Sulphur dyes application

Sulphur dyes in the insoluble disulphide form and the Cl Solubilised Sulphur brands are reduced by the dyer as part of the application procedure. In the case of the Cl Leuco Sulphur brands reduction has already been carried out by the manufacturer, so that they are substantially in a form suitable for immediate application (section 1.6.2) The chemistry of the reduction of sulphur dyes is complex, as is the chemistry of the dyes themselves it has been well described elsewhere [204]. It is possible to describe the state of a reduced sulphur dye in alkaline sulphide or polysulphide solution by the general formula 12.42, but there are certain complications. In many cases the chromogen is not itself reduced, but in others, notably reddish browns, blues and navy blues based on indophenols, the chromogenic... 

Table 12.27 Typical print paste formulation for the application of liquid jaggery as a reducing system for sulphur dyes [211]...

Table 12.30 Suitability of various sulphur dye types for application with anthra-quinonoid or iron-complex redox systems [214]...

Hydroxyacetone (12.48), mentioned in section 12.8.1 in connection with sulphur dyes, is sulphur-free and biodegradable. This compound was originally proposed for use with vat dyes and continues to generate some interest. This agent can be used for the pad-steam application of vat dyes in the presence of high concentrations of sodium hydroxide (about 3.5-4.5 g/1). Hydroxyacetone does not cause over-reduction of indanthrone vat dyes but does give different shades with carbazole dyes, compared with sodium dithionite [218]. 

These resemble the vat dyes in certain ways, although they are of indeterminate constitution and usually mixtures of different chemical species (section 6.4). The characteristic disulphide group (D-S-S-D in Scheme 1.2) is always present in the insoluble form of a sulphur dye, which is brought into aqueous solution by reduction to the alkali-soluble (leuco) form (D-S ). The soluble sodium thiolate form of the leuco sulphur dye has substantivity for cellulose. Thus the application of sulphur dyes to cellulosic fibres is a three-stage process (Scheme 1.2) broadly similar to that already outlined for vat dyes. 

Although many types of dye contain sulphur other than in sulphonic acid groups, sulphur dyes are usually considered to be those dyes that are best applied from a sodium sulphide dyebath. Like vat dyes, sulphur dyes are water-insoluble before and after application to cellulosic fibres. Disulphide linkages in the dye molecules are readily reduced by sodium... 

Dye Classification Based on chemical structure or chromophore, 20-30 different groups of dyes can be discerned. Azo (monoazo, disazo, triazo, polyazo), anthraquinone, phtha-locyanine and triarylmethane dyes are quantitatively the most important groups. Other groups are diarylmethane, indigoid, azine, oxazine, thiazine, xanthene, nitro, nitroso, methine, thiazole, indamine, indophenol, lactone, aminoketone and hydroxyketone dyes and dyes of undetermined structure (stilbene and sulphur dyes). The vast array of commercial colourants is classified in terms of colour, structure and application method in the Colour Index (C.I.), which has been edited since 1924 (and revised every three months) by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. Each dye is given a C.I. generic name determined by... 

The research tasks of the central laboratory at BASF between 1890 and 1914 were related mainly to the well established requirements of the dye-using industries. Direct azo dyes and the rhodamines were major research fields. In 1897 these were supplemented by the sulphur dyes, at that time also a main research area. In 1899, azo lake dyes were a new and very successful form of application. The twentieth century started with novel research into the anthraquinones, until then completely dominated by the alizarin laboratory. This widened the research potential for research into the important indanthrene-type vat dyes. Just before World War I the main laboratory participated in diversification with catalytic hydrogenation and the invention of synthetic tanning agents. In this period, the central laboratory controlled the core technology, and the most important market of BASF, namely the dyestuff business. The research laboratories of the aniline and the alizarin departments continued with the same tasks in their respective fields. 

Approach (a) is normally the easiest to control, and is used in the application of levelling acid and 1 1 metal-complex dyes to wool or nylon, and of the reactive, sulphur or vat dyes to cellulosic fibres. The agents traditionally used are the stronger acids and alkalis such as sulphuric, hydrochloric and formic acids, sodium carbonate and sodium hydroxide. In... 

The fact that the aftertreatment of direct dyes has a long history is not surprising since wet fastness within this class is not particularly good. Their prime advantages are ease of application and economy compared with dyes of higher fastness (reactive, sulphur or vat) -hence the continued search for highly effective aftertreatments that improve wet fastness... 

