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1.
The acid‐catalyzed hydrolysis of a series of 5‐substituted‐1H,3H‐2,1,3‐benzothiadiazole 2,2‐dioxides has been investigated in aqueous solutions of sulfuric, perchloric, and hydrochloric acid at 85.0 ± 0.05 °C. Analysis of the kinetic data by the excess acidity method, Arrhenius parameters, the order of the catalytic effects of strong acids, the kinetic deuterium isotope effect, and the substituent effect have indicated that the hydrolysis of 5‐substituted benzosulfamides 1a , 1b , 1c , 1d occur with a mechanistic switchover from A2 to A1 in the studied range: an A2 mechanism in low acidity regions and an A1 mechanism in high acid concentrations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
2.
Martti Lajunen Rita Yli‐Mannila Outi Salminen 《Journal of Physical Organic Chemistry》2000,13(2):133-138
The disappearance of 3‐ and 1‐acetoxynortricyclanes (1 and 2) in aqueous perchloric acid was followed by capillary gas chromatography at different temperatures and acid concentrations. According to the activation parameters, solvent deuterium isotope effects and parameters of excess acidity equations, the AAC2 ester hydrolysis with two water molecules in the transition state is dominant at the lower acid concentrations studied (1–5.5 M HClO4) and the AdE2 hydration of the cyclopropane ring is dominant at higher acid concentrations (6–8 M HClO4) at 298 K. 3‐Nortricyclanol (3) is formed via hydrolysis from 1, whose hydration products were not analyzed. 2‐Norbornanone (4) is formed via both hydrolysis and hydration from 2. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
3.
The acid‐catalyzed hydrolyses of N‐(4‐substituted‐arylsulf inyl)phthalimides were studied in aqueous solutions of perchloric and sulfuric acids at 50.0 ± 0.1 and of hydrochloric acid at 40.0 ± 0.1 °C. Analysis of the data by the Cox–Yates excess acidity method and substituent, temperature and solvent isotope effects indicate hydrolysis by an A2 mechanism at low acidity. At higher acidities a changeover to an A1 mechanism is observed. Copyright© 2001 John Wiley & Sons, Ltd. 相似文献
4.
The disappearance of 1‐ and 3‐acetylnortricyclanes ( 1‐Ac and 2‐Ac ) in aqueous perchloric acid was followed by capillary gas chromatography at different temperatures and acid concentrations. 1‐Ac is much less reactive than 2‐Ac . The activation parameters, solvent deuterium isotope effects and parameters of excess acidity equations were measured and the products studied. 1‐Acetylnortricyclane is hydrated according to the A‐2 mechanism, i.e. the carbonyl oxygen is protonated in the fast pre‐equilibrium and one water molecule attacks at the rate‐limiting stage the partially open cyclopropane ring, producing 6‐acetyl‐2‐norborneols. 3‐Acetylnortricyclane is hydrated according to the AdE2 mechanism, i.e. the cyclopropane ring is slowly protonated and opened, with subsequent fast attack of water producing 3‐, 5‐ and 7‐acetyl‐2‐norborneols. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
The disappearance of 1- and 3-nortricyclanols ( 1-OH and 2-OH ) in aqueous perchloric acid was followed by capillary GC at different temperatures and acid concentrations. 1-OH is ca 1000 times more reactive than 2-OH . The activation parameters, solvent deuterium isotope effects and parameters of excess acidity equations were measured and the products were studied. Both isomeric nortricyclanols react according to the AdE2 mechanism, i.e. the cyclopropane ring is protonated at the rate-determining stage of the reaction. The protonation causes, in the case of 1-OH , an isomerization called homoketonization with 2-norbornanone as the only product and, in the case of 2-OH , hydration, i.e. the formation of hydroxyl-substituted norbornyl cations, the fast attack of which by water produces several norbornanediols. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
6.
