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 °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 (~350 °C), sodium lactate decomposes to sodium propanoate and sodium acetate, which may explain reduced 2,3-pentanedione yields at higher temperatures.