This lesson is intended for independent study of the topic “Alcohols. Classification of alcohols. Saturated monohydric alcohols: structure and nomenclature.” You will learn that alcohols are hydrocarbons in which one hydrocarbon atom (or several) is replaced by hydroxyl, the types of alcohols, and their structure.
In this lesson you studied the topic “Alcohols. Classification of alcohols. Saturated monohydric alcohols: structure and nomenclature.” You learned that alcohols are hydrocarbons in which one hydrocarbon atom (or several) is replaced by hydroxyl, about the types of alcohols, about their structure.
Bibliography
1. Rudzitis G.E. Chemistry. Fundamentals of general chemistry. 10th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.
2. Chemistry. Grade 10. Profile level: academic. for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2008. - 463 p.
3. Chemistry. Grade 11. Profile level: academic. for general education institutions/ V.V. Eremin, N.E. Kuzmenko, V.V. Lunin et al. - M.: Bustard, 2010. - 462 p.
4. Khomchenko G.P., Khomchenko I.G. Collection of problems in chemistry for those entering universities. - 4th ed. - M.: RIA "New Wave": Publisher Umerenkov, 2012. - 278 p.
Homework
1. Nos. 3, 4 (p. 85) Rudzitis G.E., Feldman F.G. Chemistry: Organic chemistry. 10th grade: textbook for general education institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. M.: Education, 2012.
2. Write the structural formula of glycerol. Call it according to IUPAC nomenclature.
3. Write the reaction equations for the combustion of ethanol.
(alcohols) a class of organic compounds containing one or more COH groups, with the hydroxyl group OH bonded to an aliphatic carbon atom (compounds in which the carbon atom in the COH group is part of the aromatic ring are called phenols)The classification of alcohols is varied and depends on which structural feature is taken as a basis.
1. Depending on the number of hydroxyl groups in the molecule, alcohols are divided into:
a) monohydric (contain one hydroxyl OH group), for example, methanol CH 3 OH, ethanol C 2 H 5 OH, propanol C 3 H 7 OH
b) polyatomic (two or more hydroxyl groups), for example, ethylene glycol
HO С H 2 CH 2 OH , glycerol HOCH 2 CH(OH)CH 2 OH, pentaerythritol C(CH 2 OH) 4.Compounds in which one carbon atom
There are two hydroxyl groups, in most cases they are unstable and easily turn into aldehydes, eliminating water: RCH (OH) 2 ® RCH = O + H 2 O , does not exist.2. Based on the type of carbon atom to which the OH group is bonded, alcohols are divided into:
a) primary, in which the OH group is bonded to the primary carbon atom. A carbon atom (highlighted in red) that is bonded to just one carbon atom is called primary. Examples of primary alcohols ethanol C
H 3 CH 2 OH, propanol C H 3 CH 2 CH 2 OH. b) secondary, in which the OH group is bonded to a secondary carbon atom. A secondary carbon atom (highlighted in blue) is bonded to two carbon atoms at the same time, for example, secondary propanol, secondary butanol (Fig. 1).
Rice. 1. STRUCTURE OF SECONDARY ALCOHOLS
c) tertiary, in which the OH group is bonded to the tertiary carbon atom. The tertiary carbon atom (highlighted in green) is bonded to three neighboring carbon atoms simultaneously, for example, tertiary butanol and pentanol (Figure 2).
Rice. 2. STRUCTURE OF TERTIARY ALCOHOLS
According to the type of carbon atom, the alcohol group attached to it is also called primary, secondary or tertiary.
In polyhydric alcohols containing two or more OH groups, both primary and secondary HO groups may be present simultaneously, for example, in glycerol or xylitol (Fig. 3).
Rice. 3. COMBINATION OF PRIMARY AND SECONDARY OH-GROUPS IN THE STRUCTURE OF POLYATOMIC ALCOHOLS.
3. According to the structure of organic groups connected by an OH group, alcohols are divided into saturated (methanol, ethanol, propanol), unsaturated, for example, allyl alcohol CH 2 = CHCH 2 OH, aromatic (for example, benzyl alcohol C 6 H 5 CH 2 OH), containing as part of the group
R aromatic group.Unsaturated alcohols in which the OH group is “adjacent” to the double bond, i.e. bonded to a carbon atom simultaneously involved in the formation of a double bond (for example, vinyl alcohol CH 2 =CHOH), are extremely unstable and immediately isomerize ( cm.ISOMERIZATION) into aldehydes or ketones:
CH 2 =CHOH ® CH 3 CH=O Nomenclature of alcohols. For common alcohols with a simple structure, a simplified nomenclature is used: the name of the organic group is converted into an adjective (using the suffix and ending “ new") and add the word "alcohol":In the case where the structure of an organic group is more complex, rules common to all organic chemistry are used. Names compiled according to such rules are called systematic. In accordance with these rules, the hydrocarbon chain is numbered from the end to which the OH group is located closest. Next, this numbering is used to indicate the position of various substituents along the main chain; at the end of the name, the suffix “ol” and a number indicating the position of the OH group are added (Fig. 4):
4. SYSTEMATIC NAMES OF ALCOHOLS. Functional (OH) and substituent (CH 3) groups, as well as their corresponding digital indices, are highlighted in different colors.The systematic names of the simplest alcohols follow the same rules: methanol, ethanol, butanol. For some alcohols, trivial (simplified) names that developed historically have been preserved: propargyl alcohol NSє
CCH 2 OH, glycerol HOCH 2 CH(OH)CH 2 OH, pentaerythritol C(CH 2 OH) 4, phenethyl alcohol C 6 H 5 CH 2 CH 2 OH.Physical properties of alcohols.
