Hydrohalide elimination

The hydrohalide elimination route has also been used for the synthesis of cyclosila-zanes and cyclosilthianes ... 

The hydrohalide elimination route is also widely employed for the synthesis of cyclic sulfur-nitrogen compounds, such as tetrasulfur tetranitride (cyclotetrathiazyl), thiazyl halides, and sulfanuric halides ... 

The reaction of an indolenine with an alkyl halide having the alkyl group ethyl or longer can also lead to elimination rather than alkylation, with the formation of the hydrohalide salt of the indolenine. This salt can be mistaken for the expected quaternary salt. In this case, treatment with base will merely regenerate the starting indolenine, which is easily distinguished by IR spectrum, as indicated earlier, from the Fischer s base formed from the quaternary salt. Often the solid isolated is a mixture of the two salts, and both components can be identified in the spectmm of the corresponding mixture of bases. 

When two of the substituents R in II are hydrogen, two moles of hydrogen halide can be eliminated, and the resulting product is the corresponding carbodiimide (IV). The reversal of this reaction, i.e., the addition of hydrogen halide to carbodiimides, is a useful method of synthesis of haloformamidine hydrohalides. 

---