POLAROGRAPHY OF SULFONIUM SALTS¹

Abstract

Polarographic studies of sulfur linkages other than the disulfide group have been reported. Schwabe (1) studied the polarographic reduction of p-rhodaniline. Bonner and Kahn (2) investigated the polarography of several carbohydrate analogs of S-alkylthiuronium salts. The present report deals with the polarographic reduction of trimethylsulfonium and cresyldimethylsulfonium salts.Early reports on the polarographic reduction of substituted ammonium and quaternary ammonium salts were made by Podrauzek (3) and Pech (4). The poorly defined waves found by Pech for quaternary ammonium salts suggested (5) the possibility that these reductions correspond merely to the decomposition voltage of water. Van Rysselberghe and McGee (6) showed that specific halfwave potentials can be found for different ammonium and quaternary ammonium ions. This later work (6) seems to indicate a "true" polarographic reduction for quaternary ammonium salts at the dropping mercury electrode.A previous report (7) from this laboratory dealt with the mechanism of the polarographic reduction of iodonium salts. The present investigation of sulfonium salts extends the polarographic study of "onium" compounds.Symmetrically substituted sulfonium salts are easily prepared by the usual bimolecular SN2 "onium" reaction. If the sulfonium salt is not symmetrical, it will usually decompose partially into other more stable sulfonium salts that have smaller molecular weights and are symmetrically substituted. Disproportionation and recombination finally yields an equilibrium mixture if sufficient time is allowed. Ray and Levine (8) discuss the equilibrium problem in preparing "mixed" sulfonium salts. Alkyl and aralkyl halides or methosulfates formed in disproportionation reactions are capable of exchange type recombinations, thereby yielding "mixed" water-soluble sulfonium salts. By-products that are water-insoluble are often formed if aryl groups are involved in the reaction.In the present case, sulfate analyses indicate that the water-soluble layers correspond to two-thirds 0-and m-cresyldimethylsulfonium methosulfates and onethird trimethylsulfonium methosulfate. No attempt has been made to separate these similarly soluble salts from their mixtures. Polarographic results on these naturally formed mixtures and on pure trimethylsulfonium salts confirm the conclusions indicated by sulfate analyses. Typical composite recorded sulfonium salt polarograms are shown in Figure 1. Pertinent polarographic results are given in Tables I and II. Pure trimethyl-

Binding Energy in the One-Electron Reductive Cleavage of S-Adenosylmethionine in Lysine 2,3-Aminomutase, a Radical SAM Enzyme

“…The one-electron reductive cleavage of trialkyl sulfonium ions leads to alkyl radical products. Both electrolytic reduction at electrodes and chemical reduction by low potential iron sulfur clusters of the type [4Fe-4S(SR) 4 ] in acetonitrile effect electron transfer-induced cleavages to radicals (14,16,35). The chemical cleavages by [4Fe-4S(SR) 4 ] in acetonitrile appear similar to the processes in radical SAM enzymes, but they are mechanistically unlike the enzymatic reactions.…”

Catalytic and Kinetic Waves in Polarography

“…(XXXI) an unstable, uncharged particle is formed that has the character of a free radical. In the reduction of tetrasubstituted ammonium [753][754][755] and phosphonium salts [756] or trisubstituted sulfonium cations [757], the unstable products formed either dimerize, as, for example, in the discharge of N-alkyl pyridinium salts (see section B-2 in Chapter VllI), or fall apart at the carbon-heteroatom bond, giving the corresponding tertiary amines, phosphines, or disubstituted sulfides and hydrocarbon radicals. These later can be reduced on the cathode, can react with the solvent, dimerize, or disproportionate.…”

“…A catalytic hydrogen evolution caused by doubly substituted sulfide sulfur was observed quite frequently. For example, it takes place in solutions of ethylene bisthioglycolic acid [739], HOOCCH 2 SCH 2 • SCH 2 COOH, and for sulfides, formed in the electroreduction (with n = 2) of trisubstituted sulfonium ions [757]. The mechanism of the process, assuming a discharge of sulfonium cations as shown by Frumkin andAndreeva [752], seems more probable from the viewpoint of the electrical double-layer structure at the electrode surface.…”

Alkyl Radical Generation by an Intramolecular Homolytic Substitution Reaction between Iron(II) and Trialkylsulfonium Groups

“…[1][2][3] One-electron reduction of as ulfonium cation by chemical or electrochemical means in many cases leads to fragmentation into as ulfide and ar adical species. [8] However, in this work we show that trialkylsulfonium species can easily be cleaved reductively via an intramolecular homolytic substitution reaction. [8] However, in this work we show that trialkylsulfonium species can easily be cleaved reductively via an intramolecular homolytic substitution reaction.…”