Cacodylic acid concentrations, dissolved arsenate

The predicted arsenate vs time curves for demethylation of cacodylic acid are shown Tn Figure 5. Both curves are for first order decay with a rate constant of 0.04 day" but with different amounts of adsorbent present. Adsorption of arsenate results in dissolved arsenate concentrations that are lower than total arsenate. An s-shaped curve results because arsenate produced during the first few days is almost entirely adsorbed. 

Predicted arsenate and cacodylic acid vs time curves for methylation of arsenate to produce cacoi ylic acid are plotted in Figures 6 and 7, respectively. Adsorption of arsenate lowers the dissolved arsenate concentration and, therefore, results in a slower rate of methylation. The... 

Figure 10. Dissolved arsenate and cacodylic acid (DMAA) concentrations in pore waters of sediments spiked with DMAA and predictions of sorption/kinetic model. Model parameters k = 0.03 day Tcc,asoj, = 3.5 fxmol g Kaso = 5.0 fxmol 00. DMAA = 3.6 fimol Kdmaa = 320.0 fxmol L K (a) Arsenate, measured (h) arsenate, predicted (c) DMAA, measured (d) DMAA, predicted.

Nitric Acid. By the action of concentrated nitric acid on /3/3 dichlorovinyl chloroarsine a crystalline product is obtained which melts at 97° to 99° C. this is the nitrate of )8)8 dichlorovinyl arsenic acid (ClCH=CH)2As00H.HN03. This compound apparently does not ionise in solution, but when dissolved in aqueous alcohol and treated with sodium hydroxide solution until the nitric acid is neutralised, decomposition takes place. On extracting with chloroform and evaporating the extract, a crystalline mass remains which consists of dichlorovinyl arsenic acid (Mann and Pope), (CHCl=CH)2AsOOH. This is purified by recrystallisation from water or carbon tetrachloride, when it melts at 120° to 122° C. Like cacodylic acid, it is amphoteric, forming salts with acids as well as with bases. 

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