Yijun Du

An efficient and recyclable heterogeneous palladium catalyst utilizing naturally abundant pearl shell waste

An efficient and recyclable ligand-free heterogeneous catalyst has been prepared by the immobilization of palladium onto ground pearl shell powders (Pd/shell powders, Pd/SP). The catalytic activity and recyclability of the prepared Pd/SP along with the charcoal and calcium carbonate supported palladium (Pd/C and Pd/CaCO3) catalysts have been evaluated using the reductive homocoupling of aromatic halides. Pd/SP not only has higher catalytic activity, but also exhibits much stronger stability than Pd/C and Pd/CaCO3. The remarkable Pd/SP stability has been attributed to the chelation of palladium species with the surface chitin and protein molecules of the supported pearl shell powders. The X-ray photoelectron spectroscopy (XPS) studies show that the reductive Pd0 species can be regenerated in situ from the oxidative Pd2+ species for the Pd/SP catalyzed reductive homocoupling of aromatic halides in ethanol/DMSO solution, suggesting that the heterogeneous and homogeneous palladium catalysis proceeds through a similar Pd0/Pd2+ cycle catalytic mechanism.

Polyacrylonitrile fiber mat supported solid acid catalyst for acetalization

A novel polyacrylonitrile hybrid fiber mat supported solid acid catalyst was prepared by electrospinning, and its catalytic activities were carefully investigated through acetalization reactions. The results showed that this hybrid fiber mat exhibits high activity for the reactions, with average yields over 95%. Besides having catalytic activities similar to the solid acid, the heterogeneous solid acid/polyacrylonitrile mat can be reused in six runs without significant loss of catalytic activities. The large size of the hybrid fiber mat greatly facilitates recovery of the catalyst from the reaction mixture. The high and stable catalytic activities of the hybrid fiber mat hold great potential for green chemical processes and preparation of membrane reactors in the future.Graphical Abstract.

Synthesis of a novel multi-SO3H functionalized ionic liquid and its catalytic activities

A novel multi-SO3H functionalized ionic liquid is synthesized and a detailed account of its catalytic activities in acetalization and acetylation is given. The results showed that the ionic liquid is very efficient in the conventional acid-catalyzed reactions with good to excellent yields within a short reaction time. Operational simplicity, small amounts required, low cost of the catalyst, high yields, scalability and reusability are the key features of this methodology, which indicates the high potentialities of the novel ionic liquid to be used in environmentally friendly processes.

Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C−H Bonds in Phosphonates and Related Phosphorus Containing Compounds

The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in a series of phosphonates and related phosphorus-containing compounds have been determined by a combination (eq 3) of their equilibrium acidities (pK(HA)s) and the oxidation potentials [E(ox)(A(-))s] of their conjugate anions, which were measured in DMSO solution. The equilibrium acidity increases by 15.5, 14.9, and 10.9 pK units for the introduction of an alpha-P(O)(OEt)(2) group into toluene, acetonitrile, and ethyl acetate, respectively. Comparison with the published equilibrium acidity increases by 25.6, 24.4, and 21.0 pK units for the introduction of an alpha-(+)PPh(3) group into the same series of substrates indicates that the phosphoryl carbanions (Horner-Wadsworth-Emmons reagents) are about 10 pK units more reactive than the corresponding triphenylphosphonium ylides (Wittig reagents). However, both alpha-P(O)(OEt)(2) and alpha-(+)PPh(3) groups have negligible effects on the adjacent C-H BDEs, indicating that there is no resonance delocalization into the 3d vacant orbitals of phosphorus and that their acidifying effects are exclusively associated with the field/inductive (electrostatic) and polarizability effects. The acidifying effect of an alpha-CO(2)Et group is shown to be ca. 3.5 pK units stronger than that of an alpha-P(O)(OEt)(2) group in the same substrates, suggesting that the larger acidifying effect of the alpha-CO(2)Et group is predominantly associated with the resonance delocalization rather than with the field/inductive (electrostatic) and polarizability effects.

Novel efficient procedure for the conjugate addition of amines to electron deficient alkenes

The novel efficient procedure has been developed for the conjugate addition of amines to electron deficient alkenes using the novel SO3H functionalized ionic liquid as catalyst. The results showed that the novel catalyst owned high activities for the reactions with excellent yields within several minutes. Various amines and electron deficient alkenes were successfully transformed to the corresponding products in the catalytic system. Operational simplicity, without need of any solvent, low cost of the catalyst used, room temperature, high yields, reusability, excellent chemoselectivity and wide applicability are the key features of this methodology.