Primary Alcohols to Acid Chlorides

Acid or acyl chlorides are carboxylic acid derivatives, therefore, to convert a primary alcohol to an acid chloride, we need to first oxidize to a carboxylic acid. The carboxylic acid then can be converted to the corresponding acid chloride using thionyl chloride (SOCl₂), PCl_3, or PCl₅.

Secondary Alcohols to Acid Chlorides

Secondary alcohols cannot be oxidized to carboxylic acids as the reaction stops at ketones. Therefore, we can either convert the ketone to a carboxylic acid via a haloform (if it is a methyl ketone) reaction or to ester via the Baeyer-Villiger Oxidation and hydrolyze the ester to the corresponding acid. The acid is then converted to acyl chloride as we saw above:

You can read the post on the conversion of aldehydes and ketones to carboxylic acids for details about the mentioned reactions.

Another strategy to convert secondary alcohols to acid chlorides is to first convert the alcohol to an alkene via dehydration and cleave the double bond with a strong oxidizing agent such as ozone with H₂O₂ or KMnO₄ is acidic media:

Remember that the acid-catalyzed dehydration of alcohols goes via a carbocation intermediate thus rearrangements are possible. To avoid rearrangements, you can convert the alcohol to an alkyl halide, mesylate, or a tosylate and do a Zaitsev or Hofmann elimination to prepare the needed alkene:

Tertiary Alcohols to Acid Chlorides

Tertiary alcohols have room for further oxidation, so the only strategy here would be converting them to alkenes and oxidizing the latter to a carboxylic acid.

Check Also

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