采用溶胶-凝胶技术,以乙醇钽为前躯体,乙醇为溶剂,分别以盐酸、硝酸、硫酸为催化剂,结合CO2超临界干燥技术制备了Ta2O5气凝胶。研究发现:硫酸作催化剂的体系,其胶凝时间远远小于其他体系,且溶剂交换及超临界干燥过程中的收缩开裂现象明显改善;扫描电镜分析结果显示,硫酸为催化剂制备的Ta2O5气凝胶骨架颗粒间存在较严重的团簇现象,比表面积约167 m2/g,明显低于以盐酸、硝酸为催化剂的体系。X射线光电子能谱测试结果显示,Ta2O5气凝胶中无相应的Cl元素或N元素残留,而S元素则基本上滞留在Ta2O5气凝胶中。说明S元素进入了Ta-O-Ta交联结构,正是因为这种结构的引入,Ta2O5气凝胶的收缩龟裂现象得以明显改善并呈现出相对较高的力学性能。 相似文献
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采用溶胶-凝胶技术,以乙醇钽为前躯体,乙醇为溶剂,分别以盐酸、硝酸、硫酸为催化剂,结合CO2超临界干燥技术制备了Ta2O5气凝胶。研究发现：硫酸作催化剂的体系,其胶凝时间远远小于其他体系,且溶剂交换及超临界干燥过程中的收缩开裂现象明显改善;扫描电镜分析结果显示,硫酸为催化剂制备的Ta2O5气凝胶骨架颗粒间存在较严重的团簇现象,比表面积约167 m2/g,明显低于以盐酸、硝酸为催化剂的体系。X射线光电子能谱测试结果显示,Ta2O5气凝胶中无相应的Cl元素或N元素残留,而S元素则基本上滞留在Ta2O5气凝胶中。说明S元素进入了Ta-O-Ta交联结构,正是因为这种结构的引入,Ta2O5气凝胶的收缩龟裂现象得以明显改善并呈现出相对较高的力学性能。 相似文献
9.
Old&#x;ich Pytela Roman Bedn&#x; Jaromír Kavlek 《Journal of Physical Organic Chemistry》2004,17(4):343-349
Eight 3‐alkyl‐1,3‐diaryltriazenes with methyl, ethyl, propyl, butyl, pentyl, isopropyl, sec‐butyl and cyclohexyl substituents were synthesized and their rate constants of decomposition by trichloroacetic acid (0.01–0.25 mol dm−3) in hexane at 25°C were measured. The kinetic model and mechanism thereof were studied by modelling of the dependences of kobs on the concentration of trichloracetic acid. On the basis of this kinetic model and the interpretation of solvent effects, a reaction mechanism was suggested according to which the triazene reacts with monomer and obviously also opens the dimer of trichloroacetic acid in a single reaction step. At the same time, a non‐reactive associate between the N1 nitrogen of triazene and two molecules of trichloroacetic acid is formed in the reaction mixture. The equilibrium and rate constants depend on the addition of trichloroacetic acid as the co‐solvent. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
10.
M. Niyaz Khan 《Journal of Physical Organic Chemistry》1998,11(3):216-222
Phthalic anhydride was detected spectrophotometrically in the hydrolysis of o-carboxybenzohydroxamic acid (OCBA) in CH3CN–H2O solvent containing 0.03 mol dm−3 HCl. Pseudo-first-order rate constants (k1) for hydrolysis of OCBA are almost independent of the change in CH3CN content from 10 to 80% (v/v) in mixed aqueous solvents. The rate constants k1 are more than 10-fold larger than the corresponding rate constants for hydrolysis of phthalamic acid. These observations are explained in terms of a mechanism slightly different from the mechanism for hydrolysis of phthalamic acid. The activation parameters, ΔH* and ΔS*, are not affected appreciably by an increase in CH3CN content from 10 to 80% in mixed aqueous solvents. © 1998 John Wiley & Sons, Ltd. 相似文献
11.
