An efficient method for the a-phenylhydrazation of heterocyclic systems under mild and heterogeneous conditions Zahra Sadeghi, Javad Safari * Department of Chemistry, Faculty of Sciences, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran Received 12 September 2005; received in revised form 24 January 2006; accepted 12 June 2006 Available online 18 September 2006 Abstract A combination of silica modified sulfuric acid and aryldiazonium salt was used as an agent for the a-phenylhydrazation of 2-ketomethyl- quinoline under mild and heterogeneous conditions to provide moderate to excellent yield. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: a-Phenylhydrazation; 2-Ketomethylquinoline; Heterogeneous conditions 1. Introduction Diazonium salts are occasionally used to introduce groups other than fluorine into an aromatic ring. For example, the diazonium salt group may be replaced by different groups such as the acetoxyl, nitro, nitrile, hydrogen, halogen, methyl, vinyl, arsenic, mercury and copper. Numerous methods are available for the reduction of arenediazonium salts [1]. The reactions of arenediazonium salts with various carbon nucleo- philes such as Grignard reagents, enamines, enolether, lithium enolates of ketones or esters, and ketene silyl acetals [2] lead to the formation of azo or hydrazo compounds. The structure of azo-coupling products is obtained from the investigation of amines, phenoxides, and anions of C-acids. This problem has been satisfactorily solved as late as after applying the methods of nuclear magnetic resonance [3e5]. The carbon in aliphatic azo compounds is attached to a hy- drazone, which is the product of the reaction. In the current research we decided to choose a new system. Our goal, in undertaking this line of work, was three-fold: (a) to overcome the limitations and drawbacks of the reported methods such as tedious work-up and low yields; (b) to replace labour-extensive trial and error improvements with a rational design; and moreover (c) to constrain a reaction to the surface of solid habitually allowing exposure to milder conditions and increasing its reactivity [6]. In this study, we wish to report a one-pot heterogeneous procedure for a-phenylhydrazation of 2-ketomethylquinoline by aryldiazonium salt and sodium nitrite. 2. Results and discussion 2-Ketomethylquinolines are important components in or- ganic chemistry because of the applications of these compounds in heterocyclic synthesis and chemical transformations [7e12]. Different kinds of 2-ketomethylquinolines (1) were subjected to a-phenylhydrazation reaction in the presence of sodium nitrite, derivatives of aniline and silica modified sulfuric acid (I) in di- chloromethane (Scheme 1). a-Phenylhydrazation reaction was performed under mild and completely heterogeneous condition and gave moderate to excellent yields (Table 1). When reactions occur at the methylene group, the azo compound formed ini- tially rapidly rearranges to form the a-hydrazokethones (3) [13]. The reported a-phenylhydrazation reaction can be readily carried out simply by placing sodium nitrite, derivatives of an- iline, silica modified sulfuric acid (I), 2-ketomethylquinoline (1), and CH 2 Cl 2 as inert solvents in a reaction vessel and effi- ciently stirring the resultant heterogeneous mixture at 5  C for 30 min. * Corresponding author. Fax: þ98 361 555 2930. E-mail address: sadeghi@kashanu.ac.ir (J. Safari). 0143-7208/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2006.06.042 Dyes and Pigments 75 (2007) 432e433 www.elsevier.com/locate/dyepig