BaHfO_3∶Ce粉体活化能对烧结透光性影响

用正、反向共沉淀法制备了BaHfO3∶Ce粒子;用XRD、TG-DTA、SEM等测试手段对样品的物相、形貌及发光性能进行了表征;在不同升温速率条件下研究了粒子合成动力学。结果表明:由正向和反向沉淀法得到的前驱体物相变化分3个阶段,用Doyle-Ozawa和Kissinger法分别计算了各阶段的表观活化能,其平均值分别为83.41、61.70、262.11 kJ·mol-1和81.70、42.86、253.44 kJ·mol-1,计算正反向沉淀法样品的晶粒生长活化能分别为27.36 kJ·mol-1和23.07 kJ·mol-1;反向法的样品分别在530nm波长下的激发光谱和399 nm波长的发射光谱的相对发光强度优于正向法,在2 073 K真空烧结保温3 h获得具有一定透光性的BaHfO3∶Ce透明陶瓷。     

正、反向共沉淀法对Pr_2Zr_2O_7纳米粒子表观活化能的影响

以氨水作为沉淀剂,采用正、反向共沉淀法制备Pr2Zr2O7纳米粒子。利用XRD、SEM、TEM、TG-DTA等测试手段表征了样品物相及形貌;研究其制备过程中合成动力学和晶粒生长动力学,采用Doyle-Ozawa法和Kissinger法分别计算正、反向沉淀粒子在主要反应阶段的表观活化能。结果表明:反向沉淀的滴定速率为2 mL·min-1、母盐溶液初始浓度0.05 mol·L-1、反应体系温度273 K、pH值11、煅烧温度为1 173 K,保温2 h的条件下获得的样品形貌近球形、无团聚现象、一次粒径约60 nm。Pr2Zr2O7前驱体的分解过程分为3个阶段,正、反向粒子各阶段平均表观活化能分别为:71.2、97.8、183.2 kJ·mol-1和45.37、84.34、152.16kJ·mol-1;晶粒生长活化能分别为19.02和11.95 kJ·mol-1,后者比前者的晶粒生长活化能降低了7.07 kJ·mol-1;反向共沉淀制备工艺优于正向共沉淀法。     

2,4,6-三(羟基苯甲基氨基)-均三嗪的合成及其与双酚A型环氧树脂的固化行为研究

合成了一种含三嗪环结构的环氧树脂固化剂2,4,6-三(羟基苯甲基氨基)-均三嗪(MFP).用动态DSC和原位红外光谱对MFP/DGEBA(双酚A型环氧树脂)体系的固化行为进行了研究.动态DSC研究表明,由于MFP分子结构中存在两种活泼氢(酚羟基氢和仲胺氢),固化反应存在明显的两个峰,相对应的表观活化能分别为70.5 kJ.mol-1和86.5 kJ.mol-1(Kissinger法),通过与另一相似化合物固化DGEBA的比较可知,在MFP固化DGEBA的过程中,酚羟基与环氧基反应相对较难.原位红外动力学结果很好地支持了上述结论.     

氢氧化镁分解动力学的研究

以硼泥为原料与硫酸反应制备出七水硫酸镁,以氢氧化钠为沉淀剂制备出符合标准HG/T 3607-2000的氢氧化镁.利用XRD,SEM和TEM对氢氧化镁进行了表征,DTA-TG对氢氧化镁的热分解动力学进行了研究.XRD结果表明:制备粉体为单一Mg(OH)2.SEM和TEM结果表明:样品为片状或针状纤维,片直径大小不一,在20～50 nm之间,针状纤维形状不规则,大小不一致,长度在20～100 nm之间.利用Kissinger法和Ozawa法计算出的氢氧化镁热分解反应活化能分别为135.14和141.61 kJ·mol-1.利用Coats-Redfern法和Dolye法判断氢氧化镁热分解反应机理函数为A1.5.     

