Alcohols chemistry. Organic chemistry
These are derivatives of hydrocarbons in which one hydrogen atom is replaced by a hydroxy group. The general formula of alcohols is C&H 2 n +1 Oh.
Classification of monohydric alcohols.
Depending on the location where HE- group, distinguish:
Primary alcohols:
Secondary alcohols:
Tertiary alcohols:
.
Isomerism of monohydric alcohols.
For monohydric alcohols characteristic isomerism of the carbon skeleton and isomerism of the position of the hydroxy group.
Physical properties of monohydric alcohols.
The reaction proceeds according to Markovnikov's rule, therefore, only primary alcohol can be obtained from primary alkenes.
2. Hydrolysis of alkyl halides under the influence of aqueous solutions of alkalis:
If the heating is weak, then intramolecular dehydration occurs, resulting in the formation of ethers:
B) Alcohols can react with hydrogen halides, with tertiary alcohols reacting very quickly, while primary and secondary alcohols react slowly:
The use of monohydric alcohols.
Alcohols They are mainly used in industrial organic synthesis, in the food industry, in medicine and pharmacy.
DEFINITION
Alcohols- compounds containing one or more hydroxyl groups -OH, associated with a hydrocarbon radical.
The general formula for the homologous series of saturated monohydric alcohols is C n H 2 n +1 OH. In the name of alcohols there is a suffix - ol.
Depending on the number of hydroxyl groups, alcohols are divided into one- (CH 3 OH - methanol, C 2 H 5 OH - ethanol), two- (CH 2 (OH) -CH 2 -OH - ethylene glycol) and triatomic (CH 2 (OH )-CH (OH) -CH 2 -OH - glycerin). Depending on the carbon atom at which the hydroxyl group is located, primary (R-CH 2 -OH), secondary (R 2 CH-OH) and tertiary alcohols (R 3 C-OH) are distinguished.
Limiting monohydric alcohols are characterized by isomerism of the carbon skeleton (starting from butanol), as well as isomerism of the position of the hydroxyl group (starting from propanol) and interclass isomerism with ethers.
CH 3 -CH 2 -CH 2 -CH 2 -OH (butanol - 1)
CH 3 -CH (CH 3) - CH 2 -OH (2-methylpropanol - 1)
CH 3 -CH (OH) -CH 2 -CH 3 (butanol - 2)
CH 3 -CH 2 -O-CH 2 -CH 3 (diethyl ether)
Chemical properties of alcohols
1. The reaction proceeding with the breaking of the O-H bond:
- the acidic properties of alcohols are very weakly expressed. Alcohols react with alkali metals
2C 2 H 5 OH + 2K → 2C 2 H 5 OK + H 2
but do not react with alkalis. Alcoholates are completely hydrolyzed in the presence of water:
C 2 H 5 OK + H 2 O → C 2 H 5 OH + KOH
This means that alcohols are weaker acids than water.
- the formation of esters under the action of mineral and organic acids:
CH 3 -CO-OH + H-OCH 3 ↔ CH 3 COOCH 3 + H 2 O
- oxidation of alcohols under the action of potassium dichromate or potassium permanganate to carbonyl compounds. Primary alcohols are oxidized to aldehydes, which in turn can be oxidized to carboxylic acids.
R-CH 2 -OH + [O] → R-CH \u003d O + [O] → R-COOH
Secondary alcohols are oxidized to ketones:
R-CH(OH)-R’ + [O] → R-C(R’) = O
Tertiary alcohols are more resistant to oxidation.
2. Reaction with a break in the C-O bond.
- intramolecular dehydration with the formation of alkenes (occurs with strong heating of alcohols with water-removing substances (concentrated sulfuric acid)):
CH 3 -CH 2 -CH 2 -OH → CH 3 -CH \u003d CH 2 + H 2 O
- intermolecular dehydration of alcohols with the formation of ethers (occurs with weak heating of alcohols with water-removing substances (concentrated sulfuric acid)):
2C 2 H 5 OH → C 2 H 5 -O-C 2 H 5 + H 2 O
- weak basic properties of alcohols are manifested in reversible reactions with hydrogen halides:
C 2 H 5 OH + HBr → C 2 H 5 Br + H 2 O
Physical properties of alcohols
Lower alcohols (up to C 15) are liquids, higher alcohols are solids. Methanol and ethanol are miscible with water in any ratio. As the molecular weight increases, the solubility of alcohols in water decreases. Alcohols have high boiling and melting points due to the formation of hydrogen bonds.
Obtaining alcohols
Alcohols can be obtained using a biotechnological (fermentation) method from wood or sugar.
The laboratory methods for obtaining alcohols include:
- hydration of alkenes (the reaction proceeds when heated and in the presence of concentrated sulfuric acid)
CH 2 \u003d CH 2 + H 2 O → CH 3 OH
— hydrolysis of alkyl halides under the action of aqueous solutions of alkalis
CH 3 Br + NaOH → CH 3 OH + NaBr
CH 3 Br + H 2 O → CH 3 OH + HBr
— reduction of carbonyl compounds
CH 3 -CH-O + 2 [H] → CH 3 - CH 2 -OH
Examples of problem solving
EXAMPLE 1
| Exercise | Mass fractions of carbon, hydrogen and oxygen in a molecule of saturated monohydric alcohol are 51.18, 13.04 and 31.18%, respectively. Derive the formula for alcohol. |
| Solution | Let us denote the number of elements included in the alcohol molecule by indices x, y, z. Then, the general formula for alcohol will look like - C x H y O z. Let's write the ratio: x:y:z = ω(C)/Ar(C): ω(H)/Ar(H) : ω(O)/Ar(O); x:y:z = 51.18/12: 13.04/1: 31.18/16; x:y:z = 4.208: 13.04: 1.949. We divide the resulting values by the smallest, i.e. at 1.949. We get: x:y:z = 2:6:1. Therefore, the formula of alcohol is C 2 H 6 O 1. Or C 2 H 5 OH is ethanol. |
| Answer | The formula of limiting monohydric alcohol is C 2 H 5 OH. |
Along with hydrocarbons C a H in, which include atoms of two types - C and H, oxygen-containing organic compounds of type C are known a H in O With. In topic 2, we will look at oxygen-containing compounds that differ in:
1) the number of O atoms in the molecule (one, two or more);
2) the multiplicity of the carbon–oxygen bond (single C–O or double C=O);
3) the type of atoms connected to oxygen (C–O–H and C–O–C).
