Selective catalytic oxidation of cyclohexylbenzene to cyclohexylbenzene-1-hydroperoxide: a coproduct-free route to phenol Isabel W. C. E. Arends, a Manickam Sasidharan, a,† Adolf Ku ¨hnle, b Mark Duda, b Carsten Jost b and Roger A. Sheldon a, * a Laboratory for Biocatalysis and Organic Chemistry, Department of Biotechnology, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands b CREAVIS Gesellschaft fu ¨r Technologie und Innovation mbH, D-45764 Marl, Germany Received 17 May 2002; revised 15 August 2002; accepted 5 September 2002 Abstract—A method is described for the highly selective oxidation of cyclohexylbenzene to cyclohexylbenzene-1-hydroperoxide. In the presence of 0.5 mol% N-hydroxyphthalimide (NHPI) and 2 mol% of the hydroperoxide product, without solvent, a selectivity of ca. 98% to the desired product was obtained at 32% conversion. The use of NHPI increases the selectivity for initial H-abstraction from the 1-position, vs the other positions in the cyclohexyl ring, suppresses byproduct formation via transannular hydrogen abstraction and increases the overall rate of reaction. q 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction The production of phenol via the Hock process is a well- established commercial process that accounts for .1 million tons of phenol production annually on a world- wide basis. 1,2 Cumene, which is prepared by reaction of benzene with propylene, is oxidized with molecular oxygen to give the corresponding hydroperoxide (Scheme 1). Acid- catalyzed decomposition of the latter affords one equivalent of both phenol and acetone. Herein lies the disadvantage of the Hock-process: coproduction of acetone. A coproduct- free route to phenol would, therefore, be an economically attractive alternative. One possible alternative involves the use of cyclohexyl- benzene (CHB) (see Scheme 1). Analogous to cumene, the corresponding tertiary hydroperoxide can be easily con- verted into phenol and cyclohexanone. 3 However, in this case, the cyclohexanone coproduct can be dehydrogenated to give a second molecule of phenol, 4 thus providing an overall coproduct-free route to phenol. The complete process scheme is depicted in Scheme 2. CHB can be made from benzene via two possible routes (Scheme 2): (a) selective hydrogenation of benzene to cyclohexene over a ruthenium catalyst 5 followed by Friedel – Crafts alkylation of a second molecule of benzene or (b) oxidative coupling of benzene to biphenyl 6 followed by selective hydrogen- ation of the latter. 7 Route (a) requires no net consumption of hydrogen and is 100% atom efficient. 8 Route (b), on the other hand, involves the consumption of one equivalent of hydrogen and the formation of one equivalent of water. Recently a palladium based catalytic system was described, 0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(02)01131-6 Tetrahedron 58 (2002) 9055–9061 Scheme 1. Production of phenol via cumene hydroperoxide and cyclohexylbenzene-1-hydroperoxide, respectively. † Present address: Catalysis Laboratory—Material Science and Chemistry Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan. * Corresponding author. Tel.: þ31-15-278-2683; fax: þ31-15-278-1415; e-mail: r.a.sheldon@tnw.tudelft.nl Keywords: autoxidation; cyclohexylbenzene; phenol; N-hydroxyphthalimide.