New Production Processes of Dichlorohydrins from Glycerol Using Acyl Chlorides as Catalysts or Reactants

A new class of catalysts promoting the hydrochlorination of glycerol to obtain selectively 1,3-dichlorohydrin has recently been discovered. These catalysts are acyl chlorides and prove to be much more active and sometimes more selective than the corresponding carboxylic acids, usually employed to promote this reaction. Many different kinetic runs have been performed to compare the performances of acetyl chloride and acetic acid, propanoyl chloride and propionic acid, adipoyl dichloride and adipic acid, succinyl dichloride and succinic acid, and malonyl dichloride and malonic acid, respectively. In all cases, the activity of the acyl chloride proved to be much higher. This behavior has been discussed and explained on the basis of a possible reaction mechanism. The reaction occurs rapidly even if glycerol is contaminated with NaCl. By adding a stoichiometric amount of an acyl chloride to glycerol, the hydrochlorination occurs in a short time, with a high selectivity, without any external supply of HCl, because acyl chlorides react promptly and quantitatively with glycerol forming HCl in situ. To avoid an excessive increase of the HCl pressure, acyl chlorides must be fed into a reactor containing glycerol with an opportune flow rate. The flow rate employed affects both the activity and the selectivity as has been demonstrated in two kinetic runs performed at two different flow rate levels of acetyl chloride.