INTERCONVERSION OF COMPOUNDS WITH PENTA-AND HEXACOORDINATE PHOSPHORUS. CRYSTAL AND MOLECULAR STRUCTURE OF THE TRIALKYLAMMONIUM HEXAOXYPHOSPHORIDE, [(PO6)(C6H5)2(C6H4)(CF3C˭CCF3)]−[(C2H5)3NH]+

Abstract

The structure of triethylammonium diphenoxy-o-phenylenedioxy-1,2-bistrifluoromethylethenylenedioxyphosphoride, a compound with hexacoordinate phosphorus obtained by addition of triethylammonium phenoxide to the pentacoordinate phosphorus precursor, has been determined by x-ray crystallographic methods. The compound crystallizes from ether in space group P2_1/n of the monoclinic system. There are four formula units, (C₂₂H₁₄O₆P)-(NC₆H₁₅)⁺ in the unit cell (Z=4), with one ion-pair constituting the asymmetric unit of the crystal. The cell dimensions are a=10.787(5), b=16.604(6), c=16.668(4) Å; β=102.84°(3); D _ctlc=1.415 g cm^?3, D _meas=1.412 g cm^?3 (25°). Data were obtained on a CAD4 automatic diffractometer; 5310 unique non-zero reflections were collected with θ≤ 75° using (θ-2θ) scan, with a scan width of 1.0°. The phosphorus and oxygen atoms were located using the MULTAN program. All other non-hydrogen atoms were found in subsequent iterations of partial-structure phased Fourier maps. The structure was refined by full-matrix least-squares techniques to a final R _w value of 7.5% on F based on 4855 independent reflections. The phosphorus atom is hexacoordinate and at the center of a nearly regular octahedron, with the two phenoxy groups cis to each other. The two P–O (exocyclic) bonds are shorter (ave. 1.656(4) Å) than the four P–O (endocyclic) bonds (ave. 1.711(4) Å). The positively charged nitrogen is closer to two of the uncharged oxygen ligands (3.000 and 3.108(6) Å) than to the negatively charged phosphorus (4.063(6) Å) within the formula unit. The changes in molecular parameters when an oxyphosphoride is derived from an oxyphosphorane by addition of a sixth oxy-ligand are discussed.     

Kinetic and mechanistic insight into the thermodynamic degradation of saxagliptin

The dipeptidyl peptidase-IV inhibitor saxagliptin (Onglyza) can undergo a thermodynamically favored cyclization to form the corresponding cyclic amidine. The kinetics and mechanism of this conversion were examined to develop a commercial synthesis that afforded saxagliptin with only trace levels of this key byproduct. Important findings of this work are the identification of a profound solvent effect and the determination of an autocatalytic pathway. Both of these phenomena result from transition structures involving proton transfer.     

Thermal and chromatographic behaviour of metal complexes. Part II. Complexes of platinum(II) with dipeptide ester

Experimental measurements of the rate of reduction of particles of Carol Lake and Kiruna ores have been made using pure hydrogen and pure carbon monoxide and mixtures of these two gases. The temperature range covered was 773–1143 K and throughout this range the reduction rate with hydrogen was greater than that with carbon monoxide. A retracting core model was found to best fit the experimental data even when granules of 9 × 10^?4 m diameter were used. Reduction with gas mixtures of hydrogen and carbon monoxide give rates intermediate between those of the pure gases.     

New reactivity of oxaziridine: Pd(II)-catalyzed aromatic C-H ethoxycarbonylation via C-C bond cleavage

A novel Pd(II)-catalyzed aromatic C-H ethoxycarbonylation with oxaziridine involving C-C bond cleavage is described. Various aromatic 2-phenylpyridines and related compounds as well as aryl ureas can be effectively ethoxycarbonylated. A catalytic cycle involving Pd(II) and Pd(IV) is proposed.     

Kinetic study of the thermal decomposition of low-grade nickeliferous laterite ores

This study presents an evaluation of the decomposition kinetic of low-grade nickeliferous laterite by thermogravimetric analysis. Kinetic parameters were calculated using the Ozawa and the iso-conversional Friedman methods. Simplified kinetics models like those based on the reaction order were also applied for the simulations. Two-dimensional shrinkage models of the reaction interface mechanism were adopted as describing the thermal transformation process from non-isothermal kinetic analysis. The iso-conversional method (model-free kinetics) reveals that the decomposition of low-grade nickeliferous laterite does not follow a single mechanism because the determined activation energies and pre-exponential factor are not constant during the course of the reaction.