Rapid Fast Dyes

Stable mixtures of anti-diazotates and Naphtols were marketed as Rapid Fast colours for printing onto fabric with development of the azoic dye by steaming. The anti-diazosulphonates (4.113) [113], which were prepared by treatment of a diazonium salt with sodium sulphite and which regenerate the diazonium ion on treatment with an oxidising agent, found similar use. Both ranges are now of only historical interest. 

Pad Roll Process (see Section 4.1.1). Disperse dyes are fixed only incompletely to PES fibers under the conditions of the pad roll process (padding and subsequent rotation of the batch in saturated steam atmosphere). Only light colors can be produced economically with adequate fastness. Carrier additions are not useful because very large amounts would be required. In the pad roll process, rapidly diffusing dyes must be used. 

The development of the synthetic dye industry led to the emergence of classical organic chemistry. Its application in industry was rapid. From the end of the nineteenth century the intermediates employed in the manufacture of synthetic dyes were used to make pharmaceutical products such as aspirin. Some synthetic dyes exhibited bactericidal properties they were called medicinal dyes. Sulfonamides, drugs introduced in the 1930s, are based on research into dyestuffs and their intermediates. Less fast dyes have... 

The photo-oxidising method produces blue dyes, but they are not fast and fade rapidly. These dyes are primarily produced from the hchens of the Xanthoria species. The hchens are soaked in a small amount of ammonia for two days and then water is added. After about three weeks a pink colour is produced, but a further couple of months of soaking is required. Following this time, the pink liquid is strained off and water added. The material to be dyed is then added, and the bath heated to 28 C for an hour. A pink dye is produced on the substrate. On removal from the bath, the material must then be dried in sunlight and a blue colour forms (Diadick Cassehnan, 2001). 

It has been observed, with many types of fibres, that the most even dyeings are usually obtained with dyes that diffuse most rapidly inside the fibres. On the other hand, rapidly diffusing dyes generally have wet-fastness properties that are poorer than those which diffuse more slowly. Compromises between eveimess and wet fastness must thus be struck for many practical purposes. 

A simple, reliable, and fast method of determining the pH of a solution and of monitoring a titration is with a pH meter, which uses a special electrode to measure H 0+ concentration. An automatic titrator monitors the pH of the analyte solution continuously. It detects the stoichiometric point by responding to the characteristic rapid change in pH (Fig. 11.9). Another common technique is to use an indicator to detect the stoichiometric point. An acid-base indicator is a water-soluble organic dye with a color that depends on the pH. The sudden change in pH... 

The rate of dyeing of acid dyes of relatively small molecular size decreases with increasing degree of sulphonation. Simple monoazo monosulphonate types are rapidly absorbed but readily desorbed again. Thus they migrate easily but show extremely poor fastness to wet treatments. There are two main types of levelling acid dye ... 

The Berry spot test provides a rapid qualitative evaluation of urine. GAGs react with toluidine blue, a cationic dye, to yield a pink-colored compound. Alternative spot tests have been published but suffer from the same drawbacks regarding false-negative and false-positive specimens [2, 10, 15, 34]. Nevertheless, this fast procedure may pick up patients who have been referred to a laboratory for other metabolic examinations. For specific, initial MPS testing, the 1,9-dimethylene blue (DMB) assay, described below, is recommended. 

For covalently attached dyes, the mechanism is more complex, involving trap states as intermediates and entailing coupled proton transfer. Why do the mechanisms differ It appears likely that phosphonate- and carboxylate-binding perturb semiconductor surfaces sufficiently to create new trap states that can be rapidly populated following injection. The states are necessarily spatially proximal to the attached dyes, but apparently sufficiently separated from each other to preclude fast trap-to-trap hopping. 

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