Thermoregulated phase transfer ligands and catalysis XVIII: synthesis of N,N-dipolyoxyethylene-substituted-2-(diphenylphosphino)phenylamine (PEO–DPPPA) and the catalytic activity of its rhodium complex in the aqueous–organic biphasic hydroformylation of 1-decene

Abstract

A novel water soluble phosphine, N,N-dipolyoxyethylene-substituted-2-(diphenylphosphino)phenylamine (PEO–DPPPA), was synthesized by a two-step ethoxylation of 2-(diphenylphosphino)phenylamine (2-Ph2P–C6H4NH2, DPPPA). In the first step, DPPPA was ethoxylated without catalyst to give an intermediate with an average polyethylene glycol (PEG) chain length (L=m+n) of 3. Thereafter, this intermediate was further ethoxylated by using KOH as a catalyst to obtain the products with needed values of L. The solubility of the products in water increases with increasing of L. When L is more than 35, the products are water-soluble and possess the property of inverse temperature-dependent solubility in water (cloud point, Cp) as nonionic surfactants. The PEO–DPPPA/Rh complex catalyst formed in situ by RhCl3·3H2O and PEO–DPPPA (L=45) has been applied to the aqueous–organic biphasic hydroformylation of 1-decene. The conversion of olefin and the yield of aldehyde are 99.5 and 99.0%, respectively, under the conditions of 120 °C, 5.0 MPa (CO/H2=1), P/Rh=4 (molar ratio), 1-decene/Rh=1000 (molar ratio) and 5 h. Recycling test shows that both the conversion of olefin and the yield of aldehyde are still higher than 94.0% even after the catalyst has been recycled 20 times. The high reactivity of PEO–DPPPA/Rh complex can be attributed to a process termed thermoregulated phase transfer catalysis.