Lesson 16
Monohydric saturated alcohols
Alcohols are derivatives of hydrocarbons of the general formula ROH, where R is a hydrocarbon radical. The formula of alcohol is obtained from the formula of the corresponding alkane by replacing the H atom with the OH group: RN RON.
You can derive the chemical formula of alcohols in another way, including the oxygen atom O between the atoms
С–Н hydrocarbon molecules:
RN RON, CH 3 -H CH 3 -O-H.
The hydroxyl group OH is functional group of alcohols. That is, the OH group is a feature of alcohols; it determines the main physical and chemical properties of these compounds.
The general formula of monohydric saturated alcohols is C n H2 n+1OH.
Names of alcohols obtained from the names of hydrocarbons with the same number of C atoms as in alcohol, by adding the suffix - ol-. For example:
The name of alcohols as derivatives of the corresponding alkanes is typical for compounds with a linear chain. The position of the OH group in them is at the extreme or at the internal atom
C - indicate the number after the name:
The names of alcohols - derivatives of branched hydrocarbons - are made in the usual way. The main carbon chain is chosen, which should include a C atom connected to an OH group. The C atoms of the main chain are numbered so that the carbon with the OH group gets a lower number:
The name is composed, starting with the number indicating the position of the substituent in the main carbon chain: “3-methyl ...” Then the main chain is called: “3-methylbutane ...” Finally, the suffix is \u200b\u200badded - ol-(name of the OH group) and the number indicates the carbon atom to which the OH group is bound: "3-methylbutanol-2".
If there are several substituents on the main chain, they are listed sequentially, indicating the position of each with a number. Repeating substituents in the name are written using the prefixes "di-", "tri-", "tetra-", etc. For example:
Isomerism of alcohols. Isomers of alcohols have the same molecular formula, but a different order of connection of atoms in molecules.
Two types of alcohol isomerism:
1) isomerism of the carbon skeleton;
2)isomerism of the position of the hydroxyl group in the molecule.
Let's imagine the isomers of alcohol C 5 H 11 OH of these two types in a linear-angular notation:
According to the number of C atoms associated with the alcohol (–C–OH) carbon, i.e. adjacent to it, alcohols are called primary(one neighbor C), secondary(two C) and tertiary(three C-substituents at carbon –C–OH). For example:
A task. Make up one isomer of alcohols of the molecular formula C 6 H 13 OH with main carbon chain:
a) C 6, b) From 5 , in) From 4 , G) From 3
and name them.
Solution
1) We write down the main carbon chains with a given number of C atoms, leaving room for H atoms (we will indicate them later):
a) C-C-C-C-C-C; b) C–C–C–C–C; c) C–C–C–C; d) C-C-C.
2) Arbitrarily choose the place of attachment of the OH group to the main chain and indicate the carbon substituents at the internal C atoms:
In example d) it is not possible to place three substituents CH 3 - at the C-2 atom of the main chain. Alcohol C 6 H 13 OH has no isomers with a three-carbon main chain.
3) We arrange the H atoms at the carbons of the main chain of isomers a) - c), guided by the valency of carbon C (IV), and name the compounds:
EXERCISES.
1. Underline the chemical formulas of saturated monohydric alcohols:
CH 3 OH, C 2 H 5 OH, CH 2 \u003d CHCH 2 OH, CHCH 2 OH, C 3 H 7 OH,
CH 3 CHO, C 6 H 5 CH 2 OH, C 4 H 9 OH, C 2 H 5 OS 2 H 5, NOCH 2 CH 2 OH.
2. Name the following alcohols:
3.
Make structural formulas according to the names of alcohols: a) hexanol-3;
b) 2-methylpentanol-2; c) n-octanol; d) 1-phenylpropanol-1; e) 1-cyclohexylethanol.
4.
Compose the structural formulas of the isomers of alcohols of the general formula C 6 H 13 OH :
a) primary; b) secondary; c) tertiary.Name these alcohols.
5. According to the linear-angular (graphical) formulas of compounds, write down their structural formulas and give names to the substances:
Lesson 17
Low molecular weight alcohols - methanol CH 3 OH, ethanol C 2 H 5 OH, propanol C 3 H 7 OH, and isopropanol (CH 3) 2 CHOH - colorless mobile liquids with a specific alcoholic odor. High boiling points: 64.7 ° C - CH 3 OH, 78 ° C - C 2 H 5 OH, 97 ° C - n-C 3 H 7 OH and 82 ° C - (CH 3) 2 CHOH - are due to intermolecular hydrogen bond existing in alcohols. Alcohols C (1) -C (3) are miscible with water (dissolve) in any ratio. These alcohols, especially methanol and ethanol, are the most widely used in industry.
1. methanol synthesized from water gas:
2. ethanol receive ethylene hydration(by adding water to C 2 H 4):
3. Another way to get ethanol – fermentation of sugary substances by the action of yeast enzymes. The process of alcoholic fermentation of glucose (grape sugar) has the form:
4. ethanol receive from starch, as well as wood(cellulose) by hydrolysis to glucose and subsequent fermentation to alcohol:
5. Higher alcohols receive from halogenated hydrocarbons by hydrolysis under the action of aqueous solutions of alkalis:
A task.How to get propanol-1 from propane?
