Desiccant efficiency in solvent drying. A reappraisal by application of a novel method for solvent water assay

Abstract

The chemical literature, very inconsistent on the subject of the drying of solvents, abounds with contradictory statements as to the efficiency of even the more common desiccants. The recent advent of a novel, highly sensitive method which utilizes a tritiated water tracer for the assay of solvent water content has enabled the first compre-hensive study to be made of the efficiency of various desiccants which pertains unambiguously to solvents. Ben-zene, 1,4-dioxane, and acetonitrile, chosen as model solvents, were wetted with known amounts of tritiated water and treated with a spectrum of desiccants, and the residual water contents were then assayed. The results range from the expected to the highly surprising. Some anomalous results, obtained for benzene and acetonitrile with acidic and basic desiccants, respectively, are discussed in terms of isotopic exchange reactions. The bench chemist is often confronted by the problem of the selection of desiccants for solvent drying, and although dry solvents are frequently required for use in both prepara-tive situations and in physicochemical studies, there is a paucity of real information in the literature. Some authors2 are content to dismiss drying with statements such as “Fre-quently a liquid can be freed from water by shaking with a