- NOVEL METHODS FOR PREPARATION OF SUBSTITUTED PYRIDINES AND RELATED NOVEL COMPOUNDS
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The present invention relates to novel methods of preparation of substituted pyridines and the compounds produced therefrom. In particular, the present invention provides efficient methods for the construction of diversely substituted pyridines, with varying substitution patterns under simple and metal-free conditions with high atom- and pot-economy and excellent functional group tolerance, and which are useful for the synthesis of natural products.
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Paragraph 0195; 0196; 0197; 0220; 0221
(2020/04/10)
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- Mesoporous Aluminosilicates in the Synthesis of N-Heterocyclic Compounds
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Abstract: The catalytic properties of samples of amorphous mesoporous aluminosilicate ASM with different Si/Al molar ratios (40, 80, 160) were studied in the synthesis of practically important pyridines (by the interaction of С2–С5 alcohols with formaldehyde and ammonia, cyclocondensation of acetaldehyde and propionic aldehyde with ammonia), dialkylquinolines and alkyltetrahydroquinolines (by reaction of aniline with C3, C4 aldehydes) and alkyldihydroquinolines (by interaction of aniline with ketones, acetone and acetophenone). It is found that mesoporous aluminosilicate ASM sample with a molar ratio of Si/Al = 40, which has the highest acidity among the studied samples, exhibits the highest activity and selectivity in these reactions.
- Agliullin, M. R.,Bikbaeva, V. R.,Bubennov, S. V.,Filippova, N. A.,Gataulin, A. R.,Grigor’eva, N. G.,Kostyleva, S. A.,Kutepov, B. I.,Narender, Nama
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p. 733 - 743
(2020/02/25)
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- A simple, tandem approach to the construction of pyridine derivatives under metal-free conditions: A one-step synthesis of the monoterpene natural product, (-)-actinidine
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A simple and modular one-step synthesis of diversely substituted pyridines from readily available α,β-unsaturated carbonyl compounds and propargylic amines has been developed. The present protocol has a broad substrate scope and allows access to multi-substituted pyridines with select control of the substitution pattern under mild and metal-free conditions. The reaction involves imine formation followed by concomitant cyclization through an allenyl intermediate to afford pyridines in excellent yields, with water as the sole by-product. This mild strategy is also suitable for functionalization of natural products or other advanced intermediates having α,β-unsaturated carbonyl functionality. The utility of the present protocol was showcased with the synthesis of the monoterpene alkaloid, (-)-actinidine, an ant-associated iridoid.
- Uredi, Dilipkumar,Motati, Damoder Reddy,Blake Watkins
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supporting information
p. 3270 - 3273
(2019/03/30)
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- Template-free synthesis of high degree crystallinity zeolite y with micro-meso-macroporous structure
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In this paper a new approach to the creation of a micro-meso-macroporous structure of Y zeolite was proposed. It was based on the selective crystallization into the integral cluster crystals of the preliminarily molded granules containing crystals of the zeolite in question and a porous binder matrix. The synthesized material was characterized by the high crystallinity degree of 95% and the volume of micro-, meso-, and macro-pores of 0.30, 0.15 and 0.15 cm3 g-1, respectively. It was shown that the Y zeolite with the hierarchical structure in H-form had the total acidity of about 830 μmol g-1 and revealed the high activity and selectivity in the synthesis of pyridines.
- Travkina,Agliullin,Filippova,Khazipova,Danilova,Grigor'Eva,Narender, Nama,Pavlov,Kutepov
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p. 32581 - 32590
(2017/07/07)
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- Synthesis of two potential heterocyclic amine food mutagens
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(Chemical Equation Presented) The syntheses of two potential food mutagens formed during cooking, 2-amino-3,6,7-trimethyl-3H-imidazo[4,5-b]pyridine (1) and 2-amino-3,6,7-trimethyl-3H-imidazo[4,5-c]pyridine (2), are described.
- Tanga, Mary J.,Kozocas, Joseph A.,Tochimoto, Todd K.
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p. 661 - 665
(2008/09/21)
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- DABCO and DMAP - Why are they different in organocatalysis?
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(Chemical Equation Presented) What makes a good organocatalyst? DABCO (1,4-diazabicyclo[2.2.2]octane) is a thousandfold better nucleophile (k →) and at the same time a million times better leaving group (k←) than DMAP (4-(dimethylamino)pyridine). This apparent contradiction is resolved by consideration of the intrinsic reaction barriers.
- Baidya, Mahiuddin,Kobayashi, Shinjiro,Brotzel, Frank,Schmidhammer, Uli,Riedle, Eberhard,Mayr, Herbert
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p. 6176 - 6179
(2008/04/05)
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- Kinetics and mechanisms of the pyridinolysis of phenyl and 4-nitrophenyl chlorothionoformates formation and hydrolysis of 1-(aryloxythiocarbonyl) pyridinium cations
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The title reactions are subjected to a kinetic study in water, at 25.0 °C, and an ionic strength of 0.2 M (KCl). By following the reactions spectrophotometrically two consecutive reactions are observed: the first is formation of the corresponding thionocarbamates (1-(aryloxythiocarbonyl)- pyridinium cations) and the second is their decomposition to the corresponding phenol and pyridine, and COS. Pseudo-first-order rate coefficients (k obsd1 and kobsd2, respectively) are found under excess amine. Plots of kobsd1 vs free pyridine concentration at constant pH are linear, with the slope (kN) independent of pH. The Bronsted-type plots (log kN vs pKa of the conjugate acids of the pyridines) are linear with slopes β = 0.07 and 0.11 for the reactions of phenyl and 4-nitrophenyl chlorothionoformates, respectively. These Bronsted slopes are in agreement with those found in other stepwise reactions of the same pyridines in water, where the formation of a tetrahedral intermediate is the rate-determining step. In contrast to the stepwise mechanism of the title reactions that for the reactions of the same substrates with phenols is concerted, which means that substitution of a pyridino moiety in a tetrahedral intermediate by a phenoxy group destabilizes the intermediate. The second reaction corresponds to the pyridine-catalyzed hydrolysis of the corresponding 1-(aryloxythiocarbonyl)pyridinium cation. Plots of k obsd2 VS free pyridine concentration at constant pH are linear, with the slope (kH) independent of pH. The Bronsted plots for kH are linear with slopes β = 0.19 and 0.26 for the reactions of the phenyl and 4-nitrophenyl derivatives, respectively. These low values are explained by the fact that as pKa increases the effect of a better pyridine catalyst is compensated by a worse leaving pyridine from the corresponding thionocarbamate.
- Castro, Enrique A.,Cubillos, Maria,Santos, Jose G.
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p. 4802 - 4807
(2007/10/03)
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- Inhibitors of cell proliferation, angiogenesis, fertility, and muscle contraction
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The invention concerns inhibitors of cell proliferation, angiogenesis, fertility, and muscle contraction, characterized by formula I wherein, X, Y and Z independently represent C or N; ------ is an optional double bond; n is 0 or 1; R1, R2, and R4 independently represent hydrogen, a chemical bond, C1-10 alkyl; C2-10 alkenyl; C2-10 alkinyl; aryl; aryl-C1-10 alkyl; C3-10 heterocyclyl; C5-10 heteroaryl; halo, CF3; NO2; NHC(O)R*, OR, said alkyl, alkenyl, alkinyl, aryl, arylalkyl, heterocyclyl, or heteroaryl being optionally substituted; R3, R5, and R6 independently represent hydrogen, C1-10alkyl; C2-10 alkenyl; C2-10 alkinyl; aryl; aryl-C1-10alkyl; C3-10 heterocyclyl; C5-10 heteroaryl; halo, CF3; NO2; NHC(O)R*, OR, said alkyl, alkenyl, alkinyl, aryl, heterocyclyl, or heteroaryl being optionally substituted; or R5 and R6 together form a 5- or 6-member aryl, heterocyclyl or heteroaryl group; R is hydrogen or C1-6 alkyl; R* is hydrogen, or C1-6 alkyl, or OH, wherein the optional substituents are preferably selected from the group of one to three OH, C1-6 alkyl, halo, NO2, C1-6 alkoxy, and CF3, or a pharmaceutically acceptable salt thereof.
