STUDIES ON THE STABILITIES OF THIAMINE AND ITS MODIFIED COMPOUNDS : (XIII)DEGRADATION OF O-, S-, AND O, S-BIS (ETHOXYCARBONYL) THIAMINES IN ALKALINE AQUEOUS SOLUTION

Abstract

No other reports have been found on the transformation of S-alkoxycarbonylthiamines such as S-ethoxycarbonylthiamine(CET) or O, S-bis(ethoxycarbonyl)thiamine(DCET)in alkaline aqueous solution. However, these derivatives are known to be determined with "alkali-method" on the basis of their easy transformation into thiochrome-reaction-positive compounds on treatment with NaOH in aqueous solution. The present experiments were made to obtain informations on the degradation of CET and DCET, and of O-ethoxycarbonylthiamine (OCET) in alkaline aqueous solution of a pH ranging from 10 to 13 at 30℃. CET readily gave OCET as a result of translocation of ethoxycarbonyl group from S- to O-position, and OCET was hydrolyzed to thiamine (B_1). DCET was hydrolyzed similarly to OCET and B_1,but not so readily as did CET. When O-butoxycarbonyl-S-ethoxycarbonylthiamine (OCBSCET) was treated under the same conditions as was DCET, OCBSCET gave B_1 OCET, and O-butoxycarbonylthiamine (OCBT). OCET was produced in larger amounts than OCBT. This indicates. easier hydrolysis of O-ester linkage than the S-ester linkage of OCBSCET and, presumedly, of DCET. Each of the degradation rate constant-pH profiles of OCET, CET, and DCET in NaOH aqueous solution was a line having a slope of unity, where variation of ionic strength gave no influence on the rate at a fixed pH. When the pH value was adjusted with a glycine buffer, of a fixed ionic strength, instead of NaOH aqueous solution, an increase in concentration of glycine produced an increase in the degradation rate of DCET considerably at pH 10.0,slightly at pH 11.0,but not at pH 12.0,while the rate of CET was remained unchanged at these pH.