The vat dyes section of the Colour Index incorporates a subgroup called solubilised vat dyes. These are sodium salts of sulphuric acid esters of the parent leuco vat dyes, such as Cl Solubilised Vat Blue 6 (1.50). In contrast to the leuco compounds, the vat leuco esters dissolve readily in water at neutral pH. They have relatively low substantivity for cellulose and thus have been used mainly in continuous dyeing and printing. In the presence of an oxidant in mineral acid solution (sodium nitrite and sulphuric acid, for example) the leuco ester is rapidly decomposed and the insoluble vat dye regenerated. Thus application of a vat leuco ester represents a simpler (but more costly and less versatile) alternative to conventional dyeing methods via the alkaline leuco compound. 

An application has been suggested for this sesquioxide in the preparation of certain organic dyes containing sulphur.8... 

The anthraquinones may be reduced to the corresponding anthra-quinols (hydroxyanthranols) with alkaline sodium hydrosulphite this reaction has a wide application in the dye industry. These compounds are difficult to isolate pure, for they rapidly oxidise in air. The anthranols —y-monohydroxyanthracenes—however, are stable, and may be obtained by reducing anthraquinone with acid-reducing agents—tin and hydrochloric acid, zinc and glacial acetic acid, copper or aluminium, and sulphuric acid, etc. For the complete reduction of anthraquinone, see Reaction LYIII. (a). 

With a few exceptions, sulfur dyes are used for dyeing cellulosic fibres. They are insoluble in water and are reduced to the water-soluble leuco form for application to the substrate by using sodium sulfide solution. The sulfur dye proper is then formed within the fiber pores by atmospheric or chemical oxidation. Sulfur dyes constitute an important class of dye for producing cost-effective tertiary shades, especially black, on cellulosic fibers. One of the most important dyes is C.I. Sulphur Black 1, prepared by heating 2,4-dinitrophenol with sodium polysulfide. 

Leuco Sulfur Dyes (C.I. Leuco Sulphur). These liquid dyes already contain the reducing agent required for dyeing. They must simply be diluted with water before application. Ecologically more favorable, low-sulfide types have come onto the market recently. 

With respect to both application and fastness, a distinction is made between sulfur dyes and sulfur vat dyes. The latter include dyes of the type Hydron Blue C.I. Vat Blue 43, 53630 [1327-79-3]) and Indocarbon C.I. Sulphur Black 11, 53290 [1327-14-6]). 

Is obtained by aetion of p-diazobenzenesulphonic acid on an acid, alcoholic, dipheriylamine solution. The free aeid forms needles resembling graphite, which dissolve sparingly in water with a red-violet colour. The salts are well crystallised, and, with the exception of the insoluble calcium and barium salts, dissolve easily in hot water, less easily in cold water. Concentrated sulphuric acid dissolves the compound, forming a violet solution. The sodium salt has a large application, and comes into commerce under the above designations. It dyes wool and silk a beautiful orange. 

Morin is used largely in wool and cotton dyeing as decoction or extract of fustic. Its principal application is in shading blacks, browns, c. Wool is generally mordanted with potassium bichromate and sulphuric acid. The morin is fixed as a very stable chromium lake, which has a dull yellow colour. 

The amidoazobenzene hydrochloride came into the market formerly, as a yellow dye, under tire name of Aniline Yellow. At present, it is scarcely used, but there is prepared from it, by heating with sulphuric acid, a mono- or di-sulphonic acid, which in the form of its alkali salts finds application as a dye under the name of Acid Yellow, or Fast Yellow. As already mentioned under the dis-azo dyes, from the diazo-compound of this dye, Biebrich Scarlet may be made-by combination with /3-naphthol. Finally, the amidoazobenzene is still used for the preparation of the Induline dyes. 

The most significant assistant in the application of these dyes is the acid added to the dyebath. Many acid dyes will not exhaust on wool at all unless the dyebath has been acidified. If, for example, wool is boiled gently for half an hour with 5 per cent of Acid Magenta, it is only faintlystained. When 4 to 5 per cent of sulphuric acid is also added, however, the wool is dyed a heavy shade, and exhaustion is virtually complete. Some experiments reported by Lister (J.S.D.C., 1949, 98) show the relationship between acid and exhaustion of Azo Rhodine 2G (C.I. acid red 1) and Xylene Fast Yellow P (C.I. ACID YELLOW 61) on purified wool. 

The mononitration of chlorobenzene to chloronitrobenzene and especially to para-chloronitrobenzene is one of the most widely studied reaction because of its versatile industrial applications such as intermediates for dyes, pharmaceuticals and perfumes[l-4]. Most of the aromatic nitration reactions as classically conducted with a mixture of nitric and sulphuric acids give mixtures of ortho- and para-products close to the thermodynamic ratio 1 2[5,6]. But the presence of acetic anhydride along with mixture of sulphuric and nitric acids, increases the para-selectivity at low reaction temperature[7,8]. 

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