Solution
Of the five methods proposed above for the production of alcohols, none of them considers the production of alcohol from an alkane (propane, etc.). Therefore, the synthesis of propanol-1 from propane will include several stages. According to method 2, alcohols are obtained from alkenes, which in turn are available by dehydrogenation of alkanes. The process flow is as follows:
Another scheme for the same synthesis is one step longer, but it is easier to implement in the laboratory:
The addition of water to propene at the last stage proceeds according to Markovnikov's rule and leads to secondary alcohol - propanol-2. The task requires obtaining propanol-1. Therefore, the problem is not solved, we are looking for another way.
Method 5 consists in the hydrolysis of haloalkanes. The necessary intermediate for the synthesis of propanol-1 - 1-chloropropane - is obtained as follows. Chlorination of propane gives a mixture of 1- and 2-monochloropropanes:
1-chloropropane is isolated from this mixture (for example, using gas chromatography or due to different boiling points: for 1-chloropropane t bp = 47 °C, for 2-chloropropane t bp = 36 °C). The target propanol-1 is synthesized by the action of KOH or NaOH on 1-chloropropane with aqueous alkali:
Please note that the interaction of the same substances: CH 3 CH 2 CH 2 Cl and KOH - depending on the solvent (alcohol C 2 H 5 OH or water) leads to different products - propylene
(in alcohol) or propanol-1 (in water).
EXERCISES.
1. Give the reaction equations for the industrial synthesis of methanol from water gas and ethanol by ethylene hydration.
2. Primary alcohols RCH 2 OH obtained by hydrolysis of primary alkyl halides RCH 2 Hal, and secondary alcohols are synthesized by hydration of alkenes. Complete the reaction equations:
3.
Suggest methods for obtaining alcohols: a) butanol-1; b) butanol-2;
c) pentanol-3, based on alkenes and alkyl halides.
4. During the enzymatic fermentation of sugars, along with ethanol, a mixture of primary alcohols is formed in a small amount. C 3 -C 5 - fusel oil. The main component in this mixture is isopentanol.(CH 3) 2 CHCH 2 CH 2 OH, minor components – n-C 3 H 7 OH, (CH 3) 2 CHCH 2 OH and CH 3 CH 2 CH (CH 3) CH 2 OH. Name these "fusel" spirits according to the IUPAC nomenclature. Write an equation for the reaction of glucose fermentation C 6 H 12 O 6, in which all four impurity alcohols would be obtained in a molar ratio of 2:1:1:1, respectively. Enter the gas CO 2 to the right side of the equation in the amount of 1/3 mol of all initial atoms FROM , as well as the required number of molecules H 2 O.
5.
Give the formulas of all aromatic alcohols of the composition C 8 H 10 O. (In aromatic alcohols, the group HE removed from the benzene ring by one or more atoms FROM:
C 6 H 5 –
(CH 2)n –
HE.)
Answers to exercises for topic 2
Lesson 16
1. The chemical formulas of saturated monohydric alcohols are underlined:
CH 3 HE, FROM 2 H 5 HE, CH 2 \u003d CHCH 2 OH, CH CH 2 OH, FROM 3 H 7 HE,
CH 3 CHO, C 6 H 5 CH 2 OH, FROM 4 H 9 HE, C 2 H 5 OS 2 H 5, NOCH 2 CH 2 OH.
2. Names of alcohols according to structural formulas:
3. Structural formulas by the names of alcohols:
4. Isomers and names of alcohols of the general formula C 6 H 13 OH:
5. Structural formulas and names compiled according to graphical connection diagrams:
Depending on the type of hydrocarbon radical, and also, in some cases, the features of attaching the -OH group to this hydrocarbon radical, compounds with a hydroxyl functional group are divided into alcohols and phenols.
alcohols refers to compounds in which the hydroxyl group is attached to the hydrocarbon radical, but is not attached directly to the aromatic nucleus, if any, in the structure of the radical.
Examples of alcohols:
If the structure of the hydrocarbon radical contains an aromatic nucleus and a hydroxyl group, and is connected directly to the aromatic nucleus, such compounds are called phenols .
Examples of phenols:
Why are phenols classified in a separate class from alcohols? After all, for example, formulas
very similar and give the impression of substances of the same class of organic compounds.
However, the direct connection of the hydroxyl group with the aromatic nucleus significantly affects the properties of the compound, since the conjugated system of π-bonds of the aromatic nucleus is also conjugated with one of the lone electron pairs of the oxygen atom. Because of this, the O-H bond in phenols is more polar than in alcohols, which significantly increases the mobility of the hydrogen atom in the hydroxyl group. In other words, phenols have much more pronounced acidic properties than alcohols.
Chemical properties of alcohols
Monohydric alcohols
Substitution reactions
Substitution of a hydrogen atom in the hydroxyl group
1) Alcohols react with alkali, alkaline earth metals and aluminum (purified from the protective film of Al 2 O 3), while metal alcoholates are formed and hydrogen is released:
The formation of alcoholates is possible only when using alcohols that do not contain water dissolved in them, since alcoholates are easily hydrolyzed in the presence of water:
CH 3 OK + H 2 O \u003d CH 3 OH + KOH
2) Esterification reaction
The esterification reaction is the interaction of alcohols with organic and oxygen-containing inorganic acids, leading to the formation of esters.
