(1) CONVERSION OF ALCOHOL INTO ALKYL CHLORIDE (DARZEN’S METHOD): Alkyl chlorides can be prepared from corresponding alcohols by the reaction with SOCl2. The reaction take place by SNi mechanism (retention in configuration) but if we use base such as pyridine C5H5N then inversion takes place and reaction occurs by normal SN2. SOCl2 is preferred over other reagents such as PCl5 and PCl3 because in case of SOCl2 by-products are gases (SO2 and HCl and escape from the reaction vessel but in case of PCl5 and PCl3 the by-products are POCl3 and H3PO3) and these are non-volatile so purification of alkyl halide requires separation.
(2) CONVERSION OF CARBOXYLIC ACID INTO ACID CHLORIDE: Acid chlorides can be obtained by reacting carboxylic acid with SOCl2.
(3) CONVERSION OF PRIMARY AMIDES INTO NITRILES: Primary amides when heated with SOCl2 they undergo dehydration to yield nitriles. For dehydration of primary amides, we can also use PCl5, P4O10, POCl3 C6H5SO2Cl and Al2O3.
(4) BECKMANN REARRANGEMENT (CONVERSION OF KETOXIMES INTO AMIDES): Ketoximes (RR’C=NOH) when treated with acidic reagents such as SOCl2, they rearrange to substituted amides (RCONHR’ or R’CONHR). The group that migrates is generally the one anti to -OH of oxime but when attached alkyl groups of oximes are both bulky then mixtures of two amides are possible (RCONHR’ and R’CONHR). The oximes of cyclic ketones give ring enlargement. Among other reagents used are PCl5, Concentrated H2SO4, HCOOH, Liquid SO2, HMPA, P2O5-Methanesulphonic acid, HCl-HOAc-AC2O, Silica gel and polyphosphoric acid.