Patent GB-640363-A (GB)
Title: Improvements in and relating to a dehydrogenation process for the production of phenols
IPC: C07C37/07
Filed: 1947-04-09
Abstract: Phenols having the same number of carbon atoms in the molecule as the compounds from which they are derived are obtained by dehydrogenating at elevated temperature an organic compound having at least one ring containing six carbon atoms, one of the said carbon atoms having attached directly thereto a keto oxygen atom or a hydroxyl group, at least two of the carbon atoms being saturated with respect to hydrogen, in the presence of a catalyst comprising in the metallic state a metal selected from: platinum, palladium, rhodium, osmium, iridium and ruthenium and of added hydrogen.  The quantity of hydrogen added should not cause hydrogenation to predominate, satisfactory results being obtained when equimolecular quantities of hydrogen are used.  The rate of flow should be as high as possible, although if too rapid, separation of phenols from unreacted compounds is difficult and for this reason the rate of flow may be adjusted by using an inert gas such as nitrogen or hydrogen itself.  Compounds instanced for dehydrogenation are cyclohexanol, cyclohexanone and tetrahydro-alpha-naphthalene which compounds may contain substituent groups such as lower alkyl, nitrile and lower carbalkoxy groups. Catalysts may be supported on e.g. pumice, kieselguhr or alumina or silica gel containing e.g. about 5 per cent by weight of chosen metal.  Activated carbon is a preferred support, particularly when combined with platinum or palladium, 250 DEG  to 400 DEG  C. are temperatures instanced.  In the above reactions there is a tendency towards hydrocarbon formation due to dehydration of the products, it being believed that the supports act as dehydration catalysts.  This tendency to dehydration is inhibited, sometimes completely, by adding to the catalyst an alkali metal compound such as sodium or potassium hydroxide or a carbonate, chloride or salt of a carboxylic acid in amount of e.g. 40 to 100 per cent by weight of metal chosen. Preferred supports are pumice, kieselguhr and particularly activated carbon.  Platinum is the preferred metal.  The preparation of the catalysts is described in Group III.  In examples (1), (2), (4), (5) and (6) phenol with small quantities of cyclohexanone, water, benzene and in (6) unchanged cyclohexanol are obtained from (1), (5) and (6) cyclohexanol and (2) and (4) cyclohexanone by passing over (1), (2), (5) and (6) a platinum on activated charcoal catalyst and (4) a platinum on silica gel catalyst, the catalyst of (5) containing potassium carbonate and the active charcoal thereof being pretreated with hydrochloric acid for the removal of alkaline compounds, at temperatures of 400 DEG , 350 DEG , 350 DEG , 400 DEG  and 400 DEG C. respectively, with feed rates of 3.70, 7.00, 3.42, 3.84 and 3.82 kg. per litre of catalyst volume per hour respectively and an equimolecular quantity of hydrogen in all cases and in (2) with an additional 0.5 mol. of nitrogen per mol. of ketone, in (3) a mixture of 90 per cent tetrahydro-alpha naphthalone and 10 per cent by weight tetrahydro-naphthalene together with an equimolecular quantity of of hydrogen is passed at 2.98 kg. per hour over the catalyst of (2) above at 355 DEG  C. to give a mixture of alpha-naphthol, naphthalene, tetrahydro-naphthalene, tetrahydro-alpha-naphthalone and water.  Specification 577,008, [Group III], is referred to.ALSO:Phenols are obtained by dehydrogenating at elevated temperature an organic compound having at least one ring containing six carbon atoms, one of the carbon atoms being directly attached to a keto oxygen atom or a hydroxyl group and at least two of the carbon atoms being saturated with respect to hydrogen, in the presence of added hydrogen and a catalyst comprising in the metallic state a metal selected from: platinum, palladium, rhodium, osmium, indium and ruthenium.  For details of the compounds to be used and the working of the process (see Group IV (b)).  The catalyst may be supported on e.g. kieselguhr, pumice, and alumina or silica gel, satisfactory results being obtained when about 5 per cent by weight of metal is present.  Catalysts may be prepared by impregnating activated carbon granules with platinic chloride in hydrochloric acid and, after drying, heating to 300 DEG  to 600 DEG  C., e.g. 350-400 DEG  C., preferably in the presence of hydrogen and in the vessel in which the dehydrogenation is to be effected. Reactivation may be effected by heating with hydrogen at elevated temperatures generally at 20 DEG to 30 DEG  C. above that used in the process.  The preferred catalyst is platinum on active charcoal.  A measure of dehydration also occurs in the above reaction and in other dehydrogenations with the above metal catalysts of oxygen containing organic compounds at elevated temperatures, and to minimize or prevent this an alkali metal compound such as sodium or potassium hydroxide, an alkali metal carbonate or chloride or salt of a carboxylic acid is incorporated in the catalyst in amounts of, e.g., 40-100 per cent by weight of catalytic metal.  In this case preferred supports are pumice, kieselguhr or activated charcoal, the alkali metal compound being added before or after reduction.  The alkali metal content of the support should be considered in the quantity of such metals present in the final catalyst and it may be desirable to treat the support for the removal of alkali metal as, e.g. by treatment with dilute hydrochloric acid, when other deleterious substances may also be removed.  The preferred catalyst is metallic platinum with an alkali metal compound on activated carbon which has been treated for the removal of alkali.  In examples: (5) granular active carbon, washed with dilute hydrochloric acid, is impregnated with an aqueous 1 per cent solution by weight of hydrochlorplatinic acid to give a catalyst containing 5 per cent of platinum, dried at 110-120 DEG  C. for 24 hours, treated with 5 per cent potassium carbonate solution to give a finished catalyst containing 2 per cent by weight of potassium carbonate, dried at 110-120 DEG  C. for 24 hours and reduced immediately before use by heating at 400 DEG  C. in the presence of hydrogen; and in (7) hydrochloric acid washed granular active carbon is impregnated with 1 per cent by weight aqueous hydrochlor-platinic acid to give a catalyst containing 5.1 per cent by weight of platinum, dried at 110-120 DEG  C. for 24 hours, reduced at 400 DEG C. with hydrogen for 36 hours, cooled in nitrogen and treated with 8 per cent by weight aqueous potassium carbonate solution to give a catalyst containing 2 per cent by weight of potassium carbonate when dried at 110-120 DEG  C. for 24 hours.  The second Provisional Specification contains a further example (1) in which a catalyst comprising 5.9 per cent platinum and 4 per cent potassium carbonate on activated carbon as support, is obtained by a method similar to that of (5) above.  Specification 577,008 is referred to.