Reaction and spectroscopic studies of sodium salt catalysts for lactic acid conversion

Catalytic conversion of lactic acid to 2,3-pentanedione over sodium salts and base on low surface area-silica support has been studied. Yield and selectivity toward 2,3-pentanedione are optimal at around 300 degrees C, 3-4 s residence time, and 0.5 MPa total pressure. Anions of initial salt catalysts used do not participate-in lactic acid condensation to 2,3-pentanedione once steady-state conditions have been achieved; instead, sodium lactate has been identified by postreaction FTIR spectroscopy as the primary,stable species on the support during reaction. Sodium lactate is believed to be an intermediate in 2,3-pentanedione formation. Conversion of a sodium salt to sodium lactate is greatest when the salt used has a low melting point and a volatile conjugate acid; the extent of conversion depends weakly on reaction time and temperature within experimental conditions. At high temperature (similar to 350 degrees C), sodium lactate decomposes to sodium propanoate and sodium acetate, which may-explain reduced 2,3-pentanedione yields at higher temperatures.