Write three general methods for the preparation of ethanal or propanal
Answers
Alcohols Preparation
A number of general methods for the preparation of aliphatic alcohols are described as follows. Preparation of Alcohols by Hydration of an Alkene The hydrolysis of Alkenes using sulphuric acid (i.e. the direct addition of water). The mechanism of the hydration reaction involves the addition of the Sulphuric Acid across the double bond of the alkene, followed by the displacement of the bisulphate ion by hydroxide ion to form the alcohol.
CH2=CH2 + H2SO4 ==> CH3CH2OSO3H + H20 ==> CH3CH2OH
Ethylene Ethyl Hydrogen Sulphate Ethanol
(Primary
Alcohol)
The only primary alcohol which may be obtained in this way is ethyl alcohol, and this method is not suitable for the preparation of methanol.
Preparation of Alcohols by reduction of Aldehydes The reduction of aldehydes , to primary alcohols, ketones to secondary alcohols by passing the vapour and molecular hydrogen over a heated nickel catalyst.
CH3CH2 CHO + 2H ==> CH3CH2CH2OH
Propionaldehyde Propanol
CH3COCH3 + 2H ==> CH3CHCH3
OH
Acetone Isopropanol
Preparation of Alcohols from Amines The action of Nitrous Acid, HNO2, on Primary Amines, RNH2.
C2H5NH2 + HON=O ==> C2H5OH + N2 + H2O