Sulphites, SO

Sulphur Dioxide as an Oxidising Agent.—Sulphur dioxide does not support the combustion of most substances which burn in oxygen, but many metals, e.g. sodium, potassium, magnesium and finely divided lead, when heated in a stream of the gas undergo conversion into a mixture of sulphide and oxide or sulphite, so much heat being liberated that the mass becomes incandescent in the case of the alkali metals some thiosulphate also may be formed.12... 

In the presence of such reagents as bromate, iodate or dichromate, the rate of oxidation is independent of the nature or concentration of the oxidising agent, but is the same as the rate of decomposition to sulphate and sulphite, so that it is evident that hydrolysis is the first stage in the oxidation.2... 

A chain (Sj, ) mechanism is proposed for the light initiated substitution of halogen by sulphite in halo-substituted naphthols. The reaction is initiated by electron transfer from sulphite to an excited sensitiser dye. The sulphite anion radical produced then attacks the halonaphthol loss of halide from this species to give the product is coupled with electron transfer from a second sulphite, so propagating the chain. 

Water not only dissolves tlie gas but combines with it to form the true sulphurous acid, H SO,. With solutions of metallic hydrates it forms metallic sulphites SO, + KHO = KHSO, or SO. -h 2KHO = K.,80, 4 ... 

However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

This direct sulphonation should be compared with the indirect methods for the preparation of aliphatic sulphonic acids, e.g., oxidation of a thiol (RSH -> RSOjH), and interaction of an alkyl halide with sodium sulphite to give the sodium sulphonate (RBr + Na,SO, -> RSO,Na + NaBr). 

Cuprous chloride. Hydrated copper sulphate (125 g.) and sodium chloride (32-5 g.) are dissolved in water (400 ml.) boiling may be necessary. An allialine solution of sodium sulphite (from 26 5 g. of sodium bisulphite and 17 -5 g. of sodium hydroxide in 200 ml. of water) or the solution of the sodium bisulphite alone is added to the resulting hot solution during about 5 minutes with constant shaking. The solution will be decolourised or nearly so. It is then cooled to room temperature (or in an ice bath), and the supernatant liquid is decanted... 

It may also be prepared by the reduction of phenyldiazonium chloride with the calculated amount of a solution of stannous chloride in hydrochloric acid, but the yield is not so high as that obtained by the above sulphite method ... 

The soluiiou of silver nitrate is acidified with dilute uitric scid, boiled so 49 to decompose an v ailvov sulphite that might have been formed, aud the precipitate filtered, washed, etc. 

Procedure. Place 10.0 mL of the working lead solution in a 250 mL separatory funnel, add 75 mL of the ammonia-cyanide-sulphite solution and then by the cautious addition of dilute hydrochloric acid adjust the pH of the solution to 9.5 (pH-meter). This operation must be carried out slowly if the pH of the solution falls even temporarily below 9.5, HCN may be liberated and so use of a fume cupboard is necessary. Now add 7.5 mL of the dithizone reagent to the separatory funnel, followed by a further 17.5 mL of chloroform. Shake for 1 minute, allow the layers to separate, then remove the chloroform layer. Measure the absorbance of this against a blank solution, using a 1 cm cell and a wavelength of 510 nm (green filter). 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromie acid test of qualitative inorganic analyw (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,2). The peroxides are nonvolatile and may accumulate in the fiask during the distillation of the ether the residue is explosive and may detonate, when distilled, with suffident violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,2) or with sodium sulphite solution or with stannous chloride solution (Section VI,12). The common extraction solvents diethyl ether and di-t so-propyl ether are particularly prone to the formation of peroxides. 

In this reaction phenylhydroxylamine behaves like a secondary amine. To the class of nitrosohydroxylamines there belong also the so-called isonitramines and the compound of nitric oxide and potassium sulphite. 

The resulting mixture is cooled to room temperature and the residual iodine is removed by titration with 0.1 N sodium sulphite solution. Now, the solution is treated with sodium hydroxide solution to make it alkaline and then acidified carefully with dilute H2S04 to remove the free NaOH. Finally, the resulting solution is made alkaline with NaHC03 so that the equilibrium is shifted to the right (i.e., AS3+ gets converted to As5+) quantitatively on carrying out the titration with 0.1 N iodine solution. Thus, we have ... 

Sulphocbromio acid. SO,Ho (Bihgdrio sulphite < O droinate.) Fig. 7. iOrO,Ho... 

In 1862, E. C. C. Stanford proposed the carbonization of the drift-weed in closed retorts so as to recover tar and ammoniacal liquor in suitable condensers. This modification did not flourish because of the subsequent difficulties in extracting soluble iodides from the charcoal. V. Vincent (1916) claims that soln. containing aluminium sulphate extract the alkali iodides from seaweed leaving behind the organic matter which prevents the direct precipitation of iodine or iodides. The alkali iodide soln. is treated with copper sulphate for cuprous iodide, or by soln. of sulphites for iodine. M. Paraf and J. A. Wanklyn proposed to heat the drift-weed first with alkali hydroxide so as to form oxalic and acetic acids, which could be crystallized from the lixivium. The economical treatment of seaweed for iodine has been discussed by A. Puge. 

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