This type of reaction is reversible, therefore, in order to shift the equilibrium towards the formation of an ester, it is desirable to carry out the reaction under heating, as well as in the presence of concentrated sulfuric acid as a water-removing agent:
Substitution of the hydroxyl group
1) When alcohols are treated with halogen acids, the hydroxyl group is replaced by a halogen atom. As a result of this reaction, haloalkanes and water are formed:
2) By passing a mixture of alcohol vapors with ammonia through heated oxides of some metals (most often Al 2 O 3), primary, secondary or tertiary amines can be obtained:
The type of amine (primary, secondary, tertiary) will depend to some extent on the ratio of the starting alcohol and ammonia.
Elimination reactions (cleavage)
Dehydration
Dehydration, which actually involves the splitting off of water molecules, in the case of alcohols differs by intermolecular dehydration and intramolecular dehydration.
At intermolecular dehydration alcohols, one water molecule is formed as a result of the elimination of a hydrogen atom from one alcohol molecule and a hydroxyl group from another molecule.
As a result of this reaction, compounds belonging to the class of ethers (R-O-R) are formed:
intramolecular dehydration alcohols proceeds in such a way that one molecule of water is split off from one molecule of alcohol. This type of dehydration requires somewhat more stringent conditions, consisting in the need to use a markedly higher heating compared to intermolecular dehydration. In this case, one alkene molecule and one water molecule are formed from one alcohol molecule:
Since the methanol molecule contains only one carbon atom, intramolecular dehydration is impossible for it. When methanol is dehydrated, only an ether (CH 3 -O-CH 3) can be formed.
It is necessary to clearly understand the fact that in the case of dehydration of unsymmetrical alcohols, intramolecular elimination of water will proceed in accordance with the Zaitsev rule, i.e. hydrogen will be split off from the least hydrogenated carbon atom:
Dehydrogenation of alcohols
a) Dehydrogenation of primary alcohols when heated in the presence of metallic copper leads to the formation aldehydes:
b) In the case of secondary alcohols, similar conditions will lead to the formation ketones:
c) Tertiary alcohols do not enter into a similar reaction, i.e. are not dehydrated.
Oxidation reactions
Combustion
Alcohols readily react with combustion. This produces a large amount of heat:
2CH 3 -OH + 3O 2 \u003d 2CO 2 + 4H 2 O + Q
incomplete oxidation
Incomplete oxidation of primary alcohols can lead to the formation of aldehydes and carboxylic acids.
In the case of incomplete oxidation of secondary alcohols, the formation of only ketones is possible.
Incomplete oxidation of alcohols is possible when they are exposed to various oxidizing agents, such as air oxygen in the presence of catalysts (copper metal), potassium permanganate, potassium dichromate, etc.
In this case, aldehydes can be obtained from primary alcohols. As you can see, the oxidation of alcohols to aldehydes, in fact, leads to the same organic products as dehydrogenation:
It should be noted that when using such oxidizing agents as potassium permanganate and potassium dichromate in an acidic medium, deeper oxidation of alcohols, namely to carboxylic acids, is possible. In particular, this manifests itself when using an excess of an oxidizing agent during heating. Secondary alcohols can only oxidize to ketones under these conditions.
LIMITED POLYTOMIC ALCOHOLS
Substitution of hydrogen atoms of hydroxyl groups
Polyhydric alcohols as well as monohydric react with alkali, alkaline earth metals and aluminum (cleaned from the filmAl 2 O 3 ); in this case, a different number of hydrogen atoms of hydroxyl groups in an alcohol molecule can be replaced:
2. Since the molecules of polyhydric alcohols contain several hydroxyl groups, they influence each other due to the negative inductive effect. In particular, this leads to a weakening of the O-H bond and an increase in the acidic properties of hydroxyl groups.
B about The greater acidity of polyhydric alcohols is manifested in the fact that polyhydric alcohols, in contrast to monohydric ones, react with some hydroxides of heavy metals. For example, one must remember the fact that freshly precipitated copper hydroxide reacts with polyhydric alcohols to form a bright blue solution of the complex compound.
Thus, the interaction of glycerol with freshly precipitated copper hydroxide leads to the formation of a bright blue solution of copper glycerate:
This reaction is qualitative for polyhydric alcohols. To pass the exam, it is enough to know the signs of this reaction, and it is not necessary to be able to write the interaction equation itself.
3. Just like monohydric alcohols, polyhydric ones can enter into an esterification reaction, i.e. react with organic and oxygen-containing inorganic acids to form esters. This reaction is catalyzed by strong inorganic acids and is reversible. In this regard, during the esterification reaction, the resulting ester is distilled off from the reaction mixture in order to shift the equilibrium to the right according to the Le Chatelier principle:
If carboxylic acids with a large number of carbon atoms in the hydrocarbon radical react with glycerol, resulting from such a reaction, esters are called fats.
In the case of esterification of alcohols with nitric acid, the so-called nitrating mixture is used, which is a mixture of concentrated nitric and sulfuric acids. The reaction is carried out under constant cooling:
An ester of glycerol and nitric acid, called trinitroglycerin, is an explosive. In addition, a 1% solution of this substance in alcohol has a powerful vasodilating effect, which is used for medical indications to prevent a stroke or heart attack.
Substitution of hydroxyl groups
Reactions of this type proceed by the mechanism of nucleophilic substitution. Interactions of this kind include the reaction of glycols with hydrogen halides.
So, for example, the reaction of ethylene glycol with hydrogen bromide proceeds with the successive replacement of hydroxyl groups by halogen atoms:
Chemical properties of phenols
As mentioned at the very beginning of this chapter, the chemical properties of phenols differ markedly from those of alcohols. This is due to the fact that one of the lone electron pairs of the oxygen atom in the hydroxyl group is conjugated with the π-system of conjugated bonds of the aromatic ring.
