Sodium sulphite solution

Evaporation and crystallisation of the sodium sulphite solution gives crystals of the heptahydrate NajSOj.THjO. However, on evaporation of the hydrogensulphite solution, the solid obtained is chiefly sodium pentaoxodisulphate(IV) ( metabisulphite ) Na2S20j, and contains little if any of the hydrogensulphite. However, the hydrogen sulphite ion is obtained when the solid redissolves in water ... 

Oxidation to acids. Varm together in a small conical flask on a water-bath for lo minutes a mixture of 0 5 ml. of benzaldehyde or salicylaldehyde, 15 ml. of saturated KMn04 solution, and 0-5 g. of NajCOj. Then acidify with cone. HCl, and add 25% sodium sulphite solution until the precipitated manganese dioxide has redissolved. On cooling, benzoic or salicylic acid crystallises out. 

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-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient 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 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

Phenylhydrazine may be prepared by reducing phenyldiazonium chloride solution with excess of warm sodium sulphite solution, followed by acidification with hydrochloric acid, when the hydrochloride crystallises out on cooling. Treatment of the latter with excess of sodium hydroxide solution liberates the free base. The reaction is believed to proceed through the following stages —... 

The sodium sulphite solution may also be prepared by dissolving 100 g. of pure (or a corresponding quantity of commercial) sodium hydroxide in about 125 ml. of water, and then diluting to 750 ml. The flask is cooled in running water, a few drops of phenolphthalein indicator are added, and sulphur dioxide passed in until the pink colour just disappears (it is advisable to add a further 1-2 drops of the indicator at this point) and then for 2-3 minutes longer. It is best to remove a sample for test from time to time, dilute with 3-4 volumes of water, and test with I drop of phenolphthalein. 

The alkaline sodium sulphite solution may be replaced by saturated amtnonlum sulphite solution prepared as follows. Pass sulphur dioxide into a mixture of 1 part of concentrated ammonia solution (sp. gr. 0-88) and two parts of crushed ice in a freezing mixture imtil the liquid smells strongly of sulphur dioxide, and then neutralise with ammonia solution. This solution slowly deposits ammonium sulphite crystals and contains about 0-25 g. of SOj per ml. Use 60 ml. of this ice-cold ammonium sulphite solution to which 8 ml. of concentrated ammonia solution are added. After the addition of the solution of p-nitrophenyldiazonium chloride, allow the mixture to stand for 1 hour in a freezing mixture, filter oft the yellow precipitate of ammonium p-nitrophenyUiydrazine disulphonate, heat it on a water bath with 20 ml. of concentrated hydrochloric acid at 70-80° for 7 minutes, cool the blood-red solution, and dissolve the resulting precipitate of p-nitrophenylhydr-azine hydrochloride and ammonium salts in water, and isolate the base as above. 

The reaction products are chemicals that commonly occur in the hypochlorite solution, which is an advantage over using a sodium sulphite solution as an absorption medium, for example, as its use would entail removal of sulphuric impurities. 

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 ... 

Reaction of Potassium lodate with Sodium Sulphite in a Sulphate Medium. Pour 20jml of a sodium sulphite solution acidified with sulphuric acid and containing a small amount of starch into a 100-ml beaker. Pour 20 ml of a potassium iodate solution into a second 100-ml beaker. The potassium iodate solution must contain... 

Preparation. Put 3.5 g of sodium sulphite and 50 ml of water into a small conical flask. Weigh 2.5 g of flowers of sulphur and, after wetting the sulphur with ethanol (why ), transfer it into the flask with the sodium sulphite solution. Heat the mixture up to boiling. The end of the process is featured by a neutral reaction of the solution with litmus. Filter the hot solution and evaporate it on a water bath up to the beginning of crystallization. Filter off the crystals that precipitated after cooling in a Buchner funnel. Write... 

Tetryl is reduced at 80-90°C by the action of a 10% sodium sulphite solution to form a non-explosive product. In a similar manner tetryl reacts with sodium thiosulphate to yield yellow-coloured, unidentified products. 

This equilibrium affords an explanation for the fact that a trace of hydrogen sulphide accelerates the reaction between sodium sulphite and sulphur 4 sometimes there is a long delay before sulphur begins to dissolve in boiling sodium sulphite solution, and in such cases the effect of passing a few bubbles of hydrogen sulphide into the solution is very marked when once the reaction begins it proceeds smoothly. ... 

The results obtained for the oxidation of sodium sulphite solutions containing various alcohols as inhibitors are particularly instructive. The rate of reaction depends upon the concentration of the inhibitor, C, in the following way. 

Literature data for Newtonian batches (water [3,4,16,17] and for sodium sulphite solutions [3,19]) together with our Newtonian data were also evaluated according to relation... 

