Oxidation of benzyl alcohol derivatives into carboxylic acids with a new Acetobacter malorum strain: boosting the productivity in a continuous flow system

The one-shot green oxidation of different benzyl alcohol derivatives into the corresponding carboxylic acids was achieved by using Acetobacter malorum DSM 112354, a newly isolated strain. Oxidation of benzyl alcohol was initially optimized considering productivity after 8 h as response parameter. Under optimized conditions, a set of para-substituted benzyl alcohols was tested, showing the great versatility of Acetobacter malorum DSM 112354 which was able to oxidize all the substrates albeit with different rates and conversions. The effect of the substituent position was subsequently studied using 2-(hydroxymethyl)phenol, 3-(hydroxymethyl)phenol, and 4-(hydroxymethyl)phenol as starting materials, showing that all the substrates were efficiently transformed (74-98% molar conversion in 2-24 h). Finally, the oxidation of 1,4-phenylenedimethanol gave 4-(hydroxymethyl)benzoic acid proceeded with excellent regioselectivity, since <3% of terephthalic acid was observed. This regioselective reaction was optimized using Ba-alginate immobilized cells of Acetobacter malorum DSM 112354 in a continuous multiphasic flow reactor. The process continuously run for 24 h allowed the obtainment of 0.65 g of HMBA using a 14.4 mL reactor. This intensification was associated with upgraded biocatalyst productivity (37.1 mmol_P/g_{cells dry weight}) and space-time yield (45.1 mg_P/mL d).