Sodium anthraquinone-p -sulphonate

Sodium anthraquinone-p-sulphonate ( silver salt ). Place 60 g. of fuming sulphuric acid (40-50 per cent. SO3) in a 250 or 500 ml. round-bottomed flask and add 50 g. of dry, finely-powdered anthra-quinone (Section IV,145). Fit an air condenser to the flask and heat the mixture slowly in an oil bath, with occasional shaking, so that at the end of 1 hour the temperature has reached 160°. Allow to cool and pour the warm mixture carefully into a 2 litre beaker containing 500 g. of crushed ice. Boil for about 15 minutes and filter off the unchanged anthraquinone at the pump. Neutralise the hot filtrate with sodium hydroxide and allow to cool, when the greater part of the sodium anthra-quinone-p-sulphonate separates as silvery glistening plates ( silver salt ). Filter these with suction and dry upon filter paper or upon a porous plate. A second crop of crystals may be isolated by concentration of the trate to half the original volume. The yield is 40-45 g. 

Alizarin. Dissolve successively in 75 ml. of water 6 g. of potassium chlorate, 20 g. of sodium anthraquinone- p-sulphonate and 75 g. of sodium hydroxide. Transfer the mixture to a 500 ml. autoclave (compare Section VI,4) and heat for 20 hours at 170°. After coohng, scrape out... 

Upon heating anthraquinone with fuming sulphuric acid at 160° for about 1 hour, the main product Is anthraquinone-p-sulphonic acid, which is isolated as the sparingly soluble sodium salt. The latter when heated imder pressure with sodium hydroxide solution and an oxidising agent (sodium or potassium chlorate) yields first the corresponding hydroxy compound further hydroxy-lation occurs in the a-position through oxidation by the chlorate and 1 2-di-hydroxyanthraquinone (alizarin) is formed. 

The sulphonation of toluene (Expt 6.37) with concentrated sulphuric acid at 100-120°C results in the formation of toluene-p-sulphonic acid as the chief product, accompanied by small amounts of the ortho and meta isomers these are easily removed by crystallisation of the sodium salt of the para isomer in the presence of sodium chloride. Sulphonation of naphthalene at about 160°C yields largely the 2-sulphonic acid (the product of thermodynamic control) (Expt 6.38) at lower temperatures (0-60 °C) the 1-sulphonic acid (the product of kinetic control) is produced almost exclusively. In both cases the product is isolated as its sodium salt. In anthraquinone the carbonyl groups deactivate the aromatic nucleus towards electrophilic attack and vigorous conditions of sulphonation are required, i.e. oleum at about 160 °C. The product is largely sodium anthraquinone-2-sulphonate (Expt 6.39). 

Cognate preparation. Alizarin. Dissolve successively in 75 ml of water 6g (0.049 mol) of potassium chlorate, 20 g (0.065 mol) of sodium anthraquinone-2-sulphonate (Expt 6.39) and 75 g of sodium hydroxide. Transfer the mixture to a 500-ml autoclave (compare Section 2.17.2, p. 97) and heat for 20 hours at 170°C. After cooling, scrape out the violet-coloured mass and extract it three or four times with 100 ml portions of boiling water. Acidify the filtered extract with hydrochloric acid. When cold, filter the orange precipitate of alizarin at the pump, wash it thoroughly with cold water and dry at 100 °C. The yield of alizarin is 14 g (90%). It may be purified by recrystallisation... 

This product melts at 15° C., boils at 171° C. at 4 mm. and has a density of 1 4724 at 25° C. Replacement of the sulphide by / j8 -dichlorodiethyl sulphone or sulphoxide yields respectively di-p-ethylselenolethyl sulphone9 S02(CH2.CH2.SeC2H5)2, M.pt. 72 5° C., and the corresponding sulphoxide, SO(CH2.CH2.SeC2H5)2, an oil, decomposing on distillation at 4 mm. Condensation of sodium ethyl selenide with sodium anthraquinone-1-n-butylsulphone-5-sulphonate similarly yields 5-ethylselenol-l-n-butyl-sulphone anihraquinone, which does not melt below 300° C. ... 

Reaction LXX. Oxidation of certain Hydrocarbons. (B., 14, 1944 A. Spl., 1869, 300 E.P., 1948 (1869).)—This reaction is confined in the aliphatic series almost exclusively to the replacement by hydroxyl of the hydrogen attached to tertiary carbon atoms. A powerful oxidising agent, e.g., chromic acid in glacial acetic acid, is necessary. In the aromatic series the reaction is somewhat more easy to accomplish when the sodium salt of anthraquinone-jS-monosulphonic acid, for example, is fused under pressure with caustic soda and a little potassium chlorate, replacement of both a hydrogen atom and the sulphonic acid group by hydroxyl occurs, and alizarin ( /f-dihydroxyanthraquinone) is obtained. 

Other derivatives of p-quinones, such as anthraquinone, mono- and di-sodium sulphonates are photosensitizers of the oxidation of isopropanol [Refs. 84, 105, 106, 158, 662, 663]. Lock and Sagar [377] have suggested that a similar mechanism may occur in the photosensitized oxidation of JV-alkylamides which they studied as a model system simulating the photo-sensitized degradation of polyamides. They suggest that the AT-alkyl radical initially produced may add molecular oxygen to give peroxy radicals which are the precursors of the observed oxidation reaction. 

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