Question

Write the preparation of dehydrohalogenation vicinal and geminal dihalides

Answer 1

the preparation of dehydrohalogenation vicinal and geminal dihalides

In organohalogen compound: Dehydrohalogenation of a dihalide. Treatment of a geminal dihalide (both halogens on the same carbon) or a vicinal dihalide (halogens on adjacent carbons) with a base such as sodium ethoxide (NaOCH2CH3) yields a vinylic halide.

industrial process for the manufacture of acetylene. However, the method has now been replaced by a process in which methane is pyrolyzed in a flow system with short contact time.



This reaction is endothermic at ordinary temperatures, but is thermodynamically favored at high temperatures.

Laboratory Methods of Preparation of Alkynes:

1.   Dehydrohalogenation of vic-Dihalides or gem-Dihalides



2.   Dehalogenation of vic-Tetrahalogen Compounds



This reaction has the drawback that the halogen compound is itself prepared by halogen addition to alkynes.

3.   Alkyl Substitution in Acetylene; Acidity of  



There is a fair amount of variety possible using this method. Acetylene itself may be alkylated either once to make a terminal alkyne or twice to make an internal alkyne. 



Since acetylide ions are highly basic, competing elimination is a common side reaction.

The products of such an elimination reaction are an alkene (from the alkyl halide) and an alkyne.