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- A method for producing pyridine bases
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A method for producing pyridine bases which comprises reacting in a gas-phase an aliphatic aldehyde, aliphatic ketone or mixture thereof with ammonia in the presence of a zeolite comprising titanium and/or cobalt and silicon as zeolite constituent elements in which the atomic ratio of silicon to titanium and/or cobalt is about 5 to 1000 gives improved yield.
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- AlCl3·6H2O/KI/CH3CN/ H2O system: An efficient general system for deoxygenation of organic N-oxides in hydrated media
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An efficient general system for deoxygenation of organic N-oxides such as N-aryl nitrones, azoxy benzenes and N-heteroarene N-oxides uses AlCl3·6H2O/KI/CH3CN/H2O system at room temperature in hydrated media. The deoxygenated products were found in good yields.
- Boruah,Konwar
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p. 795 - 796
(2007/10/03)
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- Effect of neutral pyridine leaving groups on the mechanisms of influenza type A viral sialidase-catalyzed and spontaneous hydrolysis reactions of α-D-N-acetylneuraminides
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A reagent panel, comprised of five pyridinium salts of α-D-N-acetylneuraminic acid, was synthesized and then used to probe enzymatic (α-sialidase) and nonenzymatic mechanisms of neuraminide hydrolysis. Spontaneous hydrolysis of the pyridinium salts proceeded via two independent pathways, where unassisted C-N bond cleavage was the rate-determining step. Cationic species (i.e., anomeric carboxylate protonated) displayed apparent pK(a) values in the range of 0.4-0.7. However, spontaneous hydrolyses of the cationic and zwitterionic species had similar β(1g) values of -1.22 ± 0.16 and -1.22 ± 0.07, respectively. The results, plus the activation parameters calculated from the hydrolysis of pyridinium α-D-N-acetylneuraminide (ΔH(+) = 112 ± 2 kJ mol-1 and ΔS(+) = 28 ± 4 J mol-1 K-1), strongly suggest that the anomeric carboxylate does not assist in the departure of neutral pyridine leaving groups. Enzymatic hydrolysis was studied using an influenza viral α-sialidase (A/Tokyo/3/67) which was recombinantly expressed using a baculovirus/insect cell expression system. Sialidase protein was purified by a combination of density gradient centrifugation and gel filtration chromatography. Kinetic parameters for the enzymatic hydrolysis of the pyridinium salts were measured at 37 °C and at pH values of 6.0 and 9.5. The β(1g) values derived for k(cat)/K(m) and k(cat) were essentially zero, indicating that chemical transformations/events are not rate-determining. Rather, this observation is consistent with a model for α-sialidase-catalyzed hydrolyses (Guo, X.; Laver, W. G.; Vimr, E.; Sinnott, M. L., J. Am. Chem. Soc. 1994, 116, 5572) in which k(cat)/K(m) is determined by a conformational change of the first-formed Michaelis complex and k(cat) is determined by the virtual transition state made up of two separate conformational events.
- Chou, Doug T. H.,Watson, Jacqueline N.,Scholte, Andrew A.,Borgford, Thor J.,Bennet, Andrew J.
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p. 8357 - 8364
(2007/10/03)
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- Vapor-phase photochemistry of dimethylpyridines
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Irradiation of dimethylpyridine vapors (2-5 Torr) at 254 nm results in the formation of two sets of isomerization products. One set, formed in the larger yield, is substantially quenched when the irradiations are carried out in the presence of 15-21 Torr of nitrogen and is not formed when the irradiations are carried out with light of λ > 290 nm. In addition, a second set of reactions, which involve the interconversion of 2,3- and 2,5- dimethylpyridines, is enhanced by the addition of nitrogen, and these reactions are the only photoisomerization reactions observed when the irradiations are carried out with light of λ > 290 nm. In addition to the photoisomerizations, four of the dimethylpyridines also undergo demethylation to yield monomethylpyridines, and 2,6-dimethylpyridine undergoes methylation to yield a trimethylpyridine product. A variety of crossover experiments confirmed that the photoisomerizations are intramolecular. Based on the major phototransposition products, the six dimethylpyridines can be divided into two triads. Interconversion of the three members of each triad results in the major phototransposition products. These intra-triad interconversions are suggested to occur via 2,6-bonding, originating in a vibrationally excited S2 (π,π*) state of the dimethylpyridine, followed by nitrogen migration and rearomatization. This allows nitrogen to insert within each carbon- carbon bond. Phototransposition of 2,6-dideuterio-3,5-dimethylpyridine to a mixture of 5,6-dideuterio-2,4-dimethylpyridine and 3,4-dideuterio-2,5- dimethylpyridine is consistent with this mechanism. In addition to these intra-triad reactions, 2,5-dimethylpyridine, a member of triad 1, was observed to interconvert with 2,3-dimethylpyridine, a member of triad 2. These inter-triad reactions are suggested to occur via interconverting Dewar pyridine intermediates, formed from the triplet state of the dimethylpyridines. These Dewar pyridine intermediates were also observed by 1H NMR spectroscopy after irradiation of the dimethylpyridines in CD3CN at -30 °C.
