Replacing benzyl chloride with benzyl alcohol in heterogeneous catalytic benzylation of aromatic compounds

Candu, Natalia; Wuttke, Stefan; Kemnitz, Erhard; Coman, Simona M.; Pârvulescu, Vasile I.

doi:10.1351/PAC-CON-11-09-34

Pure Appl. Chem., 2012, Vol. 84, No. 3, pp. 427-437

http://dx.doi.org/10.1351/PAC-CON-11-09-34

Published online 2012-02-03

Replacing benzyl chloride with benzyl alcohol in heterogeneous catalytic benzylation of aromatic compounds*

Natalia Candu¹, Stefan Wuttke², Erhard Kemnitz³, Simona M. Coman¹* and Vasile I. Pârvulescu¹*

¹ Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of Bucharest, Bdul Regina Elisabeta, 4-12, Bucharest, 030016, Romania
² Department of Chemistry, University of Munich (LMU), Butenandstr. 5-13 (E), D-81377 Munich, Germany
³ Institut für Chemie, Humboldt‑Universität zu Berlin, Brook-Taylor-Straße 2, D-12489 Berlin, Germany

Abstract: Comparative catalytic liquid-phase benzylation of aromatic compouds (e.g., benzene and ethylbenzene) to diphenylmethane (DPM) derivatives with benzyl alcohol (BnOH) was investigated over various catalysts like zeolite (HSZ 600 mordenite, CBV 20A mordenite, H-beta zeolites with Si/Al ratios of 10.8 and 35.8, respectively) and nano-structured inorganic fluorides (MgF₂) at 80–120 °C under atmospheric pressure. The reactions were carried out in batch reactors using two methodologies: (i) by introducing both the solution of substrate and BnOH at the beginning of the reaction, and (ii) by drop-wise addition of BnOH (1–2 drops/min for 4 h) to the reaction mixture. The analysis of the reaction products indicated that the conversion and product distribution depend on the experimental method and the nature of the catalyst. The reaction rate was found to correlate to the nucleophilicity of the substrates and their ability to delocalize the positive charge in the Wheland intermediate by inductive and resonance effects.

*Pure Appl. Chem. 84, 411–860 (2012). A collection of invited papers for the IUPAC project 2008-016-1-300 “Chlorine-free Synthesis for Green Chemistry”.