Alcohol | physical properties of alcohol, reactions, & uses |

What is alcohol?

            Alcohol is a class of acyclic organic compounds made up of carbon, oxygen, and hydrogen. Alcohols are considered derivatives of water. When we replace one hydrogen of water with an alkyl group then alcohol is formed. Alcohol has a close resemblance with phenol class because both have the same functional group ( hydroxyl group –OH ).

          

alcohol

    On the basis of a number of no of hydroxyl group present in a compound they are designated as mono, di, tri, or polyhydric alcohol. Monohydric alcohol is further classified into three types:

·        Primary alcohol

          If  the hydroxyl group attached to that carbon atom which is further attached to one more carbon atom or no carbon atom, this compound is known as primary alcohol.

·        Secondary  alcohol

          If  the hydroxyl group attached to that carbon atom which is further attached to two more carbon atoms, than this compound is known as secondary alcohol.

·        Tertiary  alcohol

          If the hydroxyl group attached to that carbon atom which is further attached to three more carbon atoms, then this compound, is known as tertiary alcohol.

alcohol

Physical properties of alcohol

• 1.     The trivial name of alcohol is alkyl alcohol.
• 2.     The general formula of alcohol is R-OH.
• 3.   Alcohols are polar molecules, due to the presence of hydroxyl group so they are easily dissolve in water. They are able to make hydrogen bonding with water, but this ability decreases in higher alcohols
• 4.    Lower member of alcohol are colorless toxic liquids that have burning taste and sweat smell.

Methods for the preparation of alcohol

            Alcohols are prepared by different methods which are as follow:

v Hydration of alkene

          When hydrolysis of alkene is carried out then alcohol is formed in this reaction.

 Hydration of alkene

v Hydrolysis of alkyl halide

           When alkyl halides react with an aqueous solution of potassium hydroxide, alcohol is formed in this reaction by nucleophilic substitution reaction.

hydrolysis of alkyl halide

1. preparation on an industrial scale

          Methanol is prepared on an industrial scale by the distillation of wood. The other name of methanol is wood spirit. It is prepared from CO and hydrogen.

Preparation  of alcohol on an industrial scale

v Reaction of the Grignard reagent with aldehyde or ketones

          When Grignard reagent reacts with carbonyl compounds in the presence of ether the resulting product is alcohol.

alcohol from Grignard reagent

v From starch

          When starch reacts with water in the presence of the diastase enzyme in yeast, it is converted into maltose.  When fermentation of Maltose is carried out in the presence of the maltase enzyme in yeast, it is converted into glucose. Glucose is converted into alcohol in the presence zymase enzyme in yeast.

           But alcohol obtained through fermentation very little, only 12 to 14%. This obtained alcohol is distilled again and again to obtain 95% alcohol. This alcohol is known as rectified spirit.

preparation of alcohol from starch

v From molasses

          When the fermentation of molasses in the presence of the Zymase enzyme in yeast is carried out then alcohol is formed. Molasses is a residue that is obtained after the crystallization of sugar from the con. Sugar can juice.

 

preparation of alcohol from molasses

v Reduction of carboxylic acid

          When reduction of a carboxylic acid is carried out then alcohol is formed. This reduction occurs in very strong reducing an agent that is Lithium aluminum hydride in ether.

reduction of carboxylic acid

Reactions of alcohols

          The reaction of alcohol with other compounds occurs in two ways.

1.     Reaction in which O-H bond break

2.     Reaction in which C-O bond break

          Which the bond will break in a reaction, it depends upon the attacking reagent, if any electrophile attack on alcohol then O-H will break. If nucleophile attacks on alcohol then the C-O bond will break.

1.     Reaction in which O-H bond break

          The reaction in which O-H bond break is as follow:

Ø Reaction with sodium

          Alcohol reacts with sodium and form sodium ethoxide.

sodium ethoxide

1. Reaction with Grignard reagent

          Alcohol reacts with the Grignard reagent to form alkane.

reaction  of alcohol with Grignard reagent

1. Reaction with acetic acid

          Alcohol reacts with acetic acid to ethyl acetate.

1. Reaction  of alcohol with acetic acid

2.     Reaction in which C-O bond break

          The reactions in which the C-O bond breaks are as follow:

Ø Reaction with hydrochloric acid

          When alcohol reacts with hydrochloric acid then alkyl halides are formed.

ethyl chloride

Ø Reaction with thionyl chloride

          When alcohol reacts with thionyl chloride then alkyl halides are formed.

 Reaction  of alcohol with thionyl chloride

Ø Reaction with nitric acid

          When alcohol reacts with nitric acid then ethylamine is formed.

 Reaction with nitric acid

3.      Other reactions of alcohols

          Alcohols also, give some other reactions.

Ø Dehydration of alcohol

          When alcohol reacts with con. H₂SO₄ then it gives different products on different temperatures.

Dehydration of alcohol

_Ø   Reaction with PCl₃, PCl₅

          Alcohol reacts with PCl₃, PCl₅ to form alkyl halides.

alcohol

Ø Oxidation reaction of alcohol

          When oxidation of alcohol is carried out then ketones and aldehyde are formed. Acid dichromate reagent is used in this reaction.

oxidation of alcohol

Uses of Alcohols

1.     Ethanol is used as a solvent, fuel in many countries, and as a drink.
2.     Ethanol is also used as a preservative in biological specimen.
3.     Methanol is used as an antifreeze in the radiator of automobiles.
4.     Methanol is also used for denaturing alcohol.
5.     Alcohols are used as solvents for varnishes and paints.
6.     Ethanol is also used in the pharmaceutical industry.
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