Jingyang Jiang

Thermoregulated phase transfer ligands and catalysis. III. Aqueous/organic two-phase hydroformylation of higher olefins by thermoregulated phase-transfer catalysis

Abstract A series of poly(ethylene oxide)-substituted triphenylphosphines, Ph3−mP[C6H4-p-(OCH2CH2)nOH]m (PEO-TPPs; 1a m=1, 1b m=2, 1c m=3; N=m×n=8–25), have been prepared by the ethoxylation of mono-, di-, and tri-p-hydroxytriphenylphosphines. PEO-TPPs demonstrate an inverse temperature-dependent solubility in water, and possess distinct cloud points range from 26°C to 90°C. Based on the clouding property of PEO-TPPs, a new line of aqueous/organic two-phase catalysis termed the thermoregulated phase-transfer catalysis (TRPTC) has been described. That is, the catalyst transfers into the organic phase to catalyze a reaction at a higher temperature, and returns to the aqueous phase to be separated from the products at a lower temperature. Application of this novel strategy to the rhodium-catalyzed two-phase hydroformylation of higher olefins gave desirable results with an average turnover frequency of 180xa0h−1 for 1-dodecene. The TRPTC is suitable for carrying out a reaction with extremely water-immiscible substrate in the aqueous/organic two-phase system. Thus, the application scope of the classical two-phase catalysis has been widened.

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-Ph 2 P–C 6 H 4 NH 2 , 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, C p ) as nonionic surfactants. The PEO–DPPPA/Rh complex catalyst formed in situ by RhCl 3 ·3H 2 O 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 120xa0°C, 5.0xa0MPa (CO/H 2 =1), P/Rh=4 (molar ratio), 1-decene/Rh=1000 (molar ratio) and 5xa0h. 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.

The selective reduction of nitroarenes to N-arylhydroxylamines using Zn in a CO2/H2O system

Nitroarenes are reduced to the corresponding N-arylhydroxylamines with high selectivity using Zn dust in a CO2/H2O system under mild conditions. The yield of N-phenylhydroxylamine from nitrobenzene is 88% when the reaction is carried out at 25 °C for 1.5 hours with a Zn to nitrobenzene molar ratio equal to 3 under 0.1 MPa CO2. Other nitroarenes, which contain reducible functionality other than a nitro group, are also reduced to the corresponding N-arylhydroxylamines with yield from 88% to 99%. The process fully removes the need to use NH4Cl and is environmentally benign.

Thermoregulated phase transfer ligands and catalysis: Part XIII. Use of nonionic water-soluble phosphine ligands to effect homogeneous catalyst separation and recycling

Abstract Nonionic tensioactive water-soluble phosphines that act as ligands for rhodium-catalyzed hydroformylation of higher olefins under aqueous-organic biphasic conditions are described with emphasis on the recycling efficiency of homogeneous catalyst. Phosphines discussed are P-[p-C6H4(OCH2CH2)nOH]3 (1a: N=3n=18, 1b: N=3n=25) and Ph2P-[p-C6H4(OCH2CH2)nOH] (2a: N=n=16, 2b: N=n=25) (PEO-TPPs). The rhodium catalyst combined with these ligands gave an average turnover frequency (TOF) of 182xa0h−1 for 1-hexene. More importantly, recovery and reuse of catalyst is possible because of the inverse temperature-dependent water solubility of the phosphines.

Hydroformylation of diisobutylene using thermoregulated phase-separable phosphine rhodium complex catalyst

Abstract Based on the critical solution temperature (CST) of non-ionic phosphine ligand, a thermoregulated phase-separable catalyst formed in situ from P[ p -C 6 H 4 O(CH 2 CH 2 O) n H] 3 (PETPP, n =10) and RhCl 3 ·3H 2 O was applied for the first time in the hydroformylation of diisobutylene. It was found that the reaction temperature, total pressure and reaction time, as well as the P/Rh molar ratio had great influence on the reactivity of the catalyst. Under the optimum conditions, the conversion of diisobutylene and yield of aldehyde are 93.1 and 82.5%, respectively. Recycling of the PETPP/Rh complex catalyst up to three times without loss of activity has been observed.

Thermoregulated liquid/liquid biphasic catalysis and its application

A brief overview of our recent research results of thermoregulated liquid/liquid biphasic catalysis is presented. Emphasis is given to the general principles of thermoregulated phase-transfer catalysis (TRPTC) and thermoregulated phase-separable catalysis (TPSC). In addition, the applications of TRPTC and TPSC in biphasic catalysis are also discussed. The introduction of TRPTC to biphasic system is free from the shortcomings of classical aqueous/organic two-phase catalysis, in which the application scope is restrained by the water solubility of the substrate. Meanwhile, TPSC provides a very simple and reliable way to deal with the separation of catalyst in homogeneous catalysis. The common advantages of TRPTC and TPSC are characterized by homogeneous catalysis coupled with convenient biphasic separation.

Selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in a CO2–H2O system, promoted by ultrasound

The promoting effect of ultrasound on the selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in an environmentally benign CO2–H2O system has been demonstrated. The yield of N-phenylhydroxylamine reaches 95xa0% when the reaction is carried out with a Zn-to-nitrobenzene molar ratio of 2.2 under ultrasound (40xa0kHz) at 25xa0°C and normal pressure of CO2 for 60xa0min. Application of ultrasound to the reaction has the advantages of higher yield of N-arylhydroxylamines, shorter reaction time, and consumption of less Zn.