Alcohols are soluble in most organic solvents; the first three simplest representatives - methanol, ethanol and propanol, as well as tertiary butanol (H 3 C) 3 СОН are mixed with water in any ratio. With an increase in the number of C atoms in the organic group, the hydrophobic (water-repellent) effect begins to affect, solubility in water becomes limited, and when R containing more than 9 carbon atoms practically disappears. Due to the presence of OH groups, hydrogen bonds arise between alcohol molecules.
Rice. 5. HYDROGEN BONDS IN ALCOHOLS(shown in dotted line)
As a result, all alcohols have a higher boiling point than the corresponding hydrocarbons, e.g. bp. ethanol +78° C, and T. boil. ethane 88.63° C; T. kip. butanol and butane, respectively, +117.4° C and 0.5° C.
Chemical properties of alcohols. Alcohols have a variety of transformations. The reactions of alcohols have some general principles: the reactivity of primary monohydric alcohols is higher than secondary ones, in turn, secondary alcohols are chemically more active than tertiary ones. For dihydric alcohols, in the case when OH groups are located at neighboring carbon atoms, increased (compared to monohydric alcohols) reactivity is observed due to the mutual influence of these groups. For alcohols, reactions are possible that involve the breaking of both CO and OH bonds.1. Reactions occurring through the OH bond.
When interacting with active metals (Na, K, Mg, Al), alcohols exhibit the properties of weak acids and form salts called alcoholates or alkoxides:
CH 3 OH + 2 Na ® 2 CH 3 OK + H 2Alcoholates are chemically unstable and, when exposed to water, hydrolyze to form alcohol and metal hydroxide:
C 2 H 5 OK + H 2 O
® C 2 H 5 OH + KOHThis reaction shows that alcohols are weaker acids compared to water (a strong acid displaces a weak one); in addition, when interacting with alkali solutions, alcohols do not form alcoholates. However, in polyhydric alcohols (in the case when OH groups are attached to neighboring C atoms), the acidity of the alcohol groups is much higher, and they can form alcoholates not only when interacting with metals, but also with alkalis:
HOCH 2 CH 2 OH + 2NaOH ® NaOCH 2 CH 2 ONa + 2H 2 OWhen HO groups in polyhydric alcohols are attached to non-adjacent C atoms, the properties of alcohols are close to monoatomic ones, since the mutual influence of HO groups does not appear.When interacting with mineral or organic acids, alcohols form esters compounds containing a fragment
ROA (A acid residue). The formation of esters also occurs during the interaction of alcohols with anhydrides and acid chlorides carboxylic acids(Fig. 6).Under the action of oxidizing agents (K 2 Cr 2 O 7, KMnO 4), primary alcohols form aldehydes, and secondary alcohols form ketones (Fig. 7)
Rice. 7. FORMATION OF ALDEHYDES AND KETONES DURING THE OXIDATION OF ALCOHOLS
The reduction of alcohols leads to the formation of hydrocarbons containing the same number of C atoms as the molecule of the original alcohol (Fig. 8).
8. BUTANOL RESTORATION2. Reactions occurring through the CO bond.
In the presence of catalysts or strong mineral acids, dehydration of alcohols (elimination of water) occurs, and the reaction can proceed in two directions:
a) intermolecular dehydration with the participation of two alcohol molecules, in which the CO bonds in one of the molecules are broken, resulting in the formation of ethers - compounds containing a fragment
R О R (Fig. 9A).b) intramolecular dehydration produces alkenes - hydrocarbons with a double bond. Often both processes, the formation of an ether and an alkene, occur in parallel (Fig. 9B).
In the case of secondary alcohols, during the formation of an alkene, two reaction directions are possible (Fig. 9B), the predominant direction is one in which, during the condensation process, hydrogen is split off from the least hydrogenated carbon atom (marked by number 3), i.e. surrounded by fewer hydrogen atoms (compared to atom 1). Shown in Fig. 10 reactions are used to produce alkenes and ethers.
The cleavage of the CO bond in alcohols also occurs when the OH group is replaced by a halogen or amino group (Fig. 10).
Rice. 10. REPLACEMENT OF OH-GROUP IN ALCOHOLS WITH HALOGEN OR AMINO GROUP
The reactions shown in Fig. 10 is used for the production of halocarbons and amines.
