Abstract

1. The sodium salts of the following arsenicals are relatively very stable towards atmospheric oxygen: arsenious acid, methyl and ethyl arseniousoxide, phenyl and diphenylarsenious oxide, p-amino phenylarseniousoxide.

2. Arsphenamine (dihydrochloride) contrary to the prevalent views, is exceedingly stable towards atmospheric oxygen. The addition of alkali leads to a rapid increase in the rate of oxidation of the compound, the rate of oxidation being roughly inversely proportionate to the hydroxyl ion concentration.

3. The sodium salt of arsphenamine is first oxidized to the corresponding oxide and this compound is simultaneously oxidized to the pentavalent arsenical.

The relative concentration of unchanged arsphenamine and oxide depends on the rate of reaction. The slower the reaction the more oxide is formed, but in every case the last portion to be oxidized consists of 50 per cent arsphenamine and 50 per cent oxide.

4. m-amino-p-oxyphenylarsenious oxide ("arsenoxide") is oxidized only in alkaline solution. The nature of the process curve indicates that the reaction is catalyzed by a reaction product.

5. Neoarsphenamine shows a rapid oxidation on exposure to air, amounting to about 50 per cent in the first ten minutes, after which the rate decreases rapidly.

6. The nature and rate of oxidation of arsphenamine and neoarsphenamine to the corresponding oxides furnish an explanation of the increase in toxicity and trypanocidal activity of these compounds, when their solutions are exposed to air.