Comparative study of various polyols as complexing agents for the acidimetric titration of tungstate.
Most polyols (L = alditol or carbohydrate) form dinuclear tungstate complexes according to the over-all equilibrium 2WO4(2-) + 2H+ + L equal equilibrium [W2O7L]2- + H2O. When the reaction is fast and complete, it allows the acidimetric titration of tungstate. The formation constants of the complexes of a series of polyols were determined by potentiometry. Their values were higher at low ionic strengths. Opposite structural factors govern the stabilities and the formation rates of complexes: alditols of threo configuration react with tungstate faster than those of erythro configuration, but the stability order is erythro greater than threo. Of the polyols investigated, only xylitol and D-glucitol (sorbitol) allowed a fast and accurate potentiometric titration. Using 0.02 M HCl as titrand, 0.04 mmol of tungstate was determined in a volume of 100 cm3. The interference of molybdate is discussed in detail.
Verchère
J F
JF
Unité de Recherche Associée 500 du Centre National de la Recherche Scientifique, Faculté des Sciences de Rouen, Mont-Saint-Aignan, France.
Sauvage
J P
JP
Rapaumbya
G R
GR
D000438:Alcohols; D002241:Carbohydrates / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007700:Kinetics; D008353:Mannitol / Q000032:analysis; D013402:Sugar Alcohols; D014414:Tungsten / Q000032:analysis*; D017973:Tungsten Compounds
D000438:Alcohols; D002241:Carbohydrates; D007202:Indicators and Reagents; D013402:Sugar Alcohols; D017973:Tungsten Compounds; D008353:Mannitol; C045951:tungstate; D014414:Tungsten