Preparation of alcohols. Some of the reactions shown above (Fig. 6,9,10) are reversible and, when conditions change, can proceed in the opposite direction, leading to the production of alcohols, for example, during the hydrolysis of esters and halocarbons (Fig. 11A and B, respectively), as well as by hydration alkenes by adding water (Fig. 11B).
Rice. eleven. OBTAINING ALCOHOLS BY HYDROLYSIS AND HYDRATION OF ORGANIC COMPOUNDS
The hydrolysis reaction of alkenes (Fig. 11, Scheme B) underlies the industrial production of lower alcohols containing up to 4 C atoms.
Ethanol is also formed during the so-called alcoholic fermentation of sugars, for example, glucose C 6 H 12 O 6. The process occurs in the presence of yeast and leads to the formation of ethanol and CO 2:
® 2C 2 H 5 OH + 2CO 2Fermentation can produce no more than a 15% aqueous solution of alcohol, since at a higher concentration of alcohol the yeast fungi die. Higher concentration alcohol solutions are obtained by distillation.
Methanol is produced industrially by the reduction of carbon monoxide at 400
° C under a pressure of 2030 MPa in the presence of a catalyst consisting of oxides of copper, chromium, and aluminum:® H 3 SON If instead of hydrolysis of alkenes (Fig. 11) oxidation is carried out, then dihydric alcohols are formed (Fig. 12)
12.
PREPARATION OF DIOHOMIC ALCOHOLSUse of alcohols.
The ability of alcohols to participate in a variety of chemical reactions allows them to be used to produce all kinds of organic compounds: aldehydes, ketones, carboxylic acids, ethers and esters, used as organic solvents in the production of polymers, dyes and drugs. Methanol CH 3 OH is used as a solvent, as well as in the production of formaldehyde, used to produce phenol-formaldehyde resins; methanol has recently been considered as a promising motor fuel. Large volumes of methanol are used in the production and transportation of natural gas. Methanol the most toxic compound among all alcohols, lethal dose when taken orally 100 ml.
Ethanol C 2 H 5 OH the starting compound for the production of acetaldehyde, acetic acid, as well as for the production of esters of carboxylic acids used as solvents. In addition, ethanol is the main component of all alcoholic beverages; it is widely used in medicine as a disinfectant.
Butanol is used as a solvent for fats and resins; in addition, it serves as a raw material for the production of fragrant substances (butyl acetate, butyl salicylate, etc.). In shampoos it is used as a component that increases the transparency of solutions.
Benzyl alcohol C 6 H 5 CH 2 OH in the free state (and in the form of esters) is found in the essential oils of jasmine and hyacinth. It has antiseptic (disinfecting) properties; in cosmetics it is used as a preservative for creams, lotions, dental elixirs, and in perfumery as a fragrant substance.
Phenethyl alcohol C 6 H 5 CH 2 CH 2 OH has a rose scent, is found in rose oil, and is used in perfumery.
Ethylene glycol HOCH 2 CH 2 OH is used in the production of plastics and as an antifreeze (an additive that reduces the freezing point of aqueous solutions), in addition, in the manufacture of textile and printing inks.
Diethylene glycol HOCH 2 CH 2 OCH 2 CH 2 OH is used to fill hydraulic brake devices, as well as in the textile industry for finishing and dyeing fabrics.
Glycerol
HOCH 2 CH (OH ) CH 2 OH It is used to produce polyester glyphthalic resins; in addition, it is a component of many cosmetic preparations. Nitroglycerin (Fig. 6) is the main component of dynamite, used in mining and railway construction as an explosive.Pentaerythritol (
HOCH 2) 4 C is used to produce polyesters (pentaphthalic resins), as a hardener for synthetic resins, as a plasticizer for polyvinyl chloride, and also in the production of the explosive tetranitropentaerythritol.Polyhydric alcohols xylitol HOCH 2 (CHOH) 3 CH 2 OH and sorbitol neHOCH 2 (CHOH) 4 CH 2 OH have a sweet taste, they are used instead of sugar in the production of confectionery products for patients with diabetes and people suffering from obesity. Sorbitol is found in rowan and cherry berries.
Mikhail Levitsky
LITERATURE Shabarov Yu.S. Organic chemistry. Moscow, “Chemistry”, 1994Ethyl alcohol or wine alcohol is a widespread representative of alcohols. There are many known substances that contain oxygen, along with carbon and hydrogen. Among the oxygen-containing compounds, I am primarily interested in the class of alcohols.
Ethanol
Physical properties of alcohol . Ethyl alcohol C 2 H 6 O is a colorless liquid with a peculiar odor, lighter than water (specific gravity 0.8), boils at a temperature of 78 °.3, and dissolves well many inorganic and organic substances. Rectified alcohol contains 96% ethyl alcohol and 4% water.
The structure of the alcohol molecule .According to the valency of the elements, the formula C 2 H 6 O corresponds to two structures:
To resolve the question of which of the formulas actually corresponds to alcohol, let us turn to experience.
Place a piece of sodium in a test tube with alcohol. A reaction will immediately begin, accompanied by the release of gas. It is not difficult to establish that this gas is hydrogen.
