Question

Give the synthesis of malic acid starting from succinic acid.

Answer 1

Succinic acid has been the object of intense study over the past decade as a possible fermentation derived platform molecule.  The conversion of succinic acid to maleic acid and fumaric acid open up a larger range of chemical derivatives beyond those of succinic acid alone.  To assess the technical feasibility of the conversion, oxydehydrogenation of succinic acid to maleic acid with an iron-phosphate catalyst was studied in the temperature range between 300 and 475C at atmospheric pressure.  The succinic acid was fed as an aqueous solution in ranging in concentration from 40 to 60 grams of succinic acid per liter of distilled water.  The catalysts were calcined prior to use at temperatures from 450 to 720C from 6.5 to 8 hours.  This oxydehydrogenation step was combined with a subsequent isomerization step of maleic acid to fumaric acid. The isomerization was performed in dimethyl succinate or diethyl succinate at temperatures ranging from 135C up to 190C.  The conversion of succinic acid to maleic acid was typically in excess of 90% while the selectivity was nearly stoichiometric in a single pass of the reactor.  The isomerization reaction reached conversion of over 90% in the 150-160°C temperature range.  The relative ease of the oxydehydrogenation and isomerization reactions indicate that commercial feasibility primarily resides in the cost of the feedstock, succinic acid