Replacement of hydrogen by halogen in acetylenes

Replacement of hydrogen on triply bonded carbon by halogen can be effected directly or by way of a C=C-metal compound which, without isolation, is converted into the halogen compound by a further reaction. 

The procedure for chlorination, bromination, and iodination of acetylenes in alkaline hypohalite solution432 is applicable to alkynes, alkynols, and acetylenemonocarboxylic acids with at least one hydrogen on the C=C group. 

Reactions with hypoiodite are the fastest, those with hypochlorite the slowest. Free hypohalous acid does not substitute alkynes but affords a,dx-dihalo carbonyl compounds  

Gaseous alkynes are passed into alkaline (up to 23% referred to KOH) hypo-halite solution at 0°. Liquid alkynes or solutions of solid ones in light petroleum are shaken or stirred with the hypohalite solution at room temperature, sometimes with addition of an emulsifier. The necessary hypohalite solutions are prepared as follows 432 

Bromine (25 ml) is dropped into a solution of KOH (180 g) in water (800 ml) with vigorous stirring, producing a solution that is about 0.55n in KOBr and 2n in free KOH. 

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