(198a) One Pot Synthesis of Lactic Acid From Sugars and Polyols

With depleting reserves of fossil fuels (including petroleum, coal resources) worldwide, the chemical industry is actively exploring the possibility of replacing fossil-based raw materials with renewable feedstocks such as plant-based biomass. Sugars and sugar-derived polyols, which can be obtained from cellulosic biomass, are regarded as one of the most promising feedstocks for value-added commodity chemicals. Lactic acid is one such example with promising applications in food and pharmaceutical industries as well as being an intermediate to industrial chemicals. Conventional production of lactic acid employs fermentation or hydrothermal treatment of glucose at elevated temperatures (>573K). The major disadvantage of those processes is lower productivity, and several side reactions leading to lower overall yield of lactic acid¹. In another process², 43% lactic acid yield from glucose is reported over Pt/C catalyst in the presence of air and excess alkali (molar OH^-/sugars = 20).

Here we report a detailed study on one-pot catalytic synthesis of lactic acid from sugars and polyols in significant yields at low temperatures (as low as 338 K). It is shown that using supported noble metal catalysts and alkali promoters, sugars (glucose, fructose) and polyols (glycerol, sorbitol) are converted to lactic acid in high yields (62~81%). The catalytic activity of Cu, Ni, Pt, Ru, Rh and Pd based catalysts for the one pot synthesis has been investigated for glycerol, xylitol and sorbitol as substrates. Catalytic conversion of sugars to lactic acid is more efficient compared to polyols as substrates at significantly low temperatures (338 K). A possible reaction pathway is discussed based on observed experimental results. Detailed kinetic study on conversion of glycerol and sorbitol to lactic acid will also be presented along with rate equations and kinetic parameters.

1.  (a) Yan, X. Y.; Jin, F. M.; Tohji, K.; Kishita, A.; Enomoto, H., Hydrothermal Conversion of Carbohydrate Biomass to Lactic Acid. AIChE J 2010, 56 (10), 2727-2733; (b) Ramirez-Lopez, C. A.; Ochoa-Gomez, J. R.; Fernandez-Santos, M.; Gomez-Jimenez-Aberasturi, O.; Aonso-Vicario, A.; Torrecilla-Soria, J., Synthesis of Lactic Acid by Alkaline Hydrothermal Conversion of Glycerol at High Glycerol Concentration. Ind Eng Chem Res 2010, 49(14), 6270-6278.

2.  Onda, A.; Ochi, T.; Kajiyoshi, K.; Yanagisawa, K., A new chemical process for catalytic conversion Of D-glucose into lactic acid and gluconic acid. Appl Catal a-Gen 2008, 343 (1-2), 49-54.