Abstract We have studied the reaction of 10-methyl (phenyl)-5, 10-dihydrophenarsazine 10- oxides with hydriodic acid and we have established the structure of the products by high- resolution mass spectrometry. We have shown that when the methyl group is replaced by a phenyl group in 5, 10-dihydrophenarsazine 10-oxides, cleavage of the endocyclic arsenic– carbon bonds occurs.
