45 gms.

NaOH

+H2S.

6 litres Ice+water.

About 30 gms. Na2Co3.

may again become of importance, since the discovery by Frasch of the great sulphur deposits in Louisiana and the electro-thermal preparation of sodium cyanide and carbon disulphide this possibility must always be borne in mind.

Alizarin from Pure Anthraquinone.

Reaction:

2-Anthraquinone Sulphonic Acid.

1:2-Hydroxyanthraquinone Sulphonic Acid.

Alizarin.

(a) 2-Anthraquinone Monosulphonic Acid Sodium Salt

{Silver Salt).

On treating anthraquinone with fuming sulphuric acid two sulphonic groups readily enter the nucleus so that it is necessary to reduce the quantity of So3 to such an extent that a fairly large portion of the anthraquinone remains unchanged.

100 Gms. of dry finely divided anthraquinone are added cautiously to 150 gms. of oleum containing 25 gms. of S03. The temperature must not exceed 300, and stirring must be continued without interruption in order to prevent any local overheating. The temperature is raised during 4 hours to 120o by means of an oil-bath, and after a further 2 hours to 140o. The vessel must be kept well closed to prevent So3 from distilling off (see Fig. 4). After cooling, the mixture is poured into 3 litres of water and the unchanged anthraquinone filtered off. Some 25-40 gms. are recovered, according to the manner in which the sulphonation has been effected. The sulphuric acid solution is now completely neutralized by means of chalk or limestone as described on p. 15, and the calcium sulphate filtered off. The lime is then precipitated with dilute sodium carbonate until a filtered test-portion gives no further precipitate with soda. The filtered solution is evaporated down to 400 c.cs. over a gas-ring, and is then allowed to cool. The sodium salt of the anthraquinone-2-sulphonic acid separates out in the course of a couple of days as a glistening, silvery precipitate. It is filtered off and washed with a little water. The yield of dry substance is 60-90 gms. A few grams of less pure substance may be recovered from the mother-liquor, but always contain a little disulphonic acid, no matter how carefully the sulphonation is carried out.

100 gms. Anthraquinone. 150 gms.

25% Oleum.

About 180 gms. CaCo3.

It is also possible to avoid liming-out, as is usually done technically, by pouring the sulphonation product into a litre of water, filtering from unchanged anthraquinone after standing for an hour, and then salting out with 20 % of common salt. The precipitated sodium salt is filtered off, washed with a little concentrated brine, and pressed. It is then pure enough for the melt. With proper working the mother-liquors contain only 2-2 1/2 % of disulphonic acids, which may be rejected. In the works rather more concentrated oleum is used, about 40 %, as in this case there is less danger of over-sulphonating.

(b) The Alizarin Melt.

The alizarin melt was first introduced into chemical technology by Caro, and the addition of an oxidizing agent, saltpetre, was first made use of by the Society of Chemical Industry in Basle. At the beginning of the 'seventies chlorates were made use of, following the suggestion of Koch, and at the present day only the cheap electrolytic sodium chlorate is utilized.

100 Gms. of 100 % silver salt are heated with 260 gms. 100 % caustic soda, 28 gms. sodium chlorate, and sufficient water to make the total volume up to 670 c.cs., the mixture being heated up with continuous stirring in an autoclave to 185o, the pressure attaining 5-6 atmospheres. After 48 hours the melt is allowed to cool, and is then examined to see if it is finished. For this purpose 2 c.cs. of the melt are taken, the Alizarin precipitated with the requisite quantity of concentrated hydrochloric acid, and the filtrate extracted twice with a little ether. The liquid, from which all Alizarin has been removed, is now diluted to 15 c.c, and the fluorescence observed, which is due to unchanged silver salt or to monohydroxyanthra-quinone sulphonic acid. Only a very faint fluorescence should be observable, or none at all, and if necessary the melt is heated up again to 1900 for 24 hours. The product is then diluted with 2 litres of water and the Alizarin precipitated at the boil with 50 % sulphuric acid; after filtering off at 500 it is washed until the mother-liquor is free from salt. The Alizarin is not dried, as when once dry it no longer dyes properly. The yield is estimated by determining the moisture and by test-dyeings. Usually the finished product contains 20 % of colouring matter.

100 gms. Silver salt. (100 %).

