl (sulfur) ether is formed. - The interaction of alcohols with organic and inorganic acids to form esters (esterification reaction)
The esterification reaction is catalyzed by strong inorganic acids. For example, when ethyl alcohol and acetic acid react, ethyl acetate is formed:
- Intramolecular dehydration of alcohols occurs when alcohols are heated in the presence of water-removing agents to a higher temperature than the temperature of intermolecular dehydration. As a result, alkenes are formed. This reaction is due to the presence of a hydrogen atom and a hydroxyl group at adjacent carbon atoms. An example is the reaction of producing ethene (ethylene) by heating ethanol above 140°C in the presence of concentrated sulfuric acid:
- Oxidation of alcohols usually carried out with strong oxidizing agents, for example, potassium dichromate or potassium permanganate in an acidic environment. In this case, the action of the oxidizing agent is directed to the carbon atom that is already bonded to the hydroxyl group. Depending on the nature of the alcohol and the reaction conditions, various products can be formed. Thus, primary alcohols are oxidized first to aldehydes and then to carboxylic acids:
The oxidation of secondary alcohols produces ketones: 
Tertiary alcohols are quite resistant to oxidation. However, under harsh conditions (strong oxidizing agent, high temperature), oxidation of tertiary alcohols is possible, which occurs with the rupture of carbon-carbon bonds closest to the hydroxyl group. - Dehydrogenation of alcohols. When alcohol vapor is passed at 200-300 °C over a metal catalyst, such as copper, silver or platinum, primary alcohols are converted into aldehydes, and secondary alcohols into ketones:
- Qualitative reaction to polyhydric alcohols.
The presence of several hydroxyl groups in the alcohol molecule at the same time determines the specific properties of polyhydric alcohols, which are capable of forming bright blue complex compounds soluble in water when interacting with a freshly obtained precipitate of copper (II) hydroxide. For ethylene glycol we can write:
Monohydric alcohols are not able to enter into this reaction. Therefore, it is a qualitative reaction to polyhydric alcohols.
Preparation of alcohols:
Use of alcohols
Methanol(methyl alcohol CH 3 OH) is a colorless liquid with a characteristic odor and a boiling point of 64.7 ° C. Burns with a slightly bluish flame. The historical name of methanol - wood alcohol is explained by one of the ways of its production by distilling hard wood (Greek methy - wine, get drunk; hule - substance, wood).
Methanol requires careful handling when working with it. Under the action of the enzyme alcohol dehydrogenase, it is converted in the body into formaldehyde and formic acid, which damage the retina, cause death of the optic nerve and complete loss of vision. Ingestion of more than 50 ml of methanol causes death.
Ethanol(ethyl alcohol C 2 H 5 OH) is a colorless liquid with a characteristic odor and a boiling point of 78.3 ° C. Flammable Mixes with water in any ratio. The concentration (strength) of alcohol is usually expressed as a percentage by volume. “Pure” (medicinal) alcohol is a product obtained from food raw materials and containing 96% (by volume) ethanol and 4% (by volume) water. To obtain anhydrous ethanol - “absolute alcohol”, this product is treated with substances that chemically bind water (calcium oxide, anhydrous copper (II) sulfate, etc.).
In order to make alcohol used for technical purposes unsuitable for drinking, small amounts of difficult-to-separate toxic, bad-smelling and disgusting-tasting substances are added to it and tinted. Alcohol containing such additives is called denatured or denatured alcohol.
Ethanol is widely used in industry for the production of synthetic rubber, medicines, is used as a solvent, is part of varnishes and paints, and perfumes. In medicine, ethyl alcohol is the most important disinfectant. Used for preparing alcoholic drinks.
When small amounts of ethyl alcohol enter the human body, they reduce pain sensitivity and block inhibition processes in the cerebral cortex, causing a state of intoxication. At this stage of the action of ethanol, water separation in the cells increases and, consequently, urine formation accelerates, resulting in dehydration of the body.
In addition, ethanol causes dilation of blood vessels. Increased blood flow in the skin capillaries leads to redness of the skin and a feeling of warmth.
In large quantities, ethanol inhibits brain activity (inhibition stage) and causes impaired coordination of movements. An intermediate product of ethanol oxidation in the body, acetaldehyde, is extremely toxic and causes severe poisoning.
Systematic consumption of ethyl alcohol and drinks containing it leads to a persistent decrease in brain productivity, death of liver cells and their replacement with connective tissue - liver cirrhosis.
Ethanediol-1,2(ethylene glycol) is a colorless viscous liquid. Poisonous. Unlimitedly soluble in water. Aqueous solutions do not crystallize at temperatures significantly below 0 °C, which makes it possible to use it as a component of non-freezing coolants - antifreeze for internal combustion engines.
Prolactriol-1,2,3(glycerin) is a viscous, syrupy liquid with a sweet taste. Unlimitedly soluble in water. Non-volatile. As a component of esters, it is found in fats and oils.
Widely used in cosmetics, pharmaceutical and food industries. In cosmetics, glycerin plays the role of an emollient and soothing agent. It is added to toothpaste to prevent it from drying out.
