The reactions of carbohydrates and other polyhydroxy compounds with certain weak inorganic oxyacids and oxyacid anions have been the subject of several publications l -4. With telluric acid, the formation of mainly 1: 1 chelates was claimed2J, although little attention was paid to higher pH values where significant results have recently been obtained6-*. The investigation has been extended* to the isostructural and isoelectronic hexahydroxyanions of Sn(IV) and Sb(V), since relatively little is known about their chelates with higher polyoM~9, and this aspect is now further reported.
The conductance and pH of an alkaline solution of telluric acid decrease when a suitable sugar is added. This effect is accompanied by a decrease in equilibration time, which reduces from -24 h at pH 4.8 to within 15 min at pH 11. Upon plottinglO the measurements against the tellurate-polyol molar ratio, the presence of solely 1: 1 complexes at low pH was confirmed with D-erythrose, Lthreose, D-ribose, L-arabinose, D-xylose, D-lyXOSe, D-glucose, D-gulose, D-altrose, D-allose, D-galactose, D-mannose, D-talose, D-idose, L-rhamnose, D-fructose, Lsorbose, and D-tagatose. With the exception of the aldotetroses, complexes of higher tellurate-polyol composition were indicated at alkaline pH. Thus, at pH 11, in addition to the expected 1:l complexes, 1:2 polyol-tellurate chelates were observed with each of the above aldopentoses, aldohexoses, and ketoses. Evidence for 1:3 complexes was obtained with maltose, lactose, cellobiose, and sophorose, whereas sucrose6, nigerose, melibiose, gentiobiose, isomaltose, and trehalose formed 1: 4 complexes. Raffinose and melezitose formed 1: 2 and 1: 5 chelates (Fig. 1). In the pH range 8-10, evidence for complexes of intermediate stoichiometries were obtained with some of these oligosaccharides (cJ Fig. 1).
The above data were consistent with those obtained by polarimetry. The [o]n values of D-fructose, sucrose6, lactose, and galactose were enhanced in the presence of telluric acid, progressively with increase in pH. With maltose and L-arabinose (Fig. 2a), chelation diminished the [(~]b value. Similar investigations also confirmed the existence of a chelate of the type raffinose-(tellurate), at pH >lO (Fig. 2b),