Electrophilic attack on acetylenes

The generalisation is often made that acetylenes undergo electrophilic attack less readily than olefins this is usually attributed to the lower polarisa-bility of the triple bond. In some cases, as in the acid-catalysed hydration of acetylenic ethers , the generalisation does not hold. However, the lower reactivity of acetylenic bonds in many electrophilic reactions explains the use of metal-ion catalysts, such as the well-known mercuric-ion-catalysed hydration of acetylene, and the greater tendency towards nucleophilic addition reactions. 

Hydration of acetylenes will occur in acidic media. The products of the reaction are carbonyl compounds derived from rearrangement of the intermediate vinyl alcohol, uiz. 

The addition of halogens to acetylenes has received rather more attention. In bromine addition, the principal kinetic form is 

The order of susceptibility towards substituent effects is much less in the acetylene series than in the olefins, but its direction is similar. A similar statement may be made about the direction, rates, and kinetics of addition of sulphenyl halides. While the simple acetylenes, such as sym-diphenylacetylene and 3-hexyne, required catalytic quantities of aluminium chloride before undergoing addition by 2,4-dinitrobenzene sulphenyl chloride , the rates of reaction of acetylene itself with some p-substituted benzene sulphenyl chlorides alone have been measured. The effect of the p-substituents 

The reaction of acetylenes with peracids has not received detailed investigation. The products of such oxidations are complex and usually arise from an initial cleavage of the epoxide to give acids or esters, e.g. 

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