Bunsen, the discoverer of the cacodyl compounds.
Analytical problems, such as the isolation of certain organic radicals, attracted his attention to begin with, but he soon turned to synthetical studies, and he was only about twenty-five years of age when an investigation, doubtless suggested by the work of his master, Bunsen, on cacodyl, yielded the interesting discovery of the organo-metallic compounds.
Arsenic compounds can be detected in the dry way by heating in a tube with a mixture of sodium carbonate and charcoal when a deposit of black amorphous arsenic is produced on the cool part of the tube, or by conversion of the compound into the trioxide and heating with dry sodium acetate when the offensive odour of the extremely poisonous cacodyl oxide is produced.
The dimethyl arsine (or cacodyl) compounds have been most studied.
Bunsen, who gave it the name cacodyl oxide (KaKeans, stinking); its formation may be shown thus: As4O6 + 8CH3CO2K = 2 (CH3)2As2O+4K2CO3)+ 4CO2.
The liquid is spontaneously inflammable owing to the presence of free cacodyl, As2(CH3)4, which is also obtained by heating the oxide with zinc clippings in an atmosphere of carbon dioxide; it is a liquid of overpowering odour, and boils at 170° C. Cacodyl oxide boils at 150° C., and on exposure to air takes up oxygen and water and passes over into the crystalline cacodylic acid, thus: [(CH3)2As]2O + H2O + O2 = 2(CH3)2AsOOH.