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 comprehensive study to be made of the efficiency of various desiccants which pertains unambiguously to solvents. Benzene, 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 preparative 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 "Frequently a liquid can be freed from water by shaking with a drying agent such as anhydrous calcium chloride or phosphorus pentoxide". In the field of organic synthesis, the situation is little better; different reference texts are replete with bewildering contradictions. Thus, magnesium sulfate, described as either neutral3a.b~~ or acidic,3c,e is alternately an excellent drying agent, rapid in its a c t i~n ,~a ,~, d ,~ or is ~1 0~, 3 h removing only small amounts of water.4 Aluminum oxide is recommended mainly for use in desiccators,3f or as being preferred by many workers for ultimate solvent or reagent drying.Jp Calcium chloride is " f a~t " ,~~-~*~ or alternately "not rapid" sf in its action, and in any case, the consensus appears to be that calcium sulfate is to be preferred as a and a more e f f i~i e n t~~.~ desiccant, even though the only existing quantitative comparison for solvents4 shows the complete reverse to be true. Metallic sodium, generally agreed upon3b.d as being efficient, but slow in its drying action, is ridiculed as a desiccant by Ple~ch,~E: who states that "the widespread use of sodium as a drying agent by organic chemists is more a ritual than an effective process". Furthermore, there is no doubt that many literature prescriptions for desiccation rely, at least to some extent, on the "chemical intuition" of the author, inspired perhaps by the existence of ubiquitous indices of siccative e f f i c i e n~y .~~~?~?~~,~ These are usually based on the results of detailed studies of the comparative drying efficiency of desiccants which have been made with regard to the dryness of gases ,3h,6 and direct extrapolation to the condensed phase often gives misleading if not totally erroneous information. For example, phosphorus pentoxide, long considered the ultimate drying standard? i...

Unter Verwendung von T‐markiertem Wasser werden für verschiedene Lösungsmittel wie Benzol, Dioxan und Acetonitril beschriebene und bekannte Trockenverfahren untersucht.