Patent GB-798167-A (GB)
Title: Improvements in or relating to the manufacture of anthracenes
Inventor: SCOTT GERALD
IPC: C07C5/41
Filed: 1955-08-22
Abstract: Anthracenes (including benz- and polybenzanthracenes) are prepared by the cyclization of diarylmethanes of the formula R1R2R3R4C, where R1 and R2 are aryl groups, R1 having a methyl group and R2 a hydrogen atom ortho to the methane carbon atom and R3 and R4 are hydrogen or alkyl groups, by heating in the absence of oxygen and in the presence of at least one metal of groups Ib, II, III, IVa, Va, VIa, VIIa and VIII of the Periodic Table, or an oxide or sulphide thereof, as catalyst (see Group III).  The reaction may be carried out by passing the vaporized diarylmethane through a tube heated to 350-550 DEG  C. and containing the catalyst, at a rate such that the residence time is 1-100 seconds.  Inert diluents such as carbon dioxide, hydrogen, nitrogen, water vapour, toluene vapour or the vapour of a diarylmethane without a methyl or methylene group ortho to the methane carbon atom may be added.  The starting diarylmethane may have as the aryl groups R1 and R2 groups containing fused aromatic rings such as naphthyl as well as phenyl and these aryl groups may contain further substituents such as alkyl, cycloalkyl, aralkyl, alkenyl and aryl radicals.  Representative are ortho - benzyltoluene, 2 : 4 - dimethyldiphenylmethane, 2 : 5 - dimethyldiphenylmethane, a - phenyl - a  - (2 - methylphenyl) - ethane, a  - phenyl - a  - (2 : 4 - dimethylphenyl) - ethane, 2 : 4 - dibenzyltoluene, 2 - methyl - 4 - tert. - butyldiphenylmethane, 2 : 41-dimethyldiphenylmethane, 2 : 4 : 6 - trimethyldiphenylmethane, 2 : 5 : 41 - trimethyldiphenylmethane, 1 - benzyl - 2 - methylnaphthalene, and 1 - (21 - naphthylmethyl) - 2 - methylnaphthalene. Some decomposition of substituted anthracenes formed may occur to give less substituted anthracenes.  Suitable catalysts are MgO, ZnO, Al2O3, ZrO2, MnO, ZnO on alumina, V2O5 on pumice, Cr2O3 on alumina, MoO3 on alumina, Fe2O3 on alumina, Co3O4 on alumina, NiO on alumina, Pd on carbon and Ag or Pt on alumina.  An oxide of a Group Ia metal in small amount may also be added.  The examples illustrate the preparations of (1) anthracene from o-benzyltoluene over 10 per cent Fe2O3 on Al2O3; (2) anthracene from o-benzyl-toluene over a catalyst of composition Cr2O3 43 per cent, Al2O3 54 per cent, CaO 2 per cent, K2O 1 per cent; (3) b -methylanthracene from 2 : 5-dimethyl-diphenylmethane over 10 per cent zinc oxide on alumina; (4) b -methylanthracene from 2 : 5-dimethyldiphenylmethane over 10 per cent cobalt oxide on alumina; (5) b -methylanthracene from 2 : 5-dimethyldiphenylmethane over a catalyst of composition Cr2O3 12 per cent, Al2O3 86 per cent, MgO 2 per cent; and (6) anthracene and 2-benzylanthracene from 2 : 4-dibenzyltoluene over the catalyst of (2); and (7) anthracene and 2-tert.-butylanthracene from a mixture of 2-benzyl-4-tert.-butyltoluene (90 parts by wt.) and 2-benzyl-5-tert.-butyl-toluene (10 parts by wt.).  Specifications 253,911, [Class 2 (iii)], and 793,565 are referred to.ALSO:A catalyst for use in the preparation of anthracenes from diarylmethanes (see Group IV (b)) comprises at least one metal of groups Ia, II, III, IVa, Va, VIa, VIIa or VIII or the Periodic Table, or an oxide or sulphide thereof.  One or more group Ia metal oxides may also be present.  It may be in granular lump or powder form but is preferably pelleted and may be supported on pumice or carbon.  Preferred are MgO, ZnO, Al2O3, ZrO2, MnO, ZnO on Al2O3, V2O5 on pumice, Cr2O3 on Al2O3, MoO3 on Al2O3, Fe2O3 on Al2O3, Co3O4 on Al2O3, NiO on Al2O3, Ag on Al2O3, Pt on Al2O3, Pd on carbon. In the examples are employed (1) 1/8 pellets of 10 per cent ferric oxide on alumina prepared by impregnating alumina pellets with a solution of ferric nitrate followed by calcination; (2) 1/8 inch pellets of composition Cr2O3 43 per cent, Al2O3 54 per cent, CaO 2 per cent and K2O 1 per cent; (3) 1/8 inch pellets of a coprecipitated mixture of 10 per cent zinc oxide on alumina; (4) 1/8 inch pellets of 10 per cent cobalt oxide on alumina prepared by impregnating alumina pellets with cobalt nitrate solution followed by calcination and heating in hydrogen at 500 DEG C.; (5) 1/8 inch pellets of composition Cr2O3 12 per cent, Al2O3 86 per cent, MgO 2 per cent which have been heated in hydrogen at 500 DEG  C. for 8 hours.  Specifications 253,911, [Class 2 (3), and 793,565, [Group IV (b)], are referred to.