- Pavlik, James W.,Kebede, Naod,Thompson, Michael,Day, A. Colin,Barltrop, John A.
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p. 5666 - 5673
(2007/10/03)
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- An Efficient Deoxygenation of Nitrones and Heteroarene N-Oxides
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Selective deoxygenation of nitrones and heteroarene N-oxides with the Zn-AlCl3·6H2O-THF system produces the corresponding imines and heteroarenes in high yield.
- Dutta, Dilip K.,Konwar, Dilip
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p. 266 - 267
(2007/10/03)
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- Synthesis of alkyl- and aryl-substituted pyridines from (α,β-unsaturated) imines or oximes and carbonyl compounds
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Reaction of a variety of (α,β-unsaturated) imines or oximes with aliphatic aldehydes or cyclic ketones in the presence of a secondary amine afforded alkyl-, and/or aryl-, and/or cycloalkyl-substituted pyridines. To explain their formation, a hetero Diels-Alder reaction has been postulated, in which an 1-aza-1,3-butadiene reacts with an in situ generated enamine.
- Vijn,Arts,Green,Castelijns
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p. 573 - 578
(2007/10/02)
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- 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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- Rate-Determining Steps in Michael-Type Additions and E1cb Reactions in Aqueous Solution
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Rates of equilibration of a series of 10 substituted pyridines and five Michael acceptors (CH2=CHZ, Z = CHO, COCH3, SO2CH3, CN and CONH2) with the corresponding N(ZCH2CH2) pyridinium cations have been measured in aqueous solution at ionic strength 0.1 and 25 deg C.Analysis of the dependence of the pseudo-first-order rate constants for equilibration as a function of acceptor concentration and of pH allows the evaluation of the second-order rate constants (kNu) for the nucleophilic attack of each of these pyridines upon each of these acceptors and also the second-order rate constants (kOH) for the hydroxide ion catalyzed E1cb elimination reaction which is the microscopic reverse of each of these Michael-type addition reactions.Broensted-type plots for each of these processes as a function of the basicity of the substituted pyridine are concave down for each of Z = CHO, COCH3, and CN and are consistent with a change from rate-determining nucleophilic attack for the more basic pyridines to rate-determining protonation of the carbanionic intermediate by a water molecule for less basic pyridines and the corresponding microscopic reverse processes in the elimination reactions.The "break" in these Broensted-type plots is shown to occur at a pyridine basicity that is a function of the Z-activating substituent.Broensted β1g and βnuc are evaluated for each rate-determining step (wherever accessible); these two parameters are shown to pass through minima as a function of reactivity. βeq is shown to be a simple linear function of reactivity (as log kNu) for nucleophilic addition to the acceptor species, although Keq is relatively insensitive to the nature of the Z-activating substituent.
- Heo, Christina K. M.,Bunting, John W.
