US1724928A - Electrolytic desulphonation of anthraquinone sulphonic acids - Google Patents

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1929- A. J. HAILWOOD 1,724,928

ELECTROLYTIC DESULPHONATION OF ANTHRAQUINONE SULPHONIC ACIDS Filed Dec. 8, 1926 INVEN TOR Fl J, HAILWOOD by K? we Patented Aug. 20, 1929.

IJNITED STATES.

PATENT OFFICE.

ANTHONY JAMES H AILWOOD, OI BLACKLEY, MANCHESTER, ENGLAI ID, ASSIGNOB TO BRITISH DYESTUFFS CORPORATION LIMITED, OF MANCHESTER, LANCASHIRE,

ENGLAND.

ELECTROLYTIC DESULPHONATIQN OF AHTHRAQUINONE SULPHONIG ACIDS.

Application filed December a, 1926, Serial No.

The desulphonation of anthraquinone sul honic acids has previously been carried out by heating solutions of the acids in 80 per cent sulphuric acid to high temperatures with the addition of mercury as a catalyst. I now find that by electrolytic reduction of the sodium or potassium salts of anthraquinone sulphonic acids in a divided cell, in alkaline solution, those acid groups occupying a-positions are in great part removed and replaced by hydrogen, while those ,B-positions are scarcely-affected. I find that under the reducing conditions of the cathode chamber reduction of the carbonyl groups of the anthra 'uinone residue readily takes place so that the, product from which the a-SlllPhODlC acid groups have been removed is found in the cathode solution as an oxanthrol. In alkalinesolution a current of air suflices to oxidize this to the anthraquinone in Whichform it is usually desired and separated. ,I find also from my work that under the conditions I use,the desulphonation is largely subsequent 'to reduction to the oxanthrol, and because in the alkaline medium the oxanthrol is easily oxidized back to the quinone by air, it is necessary to exclude air or oxygen as much as possible from the cathode chamber in order to ensure eflicient working. Many different metals or alloys may be used as cathode; for example, mercury or amalgamated copper. The current density may be varied withm wide limits, an advantageous currentdensity being 2-3 amperes per square decimetre. The quantity of electricity required is usually about 1.4 times that required by theory, due allowance being made for the two atoms of hydrogen required to reduce each molecule of anthraquinone to the corresponding oxanthrol. Although the process proceeds well at ordinary temperatures, it is advantageous in most cases to carry out the operations at a higher temperature, particularly if the salts of the anthraquinone sulphonic acid or 153,473, and in Great Britain April 15, 1926.

oxanthrol sulphonic acid are sparingly soluble in the catholyte. The separation of the cathode and anode solutions may be achieved lthel by using a porous division of the pot type, or an impermeable division which clips into a mercury trap connecting the two solutions and which serves as cathode.

In the accompanying drawing, there is shown in longltudinal cross-section an apparatus for conducting the electrolysis. A receptacle or beaker 10 is provided with a porous pot-11, in the bottom of which is placed a layer 12- of mercury serving as the cathode. Above the mercury is the catholyte 13, the composition of which-is explained more fully below. The pot 11 is provided with an airtight cover 14 through which passes a stirrer 15, an incased wire 16 leading to the mercury 12, and a vent tube 17 permitting the escape of gases generated during the electrolysis. It

will, of course, be understood that the essential elements contained within the porous pot 11, and forming a portion of the entire apparatus, constitute the dathode chamber. Surrounding the cathode chamber is the anolyte 18 of sodium hydroxid solution, into which extend anodes 19.

The following examples are intended to ill'istrate. the nature of my invention but I do not limit myself to the particular details thereof Example 1.25 grams disodium anthraquinone-1:5-disulphonate are dissolved in 1 litre of hot water containing 14 grams of sodium hydrate solution. The solution so obtained is introduced into a cathode chamber, which consists of a porous pot on the bottom of which is a layer of mercury serving as the cathode. The porous pot is fitted with an air-tight lid through which passes a stirrer, a cathode lead and a tube to carry off excess hydrogen. -The cathode chamber is surrounded by a 25 per cent aqueous'solution of sodium hydrate which acts as the anolyte.

' passed until about 1317 ampere-hours have OiNa ONa ' +NaOH (LNa The anthraquinone is filtered off, washed with water and dried. It is already very pure and may be obtained quitepure by a single 'sublin ation or recrystallization for example from toluene. The yield of anthraquinone is about 70 per cent calculated on the disulphonic acid used. In addition, there is an appreciable quantity of mono-sulphonic acid left in the solution.

Ewa'rr'tple 2.-11 grams of the dipotassium' salt of anthraquinone-l:8-disulphonic acid, 6 grams potassium chloride and 300 grams of water forms the catholyte and a 10 per cent aqueous solution of potassium carbonate 25 forms the anolyte. The cell-arrangement-is the same as in Example 1, a mercury cathode being used. The temperature conditions are the same as before and 6 ampere-hours of electricity at a current density of 2 amperes per square decimetre are passed. The product is worked up as in Example 1.

' Example 3.300 cc. of a 2.2 per cent solution of the disodium salts of 1:6- and 1:7- disulphonic acids of anthraquinone containing small quantities of the sodium salts of the SOaN L excess H01 4- o y e beta-naphthylamine The reaction is as follows: 10

ONa SOzNa NazSO:

+ NazSO;

1 5- and '1 8- disulphonic acids obtained .as a waste product, are treated with 4.2 grams of sodium hydrate and subjected to electrolytic reduction in the cathode chamber of the cell described in Example 1 under the same conditions. After 3.5 ampere-hours of electrlclty are used, the brownish-red solution is oxidized with a current of air and filtered 3NaCl oo Example 4.- 5 grams of the sodium salt of in 300 cc. water containing 4.2 grams of soanthraqumone-a-sulphonic acid are dissolved dium hydrate in solution and the product is subjected to electrolysis, as in Example 1, 2 5, ampere-hours of electricity being'used. The product is oxidized by air as before described. The anthraquinone produced is filtered otl', washed with Water, and dried. The yield is 66 per cent of theory. What I claim and desire to secure by Letters Patent is 1. A process for the manufacture of oxanthrol derivatives from anthraquinone compounds containing a-sulphonic acid groups, consisting in the reduction of, and the removal of such a-SlllPllOIllC acid groups from, such anthraquinone compounds by electrolytic reduction in alkaline solution.

2. A process for the manufacture of anthraquinone and anthraquinone compounds derivatives from compounds containing asulphonic acidgroups thereof, consisting in the reduction of, and the removal of such a-sulphonic acid groups from. such anthraquinone by electrolytic reduction in alkaline solution to produce oxanthrol derivatives, followed by oxidation of the resulting oxanthrol followed by oxidation of the resulting oxanthrol derivatives, substantially as described. i

In testimonv whereof'I afiix my signature.

ANTHONY JAMES HAILWOOD.

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