260 gms. NaOH. 28 gms. NaC1O3.

About 70 gms. pure Alizarin are obtained from 100 gms. of pure silver salt.

Notes on Works Technique and Practice. - Next to Indigo, Alizarin is the most important product produced by the colour factories. Owing to its low price it is now made only at a few works, but on a very large scale. The sulphonation is effected in apparatus of the usual type, but the melts are being carried out more and more frequently in Frederking apparatus such as was shown on Plate VIII. (Fig. 23). As the chlorate melt attacks the apparatus very vigorously, a liner of alkali-resistant cast-iron is always used, which may be replaced. There are many different forms of such apparatus. On the works scale very large charges are used, so that as much as 2000-2500 kilos. 100 % Alizarin may be obtained at one operation in one pot; the dye is then made up to 16 % or 20 % paste, the standardizing being done by determining the moisture content, and by dye-trials. Again it is possible technically to work with much less caustic soda, only no % of the theoretical quantity being required, corresponding to 40 gms. instead of 260 gms. in the present case. Alizarin which has been dried may be reconverted into a form suitable for dyeing by dissolving in borax and reprecipitating with acetic acid or sulphuric acid. Dyes of the alizarin type must, owing to their sparing solubility, be precipitated at the boil, as only in this manner can they be obtained in a suitably fine state of subdivision (cf. also Anthracene Brown). The world's production of 100 % Alizarin was about 2,800,000 kilos., of which the Badische Anilin and Soda Fabrik alone produced 2,000,000 kilos. For the Oriental market a solid preparation is made by adding sufficient starch to the dye to convert it into dry lumps which swell up to a paste on boiling with water, and dye easily. (For dyeing with Alizarin, see the pattern cards issued by the various firms, and Gnehm's "Taschen-buch.")

Anthracene Brown FF from Benzoic Acid and Gallic

Acid.

Reaction:

1:2:3- Trihydroxyanthraquinone, Anthracene Brown or Anthragallol.

36.6 Gms. (3/10 mol.) pure benzoic acid are dissolved in 300 gms. sulphuric monohydrate contained in a glass, porcelain, or iron beaker, and stirred until complete solution is effected. It is then heated up slowly to 900, at which temperature 50 gms. pure dry gallic acid (dried at 110°) are added in small portions during an hour. The temperature is kept at 118° for 6 hours, and then the melt is allowed to drop very cautiously into a litre of boiling water with continuous stirring. The product is filtered off from the absolutely boiling liquid into a previously warmed jar, and the dye is well washed with hot water. The excess of benzoic acid crystallizes out in a pure form in a short time from the mother-liquor. After stirring up with water to 20 % paste the dye is ready for use. The dyeing is effected upon chrome-mordanted wool, chromium fluoride giving the handsomest and fullest shades.

Notes on Works Practice. - The most important factor in this manufacture is the absolute purity of the gallic acid used. No "second-quality" crystals may be used as these probably contain homologues of gallic acid which cause troublesome foaming during the condensation, and diminish the yield to 50 %. On the works also the boiling liquids are filtered through filter-presses made of pitch-pine and provided with nitro-filters. These latter will last out about 50 operations, but must of course be very carefully manufactured if they are to meet these exacting demands.

For the production of Anthracene Brown for printing (F. D.= fur Druck) the process is very similar. The condensation, however, is carried out at 130-140° instead of at 118°. The product obtained by precipitating in boiling water is not sufficiently finely divided, but gives a mottled effect on printing. It is therefore necessary, after washing, to convert the product, as a 10 % suspension, into the sodium salt by means of soda at 80-90°, and then to precipitate cautiously with hydrochloric acid. After filtering off again, the product is made up to the desired strength in a Werner and Pfleiderer mixer What was said before as to the purity of the gallic acid applies still more forcibly in the present case.

36.6 gms. Benzoic acid. 300 gms. 100 % H2So4.

50 gms. Gallic acid.

A good quality gallic acid may be easily prepared by hydrolysing tannin at 700 in concentrated solution with caustic soda lye of at least 40 %.1 In order to protect the gallic acid from oxidation a little sodium bisulphite is added. The gallic acid is precipitated with concentrated hydrochloric acid (sulphuric acid must not be used), and is then crystallized from boiling water.