Kinetics and mechanism of the gas phase reactions of thermally and chemically activated alkyloxiranes
Kinetics and mechanism of the gas phase reactions of thermally and chemically activated alkyloxiranes
The gas phase thermal decompositions of 2, 3-epoxy-1.1, 1-trifluoropropane (A) (677-741 K. 6-130 torr), 2,3-direthyl-2,3-epoxyhutane (B) (642-733 K. 6-25 torr) and 2,3-dimethyl-2.3-epoxypentane (C) (638-727 K, 4-14 torr) have been investigated in aged reaction vessels Arrhenius parameters were determined for the homogeneous, unimolecular formation of the major products. Pyrolysis of A, in the presence of 8% nitric oxide to reduce the amount of fragmentation, gave 1.1, 1-trifluoroproparone and 3. 3. 3-trifluoropropanal as major products. Some pressure dependence was observed in the measured rate constants which could be explained in terms of chemical activation effects. When pyrolysed B gave propene, propanone, 3,3-dimethylbutan-2-oneand 2,3-dimethylbut-l-en-3-ol as major products with rate constants for their formation independent of pressure.The pyrolysis of C gave the following major products ; propene,propanone, but-l-ene, hut-2-ene, butanone, 2,2-dimethylpentan-3-one, 3,3-dimethylpentan-2-one. 2,3-dimethylpent-l-en-3-ol, 3-ethyl-2--methylbut-3-en-2-ol and 2,3-dirrethylpent-3-en-2-ol. The rate constants for the formation of these products were independent of pressure. The mechanism for formation of the major products is discussed with a biradical mechanism proposed for formation of isomeric ketones (and/ or aldehydes) and a concerted mechanism for formation of allylic alcohols. Some degree of ionic character in the transition states for these reactions is supported. Vinyl ethers are also thought to be a major primary product formed via a biradical mechanism, but at the temperature of the study these ethers rapidly decomposed to an alkene and a carbonyl compound. This was confirmed in the current work by a separate investigation of the thermal decomposition of 2-(1-methylethoxy)propene (554-610 K, 12-70 torr) to form propene and propanone. The reaction of B with methylene in the presence of oxygen wasinvestigated with ketene as the methylene precursor. Four major r products were found ; C, propanone. 2, 3-dimethyl-2, 3-epoxybutanalrand 2,3-dimethylbut-2-ene. When diazomethane was the methylene precursor, only C and 2,3-dimethyl-2,3-epoxybutanal resulted from photolytic reactions. 2, 3-dimethylbut-2-ene was formed by a dark reaction. The mechanism of the formation of each of the products is discussed. No products resulting from the chemically activated decomposition of C were observed and RRKM calculations showed that this was the expected behaviour.
University of Southampton
Honeyman, Malcolm Richard
1981
Honeyman, Malcolm Richard
Honeyman, Malcolm Richard
(1981)
Kinetics and mechanism of the gas phase reactions of thermally and chemically activated alkyloxiranes.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The gas phase thermal decompositions of 2, 3-epoxy-1.1, 1-trifluoropropane (A) (677-741 K. 6-130 torr), 2,3-direthyl-2,3-epoxyhutane (B) (642-733 K. 6-25 torr) and 2,3-dimethyl-2.3-epoxypentane (C) (638-727 K, 4-14 torr) have been investigated in aged reaction vessels Arrhenius parameters were determined for the homogeneous, unimolecular formation of the major products. Pyrolysis of A, in the presence of 8% nitric oxide to reduce the amount of fragmentation, gave 1.1, 1-trifluoroproparone and 3. 3. 3-trifluoropropanal as major products. Some pressure dependence was observed in the measured rate constants which could be explained in terms of chemical activation effects. When pyrolysed B gave propene, propanone, 3,3-dimethylbutan-2-oneand 2,3-dimethylbut-l-en-3-ol as major products with rate constants for their formation independent of pressure.The pyrolysis of C gave the following major products ; propene,propanone, but-l-ene, hut-2-ene, butanone, 2,2-dimethylpentan-3-one, 3,3-dimethylpentan-2-one. 2,3-dimethylpent-l-en-3-ol, 3-ethyl-2--methylbut-3-en-2-ol and 2,3-dirrethylpent-3-en-2-ol. The rate constants for the formation of these products were independent of pressure. The mechanism for formation of the major products is discussed with a biradical mechanism proposed for formation of isomeric ketones (and/ or aldehydes) and a concerted mechanism for formation of allylic alcohols. Some degree of ionic character in the transition states for these reactions is supported. Vinyl ethers are also thought to be a major primary product formed via a biradical mechanism, but at the temperature of the study these ethers rapidly decomposed to an alkene and a carbonyl compound. This was confirmed in the current work by a separate investigation of the thermal decomposition of 2-(1-methylethoxy)propene (554-610 K, 12-70 torr) to form propene and propanone. The reaction of B with methylene in the presence of oxygen wasinvestigated with ketene as the methylene precursor. Four major r products were found ; C, propanone. 2, 3-dimethyl-2, 3-epoxybutanalrand 2,3-dimethylbut-2-ene. When diazomethane was the methylene precursor, only C and 2,3-dimethyl-2,3-epoxybutanal resulted from photolytic reactions. 2, 3-dimethylbut-2-ene was formed by a dark reaction. The mechanism of the formation of each of the products is discussed. No products resulting from the chemically activated decomposition of C were observed and RRKM calculations showed that this was the expected behaviour.
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Published date: 1981
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Local EPrints ID: 459717
URI: http://eprints.soton.ac.uk/id/eprint/459717
PURE UUID: e0212d10-d53c-4d21-99f2-4f90fad6e6d7
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Date deposited: 04 Jul 2022 17:17
Last modified: 04 Jul 2022 17:17
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Malcolm Richard Honeyman
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