Crosslinking of chlorine‐containing polymers by dicyclopentadiene dicarboxylic salts

Alkali‐ and alkali‐earth‐metal salts of dicyclopentadiene dicarboxylic acid (DCPDCA) were prepared and employed as crosslinkers for chlorine‐containing polymers such as polychloromethylstyrene (PCMS), chlorinated polypropylene (CPP), polyepichlorohydrin (PECH), and poly(vinyl chloride) (PVC). Thermally reversible covalent crosslinks (i.e.,  DCPD bridges) between polymer chains were generated through esterification between the chlorine–carbon bonds of the polymer and the carboxylic salt groups of the crosslinker. The crosslinking reactivity decreased in the following sequence: K > Na > LiDCPDCA > alkali‐earth‐metal salts of DCPDCA. In addition, PCMS and CPP had higher gelation rates than PECH and PVC. Good flowability at about 195 °C and solubility in maleimide‐containing dichlorobenzene on heating indicated that the crosslinked PCMS and CPP exhibited thermally reversible crosslinking because of dimer/monomer (cyclopentadiene) conversion of  DCPD moieties via reversible Diels–Alder cycloaddition. Samples of PECH and PVC crosslinked by the alkali salts of DCPDCA were insoluble even when heated in maleimide‐containing dichlorobenzene. However, these crosslinked polymers could be dissolved partially after the same treatment when the crosslinker was an alkali‐earth‐metal salt of DCPDCA. Thermal degradation such as dehydrochlorination of the PECH and PVC might have been responsible for uncontrolled crosslinking because these two polymers are known to be thermally unstable. The unreacted COOK, COONa, or COOLi of the crosslinkers might have initiated base‐induced dehydrochlorination when PECH and PVC were heated at high temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 818–825, 2000     

CX_2(X=H,F,Cl)与甲基异丙基醚C-H键插入反应的理论研究

用从头计算方法在MP2 /6 31G(d)水平上研究了CX2 (X =H ,F ,Cl)与甲基异丙基醚的C -H键插入反应。CCl2 与甲基异丙基醚两个不同的α C的C -H键插入势垒分别为 117.2kJ/mol (甲基 )和 2 0 .6kJ/mol (异丙基 )。CF2 与异丙基α C的C -H键上插入势垒为 12 0 .0kJ/mol,在插入甲基上C -H键时会引起C -O键的断裂。CH2 的插入反应则不需要势垒。对CX2 与二甲醚、甲乙醚、甲基异丙基醚、甲基苄基醚上各种不同的C -H键插入势垒进行了比较 ,甲基和苯基都促使其毗邻的C -H键更容易被CX2 所插入     

碳锂化反应的研究进展

介绍了近年来碳锂化反应在分子间和分子内以及不对称反应方面的研究进展。     

手性3-溴-2(5H)-呋喃酮的合成及其串联的不对称Michael加成 反应的研究

研究了新的手性试剂,5-(l-孟氧基)-3-溴-呋喃酮(5a)的合成及其与亲核性醇发生的串联不对称双Michael加成/分子内亲取代反应。通过此反应,一举生成了四个新的手性中心,得到了一般方法难以合成的含有多个手性中心的丁内酯并螺－环丙烷类化合物8a～8d。详细报道了8a～8d的合成方法以及它们的[α]、IR、UV、^1^HNMR、^13^CNMR、MS、元素分析等结构分析数据。此不对称双Michael加成/分子内亲核取代反应可以为某些新的光学活性螺－环内丙烷类化合物以及某些复杂结构的分子提供合成策略。     

硝基苯并噻唑重氮氨基偶氮苯与汞的显色反应研究

报道了新试剂硝基苯并噻唑重氮氨基偶氮苯 ( NBTDAA)与汞的显色反应。结果表明 ,在非离子表面活性剂 Triton X-1 0 0存在下 ,p H为 9.5～ 1 0 .0的 Na2 B4O7-Na OH缓冲体系中 ,汞与该试剂能形成 1∶ 4的络合物 ,其最大吸收波长为 51 5nm ,表观摩尔吸光系数为 1 .3 5× 1 0 5 L· mol- 1 · cm- 1 ,线性范围 0～ 1 2μg/ 2 5m L。用拟定的方法测定了废水中的汞 ,结果满意。     

