Short Communication Photoactivated and photopassivated benzylic oxidation catalyzed by pristine and oxidized carbons Grigoriy Sereda ⁎, Vikul Rajpara The University of South Dakota, Department of Chemistry, 414 E. Clark St., Vermillion, SD 57069, USA abstract article info Article history: Received 28 November 2010 Received in revised form 15 December 2010 Accepted 17 December 2010 Available online 28 December 2010 Keywords: Hydrocarbons Organic synthesis Oxidation Photocatalysis Carbon The link between the structure of carbons and their performance toward catalytic benzylic oxidation by air is studied. Catalytic activity and selectivity of pristine and oxidized carbons can be enhanced, altered, or suppressed by ambient light. The photocatalytical performance of a carbonaceous material depends on the presence of defects, surface area, porosity, and surface oxidation. Adsorption of the hydroperoxide intermediate on the catalyst's surface is suggested as a key process that links the structure of the carbonaceous material with its catalytic activity. The potential of catalysis by carbon black and photocatalysis by graphite nanofibers for greener organic synthesis has been demonstrated. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Elemental carbon presents significant interest as a building block for engineering new catalytic materials due to its versatile morphol- ogy, potential for conjugation with co-catalysts, and availability. Carbonaceous materials are popular solid supports for deposition of catalytic materials [1]. Over the last decade, the area of interest started to expand toward carbons of different morphology as independent catalysts, especially toward redox-processes [2], such as reduction of nitrobenzene with hydrazine [3]. Recent studies have reported promising results on the use of carbonaceous materials in photo- chemical processes. Deposition of carbon on titania improves its photocatalytic properties [4]. Fullerenes [5] and single wall carbon nanotubes [6] were shown to be efficient photosensitizers of triplet O 2 . Recently, we reported benzylic oxidation and photooxidation of p- xylene 1, catalyzed by graphite with and without the presence of cyclohexene, leading to a mixture of up to seven different products (2–8, Scheme 1) [7]. Although optimization of the reaction conditions has allowed us to isolate peroxide 2 as the major product, we continued our efforts to better understand the reaction mechanism and gain more control over its product distribution. In this regard, we extended our study to a series of other pristine carbonaceous catalysts (carbon black (CB), graphite nanofibers (GNFs), ultrapure graphite (UPG), multiwall carbon nanotubes (MWCNTs), and fullerenes C 60 ). Here we report how the catalytic and photocatalytic activity of a series of pristine and modified carbonaceous materials is affected by the structure, and composition of the catalyst. 2. Experimental Pristine carbonaceous materials (Graphite, CB, GNFs, UPG, MWCNTs, and C 60 ) were purchased from Aldrich. Oxidized graphite (OG) and oxidized multiwall carbon nanotubes (OMWCNTs) were prepared by oxidation for 10 h with aqueous nitric and sulfuric acids [8]. The reactions of benzylic oxidation were performed by passing air at a rate of 1 mL/min through 37 mg of a catalyst, suspended in 5 mL of p-xylene under reflux at 138 °C for 24 h. After addition of 10 mL of hexane, the catalyst was removed by filtration. The filtrate was concentrated in a vacuum and the residue was analyzed by non-overlapping 1 H NMR signals, characteristic for hydroperoxide 2 [9] (singlet at 4.95 ppm), alcohol 3 [10] (singlet at 4.60 ppm), aldehyde 4 [11] (singlet at 9.95 ppm), acid 5 [12] (doublet at 8.0 ppm), ester 6 [13] (singlet at 5.30 ppm), ether 7 [14] (singlet at 4.50 ppm), hydrocarbon 8 [15] (singlet at 3.85 ppm), and phenolic products (multiplet at 6.8–6.9 ppm). The molar ratios of products estimated by the integral intensity of the corresponding signals, are presented in Table 1. Conversion of the oxidation was characterized by the mass of the product mixture (total yield). Surface analysis of the catalysts was performed by the nitrogen adsorption/desorption measurements. The samples were outgassed for 1 h at 100 °C and analyzed at 77 K using a Quantachrome Nova 2200e gas adsorption analyzer. The turnover frequencies are calculated as the number of molecules of the hydrocarbon reacted for 1 h per 1 nm 2 of the catalyst's surface. Catalysis Communications 12 (2011) 669–672 ⁎ Corresponding author. Tel.: +1 605 677 6190. E-mail address: gsereda@usd.edu (G. Sereda). 1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2010.12.027 Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom