Preparation of alcohols from alkene by hydration

Alkenes undergo hydration (addition of water across C=C bond) in presence of dilute H₂SO₄ to produce alcohols.


In the case of unsymmetrical alkenes, addition of water to the double bond is in accordance with Markownikoff’s rule.


Industrially, the alkene obtained by cracking of hydrocarbons, is absorbed by passing it into sulphuric acid at k and atmospheric pressure. The acid is diluted and treated with steam to release the alcohol.

Preparation of Alcohols from alkyl halides

Alkyl halides are hydrolysed to the corresponding alcohols on boiling with aqueous alkali (NaOH or KOH) or moist silver oxide (Ag₂O).

RX + NaOH --------> R-OH + NaX
CH₃Br + NaOH -----------> CH₃OH + NaBr

Primary alkyl halides give a high yield of alcohols. But tertiary alkyl halides get dehydrogenated into alkenes.





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Preparation of alcohols from alkene by hydration

Preparation of Alcohols from alkyl halides

Preparation of Ethanol (Drinking Alcohol)

Preparation of alcohols from Aldehydes and ketones

Preparation of Methanol

Preparation of alcohols from Aldehydes and ketones

Aldehydes and ketones are converted into alcohols by different methods, they are
1. Reduction
2. Using Grignard reagent

Reduction

Aldehydes and Ketones are reduced to the corresponding alcohols by
1. Addition of hydrogen in the presence of catalysts (catalytic hydrogenation), such as finely divided platinum, palladium, nickel and ruthenium

2. Treating aldehydes and ketones with chemical reagents such as sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4). Aldehydes yield primary alcohols while ketones give secondary alcohols.

R – CHO (Aldehyde) + H2 ----pd------> R CH2OH (primary alcohol)

CH3CHO (Acetaldehyde) + H2 ----Ni------> CH3CH2OH (Ethanol)

R CO R’ (Ketone) -----^1.NaBH4,_2.H2O---> R – CH –R’–OH (secondary alcohol)




UsIng Grignard reagent

When Grignard reagent are treated with aldehydes or ketones, addition products (magnesium salt) are formed. These products on hydrolysis give alcohols. The overall result is to blind the alkyl group of Grignard reagent to carbon of the carbonyl group and hydrogen to oxygen.
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While formaldehyde gives primary alcohols other aldehydes give secondary alcohols and ketones yield tertiary alcohols.