Synthesis and X-ray structural characterisation of the tetramethylene oxonium derivative of the hydrodecaborate anion. A versatile route for derivative chemistry of [B10H10]

The oxonium derivative P(C₆H₅)₄[2-B₁₀H₉O(CH₂)₄] (1) has been prepared from [B₁₀H₁₀]²⁻ by a solvent-addition reaction route, promoted by Et₂O · BF₃. Its structure has been confirmed by single crystal X-ray analysis. 1 is assumed to be a useful synthon for the derivative chemistry of [B₁₀H₁₀]²⁻. As an illustration, ring-opening reaction occurred in presence of the strong nucleophilic agent OH⁻, giving the monoanionic derivative [P(C₆H₅)₄]₂[2-B₁₀H₉O(CH₂)₄OH] (2).     

Use of isothermal microcalorimetry in pharmaceutical preformulation studies

Excipient compatibility of a new chemical entity was assessed using an isothermal microcalorimeter. Mixtures of an active pharmaceutical ingredient with a primary amine group and excipients were prepared in a 1:1 ratio and compatibility monitored by exposing to 50, 60 and 70°C in presence of 200 mL of water. The new chemical entity, a primary amine, reacted with reducing sugars such as lactose and resulted in a brown discoloration. This reaction is the Maillard type condensation reaction between amines and reducing sugars. The rate of reaction was dependent on the temperature with rapid degradation at higher temperatures. No other incompatibility was apparent between the primary amine and other excipients This revised version was published online in July 2006 with corrections to the Cover Date.     

The reaction of substituted N-phenacyl-pyridinium bromides in the pyridine ring with DABCO and DBU in water and DMSO. Kinetics and DFT studies

The rate constants have been measured for deprotonation reaction of substituted N-phenacyl-pyridinium bromides, in the pyridine ring, with 1,4-diazabicyclo[2,2,2]octane in water and DMSO, and some with 1,8-diazabicyclo[5,4,0]undec-7-ene. The dependence of the rate constant, k, on pK_a of substituted pyridines is made of two distinct linear branches obtained for the salts with electron-withdrawing and electron-donating substituents, respectively. The structures of four salts have been determined by the B3LYP/6-31G(d,p) level of theory and compared with the available X-ray structure. The effect of the substituent and solvent on k values has been discussed.     

Application of the semilocalized approach to chemical reactivity of butadiene

The semilocalized approach to chemical reactivity (J. Mol. Struct. (Theochem) 588 (2002) 99; Int. J. Quant. Chem. 94 (2003) 302) is applied to study the addition reaction of an electrophile or nucleophile to the butadiene molecule. In accordance with the classical concept of the reaction center and its neighborhood (substituent), only one of the two H₂C=CH-fragments of butadiene is supposed to be under a direct attack of the reagent, whereas the remaining H₂C=CH-group is assumed to play the role of the substituent and thereby to participate in the process indirectly by exerting certain electron-donating or accepting effect upon the former group and/or the reagent. The main aim of the study consists in revealing the role of the H₂C=CH-substituent in the formation of the known higher reactivity of the terminal carbon atom of the attacked C=C-bond (as compared to the internal atom) irrespective of the nature of the reagent. To this end, we seek to obtain an explicit algebraic representation of the interdependence between the direction and the extent of the total influence of the H₂C=CH-substituent, on the one hand, and the nature of the reagent, on the other hand. The expressions for electron density and bond order redistributions among separate fragments of contacting molecules derived previously in the form of power series are shown to yield the above-anticipated representation. On this basis, it is demonstrated that the electron-donating effect of the initially occupied (bonding) orbital of the substituent and the electron-accepting effect of its initially vacant (antibonding) orbital upon the remaining fragments of the whole reacting system may be considered independently whatever the nature of the reagent. However, a strong interdependence is established between the actual relative extents of these two components of the total effect of the H₂C=CH-group and the electron-donating (accepting) properties of the reagent. Moreover, this group of atoms is shown to manifest itself as an electron-donating (accepting) substituent under influence of an electrophilic (nucleophilic) attack. Using this principal result of the paper, the actual reactivity of butadiene with respect to electrophile (nucleophile) is interpreted by invoking a model system of a substituted ethene containing a simple (one-orbital) electron-donating (accepting) substituent, and a terminal addition easily follows for both types of the reagent.