Selective propionylation of veratrole to 3,4-dimethoxypropiophenone using zeolite H-beta catalysts

The catalytic liquid phase propionylation of veratrole (VT) (1,2-dimethoxyb enzene. 1,2-DMB) is investigated over a number of zeolite catalysts. Zeolit e H-beta is found to be an effective catalyst for the selective conversion of VT to 3,4-dimethoxypropiophenone (3,4-DMPP). The SiO2/Al2O3 ratio of zeo lite H-beta is higher (SiO2/Al2O3) = 26 than the H-Y and RE (70.6)-Y (SiO2/ Al2O3 = 4.1). The performance of zeolite H-beta is compared with that of co nventional catalyst, AlCl3. The conversion of VT, the rate (turn over frequ ency. TOF) of VT conversion (10(-4) s(-1) mol(-1) Al), turnover number (TON ) (mol of VT converted per mol Al in the catalyst) and the selectivity to 3 ,4-DMPP over H-beta after 1 h reaction time and at 403 K are found to be 40 .8 wt.%. 18.8 x 10(-4) s(-1) mol(-1) Al, 67.8 and 89 wt.%, respectively. Fo r comparison, the conversion of VT, TOE TON and selectivity to 3,4-DMPP ove r AlCl3 under identical reaction conditions are estimated to be 48.5 wt.%. 3.6 x 10(-4) s(-1) mol(-1) Al, 1.3 and 68.9 wt.%, respectively. The acidity of the zeolite catalysts is measured by the temperature programmed desorpt ion (TPD) of ammonia. The effects of acidity of the zeolite catalysts, reac tion time, catalyst concentration, reaction temperature and VT to propionyl chloride (PC) molar ratio on the catalyst performance are examined in orde r to optimise the conversion of VT and selectivity to 3,4-DMPP. The convers ion of VT increases with the increase in reaction time, catalyst concentrat ion and reaction temperature, whereas it decreases with the increase VT/PC molar ratio. The propionylation of 1,3-dimethoxybenzene (1.3-DMB) and 1,4-d imethoxybenzene (1,4-DMB) is also investigated over zeolite H-beta catalyst . The zeolite H-beta was recycled two times with a marginal decrease in cat alytic activity, but without the loss of 3,4-DMPP selectivity and crystalli nity of H-beta. Mechanistically, the PC is first polarised (CH3CH2COdelta+, Cldelta-) by the zeolite catalyst. The generated electrophile (CH3CH2CO+) attacks the ring of VT, resulting in the formation of 3,4-DMPP. (C) 2001 El sevier Science B.V. All rights reserved.