蔗渣的热解与燃烧动力学特性研究

利用热重分析仪对蔗渣在不同升温速率下的热解、燃烧失重特性进行了研究。采用Friedman法对反应过程中可能存在的反应机理进行初步判断，蔗渣热解过程由其主要组分半纤维素、纤维素和木质素热解的三个独立的平行反应来描述，相应的反应活化能分别为203.92 kJ·mol-1、238.50 kJ·mol-1和77.11 kJ·mol-1； 蔗渣燃烧过程分为两段，第一段类似于其热解过程，第二段由木质素热解和残焦燃烧共同组成的连续反应，反应活化能为255.57 kJ·mol-1和159.11 kJ·mol-1。通过非线性回归法拟合获得的曲线与实验曲线基本一致，证实了蔗渣的热解、燃烧过程中存在着上述假定的反应机理。     

甲基羟基铀酰离子与水的复分解反应

以醋酸铀酰为主要试剂, 在负离子检测模式下, 采用电喷雾串联质谱法制备了甲基羟基铀酰负离子. 实验发现, 气相中的甲基羟基铀酰离子与水分子发生分子离子复分解反应, 并用串联质谱法对反应产生的离子性产物进行了结构确认, 提出了反应的可能机理. 热力学计算结果表明, 该反应的ΔGReaction为-473.0 kJ/mol, ΔHReaction为-236.5 kJ/mol, ΔSSystem为0.792 kJ·mol-1·K-1. 该反应的速率常数为2.26 s-1.     

中国化学会第21届全国高中学生化学竞赛（决赛）理论试题答案

第1题计算A、B两条直线的斜率:直线A的斜率为-3.76×104直线B的斜率为-1.01×104由Clausius-Clapeyron方程lnp=-ΔvRapTHm C及直线A和直线B的斜率分别得到:ΔHA=84.0kJ.mol-1ΔHB=312.6kJ.mol-1ΔH=ΔHB-ΔHA=312.6kJ.mol-1-84.0kJ.mol-1=229kJ.mol-11-4设xA、xB分别为为DEAA三     

LiFePO4锂嵌脱动力学过程研究

采用固相法和微乳液法制备LiFePO4正极材料,制备样品分别用XRD和SEM进行表征,通过交流阻抗和充放电测试电化学性能.结果显示:微乳液法制备样品平均粒径约0.15μm,在2.5-4.0V(vs.Li/Li )范围内、15 mA·g-1电流密度下放电,首次放电容量达到163 mAh·g-1,该样品的表观Li 扩散活化能和表观电荷转移活化能计算值分别为4.95、21.4 kJ·mol-1.制备粒度小的活性物质颗粒有利于减小Li 离子脱嵌动力学限制,提高LiFePO4材料的电化学性能.     

光谱法及热动力学法研究环糊精与三氟氯氰菊酯的包合作用

制备了β-环糊精(β-CD)-三氟氯氰菊酯(CHL)包合物,采用差示扫描量热分析法和核磁共振波谱法对包合物进行表征.实验采用1HNMR研究包合物的空间结构,推测出三氟氯氰菊酯同β-CD的包合方式是从大口端进入β-CD.用化学软件对β-CD与CHL包合方式计算发现,CHL从β-CD的大口端和小口端进入,总能量分别为108.1kJ/mol与129.2kJ/mol,表明CHL从β-CD的大口端进入形成的包合物能量最低,结构最稳定.在25℃下,实验测得β-CD-三氟氯氰菊酯包合物形成常数为340.6L?mol-1,包合比是1∶1.热动力学方法研究了温度变化对包合反应的影响,计算得出包合过程的焓变-50.29kJ?mol-1、熵变120.6J?K-1?mol-1及自由能变化-14.45kJ?mol-1,进而确定了包合反应的主要驱动力是焓.     

新型无卤阻燃剂双酚S-二(5,5-二甲基-1,3-二氧杂己内磷酸酯)的热分解动力学研究

以TG-DTG为手段,研究了双酚S-二(5,5-二甲基-1,3-二氧杂己内磷酸酯)(FR)在氮气气氛中的热分解动力学,利用Kissinger和Flynn-Wall-Ozawa(FWO)法对FR进行热分解动力学分析,求出了该物质的热分解动力学参数.结果表明,Kissinger法所求得的活化能为190.16 kJ.mol-1,指前因子lgAk为17.42 s-1;FWO法所求得的活化能为198.48 kJ.mol-1.Coats-Redfern方法得到其热分解动力学方程为g(α)=(1-α)-2.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.