No description available.

The HOF.MeCN complex, formed from the reaction of elementary fluorine with aqueous acetonitrile, was discovered by Shlomo Rozen in 1987 and, in a series of publications, he demonstrated that the complex is a uniquely effective electrophilic oxygen transfer agent. However, it is estimated that the HOF.MeCN complex has a half life of a few hours at 0ºC and thus, must be produced and used immediately when required. In addition to this, highly exothermic, rapid oxidation processes can be problematic with reaction control and safety when reagents are added into an excess of a highly oxidizing medium. Consequently, scale-up of oxidations to a larger industrial level using the HOF.MeCN complex in batch processes would not be possible. In recent years, continuous flow reactors using microchannels have been viewed as a viable method for avoiding many of the problems encountered when a laboratory process is scaled-up. The low chemical inventory of such reactors means that even highly reactive reactions can be performed safely and, with the application of multiple reaction channels in parallel, large quantities of product can be easily obtained. In this thesis we present new continuous flow methodology for the in situ generation of HOF.MeCN and, without isolation, immediate substrate oxidation in a two-step process. The continuous process, therefore, provides a genuine method for oxidizing large quantities of material, without the problems associated with batch oxidations. Scale-up oxidations of various amines, alkenes, and anilines are also presented along with a safe and accurate method for calibrating HOF.MeCN amounts.

The aim of this work was to synthesis a range of substituted arene hydrates, determine their second-order rate constant for dehydration and generate a Hammett plot for comparison with other published p-values for similar carbocation-forming reactions. The first hydrate presented is the methyl benzoate hydrate (see section 2.1). A number of first order rate constants for the aromatisation (dehydration) reaction were determined in dilute perchloric acid at ionic strength 0.5 maintained with sodium perchlorate. The reaction was followed by UV-Vis spectrophotometry and (^1)H NMR spectroscopy. The second order rate constant was determined to be 9.32 X l0(^-2) М(^-1)s(^-1) which corresponds to a half-life of 7 seconds in 1M HCIO(_4). The arene hydrate of biphenyl was also synthesised (see section 2.2). The solubility issues discussed in section 2.2.2 meant the aromatisation reaction could not be followed by (^1)H NMR spectroscopy. The first order rate constants were determined in acetate and phosphate buffers, at ionic strength 0.5, maintainted with sodium Perchlorate, from pH 5 to 7. The second order rate constant was determined to be 2.11 X 10(^2) M(^-1)s(^-1) which corresponds to a half-life of 3.3 X 10(^-4)s in 1M HCIO(_4). As presented in sections 2.3-2.7, the synthetic route to the alkyl substituted hydrates gave two products - the ortho and the ipso hydrates. In the case of the ethyl substituted hydrate only the ortho hydrate was synthesised. For R = tBu, only a small proportion of the products formed was the ipso hydrate due to Its reactivity. The ortho and ipso hydrates of toluene and cumene were both synthesised. These could not be separated and so the aromatisation kinetics were followed in situ and fitted to a double exponential equation. The aromatisation reactions were followed by UV-vis spectrophotometry in acetate and phosphate buffers at 25 С and ionic strength 0.5 M, maintained with sodium perchlorate. The second-order rate constants for aromatisation for the ortho-hydrates were determined to be for R = Me, Et, iPr, tBu and are 514, 538, 642 and 949 M (^-1)s(^-1), respectively. The second-order rate constants for aromatisation for the ipso-hydrates isolated were determined to be for R = Me and iPr are 9.81x10(^3) and 1.47 X 10(^4) (^-1)s(^-1). A number of linear free energy correlations were attempted and the best correlation was found with σ(^+), this is consistent with a reaction involving a planar carbocation with through-bond stabilisation. The p-value was determined to be -6.5. The published p- value for the cis dihydrodiols, where a better correlation with Op was reported, is -8.2(^1). The magnitude of p suggests the hydrates have an earlier transition state to carbocation formation than the diols with less positive charge build-up. The computational results show that the carbocation intermediate formed during the aromatisation reaction of the hydrates is planar whereas the carbocation intermediate generated from the diols is puckered. This corroborates the results from the kinetic analysis and also the magnitude and sign of the p-values from the Hammett correlations. When the carbocation intermediate is puckered, the through-bond stabilisation is hindered and so a poor correlation with σ(^+) is observed. The rate constant for acid-catalysed isomerisation of optically active cis-indene dihydrodiol was determined. This represents the rate constant for formation of the corresponding carbocation intermediate. The second-order rate constant for carbocation formation (k(_H)) was determined by (^1)H NMR spectroscopy in concentrated perchloric acid to be 1.11 X 10(-6) M (^-1)s(^-1). This is comparable with the second-order rate constant for carbocation formation in teri-butanol which is 1.4 X 10(^-6) M(^-1)s(^-1). The rate constant for reaction of the carbocation intermediate with water k(_H20) determined using the azide- trapping technique, is 4.99 X 10(^8) s(^-1). Combining k(_H20) with k(_H) allows the (_p)K(_R) of the indene dihydrodiol carbocation to be calculated. The (_p)K(_R) was determined to be -14.6. This is greater than the (_p)K(_R) of the indanol carbocation. The effect of the adjacent hydroxyl group counteracts the stabilising effect of the benzylic substituent.

