Starbons Acid

Catalysis Communications 12 (2011) 1471–1476

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Catalysis Communications
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c a t c o m

Short Communication

Starbon® acids in alkylation and acetylation reactions: Effect of the Brönsted-Lewis acidity
Rafael Luque ⁎, Vitaly Budarin, James H. Clark, Peter Shuttleworth,Robin J. White
Green Chemistry Centre of Excellence, The University of York, Heslington, YO10 5DD, York, UK

a r t i c l e

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a b s t r a c t
Various Starbon® supported solid acids were prepared and investigated in two test reactions, namely the acetylation of 5-acetyl-methylsalicylate and the alkylation of phenol with cyclohexene. Starbon®-SO3H materials exhibited in general anoptimum balance of Lewis and Bronsted acid sites, making them ideal catalysts for the investigated processes. Starbon acids were comparably active and differently selective compared to similar solid acids utilised in the proposed acid catalysed processes including commercial sulphated zirconia and beta zeolite. Materials were also highly reusable under the different reaction conditions, preserving theiractivities almost unchanged after 4 reuses. © 2011 Elsevier B.V. All rights reserved.

Article history: Received 3 March 2011 Received in revised form 2 June 2011 Accepted 7 June 2011 Available online 15 June 2011 Keywords: Starbon acids Heterogeneous catalysis Alkylation Acylation Brönsted and Lewis acidity

1. Introduction Acid catalysed reactions applied to the synthesis of high addedvalue chemicals have been used for decades in industrially relevant processes [1,2]. The acetylation of a wide range of compounds can be easily carried out through the use of an acid catalyst under different conditions [3–6]. Alkylations are also very useful reactions in Organic Chemistry [7–9] and together with acetylations constitute two key processes to prepare many important intermediates in thepharmaceutical [10] and fine chemical industries [11–13]. These liquid phase alkylation and/or acylation processes have been traditionally catalysed by Lewis acids including AlCl3, FeCl3, BF3 and ZnCl2 [1,2,12]. The inherent drawbacks of all homogeneous systems are the production of significant quantities of hazardous waste (e.g. salts, acids, etc.) that needs thorough washing and neutralisation aswell as the difficulties in the catalysts recovery. The water employed to quench the reaction leads to large amounts of gaseous and aqueous waste as well as loss of catalyst, in the sense that the excess of Lewis acid is eventually released by hydrolysis and leads to various hydroxides (e.g. aluminium hydroxide from AlCl3) as waste. The Lewis catalysts are also toxic and corrosive. The process hastherefore a large E-factor as all the Lewis acid employed is wasted. A combination of green technologies is therefore needed to improve the green credentials of such reactions.

⁎ Corresponding author at: Departamento de Química Orgánica, Universidad de Córdoba, Edificio Marie Curie (C-3), Ctra. Nnal IVa, Km 396, E-14014, Córdoba (Spain). Tel.: +34 957 211050; fax: +34 957 212066. E-mail address:q62alsor@uco.es (R. Luque). 1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2011.06.008

The replacement of the Lewis acids for more environmentally compatible catalysts can be done via implementation of solid acids and heterogeneous catalysis, overcoming problems with catalyst recycling and generation of waste [14,15]. However, the implementationsof such solid acids were mostly limited to alkylation reactions with acylation reactions requiring at least stoichiometric quantities of the solid acid and/or very long times of reaction [3]. Several alternative solid acids have been reported in alkylation processes including modified H–Y, H-ZSM-5 and H-β zeolites [16–18], Fe2O3 or FeCl3 supported on micro- [17], meso- [17,19] and macroporous...