Giorgio Cevasco Andrea Galatini Necmettin Pirinççioğlu Sergio Thea Andrew Williams 《Journal of Physical Organic Chemistry》2008,21(6):498-504
The host molecule octacarboxymethyl calix[4]resorcinarene 1 catalyses the hydrolysis of substituted phenyl N‐methylpyridinium‐4‐carboxylate esters 3a–f by complexation followed by intracomplex reaction via an anhydride intermediate. The reactivity in the presence of 1 is higher than that of the background at low pH; at high pH an inversion of reactivity occurs, the background becomes predominant since the host inhibits hydrolysis of the esters. The reactivity of esters 3a–f complexed with the host suffers little change in effective charge on the phenolic oxygen (?0.15 units) in contrast with the changes observed in alkaline hydrolysis (?0.28 units) and in the hydrolysis of the model monoaryl glutarate esters (‐1.02 units). The less negative effective charge in the transition state for host 1 catalysis compared with that in the glutarate case is ascribed to stronger solvation by water molecules in the complex compared with that due to water molecules in the bulk solvent. 相似文献
12.
Santiago F. Yunes Jos C. Gesser Hernan Chaimovich Faruk Nome 《Journal of Physical Organic Chemistry》1997,10(6):461-465
The hydrolysis of the 2′,2′,2′-trifluoroethyl monoester of 1,8-naphthalic acid ( 1 ) proceeds via the monoanion with the intermediate formation of the corresponding anhydride. The rate constant for the formation of 1,8-naphthalic anhydride ( 2 ) is ca 2500 times faster than its rate of hydrolysis. The isotope effect in the plateau region and theoretical calculations at the PM3 level suggest that elimination of the alkoxide is the rate-limiting step for the reaction. Accordingly, decomposition of the isopropyl monoester of naphthalic acid proceeds 104 times slower than the spontaneous decomposition of 1 . The remarkably high rate of monoester decomposition derives from the special configuration of the substrates and important contributions that arise from relief of torsional strain, which clearly includes electron redistribution due to the decrease in steric hindrance to resonance and the fact that proximity obviates solvation. © 1997 John Wiley & Sons, Ltd. 相似文献
13.
A comparative study of specific acid catalysis and Lewis acid catalysis of Diels–Alder reactions between dienophiles ( 1 , 4 and 6 ) and cyclopentadiene ( 2 ) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas hydrochloric acid was employed for specific acid catalysis. At equimolar amounts of copper(II) nitrate and hydrochloric acid (0.01 M , for example) and under the same reaction conditions, the reaction rate for 1a with 2 is about 40 times faster with copper catalysis than with specific acid catalysis. Moreover, at 32°C and 0.01 M HCl, the reaction of 1b with 2 is about 21 times faster than the same uncatalyzed reaction in pure water under the same reaction conditions. The inverse solvent kinetic isotope effect shows that these Diels–Alder reactions undergo specific acid catalysis. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
14.
Lai C. Chan Brian G. Cox Ian C. Jones Simone Tomasi 《Journal of Physical Organic Chemistry》2011,24(9):751-763
A detailed kinetic analysis and computational study of an SNAr reaction between 2,5,6‐trifluoronicotinonitrile, 2 , and the ambident 3‐isopropoxy‐1H‐pyrazol‐5‐amine, 3 , is presented. The selectivity with respect to the reaction at the primary amino group of 2 , to give the desired product, 2,5‐difluoro‐6‐[(3‐isopropoxy‐1H‐pyrazol‐5‐yl)amino]nicotinonitrile, 1 , is strongly dependent upon reaction conditions. Reaction is found to proceed via both uncatalysed and base catalysed routes, and selectivity towards 1 is strongly enhanced in the presence of the base diazabicyclo[2,2,2]octane (DABCO). Computational studies in tetrahydrofuran solution at the B3LYP/6‐31G* level of theory have provided valuable insight into alternative kinetically indistinguishable reaction pathways. The results suggest that for reaction at the primary amino group, proton removal by DABCO accompanying amine addition allows avoidance of a high‐energy, zwitterionic Meisenheimer intermediate. Reactions at the alternative pyrazole nitrogen atoms are less sensitive to the presence of base because of stabilisation of the Meisenheimer zwitterions by intramolecular hydrogen bonding. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
15.