Reactions involving the hydroxyl group
Acid properties
Phenols are stronger acids than alcohols and dissociate to a very small extent in aqueous solution:
B about The greater acidity of phenols compared to alcohols in terms of chemical properties is expressed in the fact that phenols, unlike alcohols, are able to react with alkalis:
However, the acidic properties of phenol are less pronounced than even one of the weakest inorganic acids - carbonic. So, in particular, carbon dioxide, when passed through an aqueous solution of alkali metal phenolates, displaces free phenol from the latter as an acid even weaker than carbonic acid:
Obviously, any other stronger acid will also displace phenol from phenolates:
3) Phenols are stronger acids than alcohols, while alcohols react with alkali and alkaline earth metals. In this regard, it is obvious that phenols will also react with these metals. The only thing is that, unlike alcohols, the reaction of phenols with active metals requires heating, since both phenols and metals are solids:
Substitution reactions in the aromatic nucleus
The hydroxyl group is a substituent of the first kind, which means that it facilitates substitution reactions in ortho- and pair- positions in relation to oneself. Reactions with phenol proceed under much milder conditions than with benzene.
Halogenation
The reaction with bromine does not require any special conditions. When bromine water is mixed with a solution of phenol, a white precipitate of 2,4,6-tribromophenol is instantly formed:
Nitration
When a mixture of concentrated nitric and sulfuric acids (nitrating mixture) acts on phenol, 2,4,6-trinitrophenol is formed - a yellow crystalline explosive:
Addition reactions
Since phenols are unsaturated compounds, they can be hydrogenated in the presence of catalysts to the corresponding alcohols.
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INTRODUCTION
CHAPTER I. PROPERTIES OF ALCOHOLS.
1.1 PHYSICAL PROPERTIES OF ALCOHOLS.
1.2 CHEMICAL PROPERTIES OF ALCOHOLS.
1.2.1 Interaction of alcohols with alkali metals.
1.2.2 Substitution of the hydroxyl group of an alcohol with a halogen.
1.2.3 Dehydration of alcohols (water splitting).
1.2.4 Formation of esters of alcohols.
1.2.5 Dehydrogenation of alcohols and oxidation.
CHAPTER 2. METHODS FOR OBTAINING ALCOHOLS.
2.1 PRODUCTION OF ETHYL ALCOHOL.
2.2 PROCESS FOR OBTAINING METHYL ALCOHOL.
2.3 METHODS FOR OBTAINING OTHER ALCOHOLS.
CHAPTER 3. USE OF ALCOHOLS.
CONCLUSION.
BIBLIOGRAPHY
Introduction
Alcohols are called organic substances, the molecules of which contain one or more functional hydroxyl groups connected to a hydrocarbon radical.
They can therefore be considered as derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms are replaced by hydroxyl groups.
Depending on the number of hydroxyl groups, alcohols are divided into one-, two-, trihydric, etc. Dihydric alcohols are often called glycols by the name of the simplest representative of this group - ethylene glycol (or simply glycol). Alcohols containing more hydroxyl groups are usually referred to as polyols.
According to the position of the hydroxyl group, alcohols are divided into: primary - with a hydroxyl group at the end link of the chain of carbon atoms, which, in addition, has two hydrogen atoms (R-CH2-OH); secondary, in which the hydroxyl is attached to a carbon atom connected, in addition to the OH group, with one hydrogen atom, and tertiary, in which the hydroxyl is attached to a carbon that does not contain hydrogen atoms [(R)C-OH] (R-radical: CH3 , C2H5, etc.)
Depending on the nature of the hydrocarbon radical, alcohols are divided into aliphatic, alicyclic and aromatic. Unlike halogen derivatives, aromatic alcohols do not have the hydroxyl group directly bonded to the carbon atom of the aromatic ring.
According to the substitutional nomenclature, the names of alcohols are made up of the name of the parent hydrocarbon with the addition of the suffix -ol. If there are several hydroxyl groups in the molecule, then a multiplying prefix is used: di- (ethanediol-1,2), tri- (propanetriol-1,2,3), etc. The numbering of the main chain starts from the end closest to which is hydroxyl group. According to the radical-functional nomenclature, the name is derived from the name of the hydrocarbon radical associated with the hydroxyl group, with the addition of the word alcohol.
The structural isomerism of alcohols is determined by the isomerism of the carbon skeleton and the isomerism of the position of the hydroxyl group.
Consider isomerism using the example of butyl alcohols.
Depending on the structure of the carbon skeleton, two alcohols will be isomers - derivatives of butane and isobutane:
CH3 - CH2 - CH2 -CH2 - OH CH3 - CH - CH2 - OH
Depending on the position of the hydroxyl group on either carbon skeleton, two more isomeric alcohols are possible:
CH3 - CH - CH2 -CH3 H3C - C - CH3
The number of structural isomers in the homologous series of alcohols is rapidly increasing. For example, based on butane, there are 4 isomers, pentane - 8, and decane - already 567.
Chapter I. Properties of alcohols
1.1 Physical properties of alcohols
The physical properties of alcohols significantly depend on the structure of the hydrocarbon radical and the position of the hydroxyl group. The first representatives of the homologous series of alcohols are liquids, higher alcohols are solids.
Methanol, ethanol and propanol are miscible with water in all proportions. With an increase in molecular weight, the solubility of alcohols in water drops sharply, so, starting from hexyl, monohydric alcohols are practically insoluble. Higher alcohols are insoluble in water. The solubility of alcohols with a branched structure is higher than that of alcohols with an unbranched, normal structure. The lower alcohols have a characteristic alcoholic odor, the odor of the middle homologues is strong and often unpleasant. Higher alcohols are practically odorless. Tertiary alcohols have a particular characteristic musty smell.
Lower glycols are viscous, colorless, odorless liquids; highly soluble in water and ethanol, have a sweet taste.