Now let’s set up the experiment so that we can determine how many hydrogen atoms are released during the reaction from each alcohol molecule. To do this, add a certain amount of alcohol, for example 0.1 gram molecule (4.6 grams), drop by drop from a funnel to a flask with small pieces of sodium (Fig. 1). The hydrogen released from the alcohol displaces water from the two-necked flask into the measuring cylinder. The volume of displaced water in the cylinder corresponds to the volume of released hydrogen.
Fig.1. Quantitative experience in producing hydrogen from ethyl alcohol.
Since 0.1 gram of alcohol molecule was taken for the experiment, it is possible to obtain about 1.12 hydrogen (in terms of normal conditions) liters This means that sodium displaces 11.2 from a gram molecule of alcohol liters, i.e. half a gram molecule, in other words 1 gram hydrogen atom. Consequently, sodium displaces only one hydrogen atom from each alcohol molecule.
Obviously, in the alcohol molecule, this hydrogen atom is in a special position compared to the other five hydrogen atoms. Formula (1) does not explain this fact. According to it, all hydrogen atoms are equally bonded to carbon atoms and, as we know, are not displaced by metallic sodium (sodium is stored in a mixture of hydrocarbons - in kerosene). On the contrary, formula (2) reflects the presence of one atom located in a special position: it is connected to carbon through an oxygen atom. We can conclude that it is this hydrogen atom that is less tightly bound to the oxygen atom; it turns out to be more mobile and is replaced by sodium. Therefore, the structural formula of ethyl alcohol is:
Despite the greater mobility of the hydrogen atom of the hydroxyl group compared to other hydrogen atoms, ethyl alcohol is not an electrolyte and does not dissociate into ions in an aqueous solution.
To emphasize that the alcohol molecule contains a hydroxyl group - OH, connected to a hydrocarbon radical, the molecular formula of ethyl alcohol is written as follows:
Chemical properties of alcohol . We saw above that ethyl alcohol reacts with sodium. Knowing the structure of alcohol, we can express this reaction with the equation:
The product of replacing hydrogen in alcohol with sodium is called sodium ethoxide. It can be isolated after the reaction (by evaporation of excess alcohol) as a solid.
When ignited in air, alcohol burns with a bluish, barely noticeable flame, releasing a lot of heat:
If you heat ethyl alcohol with a hydrohalic acid, for example HBr, in a flask with a refrigerator (or a mixture of NaBr and H 2 SO 4, which gives hydrogen bromide during the reaction), then an oily liquid will be distilled off - ethyl bromide C 2 H 5 Br:
This reaction confirms the presence of a hydroxyl group in the alcohol molecule.
When heated with concentrated sulfuric acid as a catalyst, the alcohol easily dehydrates, that is, it splits off water (the prefix “de” indicates the separation of something):
This reaction is used to produce ethylene in the laboratory. When alcohol is heated weaker with sulfuric acid (not higher than 140°), each molecule of water is split off from two molecules of alcohol, resulting in the formation of diethyl ether - a volatile, flammable liquid:
Diethyl ether (sometimes called sulfuric ether) is used as a solvent (tissue cleaning) and in medicine for anesthesia. He belongs to the class ethers - organic substances whose molecules consist of two hydrocarbon radicals connected through an oxygen atom: R - O - R1
Use of ethyl alcohol . Ethyl alcohol is of great practical importance. A lot of ethyl alcohol is consumed to produce synthetic rubber using the method of Academician S.V. Lebedev. By passing ethyl alcohol vapor through a special catalyst, divinyl is obtained:
which can then polymerize into rubber.
The alcohol is used to produce dyes, diethyl ether, various “fruit essences” and a number of other organic substances. Alcohol as a solvent is used to make perfumes and many medicines. Various varnishes are prepared by dissolving resins in alcohol. The high calorific value of alcohol determines its use as a fuel (motor fuel = ethanol).
Obtaining ethyl alcohol . World alcohol production is measured in millions of tons per year.
A common method for producing alcohol is the fermentation of sugary substances in the presence of yeast. These lower plant organisms (fungi) produce special substances - enzymes, which serve as biological catalysts for the fermentation reaction.
Cereal seeds or potato tubers rich in starch are taken as starting materials in the production of alcohol. Starch is first converted into sugar using malt containing the enzyme diastase, which is then fermented into alcohol.
Scientists have worked hard to replace food raw materials for alcohol production with cheaper non-food raw materials. These searches were crowned with success.
Recently, due to the fact that when cracking oil a lot of ethylene is formed, steel
The reaction of ethylene hydration (in the presence of sulfuric acid) was studied by A. M. Butlerov and V. Goryainov (1873), who also predicted its industrial significance. A method of direct hydration of ethylene by passing it in a mixture with water vapor over solid catalysts has also been developed and introduced into industry. Producing alcohol from ethylene is very economical, since ethylene is part of the cracking gases of oil and other industrial gases and, therefore, is a widely available raw material.
