NATURE OF CHROMOGENS FORMED BY HEXOSES WITH PHENOLS IN SULFURIC-ACID MEDIUM

Hexoses on dehydration in 75% sulfuric acid with attendant heat of dilution, produced hydroxymethylfuraldehyde (HMF) which condensed with resorcinol and orcinol to form chromogens with lambda-max at 495 and 480 nm respectively. The relative yield of HMF based on color intensities with resorcinol was, 93.6 for glucose, 41.6 for mannose and 45.7 for galactose taking the value for fructose as 100. In 50% acid in presence of heat, HMF formed from hexoses condensed with thiobarbituric acid to form chromogens with lambda-max at 443 nm and the relative concentrations of HMF were 28.6% for glucose, 34.3% for mannose and 40% for galactose. In 50% acid with heating, resorcinol formed two chromogens with hexoses, with absorption maxima at 420-430 nm and 480 nm. With orcinol, the single absorption maximum was at 420 nm. The relative yield of the chromogen absorbing at lower wavelength with resorcinol and orcinol were 71.4 and 68.2% for glucose, 175.0 and 172.0% for mannose and 117.9 and 118.2% for galactose, compared to fructose. It is suggested that a partially dehydrated side product and a degradation product of HMF are responsible for formation of chromogens with absorption maxima around 420-430 nm.