Electrolytic alternative to some Clemmensen reductions
Electrolytic alternative to some Clemmensen reductions
Some electrochemical procedures have been developed as alternatives to those reductions presently carried out with metal powders in aqueous acid; emphasis have been placed on defining conditions where the electrolyses can be carried out in high yield and at high enough current density to permit the possibility of an acceptable space-time yield. The reductions studied include that of 2,3,5-tribromothiophen to 3-bromothiophen, acetophenones to ethylbenzenes and nitrocompounds to anilines. The reduction of 2,3,5-tribromothiophen was carried out in aqueous dioxan containing sodium bromide. The yield of 3-bromothiophen was highest (92%) at very negative potential close to that for hydrogen evolution, elevated temperature and in a solvent consisting of 70% dioxan/30% water; the electrode material was relatively unimportant. The maximum current density in the laboratory cell was 60 mA cm-2. The choice of a bromide electrolyte allowed recovery of bromine at the anode but other scale up strategies including in situ bromination of thiophen in an undivided cell were also considered. A number of conditions were considered for the reduction of the acetophenones to the hydrocarbons but the reaction was only successful using a Pt/Pt cathode in acidic anhydrous ethanol. In constant current electrolyses,l-phenylethanol was also formed but it was found that the ratio of ethylbenzene/1-phenylethanol increased sharply if the current was reversed periodically in order to reactivate the surface of the electrode. In this reaction current densities up to 200 mA cm -2 were possible and the yield of ethylbenzene was 85%. Finally it was shown that the reduction of nitrobenzene and o-fluoronitrobenzene to the anilines was possible with a current density of 500 mA cm 72 using a novel indirect reduction. The reactions were carried out in an emulsion, the two phases being aqueous zinc chloride and the substrate and the cathode reaction was the deposition of zinc. The high current density deposition produces a fine metal powder which is free of oxidised film and hence very reactive. The yield of aniline exceeded 90%.
University of Southampton
1981
Razaq, Mohammad
(1981)
Electrolytic alternative to some Clemmensen reductions.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Some electrochemical procedures have been developed as alternatives to those reductions presently carried out with metal powders in aqueous acid; emphasis have been placed on defining conditions where the electrolyses can be carried out in high yield and at high enough current density to permit the possibility of an acceptable space-time yield. The reductions studied include that of 2,3,5-tribromothiophen to 3-bromothiophen, acetophenones to ethylbenzenes and nitrocompounds to anilines. The reduction of 2,3,5-tribromothiophen was carried out in aqueous dioxan containing sodium bromide. The yield of 3-bromothiophen was highest (92%) at very negative potential close to that for hydrogen evolution, elevated temperature and in a solvent consisting of 70% dioxan/30% water; the electrode material was relatively unimportant. The maximum current density in the laboratory cell was 60 mA cm-2. The choice of a bromide electrolyte allowed recovery of bromine at the anode but other scale up strategies including in situ bromination of thiophen in an undivided cell were also considered. A number of conditions were considered for the reduction of the acetophenones to the hydrocarbons but the reaction was only successful using a Pt/Pt cathode in acidic anhydrous ethanol. In constant current electrolyses,l-phenylethanol was also formed but it was found that the ratio of ethylbenzene/1-phenylethanol increased sharply if the current was reversed periodically in order to reactivate the surface of the electrode. In this reaction current densities up to 200 mA cm -2 were possible and the yield of ethylbenzene was 85%. Finally it was shown that the reduction of nitrobenzene and o-fluoronitrobenzene to the anilines was possible with a current density of 500 mA cm 72 using a novel indirect reduction. The reactions were carried out in an emulsion, the two phases being aqueous zinc chloride and the substrate and the cathode reaction was the deposition of zinc. The high current density deposition produces a fine metal powder which is free of oxidised film and hence very reactive. The yield of aniline exceeded 90%.
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Published date: 1981
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Local EPrints ID: 460455
URI: http://eprints.soton.ac.uk/id/eprint/460455
PURE UUID: 9deb1d35-7eb7-4e36-8263-9180333046e8
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Date deposited: 04 Jul 2022 18:22
Last modified: 04 Jul 2022 18:22
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Author:
Mohammad Razaq
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