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p. 3570 - 3578
(2007/10/02)
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- A Change in the Rate-Determining Step in the E1cB Reactions of N-(2-(4-Nitrophenyl)ethyl)pyridinium Cations
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Second-order rate constants have been measured (aqueous solution, I = 1.0, 25 deg C) for the hydroxide ion catalyzed elimination reactions of 12 N-(2-(4-nitrophenyl)ethyl)pyridinium cations (3) bearing a variety of substituents in the pyridine ring.Broensted plots as a function of the basicity of the pyridine leaving group are concave-down, which is consistent with a change in rate-determining step within an E1cB mechanism.These plots are characterized by βlg = -0.17 for the rate-determining deprotonation for pKBH lg = -0.39 for the rate-determining expulsion of the pyridine nucleofuge from the carbanionic intermediate for pKBH > 6.5.Elimination reactions in basic D2O occur without any significant incorporation of deuterium into the 4-nitrostyrene product, and require the presence of a hydrogen-bonded carbanionic intermediate in which nucleofuge expulsion occurs faster than exchange of hydrogen-bonding water molecules.Rate-determining deprotonation in these elimination reactions occurs 50-fold more slowly than for the corresponding reactions of the N-quinuclidinium cations that have also been reported to have βlg = -0.17, but which do not show an analogous change in the rate-determining step upon variation of the nucleofuge basicity.The analogous elimination of the 1-methyl-3-imidazolium cation occurs a further 30-fold more slowly than that predicted for 3 having a pyridine leaving group of the same basicity as 1-methylimidazole.The E1cB reactions of 3 are similar to the analogous reactions of N-(2-cyanoethyl)pyridinium cations (1) in displaying a change in the rate-determining step with nucleofuge basicity; however, theβlg values for 1 and 3 are quite different for both k1 and k2/k-1.
- Bunting, John W.,Kanter, James P.
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p. 6950 - 6954
(2007/10/02)
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- SYNTHESIS OF ALKYL-SUBSTITUTED PYRIDINES FROM CO, C2H4, H2, and NH3 ON HETEROGENEOUS CATALYSTS
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The reaction of preparation of alkyl-substituted pyridines by hydroformylation of ethylene in the presence of ammonia on heterogeneous Rh-containing catalysts with the formation of 2-ethyl-3,5-dimethylpyridine (I) as the basic product with up to 70-80percent conversion of gases and up to an 80 wt. percent concentration of the basic product was investigated.The dependence of the activity and selectivity of the catalysts on the concentration of Rh and nature of the support was determined.A correlation between the activity of the catalysts and their acid properties was established by IR spectroscopy.
- Kosolapova, B. S.,Levin, D. Z.,Sominskii, S. D.,Rar, L. F.,Mortikov, E. S.,Lapidus, A. L.
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p. 2244 - 2248
(2007/10/02)
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- Equilibration of N-(2-cyanoethyl)pyridinium cations with substituted pyridines and acrylonitrile. A change in rate-determining step in an E1cb reaction
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The rates of equilibration of N-(2-cyanoethyl)pyridinium cations (1) with the corresponding pyridines and acrylonitrile have been measured in aqueous solutions of ionic strength 0.1 at 25 °C. Second-order rate constants (kOH) have been obtained for the hydroxide ion catalyzed elimination reactions of 16 ring-substituted 1 having pyridine leaving groups of pKBH in the range 1.5-9.7. Bronsted plots of log kOH vs pKBH are "concave down" with two distinct linear regions having β1g = -0.30 (for pKBH 1g = -0.93 (for pKBH > 5.8). This observation is consistent with a change in rate-determining step within an E1cb reaction mechanism from rate-determining deprotonation of 1 (i.e., (E1cb)irrev) for pKBH rev) for pKBH > 5.8. This interpretation is supported by 1H NMR spectral observations in basic D2O, which show no incorporation of deuterium into the acrylonitrile product for pKBH BH > 5.8. Rates of nucleophilic attack of pyridines and pyridinone anions (pKBH > 6) upon acrylonitrile have also been measured. These display a linear Br?nsted plot of βnuc = 0.20. Combination of β1g and βnuc gives βeq = 0.13 for the Michael-type addition of pyridinium cations to acrylonitrile to produce 1. Although the rates of the addition of pyridines of pKBH nuc = 0.20 for pyridines of pKBH > 5.8 to rate-determining protonation of the carbanionic intermediate with βnuc = 0.83 for pyridine nucleophiles of pKBH irrev region but is extremely weak under the current experimental conditions.
- Bunting, John W.,Toth, Andrea,Heo, Christina K. M.,Moors, Rodney G.
