Chloroaluminate ionic liquids formed from either 1-ethyl-3-methyl-1H-imidazolium-chloride (EMIM-Cl) or 1-butyl-3-methy-1H-imidazolium chloride (BMIM-Cl) were examined as conversion agents for toluene carbonylation at room temperature and at pressures of 150 and 1100 psig. The effect was examined upon the toluene conversion and selectivity for changing the ratio of AlCl3/EMIM-Cl or AlCl3/BMIM-Cl from 1/2 to 2 mol/mol at a constant HCl partial pressure of 30 psig as well as the effect of changing the HCl partial pressure from 0 to 30 psig at a constant value of AICl(3)/EMIM-Cl orAICl(3)/BMIM-Cl = 2. The effect upon reactivity was also determined for changing the Al3+ /toluene ratio at a constant value of AlCl3,/EMIM-Cl = 2 when the P-HCl was 30 psig for pressures of 150 and 1100 psig. (C) 2004 Elsevier B.V. All rights reserved.