Platinum thiophene, reactions with

The reaction of butadiene with the sulfone of 3-benzo[6]thiophene-carboxylic acid under Diels-Alder conditions gives the adduct (32). Catalytic reduction over platinum oxide removes the 2,3-double bond. 

Bauerle and co-workers have synthesized a macrocycle consisting of 8 thiophenes in conjugation by an oxidatively induced elimination of platinum complexes <03CC948>. The platinum complexes 55 were obtained by reaction of terthiophene with terminal acetylenic groups with cw-Pt(dppp)Cl2 in the presence of Cul and EtsN. C-C bond formation was effected by oxidatively induced elimination using iodine and the diacetylene bridged thiophene macrocycle 56 was converted to an all thiophene macrocycle 57 by reacting with sodium sulfide. 

The detoxification of catalysts poisoned by Group V or VI compounds can be accomplished by reactions in which these inhibitors are converted to substances that do not have unshared electron pairs. For instance, bivalent sulfur compounds can be oxidized to sulfones or sulfonic acids by treatment with hypochlorite or hydroperoxides. "2,108 Thiophene, dimethyl sulfide and other sulfur and metal ion poisons as well as phosphorous"" and arsenic compounds " can be removed from platinum by washing the catalyst with acetic acid. This method for the reactivation of the catalyst is simpler than the oxidation techniques. Acidic or basic inhibitors are removed by the addition of an appropriate amount of base or acid, respectively. The effect of a small amount of inhibitor can frequently be overcome by the use of a larger amount of catalyst. 

The effect, for this reaction, is apparently peculiar to catalysts of the nickel chromite type, since the addition of thiophene to a system containing Raney nickel, or of either thiophene or biphenyl sulfide to a similar system containing either platinum or palladium, did not lead to similar results. It may be noted that this reaction is not one involving the isolation of an intermediate product and the action of the sulfur compound seems difficult to explain. In another paper, by Adkins and Billica (44), it was also shown that the hydrogenation of ethyl lactate to 1,2-propanediol with Raney nickel is accelerated by adding small quantities of triethylamine. 

Electrosynthesis is based on the use of an electrochemical cell and a requisite for this technique is the use of electroactive moleeules, for example thiophene, pyrrole and aniline among organic monomers. The experimental setup is based on a galvanic cell, a potent ostat and two electrodes [206], as schematized in Fig. 1.18. The monomer is solubilized typically into organic solvents or in aqueous media and usually an electrolyte (e.g. lithium perchlorate or tetrabutylammonium acetate) is added. Platinum, carbon rods, magnesium, mercury, stainless steel can be used as electrodes and the electrosynthesis can be carried out with constant potential or constant current. The choice of the electrodic material, its shape and size play a cmcial role in many electrochemical reactions. 

Electrochemical Reactions.— The electrochemical oxidation of 2- and 3-methylthiophens with methanolic ammonium bromide as electrolyte on a carbon or platinum anode gives 5-bromo-2-methylthiophen and 2-bromo-3-methylthiophen as main products. Electrochemical oxidation of methyl thiophen-2-carboxylate on a graphite anode in methanolic sulphuric acid gives the cis and trans forms of (133). Methyl thiophen-3-carboxylate yields (134). On the other hand, electrolysis of thiophen-2-carboxylic acid in DMF on platinum electrodes gives (135). ... 

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