Applying a continuous capillary-based process to the synthesis of 3-chloro-2-hydroxypropyl pivaloate

Abstract

Nowadays, continuous chemical processes (‘flow chemistry’) using micro process technology are becoming highly competitive, both for cost (better selectivity, higher productivity) and sustainability (low environmental impact) reasons. The first needs true process intensification and the second, among others, new eco-efficient starting and product materials. In this context, a new application for glycerol is reported with increasing industrial interest and tested here under highly intensified conditions. Starting from prior batch processing experience, it is reported about the transfer to a continuous process to transform dichloropropyl pivaloate, prepared from glycerol, into 3-chloro-2-hydroxypropyl ester. The continuous microreactor based process has up to three orders-of-magnitude reduced reaction times (5760×) by virtue of exploiting unusual experimental conditions in organic chemistry (Novel Process Windows), i.e. superheated pressurised processing much above the boiling point. The yields are fully comparable with the ones obtained under batch conditions, but with (expected) loss in selectivity through enhanced diproduct formation. This principally enables the new continuous process to target much higher productivities; however this also results in a more complex reaction mixture therefore the ease of separation and commercial value of the second product will decide its exploitation. Beyond such benefits for the individual reaction under investigation, this is among the very first reports about a superheated reaction with a distinct selectivity issue with two known byproduct pathways, and thus provides the first respective generic information after an upheavalled reporting on capillary- or microreactor-based superheated processing, so far mostly done for less complex reactions.