ON COMPOUNDS OF MOLYBDENUM WITH THIOGLYCOLIC ACID AND ON A NEW PHOTOMETRIC METHOD FOR THE DETERMINATION OF MOLYBDENUM

Under certain conditions molybdenum forms with HSCH/sub 2/COOH yellow compounds in pentavalent and sexavalent state in the molar ratio of 1: 2. The maximum absorbances are correspondingly at 352.5 and 365 m mu , and molar extinction coefficients are 2400 and 4400. Molybdenum (III) does not form such a compound. The stability of molybdenum(V) and molybdenum(VI) compounds with HSCH/ sub 2/COOH depends on the acidity of the solution. In a moderately acid medium (pH 2.5) the molybdenum(VI) compound is unstable due to the reduction of molybdenum(VI) to molybdenum(V) with the reagent and formation of a molybdenum(V) compound with the excess HSCH/sub 2/COOH. The molybdenum (V) compound obtained is stable in acid solutions (pH 0.7 to 6). In acid solutions molybdenum (VI) reduces to molybdenum (V) quantitatively. In a weak acid medium (pH 2.5 to 6), molybdenum(Vl) is slowly reduced with the reagent to molybdenum (V) only in the presence of a large excess of the reagent. When there is no large excess of the reagent, molybdenum(VI) compound is rather stable at a pH of 2.5 to 6. At higher pH there is a tendency to the oxidation of molybdenum(V) in a compound with HSCH/ sub 2/COOH to molybdenum (VI). Themore » selectivity of the reaction of molybdenum(V) with HSCH/sub 2/COOH in a weak acid medium (in 0.3M HCl) is considerably higher than that of molybdenum(VI) at a pH of 3 to 5. But the sensitivity of the reaction is lower. A highly selective photometric method was developed for the determination of small amounts of molybdenum (1 to 40 gamma /ml) in alloy steels. Vanadium, large quantities of titanium, rare earths, iron, copper, and tungsten do not interfere. (auth)« less