J. Chem. Research (S), 1997, 52–53† Zeolite-catalysed Selective Decomposition of Cumene Hydroperoxide into Phenol and Acetone† Manickam Sasidharan and Rajiv Kumar* Catalysis Division, National Chemical Laboratory, Pune-411 008, India Crystalline, microporous molecular sieves efficiently catalyse the selective decomposition of cumene hydroperoxide into phenol and acetone, both under batch (25 °C) and down-flow fixed-bed (60 °C) conditions; large-pore high-silica zeolites, mainly zeolite Beta and its metallo-silicate (B-, Fe- and Ga-silicate) analogues, are found to be particularly useful catalysts in this reaction giving ca. 92�3% phenol selectivity. Owing to their Br�onsted acidity, shape selectivity and thermal stability, crystalline microporous aluminosilicates, commonly known as zeolites, have been extensively used as environmentally friendly heterogeneous catalysts in a variety of organic transformations.1,2 Phenol is an industrially important chemical generally produced via acid-catalysed decomposition of cumene hydroperoxide.3 Various Br�onsted and Lewis acids in homogeneous systems4–7 at 0–50 °C and cation exchange resins in pseudo-heterogeneous systems8–10 have been reported as catalysts for cumene hydroperoxide decomposition. Phenol selectivity in the presence of an acid catalyst such as sulfuric acid was in the range 95–98% with more than 99% conversion.11 Commercially, the concentrated cumene hydroperoxide (CHP) solution is cleaved in the presence of sulfuric acid catalyst, the phenol yield being 95–98% mol%.The cleavage effluent, containing the acid used as catalyst as well as formic and acetic acids, formed as by-products, has to be neutralized and extracted to avoid corrosion and environmental problems.12 Now we report, for the first time, an efficient catalytic conversion of cumene hydroperoxide into phenol and acetone using solid zeolite catalysts under heterogeneous liquidphase conditions both in a batch and fixed-bed reactor system at between room temperature and 60 °C.Experimental In a typical batch experiment, to a solution of cumene hydroperoxide (2 g; 20% solution in cumene) in a 50 ml round bottomed flask was added the zeolite catalyst (0.2 g), obtained according to a known literature procedure.13–16 After completion of the reaction, the solid catalyst was filtered off before the products were analysed. In a fixed-bed down-flow reactor system, the H-form of the catalyst (zeolite Beta) was made into pellets (20–30 mesh size), and the binder-free zeolite (1 g anhydro.) was loaded at the centre of the down-flow silica-reactor (1 cm i.d., 30 cm length) using porcelain beads as the inert material.Cumene hydroperoxide (20% solution in cumene; 2 ml hµ1) along with carrier gas nitrogen (40 ml minµ1) was fed through a syringe pump (Sage Instruments, USA). The reactor temperature was maintained by an electrical heater. The products were analysed by capillary gas chromatography (HP-5880, using FID detector).Results and Discussion Table 1 indicates that the reaction was completed within 5 min at 25 °C and the phenol selectivity was 90�2% in all the cases where zeolite Beta analogues were used as catalyst (entries 1–4). Entries 2–4 suggest that not only aluminosilicate zeolites but their Fe, Ga or B analogues can also be effectively used as catalyst. The phenol selectivity is slightly higher for Fe, Ga and B-Beta samples.Zeolite ZSM-5 (entries 5–7) and Mordenite (entry 8) are also quite efficient catalysts. However, with these catalysts the phenol selectivity is slightly lower (86–88.5%) compared to that exhibited by Beta zeolites (88–95%). Over zeolite Y (entry 9), the conver- 52 J. CHEM. RESEARCH (S), 1996 *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem.Research (M). Table 1 Catalytic decomposition of cumene hydroperoxide over various zeolites SiM Reaction Conversion Phenol selectivity Entry Zeolite Ratioa Tb/°C time/min mass% mol% 123456789 10 11 12 13 14 15 16 17 18 19 H-[Al]-Bta H-[Ga]-Beta H-[Fe]-Beta H-[B]-Beta H-[Al]-ZSM-5 H-[Ga]-ZSM-5 H-[Fe]-ZSM-5 H-Mordenite H-Y H-[Al]-ZSM-12 H-[Al]-NCL-1 H-[Al]-ZSM-22 H-[Al]-MCM-22 H-[Al]-ZSM-48 H-[Al]-EU-1 H-SAPO-5 H-AlPO-5 H-[Al]-Betac No catalyst 14 20 22 30 30 35 30 7.0 2.5 40 40 60 30 50 50 —— 14 — RT RT RT RT RT RT RT RT 40 40 40 40 40 60 60 60 60 60 — 55555555 10 30 15 15 15 60 30 60 60 60 — 100 100 100 100 100 100 100 100 96.0 95.0 85.0 65.0 90.0 45.0 80.0 10.0 25.0 99.0 — 88.0 92.0 91.0 92.0 86.0 88.5 88.0 86.5 85.0 82.0 83.5 87.5 87.0 80.0 88.7 88.0 86.0 95.0 — aM=Al, Ga or Fe.bRT=room temperature. cFixed bed reaction: temperature=60 °C, catalyst=H-Beta (1 g), feed rate=2 ml hµ1, carrier gas=nitrogen (40 ml minµ1). Products were collected after 1 h.Mordenite and H-Y zeolites were obtained from Degussa, other catalysts were prepared according to the corresponding referenced method. The selectivity of phenol was confirmed by GC-5880 using a capillary column. The other products include quinones, catechol, acetophenone and higher boiling products such as a-methylstyrene and a-cumylphenol.sion was slightly less (96%) and the phenol selectivity was ca. 85%. However, over ZSM-12,13 NCL-1,14 ZSM-22,13 EU-1,13 MCM-2215 and ZSM-4813 (entries 10–15), lower conversions as well as selectivities were obtained.Medium-pore zeolites with unidimensional channels, such as ZSM-22, ZSM-48 and EU-1, exhibit lower conversions and selectivities due to diffusional restrictions imposed by the channel system of these zeolites on the reactant and products. However, large-pore unidimensional zeolites, such as ZSM-12, NCL-1 and MCM- 22, show ca. 85–90% conversion and selectivity.Entries 16 and 17 show the conversions and selectivities of cumene hydroperoxide over AlPO4-516 and SAPO-517 molecular sieves. Unlike aluminosilicates with strong Br�onsted acidity, aluminophosphates (neutral) and silicoaluminophosphates (weak Br�onsted acidity) exhibit lower activity in the cumene hydroperoxide decomposition, clearly suggesting the requirement of strong Br�onsted acid-sites for the decomposition of cumene hydroperoxide into phenol and acetone.The above results indicate that strong Br�onsted acid sites are needed for this reaction. Since Beta, ZSM-5 and Mordenite possess stronger acid sites compared to zeolites like Y, ZSM-22, ZSM-48, etc.,18,19 the conversion is complete using the former. Furthermore, with the reaction being quite fast, the quick diffusion of the reactants into the zeolite channels and of the products from the zeolite channels (as is the case of zeolite Beta with three-dimensional 12-membered-ring large-pore channels) will reduce the formation of secondary products such as quinones, a-methylstyrene, catechol, etc. and also the small amount of acetophenone.Hence it may be stated that a combination of strong Br�onsted acid sites and large pore intersecting channels in a high silica zeolite catalyst is suitable for this reaction. Entry 18 exhibits the results obtained using a fixed-bed, down-flow reactor giving 95% phenol selectivity at 99% conversion. The advantages of fixed-bed reaction conditions are: (i) there is no need to separate the solid catalyst from the products and (ii) higher phenol selectivities are obtained.These preliminary studies under unoptimised reaction conditions suggest the feasibility of the use of solid catalysts to replace environmentally hazardous mineral acids like sulfuric acid catalysts in CHP cleavage. Since under fixed-bed conditions the deactivation of the catalyst with time-on-stream is an important parameter, the effect of time-on-stream on activity and selectivity for the decomposition of cumeme hydroperoxide into phenol and acetone under fixed-bed conditions using H-Al-Beta catalyst was studied (Fig. 1). The time-on-stream data show that over 10 h, while the conversion remained the the phenol selectivity decreased slightly from ca. 95 to 90%. The successful use of a zeolite catalyst is thus demonstrated for the first time. Another advantage is that the zeolite can be regenerated in situ, regaining the initial activity and selectivity. Received, 24th July 1996; Accepted, 21st October 1996 Paper E/6/05186C References 1 R.P. Townsend, The Properties and Application of Zeolites, The Chemical Society, London, special publication no. 33, 1980. 2 W. F. H�olderich, M. Hesse and F. N�aumann, Angew. Chem., Int. Ed. Engl., 1988, 27, 226. 3 H. Hocks and S. Loung, Ber. Dtsch. Chem. Ges., 1944, 77, 257. 4 H. Hock, Angew. Chem., 1957, 69, 313. 5 R.A. Sheldon and J. A. Van Doorn, Tetrahedron Lett., 1973, 1021. 6 N. C. Deno, W. E. Billups, K. E. Kramer and R. R. Lastomirsky, J. Org. Chem., 1970, 35, 3080. 7 J. O. Turner, Tetrahedron Lett., 1971, 887. 8 R. M. Barrer, Hydrothermal Chemistry of Zeolites, Academic Press, London, 1982, pp. 251. 9 R. Szostak and T. L. Thomas, J. Catal., 1979, 59, 269. 10 J. Vodnar, P. Fejes, K. Varga and F. Berrger, Appl. Catal., 1995, 122, 33 and references cited therein. 11 K. 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RESEARCH (S), 1996 53 Fig. 1 Decomposition of cumene hydroperoxide into phenol and acetone over zeolite Beta (Si/Al=14): temperature=60 °C, LHSV, 2 hµ1; Conv=cumene hydroperoxide conversion, mol%; Sel=phenol selectivity,