US2130151A - Production of quinone and hydroquinone - Google Patents

Description

Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE PRODUCTION OF QUINONE AND HYDRO- QUINONE No Drawing. ApplicationDecember 12, 1934, Se-

rial N0. 757,236. In

9 Claims.

This invention relates to the production of quinone (p-benzoquinone) and hydroquinone (1.4 dihydroxy-benzene) It is known that when benzene, agitated with a neutral or acid electrolyte, for example sulphuric acid which is maintained cool, is electrolyzed between electrodes which are unattacked by the electrolyte e. g. lead electrodes, the benzene is partially converted into quinone at the anode.

Since quinone is soluble in water and in aqueous solutions and is cathodically reduced to hydroquinone it has been usual to carry out the oxidation in a cell divided into two, by a porous diaphragm so as to avoid the wastage of current by 15 the passage of quinone and hydroquinone between the electrodes.

An object of this invention is to provide an improved process for the production of quinone by anodic oxidation.

A further object of this invention isto provide an improved process for the production of hydroquinone from the dilute solution of quinone in benzene obtained by the anodic oxidation process of the invention.

It has been found according to this invention that a high yield of quinone can be obtained without the use of a diaphragm, the disadvantages of which are well known.

According to the process of this invention for 30 the production of quinone, benzene is passed through or stirred with an electrolyte preferably consisting of dilute sulphuric acid or a mixture of sulphuric acid and a soluble sulphate such as sodium sulphate, and subjected to electrolysis in 35 an electrolytic cell in which an active and stable anode and an inactive cathode are disposed preferably close to each other, the concentration of quinone in the cell being kept low by its continuous or frequent removal.

The electrolyte is preferably dilute sulphuric acid and it maybe of any concentration up to 20% of H2804. Too low an acid concentration results in an electrolyte of low electrical conductivity, while too high a concentration results in the destruction of quinone. An acid concentration of 10% of H2804 has been found to be satisfactory.

The addition to the electrolyte 0.? acetic acid or other organic acids or salts of o ganic acids has been proposed for the purpose of increasing the solubility of the benzene in the electrolyte.

We have tried these additions but have found that they do not increase the eificiency of the process.

The temperature of the electrolyte should not Great Britain December exceed 25 C. and ordinarilya temperature of 20 C. is a suitable temperature at which to operate. Temperatures higher than 25 C. do not give a good yield. Although temperatures lower than 20 C. may be used they do not possess any advantage to compensate for the extra cost of cooling and the higher cell voltage which lower temperatures entail. The temperature may be maintained within the required limits by the passage of cold water through a coil serving as cathode as described hereafter.

The anode may be of lead or an alloy of lead. Its surface becomes coated with lead peroxide when current is passed and the condition of this coating of peroxide influences the efliciency of the formation of quinone. It has been found that the peroxide coating should not be too thick and should not be of such a nature as to scale off and that a hard lead alloy for example an alloy of lead with antimony or an alloy of lead with bismuth forms a more stable peroxide surface than pure lead.

The anode surface may be rendered active and stable by the passage of an alternating current or an alternating current superimposed on a direct current through the cell in the absence of the cathode and before the introduction of the benzene, or in another cell.

Thus, for example, the electrode to be used together with a similarly shaped piece of lead may be disposed in an electrolytic cell, the electrolyte being dilute sulphuric acid. Electric current is passed through the cell, the direction of the current being frequently reversed by means of a suitable switch. The last change of currentis efi'ected so that a coating of lead peroxide is formed on the electrode to be used. The anodic current density may vary between fairly wide limits but it has been found that densities of between 5 and amperes per square decimetre give the best results.

The cathode may be of any metal that is unattacked by the electrolyte but metals such as copper which promote the reduction of quinone should be avoided. Lead is a satisfactory metal to use as the cathode. The cathcathode,

for cooling is passed through the cathode which may conveniently consist of a lead coil.

High cathodic current density is accompanied by low reduction of quinone and the cathodic current density should therefore be higher, preferably at least 50% higher, than the anodic current density. In other words the area of the oathode should be less than that of the anode.