Glycerin is added to confectionery products to prevent their crystallization. It is sprayed onto tobacco, in which case it acts as a humectant that prevents the tobacco leaves from drying out and crumbling before processing. It is added to adhesives to prevent them from drying out too quickly, and to plastics, especially cellophane. In the latter case, glycerin acts as a plasticizer, acting like a lubricant between polymer molecules and thus giving plastics the necessary flexibility and elasticity.
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 areas 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 to the environment and humans 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 of 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 a linear structure, while a dihydric alcohol has a kind of trans configuration in the placement of hydroxyl groups in relation 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 has a more serious scale 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. These are distinctive features characteristic only of this class of 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 content of glycol, the opposite effect begins - the freezing temperature increases with increasing percentage of the soluble substance. 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 - a gaseous substance such as 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. Under normal conditions, the density is 1.11 g/cm3.
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, we will consider the most important ones.
The first method for producing ethylene glycol from dibromoethane has already been described above. The formula of ethylene, the double bond of which is broken and the free valences are occupied by halogens, the main starting material in this reaction, contains, in addition to carbon and hydrogen, 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 the process of further development of science, it became 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 the alkaline group or (a 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.
The method of producing ethylene glycol from ethylene chlorohydrin by hydrolysis with carbonic salts of alkaline metals also played a role in the development of organic chemistry. 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 resolved this issue by developing a method using the same starting material, but breaking the process into two stages.
The hydrolysis of ethylene glycol acetates, previously the final stage of the Wurtz method, became a separate method when they managed to obtain the starting reagent by oxidation of ethylene in acetic acid with oxygen, that is, without the use of expensive and completely non-environmental 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 in reactivity is that due to the presence of several hydroxyls in a polyhydric alcohol and their mutual influence, they are stronger than those of their monohydric “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, acetic acid aldehyde is released - due to the elimination of a hydrogen atom from the molecule.
Reactions with active metals
The interaction of ethylene glycol with active metals (standing after hydrogen in the chemical tension series) at elevated temperatures produces 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 deep blue - as a result of the formation of copper glycolate (2).
Polymerization
The chemical properties of ethylene glycol are of great importance 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 interacts 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, butyric, valerian, etc.), the formation of complex and, accordingly, simple monoesters occurs. At others, the concentration of nitric acid is di- and trinitroesters of glycol. Sulfuric acid of a given concentration is used as a catalyst.
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 a chemical compound such as 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 a mandatory inner layer that protects the container from corrosion, only in vertical positions and in 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:
Picture 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 are 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 neighboring $CH_2$ 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:
- Diprimary glycols. Ethylene glycol contains two primary alcohol groups.
- Disecondary glycols. Contains two secondary alcohol groups.
- Two-tertiary glycols. Contain three secondary alcohol groups.
- 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 hexaphotoracetone 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).
The reduction of alcohols to hydrocarbons is carried out by reacting them with hydroiodic acid in the presence of red phosphorus, which serves to regenerate hydroiodic acid.
HOCH 2 (CHOH) 4 CH 2 OH + 12HJ → CH 3 (CH 2) 4 CH 3 + 6J 2 + 6H 2 O
Sorbitol n-Hexane
2P + 3J 2 = 2PJ 3 PJ 3 + 3H 2 O = 3HJ + H 3 PO 3
Interaction with alkali and alkaline earth metals.
Like water, alcohols react with alkali and alkaline earth metals, as well as with magnesium, to form alcoholates and hydrogen.
2 (CH 3) 3 COH + 2K → 2 (CH 3) 3 COK + H 2
2 CH 3 OH + Mg → (CH 3 O) 2 Mg + H 2
Alcoholates of alkali metals are used as bases in elimination reactions from alkyl halides leading to the formation of alkenes.
Reactions of alcohols with carbonyl compounds, aldehydes and ketones, as well as with acids - esterification of acids to form esters, are usually considered in the presentation of the properties of carbonyl compounds and acids, respectively, and therefore will not be discussed in this section.
2.15. Dihydric alcohols
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Geminal diols - 1,1-diols containing two OH groups at the same carbon atom, are unstable and decompose with the elimination of water and the formation of a carbonyl compound:
The equilibrium in this process is shifted towards the formation of a ketone or aldehyde, so geminal diols themselves are usually called ketone or aldehyde hydrates if hydrogen replaces one of the radicals. Vicinal diols are 1,2-diols containing two OH groups at adjacent carbon atoms and are stable compounds. Hereinafter, the term 1,2-diols will be used for dihydric alcohols containing hydroxyl groups at adjacent carbon atoms.
2.16. Preparation of diols
One of the simplest methods for preparing 1,2-diols is the hydroxylation of alkenes under the action of potassium permanganate. Since potassium permanganate is a strong oxidizing agent that can not only hydroxylate the double bond, but also cleave the resulting vicinal diol, careful control of the reaction conditions is necessary. Optimal results are achieved when the reaction is carried out in a slightly alkaline environment (pH≈8) at low temperature with a dilute aqueous solution of KmnO 4 .
