Arsenious acid Extraction

The toxic action of white arsenic has been attributed to its inhibitory action on the oxidative processes,9 partly owing to the effect of the change of pH on the enzyme concerned. Small quantities of arsenious acid reduce the power of suitably prepared extracts of animal tissues to oxidise reduced phenolphthalein. The oxidation of tartaric acid at the ordinary temperature and at 37-5° C. is inhibited by arsenious acid, as also is the respiration and fermentation of yeast,10 but the latter... 

C.C. of concentrated sulphuric acid slowly run in. The temperature is then allowed to rise to 15° or 20° C., and after stirring for thirty minutes, the whole is poured into 1500 c.e. of water. The nitro-oxalyl compound separates, and the oxalyl residue is split off by boiling the mixture for one hour. The yield is about 86 per cent. (3) Instead of nitrating the oxalyl derivative as above, the urethane derivative may be used. (4) o-Nitroaniline and arsenie acid are heated at 200° to 210° C. for ten minutes and the melt extracted with 10 per cent, sodium hydroxide solution, from which extract the arsinic acid is precipitated by acid. In this preparation bis- 3-nitro-4 -aminophenyl)-arsinic add results in small yield as a by-product. 

It is usually preferable to oxidise the compound directly as follows. Intimately mix 0 02-0 05 g. of the eompound with 3 g. of sodium peroxide and 2 g. of anhydrous sodium carbonate in a niekel erucible. Heat the crueible and its eontents with a small flame, gently at first, afterwards more strongly until the eontents are fused, and eontinue heating for a further 10 minutes. Allow to stand, extract the contents of the crucible with water, and filter. Add exeess of eoneentrated nitrie acid to the filtrate and test with ammonium molybdate reagent as above. A yellow preeipitate indicates the presenee of phosphorus. It must be borne in mind that the above treatment 1 eonvert any arsenie present into arsenate. 

Arsenic trisulphide is not dissolved by dry liquid hydrogen sulphide.8 The precipitated sulphide obtained by the action of hydrogen sulphide on solutions of arsenious oxide in aqueous hydrochloric or acetic acid is found to contain an amount of sulphur in excess of that required by the formula As2S3, but which cannot be extracted with carbon disulphide. This has been attributed to the formation of a hydrosulphide since, if the precipitate is dried in a vacuum and then heated at 115° C., hydrogen sulphide is evolved. The products vary in composition, but that produced in presence of hydrochloric acid approximates to 16As2S3.H2S and that from acetic acid solutions to 8As2S3.H,S.9... 

The condensation between sodium-camphor and arsenious chloride is conducted as described before and the product repeatedly extracted with aqueous sodium hydroxide. The extract is acidified, and the precipitate extracted with small quantities of benzene until a residue results consisting of dicamphorylarsinic acid. The final brown mother-liquors are taken to dryness, the residue taken up in dilute aqueous sodium hydroxide, the solution boiled with charcoal and concentrated until crystals appear. These consist of sodium dicamphorylarsinate. After filtration and acidification, the sticky precipitate is again treated with alkali and benzene. After again acidifying, the precipitate is a brown solid, which cannot be crystallised. It softens at 110° C. and melts indefinitely at 130° C. This acid is soluble in dilute alcohol, very soluble in benzene, alcohol, or acetic acid. The silver salt is a greyish-white precipitate. 

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