Phosphorus Heteroatoms Research Articles

Chemoselective Electrophilic Oxidation of Heteroatoms by Hydroperoxy Sultams.

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A substrate-versatile catalyst for the selective oxidation of light alkanes: I. Reactivity

The reactivity of niobium and pyridine-exchanged molybdophosphoric (NbPMo 12pyr) and molybdovanadophosphoric (NbPMo 11Vpyr) acid catalysts are investigated for the selective oxidation of light alkanes. Productivities and selectivities are presented for the reactions of propane to acrylic acid and n-butane to maleic acid. Pretreatment of the material to 420 °C in an inert atmosphere is required to form an active catalyst, and the combination of both niobium and pyridine is necessary for obtaining maximum activity. Vanadium is not essential for the selective formation of maleic acid from butane, but does appear to affect the selective formation of acrylic acid from propane. Other metal cations can be used instead of niobium; however, none are as effective as niobium. Comparison of activity results to those from other molybdate-based structures indicates that high activity requires the use of a reducible molybdenum species. In addition, the central phosphorus heteroatom of the polyoxometalate is important for high activity. Structures without phosphorus or with other heteroatoms have lower activity. The catalysts are effective under both hydrocarbon-rich and oxygen-rich conditions. For butane, the productivity to maleic acid exceeds that of the current industrial standard vanadium phosphorus oxide. With propane, the productivity to acrylic acid is above that of the MoVNbTe mixed-metal oxide. In addition to efficiently catalyzing the selective oxidation of propane and butane, the catalysts are active with feeds containing other substrates such as ethane, isobutane, and toluene.

Chemoselective electrophilic oxidation of heteroatoms by hydroperoxy sultams.

The synthesis of novel hydroperoxy sultams 1b-d and their potential as renewable chemoselective electrophilic oxidants for a wide range of nitrogen, sulfur, and phosphorus heteroatoms in nonaqueous media is described. Reactions of 1b,c with secondary amines 10f,g yielded the hydroxysultams 2b,c and nitrone 11f or radical 11g depending on the substrate and stoichiometry, while tertiary amines 10a-d gave amine oxides 11a-d. Compounds 1c,d oxidized various thioethers 12a-g to sulfoxides 13a-g smoothly that were isolated by chromatography in nearly quantitative yields. 1c was regenerated from 2c by treatment of the latter with acidified H2O2. Kinetic studies of the reaction of 1c with 1,4-thioxane 12f suggest that the reaction follows the second-order kinetics, first order in substrate and first order in oxidant with the second-order rate constant several orders of magnitude larger than that of the corresponding reaction with hydrogen peroxide and tert-butyl hydroperoxide without the need for any acid or heavy metal catalysts. The phosphines 14a,b were also oxidized by 1c to the respective phosphine oxides 15a,b readily in quantitative yields. The reactions may be conducted at ambient temperature or lower and appear to proceed via a nonradical mechanism. Reactions are sensitive to steric as well as electronic factors.

Facile synthesis of proline based phosphineoxazoline ligands by formation of a PN bond

A series of new PN ligands in which the phosphorus moiety is introduced by formation of a phosphorusheteroatom bond are synthesized. These ligands are based on proline with chiral centers from both proline and an oxazoline. The two chiral centers are responsible for the observed stereoselectivity. Palladium complexes of these ligands are shown to be effective in the allylation of dimethyl malonate as well as amination of allyl acetates.

Extraction of pesticides using supercritical trifluoromethane and carbon dioxide

The off-line supercritical fluid extraction of pesticides using trifluoromethane (CHF 3) and carbon dioxide (CO 2) is described. Pesticides containing nitrogen or phosphorus heteroatoms were used as analytes to determine the extraction ability of CHF 3 in comparison with CO 2 at various pressures and densities. A 15% increase in extraction efficiency was obtained when CHF 3 was used as the extraction solvent rather than CO 2. No selectivity was observed for different groups of pesticides, although CHF 3 has a dipole moment whereas CO 2 does not. Because in environmental matrices the hydrocarbons are mostly present in high excess compared with the pesticides, extractions were carried out without and with addition of alkanes and polycyclic aromatic hydrocarbons (PAHs). The extraction efficiency of the pesticides with CHF 3 performed without addition of alkanes and PAHs was significantly decreased.

Phosphorus-mediated gold aggregation on a metal cluster: syntheses, structures, dynamic behavior, and ligand addition reactions of the clusters (.mu.-H)nFe3(CO)9P[Au(PR3)]3-n (n = 0, 1, 2)

The phosphorus heteroatom in the cluster [H 2 Fe 3 (CO) 9 P] - has a high affinity for (R 3 P)Au + fragments, permitting the synthesis of a series of gold-substituted clusters, (μ-H) n Fe 3 (CO) 9 P[Au(PR 3 ] 3-n (n=0, 1, 2). Reactions betwen (R 3 P)AuCl (R=Ph, Et) and the silylphosphinidene cluster(μ-H) 2 Fe 3 (CO) 9 [μ 3 -PSi(i-Pr) 3 ] (with evolution of (i-Pr) 3 SiCl) or the desilylated anion [(μ-H)Fe 3 (CO) 9 (μ-PH)] - serve as the synthetic routes to these clusters