The reactions of benzimidazole (Bimz) with dichloro{2-(arylazo)pyridine}palladium(II), [Pd(aap)Cl2(3), aap = RC6H4N= N-2-C5H4N; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] and dichloro{2-(arylazo)pyrimidine}palladium(II), [Pd(aapm)Cl2(4), aapm = RC6H4N=N-2-C6H3N2; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] were followed separately. The kinetics were examined under pseudo-first order conditions with reference to Bimz in MeCN at 385 and 390 nm, respectively and at 298 K using a u.v.–vis. spectrophotometer. The product was isolated and characterised as trans-Pd(Bimz)2Cl2. The reaction between Pd(aap)Cl2 and Bimz follows the rate law, rate = K[Bimz]2[Pd(aap)Cl2], a single step process, whereas biphasic behaviour is observed for the reaction between Pd(aapm)Cl2 and Bimz; each step is first order with respect to the concentration of complex and to Bimz. The rate data support a nucleophilic association path and the rate decreases upon addition of Cl–(LiCl). The aryl ring substituent of the arylazoheterocycle influences the substitution rate as follows: k(e) > k(a) > k(d) > k(c) > k(b). The k-values are linearly correlated with Hammett constants with usual deviations for the m-Me and o-Me substituents because of their steric crowding. The rate follows the order: k(aap) > k(aapm). This is unusual with reference to the -acidity order of the heterocycles, pyridine < pyrimidine, as the increased -acidity will enhance the nucleophilic association. The charge density calculation by MNDO method shows that in the pyrimidine ring of arylazopyrimidine, the peripheral m-N(uncoordinated) carries a high negative charge which may retard the nucleophilic association rate. This effect is absent in the pyridine ring of arylazopyridine and may be the reason for the faster single step nucleophilic substitution in Pd(aap)Cl2. 相似文献
The atom-efficient cross-coupling reaction of triarylbismuths with a variety of aliphatic, aromatic, and hetero-aromatic acyl chlorides was demonstrated to afford high yields of cross-coupled ketones under palladium catalysis. The corresponding cross-coupling reaction with diacid chlorides also furnished bis-coupled ketones in good yields. 相似文献
Recently generalized exponential distribution has received considerable attentions. In this paper, we deal with the Bayesian
inference of the unknown parameters of the progressively censored generalized exponential distribution. It is assumed that
the scale and the shape parameters have independent gamma priors. The Bayes estimates of the unknown parameters cannot be
obtained in the closed form. Lindley’s approximation and importance sampling technique have been suggested to compute the
approximate Bayes estimates. Markov Chain Monte Carlo method has been used to compute the approximate Bayes estimates and
also to construct the highest posterior density credible intervals. We also provide different criteria to compare two different
sampling schemes and hence to find the optimal sampling schemes. It is observed that finding the optimum censoring procedure
is a computationally expensive process. And we have recommended to use the sub-optimal censoring procedure, which can be obtained
very easily. Monte Carlo simulations are performed to compare the performances of the different methods and one data analysis
has been performed for illustrative purposes.
This work was partially supported by a grant from the Department of Science and Technology, Government of India 相似文献
SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements. 相似文献
α,β‐Alkenyl carboxylic acids undergo CuII‐mediated decarboxylative annulation reactions with aliphatic cyclic ketones to provide synthetically valuable di‐heterocycles. The annulation process tolerates a variety of aliphatic ketones and heterocyclic alkenyl carboxylic acids, producing substituted fused furan derivatives with complete regioselectivity. The current protocol offers a synthetically applicable pathway to construct a variety of oligo‐heterocycles through Cu‐mediated single‐electron transfer and decarboxylation. Notably, synthesis of relatively inaccessible di‐heterocycles has been achieved successfully using this protocol. 相似文献
Summary: Hybrid microgels functionalized with silver nanoparticles (AgNP) have been prepared and their physico‐chemical properties examined. Composite particles have been obtained by formation of AgNP in presence of poly[vinylcaprolactam‐co‐(acetoacetoxyethyl methacrylate)] (VCL/AAEM) microgel particles. It has been demonstrated that hybrid particles with different AgNP amounts can be prepared. Hybrid particles are sensitive to temperature and swelling, and collapse processes are reversible. Incorporation of AgNP leads to shrinkage of microgel template due to the partial immobilization of polymer chains on the microgel surface. As a consequence, gradual loss of temperature sensitivity is observed. Hybrid microgels form highly transparent well‐organized films on solid substrates, providing homogeneous distribution of AgNP in bulk material. Presence of AgNP increases considerably the thermal stability of composite films.
Schematic representation (left) and TEM image (right) of hybrid microgels containing silver nanoparticles (AgNP). 相似文献
The catalytic activity of commercially available, air and water stable ruthenium complexes in the addition of carboxylic acids to terminal alkynes was found to be drastically enhanced by the addition of small quantities of base. Moreover, the regioselectivity of the reaction can be controlled by the choice of the base so that both the Markovnikov (Na2CO3) and the anti-Markovnikov products (DMAP) are now easily accessible in excellent selectivities. 相似文献
Nanoparticles confined in droplets of less than a picoliter are forced to organize in submicronic dry grains through solvent evaporation. The evolution of structures of the grains and the constituent nanoparticles during the slow drying process are investigated in situ with small-angle X-ray scattering (SAXS) for the first time. The scattering results have been explained on the basis of the equilibrium thermodynamics of the droplets in the drying tube. We demonstrate that this technique is really efficient in describing the internal arrangement of the nanoparticles inside the drying droplets. Distinction between an almost homogeneous repartition of the nanoparticles in droplets and formation of core shell like particles even in strongly polydispersed droplets can be made using SAXS. 相似文献
[structure: see text] The potential antitumor agent (-)-dictyostatin has been synthesized utilizing Brown crotylboration to achieve eight of the eleven chiral centers. The yield for the 26-step longest sequence is approximately 4%. The C9-C10 coupling is achieved via a stereoselective vinylzincate addition. 相似文献