With the introduction of a second hydroxyl group into the molecule, an increase in the relative density and boiling point of alcohols occurs. For example, the density of ethylene glycol at 0C is 1.13, and that of ethyl alcohol is 0.81.
Alcohols have abnormally high boiling points compared to many classes of organic compounds and what would be expected based on their molecular weights (Table 1).
Table 1.
Physical properties of alcohols.
|
Individual representatives |
Physical Properties |
|||
|
title |
structural formula |
|||
|
monatomic |
||||
|
Methanol (methyl) |
||||
|
Ethanol (ethyl) |
||||
|
Propanol-1 |
CH3CH2CH2OH |
|||
|
Propanol-2 |
CH3CH(OH)CH3 |
|||
|
Butanol-1 |
CH3(CH2)2CH2OH |
|||
|
2-Methylpropanol-1 |
(CH3)2CHCH2OH |
|||
|
Butanol-2 |
CH3CH(OH)CH2CH3 |
|||
|
diatomic |
||||
|
Ethandiol-1,2 (ethylene glycol) |
HOCH2CH2OH |
|||
|
Triatomic |
||||
|
Propantriol-1,2,3 (glycerin) |
HOCH2CH(OH)CH2OH |
This is due to the structural features of alcohols - with the formation of intermolecular hydrogen bonds according to the scheme:
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Branched alcohols boil lower than normal alcohols of the same molecular weight; primary alcohols boil above their secondary and tertiary isomers.
1.2 Chemical properties of alcohols
Like all oxygen-containing compounds, the chemical properties of alcohols are determined primarily by functional groups and, to a certain extent, by the structure of the radical.
A characteristic feature of the hydroxyl group of alcohols is the mobility of the hydrogen atom, which is explained by the electronic structure of the hydroxyl group. Hence the ability of alcohols to some substitution reactions, for example, with alkali metals. On the other hand, the nature of the bond between carbon and oxygen also matters. Due to the high electronegativity of oxygen compared to carbon, the carbon-oxygen bond is also somewhat polarized, with a partial positive charge at the carbon atom and a negative charge at the oxygen. However, this polarization does not lead to dissociation into ions, alcohols are not electrolytes, but are neutral compounds that do not change the color of the indicators, but they have a certain electric moment of the dipole.
Alcohols are amphoteric compounds, that is, they can exhibit both the properties of acids and the properties of bases.
1.2.1 Reaction of alcohols with alkali metals
Alcohols as acids interact with active metals (K, Na, Ca). When the hydrogen atom of the hydroxyl group is replaced by a metal, compounds are formed called alcoholates (from the name of alcohols - alcohols):
2R - OH + 2Na 2R - ONa + H2
The names of alcoholates are derived from the names of the corresponding alcohols, for example,
2С2Н5ОН + 2Na 2С2Н5 - ONa + H2
Lower alcohols react violently with sodium. With the weakening of acidic properties in medium homologues, the reaction slows down. Higher alcohols form alcoholates only when heated.
Alcoholates are readily hydrolyzed by water:
C2H5 - ONa + HOH C2H5 - OH + NaOH
Unlike alcohols, alcoholates are solids that are highly soluble in the corresponding alcohols.
Alcoholates of other metals, except for alkali metals, are also known, but they are formed in indirect ways. So, alkaline earth metals do not react directly with alcohols. But alcoholates of alkaline earth metals, as well as Mg, Zn, Cd, Al and other metals that form reactive organometallic compounds, can be obtained by the action of alcohol on such organometallic compounds.
1.2.2 Substitution of the hydroxyl group of an alcohol with a halogen
The hydroxyl group of alcohols can be replaced by a halogen by the action of hydrohalic acids, halogen compounds of phosphorus or thionyl chloride, for example,
R - OH + HCl RCl + HOH
The most convenient way to replace the hydroxyl group is to use thionyl chloride; the use of halogen phosphorus compounds is complicated by the formation of by-products. The water formed during this reaction decomposes haloalkyl into alcohol and hydrogen halide, so the reaction is reversible. For its successful implementation, it is necessary that the initial products contain a minimum amount of water. Zinc chloride, calcium chloride, sulfuric acid are used as water-removing agents.
This reaction proceeds with the splitting of the covalent bond, which can be represented by the equality
R: OH + H: Cl R - Cl + H2O
The rate of this reaction increases from primary to tertiary alcohols, and it also depends on the halogen: it is the highest for iodine, the lowest for chlorine.
1.2.3 Dehydration of alcohols (water elimination)
Depending on the dehydration conditions, olefins or ethers are formed.
Olefins (ethylene hydrocarbons) are formed by heating alcohol (except methyl) with an excess of concentrated sulfuric acid, as well as by passing alcohol vapor over aluminum oxide at 350 - 450. In this case, intramolecular elimination of water occurs, that is, H + and OH - are taken away from one and the same alcohol molecule, for example:
CH2 - CH2 CH2 = CH2 + H2O or
CH3-CH2-CH2OH CH3-CH=CH2+H2O
Ethers are formed by gently heating excess alcohol with concentrated sulfuric acid. In this case, intermolecular elimination of water occurs, that is, H + and OH - are taken away from the hydroxyl groups of different alcohol molecules, as shown in the diagram:
R - OH + HO - R R - O - R + H2O
2С2Н5ОН С2Н5-О-С2Н5+Н2О
Primary alcohols are more difficult to dehydrate than secondary ones, it is easier to remove a water molecule from tertiary alcohols.