Another method is based on the use of acetylene as the starting product. Acetylene undergoes hydration according to the Kucherov reaction, and the resulting acetaldehyde is catalytically reduced with hydrogen in the presence of nickel into ethyl alcohol. The entire process of acetylene hydration followed by reduction with hydrogen on a nickel catalyst into ethyl alcohol can be represented by a diagram.
Homologous series of alcohols
In addition to ethyl alcohol, other alcohols are known that are similar to it in structure and properties. All of them can be considered as derivatives of the corresponding saturated hydrocarbons, in the molecules of which one hydrogen atom is replaced by a hydroxyl group:
Table
|
Hydrocarbons |
Alcohols |
Boiling point of alcohols in º C |
| Methane CH 4 | Methyl CH 3 OH | 64,7 |
| Ethane C 2 H 6 | Ethyl C 2 H 5 OH orCH 3 - CH 2 - OH | 78,3 |
| Propane C 3 H 8 | Propyl C 4 H 7 OH or CH 3 - CH 2 - CH 2 - OH | 97,8 |
| Butane C 4 H 10 | Butyl C 4 H 9 OH orCH 3 - CH 2 - CH 2 - OH | 117 |
Being similar in chemical properties and differing from each other in the composition of the molecules by a group of CH 2 atoms, these alcohols form a homologous series. Comparing the physical properties of alcohols, in this series, as well as in the series of hydrocarbons, we observe the transition of quantitative changes into qualitative changes. The general formula of alcohols in this series is R - OH (where R is a hydrocarbon radical).
Alcohols are known whose molecules contain several hydroxyl groups, for example:
Groups of atoms that determine the characteristic chemical properties of compounds, i.e., their chemical function, are called functional groups.
Alcohols are organic substances whose molecules contain one or more functional hydroxyl groups connected to a hydrocarbon radical .
In their composition, alcohols differ from hydrocarbons corresponding to them in the number of carbon atoms by the presence of oxygen (for example, C 2 H 6 and C 2 H 6 O or C 2 H 5 OH). Therefore, alcohols can be considered as products of partial oxidation of hydrocarbons.
Genetic relationship between hydrocarbons and alcohols
It is quite difficult to directly oxidize hydrocarbons into alcohol. In practice, it is easier to do this through a halogen derivative of a hydrocarbon. For example, to obtain ethyl alcohol starting from ethane C 2 H 6, you can first obtain ethyl bromide by the reaction:
and then convert ethyl bromide into alcohol by heating with water in the presence of alkali:
In this case, an alkali is needed to neutralize the resulting hydrogen bromide and eliminate the possibility of its reaction with alcohol, i.e. move this reversible reaction to the right.
In a similar way, methyl alcohol can be obtained according to the following scheme:
Thus, hydrocarbons, their halogen derivatives and alcohols are in a genetic connection with each other (relationship by origin).
The content of the article
ALCOHOLS(alcohols) - a class of organic compounds containing one or more C–OH groups, with the hydroxyl group OH bonded to an aliphatic carbon atom (compounds in which the carbon atom in the C–OH group is part of the aromatic ring are called phenols)
The classification of alcohols is varied and depends on which structural feature is taken as a basis.
1. Depending on the number of hydroxyl groups in the molecule, alcohols are divided into:
a) monohydric (contain one hydroxyl OH group), for example, methanol CH 3 OH, ethanol C 2 H 5 OH, propanol C 3 H 7 OH
b) polyatomic (two or more hydroxyl groups), for example, ethylene glycol
HO–CH 2 –CH 2 –OH, glycerol HO–CH 2 –CH(OH)–CH 2 –OH, pentaerythritol C(CH 2 OH) 4.
Compounds in which one carbon atom has two hydroxyl groups are in most cases unstable and easily turn into aldehydes, eliminating water: RCH(OH) 2 ® RCH=O + H 2 O
2. Based on the type of carbon atom to which the OH group is bonded, alcohols are divided into:
a) primary, in which the OH group is bonded to the primary carbon atom. A carbon atom (highlighted in red) that is bonded to just one carbon atom is called primary. Examples of primary alcohols - ethanol CH 3 - C H 2 –OH, propanol CH 3 –CH 2 – C H2–OH.
b) secondary, in which the OH group is bonded to a secondary carbon atom. A secondary carbon atom (highlighted in blue) is bonded to two carbon atoms at the same time, for example, secondary propanol, secondary butanol (Fig. 1).
Rice. 1. STRUCTURE OF SECONDARY ALCOHOLS
c) tertiary, in which the OH group is bonded to the tertiary carbon atom. The tertiary carbon atom (highlighted in green) is bonded to three neighboring carbon atoms simultaneously, for example, tertiary butanol and pentanol (Figure 2).
Rice. 2. STRUCTURE OF TERTIARY ALCOHOLS
According to the type of carbon atom, the alcohol group attached to it is also called primary, secondary or tertiary.
In polyhydric alcohols containing two or more OH groups, both primary and secondary HO groups may be present simultaneously, for example, in glycerol or xylitol (Fig. 3).