In 1963, Bruce Merrifield introduced the solid-phase peptide synthesis technique using an insoluble macromolecular protecting group for synthesising peptides. Since then organic chemistry involving solid supports has been developed as an efficient technique for the synthesis of a large number of organic compounds, and therefore a significant interest has been raised in catalysis. This thesis deals with the synthesis of new supported Mo catalysts active, selective and stable for the epoxidation of olefins on an industrial scale using a continuous reactive distillation rig and also in multi-step fine chemical syntheses. Here I report on the immobilisation of molybdenum (VI) complexes supported on polymer beads or resins and an inorganic MCM-41 support for the catalytic epoxidation of alkenes with alkyl hydroperoxides as the oxidants. Specifically Mo0₂(acac)₂ has been successfully supported on a commercially sourced polybenzimidazole (PBI) resin using a simple ligand exchange reaction. In addition a number of chloromethylated polystyrene resins has been synthesised by suspension copolymerisation of appropriate mixture of vinyl benzyl chloride (VBC) and divinylbenzene (DVB), in the presence of porogenic solvents when required. The VBC residues have been reacted with several different donors ligands 2-aminomethylpyridine (AMP), 2-aminophenol (2-AMPH), glycine (GLYC), iminodiacetic acid (lMDA) ethylenediaminetetraacetic acid (EDTA) and phenylalanine (Phe) in order to create binding sites for the metal on each polymer matrix. However the inorganic MCM-41 support was first modified with aminopropyl trimethylsilane, then the thiophene-2-carboxyaldehyde ligand was attached in order to generate binding sites for the metal on this support. Ligand exchange with Mo0₂(acac)₂ again allows Mo (VI) species to be supported on these supports. Each resin supported Mo has been activated by treatment with t-butylhydroperoxide (TBHP) and then investigated as a heterogeneous catalyst in the epoxidation of cyclohexene and styrene using TBHP. An ¹H NMR spectroscopic analytical procedure has been used to monitor the progress of each epoxidation. In order to check the stability of each of these supported Mo catalysts prior to using them in a reactive distillation column, extensive study of recycling of each support Mo catalyst was undertaken by monitoring the use of a sample of each in up to 5-10 successive batch epoxidations. At the same time the supernatant solution from each epoxidation has been isolated, reduced to a dry residue, and the latter employed as a potential catalyst in an epoxidation reaction. The latter procedure is a very powerful methodology for the detection of low levels of catalyst (Mo) leaching in the heterogeneous reactions. PBI.Mo, polystyrene-supported Mo and inorganic supported Mo catalysts have proved to be very active, maintaining this activity over 5 to 10 cycles. However, the residues from supernatant solutions have also proved to be catalytically active demonstrating the occurrence of Mo leaching from PBI.Mo and polystyrene-supported Mo catalysts. In the case of the PBI supported Mo catalyst (PBI.Mo), the level of leaching fell substantially over 10 cycles until the rate of epoxidation was close to that of a control epoxidation reaction carried out in the absence of any Mo species. Leaching from one of the polystyrene-supported Ps.AMP.Mo (25) catalysts was more pronounced and remained significant even after several cycles. However, a second sample of polystyrene-supported Ps.AMP.Mo (26) with a higher ligand: metal ratio showed a much lower tendency to leach. This result has now been confirmed with a third sample of this type of polymer catalyst (Ps.AMP.Mo (27). Other polystyrene resin supported Mo catalysts employing the 2-AMPH, GLYC, IMDA and EDTA ligands have also been tested. These are all very active cyclohexene epoxidation catalysts and extensive recycling and leaching experiments have also been carried out in order to assess again if these ligands offer improved stability towards Mo leaching. A similar study has also been carried out with the inorganic MCM-4I.SB.Mo (32) catalyst. Several of these supported Mo catalysts have also been assessed on a small scale e.g. for fine chemical syntheses, and they also show relatively good conversion of olefins to their corresponding epoxides using different solvents or no solvent. PBI.Mo has also been tested in a reaction distillation column. It shows very high reproductive conversion and good selectivity in the case of cyclohexene epoxidation with conversion of TBHP up to 97% after 1 h.

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This thesis is concerned with a study of the decomposition of formic acid, and of methanol, on alloy catalysts of copper and nickel with particular reference to the electronic factor in catalysis.

No description available.

The chemistry of methoxyl has been reviewed with emphasis placed on quantitative experiments. The following reactions have been discussed: radical production, combination, disproportionation and hydrogen abstraction. There is very little quantitative information available on the metathetical reactions of methoxyl radicals, and in particular no previous studies of hydrogen abstraction from C2 to C5 alkanes has been reported for methoxyl or any other alkoxyl radical. Three approaches to the study of the metathetical reactions of methoxyl have been described. The first two methods, which depended on measuring the rate of formation of products, had to be abandoned because analysis showed that the systems were more complex than previous work had indicated. The third and apparently successful approach depended on measuring consumption of reactants when methoxyls were generated in mixtures of alkanes between 200 °C and 400°C: CH3O + R1H = CH3OH + R1 CH3O + R2H = CH30H + R2 The alkyl radicals were removed by nitric oxide. The experiments were oerformed in a cyclic flow system and the residual alkanes were estimated by the Janak technique of gas chromatography.