Mechanism of hydrogen transfer in arsane generation by aqueous tetrahydridoborate: Interference effects of AuIII and other noble metals

The generation of arsane by reaction of either NaBH4 (THB) or NaBD4 (TDB) in aqueous solution with AsIII (1 mg L-1) has been studied in the presence of several transition and noble metals at trace levels. A continuous flow generation system coupled with both atomic absorption spectrometry (AAS) and gas chromatography mass spectrometry (GC-MS) were employed to measure the effect of AuIII (0.5 – 20 mg L-1) on reaction yield and isotopic composition of arsane. In a different set of batch experiments, GC-MS was employed to measure the effect of AuIII, PdII, PtII, NiII and CuII on the isotopic composition of arsane. AuIII, PdII and PtII induce a significant perturbation in the mechanism of hydride generation, promoting the incorporation of a large amount of hydrogen derived from the solvent into the final arsane. This effect takes place at metal concentration levels which hardly affect the generation efficiency of arsane and can likely be addressed by the action of intermediate species formed in the early stage of the reaction between the metal ion and the TDB-arsenic complex. Nanoparticles and colloids arising from the interaction of the metal and TDB are able to capture the final arsane but they do not promote H/D exchange on the already formed arsane. This evidence reveals the existence of a new type of interference in chemical generation of volatile hydrides - a “mechanistic interference” - in addition to the already known yield interferences.