Artificial Indigo

USE Manuf phthaleins, phthalates, benzoic acid, synthetic indigo, artificial resins (glyptal). 

The coloured materials most frequently added are gamboge, dragon s blood, turmeric, indigo, and especially artificial organic colouring matters. For some varnishes mineral colours are used, such as ferric oxide, white lead, minium, lamp black, etc. 

Detection of Indigo Carmine and Artificial Organic Dyestuffs. 

If the wool is intensely coloured, tin presence of artificial organic dye or of indigo carmine is probable. In this case the operation is nqn-.ited in an add or alkaline bath according to which gives the more intensely coloured wool the colouring matter is then extracted from the w(x> and identified by the methods describ d for artificial organic dyes (.see Chapter XV). 

The colouring matter may be an artificial organic dye or a vegetable colour (extracts of dye wood or of other parts of plants, indigo) or an animal colour (cochineal) lakes are also made with mixtures of several colouring matters. 

Certain vegetable colouring matters, such as alizarin (from madder) and indigo, are now prepared artificially and are hence considered both as natural and as artificial organic dyes. 

Both natural and artificial or synthetic indigo are now sold. 

Artificial indigo is sold as a deep azure powder with coppery reflection, or more commonly as a moist paste. 

Powdered artificial indigo usually consists of almost pure indigotin (about 98%) in the paste its concentration varies (usually 20%). 

Artificial Organic Dyes.—Indigo carmine may be adulterated with artificial organic dyes, especially aniline blue. If silk is dyed with an acidified solution of the carmine and then washed and boiled with water, the fibre will become colourless if the carmine is pure, but remains blue if aniline blue is present. 

Also by oxidising the carmine solution with permanganate for the determination of the mdigotin, many artificial organic dyes may be detected thus, pure indigo carmine solution remains yellow, whereas it may be bluish, violet, grey or reddish in presence of artificial organic dyes. 

Only a few natural dyestuffs (indigo, alizarin, and purpurin) have been prepared synthetically, but the number of artificial dyestuffs is very large. Some of these, especially the phthalei ns and rosolic acid, seem to approach the natural dyestuffs in constitution, but the greater number belong to special classes, which are without analogue in either the animal or the vegetable kingdom. 

Natural dyestuffs, with few exceptions (indigo, berberine), contain only carbon, hydrogen, and oxygen while many classes of artificial colouring-matters contain nitrogenous groups, often of a decided basic nature. Some others again contain chlorine. 

In 1880 Bayer took out the first patent for the production of artificial indigo [31]. 

This group comprises most natural dyestuffs the constitution of some of these (alizarin and indigo) is known, and admits of systematic classification wfith just as much justice as the purely artificial dyestuffs and it would be reasonable to treat of the whole in a single chapter of natural dyestuffs. 

The diflieulties in this direction have also been to a certain extent Tanquished by the introduction of artificial indigo. A thickened mixture of orthonitrophenylpropiolic acid and grape-sugar, or better an alkaline xanthate with an alkali is printed, and the indigo blue developed by steaming and drying. 

The first eertain method for produeing artificial indigo is due to Nencki, who obtained it by oxidation of indol with ozone [40]. The same chemist had already obtained indol by the panereatic fermentation of albumen [2, 40]. In 1877 Baeyer and Caro obtained indol by passing the vapour of certain aromatic amines, especially of diethylorthotoluidine, through a red-hot tube. 

Further, the reaction is of practical value in the preparation of o-amido-benzoic acid, used in the manufacture of artificial indigo. If, as above, bromine and caustic potash are allowed to act on phthalimide, there is first formed, by the addition of water, an add-amide ... 

Formaldehyde (CH20) is an important compound in the synthesis of various chemicals on an industrial scale. One of the first industrial applications was in the production of artificial Indigo. The variety of end products produced from formaldehyde include resins or glues (produced by the condensation of formaldehyde with urea, phenol, or melamine) as well as rubber, paper, fertilizers, explosives, engineering plastics, and specialty chemicals like acrolein, methacrylic acid, methyl methacrylate, etc. Because it is nearly impossible to handle in its pure gaseous form, formaldehyde is almost exclusively produced... 

We must digroas for a moment to refer to another industry in order to indicate the origin of the contact process. About thirty-six yoars ago, various methods wore discovered for the preparation of artificial indigo, and endeavours wore made to apply the best of these on a commercial scale to compete with the natural product. Tlio starting material in the most successful processes was naphthalene, at one tinto rogardod by the tar distiller as a nuisance but now rooognisod as a valnablo product. In the... 

Creosote oil is of value as a source of naphthalene, and for preserving wood from the action of. the weather and destructive insects. Naphthalene, once a waste product, is now used largely in the manufacture of dyes, being the parent substance of artificial indigo, as an insecticide, and in other minor rdlea. Anthracene oil is the source of anthracene, a condensed hydrocarbon of the benzene sories, from which the alizarin dyes are made. 

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