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Preparation of Alcohols using Grignard Reagents
Concepts tested here
- Ring opening of epoxide by RMgX
All Questions
2006 AIPMT-PRE 1 question
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Ethylene oxide when treated with Grignard reagent yields :-Ethylene oxide (oxirane) is a strained three-membered ring with a polar C-O bond; its carbon atoms carry a partial positive charge.
In the Grignard reagent $R-MgX$, the alkyl group carries a partial negative charge and acts as a nucleophile.
The alkyl group attacks one of the ring carbons and the ring opens: $(CH_2)_2O + R-MgX \rightarrow R-CH_2-CH_2-OMgX$
Hydrolysis of this addition product gives the alcohol: $R-CH_2-CH_2-OMgX \xrightarrow{H_2O/H^+} R-CH_2-CH_2-OH + Mg(OH)X$
In the product the OH group is on a carbon attached to only one other carbon, so it is a primary alcohol with two more carbon atoms than the alkyl group of the Grignard reagent.
So ethylene oxide with a Grignard reagent yields a primary alcohol.