Other possible preparation methods may include hydrolysis of vicinal dihalides:
2.17. Properties of diols
Diols are characterized by the same reactions as monohydric alcohols. In addition, 1,2-diols exhibit some specific properties due to the presence of two adjacent hydroxyl groups. They will be discussed in this section.
Dehydration of 1,2-diols can proceed in two directions: 1) formation of dienes; 2) formation of cyclic ethers. Both of these reactions are catalyzed by acids. Dehydration of two-tertiary or two-secondary 1,2-diols easily occurs when they are heated with concentrated HBr.
The formation of cyclic ethers or cyclodehydration of 1,2-diols leads to the formation of 1,4-dioxane if the 1,2-diol is 1,2-ethanediol (ethylene glycol); in this case, a six-membered ring is formed from two moles of 1,2-ethanediol.
1,4- and 1,5-diols cyclize under these conditions to form five- and six-membered rings:
A qualitative reaction for 1,2-diols is a test with copper hydroxide in an alkaline medium. In this case, the dissolution of copper hydroxide is observed and a solution colored deep blue is obtained due to the formation of a Cu(II) chelate complex.
2.18. TRICAL ALCOHOLS
The most important of the trihydric alcohols is glycerol - propanetriol-1,2,3, which is part of lipids in the form of esters with higher saturated and unsaturated acids.
Glycerol
The primary alcohol group of glycerol (CH 2 OH) is more reactive than the secondary alcohol group (CHOH) and can be selectively converted to chloride or acid, respectively, by the action of reagents such as hydrogen chloride or nitric acid.
Dehydration of glycerol gives the simplest unsaturated aldehyde - acrolein (propenal):
Just like ethylene glycol, glycerin gives a qualitative reaction, characteristic of 1,2-diols, with copper hydroxide in an alkaline medium
2.19. ETHERS
NOMENCLATURE OF ETHERS
According to IUPAC nomenclature, ethers are considered alkoxyalkanes. The parent structure is determined by the longest alkyl group:
OBTAINING ETHERS
There are two general methods for the preparation of ethers: intermolecular dehydration of alcohols and nucleophilic substitution of halogen in alkyl halides under the action of alkali metal alkoxides (Williamson reaction). Both of these methods have been described above.
2.20. PROPERTIES OF ETHERS
Chemically, ethers are characterized by high inertness towards many reagents, especially of a basic nature. They are not broken down by organometallic compounds, hydrides and amides of alkali metals, as well as complex hydrides of boron and aluminum. Therefore, compounds such as diethyl ether, tetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether, dioxane and others are widely used as solvents in reactions with the above compounds.
Esters form very strong complexes with Lewis acids - BF 3, AlBr 3, SbCl 5, SbF 5, etc. composition 1:1, in which they act as Lewis bases
In relation to strong acids, esters exhibit the properties of bases (in this case, Bronsted bases) and form dialkyloxonium salts
Individual representatives
Methanol(methyl, wood alcohol) is a colorless liquid with a faint alcoholic odor. Large quantities of it are used in the production of formaldehyde, formic acid, methyl and dimethyl aniline, methylamines and many dyes, pharmaceuticals, and fragrances. Methanol is a good solvent, so it is widely used in the paint and varnish industry, as well as in the oil industry when purifying gasoline from mercaptans, and when isolating toluene by azeotropic rectification.
Ethanol(ethyl, wine alcohol) is a colorless liquid with a characteristic alcoholic odor. Ethyl alcohol is used in large quantities in the production of divinyl (processed into synthetic rubbers), diethyl ether, chloroform, chloral, high purity ethylene, ethyl acetate and other esters used as solvents for varnishes and fragrances (fruit essences). As a solvent, ethyl alcohol is widely used in the production of pharmaceuticals, fragrances, dyes and other substances. Ethanol is a good antiseptic.
Propyl and isopropyl alcohols. These alcohols, as well as their esters, are used as solvents. In some cases they replace ethyl alcohol. Isopropyl alcohol is used to produce acetone.
Butyl alcohol and its esters are used in large quantities as solvents for varnishes and resins
Isobutyl alcohol used to produce isobutylene, isobutyraldehyde, isobutyric acid, and also as a solvent.
Primary amyl and isoamyl alcohols make up the main part of fusel oil (by-products when producing ethyl alcohol from potatoes or cereals). Amyl alcohols and their esters are good solvents. Isoamyl acetate (pear essence) is used in the manufacture of soft drinks and some confectionery products.
Lecture No. 15.Polyhydric alcohols
Polyhydric alcohols. Classification. Isomerism. Nomenclature. Dihydric alcohols (glycols). Trihydric alcohols. Glycerol. Synthesis from fats and propylene. Application of glycol and glycerin in industry.
Two hydroxyl groups cannot be located on one carbon atom; such compounds easily lose water, turning into aldehydes or ketones:
This property is typical for everyone heme-diols. Sustainability heme-diols increases in the presence of electron-withdrawing substituents. An example of sustainable heme-diol is chloral hydrate.