Mesoporous SBA-15 nanoparticles : An efficient and eco-friendly Catalyst for one-pot synthesis of 3 , 4-dihydropyrimidin-2 ( 1 H )-ones under solvent-free conditions

Article history: Received June 28, 2013 Received in Revised form December 10, 2013 Accepted 20 December 2013 Available online 21 December 2013 A simple and efficient procedure for the synthesis of 3, 4-dihydropyrimidin-2(1H)-ones under solvent-free condition using non-toxic and mild acid mesoporous SBA-15 nanoparticles as a catalyst has been investigated. This method has the advantages of the excellent yield, short reaction time, environmentally friendly conditions and simple experimental procedure. © 2014 Growing Science Ltd. All rights reserved.


Introduction
In recent decades there was an exponential growth in the application of inorganic solid acid catalysts in order to carry out organic synthesis because of its importance in terms hazardous chemicals in the present industrial scenario 1 .Inorganic solid catalysts such as SBA-15 are interesting for organic synthesis since they are environmental protection 2 .Mesoporous SBA-15 nanoparticles have a highly ordered hexagonal structure, large pore, high surface area, high thermal stability and thicker walls in comparison with Mobile composition of matter number 41 (MCM-41) 3 .Green chemistry approaches hold out significant potential not only for save energy, prevent solvent wastes, hazards and toxicity but also in development of new methodologies towards previous unobtainable materials, using existing technologies 4 .The elimination of volatile organic solvents in green chemistry is desirable in order to reduce the amount of residual solvent and atmospheric pollution.However using solvent-free organic reactions can reduce waste products and energy costs of synthesis 5 .
However, some of these methods have drawbacks such as the need of strong and protic acids 11,12 , toxic solvent 15 , longer reaction time, tedious workup, environmental disposal problems 13,[16][17] and lower yields of the products 2 .Therefore, the utilization of a simple and environmentally friendly method for the preparation of 3, 4-dihydropyrimidin-2-(1H)-ones is of prime importance.Cause of emerging importance of mesoporous SBA-15 nanoparticles as a catalyst that is related to our research for reactions proceeding in solvent-free condition 18,19 , we would report a simple and facile synthesis of dihydropyrimidiones by using mesoporous SBA-15 nanoparticles as a heterogeneous and ecofriendly catalyst under solvent-free conditions in high yields.

Catalyst preparation
Amorphous Silica was extracted from Stem Sweep Ash (SSA) by a suitable alkali solution with approximately 80% purity, converted to silicate solution with SiO 2 /Na 2 O=2.88 and used as silica source for the synthesis of mesoporous SBA-15 nanoparticles by a sol-gel method in the presence of non-ionic block co-polymer (P123) as co-template 20 .Mesoporous SBA-15 nanoparticles was acidified by ammonium chloride (1M) then calcined at 550 o C for 5h.

Results and Discussion
At first, mesoporous SBA-15 nanoparticles with rod like pore structure was synthesized from rice husk (RiH) using the SSA as silicon source and sol-gel method.We began to extract.The crystal like external morphology of the particle, determined by SEM.crystallite size observed from this technique is 82nm.The SEM image reveals agglomeration of rod-like shape SBA-15 particles 20 .
The approach involved the use of synthesized mesoporous SBA-15 nanoparticles from RHA for synthesis of dihydropyrimidiones under solvent-free conditions.Therefore, this method provides an efficient route for synthesis of dihydropyrimidiones which saves energy, and prevents from solvent wasting, hazards, and toxicity.The reaction conditions were initially optimized by considering three component condensations of a variety of aromatic aldehydes carrying electron donating or electronwithdrawing substituents, ethyl acetoacetate and urea to afford the corresponding product as a model reaction under various reaction conditions.The best results were obtained using 0.04gr of mesoporous SBA-15 nanoparticles, 1.5mmol of urea, ethylaceto acetate and 1mmol of aldehyde, at 100 o C and under solvent free conditions Scheme 1.To illustrate the efficiency of the catalyst in this reaction, when the same reagents and conditions were used to carry out the reaction without catalyst, the reaction failed to give the desired product, even after a long reaction time (Table 1, entry 1).Scheme 1. Synthesis of 3, 4-dihydropyrimidin-2 (1H)-ones using mesoporous SBA-15 nanoparticles

Conclusions
In summary, we have developed a simple, rapid and efficient procedure for the synthesis of 3, 4dihydropyrimidine-2(1H)-one derivatives by using mesoporous SBA-15 nanoparticles as catalyst under solvent free condition.This method offers several advantages such as green reaction conditions, short reaction time, high yields and simple work-up procedure use of environmental friendly catalyst.