Addition of water to acetylenic bonds

Experiments with cycloalkenes have shown that hydration of a double bond by addition of borane involves cw-addition to the double bond thus 85% of fraw.y-2-methylcyclopentanol is formed from 1-methylcyclopentene.77 

Addition of water to acetylenes occurs in acid media, particularly in the presence of mercury compounds. Acetylene itself gives acetaldehyde 78 

Addition of water to acetylenes with terminal triple bonds affords ketones exclusively — trifluoromethylacetylene is an exception.79 

Hydration of mono- and di-substituted acetylenes can in many cases be effected by acid alone, particularly readily by sulfuric acid thus (/ -bromophenyl)prop-iolic acid in concentrated sulfuric acid gives (/ -bromobenzoyl)acetic acid quantitatively 80 

4 -Dimethyltolane81 and phenylacetylene82 are hydrated in glacial acetic acid containing appropriate amounts of dilute sulfuric acid. 

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