Sodium formaldehyde-sulphoxylate

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. 

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 a few cases other redox systems are recommended to initiate grafting to cellulose. Asahi Chemical Industries (62) was granted a patent to graft acrylonitrile to viscose rayon fibers using ferrous sulphate and sodium formaldehyde-sulphoxylate as initiator. 

The solubilized brands are derived from the conventional sulphur dyes by preparation of the reduced form in a stable state. In some cases the reduction is carried out in aqueous solution and the product is obtained by evaporation and pulverization or alternatively prepared as a liquid mixture. In other cases, sodium formaldehyde sulphoxylate, mild alkali, and the dye are mixed and packed in the dry state. 

Water-soluble initiators used in emulsion polymerization are preferentially sodium, potassium or ammonium persulphate operating at 50-80°C. Redox systems use hydrogen peroxide or a persulphate as the oxidizing moiety and sodium metabisulphite, sodium hydrosulphate (also known as hyposulphite or dithionite), sodium thiosulphate and sodium formaldehyde sulphoxylate as the reductant. 

The bleaching process also has peculiarities depending on the type of fibre which is treated. The most common and environmentally friendly bleaching agent used for fibres is hydrogen peroxide. Cotton is also partly bleached while scouring, under the action of sodium chlorite. Some yellow wools or bast fibres may require a harsher bleaching, for which reason sodium dithionite or sodium formaldehyde sulphoxylate (for wool) and sodium chlorite (for bast fibres) are also used. 

However, great care must be taken if it is intended to put such findings to practical use. It is known that certain redox agents are more aggressive to isothiazolin-3-one biocides than others. For example. Conquer (1993) found that sodium formaldehyde sulphoxylate (formasol) destabilised CIT over a wide pH range and persulphates had a similar effect on BIT. 

During the main period of development a large number of redox systems were investigated. As reductant, in approximate order of development, were diazoether, sugar-iron pyrophosphate, polyamine and sodium formaldehyde sulphoxylate. Amongst the peroxides cumene and p-menthane hydroperoxides have found favour. The SFS system based on sodium formaldehyde sulphoxylate has been particularly useful because of its low cost, ease of preparation and reproducibility. A simplified mechanism for the initiation stage may be given as ... 

Sodium naphthalene sulphonate Potassium chloride fert-Dodecyl mercaptan p-Menthane hydroperoxide Ferrous sulphate (FeS04-7H20) Ethylenediamine tetraacetic acid sodium salt Sodium formaldehyde sulphoxylate... 

Until the early 1950s, the major method of emulsion polymerisation involved water-soluble initiators, such as potassium persulphate, being used to initiate polymerisation in an emulsion system stabilised by a fatty acid soap. Molecular weight was controlled by the use of a mercaptan and polymerisation proceeded at about 50 °C until approximately 72% of the monomer had been converted into polymer. This process yielded the so-called hot rubbers. Today, the bulk of SBR materials are prepared using so-called redox initiators which comprise a reductant such as ferrous sulphate with sodium formaldehyde sulphoxylate in combination with an oxidant such as /7-menthane hydroperoxide. In this case, the polymerisation temperatures are as low as 5 °C and conversion of monomer to polymer is only about 60%. Both the hot and cold rubbers are taken to number average molecular masses (molecular weights) of about 100 000, unless they are being used for oil extension (see later). 

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