早在1989年芶清泉教授就以原子分子物理和晶体物理为基础提出了冷聚变机理的理论.按照此理论,在晶体中可以实现冷聚变,产生超热和聚变产物4He.在此理论提出后,我们在实验研究中观测到了以Pd或Tin为阴极电解重水过程中产生的明显的超热效应与聚变产物4He.这表明我们提出的理论预言是正确的,在过去的18年中我们进一步进行了反复深入的理论和实验研究,所得结果将在本文中进行系统总结和讨论. 相似文献
16.
Teresa Cristina de Barros Pedro Berci Filho Michel Loos Mario José Politi Hernan Chaimovich Iolanda Midea Cuccovia 《Journal of Physical Organic Chemistry》2011,24(5):385-397
The kinetics of hydrolysis of 1,8‐N‐butyl‐naphthalimide (1,8‐NBN) to 1,8‐N‐butyl‐naphthalamide (1,8‐NBAmide) and of 2,3‐N‐butyl‐naphthalimide (2,3‐NBN) to 2,3‐N‐butyl‐naphthalamide (2,3‐NBAmide), as well as the formation of the respective anhydrides from the amides were investigated in a wide acidity range. 1,8‐NBN equilibrates with 1,8‐NBAmide in mild alkali. Under the same conditions 2,3‐NBN quantitatively yields 2,3‐NBAmide. Over a wide range of acidities the reactions of the 1,8‐ and 2,3‐N‐butyl‐naphthalamides (or imides) yield similar products but with widely different rates and at distinct pH's. Anhydride formation in acid was demonstrated for 1,8‐NBAmide. The reactions mechanisms were rationalized in the manifold pathways of ab initio calculations. The differences in rates and pH ranges in the reactions of the 1,8‐ and 2,3‐N‐butyl‐naphthalamides were attributed to differences in the stability of the tetrahedral intermediates in alkali as well as the relative stabilities of the five and six‐membered ring intermediates. The rate of carboxylic acid assisted 1,8‐N‐Butyl‐naphthalamide hydrolysis is one of the largest described for amide hydrolysis models. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
17.
采用量子化学从头算方法在HF/6-31G(d)水平上对氯磺隆、甲嘧磺隆和氟嘧磺隆三种典型的磺酰脲类除草剂在酸性和中性条件下水解反应的机理进行理论研究,分别优化了各反应途径中反应物、过渡态、中间体以及产物的几何构型,并通过振动分析确定反应的过渡态和中间体的真实性。同时,在B3LYP/6-31G(d)水平上计算各驻点的单点能,以及溶剂效应对水解反应的影响。从能量上看,酸性条件更有利于水解反应的进行,与实验结果较为吻合. 相似文献
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For hexanoic acid and its seven isomers, relative rates have been determined for acid catalysed esterification with methanol, and compared with those for saponification of the methyl esters. A good correlation between logarithms of relative rates for the two reactions is obtained, and it is suggested that the eight isomers provide a test set of compounds in which steric effects alone act on reactivity at the acyl carbon. A full set of steric parameters ( values) are presented. Rates of solvolyses of the acid chlorides of the isomers have been determined conductometrically in 3:1 wt:wt acetonitrile water. Logarithms of relative rates show a poor correlation with , and, taking into account the solvent dependence of the rates, the pattern excludes both rate‐limiting formation of a tetrahedral intermediate and rate‐limiting dissociation of chloride to form acylium ions. The remaining possibilities, a concerted process (AND) and rapid reversible formation of a hydrate followed by rate‐limiting dissociation of chloride (AN + D) are considered. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献