Sulphoxylates

Sodium formaldehyde-sulphoxylate (12.46 sodium hy droxy me thane sulphinate) and alkali, although more stable than alkaline dithionite, tends to share the same disadvantages... 

Greater commercial significance is attached to certain derivatives of sodium dithionite, including sodium formaldehyde-sulphoxylate (12.53 hydroxymethanesulphinate) (Scheme 12.23) and the less important sodium acetaldehyde-sulphoxylate (12.54 hydroxye thane -sulphinate). These reducing agents have been of particular interest in printing, especially in the flash-ageing process [228-231]. The formation of sodium formaldehyde-sulphoxylate by reaction of sodium dithionite with formaldehyde is shown in Scheme 12.23 the bisulphite formed can be further reduced with zinc to produce another molecule of the sulphoxylate. 

These reducing agents are much more stable than sodium dithionite at lower temperatures hence they can be used to prepare stable pad liquors and print pastes. At higher temperatures, as in steam fixation treatments, they are capable of bringing about rapid reduction of vat dyes. Sodium formaldehyde-sulphoxylate was used first in conventional steam fixation of vat prints, although the acetaldehyde analogue was initially preferred for the flash-ageing process. As vat dyes are invariably fixed under alkaline conditions, the sodium salts of the sulphoxylates are preferred to the basic salts of zinc (12.55) or calcium (12.56), which are unstable under alkaline conditions. 

Sodium hyposulphite (hydrosulphite) is converted by aldehydes into aldehyde bisulphite compound and aldehyde sulphoxylate ... 

The sulphoxylate obtained from formaldehyde is much used as a reducing agent in discharge printing in dyeworks. 

Tellurophene. A mixture of tellurium (4.0 g, 31 mmol), sodium formaldehyde sulphoxylate of 85% (28 g, 200 mmol), sodium hydroxide (17 g, 425 mmol) in 150 mL water is heated at reflux, under N2 atmosphere for 15 min, and then cooled at 20°C. A solution of 1,4-bis(trimethylsilyl)-l,3-butadiene (8.2 g, 42 mmol) in 100 mL of ethanol is slowly added to the stirred sodium telluride solution, the mixture is heated at reflux for 15 min, then stirred at 20°C for 3 h and extracted with ether. The extract is dried (Na2S04), filtered, and 10 mL (200 mmol) of bromine are added dropwise until the bromine colour persists. This solution is concentrated in a water bath under aspiration vacuum to a volume of 50 mL, and the red precipitate of tellurophene dibromide is collected 8.9 g (84%), m.p. 120°C dec. 

In ether solution sulphuryl chloride reacts with zinc, giving zinc chloride and zinc sulphoxylate, ZnS02. 

Sexavalent sulphur is the most stable form of combined sulphur. Various hydroxy-derivatives are known. The lowest is the unisolated sulphoxylic acid, H2S02, of which the zine salt has been obtained by the action of zinc dust on an ether solution of sulphuryl chloride.1... 

Sodium Sulphoxylate, Na2S02, maybe obtained by the action of sulphur sesquioxide (p. 224) on sodium ethoxide on the addition of sulphuric acid to the mixture, sodium cthylsulphoxylate, Na.C2H .S02, is first formed, which, when kept overnight, undergoes hydrolysis. The solution, acidified with more dilute sulphuric acid, then yields the required sodium salt as a white precipitate which may be separated and dried over phosphorus pentoxide.3 The salt is fairly stable and may be heated to 110° C. without change on exposure to air, however, it turns yellowish-brown. It is readily soluble in hot water, unattacked by hot mineral acids, but decomposed by a hot mixture of fuming nitric acid and bromine. 

The hydrosulphites, M2S204, may be regarded as derived simultaneously from sulphoxylic and sulphurous acids, having the constitution... 

The direct sulphur to sulphur linking in the first formula is in harmony with the formation of the salt by reduction of the sulphite and with the stability of the salt in the presence of alkalis,1 but it is discounted by the absence of dithionate from the oxidation products, and by the easy fission of the substance into sulphite and sulphoxylate on treatment with an aldehyde. 

Aqueous solutions of hydrosulphites become orange-yellow on acidification and the presence of sulphur dioxide is soon evident. The yellow colour is not due to colloidal sulphur, nor, since its salts are colourless, would it be expected that tlie free acid should be yellow, unless there is some change in constitution. It has therefore been suggested 4 that the decomposition on acidification involves the formation of a coloured isomeride of the type (H0)2S.S02 by co-ordination of a molecule of sulphur dioxide with the sulphur atom of sulphoxylic acid. The decomposition may proceed thus ... 

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