Rhodium Metal Complex and Hydrotalcite Based Environmentally Friendly Catalyst System for the Selective Synthesis of C8-Aldehydes from Propylene

Catalytic activity of a novel catalyst [HFN + HT] containing a rhodium complex, HRh(CO)(PPh 3 ) 3 [HFN], and a solid base, hydrotalcite Mg 1-x Al x (OH 2 ) x+ (CO 3 2- ) x/n •mH 2 O [HT], was evaluated for carrying out hydroformylation, aldol condensation, and hydrogenation in a single pot for the synthesis of C 8 -aldehydes, 2-ethylhexenal and 2-ethylhexanal, from propylene. In typical catalytic experiments conducted in a highpressure reactor of 100 mL capacity, the selectivity for the formation of 2-ethylhexanal (54%) was found to be four times more than that of 2-ethylhexenal (13%) at 150 °C with employed partial pressures of propylene, carbon monoxide, and hydrogen at 10, 5, and 15 bar, respectively. Detailed investigations were performed on the effects of various reaction parameters, Mg/Al molar ratio (X) of [HT], amount of [HFN] complex, amount of [HT], and reaction temperature, on the formation of C 8 -aldehydes from propylene in a single pot. Under the employed reaction conditions, the maximum selectivity for 2-ethylhexanal was observed using hydrotalcite of Mg/Al molar ratio 3.5. Increasing the amounts of both [HFN] complex and [HT] favored the selectivities for the formation of 2-ethylhexanal up to certain amounts, and after that, on further increasing the amounts, the selectivities for the same were decreased. The kinetic profiles for the formation of various products with time and reaction rates were determined. For comparative studies, the kinetic profiles and reaction rates with the commercially employed catalyst, [HFN + KOH], were also determined under identical reaction conditions of [HFN + HT(3.5)], and the selectivity of 2-ethylhexanal was found to be almost identical at 7 h for the both systems. On the basis of experiments and kinetic profiles, reaction pathways are suggested for the formation of C 8 -aldehydes from propylene in a single pot.