Chemistry: electrical and wave energy – Processes and products
Patent
1979-08-13
1983-03-22
Edmundson, F.
Chemistry: electrical and wave energy
Processes and products
204 59R, C25B 302
Patent
active
043774539
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrochemical synthesis and to the product.
It has been desired to obtain products for intermediates which in normal electrolysis are destroyed by unwanted processes at the counter-electrode or by counter-ions from the counter-electrode. For example, the intermediate might be a nitrilium ion produced by anodic oxidation of a hydrocarbon, the nitrilium ion then being hydrolysed. Electrolysis, despite its advantages, has therefore not been available for syntheses relying on such intermediates as nitrilium ion in aqueous environments.
According to this invention, we perform a liquid-phase electrochemical reaction in the presence, in the liquid, of a solid trapping agent (such as a polymeric resin) separable from the liquid, which trapping agent bonds to a charged species produced at one electrode, so that the charged species is not further electrolysed or affected by the liquid. The bonded trapping agent may then (i.e. after the reaction, or, more generally, after sufficient reaction) be separated (by filtration or otherwise) from the liquid and regenerated, thus liberating a product derived (e.g. by hydrolysis contingent on the regeneration) from the charged species.
The particles of trapping agent should be large compared with a molecule of the charged species so that even if the particles (carrying bonded charged species) are jostled against the counter-electrode, only a negligible proportion of that charged species undergoes reaction there. The particles must also be large enough to be separable from the electrolyte. Since the trapping agent must therefore not be a solution or emulsion, and must be a solid of relatively large particle size, and since further it should have a functional group suitable for trapping the charged species (preferably not by an electrostatic ion-pairing effect, which would be reversible, but rather by a true chemical (e.g. covalent) bonding which is irreversible in situ), the preferred trapping agent is a polymer resin such as a sulphonated polystyrene; this material will covalently bond to dissolved cations, such as may be produced at the anode of an electrolytic cell.
The material may then be removed, most conveniently by filtration, from the cell and treated with an aqueous alkali (e.g. NaOH or KOH), when it liberates the cations, which are hydrolysed.
By this scheme, products can be obtained from intermediates which in normal electrolysis would be destroyed at the counter-electrode or by counter-ions from the counter-electrode. For example, as already mentioned, the intermediate may be a nitrilium ion produced by anodic oxidation of a hydrocarbon, the nitrilium ion then being hydrolysed.
The invention will now be described by way of example.
EXAMPLE 1
Production of Pentamethylbenzylacetamide
Adamantane, dissolved in acetonitrile, was oxidized conventionally in an electrolytic cell (having a sintered glass frit divider) at a platinum anode using added tetra-n-butylammonium fluoroborate (n-C.sub.4 H.sub.9).sub.4 NBF.sub.4 (0.1 M) as electrolyte. In the anolyte compartment there was present, in suspension, a cation exchange resin carrying sulphonic acid groups (available as Dowex 50W-X8 of size range 100-200 B.S. mesh). Upon oxidation, adamantane gives the 1-adamantyl carbonium ion, which on contact with the solvent gives the nitrilium ion. The nitrilium ion is trapped by the resin, that is, the negative sulphonate groups of the resin covalently bond the positive nitrilium ions. When electrolysis is complete, the resin is recovered by filtration and is washed with acetonitrile. The desired product, N-1-adamantylacetamide, is liberated readily by stirring the resin for 1 hour with sodium hydroxide solution (whereby the product is derived by hydrolysis of nitrilium ion) followed by ether extraction.
Thus oxidation of hexamethylbenzene (108 mg) in acetonitrile (40 ml) at 1.26 V with an initial current of 19 mA which fell to 0.05 mA after 18 hours gave in the presence of the resin (3.10 g), pentamethylbenzylacetamide (115 mg; 84% yield) by followin
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Bewick Alan
Mellor John M.
Pons Bobby S.
Edmundson F.
National Research Development Corporation
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