Rice. 3. COMBINATION OF PRIMARY AND SECONDARY OH-GROUPS IN THE STRUCTURE OF POLYATOMIC ALCOHOLS.
3. According to the structure of organic groups connected by an OH group, alcohols are divided into saturated (methanol, ethanol, propanol), unsaturated, for example, allyl alcohol CH 2 =CH–CH 2 –OH, aromatic (for example, benzyl alcohol C 6 H 5 CH 2 OH) containing an aromatic group in the R group.
Unsaturated alcohols in which the OH group is “adjacent” to the double bond, i.e. bonded to a carbon atom simultaneously involved in the formation of a double bond (for example, vinyl alcohol CH 2 =CH–OH), are extremely unstable and immediately isomerize ( cm ISOMERIZATION) to aldehydes or ketones:
CH 2 =CH–OH ® CH 3 –CH=O
Nomenclature of alcohols.
For common alcohols with a simple structure, a simplified nomenclature is used: the name of the organic group is converted into an adjective (using the suffix and ending “ new") and add the word "alcohol":
In the case where the structure of an organic group is more complex, rules common to all organic chemistry are used. Names compiled according to such rules are called systematic. In accordance with these rules, the hydrocarbon chain is numbered from the end to which the OH group is located closest. Next, this numbering is used to indicate the position of various substituents along the main chain; at the end of the name, the suffix “ol” and a number indicating the position of the OH group are added (Fig. 4):
Rice. 4. SYSTEMATIC NAMES OF ALCOHOLS. Functional (OH) and substituent (CH 3) groups, as well as their corresponding digital indices, are highlighted in different colors.
The systematic names of the simplest alcohols follow the same rules: methanol, ethanol, butanol. For some alcohols, trivial (simplified) names that have developed historically have been preserved: propargyl alcohol HCє C–CH 2 –OH, glycerin HO–CH 2 –CH(OH)–CH 2 –OH, pentaerythritol C(CH 2 OH) 4, phenethyl alcohol C 6 H 5 –CH 2 –CH 2 –OH.
Physical properties of alcohols.
Alcohols are soluble in most organic solvents; the first three simplest representatives - methanol, ethanol and propanol, as well as tertiary butanol (H 3 C) 3 СОН - are mixed with water in any ratio. With an increase in the number of C atoms in the organic group, a hydrophobic (water-repellent) effect begins to take effect, solubility in water becomes limited, and when R contains more than 9 carbon atoms, it practically disappears.
Due to the presence of OH groups, hydrogen bonds arise between alcohol molecules.
Rice. 5. HYDROGEN BONDS IN ALCOHOLS(shown in dotted line)
As a result, all alcohols have a higher boiling point than the corresponding hydrocarbons, e.g. bp. ethanol +78° C, and T. boil. ethane –88.63° C; T. kip. butanol and butane, respectively, +117.4° C and –0.5° C.
Chemical properties of alcohols.
Alcohols have a variety of transformations. The reactions of alcohols have some general principles: the reactivity of primary monohydric alcohols is higher than secondary ones, in turn, secondary alcohols are chemically more active than tertiary ones. For dihydric alcohols, in the case when OH groups are located at neighboring carbon atoms, increased (compared to monohydric alcohols) reactivity is observed due to the mutual influence of these groups. For alcohols, reactions are possible that involve the breaking of both C–O and O–H bonds.
1. Reactions occurring at the O–H bond.
When interacting with active metals (Na, K, Mg, Al), alcohols exhibit the properties of weak acids and form salts called alcoholates or alkoxides:
2CH 3 OH + 2Na ® 2CH 3 OK + H 2
Alcoholates are chemically unstable and, when exposed to water, hydrolyze to form alcohol and metal hydroxide:
C 2 H 5 OK + H 2 O ® C 2 H 5 OH + KOH
This reaction shows that alcohols are weaker acids compared to water (a strong acid displaces a weak one); in addition, when interacting with alkali solutions, alcohols do not form alcoholates. However, in polyhydric alcohols (in the case when OH groups are attached to neighboring C atoms), the acidity of the alcohol groups is much higher, and they can form alcoholates not only when interacting with metals, but also with alkalis:
HO–CH 2 –CH 2 –OH + 2NaOH ® NaO–CH 2 –CH 2 –ONa + 2H 2 O
When HO groups in polyhydric alcohols are attached to non-adjacent C atoms, the properties of alcohols are close to monoatomic ones, since the mutual influence of HO groups does not appear.
When interacting with mineral or organic acids, alcohols form esters - compounds containing the R-O-A fragment (A is the acid residue). The formation of esters also occurs during the interaction of alcohols with anhydrides and acid chlorides of carboxylic acids (Fig. 6).
Under the action of oxidizing agents (K 2 Cr 2 O 7, KMnO 4), primary alcohols form aldehydes, and secondary alcohols form ketones (Fig. 7)
Rice. 7. FORMATION OF ALDEHYDES AND KETONES DURING THE OXIDATION OF ALCOHOLS
The reduction of alcohols leads to the formation of hydrocarbons containing the same number of C atoms as the molecule of the original alcohol (Fig. 8).