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p. 8878 - 8885
(2007/10/02)
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- POTENTIOMETRIC STUDIES ON THE REACTION OF PICRIC ACID WITH SOME AROMATIC AMINES IN METHYL ISOBUTYL KETONE
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The reaction between picric acid and some aniline and pyridine derivatives has been investigated in methyl isobutyl ketone by the potentiometric method.Overall picrate formation constants KBHA, ammonium cationic acid dissociation constants KBH+ and apparent ion-pair formation Ki* and dissociation Kd* constants have been determined.
- Smagowski, Henryk,Bartnicka, Halina
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p. 201 - 209
(2007/10/02)
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- Process for the preparation of a diester of adipic acid
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Process for preparing adipic acid or esters thereof by: (1) reacting 1,3-butadiene with CO and water or an alcohol with formation of pentenoic acid or esters thereof in the presence of a first carbonylation catalyst comprising a Pd compound and a polydentate ligand containing P, As or Sb, (2) isolating pentenoic acid or esters thereof from the reaction mixture, and (3) reacting the isolated pentenoic acid or esters with CO and water or an alcohol in the presence of a second carbonylation catalyst.
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- A Single Transition State in the Transfer of the Methoxycarbonyl Group between Isoquinoline and Substituted Pyridines in Aqueous Solution
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N-Methoxycarbonylisoquinolinium ion reacts with nucleophiles in aqueous solution according to the equation .The rate constants, k2, for attack of substituted pyridines on the isoquinolinium species exhibit a linear Broensted relationship (βnuc=0.58) over a range of nucleophile pKa greater than and less than the pKa of isoquinoline.The Broensted data indicate a smaller change in effective charge on nucleophilic nitrogen for formation of a putative tetrahedral intermediate than for its decomposition to product.This is opposite to what is expected for the stepwise process where the largest bonding change to attacking nitrogen is in the addition step.The results are consistent with a single transition state in the transfer of the methoxycarbonyl group between pyridines in aqueous solution; they contrast with those for reaction of pyridines and tertiary amines with neutral acyl derivatives where relatively stable zwitterionic tetrahedral intermediates have been demonstrated.The transition state for transfer between pyridines is symmetrical, and the effective charge on its pyridine nitrogen is consistent with about 40percent of a single bond between nitrogen and acyl carbon.An imbalance of effective charge indicates that the MeO-CO component of the transition state has considerable acylium ion character pointing to an almost square-planar structure.
- Chrystiuk, Edwin,Williams, Andrew
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p. 3040 - 3046
(2007/10/02)
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- Solvent Effect on the Relative Nucleofugalities of Pyridines and Chloride Ion from a Tetrahedral Intermediate
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The reactions of 3- and 4-substituted pyridines with methyl chloroformate are kinetically studied in 44 wtpercent aqueous ethanol at 25 deg C, ionic strength 0.2 M (maintained with sodium perchlorate).The Broensted-type plot obtained is sharply curved with slopes β1 = 0.22 and β2 = 0.77, for high and low pKa values, respectively.The pKa value at the center of the curvature (pKa0) is 3.8, which is larger than the corresponding one found for the same reactions in water.The Broensted-type curve is described through the existence of a zwitterionic tetrahedral intermediate (T+/-) and a change in the rate-determining step.The higher pKa0 value found for these reactions in aqueous ethanol compared to water means that the nucleofugality of a pyridine from T+/- is favoured over that of chloride ion by the change of solvent from water to aqueous ethanol.
- Castro, Enrique A.,Ureta, Carmen
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p. 3008 - 3029
(2007/10/02)
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- Bonding in Phosphoryl (-PO32-) and Sulfuryl (-SO3-) Group Transfer between Nitrogen Nucleophiles as Determined from Rate Constants for Identity Reactions
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Rate constants have been measured for the bimolecular reactions of pyridines with pyridinium-N-phosphonates (kyxp) and pyridinium-N-sulfonates (kyxs) for aqueous solution at 25 deg C and 0.1 M ionic strength.The Broensted correlations with the pK of the entering or leaving pyridine can be used to calculate the rate constants for reactions where entering and leaving pyridines are identical.The Broensted selectivities of the "identity" rate constants (βi=-0.53 for kxxp and βi=-55 for kxxs) predict tightness parameters (τ) of 0.35 and 0.56 and bond orders (η) of 0.17 and 0.28 for the N-P and N-S bonds in the transition states for the transfer processes.The data are consistent with first-order "Marcus" theory governing the energy surfaces of the reactions and in particular obey the relationship βi=βnuc+βlg predicted by Lewis and Hu.
