Chemoenzymatic Synthesis of Glycolic Acid

Abstract

AbstractA chemoenzymatic process for the production of high‐purity glycolic acid has been demonstrated, starting with the reaction of formaldehyde and hydrogen cyanide to produce glycolonitrile in >99 % yield and purity. The resulting aqueous glycolonitrile was used without further purification in a subsequent biocatalytic conversion of glycolonitrile to ammonium glycolate. A high‐activity biocatalyst based on an Acidovorax facilis 72W nitrilase was developed, where protein engineering and optimized protein expression in an E. coli transformant host were used to improve microbial nitrilase specific activity by 33‐fold compared to the wild‐type strain. A biocatalyst productivity of >1000 g glycolic acid/g dry cell weight was achieved using a glutaraldehyde/polyethylenimine cross‐linked carrageenan‐immobilized E. coli MG1655 transformant expressing the A. facilis 72W nitrilase mutant, where 3.2 M ammonium glycolate was produced in consecutive batch reactions with biocatalyst recycle, or in a continuous stirred‐tank reactor. Direct conversion of the unpurified ammonium glycolate product solution to high‐purity aqueous glycolic acid was accomplished by fixed‐bed ion exchange over a strong acid cation resin.