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181.
固定pH滴定法测定弱酸弱碱性药物 总被引:8,自引:0,他引:8
报道一种水溶液吕测定弱酸弱碱性药物的新型滴定分析方法-固定pH滴定法,其理论基础是弱酸弱碱在水溶液中各种存在形式的分布系数在pH值固定时为常数,对甲硝唑,盐酸美西律等离散常数在10^-8至10^-11范围内的7种弱酸弱碱性药物进行测定。结果与药典法吻合,回收率在99.4%~100.6%,方法简便,快速,准确,制剂中的赋形剂及色物不影响测定。 相似文献
182.
Organic sulfonyl fluorides are of interest owing to their insecticidal, germicidal and enzyme inhibitory properties. In the current work, synthesis of p-toluenesufonyl fluoride was accomplished by reacting p-toluenesulfonyl chloride with solid potassium fluoride using PEG-400 as a catalyst under solid-liquid phase transfer catalysis (S-L PTC) at 30 °C. p-Toluenesulfonyl fluoride is used as peroxygen bleach activator. It also finds use in the treatment of Alzheimer's disease. The mechanism is based on homogeneous solubilization of solid. PEG forms a complex with metal cation which associates with the nucleophile and it participates in SN2 type reactions. The reaction is intrinsically kinetically controlled. A complete theoretical analysis is done to determine both the rate constant and equilibrium constant from the same set of data. The activation energy and Gibbs free energy are also calculated. 相似文献
183.
V. E. Schneider E. E. Tornau A. A. Vlasova A. A. Gurskas 《Journal of inclusion phenomena and macrocyclic chemistry》1985,3(3):235-242
Clathrate thermodynamic stability conditions and the phase transitions associated with either the orientational ordering of the guest molecules or with the condensation of the guest molecules in the host lattice are investigated by means of the common microscopic model. The theory proposed describes the thermodynamic properties of -hydroquinone (Q
) clathrates. The dielectric constant (T) was measured experimentally inQ
·CH3OH andQ
·SO2 in the temperature range from 4.2 to 300 K and the phase transitions were found. It is shown that the theory qualitatively explains the experimental data obtained.Dedicated to Professor H. M. Powell. 相似文献
184.
185.
The Stockmayer-Fixman-Burchard (SFB) and the Dondos-Benoit (DB) equations have been applied to determine the unperturbed dimensions parameterK
of wormlike polymers. An empirical relation between the Flory's constant and the Mark-Houwink-Sakurada (MHS) exponenta has been proposed. The values found by this equation are lower than the value 2.5×1023 used in the case of flexible polymers and this deviation is attributed to the influence of the draining effect. From theK
value and the so calculated value of , we calculate the Kuhn statistical segment length of wormlike polymers. The obtained — for a great number of wormlike polymers — statistical segment lengths are almost the same as these calculated by the Yamakawa-Fujii and the Bohdanecky methods. The molecular mass regions in which the SFB, the DB, and the MHS equations are valid are explored. A criterion for the distinction between flexible and wormlike polymers is proposed based on the way of approach to the power law. 相似文献
186.
The d. c. component of birefringence of aqueous carboxymethylcellulose (CMC) under an a. c. electric field was measured at frequencies ranging from 0.1 Hz to 100 kHz. Three samples of different molecular weights were studied with varying degree of neutralization, polymer concentration and added salt concentration. The dispersion curve of birefringence consists of three relaxation bands,A, B andC in order of decreasing frequency. RelaxationB with a negative relaxation strength is ascribed to end-over-end rotation of almost rodlike CMC molecules. RelaxationA with a positive strength is attributed to the relaxation of electrical polarizability along the minor axis of molecule. RelaxationC possesses also a positive strength and is induced by clusters of CMC molecules.Dedicated to Prof. Dr. F. H. Müller. 相似文献
187.
The basic hydrolysis of crystal violet has been studied in w/o microemulsions of the CTAB/alkanols/cyclohexane system (alkanols: 1-butanol and 1-hexanol). The reaction can be considered to occur in the water phase of the droplets and from the rate constant the apparent dielectric constant of the water phase was determined. The cyclohexane incorporation in the system produces a decrease in the effective dielectric constant of the water phase and in the specific conductivity. 相似文献
188.
V. V. Dunina M. Yu. Kazakova Yu. K. Grishin O. R. Malyshev E. I. Kazakova 《Russian Chemical Bulletin》1997,46(7):1321-1330
A new homochiral dimericortho-palladated complex bearing a bulkytert-butyl substituent at the carbon stereocenter was synthesized from optically activeN,N-dimethyl-α-tert-butylbenzylamine. Regioselective activation of only the aromatic C−H bond was shown to occur during the cyclometallation
process proceeding under very mild conditions due to steric effects. Spectral characteristics of mononuclear derivatives of
the new dimeric complex indicate that the five-membered palladacycle exists predominantly in one of two possible chiral conformations
with the axial position of thetert-butyl substituent.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1375–1384, July, 1997. 相似文献
189.
烯烃加成反应活性与烷基极化效应的关系 总被引:1,自引:0,他引:1
烯烃的自由基加成和亲电加成速率受不同的因素控制.对于仅仅含烷基取代的简单烯烃:(1)与OH自由基加成速率-log kOH可由π键上烷基极化效应指数的几何平均值GMPEIπ关联:-log kOH=a bGMPEIπ c(GMPEIπ)2; (2)与亲电试剂加成速率log k可由π键两端碳原子所连基团极化效应指数PEI(L)和PEI(S)关联:log k=a bPEI(L) cPEI(S),其中的PEI(L)和PEI(S)分别表示极化效应较大和较小的一端. 相似文献
190.
The binding constants of 1-alkanols with α-cyclodextrin (α-CD) were determined by indirect competitive potentiometry, although potentiometry is usually inapplicable to nonionic compounds. This novel method utilizes competitive binding of 1-alkanol and octyltrimethylammonium bromide (OTAB) to α-CD in aqueous media, where the concentration of free OTAB depending on the competitive binding is monitored with an OTAB-selective electrode. Therefore, the concentration of 1-alkanol is indirectly estimated from the observed electromotive force. The binding constants of 1-propapnol, 1-butanol, 1-hexanol, and 1-octanol with α-CD, obtained by this method, are close to the literature values. The implications and limitations of this indirect competitive potentiometry were discussed. 相似文献