1.2.4 Formation of esters of alcohols
Under the action of oxygen mineral and organic acids on alcohols, esters are formed, for example,
C2H5OH+CH3COOH C2H5COOSH3+H2O
ROH+SO2 SO2+H2O
- This kind of interaction of alcohol with acids is called an esterification reaction. The rate of esterification depends on the strength of the acid and the nature of the alcohol: with an increase in the strength of the acid, it increases, primary alcohols react faster than secondary ones, secondary alcohols - faster than tertiary ones. The esterification of alcohols with carboxylic acids is accelerated by the addition of strong mineral acids. The reaction is reversible, the reverse reaction is called hydrolysis. Esters are also obtained by the action of acid halides and anhydrides on alcohols.
1.2.5 Alcohol dehydrogenation and oxidation
The formation of different products in dehydrogenation and oxidation reactions is the most important property that makes it possible to distinguish between primary, secondary, and tertiary alcohols.
When passing vapors of primary or secondary, but not tertiary alcohol over metallic copper at an elevated temperature, two hydrogen atoms are released and the primary alcohol turns into an aldehyde, while secondary alcohols give ketones under these conditions.
CH3CH2OH CH3CHO + H2; CH3CH(OH)CH3 CH3COCH3 + H2;
tertiary alcohols do not dehydrate under the same conditions.
The same difference is shown by primary and secondary alcohols during oxidation, which can be carried out in a "wet" way, for example, by the action of chromic acid, or catalytically, moreover, with an oxidation catalyst
metallic copper also serves, and oxygen in the air serves as an oxidizing agent:
RCH2OH + O R-COH + H2O
CHOH + O C=O + H2O
Chapter 2. Methods for obtaining alcohols
In free form, many alcohols are found in volatile essential oils of plants and, together with other compounds, determine the smell of many flower essences, for example, rose oil, etc. In addition, alcohols are in the form of esters in many natural compounds - in wax, essential and fatty oils, animal fats. The most common and of the alcohols found in natural products is glycerol - an essential component of all fats, which still serve as the main source of its production. Among the compounds that are very common in nature are polyhydric aldehyde and keto alcohols, combined under the general name of sugars. The synthesis of technically important alcohols is discussed below.
2.1 Production of ethyl alcohol
Hydration processes are interactions with water. Accession of water in the course of technological processes can be carried out in two ways:
1. The direct method of hydration is carried out with the direct interaction of water and raw materials used for production. This process is carried out in the presence of catalysts. The more carbon atoms in the chain, the faster the hydration process.
2. The indirect method of hydration is carried out by the formation of intermediate reaction products in the presence of sulfuric acid. And then the resulting intermediate products are subjected to hydrolysis reactions.
In the modern production of ethyl alcohol, the method of direct hydration of ethylene is used:
CH2 \u003d CH2 + H2O C2H5OH - Q
Receiving is carried out in contact devices of the shelf type. The alcohol is separated from the reaction by-products in a separator, and rectification is used for final purification.
The reaction begins with an attack by a hydrogen ion on that carbon atom that is bonded to a large number of hydrogen atoms and is therefore more electronegative than the neighboring carbon. After that, water joins the neighboring carbon with the release of H +. Ethyl, sec-propyl and tert-butyl alcohols are prepared by this method on an industrial scale.
To obtain ethyl alcohol, various sugary substances have long been used, for example, grape sugar, or glucose, which is converted into ethyl alcohol by "fermentation" caused by the action of enzymes produced by yeast fungi.
С6Н12О6 2С2Н5ОН + 2СО2
Free glucose is found, for example, in grape juice, the fermentation of which produces grape wine with an alcohol content of 8 to 16%.
The starting product for the production of alcohol can be the starch polysaccharide contained, for example, in potato tubers, grains of rye, wheat, and corn. For conversion into sugary substances (glucose), starch is first subjected to hydrolysis. To do this, flour or chopped potatoes are brewed with hot water and, after cooling, malt is added - germinated, and then dried and pounded with water, barley grains. Malt contains diastase (a complex mixture of enzymes), which acts catalytically on the process of starch saccharification. At the end of saccharification, yeast is added to the resulting liquid, under the action of the enzyme of which alcohol is formed. It is distilled off and then purified by repeated distillation.
Currently, another polysaccharide, cellulose (fiber), which forms the main mass of wood, is also subjected to saccharification. To do this, cellulose is subjected to hydrolysis in the presence of acids (for example, sawdust at 150 -170C is treated with 0.1 - 5% sulfuric acid under a pressure of 0.7 - 1.5 MPa). The product thus obtained also contains glucose and is fermented into alcohol by the yeast. From 5500 tons of dry sawdust (waste from a sawmill of average productivity per year), you can get 790 tons of alcohol (counting as 100%). This makes it possible to save about 3,000 tons of grain or 10,000 tons of potatoes.
2.2 The process of obtaining methyl alcohol
The most important reaction of this type is the interaction of carbon monoxide and hydrogen at 400C under a pressure of 20–30 MPa in the presence of a mixed catalyst consisting of oxides of copper, chromium, aluminum, etc.
CO + 2H2 CH3OH - Q
The production of methyl alcohol is carried out in shelf-type contact apparatuses. Along with the formation of methyl alcohol, the processes of formation of reaction by-products take place, therefore, after the process has been carried out, the reaction products must be separated. To isolate methanol, a condenser cooler is used, and then the purification of alcohol is carried out using multiple rectification.
Almost all methanol (CH3OH) is obtained in industry by this method; besides it, under other conditions, mixtures of more complex alcohols can be obtained. Methyl alcohol is also formed during the dry distillation of wood, which is why it is also called wood alcohol.
2.3 Methods for obtaining other alcohols
Other methods for the synthetic production of alcohols are also known:
hydrolysis of halogen derivatives when heated with water or an aqueous solution of alkali
CH3 - CHBr - CH3 + H2O CH3 - CH(OH) - CH3 + HBr
primary and secondary alcohols are obtained, tertiary haloalkyls form olefins during this reaction;
hydrolysis of esters, mainly natural ones (fats, waxes);
oxidation of saturated hydrocarbons at 100-300 and a pressure of 15-50 atm.
