Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302641
Title: Solid-supported aromatic nitrations.
Author: Lancaster, Norman Llewellyn.
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2000
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Abstract:
The efficacy of the claycop system in the nitration and the dinitration of toluene has been investigated.Comparison of regioselectivity and of rate constant with homogeneous nitric acid nitration was made. The use of ion-exchanged montmorillonite clay as a catalyst for acetyl nitrate nitration was studied. The system was found to enhance Para selectivity in the nitration of toluene and to catalyse the reaction. Additionally, the catalyst was shown to be recyclable. The reaction of toluene was too fast to allow kinetic study. However, kinetic study was possible,using chlorobenzene as substrate.Again, the system was found to decrease both the reaction time and the o-/ p- ratio. It was possible to demonstrate a dependence of rate constant upon mass of clay. The effect of the counter ion was investigated and the use of trifluoroacetyl anhydride was studied. A new system for aromatic nitration has been developed in this work using zeolite with dinitrogenp entoxide.A series of zeolites were screened in the nitration of onitrotoluene, with the H-faujasites showing the quickest reaction times and highest degree of regioselectivity. The silica/ alumina ratio of the faujasite used was varied and this was shown to have an effect on regioselectivity. However, reactions were too fast for kinetic study. The faujasite/ dinitrogen pentoxide system was used in the nitration of some deactivated benzenes using these substrates allowed kinetic studies to be made and the order in each component to be determined. It was found that nitration was zeroth order in dinitrogen pentoxide, that the reaction obeyed a first order rate law, and that the first order rate constant was proportional to the mass of zeolite used. Comparison of the relative rates of nitration of 1-chloro-2-nitrobenzene1, -chloro-4-nitrobenzene and nitrobenzeneb y this system to the relative rate constants of nitronium ion nitration was made. The similarity suggested that the mechanism of nitration by faujasite/d initrogen pentoxide might involve nitronium ion transfer.Amongst the H-faujasites of different silica/ alumina ratio, the rate constant was shown to increase with the aluminium content. A mechanism is proposed in which zeolite protons (present in proportion to the aluminium atoms) are first replaced by nitronium ions. The latter are transferred to the aromatic in the rate-determining step. The use of non-chlorinated solvents and the recycling of zeolite were both studied, and the nitration of 2,6-dinitrotoluene was attempted. The use of the faujasite/ dinitrogen pentoxide system was extended to the nitration of nitrogen containing aromatic heterocycles direct C-nitration of quinolone was not possible, only N-nitration. However, pyrazole was converted to 1,4-dinitropyrazole quickly and cleanly under mild conditions. It was shown that the N-nitration occurred instantly, followed by slower C-nitration. The kinetics of the second nitration were studied and comparison with deactivated benzenes was made.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.302641  DOI: Not available
Keywords: Zeolite; Dinitrogen pentoxide Chemistry, Organic Chemistry, Physical and theoretical
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