Green Chemistry PAPER Cite this: Green Chem., 2013, 15, 811 Received 27th November 2012, Accepted 16th January 2013 DOI: 10.1039/c3gc36901c www.rsc.org/greenchem Chitosan: a highly efficient renewable and recoverable bio-polymer catalyst for the expeditious synthesis of α-amino nitriles and imines under mild conditions† Mohammad G. Dekamin,* Mojtaba Azimoshan and Leila Ramezani Commercial chitosan – without any post-modification with active Bronsted or Lewis acid centers – was found to be a highly efficient renewable and recoverable bio-polymer catalyst for the rapid and con- venient synthesis of α-amino nitriles or imines from aromatic aldehydes and amines under mild reaction conditions at room temperature in high to quantitative yields. The α-amino nitrile derivatives were pre- pared through the Strecker reaction using trimethylsilyl cyanide (TMSCN) and catalyzed by chitosan as a heterogeneous bifunctional organocatalyst. Introduction In recent years, development of new processes that minimize pollution in chemical synthesis has received considerable attention due to growing environmental concerns. In this respect, heterogeneous catalysis has emerged as a useful tool to reduce waste production with regard to simplicity of the pro- cesses, lower contamination of the products with the active cata- lytic species, avoiding the use of toxic solvents, separation and recycling of the catalysts, and potential to apply continuous flow versus batch configuration on technical scales. 1,2 For this purpose, metallic species or other catalytic active centers have been often immobilized on inorganic materials such as SiO 2 , Al 2 O 3 , ZrO 2 , TiO 2 or MgF 2 , synthetic organic polymers or their hybrid materials. 1–5 Further development of this strategy has resulted in exploring nano-ordered heterogeneous catalysts. 6–8 On the other hand, biopolymers such as starch, 9 cellulose, 10 chitosan 2 or wool 11 have been used as a support in hetero- geneous catalytic systems very recently. However, extensive pro- gress in designing more sustainable chemical processes takes place if biopolymers themselves without any post-modification can be used as heterogeneous catalysts. In this context, chito- san can play a major role as a natural, biodegradable, and bio- compatible polymer. Literature survey shows that a wide range of applications have been reported for chitosan in different fields such as medicine, drug delivery, food packaging, cosmetics, water treatment, membranes, fuel cells, hydrogels, adhesives, and surface conditioners. Indeed, chitosan as a linear polyamine is the most important derivative of chitin, the second most abundant natural polymer in the world after celloluse. Chitin itself is a byproduct of the fishery industry (Scheme 1). 12 The presence of free NH 2 groups in chitosan and its insolu- bility in most organic compounds and pure water explains the greater potential of chitosan than chitin for use in different areas of the chemical industry including heterogeneous cata- lysis. Since chitosan has both hydroxyl and amino groups, it can be modified chemically into many forms and can participate in different types of chemical reactions as a suitable support for different catalytic species. 2,13 Furthermore, the use of small natural or synthetic organic molecules, namely organocata- lysis, has provided attractive alternatives to the more traditional metal-catalyzed variants and in many cases has obviated the need for prior activation of the reaction components in sepa- rate steps, especially for asymmetric transformations in recent years. 14 Hence, chitosan, as a natural poly-glucosamine, can be explored without any post-modification, as a mild bifunc- tional heterogeneous catalyst in organic synthesis. In this Scheme 1 Chemical structure of chitosan (1a) and chitin (1b). † Electronic supplementary information (ESI) available: Experimental details, IR and 1 H NMR spectral data for some of the prepared imines. See DOI: 10.1039/c3gc36901c Pharmaceutical and Biologically-Active Compounds Research Laboratory, Department of Chemistry, Iran University of Science and Technology, Tehran 16846-13114, Iran. E-mail: mdekamin@iust.ac.ir This journal is © The Royal Society of Chemistry 2013 Green Chem., 2013, 15, 811–820 | 811 Downloaded by University of Science and Technology of China on 28 February 2013 Published on 16 January 2013 on http://pubs.rsc.org | doi:10.1039/C3GC36901C View Article Online View Journal | View Issue