Halogenated acetylenes acetylene bromide

The mechanism of this remarkable reaction, in which a halogen atom in a tertiary acetylenic halide is substituted by the nucleophilic group NH2 with high yields, is not completely dear. Probably the ethynyl hydrogen atom is abstracted in the first step by the strongly basic amide. The results from solvolysis experiments carried out with tertiary acetylenic bromides [22] suggest that the intermediate -C C-C(CH3)2C1 looses CP to give the Zwitter-ionic intermediate C=C-C+(CH3)2. This is subsequently attacked by NH3 or-NH2. 

A much faster reaction for bromides than chlorides usually suggests attack on halogen, since bromine is more readily attacked by nucleophilic phosphorus. However, for phenyl acetylenes (82 = Ph) these rates... 

Thus reaction with alkyl halides such as allyl bromide or pro-pargyl bromide allow for the introduction of oleflnlc2. . or acetylenic side groups onto the phosphazene ring VI, while alcohol leads to the formation of hydrido-phosphazene complexes VII. The hydrogen in these compounds can be replaced with halogen to yield the first series of iodor-phosphazene compounds VIII. 

This is illustrated by the products of addition of hydrogen bromide to vinyl acetylene (177) (Traynard, 1962) (equation 35). Only in the case of halogen addition have products formally arising from electrophilic attack to the double bond been isolated in substantial amounts (Petrov et al., 1960). 

This hquid acetylenic endothermic compound j estimated as 230-270 kj/mol, 2 kJ/g) may be decomposed by mild shock, and when heated under confinement, it decomposes with explosive violence and may detonate. Addition of 20-30 wt% of toluene makes the bromide insensitive in laboratory impact and confinement tests [1] More recently, it was classed as extremely shock-sensitive [2]. It can be ignited by impact derived from the liquid-hammer elfect of accidental pressurisation of the aerated liquid, and will then undergo sustained (monopropellant) burning decomposition. Propargyl bromide, added dropwise to bromine, exploded as it neared the halogen [3]. The chloro analogue is similar, but less readily ignited [4]. 

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