Investigations into new methods for the efficient and environmentally benign catalytic asymmetric epoxidation of alkenes

PhDThis thesis presents our investigations into the catalytic asymmetric epoxidation of alkenes. An introductory chapter highlights the importance of chirality in nature and industry. It focuses on a few relevant examples of syntheses in which the use of optically pure epoxides as building blocks is fundamental to the overall stereochemistry of the product. The introduction then continues describing the advances in the field of asymmetric epoxidation of olefins; it contains a review of a wide range of the ligands and metals employed in the recent literature together with a range of different oxidants. A section on organocatalytic epoxidations concludes this chapter. A second chapter presents attempts to impart enantioselectivity in the epoxidation of olefins by employing chiral additives (BINOL derivatives) in conjunction with a known oxidising system, TMTACN/manganese with hydrogen peroxide as the oxidant. A brief electrochemical study of the redox potential of the catalytic systems described in this chapter and a study of the effect of the electronic properties of the substrates on the reaction is also reported. The third and fourth chapters describe the synthesis of a series of tri- tetra- and pentadentate ligands based on the backbone of L-proline and trans-diaminocyclohexane. The chapters contain the results of the screening of the above mentioned ligands in the epoxidation of alkenes with a number of metal salts using either hydrogen peroxide or peracetic acid as the oxidant. Single crystal X-ray structures of some of the new ligands are also presented herein. A final experimental chapter presents the supporting characterisation data associated with the compounds synthesised

Catalytic and mechanistic studies into the epoxidation of styrenes using manganese complexes of structurally similar polyamine ligands

Two structurally similar polyamine ligands (7 and 8) have been prepared, which differ only by the presence of either a secondary or tertiary nitrogen donor within their N5 donor set. The ligands, in combination with iron and manganese salts, have been screened for their efficacy as catalysts for the epoxidation of styrene, using both hydrogen peroxide and peracetic acid as oxidants. Clear differences in activity between the two systems were observed, with 7 proving most effective in the presence of MnSO4 with H2O2, whereas ligand 8 proved to be effective with Mn(OTf)2, MnCl2 and Mn(ClO4)2 using peracetic acid as the oxidant. A Hammett analysis of the initial rate kinetics of the optimal systems, combined with analysis by UV-vis spectroscopy, indicates that the small structural differences in the ligands elicit profound changes in the nature of the active species formed

Le identit\ue0 regionali e l'Europa

Vi appare il mio saggio: "Letteratura e canone: le ragioni dell'identit\ue0 culturale. Jeanette Winterson e J.M. Coetzee", pp. 95-104. This essay examines how the choice of a literary 'canon', by adopting universal and essentialist notions of identity, history, and values, tends to erase notions of cultural and gendered difference. The essay therefore aims at showing why marginal identities (gendered, postcolonial, regionalist ones) are often forced to assume a 'strategic essentialism' in order to simply make themselves heard and thus dismantle the authoritian stance of those essentialist positions often at work in the academia and in its priviledged establishment of 'the' canon. Some works of both authors are thus examined from the point of view of these critical, cultural studies standpoints. The essay furthermore aims to show why 'critical regionalism' has to be considered an important instance of the many and possible strains of cultural studies

Initial rate kinetic studies show an unexpected influence of para-substituents on the catalytic behaviour of manganese complexes of TMTACN in the epoxidation of styrenes with H2O2

Investigations into the efficacy of a range of enantiomerically pure BINOL additives in the epoxidation of styrene substrates with a number of manganese catalysts prepared from the ligand 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN, using hydrogen peroxide as the oxidant have revealed that there are fundamental differences in reactivity between apparently similar systems. Whilst no asymmetric induction was obtained in the styrene oxide products formed, the data obtained from initial rate kinetic studies appear to be consistent with a number of different catalytically active species operating, the nature of which are profoundly affected by the starting materials used