- Williams, Andrew
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p. 6335 - 6339
(2007/10/02)
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- Single Transition State for Sulfuryl Group (-SO3-) Transfer between Pyridine Nucleophiles
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The second-order rate constants for the nucleophilic attack of pyridines on isoquinoline-N-sulfonate (25 deg C, 0.1 M ionic strength) obey an excellent linear relation, log kXpyisq = 0.23 pKXpy - 1.91 (r=0.995), with the pK of the attacking - equation - pyridine over eight pK units.The complete absence of curvature in the relationship indicates a single transition state for the reaction consistent with a concerted, symmetrical mechanism.The attack of pyridine on substituted pyridine-N-sulfonates (25 deg C, ionic strength at 0.1 M) obeys the Bronsted equation log KpyXpy = -0.9 pKXpy + 4.22 (r=0.998).The ΒEQ for the equilibrium transfer of the -SO3- group from a constant pyridine leaving group to a variant pyridine nucleophile ( +1.13) is close to that predicted from a previous study.The electronic structure of the transition state possesses considerable sulfur trioxide character as deduced from the changes in effective charge on the entering and leaving pyridine nitrogen atoms.
- Bourne, Nicholas,Hopkins, Andrew,Williams, Andrew
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p. 4327 - 4331
(2007/10/02)
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- Evidence for a Single Transition State in the Transfer of the Phosphoryl Group (-PO32-) to Nitrogen Nucleophiles from Pyridino-N-phosphonates
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The reaction of pyridinio-N-phosphonates with pyridines in aqueous buffers has been demonstrated to involve nucleophilic attack at phosphorus.The second-order rate constants obey the equation log kxpy = 0.15pKxpy - 0.86 for attack on isoquinolino-N-phosphonate over a wide range of pyridine basicity indicating a single transition state; this is consistent with a concerted transfer of the phosphoryl group rather than with a stepwise mechanism involving metaphosphate ion in a ternary encounter complex with donor and acceptor.Transfer of the phosphoryl group to pyridine from substituted pyridinio-N-phosphonates obeys the equation log k = -0.92pKxpy + 5.24 and leads to a βeq of 1.07 for substituent effect on the equilibrium constant for transfer.The effective charge at nitrogen, in the transition state, indicated by these values favors weak P-N bonding.An imbalance of -0.77 effective charge units between entering and leaving nitrogen in the transition state is proposed to derive from the charge on the PO3 atoms, which therefore do not bear a full negative charge in the transition state.Transfer of the phosphoryl group from isoquinolinio-N-phosphonate to amines has been investigated kinetically, and the results are also consistent with weak bonding between phosphorus and nitrogen in the transition state.
- Bourne, Nicholas,Williams, Andrew
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p. 7591 - 7596
(2007/10/02)
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- Preparation of pyridines
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Pyridines are prepared by reacting a 2-alkoxy-2,3-dihydro-4H-pyran or a glutaraldehyde with ammonium nitrate in the presence of an aliphatic carboxylic acid and a catalytic amount of nitric acid. The pyridines which can be prepared by the process according to the invention are useful starting materials for the preparation of dyes, drugs and pest control agents and are useful solvents.
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- Chichibabin reaction
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In a Chichibabin amination of a pyridine base by sodamide in an organic solvent, the improvement comprising conducting the reaction under pressure of at least about 50 psi in the gas phase above the reaction mixture and adding ammonia to the mixture sufficient to produce a partial pressure of ammonia of at least about 5 psi in the gas phase. Preferred temperature and pressure ranges are disclosed, as are catalysts and other preferred steps for practicing the reaction. Significant results are obtained including improved and changed yields from those classically expected in Chichibabin aminations, including new compositions of matter in at least one case.
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