| 2-methyl anthraquinone is an important organic synthetic intermediate. Thetraditional method for preparation of 2-methyl anthraquinone consists of two processes.2-(4-toluoyl)benzoic acid is usually synthesized first from methylbenzene and phthalicanhydride catalyzed by aluminum chloride, and then 2-methyl anthraquinone isprepared from dehydration of 2-(4-toluoyl)benzoic acid catalyzed by concentratedsulfuric acid. Aluminum chloride and concentrated sulfuric acid as catalyst causessevere equipment corrosion and environment pollution. In this paper, The synthsis of2-methylanthraquinone from methylbenzene and phthalic anhydride over zeolitecatalyst was studied and has a great theoretical and application significance.Firstly, catalytic activity of several solid catalysts for the acylation reaction ofmethylbenzene and phthalic anhydride was examined, and the results showed that Hβzeolite present better catalytic activity. The optimal conditions were as follow,calcination temperature 550℃, mass fraction of catalyst 4.5%, n(methylbenzene) :n(phthalic anhydride)=16:1, reaction temperature 210℃, reaction time 5h. Under theseconditions, yield of 2-methyl anthraquinone reached 20.2%. The characterization ofcatalyst by NH3-TPD and Py-IR showed that the acid amount of Hβzeolite wasdifferent with varied calcination temperature. More acid amount of Hβzeolite presenthigher catalytic activity of Hβzeolite. Catalytic activity of Hβzeolite was best when theratio of Lewis acid and Bronsted acid was close to 2.Secondly, Hβzeolite was modified by Co(NO3)2, Ce(NO3)3 and Cr(NO3)3withequal volume impregnation method and ion exchange process. When modified Hβzeolite was used in synthesis of 2-methyl anthraquinone, the selectivity of 2-methylanthraquinone was higher than that of non-modified Hβzeolite. The catalytic activity ofHβzeolite modified by ion exchange process was better than that by equal volumeimpregnation method.Hβzeolite modified by NH4(SO4)2, Al2(SO4)3was used in synthesis of 2-methyl anthraquinone. The results showed that catalytic activity of modified Hβzeolite washigher than non-modified Hβzeolite. The optimal modification conditions by(NH4)2SO4 are: concentration of (NH4)2SO4 0.75 mol/L, modification temperature 90℃.Under these conditions, the yield of 2-methyl anthraquinone was 24.2%. The optimalmodification conditions by Al2(SO4)3 are: concentration of Al2(SO4)3 0.2 mol/L,modification temperature 30℃. Under these conditions, the yield of 2-methylanthraquinone was 25.1%. The characterization of catalyst by NH3-TPD and PyIR ofmodified Hβzeolite showed that the ratio of L acid and B acid of modified Hβzeolitewas near 2 and the catalytic activity increased with the total acid amount of Hβzeoliteincreasing. Structure of modified Hβzeolite had not been destroyed, but the crystallinityincreased. The crystallinity of Hβzeolite modified by Al2(SO4)3 was better than that by(NH4)2SO4.Thirdly, the mechanism of synthesis 2-methyl anthraquinone from phthalicanhydride and methylbenzene catalyzed by Hβzeolite was investigated with Fouriertransform infrared spectroscopy. Firstly, migration of the electron pair at oxygen atom inphthalic anhydride because of the L acid over Hβzeolite, oxygen atom combines with Lacid of Hβzeolite to form C+, this step is key step in total reaction. Secondly, C+ attackscarbon atoms of benzene ring on the position of para-position of methyl, thenintermediate 2-(4-toluoyl)benzoic acid was synthesized. Thirdly, 2-(4- toluoyl) benzoicaciddehydrates catalyzed by B acid to form 2-methyl anthraquinone. |
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