Kinetics of the reduction of organic cations by cation radicals

It has been found that the reduction of substituted diazonium, iodonium, and tropylium salts by cation radicals of tetra-tert-butyl-bis-pyrylium, tetramethyl-p-phenylene diamine (I), tetraphenylbenzidine, and N-methylphenothiazine obey the kinetic equation of the second order and that it follows an electron transfer mechanism. The logarithms of the rate constants of these reactions decrease with increasing standard free energy of the electron transfer reaction. The rate of the reaction of C₆H₅N₂₊ BF₄ ^– with I and the selectivity of the reactions of the substituted diazonium salts with I increases with the electron donor capacity of the solvent. The addition of crown-ethers accelerates the reaction. The reaction rate increases also with increasing ionic strength of the solution, whereby the Cl^– anions have a specifically accelerating effect. The observed rules governing the influence of the medium contradict those found earlier for the interaction of organic cations with neutral radicals and anion radicals. This is attributed to the fact that the electron transfer takes place in ternary complexes cation-solvent (crown ether, Cl^– ion)-cation radical.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 45–51, January–February, 1985.The authors wish to express their gratitude to V. V. Lobonov for tje performance of the quantum chemical calculations.     

Decomposition mechanism of dinitramide onium salts

Thermal decomposition of dinitramide onium salts proceedsvia the dissociative mechanism when pK _a of the base is lower than 5.0 andvia the monomolecular decay of the anion at pK _a>7.0. On going from the melt to the solid state, the reaction mechanism does not change, and the rate decreases by 1–2 orders of magnitude. No anomalous effects inherent in dinitramide metal salts in the solid phase are observed during decomposition of onium salts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1951–1953, November, 1997     

Reaction of onium salts with nucleophilic reagents

Russian Chemical Bulletin -     

Phase transformation and enhancement of toughness in polyvinylidene fluoride by onium salts

We study the effect of onium salts (benzyl triphenyl phosphonium chloride, BTPC; tetrabutyl ammonium perchlorate, TAP) on the crystallization of polyvinylidene fluoride (PVDF) from a melt. The β phase of PVDF crystals is polar and has excellent piezoelectric properties, in contrast to the nonpolar α phase. Processing of PVDF results in the formation of predominantly α‐phase crystals. Different amounts of the onium salts were melt‐mixed into PVDF using a micro‐compounder. PVDF containing about 0.5 wt % of BTPC is found to have predominantly β‐phase crystals in compression molded PVDF films, with an increase in the melting temperature by about 7 °C. A significant increase in the toughness of PVDF is obtained by the addition of BTPC. Polarizing microscopy indicates that the onium salts act as nucleating agents and result in significant reduction in spherulite size. Similar results were observed for samples prepared with TAP. The results of the study indicate a facile method for producing β‐phase PVDF films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1339–1344, 2011     

Productive trapping of NAD-type radicals. Non-biomimetic reduction of pyridinium salts

One-electron reduction of pyridinium salts (NAD+ analogues) generates dihydropyridyl radicals which may then be engaged in radical addition processes to regioselectively form gamma-substituted dihydropyridines.     

Pro-oxidant action of sulfur compounds : Catalysis of autoxidation by onium salts

It is shown that the initiation of the autoxidation of cumene by triphenylsulfonium salts is due not to oxygen activation, as stated in the literature, but to a sulfonium-catalysed homolytic cleavage of cumene hydroperoxide. The activity of triphenylsulfonium chloride is considerably enhanced by addition of solid calcium carbonate, which effect is attributed to the removal of chloride ions. In keeping with this, triphenylsulfonium hydroxide was found to display an even higher activity.     

Unconventional methods of initiating cationic polymerization using onium salts

Onium salts are latent sources of cationic species that can be released on demand to initiate cationic polymerizations by the application of various external physical and chemical stimuli. This paper will report on the use of several different types of stimuli to provide interesting and useful unconventional methods for initiating cationic polymerizations.     

Photochemistry and initiation behavior of phenylethynyl onium salts as cationic photoinitiators

Phenyl(phenylethynyl)iodonium hexafluorophosphate and diphenyl(phenylethynyl)sulfonium hexafluorophosphate were synthesized for application as cationic photoinitiators using simple, straightforward methods. Quantification of the purity of the counterion was determined by FTIR analysis with subsequent mathematical peak deconvolution. Photodecomposition products for direct irradiation were determined in steady state photolysis experiments yielding diphenyl sulfide and phenyl(phenylethynyl) sulfide or iodobenzene, respectively, as main products. Heterolytic cleavage was proposed as main photodecomposition pathway because low yields of phenylacetylene radical recombination products and no photoproducts generated by phenyl radicals, including benzene, were detected. High activity as photoinitiators was verified by photo‐DSC experiments in direct irradiation and in photosensitized initiation using 9,10‐dibutylanthracene, 2‐isopropylthioxanthone, and surprisingly also benzophenone as sensitizers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3419–3430, 2009     

Mass spectrometry of onium compounds—IV: Diazonium salts

The zwitterions of diazotized ortho and para aminophenol are very volatile and give strong peaks in the mass spectra corresponding to the molecular ion. The m-isomer, which cannot be stabilized through a simple quinonoid structure, gives rise to a complex spectrum through decomposition and coupling reactions. The zwitterions of diazotized anthranilic and sulphanilic acids did not give the molecular ion peak.     

Convenient synthesis of various ionic liquids from onium hydroxides and ammonium salts

Hydroxide ionic liquids, such as 1-alkyl-3-methylimidazolium hydroxides, undergo smooth anion metathesis with ammonium salts to produce a variety of ionic liquids in excellent yields. It is a practical supplement of traditional neutralization method due to the broader range of starting materials containing desired anions.