Propylene Carbonate as a Replacement for Dichloroethane in Hydroacylation Reactions.

Hydroacylation, the addition of an aldehyde across a double or triple bond to give a ketone is an atom efficient transformation catalysed by a variety of transition metals. Intramolecularly it is very efficient, but the intermolecular reaction is plagued by a side reaction, namely the decarbonylation of the aldehyde, unless the aldehyde contains a group which can chelate to the transition metal catalyst.  Thioethers are particularly useful chelating groups and the work of Willis at the University of Oxford ( for a review see Chem Rev 2010, 110, 725-748) in this area is particularly noteworthy.

The two preferred solvents, however, for the transformation are acetone and dichloroethane.  The relatively low bp of acetone (56 deg C) means that reaction times may be extended, and by-products ( eg from reaction of aldehydes with acetone) may be expected. Dichloroethane is generally preferred in the laboratory but, of course, for scale up presents toxicity and environmental issues.  These days few plants in the Western world use dichloroethane, though it is still used in some processes in India and China.

A recent report (Lenden P et al, Green Chem, 2011, 13, 1980-2) shows that propylene carbonate is a good substitute for dichloroethane in the hydroacylation of acetylenes (for a review on the use of propylene carbonate in other reactions see Schaffner B et al, Chem Rev, 2010, 110, 4554-4581). As yet the reactions have only been done on small scale and there is no indication of the best way to work up – the only example in the paper with experimental information loaded the reaction mixture on a silica column and eluted with 30% ether/petrol – hardly environmentally friendly even in a laboratory. However yields are good and I am sure the catalyst loading of 5 mol% could be improved upon on larger scale.