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1.
This paper describes the use of potentiometric titration to determine the relevant acid–base properties of 5-hydroxypyrazine-2-carboxylic
acid (5OH-PYCA), an important intermediate in the production of tuberculostatics. The data obtained were used for calculation
of the dissociation constants of 5OH-PYCA. It was found that 5OH-PYCA dissociates in two steps, with the corresponding dissociation
constants pK
a1=3.42 and pK
a2=7.96, designating 5OH-PYCA as a medium weak acid (1st step). The distribution diagram of dissociated species and the buffer-strength
diagram of 5OH-PYCA provide useful information about its behaviour at different pH. The ionic equilibria data obtained can
be used for selection of the optimum pH for biotransformation of pyrazine-2-carboxylic acid (PYCA) and for prediction of pH
changes during the biotransformation. These data can also be used for selection of the optimum pH for precipitating 5OH-PYCA
in downstream processing. All computations have been optimized by mathematical modelling using Solver. 相似文献
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《Journal of Coordination Chemistry》2012,65(2):335-347
Abstract Mn(II) cations in the crystals of trisaquobis(μ-thiophen-2-carboxylato-O,O′)(thiophen-2-carboxylato-O)manganese(II) monohydrate are bridged by oxygen atoms donated by bidentate carboxylic groups of two thiophen-2-carboxylate ligands. In addition, each Mn(II) ion is coordinated by an oxygen atom of a monodentate carboxylic group of this ligand and three oxygen atoms of water molecules. The coordination around the Mn(II) cation is octahedral. The bridging of the ligands results in molecular ribbons propagating in the c-direction of the crystal held together by C?H…O hydrogen bonds. The crystal structure of diaquobis(μ-furan-3-carboxylato-O,O′)di(μ-furan-3-carboxylato-O,O)(μ-aqua-O)manganese(II) consists of dinuclear structural units. In each molecule Mn(II) cations are O,O′ bridged by oxygen atoms of bidentate carboxylic groups of two furan-3-carboxylate ligands and have a water located between the Mn cations. The units are O,O′ bridged to Mn(II) ions located in adjacent units by bidentate oxygen atoms, forming molecular ribbons extending in the c-direction. Octahedral coordination around each Mn(II) ion is completed by two water molecules. The octahedra around two adjacent metal ions in the unit share a common apex - the bridging oxygen atom of the water molecule. The ribbons are held together by C?H…O hydrogen bonds between furan ring oxygen atoms and the carbon atoms of adjacent furan rings. 相似文献
4.
ZHANG XingHui GENG ZhiYuan & WANG YongCheng Gansu Key Laboratory of Polymer Materials College of Chemistry Chemical Engineering Northwest Normal University Lanzhou China College of Chemical Engineering Gansu Lianhe University Lanzhou China 《中国科学B辑(英文版)》2011,(5)
The mechanisms of the acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid and mesitoic acid have been investigated based on density functional theory calculations at the B3LYP/6-311G (d,p) level. A polarizable continuum model (PCM) has been established in order to evaluate the effects of solvents on these reactions. The results of the calculations indicate that the first step of the acid-catalyzed decarboxylation of the pyrrole-2-carboxylic acid has two possible pathways,that is,the proton of H3O+ a... 相似文献
5.
2-Amino substituted benzothiazole 4a--4I and p-acetamidobenzenesulfonyl chloride 2 were used to prepare 2-(p-aminophenylsulfonamido) substituted benzothiazole 6a--6I using mixture of pyridine and acetic anhydride which formed an electrophilic complex (N-acetyl pyridinium) to facilitate condensation to give desired product by removal of HC1. 2-{p-[(3-Carboxypyrid-2-y1)amino]phenylsulfonamido}benzothiazoles 8a--81 were synthesized from 2-chloropyridine-3-carboxylic acid 7 and 6a--6I in 2-ethoxy ethanol using Cu-powder and K2CO3. Acid chlorides 9a--91 were condensed with 2-hydroxyethyl piperazine 10 and 2,3-dichloropiperazine 11 for amide deriva- tives 2-(p-((3-(4-(2-hydroxyethy1)piperazin-1-ylcarbonyl)pyrid-2-y1)amino)phenylsulfonamido)benzothiazoes 12a -121 and 2-{p-[3-(2,3-dichloropiperazin-l-ylcarbonyl)pyrid-2-ylamino]phenylsulfonamido}benzothiazoles 13a- 131 respectively. The structures of the new compounds have been established on the basis of their chemical analysis and spectral data (IR, 1↑H NMR and mass). All the compounds have been screened for their antibacterial and antifungal activities. 相似文献
6.
B. Shtrumfs D. Chernyak I. Kums I. Kalvins P. Trapencieris 《Chemistry of Heterocyclic Compounds》2004,40(6):725-733
A series of N-unsubstituted esters of aziridine-2-carboxylic acid has been obtained by transesterification in basic medium using primary, secondary, and tertiary alcohols. Methods of transesterification using various bases (K2CO3, ROLi, t-BuOK) have been compared. Transesterification with lithium alcoholates also affords the possibility of obtaining esters of N-substituted aziridine-2-carboxylic acids. Transesterification of chiral esters proceeds with retention of the configuration of the chiral center. 相似文献
7.