Olefins are converted by oxidation into cyclic oxides, which, when hydrated, give glycols, so ethylene glycol is obtained in industry:
CH2 = CH2 CH2 - CH2 HOCH2 - CH2OH;
There are methods that have mainly laboratory use; some of them are practiced in fine industrial synthesis, for example, in the production of small quantities of valuable alcohols used in perfumery. These methods include aldol condensation or the Grignard reaction. So, according to the method of the chemist P.P. Shorygin, phenylethyl alcohol is obtained from ethylene oxide and phenylmagnesium halide - a valuable fragrant substance with the smell of a rose.
Chapter 3
Due to the variety of properties of alcohols of various structures, the scope of their application is very extensive. Alcohols - wood, wine and fusel oils - have long served as the main source of raw materials for the production of acyclic (fatty) compounds. Currently, most of the organic raw materials are supplied by the petrochemical industry, in particular in the form of olefins and paraffinic hydrocarbons. The simplest alcohols (methyl, ethyl, propyl, butyl) are consumed in large quantities as such, as well as in the form of esters of acetic acid, as solvents in paint and varnish production, and higher alcohols, starting with butyl, in the form of phthalic, sebacic and other dibasic esters. acids - as plasticizers.
Methanol serves as a raw material for the production of formaldehyde, from which synthetic resins are prepared, which are used in large quantities in the production of phenol-formaldehyde plastic materials, methanol serves as an intermediate for the production of methyl acetate, methyl and dimethylaniline, methylamines and many dyes, pharmaceuticals, fragrances and other substances . Methanol is a good solvent and is widely used in the paint and varnish industry. In the oil refining industry, it is used as an alkali solvent in the purification of gasoline, as well as in the separation of toluene by azeotropic distillation.
Ethanol is used in the composition of ethyl liquid as an additive to fuels for carburetor internal combustion engines. Ethyl alcohol is consumed in large quantities in the production of divinyl, for the production of one of the most important insecticides, DDT. It is widely used as a solvent in the production of pharmaceutical, fragrance, coloring and other substances. Ethyl alcohol is a good antiseptic.
Ethylene glycol is successfully used to prepare antifreeze. It is hygroscopic, therefore it is used in the manufacture of printing inks (textile, printing and stamp). Ethylene glycol nitrate is a powerful explosive that replaces nitroglycerin to a certain extent.
Diethylene glycol - used as a solvent and for filling hydraulic brake devices; in the textile industry, it is used for finishing and dyeing fabrics.
Glycerin - is used in large quantities in the chemical, food (for the manufacture of confectionery, liqueurs, soft drinks, etc.), textile and printing industries (added to printing ink to prevent drying), as well as in other industries - the production of plastics and varnishes, explosives and gunpowders, cosmetics and medicines, as well as antifreeze.
Of great practical importance is the reaction of catalytic dehydrogenation and dehydration of wine alcohol, developed by the Russian chemist S.V. Lebedev and flowing according to the scheme:
2C2H5OH 2H2O+H2+C4H6;
the resulting butadiene CH2=CH-CH=CH2-1,3 is a raw material for the production of synthetic rubber.
Some aromatic alcohols, having long side chains in the form of their sulfonated derivatives, serve as detergents and emulsifiers. Many alcohols, such as linalool, terpineol, etc., are valuable aromatic substances and are widely used in perfumery. The so-called nitroglycerin and nitroglycols, as well as some other nitric acid esters of di-, tri- and polyhydric alcohols, are used in mining and road construction as explosives. Alcohols are needed in the production of medicines, in the food industry, perfumery, etc.
Conclusion
Alcohols can have a negative effect on the body. Methyl alcohol is especially poisonous: 5-10 ml of alcohol cause blindness and severe poisoning of the body, and 30 ml can be fatal.
Ethyl alcohol is a drug. When taken orally, due to its high solubility, it is quickly absorbed into the blood and has a stimulating effect on the body. Under the influence of alcohol, a person's attention weakens, reaction slows down, coordination is disturbed, swagger appears, rudeness in behavior, etc. All this makes him unpleasant and unacceptable to society. But the consequences of drinking alcohol can be deeper. With frequent consumption, addiction appears, addiction to it and, in the end, a serious illness - alcoholism. Alcohol affects the mucous membranes of the gastrointestinal tract, which can lead to gastritis, gastric ulcer, duodenal ulcer. The liver, where the destruction of alcohol should occur, failing to cope with the load, begins to degenerate, resulting in cirrhosis. Penetrating into the brain, alcohol has a toxic effect on nerve cells, which manifests itself in a violation of consciousness, speech, mental abilities, in the appearance of mental disorders and leads to personality degradation.
Alcohol is especially dangerous for young people, since metabolic processes are intense in a growing body, and they are especially sensitive to toxic effects. Therefore, young people can develop alcoholism faster than adults.
Bibliography
1. Glinka N.L. General chemistry. - L.: Chemistry, 1978. - 720 p.
2. Dzhatdoeva M.R. Theoretical foundations of progressive technologies. Chemical section. - Essentuki: EGIEiM, 1998. - 78 p.
3. Zurabyan S.E., Kolesnik Yu.A., Kost A.A. Organic Chemistry: Textbook. - M.: Medicine, 1989. - 432 p.
4. Metlin Yu.G., Tretyakov Yu.D. Fundamentals of General Chemistry. - M.: Enlightenment, 1980. - 157 p.
5. Nesmeyanov A.N., Nesmeyanov N.A. Beginnings of organic chemistry. - M.: Chemistry, 1974. - 624 p.
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