Question

How does a ketone react with PCl5?,

Answer 1

When ketone is reacted with phosphorous pentachloride, chlorination takes place at the carbonyl carbon with substitution of the oxygen atom to give a geminal dichloride (with 2 Cl atoms on same carbon) according to the following equation: 

so we can say that acetone is converted into 2,2-dichloropropane by action of PCl₅

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