Aqueous biphasic catalytic hydroformylation of higher olefins: Promotion effect of cationic gemini and trimeric surfactants

Six cationic gemini and trimeric surfactants: N,N′-didodecyl-N,N′-dimethyl piperazinium iodide (2), the monooxlate of N,N′-didodecylpiperazine (3), the hydrochloride of N,N′-didodecylpiperazine (4), the 1,3,5-trimethyl-1,3,5-tridodecylhexahydro-1,3,5-trazinium iodide (5), the monooxlate of 1,3,5-tridodecylhexahydro-1,3,5-triazine (6) and the hydrochloride of 1,3,5-tridodecylhexahydro-1,3,5-triazine (7) were prepared using the regular methods. These cationic surfactants and a double-chained surfactant, didodecyldimethylammonium bromide (1), were successfully applied as catalysis promotion agents in aqueous biphasic hydroformylation of higher olefins. The aqueous catalysts used in present study were RhCl(CO)(TPPTS)2–TPPTS [TPPTS: P(m-C6H4SO3Na)3]. The experimental results showed that while all these cationic surfactants could accelerate the hydroformylation reaction, surfactants 1, 2, 6, 7 exhibited more significant promotion effects. The influences of the surfactant anions on the reaction were also discussed. Of the three gemini surfactants 2, 3, and 4, which were derived from N,N′-didodecylpiperazine, surfactant 2 with iodide as anion exhibited substantially higher promotion effect than surfactants 3 with monooxalate and 4 with chloride as anion, respectively. On the other hand, among the three trimeric surfactants 5, 6, 7, which were derived from 1,3,5-tridodecylhexahydro-1,3,5-triazine, surfactants 6 with monooxalate and 7 with hydrochloride as anion displayed better acceleration effect than surfactant 5 with iodide as anion. Compared with the double-chained and single headed surfactant 1, surfactant 2 containing two alkyl chains and cationic heads and surfactant 6 with three alkyl chains and cationic heads were superior additives to accelerate the hydroformylation reactions. When they were used as catalysis promotion additives, less water-soluble phosphine (TPPTS) was required to immobilize the rhodium catalyst in aqueous phase, and the hydroformylation reaction proceeded more regioselectively toward the valuable linear aldehyde under lower syngas pressure.