《Analytical letters》2012,45(5):445-449
Abstract The reagent ethyl cyanoglyoxalate phenyl-2-carboxyllc acid hydrazone has been developed for the selective amperometric determination of thorium. Commonly associated ions like UO2+ 2, Pe3+, La3+, Ce4+, and Zr4+ do not interfere even when present in ten fold molar excess. 23μg to 4.6mg thorium can be determined within an error of ±1.5 percent. 相似文献
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The doubly decarboxylative Michael–type addition of pyridylacetic acid to chromone-3-carboxylic acids or coumarin-3-carboxylic acids has been developed. This protocol has been realized under Brønsted base catalysis, providing biologically interesting 4-(pyridylmethyl)chroman-2-ones and 2-(pyridylmethyl)chroman-4-ones in good or very good yields. The decarboxylative reaction pathway has been confirmed by mechanistic studies. Moreover, attempts to develop an enantioselective variant of the cascade are also described. 相似文献
9.
Investigations were made to determine the TLC properties of monosubstituted pyridines. The primary aim was to identify and quantitatively determine the monohydroxypyridines formed during in vitro chemical and enzymatic hydroxylation experiments.TLC studies were carried out not only on the monosubstituted pyridines, but also on 2,3-di-OH-pyridine and 3-OH-pyridine-N-oxide.The UV absorption spectra of pyridine and its substituted derivatives were recorded at a concentration of 10−3 M in ethanol, and were compared.The best TLC detection of these derivatives was elaborated too. 相似文献
2. Rf Values of Monohydroxypyridines and other Monosubstituted Pyridines (Monoamines and Monocarboxylic Acids) in Systems I and II
10.
《Analytical letters》2012,45(15):1279-1295
Abstract 5-methoxycarbonoyl-1-methyl-2-thio-1,2-dihydropyridine and 1-metyl -2-thio-1,2-dihydropyridine-5-carboxylic acid heve been studied by recent electrochemical methods. The analysis of classical, alternative (A.C.) and pulse polarograms led to precise the nature of the observed currents. The pH variatiors and the supporting electrolyte modifications have an important influence on these currents. 相似文献
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I. D. Ivanchikova G. É. Usubalieva P. V. Schastnev A. A. Moroz M. S. Shvartsberg 《Russian Chemical Bulletin》1992,41(9):1672-1679
The Cu(I)-catalyzed intramolecular cyclization of 1-phenylethynyl-and 1-hexyn-1-yl-anthraquinone-2-carboxylic acid is a 6-endo-dig-addition, whereas the reaction for 1-(3-phenoxypropyn-1-yl)anthraquinone-2-carboxylic acid proceeds in a directionally nonspecific way. It is shown that the cyclization of vicinal acetylenic derivatives of aromatic carboxylic acids leads to the formation of the more stable of the possible cyclic structures.Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Novosibirsk State University, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2138–2146, September, 1992. 相似文献
14.
A new coordination polymer with the formula of [Co(2-mpac)2(py)·4H2O)]n (1, 2-mpac = 5-methyl-2-pyrazinecarboxylic acid, py = pyrazine) has been synthesized through hydrothermal synthesis and structurally characterized by X-ray single-crystal diffraction method. 1 exhibits a 3D supramolecular network. Crystal data: monoclinic, space group C2/m, a = 15.907(9), b = 7.104(3), c = 9.793(5), β = 95.232(8)o, V = 1102.0(10)3, Z = 2, S = 0.995, the final R = 0.0509, wR = 0.1626 for 1002 observed reflections with (I > 2σ(I)) and R = 0.0530, wR = 0.1667 for all data. In addition, elemental analysis, IR and thermalgravimetric analysis are presented. 相似文献
15.
《Analytical letters》2012,45(10):2291-2306
Abstract The electrochemical behaviour of thiazolidine-4-carboxylic acid (thioproline, Thz) and its derivatives 2-propyl-thiazolidine-4-carboxylic acid (PrThz) and 2-tetrahydroxybutyl-thiazolidine-4-carboxylic acid (AThz) has been studied by cyclic, normal and reverse pulse, differential pulse and Osteryoung square wave voltam-metrics. Anodic waves, resulting from the formation of adsorbed mercury thiazolidates, were obtained for all the compounds at mercury electrodes in acetate and phosphate buffers at pH from 3.8 to 8. the initially formed mercury compounds rapidly transform into the final products accumulating on the electrode surface. the oxidation products inhibit the anodic processes and distorted voltammetric curves were obtained at the covered electrodes. Various effects of these processes in various pulse voltammetric techniques were evident. Normal pulse voltammograms were least affected by the product transformations. Osteryoung square wave voltammetry permitted very fast determinations of Thz derivatives. 相似文献
16.
《Analytical letters》2012,45(16):1311-1325
Abstract Electrochemical caracteristics of 2-mercaptopyridine-5-carboxylic acid and its methylic ester have been determined using recent polarographic techniques. Measurements have been carried out as a function of parameters such as frequency, others surimposed signals and as a function of concentration and pH. Results are compared to those obtained for selectively methylated on sulfur or nitrogen atoms derivatives. Interpretations of the data are given. The optimal conditions for a quantitative determination by D.C. and differential pulse polarography are fixed. 相似文献
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A new version of the Friedländer synthesis of 2-aminoquinoline-3-carboxylic acid and its derivatives from stable 2-tosylaminobenzaldehyde or its morpholinal was proposed. 相似文献
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