Frank Mares

Biphase and triphase catalysis. Arsonated polystyrenes as catalysts in the Baeyer-Villiger oxidation of ketones by aqueous hydrogen peroxide

Arsonated polystyrene resins, prepared by a novel procedure, proved to be versatile catalysts for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide. The insoluble beads of the catalyst can be quantitatively separated from the reaction mixture and recycled. Extensive hydrolysis of the lactone and ester products is prevented. In solvents miscible w i t h aqueous hydrogen peroxide (biphase system), the catalysts facilitate oxidation of medium size cycloalkanones (C4-C7) and their alkyl and aryl derivatives, steroid ketones, and branched-chain aliphatic ketones. Larger size cycloalkanones, acetophenone, and straight-chain aliphatic ketones react very slowly or not at all. The arsonated polystyrene beads are effective catalysts and phase transfer agents i n solvents immiscible wi th aqueous hydrogen peroxide. This represents the first example of triphase catalysis in oxidations by hydrogen peroxide. Replacement of carboxylic peroxy acids by a hydrogen peroxide-catalyst system has been of long-standing interest in the Baeyer-Villiger oxidation of ketones. This effort is important in view of the following considerations. Hydrogen peroxide is cheaper and more convenient than carboxylic peroxy acids (water is the only side product). The carboxylic acids resulting from peroxycarboxylic acids cannot be readily separated, and their equilibration with hydrogen peroxide is extremely slow.’ Although this can be accelerated by catalytic quantities of strong acids, the presence of these acids results in hydrolysis of the product of the Baeyer-Villiger oxidation.’ Therefore, in situ recycle of carboxylic acids is impossible. Thus, it becomes obvious that a good catalyst for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide has to fulfill several requirements: (1 ) fast reaction with hydrogen peroxide resulting in hydroperoxy or metal peroxo species; (2) easy separation of the catalyst from the reaction mixture; and (3) low or no protonic or Lewis acidity. Although several catalysts have been reported in the literature,2,3 they do not satisfy the above requirements and possess several shortcomings. We are now pleased to report the preparation and demonstration of a suitable catalyst based on polystyrene substituted by arsonic groups. Results and Discussion 1. Catalyst Selection. The OH/ I80H or O H / O O H exchange, and therefore formation of hydroperoxy and peroxo species, is known to be fast in oxides of groups 5, 5A, 6, and 6A element^.^ This fact has been employed in the preparation of benzeneperoxyseleninic acid in a two-phase system such as chloroform-aqueous hydrogen peroxide.s The preformed benzeneperoxyseleninic acid dissolved in the organic solvent has then been used as a stoichiometric oxidant of cyclic ketones to lactones.’ Even more interesting are the patent literature reports* suggesting that selenium and arsenic oxides may be used as catalysts for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide. I n our work,3 similar properties have been demonstrated for molybdenum and tungsten peroxo complexes stabilized by pyridinecarboxylato ligands. Unfortunately, the above-mentioned catalysts cannot be easily separated from the reaction mixtures. Furthermore, selenium and arsenic oxides are toxic, and in the presence of aqueous hydrogen peroxide they exhibit protonic and Lewis acidity causing extensive solvolysis of lactones.6 Inspection of the literature revealed that the acidity of toluenearsonic acidh (pK, = 3.82) is very close to that of mchlorobenzoic acid’ (pK, = 3.82), the peroxy form of which 0002-7863/79/15Ol-6938

Preparation and characterization of a novel catalyst for the hydrogenation of dinitriles to aminonitriles

0l .OO/O is the most common reagent for conversion of cyclic ketones to lactones. Also, the C-As bond8 in benzenearsonic acid, unlike the C-Se bond9 in benzeneseleninic acid, is very stable toward nucleophilic and electrophilic reagents. Indeed, preliminary experiments indicated that benzenearsonic acid is an efficient catalyst for oxidation of cyclic ketones to lactones. Nevertheless, only bonding of the benzenearsonic acid group to an insoluble support would allow the separation of this catalyst from the product. Our interest therefore centered on polystyrene arsonated on the benzene ring since, from all the polymers modified by peroxycarboxylic groups, only those based on polystyrene have been found stable.’O 11. Preparation and Characterization of the Catalyst. Previous attempts to derivatize polystyrene by arsonic groups have employed, as the key step, the Bart’s reaction which involves interaction of the diazotized phenyl rings with alkaline metal arsenite.’ The polystyrene derivatized by this method is contaminated’ l a x b by a substantial number of phenyl groups bearing azo, amino, and hydroxy groups which are incompatible with hydrogen peroxide. Therefore, a new procedure has been developed which is summarized in eq 1 :

Poly(ethylene terephthalate)–poly(caprolactone) block copolymer. I. Synthesis, reactive extrusion, and fiber morphology

Abstract Highly dispersed rhodium on a high-surface-area magnesia support is a very selective and efficient catalyst for the partial hydrogenation of aliphatic α,ω-dinitriles to the corresponding ω-aminonitriles. In this catalyst the content of rhodium is 4–5%. The conditions needed for reproducible preparation of the high-surface-area magnesia are described. The role of the high-surface-area magnesia and the steps leading to the preparation of this catalyst are discussed.

