Solvent-free Solid Supported and Phase Transferred Catalyzed Synthesis of Benzaniline Derivatives Using Microwave Irradiation

In this study, solvent-free and phase transfer catalysis conditions coupled with microwave irradiation and their advantages in synthesis of N-alkylation of primary anilines were reported. In this way two different microwave processing techniques were compared in terms of reaction yields. Consequently, microwave irradiation significantly reduced reaction times compared to traditional heating methods. Particularly synthesis by solventfree solid supported microwave irradiaton was found more eco-friendly and had higher reaction efficiency against to phase transfer catalysis condition. Organic reactions under solvent-free conditions is advantageous because of enhanced selectivity, efficiency and more importantly, toxic and volatile solvents are avoided. So that this eco-friendly green approach might be applied to the rapid assembly of various alkylation reactions . INTRODUCTION: Since the initial experiments in the mid-1980s, the use of microwave energy for heating chemical reactions has shown tremendous benefits in organic synthesis. Significant rate enhancements, improved yields, and cleaner reaction profiles have been reported for many different reaction types over the past two decades. Thus, when planning a reaction protocol or designing novel synthetic pathways, the use of microwave irradiation as heating source should become a first choice and not the last resort . A frequently used processing technique employed in microwave-assisted organic synthesis since the early 1990s involves solvent-less (“dry media”) procedures 27 where the reagents are pre-adsorbed onto either an essentially microwave-transparent (silica, alumina or clay) or a strongly absorbing (graphite) inorganic support, that additionally can be doped with a catalyst or reagent. An alternative technique utilizes microwave-transparent or only weakly absorbing inorganic supports such as silica, alumina or clay . These reactions are effected by the reagents/substrates immobilized on the porous solid supports and have advantages over the conventional solution-phase reactions because of their good dispersion of active reagent sites, associated selectivity, and easier work-up. The recyclability of some of these solid supports and the avoidance of the waste disposal problems associated with the use of solvents, render these processes ecofriendly “green” protocols. In general, the substrates are pre-adsorbed onto the surface of the solid support and then exposed to microwave irradiation. In addition to solvent-free processing, phase-transfer catalytic conditions (PTC) have also been widely employed as a processing technique in MAOS (Microwave Assisted Organic Synthesis) 3, . In phasetransfer catalysis, the reactants are situated into two separate phases, for example liquid-liquid or solidliquid. In liquid-liquid PTC, because the phases are mutually insoluble, ionic reagents are typically dissolved in the aqueous phase, while the substrate