Dehydrohalogenation bases commonly used

In a /3-elimination (dehydrohalogenation) reaction a halogen and a hydrogen atom are removed from adjacent carbon atoms to form a double bond between the two C s. The reagent commonly used to remove HX is the strong base KOH in ethanol (cf. Section 6.2). 

Reduced solvation of commonly used E2 bases (HO , RO ) in dipolar non-HBD solvents may elevate their reactivities to such an extent that E2 reactions of quite inert substrates occur [306]. Halide ions in dipolar non-HBD solvents are sufficiently strong bases to promote dehydrohalogenations of haloalkanes [73, 74]. Even the fluoride ion is the most efficient in this reaction [307, 308, 600] the elimination rates decrease in the order F > Cl > Br > I . 

A convenient method to prepare nitrile oxides involves dehydrohalogenation of hydroximic acid halides, which are readily obtained from the corresponding aldoximes by treating them with -chlorosuccinimide (NCS) or A-bromosuccinimide (NBS) or nitrosyl chloride or X2 (Scheme 5.36). A tertiary amine base, such as triethylamine, is commonly used for the dehydrohalogenation of hydroximic acid halides. 

The essential feature of base catalysis is formation of carbanions. Compared to acid catalysts, solid base catalysts are not as widely used commercially, but can be active for alkylation, condensation (oligomerization), isomerization, and dehydrohalogenation. Common base catalysts are alkali metal oxides, carbonates, and hydroxides, as well as alkaline earth metal oxides. 

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