β-elimination from transition metal amides

A novel poly(ethylene terephthalate)–poly(caprolactone) block copolymer (PET–PCL) is synthesized in a reactive twin-screw extrusion process. In the presence of stannous octoate, ring-opening polymerization of ϵ-caprolactone is initiated by the hydroxyl end groups of molten PET to form polycaprolactone blocks. A block copolymer with minimal transesterification is obtained in a twin-screw extruder as a consequence of the fast distributive mixing of ϵ-caprolactone into high melt viscosity PET and the short reaction time. The PET–PCL structure is characterized by IV, GPC, 1H-NMR, and DSC. Fully drawn and partially relaxed fibers spun from PET–PCL are characterized by WAXD and SAXS. A substantial decrease in the oriented amorphous fraction appears to be the major structural change in the relaxed fiber that provides the fiber with the desired stress–strain characteristics.

Homogeneous catalytic oxidation of amines and secondary alcohols by molecular oxygen

Abstract Ruthenium, rhodium, and palladium phosphine complexes are found to produce metal hydrides in high yields by a β-elimination reaction from the corresponding metal amides. Evidence is presented to support the formation of an imine as the organic product. The isotope effect for the reaction is 6 ± 1 indicative of the importance of C H bond breaking in the transition state.

Surfactant-free emulsion polymerization of chlorotrifluoroethylene with vinylacetate or vinylidene fluoride

Ruthenium trichloride catalyses the homogeneous oxidation of secondary alcohols to ketones, primary amines to nitriles, and 2-aminoalkanes to imines by O2; this is the first example of a homogeneous catalytic oxidation of an amino-group.

Oxidation of cyclic ketones by hydrogen peroxide catalysed by Group 6 metal peroxo complexes

A surfactant-free emulsion process has been developed for the preparation of copolymers of chlorotrifluoroethylene with vinylacetate or vinylidene fluoride. A redox initiator system, consisting of sodium-meta-bisulfite, t-butylhydroperoxide, and ferrous sulfate heptahydrate, has been found to be effective in preparing self-emulsifying fluoropolymers with a monodisperse particle size distribution, having up to 45% polymer solids in water. Over the range studied in this investigation, the particle number and the ultimate particle size is linearly related to the quantity of initially charged redox catalyst. Under conditions of optimal catalyst concentrations, a greater number of particles is produced in the surfactant-free process than that which can be obtained using conventional fluorosurfactants. Particle number is defined at the earliest stage of polymerization and remains constant throughout the polymerization, unless surfactant is postadded to the surfactant-free latex at a very early stage in the polymerization. The aqueous phases of various latices have been purified by ion-exchange and dialysis, enabling the sulfonic acid-terminated fluoropolymer end groups to be quantified. The highest level of bound sulfonic acid is obtained at elevated temperatures.

Polymer-bound catalysts for acrylonitrile dimerization

Molybdenum peroxo complexes stabilized by picolinato and pyridine 2,6-dicarboxylato ligands catalyse oxidation of cyclic ketones by H2O2 to lactones and their derivatives; this represents a catalytic analogue of the Baeyer–Villiger reaction.

Oxygen transfer from group 8 metal dioxygen complexes. Rhodium(I) catalysed co-oxygenation of terminal olefins with triaryl-phosphine and -arsine ligands

Alkyl diarylphosphinites bonded to various polymers via the PO and PC bonds have been prepared and their catalytic efficiency in acrylonitrile dimerization was investigated. Phosphinites bound to polystyrene-divinylbenzene (1%) copolymer beads via PC bonds were found to be very effective, selective, and stable catalysts with relatively high turnovers as tested in a flow system. Two synthetic routes have been developed. The first is based on brominated polystyrene which in two steps, reaction with butyl lithium followed by treatment with ethyl arylphosphonochloridite, gives the catalyst in high yield. The second, based on a novel Friedel-Crafts route, gives purer catalysts, requires only PC13 as the source of phosphorus, and is amenable to commercial scale-up. Phosphinites bound to polymer supports via PO bonds were found unstable or completely inactive. The reasons for the lack of activity in these systems are discussed.

Filaments having trilobal or quadrilobal cross-sections

Direct oxygen transfer in the intermediate rhodium dioxygen complex is the preferred mechanism for L3RhCl catalysed co-oxidation of terminal olefins and the ligands L.