Rice. 8. BUTANOL RESTORATION
2. Reactions occurring at the C–O bond.
In the presence of catalysts or strong mineral acids, dehydration of alcohols (elimination of water) occurs, and the reaction can proceed in two directions:
a) intermolecular dehydration involving two alcohol molecules, in which the C–O bonds of one of the molecules are broken, resulting in the formation of ethers—compounds containing the R–O–R fragment (Fig. 9A).
b) intramolecular dehydration produces alkenes - hydrocarbons with a double bond. Often both processes—the formation of an ether and an alkene—occur in parallel (Fig. 9B).
In the case of secondary alcohols, during the formation of an alkene, two reaction directions are possible (Fig. 9B), the predominant direction is one in which, during the condensation process, hydrogen is split off from the least hydrogenated carbon atom (marked by number 3), i.e. surrounded by fewer hydrogen atoms (compared to atom 1). Shown in Fig. 10 reactions are used to produce alkenes and ethers.
The cleavage of the C–O bond in alcohols also occurs when the OH group is replaced by a halogen or amino group (Fig. 10).
Rice. 10. REPLACEMENT OF OH-GROUP IN ALCOHOLS WITH HALOGEN OR AMINO GROUP
The reactions shown in Fig. 10 is used for the production of halocarbons and amines.
Preparation of alcohols.
Some of the reactions shown above (Fig. 6,9,10) are reversible and, when conditions change, can proceed in the opposite direction, leading to the production of alcohols, for example, during the hydrolysis of esters and halocarbons (Fig. 11A and B, respectively), as well as by hydration alkenes - by adding water (Fig. 11B).
Rice. eleven. OBTAINING ALCOHOLS BY HYDROLYSIS AND HYDRATION OF ORGANIC COMPOUNDS
The hydrolysis reaction of alkenes (Fig. 11, Scheme B) underlies the industrial production of lower alcohols containing up to 4 C atoms.
Ethanol is also formed during the so-called alcoholic fermentation of sugars, for example, glucose C 6 H 12 O 6. The process occurs in the presence of yeast and leads to the formation of ethanol and CO 2:
C 6 H 12 O 6 ® 2C 2 H 5 OH + 2CO 2
Fermentation can produce no more than a 15% aqueous solution of alcohol, since at a higher concentration of alcohol the yeast fungi die. Higher concentration alcohol solutions are obtained by distillation.
Methanol is produced industrially by the reduction of carbon monoxide at 400° C under a pressure of 20–30 MPa in the presence of a catalyst consisting of copper, chromium, and aluminum oxides:
CO + 2 H 2 ® H 3 COH
If instead of hydrolysis of alkenes (Fig. 11) oxidation is carried out, then dihydric alcohols are formed (Fig. 12)
Rice. 12. PREPARATION OF DIOHOMIC ALCOHOLS
Use of alcohols.
The ability of alcohols to participate in a variety of chemical reactions allows them to be used to produce all kinds of organic compounds: aldehydes, ketones, carboxylic acids, ethers and esters, used as organic solvents in the production of polymers, dyes and drugs.
Methanol CH 3 OH is used as a solvent, as well as in the production of formaldehyde, used to produce phenol-formaldehyde resins; methanol has recently been considered as a promising motor fuel. Large volumes of methanol are used in the production and transportation of natural gas. Methanol is the most toxic compound among all alcohols, the lethal dose when ingested is 100 ml.
Ethanol C 2 H 5 OH is the starting compound for the production of acetaldehyde, acetic acid, as well as for the production of carboxylic acid esters used as solvents. In addition, ethanol is the main component of all alcoholic beverages; it is widely used in medicine as a disinfectant.
Butanol is used as a solvent for fats and resins; in addition, it serves as a raw material for the production of fragrant substances (butyl acetate, butyl salicylate, etc.). In shampoos it is used as a component that increases the transparency of solutions.
Benzyl alcohol C 6 H 5 –CH 2 –OH in the free state (and in the form of esters) is found in the essential oils of jasmine and hyacinth. It has antiseptic (disinfecting) properties; in cosmetics it is used as a preservative for creams, lotions, dental elixirs, and in perfumery as a fragrant substance.
Phenethyl alcohol C 6 H 5 –CH 2 –CH 2 –OH has a rose scent, is found in rose oil, and is used in perfumery.
Ethylene glycol HOCH 2 –CH 2 OH is used in the production of plastics and as an antifreeze (an additive that reduces the freezing point of aqueous solutions), in addition, in the manufacture of textile and printing inks.
Diethylene glycol HOCH 2 –CH 2 OCH 2 –CH 2 OH is used to fill hydraulic brake devices, as well as in the textile industry for finishing and dyeing fabrics.
Glycerol HOCH 2 –CH(OH)–CH 2 OH is used to produce polyester glyphthalic resins; in addition, it is a component of many cosmetic preparations. Nitroglycerin (Fig. 6) is the main component of dynamite, used in mining and railway construction as an explosive.