The electrolyte is preferably covered with a layer of benzene which is stirred into the electrolyte by means of a suitable agitator. The agitation should be sufficient to ensure constant circulation of benzene around the whole of the anode, but it should preferably be not so violent as to cause fine emulsification of the benzene with consequent slow separation of the benzene and electrolyte. Fresh benzene is added continuously or at intervals and an equivalent volume of benzene-quinone solution is withdrawn from the cell for example by overflow. The feed and overflow should be adjusted to prevent the concentration of quinone in the benzene from rising above 15 grams per litre. This prevents the quinone concentration in the electrolyte from rising above about two grams per litre.

Some benzene is lost from the cell, being carried away by the stream of mixed gases evolved, this loss may be partly avoided by the use of a suitable condenser which may be maintained at a sufliciently low temperature to freeze out the benzene. The stream of mixed gases may alternatively be made to pass through a known absorbent and afterwards recovered therefrom, or a combination of cooling and an absorbent may be used.

The benzene which is oxidized to quinone may contain dissolved therein phenol and/or aniline which are easily oxidized to quinone during the course of the reaction. If desired regulated quantitles of aniline and phenol may be added to the benzene during the reaction.

If quinone is required as a final product it may be separated from the benzene by known methods, for example by distilling off some of the benzene and crystallizing the quinone. As hereinbefore indicated, however, the quinone may be converted into hydroquinone which as is known is extensively used for photographic purposes.

Several methods have been proposed for the production of hydroquinone. For example it has been proposed that a benzene solution of quinone should be added to the cathode compartment of a divided electrolytic cell, or that it should be agitated with water and sulphur dioxide.

In both these proposed processes quinhydrone is first formed, and its low solubility makes its further reduction to hydroquinone slow and difiicult. Also it tends to collect at the interface of the liquid phases and to cause stable emulsification of the benzene in the water.

According to the process of this invention for the production of hydroquinone the benzene solution of quinone produced in the manner hereinbefore described is subjected to reduction at about the boiling point of benzene and under such conditions that the benzene is immediately distilled 011 and the hydroquinone dissolved in water.

The reduction may be carried out by means of iron and acid, sulphurdioxide or other known reducing agents. Quinone is rapidly destroyed at these temperatures so the conditions must be such that reduction is rapid and complete and the benzene solution must be added gradually to the reduction vessel.

Thus a solution of quinone in benzene run from the cell may be treated with iron borings and water containing a little sulphuric or other suitable acid in a heat jacketed or otherwise heated vessel.

The vessel with the contents are kept at a temperature of about C., the benzene solution is run in slowly, the benzene distills over and is condensed, and the quinone is entirely reduced to hydroquinone which remains in the vessel in aqueous solution. The acid liquors from the vessel are occasionally withdrawn and the hydroquinone recovered therefrom. Preferably the hot saturated liquors are drawn oil, filtered hot and cooled when hydroquinone crystallizes out. The acid mother liquor is returned to the reduction vessel. The hydroquinone may be recrystallized from water or other solvent.

Alternatively the aforesaid quinone-benzene solution may be run into a still containing water into which sulphur dioxide is simultaneously led in amount equivalent to that of the quinone to be reduced. The benzene distils off and is condensed and the hydroquinone formed remains behind in solution in the water together with the sulphuric acid formed in the reaction. At intervals the aqueous solution is withdrawn the acid removed by means of calcium carbonate, lime or barium carbonate or hydroxide and the hydroquinone obtained by evaporation. By using an iron free distillation vessel the hydroquinone may in this way be obtained absolutely free of iron.

The following example illustrates how the process of the invention may be carried into effect:

The cell employed is capable of operating at 1000 amper'es. The anode consists of an alloy of lead containing 10% of antimony made in tubular form with leads attached to carry the current. The whole of the tubular sheet is freely perforated so that under agitation the benzene passes freely through it. This electrode has a total surface area of 125 square decimetres, the diameter being about 40 centimetres. The cathode consists of a lead pipe of outside diameter 2.5 centimetres and 1100 centimetres long made in the form of a coil of 44 centimetres internal diameter suitably stiffened. The cell container of glazed earthenware or other suitable inert material has a capacity of about 100 litres and has a bottom outlet and an overflow pipe near its upper edge. A lid of suitable form to make a tight joint is provided and the cell is charged with litres of sulphuric acid containing about grams of H2804 per litre. Current is then passed until the anode which has been activated is coated with lead peroxide, after which 15 litres of benzene are added. The cell agitator is introduced through a central hole in the lid and operates inside the anode cylinder. The agitator is of aluminium having six blades which when rotated carries the benzene downwards through the electrolyte but does not give fine emulsification. The electrolyte covers the whole of the effective electrode surface and the top blade of the agitator is just immersed in the electrolyte. The addition of 15 litres of benzene allows the passage of about 1000 ampere hours before the concentration of quinone in the benzene attains a value of about 10 grams per litre. At this point the benzene feed to the cell is started at the rate of about 15 litres per hour. Cooling water is passed through the cathode coil in sufficient volume to maintain the temperature of the electrolyte at 20 C. The benzene overflow level is fixed so that 15 litres of benzene remain in the cell, the overflow being led to a still for the separation of p-benzoand fitted with a suitable condenser, the temperature is adjusted so that the benzene is immediately distilled over. The vessel is charged with 1.5 kilograms of iron borings together with 4 litres of water and 1 to 2 grams of sulphuric or acetic acid. The cell operating at 1000 amperes maintains an overflow of about 15 litres of benzene-quinone solution which continuously passes to the reduction vessel. The benzene beingdistilled, condensed and separated from any water which may distil over, is returned to the feed vessel of the cell. The quinone is completely and efliciently reduced to hydroquinone which dissolves and accumulates in the acid water contained in the reduction vessel. This vessel is maintained at a temperature of about C. and the reduction carried on until the solution of hydroquinone is. saturated at a temperature of about 60 C. when it isrun off through a filter to remove iron oxide. The filtrate is allowed to cool and the crystallized hydroquinone separated by filtration. The acid mother liquor is returned to the reduction still together with any water separated from the benzene distillate.

The cell is kept in'continuous operation maintaining theconditions set forth until the electrolyte becomes fouled with oxidation products of benzene which dissolve in the electrolyte which is then discarded. The cell also at times needs cleaning owing to the separation of matter which 'is insoluble in both the electrolyte and the henzene but this will not occur at more frequent intervals than after a continuous run of 24 hours.

The cell under the conditions stated produces crystallized from water after being treated with a small quantity of decolourizing carbon it gives a product which has the theoretical melting point. If desired the hydroquinone may be extracted with ether or other organic solvent to obtain a pure product.

The process described in the foregoing example may be efiected in the presence of aniline and/or phenol but it should be conducted in such a way that the concentration of aniline does not exceed 5 grams per litre and the concentration of phenol does not exceed 1 gram per litre in the electrolyte.

What we claim is:-'-

1. A process for the production of quinone comprising subjecting a material selected from the group consisting of lead and alloys of lead to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

2. A process for the production of quinone comprising subjecting a material selected from the group consisting of lead and alloys of lead to the passage of an alternating current superimposed on a direct current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

3. A process for the production of quinone comprising subjecting a material selected from the group consisting of lead and alloys of lead 'to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution from exceeding 15 grams per liter.

4. A process for the production of quinone comprising subjecting a material selected from 1 the group consisting of lead and alloys of lead to the passage of an alternating current in an acid electrolyte to form an. active and stable anode, electrolyzing a mixture containing benzene and a solution containing sulphuric acid by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

5. A process for the production of quinone comprising subjecting a material selected from the group consisting of lead and alloys of lead to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and a solution containing sulphuric acid and a soluble sulphate bymeans of direct current "zene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode. said anode and said cathode being disposed close to one another and with no intervening diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

'7. A process for the production of quinone comprising subjecting a hard lead alloy to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

8. A process for the production of quinone comprising subjecting an alloy of lead and a material selected from the group consisting of anti mony and bismuth to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene and an electrolyte by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

9. A process for the production of quinone comprising subjecting a material selected from the group consisting of lead and alloys of lead to the passage of an alternating current in an acid electrolyte to form an active and stable anode, electrolyzing a mixture containing benzene, an electrolyte and at least one substance selected from the group consisting of phenol and aniline by means of direct current passed between said active and stable anode and an inactive cathode without the use of a diaphragm, removing resultant quinone as a solution in benzene and supplying more benzene to the cell, and so adjusting such removal and supply as to keep the quinone concentration of said solution relatively low.

HERBERT PALFREEMAN. NORMAN VICTOR SYDNEY KNIBBS.