William Ronald Sanderson

Cleaner industrial processes using hydrogen peroxide

Recent research progress in catalytic systems for potential use with hydrogen peroxide in industrial chemical synthesis is reviewed, with special focus on work published in the last five years. The main types of chemistry employed are critically appraised regarding their suitability for industrial exploitation. The most significant catalyst types are discussed in terms of the positive features identified to date, and the obstacles yet to be surmounted in order to become more widely adopted. It is believed that fully inorganic systems have more scope for commercialization than those containing organic ligands or supports, however robust. Critical targets are larger-pore analogs of titanium silicalite TS-1, more exploration of smectite-based materials, effective immobilization of activated metal peroxo systems, and improvements in design and manipulation of polyoxometallate compounds. Cooperation between branches of chemistry that have not traditionally worked closely together is advocated.

N,N-Dialkylalloxans—a new class of catalyst for dioxirane epoxidations

N,N-Dimethyl- and N,N-dibenzylalloxans 1a and 1b have been prepared and used as novel dioxirane catalysts for the epoxidation of a range of di- and tri-substituted alkenes in good to excellent yield. The dibenzylalloxan 1b can be recovered in high yield with no evidence of catalyst decomposition.

The selective oxidation of toluenes to benzaldehydes by cerium(III), hydrogen peroxide and bromide ion

Abstract 4- t -Butyltoluene can be oxidised in acetic acid to 4- t -butylbenzaldehyde by hydrogen peroxide in a process catalyzed by cerium(III) and bromide ions. The conversion proceeds via benzylic bromination, hydrolysis of the bromide to alcohol and the rapid oxidation of the alcohol to the aldehyde by bromine. The reaction is ineffective in the absence of bromide but is also inhibited by significant quantities of the ion, apparently because the hydrolysis step is reversible. The role of the cerium has not been clearly established. Cerium(IV) is formed in the system but the first step appears not to involve electron transfer from the aromatic ring. Nor can simple radical bromination explain the rate of formation of benzylic bromide.

Mechanisms of peroxide stabilization. An investigation of some reactions of hydrogen peroxide in the presence of aminophosphonic acids

It has been established by continuous-flow studies in conjunction with EPR spectroscopy that the aminophosphonic acids 1–4 accelerate significantly the Fenton reaction between FeII and H2O2 in aqueous solution via complexation of the metal ion (with values of the rate constant k for the generation of the hydroxyl radical up to 2 × 105 dm3 mol–1 s–1 at room temperature). To a certain extent this behaviour parallels that of EDTA and some structurally-related aminocarboxylic acids. It is also shown that the N-oxides of the aminophosphonic acids 1–3 react readily with the hydroxyl radical to give long-lived nitroxides viaβ-scission of first-formed carbon-centred radicals.Neither of these findings is believed to correspond to the major chemistry which underlies the efficacy of these ligands as peroxide stabilizers. It is suggested instead that the crucial role of these compounds depends upon their ability to stabilize the higher valence state of iron, and hence not only to encourage oxidation of FeII by O2˙– and H2O2 but also to prevent effective reduction of FeIII by O2˙–, HO2˙ and H2O2. However, radical scavenging by N-oxides may be a secondary, contributory factor in this stabilizing function, especially in peroxide systems when the sequestrant is added before storage, when slow N-oxidation is to be expected.

2-Bromocyclohexanone Perhydrate—X-ray Crystal Structure and Conformational Effects on Reactivity in Sulfoxidations

Abstract The remarkably stable crystalline perhydrate 1 derived from α-bromocyclohexanone has been characterised by X-ray crystallography providing the first example of a perhydrate crystal structure. Perhydrate 1 exists in alternative chair conformations in chloroform and tetrahydrofuran with the bromine substituent occupying equatorial and axial positions, respectively. The perhydrate 1 can oxidise sulfides to sulfoxides in good yields in dichloromethane but not in tetrahydrofuran. The requirement for bromine to be equatorial for a stable perhydrate to form is demonstrated using conformationally locked cis and trans 2-bromo-4- tert -butylcyclohexanones in which case only the cis isomer 4a forms a perhydrate.

A convenient large-scale synthesis of methyl α-maltoside: a simple model for amylose

Abstract Methyl 4- O -( α - d -glucopyranosyl)- α - d -glucopyranoside (methyl α -maltoside), a model compound for amylose, has been synthesized in four steps and 63% overall yield from relatively inexpensive d -(+)-maltose.

Novel Catalysts for Olefin Cleavage Using Hydrogen Peroxide

Abstract Transition metal oxides are well-known reagents for cleaving olefinic double-bonds. Due to toxicity and expense, catalytic amounts of the metal species, along with a co-oxidant are favoured. Whilst hydrogen peroxide and ruthenium give good results for many olefins, poor results are obtained for, amongst others, terminal double bonds. This paper reports the use of a second metal to extend the range of cleavage reactions using hydrogen peroxide as oxidant, with good efficiency of peroxide usage.

New Oxidations of Organic Substrates Using Hydrogen Peroxide and Supported Heteropolyacid Catalysts

Oxidation processes employing aqueous hydrogen peroxide in the presence of heterogeneous catalysts offer significant advantages over traditional liquid-phase processes in terms of cost, safety and environmental impact. We have previously shown1 that catalysts prepared by depositing phosphotungstic acid on gamma-alumina, followed by calcination, are active for the selective epoxidation of olefins using 35% H2O2. These catalysts have been demonstrated conclusively to operate heterogeneously, with essentially no observable leaching of tungsten into the reaction solvent (aqueous t-butanol). They may also be recycled many times without significant loss of activity. Best results are obtained with cyclic alkenes, there being no detectable steric limitations on the substrates which can react.

Decomposition of peroxydecanoic acid using BCHPC [di(4-tert-butylcyclohexyl) peroxydicarbonate] under argon atmosphere

Using BCHPC as a source of alkoxycarbonyloxyl radical at moderate temperature in benzene or cyclohexane and in the absence of O2(under argon), the peroxydecanoic acid RCO3H is transformed into nonan-1-ol ROH in good yield. A mechanism, implying the acylperoxyl radical RCO3˙ as an intermediate, is proposed.

Mechanisms of peroxide decomposition. An EPR investigation of the reactions between some transition metal ions (TiIII, FeII, CuI) and monoperoxyphthalic acid and its anion

Continuous-flow and spin-trapping experiments have been employed in conjunction with EPR spectroscopy to investigate the metal-ion induced decomposition of magnesium monoperoxy-phthalate (MMPP) in aqueous solution (at pH ca. 2 and 6). As with the corresponding reactions of peroxymonosulphate (HOOSO3–) it is shown that the behaviour of CuI(which leads to the formation of ˙OH and ArCO2–, Ar = 2-C6H4CO2H) is in complete contrast with that of TiIII and FeII, both of which bring about electron transfer to give ArCO2˙ and OH–. Some subsequent reactions of ArCO2˙ and Ar˙, formed by rapid decarboxylation, have been studied.