Sulfuric Acid → (-)-Mandelic acid

Participants

Reaction Steps

In an electrochemical cell, 25 ml of a solution of 100 mM potassium phosphate buffer at pH 7.0, 4 mM methylviologen and 40 mM phenylpyruvate were reduced with 0.5 mg of 2-oxoacid reductase according to Example 3 at a voltage of -700 mV, against a standard calomel electrode. The current of 5.8 mA decreased sharply after 9 hours. According to HPLC analysis, the reaction solution contained 88% of the phenyllactic acid expected. The solution was acidified to pH 1.8 with dilute sulfuric acid and then extracted with ether. The crystalline residue (78% of theory) was converted to the sodium salt, which had a specific rotation of [α]RT 589=21.1° (0.09 millimole/ml of H2O). A pure commercial preparation of (2S)-sodium phenyllactate gave a value of -21.4°, measured under the same conditions. (R)-mandelic acid and (R)-2-hydroxy-4-methylpentanoate were prepared by a similar method.

Provenance & Evidence