Dyestuffs precipitation

The leuco-base is prepared by heating one molecule of benzalde-hyde with two molecules of dimethylaniline in presence of hydrochloric acid. (Zinc chloride was formerly used, but has been found to be unnecessary.) The base is then dissolved in the theoretical quantity of hydrochloric acid and the calculated amount of finely suspended lead peroxide added to the solution, which must be very dilute. The lead is removed as sulphate by adding sodium sulphate, and the dyestuff precipitated by adding zinc chloride and salt. 

Reagent 0.5 g iodoeosin is dissolved in 13 ml 0.1 iV NaOH in a separatory funnel, 120 ml water and then 15 ml 0.1 N H2SO4 axe added. The dyestuff precipitates. The yellow-red mixture is vigorously shaken with 1 liter of ether and the dyestuff goes into solution. The ether layer is washed 3 times with 30 ml portions of water. The ether solution of the reagent should be stored in dark bottles... 

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

Naphthalenesulfonic Acid. The sulfonation of naphthalene with excess 96 wt % sulfuric acid at < 80°C gives > 85 wt % 1-naphthalenesulfonic acid (a-acid) the balance is mainly the 2-isomer (P-acid). An older German commercial process is based on the reaction of naphthalene with 96 wt % sulfuric acid at 20—50°C (13). The product can be used unpurifted to make dyestuff intermediates by nitration or can be sulfonated further. The sodium salt of 1-naphthalenesulfonic acid is required, for example, for the conversion of 1-naphthalenol (1-naphthol) by caustic fusion. In this case, the excess sulfuric acid first is separated by the addition of lime and is filtered to remove the insoluble calcium sulfate the filtrate is treated with sodium carbonate to precipitate calcium carbonate and leave the sodium l-naphthalenesulfonate/7J(9-/4-J7 in solution. The dry salt then is recovered, typically, by spray-drying the solution. 

Contamination by water-insoluble reaction by-products such as l-amino-2,4-dibromoanthraquinone affects the quaUty of dyestuff signiftcandy. Therefore, several methods for purification have been reported. Examples are extraction of impurities with organic solvent (18), or precipitation of bromamine acid from concentrated (60—85%) sulfuric acid (26). 

The normal sequence of addition ia the dyeiag process is pulps, filler, dyestuffs, rosia size, and alum. The dyestuffs are either taken up by the fiber because of their affinity or they must be fixed on the fiber in a finely divided form by suitable fixing agents. Alum, which is required to precipitate the rosin size, has a strong precipitating and fixing effect on dyestuffs. 

Solochrome dark blue or calcon ( C.1.15705). This is sometimes referred to as eriochrome blue black RC it is in fact sodium l-(2-hydroxy-l-naphthylazo)-2-naphthol-4-sulphonate. The dyestuff has two ionisable phenolic hydrogen atoms the protons ionise stepwise with pK values of 7.4 and 13.5 respectively. An important application of the indicator is in the complexometric titration of calcium in the presence of magnesium this must be carried out at a pH of about 12.3 (obtained, for example, with a diethylamine buffer 5 mL for every 100 mL of solution) in order to avoid the interference of magnesium. Under these conditions magnesium is precipitated quantitatively as the hydroxide. The colour change is from pink to pure blue. 

A disadvantage of adsorption indicators is that silver halides are sensitised to the action of light by a layer of adsorbed dyestuff. For this reason, titrations should be carried out with a minimum exposure to sunlight. When using adsorption indicators, only 2 x 10-4 to 3 x 10 3 mol of dye per mol of silver halide is added this small concentration is used so that an appreciable fraction of the added indicator is actually adsorbed on the precipitate. 

Other dyestuffs have been recommended as adsorption indicators for the titration of halides and other ions. Thus cyanide ion may be titrated with standard silver nitrate solution using diphenylcarbazide as adsorption indicator (see Section 10.44) the precipitate is pale violet at the end point. A selection of adsorption indicators, their properties and uses, is given in Table 10.8. 

The needle-like shape of the crystals prevents their being easily poured (into the capsule) making them liable to felt so the aim is to produce short crystals either by a suitable selection of conditions for the reactions of diazotization and precipitation of the product (D. Smolenski and Plucinski [13]) or by the addition of certain substances to the solution from which the product is to be precipitated Garfield [14], for instance, suggests for this purpose the addition of triphenylmethane dyestuffs to the solution. 

On crystallization nitromannitol forms needles which easily felt together into an unpourable mass which makes filling the detonators practically impossible. The crystallization process is therefore carried out so as to precipitate the product as granules, by adding protective colloids, triphenylmethane dyestuffs or similar substances. 

Ultra violet, modem violet, modern heliotrope, prune Colour precipitated Basic mordant Dyestuff On the addition of chromium fluonde reagent to a solution of the dyestuff 0 h 1 ... 

Tannin test for basic dyestuffs. The extract obtained with formic acid is shaken with a few drops of tannin solution, and if no precipitate forms immediately, the liquid is left at rest for a few minutes. Certain colouring matters, such as the rhodamines, the gallocyanins and the chrome colours of the rosaniline series (containing carboxyls or hydroxyls besides the basic groups) precipitate slowly and the precipitate, being highly subdivided, is sometimes difficult to see. 

The colour is completely or largely stripped, giving a coloured acid extract, which is precipitated by tannin solution Basio Dyestuff. Transfer to wool and boil with Hydrosulphlte B. 

Not precipitated Baslo Dyestuff Transfer to wool and boil with Hydrosulphite A X... 

Precipitated Or is present in ash Basie Mordant Dyestuff Boil cotton with Hydrosulphite B X... 

The colour is largely stopped and the acid extract is precipitated by tanmn solution. Basic Dyestuff. Transfer t wool and boil with Hydrosulphite A X... 

An intermediate for a dyestuff is prepared by sulfonation and nitration of an aromatic compound at 40 °C. The intermediate product has to be precipitated by dilution of the sulfuric acid with water to a final concentration of 60%. This dilution is performed under adiabatic conditions (no cooling) and the final temperature is 80 °C. This temperature of 80 °C is important for the crystallization and for the following filtration. After the temperature has reached 80 °C, the mixture is immediately cooled down to 20 °C by applying the full cooling capacity of the reactor. 

Some yeasts and bacteria are able to produce different alcohols like ethanol and butanol as well as polyols like glycerin and 2,3-butandiol. These compounds- are used in drinks such as beer and wines, and also may be used in or as solvents, drugs, chemicals, oils, waxes, lacquers, antifreezing and antifoaming agents, precipitants, dyestuff, pomades, raw materials for chemical syntheses, motor fuels, and carbon sources for SCP production. These products are mainly synthesized from petroleum — derived materials like ethylene and acetaldehyde. However, because of the insufficient availability and high prices of the raw materials, the microbial production of alcohols has become an interesting area for many researchers. 

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