Chemical methylation of germanium(II) in model aqueous solutions

Inorganic germanium(II) in micromolar concentrations was reacted with methyl iodide (CH₃I) and methylcobalamin (CH₃-CoB₁₂) at various pH values and with different salt matrices. In all experiments monomethylgermanium was the only product. The reaction with CH₃-CoB₁₂ at pH 1 yielded approximately 1.3% of the added germanium, whereas no methylation occurred at pH 7. Reaction yields with CH₃I were lowest at pH 1 in 0.1 mol dm^?3 KCl (1.6%) and highest at pH 7.6 in artificial seawater (6%). For the reaction of CH₃?CoB₁₂ with germanium(II) a free-radical mechanism is assumed, whereas methylation by CH₃I is most likely an oxidative addition mechanism.