- Kinetics and mechanism of the formation of N-vinyl pyridinium cations in elimination reactions in aqueous base
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The rates of the elimination reactions of N-(2-bromoethyl) pyridinium cations (1) and N,N'-ethylene bispyridinium dications (3) to give the corresponding N-vinyl pyridinium cations (2) have been measured spectrophotometrically in basic aqueous solutions (ionic strength 0.1, 25 deg C) for a variety of substituents in the pyridine rings of each of these classes of pyridinium cation.The reaction kinetics are first order in 1 or 3 and first order in hydroxide ion.Bronsted-type plots of the second-order rate constants (kOH) as a function of the basicity (as pKBH) of the corresponding substituted pyridine are nonlinear for each of 1 and 3 and can be interpreted in terms of E1cb reaction mechanism.For 1, the Bronsted-type plot displays two distinct ''concave down'' linear regions; rate-determining deprotonation for pKBH > 5.16 (slope = -0.30), and a change in rate-determining step to bromide ion departure for pKBH > 5.16 (slope -0.58).For 3, the Bronsted-type plot appears to be smoothly curved for symmetrically disubstituted bispyridinium dications, as a consequence of the multiple substituent effects upon each step of the E1cb reactions of these dications.However, log kOH for 3 is a smooth linear function of the previously reported log kOH for the E1cb reactions of N-(2-cyanoethyl) pyridinium cations over a range in which a change in rate-determining step has been directly demonstrated for these latter cations.Thus a change in rate-determining step as a function of pyridine basicity is also required within the E1cb mechanism for 3.The E1cb reactions of 1 are approximately 104-fold faster than the corresponding hydroxide ion catalyzed E2 eliminations from 2-phenylethyl bromides that are isoelectronic with 1.
- Bunting, John W.,Toth, Andrea,Kanter, James P.
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p. 1195 - 1203
(2007/10/02)
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- Reaction Mechanism of Cathodic Crossed Coupling of Acetone with Unsaturated Compounds in Acidic Solution
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It was confirmed that the cathodic crossed coupling of acetone with unsaturated compounds in aqueous sulfuric acid could proceed smoothly, when the compounds which had radical-acceptable double bonds and were adsorbed on a mercury cathode were used.From this fact, it was concluded that the coupling occurs via the addition of a radical intermediate formed by the one-electron reduction of acetone to the double bonds on the cathode surface.Possibility of the addition of an anionic intermediate derived from acetone was excluded by no occurrence of the coupling of acetone with a polar acetylenic triple bond compound adsorbed on the cathode.
- Koizumi, Toshio,Fuchigami, Toshio,Kandeel, Zaghloul El-Shahat,Sato, Norio,Nonaka, Tsutomu
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p. 757 - 762
(2007/10/02)
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- The Quarternisation of Tertiary Amines with Dihalomethane
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Whereas dichloromethane is inert towards reaction with most tertiary amines under atmospheric conditions, it readily reacts with a wide variety at high pressures to produce α-chloro quaternary ammonium and even bis-ammonium salts.The reaction of dichloromethane and dibromomethane with eleven tertiary amines and properties of the products are described.
- Almarzoqi, B.,George, A. V.,Isaacs, N. S.
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p. 601 - 608
(2007/10/02)
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- Direct Synthesis of Molecular Self-Complexes in the Indole Series
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A method for the alkylation of 3-unsubstituted indoles by means of 1-(ω-haloalkyl)-pyridinium salts via the Friedel-Crafts reaction with the aid of complex catalysts, viz., complexes of zinc, tin, and titanium chlorides with pyridine, was developed.On the basis of a study of the electronic spectra of the resulting 1-(3-indolyl-alkyl)pyridinium salts it was shown that they are molecular self-complexes.The stabilities of the molecular self-complexes were investigated as a function of the length of the alkyl chain and the character of the substituents in the indole ring.
- Kost, A. N.,Yurovskaya, M. A.,Vyazgin, A. S.,Afanas'ev, A. Z.
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p. 921 - 925
(2007/10/02)
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