The greater stability of the 1 1 adducts in aprotic solvents is, then, attributed mainly to the enhanced reactivity of the attacking nucleophiles in these solvents. This factor should also favour the production of di-adducts in aprotic solvents and NMR measurements do indicate that these are formed from trinitro-substituted compounds and methoxide ions in media rich in dimethyl sulphoxide. However, there is some evidence that the di-adducts are not particularly well solvated by dimethyl sulphoxide and are in fact better solvated by water. Thus it has been found that 1 2 adducts are very readily formed in water. For example 1,3,5-trinitrobenzene gives both 1 1 and 1 2 adducts in fairly dilute solutions of hydroxide ions in water, while dimethyl-picramide and the picrate ion give evidence only for the production of 1 2 adducts. Similarly a variety of trinitro-compounds are readily converted into di-adducts in aqueous sodium sulphite solution, although... 

For example, sodium sulphite solution is readily oxidised in air but sodium arsenite solution is not oxidised by passing a current of air through it. However, if air is passed through a mixture of sodium sulphite and sodium arsenite solution, the oxidation of both take place. Here the oxidation of sodium sulphite acts as a catalyst for the oxidation of sodium arsenite solution. 

When, at the end of about a week, the mass has changed to a pure red color, wash it by decantation (see Note 5 (6), page 10) in a 600-cc. beaker. Most of the excess of sulphur is floated off. Then rinse the red sulphide back into the evaporating dish, leaving behind in the beaker any lumps of black sulphide or globules of mercury. Boil the red sulphide with 50 cc. of saturated sodium sulphite solution to remove the last of the uncombined sulphur wash by decantation with boiling water and collect the mercuric sulphide on a suction filter. Dry the product on the hot plate and preserve it in a 2-ounce cork-stoppered bottle. 

In contrast, Fig. 72 shows the results of mass transfer in the system aqueous 1-n sodium sulphite solution/air. These measurements were carried out under steady-state conditions in vessels with hollow stirrers on the scale p = 1 5 [58/1, 92]. In this material system, the high salt concentration (70 g/1) fully suppresses bubble coalescence. In the case of the self-aspirating hollow stirrer (see Fig. 28), the stirrer power and gas throughput were coupled via the stirrer speed and were therefore dependent on each other. Consequently, v does not occur explicitly in the representation in Fig. 72, because it is a function of (P/V)". 

Since solutions of sodium sulphite are alkaline, which affects TNT unfavourably, a number of workers have developed other methods consisting in lowering the pH of the sodium sulphite solution by adding buffers. 

Barbiere [145] examined quantitatively the process of sulphitation of a-, p-and y- trinitrotoluenes using a 6% solution of Na2S03 at different temperatures (30-60°C) and in another series of experiments the influence of the concentration of sodium sulphite solution on the solubility of the isomeric trinitrotoluenes at 30°C. He also determined ... 

Fig. 75. Influence of the concentration of sodium sulphite solution on solubility of a-,, 3- and y- trinitrotoluene (Barbiere [146a]).

Oxidation leads to the formation of di- and tri-nitrocresols, impurities frequently met with in TNT. Nitrocresols are mainly formed during the nitration of toluene to mononitrotoluene (Noelting and Forel [11]). If they have not been removed from mononitrotoluene by washing with alkalis, they undergo either further nitration to trinitrocresol, or oxidation to oxalic acid. Trinitrocresol may be removed from TNT by mild alkali washing (e.g. with a NaHC03 or a sodium sulphite solution). 

For crystallization the molten TNT is run from vessel A into a crystallizer filled with water, heated to 90-100°C. The ratio of water to the TNT should be 1 1 by volume. The content of the crystallizer is allowed to cool. At about 75°C the TNT begins to crystallize. After the temperature has fallen to 50°C (in about 4 hr from the time the crystallizer was loaded) sodium sulphite solution is added and the mixture is allowed to react for half an hour at a temperature of 40-45°C. The concentration of Na2S03 in the crystallizer is 34%. The weight of the Na2S03... 

The suspension of crystals in sodium sulphite solution is pumped upwards by a rotary pump to a vacuum filter through a small tank in which the suspension is diluted with water. After the TNT has been separated from the liquor it is washed with cold water until its pink colour, produced during the sulphitation process, disappears. The aluminium filter plate in the filter bowl should be covered with linen cloth, which in turn is covered with a layer of pine, granulated TNT. 

The experiment may be varied by passing a current of air or oxygen through a suspension of nickel hydroxide to which small quantities of sodium sulphite solution are periodically added. This not only effects the oxidation of the sulphite, but also converts the nickel hydroxide into black mckelie oxide, a change which is not producible by oxygen only.3... 

A similar method is used for the determination of inorganic phosphates in urine. 1 to 5 c.e. of the urine, containing about 0-5 milligram of phosphorus, are diluted and treated with a solution of ammonium molybdate in 15 per cent, sulphuric acid (5 c.c.), 1 c.c. of 1 per cent, hydroquinone solution and 1 c.c. of 20 per cent, sodium sulphite solution. The blue colour is compared in Nessler glasses with that developed by the same solutions when mixed with a standard phosphate solution of which 5 c.c. contain 0-5 milligram of phosphorus. 

---