Demethylation of Methylated Arsenic Species during Generation of Arsanes with Tetrahydridoborate(1-) in Acidic Media

Demethylation during generation of volatile hydrides (HG), i.e. formation of noncorresponding arsanes from monomethylarsonic acid (MAsV), dimethylarsinic acid (DMAsV), and trimethylarsine oxide ((TMAsO)-O-V) by the reaction of sodium tetrahydridoborate(1-) (THB) with different acids under analytical conditions, was investigated and characterized. Pronounced demethylation of MAsV, DMAsV, and (TMAsO)-O-V was found during the reaction of THB with HCl, H2SO4, and HClO4, while HG from CH3COOH or TRIS buffer after prereduction with L-cysteine resulted in the formation of only the corresponding hydrides. In the case of HNO3 formation of corresponding hydrides was preserved for MAsV and DMAsV but not for (TMAsO)-O-V. The extent of demethylation strongly depends on concentration of the acid and THB. It can be strongly suppressed in HCl medium by partial hydrolysis of THB with optimal concentration of acid before it reacts with MAsV, DMAsV, or (TMAsO)-O-V. It appears that the demethylation is due to the action of specific hydrolytic products of THB (most probably by the first and second one).