en bonds, such as enolizable liydrogen. No active hydrogen was found with such moderately enolizable compounds as benzoin (Wo. 9), 4-methyldesoxybenzoin (No. 32), and malonic acid (Eo. 31). However, the very reactive bensoylacetonitrile (No. 33) did shorn extensive exchange under the conditions employed, Considerable variation of these tecliniques should be possible. Various other labeled solvents should be as good as isopropyl alcohol-for example, ether wet with tritiated water. Possibly even an ion exchange resin could be used to effect the exchange. Smaller amounts of organic material could be exchanged; only sufficient material for radioassay is actually required and this would not have to be consumed in the determination if it n-ere radioassayed by a scintillation counting technique. COMPARISON W I T H OTHER METHODS
Active hydrogen has not been consistently determined with any great degree of precision either by its exchange with isotopes or by its conversion to a gas. Measured values for active hydrogen attached to oxygen determined by the gas method in coniparison with those determined in this work show that the accuracy of the gas method is usually greater. However, hydrogen attached to cnrbon can be
expected to ciiuse difficulties more commonly with the gas method than with the exclinnge method. Thus, although benzoili and malonic acid gave satisfactory exck ange coefficients (Table I), both compot lids shorn excess active hydrogen by the gas method. Measured values for active hydrogen attached to nitrogen show the accuracy of the two methods to be about the same. With a f w types of compounds the exchange method will be superior. For example, although the hydrazine grouping has never yielded satisfactorily to the gas method and the presence of a nitro grouping i n any type of compound causes sFiirious results in the gas method, 2,4-c initrophenylhydrazine (No. 14) shows a satisfactory distribution coefficient. Frequently genwally satisfactory results by the gas Inethod have been obtained only after ( onsiderable investigation of such fartors as the proper solvent, temperature, time, etc., and the use of elaborc le special equipment for the gas produdion. The optimum conditions for one type of active hydrogen have not always coincided with the optimum conditio ’IS for another type. This is an obvious tlramback for the gas method when it is applied to an unknown polyfunctional conqJound. I n contrast, the results in Table 1 mere obtained with an exchange technique which required no careful investigstion as to the effects
of time, temperature, and solvent, required no special equipment, and could be easily applied in a routine fashion by a technician. ACKNOWLEDGMENT
The authors thank Percy Staats, Oak Ridge National Laboratory, who furnished a sample of high level (2 curies per mole) t,ritiated water for this work. LITERATURE CITED
(I) Brown, L. M., Friedman, A. S., Beckett. C. W.,Natl. Bur. Standards Circ. 562 (1956j. (2) Gold, V., Stachell, D. P. N., Quart.
Reus. ( L o n d o n ) 9, 51 (1955). (3) Ingold, C. IC., Wilson, C. L., Z. Elektrochem. 44, 62 (1938). (4) ICimball, A. H., “Bibliography of Research on Heavy Hydrogen Conipounds,” ed. by Urey, H. C., Kirshenbaum, I., AlcGraw-Hill, New York, 1949. ( 5 ) Urey, H. C., J . Chem. Soc. 1947, 562. (6) Wiberg, I
