Acid mordants

Purpurin [81-54-9] (179) is a usefiil iatemiediate for preparing acid-mordant dyes, and is prepared by oxidation of alizarin with manganese dioxide and sulfuric acid (145). 

Acid—mordant dyes have characteristics similar to those of acid dyes which have a relatively low molecular weight, anionic substituents, and an affinity to polyamide fibers and mordant dyes. In general, brilliant shades caimot be obtained by acid—mordant dyes because they are used as their chromium mordant by treatment with dichromate in the course of the dyeing procedure. However, because of their excellent fastness for light and wet treatment, they are predominandy used to dye wool in heavy shades (navy blue, brown, and black). In terms of chemical constitution, most of the acid—mordant dyes are azo dyes some are triphenyhnethane dyes and very few anthraquinone dyes are used in this area. Cl Mordant Black 13 [1324-21 -6] (183) (Cl 63615) is one of the few examples of currentiy produced anthraquinone acid—mordant dyes. It is prepared by condensation of purpurin with aniline in the presence of boric acid, followed by sulfonation and finally by conversion to the sodium salt (146,147). 

T-wash pretreatment This acid-mordant solution turns the surface black when correctly treated. Problems can occur with use of such an acid solution in situ and from its pungent odor. It must be applied to zinc in a bright condition without corrosion products on its surface. The paint manufacturer s advice must be sought before using under thick coats of two-pack epoxy or urethane. 

Many dyes that have no chemical affinity to fibrous substrates can be attached to such substrates by intermediary (go-between) substances known as mordants. These are either inorganic or organic substances that react chemically with the fibers as well as with the dyes and thus link the dyes to the fibers. Mordants are traditionally classified into two main classes, acid and metallic mordants. The acid mordants are organic substances that contain tannins (see Textbox 64) as for example, gall nuts and sumac. The metallic mordants are inorganic substances, mostly mineral oxides and salts that include metal atoms in their composition. Table 94 lists mordants of both these types, which have been used since antiquity. 

Alizarin Yellow R [5-(4-nitrophenylazosalicylic acid). Mordant Orange 1] [2243-76-7] M... 

Naturally the dyeing procedure varies with the type of colour (basic, acid, mordant, substantive). In order, however, that valid conclusions may be drawn, the procedure should be that used industrially, this being usually indicated in the instructions supplied with the colouring matter. 

Anthraquinone dyes are characterized by the presence of one or more carbonyl groups in association with a conjugated system. These dyes also may contain hydroxy, amino, or sulfonic acid groups as well as complex heterocyclic systems. Anthraquinones uses include disperse, vat, acid, mordant, and fiber reactive applications. 

Aminosalicylic acid is used in preparing azo dyes, conferring on them, as does salicylic acid, mordant dyeing properties. 

Mordant pieces of test fabric by allowing them to stand in a hot (nearly boiling) solution of 0.1 g of tannic acid in 50 mL of water for 30 min. The tannic acid mordant must now be fixed to the cloth otherwise it would wash out. For this purpose, transfer the cloth to a hot bath made from 20 mg of potassium antimonyl tartrate (tartar emetic) in 20 mL of water. After 5 min, wring the cloth and dry it as much as possible over a warm hot plate. 

The group includes many natural and synthetic dyes, the latter usually being obtained from anthracene. They have no natural affinity for textiles but are applied to cellulosic or protein fibres which have been mordanted previously with a metallic oxide. The acid mordant dyes are a special class of dyes applied to wool or polyamide fibres as if the were acid dyes, and then given very high wet-fastness by subsequent mordanting. 

A naturally-occurring mordant dye, used extensively until a few years ago, and now probably the only one still in use, is logwood. It yields a navy blue or a black, with what is called a good bloom, when dyed on chrome mordanted wool. Until the advent of acid mordant dyes, which will be described later, it was the only dyestuff with which wool could be dj ed black with any measure of fastness. 

The shades can be brightened by the addition of acid dyes at the commencement of the dyeing, but their presence will diminish the wet-fastness. The dyes must be unaffected by dichromate and such that can be dyed satisfactorily at the pH necessary to exhaust the acid mordant dye. Some recommended dyes are given below. 

If a correction to the shade is necessary and the standard of fastness is to be maintained, the most convenient procedure is to cool the liquor to 60°C (140°F) and add sufficient sodium acetate to convert any free sulphuric to acetic acid, and then correct with an acid mordant or a premetallized dye. If the amount of dye required is not great the wool will already contain sufficient Cr Os to combine with the acid mordant dye. A few dyes suitable for shading are shown below. 

An exhaustive investigation of the acid mordant dyes was made by Stevens, Rowe, and Speakman J.S.D.C., 1943, 59, 165) with a view to ascertaining why some responded to the metachrome-mordant method and others did not. In the first place they examined the behaviour of wool towards the mordant in the absence of the dye. It was found that, after boiling or 6 hours, 99-7 per cent of the chromium in the dyebath had been adsorbed by tlie wool and about 42 per cent of the total ammonia had been wolved, leaving the liquor with a p of 5 02. They suggested that the first... 

Acid mordant and premetallized dyes can be applied to polyamides. They build up well into dark shades and the light- and wet-fastnesses are good. It must, however, be borne in mind that they are worse than other classes for emphasizing yarn variations. These dyes have no migrating properties once they have been taken up by the fibre and it is therefore most important to control conditions during dyeing in such a manner that the initial adsorption is uniform. 

The acid mordant dyes are applied, in the first stage, in the manner already described for acid dyes. Because the exhaustion is not so good as with wool it is advisable to run the dye liquor off when the dyeing cycle is complete and refill with fresh water for chroming. The chroming is carried out with 3 to 4 per cent of formic acid (85 per cent) and the following quantities of dichromate ... 

Better resistance to laundering and non-staining of cellulose is obtained with virtually all the premetallized dyes. The 1 1 chromium complex dyes should not be used under conditions when very high sulphuric acid concentrations are necessary because of the risk of degrading the cellulose. Many of the acid mordant dyes can be used with success. 

The acid mordant and premetallized dyes are fast but lack brightness of shade. There are a number of fast acid colours which will dye wool and leave eellulose unstained when applied with ammonium sulphate or acetate. 

Cross-dyeing mixtures of protein and cellulosic fibres, which involves imparting two distinct colours, is not often practised. The best method is to dye the wool or silk first with an acid, acid mordant, or premetallized dyestuff, and then rinse till free from acid, preferably having previously neutralized with ammonia or sodium carbonate. The cellulosic component is next dyed with a selected direct dye in the presence of 1 to 6 per cent of Tanninol VR or Katanol W at 40° to 60°C (104° to 140°F). The addition... 

Alizarin Yellow R [5-(4-nitrophenylazosalicylic acid). Mordant Orange I] [2243-76-7] M 287.2, m 253-254"(dec), >300", Cl 14030, pK 11.17. The free acid is precipitated by adding HCl to an aqueous solution of the Na salt. After 2 recrystallisations from aqueous AcOH, it has m 255°(dec) [m 253-254°(dec) was reported by Hewitt Fox J Chem Soc 79 49 1901], The free acid recrystallises from dilute AcOH as orange brown needles. The Na salt changes colour from yellow to red when the pH is increased from... 

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