SYNTHESIS, CHARACTERIZATION OF STRONG BASE RESIN WITH GUANIDYL GROUPS AND THE APPLICATION AS CATALYST IN THE KNOEVENAGEL CONDENSATION

The strongly basic polymer-supported catalyst containing guanidine functional group has been synthesized. In order not to increase the complexity or cost of the synthetic process, macroporous polystyrene amine resin has been allowed to react nucleophilic addition with cyanamide in situ to generate strong basic guanidine resin from weak basic amine resin designated as PG. PG resin is characterized by FTIR and SEM, and the contents of the strongly basic functional groups bound to the PG resin are determined by acid-base titration and elemental analysis. The effects of pH value, material ratio and reaction temperature on the in situ reaction are also studied. The experimental results show that when pH value of solution is 2, the molar ratio of amine functional groups on the macroporous to cyanamide is 1: 3, and reaction temperature is 110 degrees C, the strong base exchange capacity is 3. 54 mmol/g. The Knoevenagel condensation has been selected to investigate the catalytic activity of the synthesized solid-supported guanidine catalyst. The Knoevenagel condensation is an effective carbon-carbon bond-forming reaction between a carbonyl compound and any compound having an active methylene group. The obtained PG resin has been found to be efficiently catalyze the Knoevenagel condensation reactions with remarkably high yields, and even the reactions of relatively inactive substrates such as ketones can be accomplished at higher temperatures. The effects of the amount of PG resin,reaction solvent and reaction time on the Knoevenagel condensation reactions between benzaldehyde and ethyl cyanoacetate (molar ratio 1: 1) are investigated. Optimum reaction conditions are obtained as follows : in ethanol media, reaction time 5 h,n(guanidine functional groups immobilized on the anion exchange resin) n (substrate) = 1: 5,the yields of 83. 1% similar to 95. 3% are gained. Lastly, the PG resin has been reused under identical reaction conditions remaining basically the efficiency in catalytic activity at the fifth cycle.