Christos P. Tsonis

Catalytic activity and selectivity of group VIB metal carbonyl complexes in dehydrohalogenation reactions

Abstract The homogeneous catalytic activities and selectivities of a series of complexes ArM(CO) 3 , where M = Cr,Mo,W, and their derivatives in dehydrohalogenation reactions have been investigated. In addition to dehydrohalogenation, double-bond migrations also occurred. For Mo-based catalysts, their activity decreased and the induction time increased in the order: (Tol)Mo(CO) 3 , (Mes)Mo(CO) 3 , Mo(CO) 6 and (CH 3 CN) 3 Mo(CO) 3 . Phosphine ligands attached to the metal poisoned the catalytic activity of the system. For W derivatives, (Mes)W(CO) 3 > W(CO) 6 . The ArCr(CO) 3 catalysts were mild and their catalytic activity was not greatly affected by the nature of the arene ligand attached on the metal. Their approximate catalytic activity decreased in the order: anisole, methyl benzoate, benzene, toluene, p -xylene, mesitylene and tetralin. The catalytic activity with respect to the metal was: Mo > W > Cr. A coordinative unsaturation mechanism, probably of the redox type, is proposed. Preliminary ESR study shows that free radicals formed in a homogeneous solution of 2-chloro-2-methylbutane and Mo(CO) 6 can be trapped using a phenyl N -butylnitrone spin trap, and the resulting six-line ESR spectrum has a g -factor of 2.0045.

Homogeneous catalytic polymerization of benzyl chloride leading to linear high molecular weight polymers: an elusive goal

Abstract After decades of trying to synthesize linear, high molecular weight, crystalline polybenzyls from the catalyzed polycondensation of benzyl chloride, it is time to look at the chemistry of their formation and examine the reasons for their failure.

Stereoselective alternating copolymerization of aliphatic acetylenes with sulphur dioxide

Abstract A number of purified terminal aliphatic acetylenic hydrocarbons has been copolymerized with liquid sulphur dioxide in the presence of t-butyl hydroperoxide at low temperature. Benzoyl peroxide, hydrogen peroxide and m-chloroperbenzoic acid were ineffective. Neither sulphur dioxide nor t-butyl hydroperoxide alone was capable of polymerizing pure alkynes. Aged (impure) alkynes were copolymerized with sulphur dioxide in the absence of t-butyl hydroperoxide. All resulting alkyne-SO2 copolymers were alternating with 100% trans configuration regardless of the nature of the alkyne, the solvent, or temperature. Several studies were performed to characterize the polysulphones, such as infra-red spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, melting point, viscosity, elemental analysis, solubility, film formation and flammability. A mechanism is proposed in which sulphur dioxide homolytically decomposes the organic hydroperoxide into free radicals which initiate the polymerization. The alkyne-SO2 charge transfer complex is formed in solution, and the initiation and propagation steps probably involve this complex in equilbrium with its monomers.

Electron paramagnetic resonance application to polymers: 4. The segmental volume of poly(phenylacetylene) using different nitroxide spin probes

Electron paramagnetic resonance (e.p.r.) studies of T50G of poly(phenylacetylene) have been carried out at X-band as a function of spin probe size over a wide range of temperatures. It was found that T50G increased with increasing probe size. The polymer glass transition temperature Tg, determined from the break on the plot of ln TRversus1T for tempone in poly(phenylacetylene), was 296 K. The apparent activation enthalpy for the Tg relaxation process increased with increasing probe size, while the segmental size of the polymer appeared to be independent of the nitroxide used, and has a range of 898–922 A3. The segmental volume measured by the spin probe technique is in excellent agreement with the volume of 970 A3 of 10 repeat units on an average chain based on number-average molecular weight of 960. Thus our results showed that there are 17–20 backbone atoms in the segment of poly(phenylacetylene). Assuming the polymer segment to be of spherical shape, the diameter of the sphere was found to have a range of 11.7–12.4 A.

Studies on the copolymer composition of sulphur dioxide and phenylacetylene

Abstract The polysulphone copolymers synthesized from the copolymerization of liquid sulphur dioxide and phenylacetylene in the presence of tert-butyl hydroperoxide at low temperature always have an alternating structure which is independent of solvent, temperature and feed ratio. At a relatively high temperature (50°C) the phenylacetylene SO 2 system initiated by AIBN gave copolymers with a 1:1 mole ratio, whereas styrene SO 2 under the same conditions produced copolymers with 2:1 molar ratio. The free radical initiators hydrogen peroxide, m-chloroperbenzoic acid, and diphenyl peroxide were inert at low temperatures. The PhC  CH SO 2 system with (CH3)3COOH at low temperature is more reactive than PhCH  CH 2 SO 2 but with AIBN at high temperature the reactivities are reversed. These observations suggest that different mechanisms should operate on the two systems.

Structural stability of poly(1-propyne) dimers and trimers

The relative thermodynamic energies of the poly(1-propyne) dimers and trimers show that both the conjugation and steric forces play an important role on the structural stability of these molecular systems. The two 1,4-disubstituted butenyne cis and trans dimers are predicted to be practically the same in energy, whereas the 2,4-disubstituted butenyne dimer is of relatively lower thermodynamic stability. The trimers, cis-trans (structure 4) and trans-trans (structure 10), are calculated to be relatively stable, and thus it is more likely that the polymer formation is based on these two trimers with the tail-head-tail-head addition.

ESR Spin radical trapping in dehydrohalogenation of alkyl halides catalyzed by molybdenum hexacarbonyl

Abstract The dehydrohalogenation of some aliphatic alkyl halides catalyzed by molybdenum hexacarbonyl produces organic free radicals in solution. These transient radical species were trapped by using spin-trapping techniques and formed stable organic compounds whose structures were elucidated. Based on the structures of these spin-radical adducts, a dehydrohalogenation mechanism was proposed for each reaction system.

Characterization of polycyclohexene by high field 13C-NMR spectroscopy

Summary13C NMR spectrum of polycyclohexene is recorded at 50.5 MHz and interpreted in terms of its different stereoisomers. The ratio of threo to erythro forms in the polymer is 2∶1. The spectrum is also sensitive to tacticity of the polymer chain.