Staff profile

Research Interests

A main area of interest is kinetic and mechanistic studies of reactions in solution. We are very well set up to make kinetic studies involving fast reactions and/or transient species. Thus in addition to conventional UV/visible spectrophotometers we have a stopped-flow spectrophotometer, allowing measurements on the millisecond timescale. The work also involves some organic synthesis and the use of NMR spectroscopy. Work is in progress in the following areas:

σ-Adduct Formation

There is much current interest in the reactions with nucleophiles of aromatic compounds activated with electron withdrawing groups. In some cases relatively stable anionic σ-adducts are formed by reversible nucleophilic attack at ring-carbon atoms while in others substitution of a leaving-group occurs. Our work in this area involves:

1. Quantitative measurement of nucleophilic reactivity and basicity. Traditionally reactivity (referring to rate of reaction) and basicity (referring to equilibria) are defined for reaction of nucleophiles with protons (e.g. pK_a values). However, in organic systems it is affinity for a carbon atom which is usually a more significant quantity. Results are being obtained which allow the comparison of carbon basicities and nucleophilic reactivities of series of oxygen, nitrogen, sulphur and carbon bases. An example is the reaction of 4,6-dinitrobenzofuroxan (DNBF) with aniline and its derivatives to produce adducts such as (1). This reaction may be regarded as nucleophilic attack on DNBF or an electrophilic substitution in aniline.
2. Rates of proton transfer reactions. Aromatic substitutions by amine nucleophiles are often subject to general base catalysis indicating that proton transfer is involved in the rate-determining step. Using model systems we are measuring the rates of proton transfer between nitrogen atoms to assess the effect that steric effects may have in reducing the rate constants for proton transfers.

Condensation of Carbonyl Compounds with Amines

Condensation reactions of amines with formaldehyde in the presence of a nucleophile are potentially useful in synthesisStudies are in progress on the kinetics and equilibria involved in the individual steps of the overall process and the identification of iminium ions as intermediates. Work at present is concentrating on reactions with sulfite and cyanide as nucleophiles, with aniline or benzylamine derivatives as the amine.

Nitration in Inert Fluids

Traditional methods of nitration may give rise to large quantities of spent acid which present a waste-disposal problem. Studies are underway to partially or totally replace the acid by polyfluorocarbons, which act as bulking agents. Nitrations of aromatic species have been successfully carried out using nitric acid or dinitrogen pentoxide as the nitrating agent. The good solubility of N₂O₅ in the polyfluorocarbons allows kinetic studies of nitrations in homogeneous solutions to be made.

References

1. M.R.Crampton, J. Atherton, J. Blacker and C. Grosjean, Org. Biomol. Chem., 2004, 2, 2567.
2. M.R. Crampton, R.A.E. Lunn and D. Lucas, Org. Biomol. Chem., 2003 1, 3438.
3. M.R. Crampton, T.A. Emokpae, J.A.K. Howard, C. Isanbor and R. Mondal, Org. Biomol. Chem., 2003, 1, 1004.
4. M.R. Crampton, E.L. Cropper, L.M. Gibbons and R.W. Millar, Green Chemistry, 2002, 4, 275.

• application of fast reaction techniques to the study of the kinetics and mechanism of reactions in solution
• organic reaction mechanisms

Journal Article

• Blacker, J., Clutterbuck, L.A., Crampton, M.R., Grosjean, C. & North, M. (2006). Catalytic, asymmetric Strecker reactions catalysed by titanium(IV) and vanadium(V)(salen) complexes. Tetrahedron asymmetry 17(9): 1449-1456.