Bidirectional Conversion Between 3‐Monochloro‐1,2‐propanediol and Glycidol in Course of the Procedure of DGF Standard Methods

Abstract NMR observation revealed that bidirectional conversion occurred between 3‐monochloropropane‐1,2‐diol (3‐MCPD) and glycidol in the course of the analytical procedure of DFG standard method C‐III 18 (09), option A; 3‐MCPD was partly converted to glycidol at the transesterification step, and glycidol was converted partly to 3‐MCPD at the derivatization step conducted at 80 °C under acidic condition in the presence of NaCl. Based on the proton numbers observed by 1H NMR, the degrees of the conversion were estimated to be 37 and >70%, respectively. In addition, epoxide ring‐opening of glycidol and its esters was found to be ca. 90% by the acid treatment described in the method, option B. Thus, it was concluded that the standard method, option A, did not correctly give the combined amount of 3‐MCPD esters and glycidyl esters in oils containing glycidyl esters, and the difference of the values obtained by options A and B did not correspond to the amount of glycidyl esters, either. In addition, derivatives of 3‐MCPD with phenylboronic acid were not observed by NMR at the derivatization step, although they were detected by GC‐MS in the organic phase at the following extraction step.