Pentaerythritol (HOCH 2) 4 C is used to produce polyesters (pentaphthalic resins), as a hardener for synthetic resins, as a plasticizer for polyvinyl chloride, and also in the production of the explosive tetranitropentaerythritol.
Polyhydric alcohols xylitol СОН2–(СНН)3–CH2ОН and sorbitol СОН2– (СНН)4–СН2ОН have a sweet taste; they are used instead of sugar in the production of confectionery products for patients with diabetes and people suffering from obesity. Sorbitol is found in rowan and cherry berries.
Mikhail Levitsky
Alcohols are soluble in most organic solvents; the first three simplest representatives - methanol, ethanol and propanol, as well as tertiary butanol (H 3 C) 3 COH - are mixed with water in any ratio. With an increase in the number of C atoms in the organic group, a hydrophobic (water-repellent) effect begins to take effect, solubility in water becomes limited, and when R contains more than 9 carbon atoms, it practically disappears.
Due to the presence of OH groups, hydrogen bonds arise between alcohol molecules.
Rice. 5.
As a result, all alcohols have a higher boiling point than the corresponding hydrocarbons, e.g. bp. ethanol +78° C, and T. boil. ethane -88.63° C; T. kip. butanol and butane, respectively, +117.4° C and -0.5° C.
Chemical properties of alcohols
Alcohols have a variety of transformations. The reactions of alcohols have some general principles: the reactivity of primary monohydric alcohols is higher than secondary ones, in turn, secondary alcohols are chemically more active than tertiary ones. For dihydric alcohols, in the case when OH groups are located at neighboring carbon atoms, increased (compared to monohydric alcohols) reactivity is observed due to the mutual influence of these groups. For alcohols, reactions are possible that involve the breaking of both C-O and O-H bonds.
1). Reactions occurring through the O-H bond.
When interacting with active metals (Na, K, Mg, Al), alcohols exhibit the properties of weak acids and form salts called alcoholates or alkoxides:
2CH 3 OH + 2Na ® 2CH 3 OK + H 2
Alcoholates are chemically unstable and, when exposed to water, hydrolyze to form alcohol and metal hydroxide:
C 2 H 5 OK + H 2 O ® C 2 H 5 OH + KOH
This reaction shows that alcohols are weaker acids compared to water (a strong acid displaces a weak one); in addition, when interacting with alkali solutions, alcohols do not form alcoholates. However, in polyhydric alcohols (in the case when OH groups are attached to neighboring C atoms), the acidity of the alcohol groups is much higher, and they can form alcoholates not only when interacting with metals, but also with alkalis:
HO-CH 2 -CH 2 -OH + 2NaOH ® NaO-CH 2 -CH 2 -ONa + 2H 2 O
When HO groups in polyhydric alcohols are attached to non-adjacent C atoms, the properties of alcohols are close to monoatomic ones, since the mutual influence of HO groups does not appear.
When interacting with mineral or organic acids, alcohols form esters - compounds containing the R-O-A fragment (A is the acid residue). The formation of esters also occurs during the interaction of alcohols with anhydrides and acid chlorides of carboxylic acids (Fig. 6).
1. Combustion with heat release:
C 2 H 5 OH + 3O 2 2C 2 + 3H 2 O + a
- 2. Interaction with active metals:
- 2C 2 H 5 OH+ Na 2C 2 H 5 O Na + H 2 - alcoholates
- 3. Interaction with hydrogens.
Ce CH 3 -Ce + H 2 O
H 2 SO 4 - chloromethane
4. When the temperature rises in the presence of water purifying substances, the maximum operating conditions are not
C 2 H 5 OH t>140 0 C C 2 H 4 +H 2 O - ethylene
The reaction in which water is eliminated is called a detration reaction.
5. Interaction with each other to form ethers.
CH 3 -O - CH 3 - dimethyl ether
Reacts with acids to form esters.
Rice. 6.
Under the action of oxidizing agents (K 2 Cr 2 O 7, KMnO 4), primary alcohols form aldehydes, and secondary alcohols form ketones (Fig. 7)
Rice. 7.
The reduction of alcohols leads to the formation of hydrocarbons containing the same number of C atoms as the molecule of the original alcohol (Fig. 8).
Rice. 8.
2) Reactions occurring through the C-O bond
In the presence of catalysts or strong mineral acids, dehydration of alcohols (elimination of water) occurs, and the reaction can proceed in two directions:
- a) intermolecular dehydration involving two alcohol molecules, in which the C-O bonds in one of the molecules are broken, resulting in the formation of ethers - compounds containing the R-O-R fragment (Fig. 9A).
- b) intramolecular dehydration produces alkenes - hydrocarbons with a double bond. Often both processes - the formation of an ether and an alkene - occur in parallel (Fig. 9B).
In the case of secondary alcohols, during the formation of an alkene, two reaction directions are possible, the predominant direction is one in which, during the condensation process, hydrogen is split off from the least hydrogenated carbon atom (marked by number 3), i.e. surrounded by fewer hydrogen atoms (compared to atom 1).