Facile and Mild Synthesis and Characterization of Some New Diazo Dyes on the Basis of Schiff Bases in the Presence of Nanocrystalline Magnesium Oxide as a Base Catalyst under Solvent-free Conditions Hossein Naeimi, a * Zahra Rashid a and Khadijeh Rabiei b a Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, 87317, I.R. Iran b Department of Chemistry, Faculty of Basic Science, Qom University of Technology, Qom, 37195-1519, I.R. Iran (Received: Jul. 6, 2015; Accepted: Sept. 21, 2015; Published Online: Nov. 6, 2015; DOI: 10.1002/jccs.201500264) In this research, some new diazo dyes including Schiff base have been synthesized by the condensation re- action between ethylenediamine and derivatives of salicylaldehyde containing diazo functional groups in the presence of nanocrystalline magnesium oxide as a solid base catalyst under solvent-free conditions. Nanocrystalline magnesium oxide has been characterized by XRD, BJH and TEM techniques. The corre- sponding products have been obtained in excellent yields and high purity. All of the obtained diazo-Schiff bases are highly colored and can be applicable as useful diazo dyes and characterized by spectroscopy data. Keywords: Azo dyes; Salicylaldehyde; Nanocrystalline magnesium oxide; Solvent-free; Schiff base. INTRODUCTION Organic reactions under solvent-free conditions have gained in popularity in recent year. This is because sol- vent-free reactions usually need shorter reaction times and simpler reactors and resulting simple and efficient work up procedures. Furthermore, reactions, which performed un- der solvent-free conditions especially have been important and attracted much attention. 1 The condensation of primary amines with carbonyl compounds yields Schiff bases. 2 Schiff base ligands have been extensively studied in coordination chemistry mainly due to their facile syntheses, easily tunable steric, elec- tronic properties and good solubility in common solvents. 3 Schiff bases that have solvent dependent Uv-Vis spectra (solvatochromicity) can be suitable NLO (non linear opti- cal active) materials. 4 Also these compounds are a class of important compounds in medicinal and pharmaceutical field. They show biological activities including antimicro- bial, 5 anticancer 6,7 and herbicidal activities and find many important catalytic applications. 8,9 Complexes of Schiff bases with some transition metals show significant biologi- cal notification including antimicrobial, antibacterial, anti- fungal and anticancer activities. 10-12 In literature survey 13-16 a number of research articles have been published on transition metal Schiff bases. Azo compounds are very important molecules and have attracted much attention in both fundamental and ap- plied research. 17 Azo dyes are compounds that contain azo groups linked to methine or aromatic sp 2 -hybridized C- atoms. The formation of diazotizing reagent starts with protonation of nitrous acid under strongly acidic condi- tions, and azo coupling carried out at low temperature in the presence of nucleophilic coupling components. The re- activity of a nucleophilic substrate increases with increas- ing basicity phenolates and amines. They have been widely used in many applications such as textile dyes, 18,19 color- ant, 20,21 printing systems, sensor, 22-24 analytical chemistry 25 and photo chromic materials. 26,27 Metal oxide nanomaterials exhibit unique physical and chemical properties, and have potential applications in magnetism, catalysis, electro-optical devices, sensors, and nanodevices. 28-30 MgO nanostructures have unique physi- cal and chemical properties due to high surface area and structural defects. Nanosize MgO can be used for reactive adsorbents; they have been used to the decontamination of chemical warfare agents, reducing chlorofluorocarbons, 31 and have strongly basic properties, which are associated with catalysts by base in many organic reactions. 32 In continuation of our work ongoing to the prepara- tion of Schiff bases 33,34 and anthraquinone derivatives 35 as useful dyes, and with attention to the basic properties of nanocrystalline MgO in our previous works 36,37 here, we hope to report the synthesis and characterization of some new Schiff bases containing diazo groups through conden- J. Chin. Chem. Soc. 2015, 62, 951-958 © 2015 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 951 JOURNAL OF THE CHINESE CHEMICAL SOCIETY Article * Corresponding author. Tel/Fax: 98-361-5552935; Email: naeimi@kashanu.ac.ir Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201500264