Direct Observation of Unstable Reaction Intermediates by Acid‐Base Complex Formation

The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X‐ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single‐crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid‐base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid‐base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X‐ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid‐base complex crystals with various alkylammonium cations. The formation of acid‐base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X‐ray techniques.     

Electrochemically Activated Reaction of Benzoyl Halides with Carbon Dioxide

The electrochemical activation and carboxylation of benzoyl halides (benzoyl bromide, chloride, and fluoride) were studied. It was found that the yield of phenylglyoxylic acid increases from zero to 88% in the transition from benzoyl fluoride to the chloride and bromide. The effect of the nature of the halogen atom in the benzoyl halide and also the nature of the supporting electrolyte and the electrode material on the electrochemical reduction and carboxylation of benzoyl halides was studied.     

Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate in Supercritical Carbon Dioxide

1,3,4,6,8-Pentamethylazulene ( 9 ), when heated at 100° in supercritical CO₂ at 150 bar in the presence of 4 equiv. of dimethyl acetylenedicarboxylate (ADM), led to the formation of 16% of a 1:1 mixture of dimethyl 3,5,6,8,10-pentamethylheptalene-1,2-dicarboxylate 12a ) and its double-bond-shifted isomer 12b as well as 4% of the corresponding azulene-1,2-dicarboxylate 13 (Scheme 4). The formation of the [1 + 2] adduct 11 (cf. Scheme 2) was not observed. Similarly, benz[a]azulene ( 25 ) yielded in supercritical CO₂ (150°/170 bar) in the presence of 4 equiv. of ADM dimethyl benzo[d]heptalene-6,7-dicarboxylate ( 29 ; 30%) and dimethyl benzo[a]cyclopent[cd]azulene-1,2-dicarboxylate ( 28 ; 22%; Scheme 5). The reaction of 5,9-diphenylbenz[a]azulene ( 26 ) and ADM in supercritical CO₂ (100°/150 bar) gave the corresponding benzo[d]heptalene-6,7-dicarboxylate 31 (22%) and dimethyl 5,9-diphenyl-4b,10-etheno-10H-benz[a]azulene-11,12-dicarboxylate( 30 ; 25%; Scheme 5).     

略论二氧化碳与澄清石灰水的反应──兼与林宜伸老师共商榷

《化学教育》1992年第9期刊登了林宜伸老师的《谈谈中学化学实验溶液浓度的选择》一文,其中谈到“饱和石灰水在各个分组实验中都可以使用”,我认为这个结论欠妥。     

Plasma Reaction Behaviors of Carbon Disulfide and Carbon Dioxide in Glow Discharges

Reaction behaviors of carbon disulfide and carbon dioxide in plasma were investigated and compared. It was found that carbon disulfide is very reactive in plasma to produce dark brown filmy polymers, but carbon dioxide does not give polymeric products at all. The difference in plasma behaviors of the two monomers can be attributed to the roles of sulfur and oxygen in the monomers. There is also some discussion on the spectro-scopic data of carbon disulfide polymers.     

Reaction of Amino-Terminated PAMAM Dendrimers with Carbon Dioxide in Aqueous and Methanol Solutions

Polyamines have been used as active materials to capture carbon dioxide gas based on its well-known reaction with amines to form carbamates. This work investigates the reactions between three amino-terminated poly(amidoamine) (PAMAM) dendrimers (G1, G3 and G5) and CO₂(g) in aqueous (D₂O) and methanolic (CD₃OD) solutions. The reactions were monitored using ¹H NMR spectroscopy, and yielded dendrimers with a combination of terminal carbamate and terminal ammonium groups. In aqueous media the reaction was complicated by the generation of soluble carbonate and bicarbonate ions. The reaction was cleaner in CD₃OD, where the larger G5 dendrimer solution formed a gel upon exposure to CO₂(g). All reactions were reversible, and the trapped CO₂ could be released by treatment with N₂(g) and mild heating. These results highlight the importance of the polyamine dendrimer size in terms of driving changes to the solution’s physical properties (viscosity, gel formation) generated by exposure to CO₂(g).     

Reaction of 2-Formyl Imidazole with Intermediates From the Baylis-Hillman Reaction

The reaction of formyl imidazole (in the presence and absence of DABCO, and with either THF or methanol as solvent) with α-hydroxylaryl derivatives of methyl acrylate affords novel synthetic intermediates. By controlling the reaction conditions, either allylic substitution products (THF, DABCO) or rearrangement (MeOH, no DABCO) products result.     

微电流法直接检测非电活性气体二氧化碳

基于非电活性气体CO_2在‘二甲亚砜/铂微电极’体系中定量的电还原反应,提出微电流法常温直接检测二氧化碳.在常规气敏微电极和硅一体化薄膜微电极器件上获得了满意的气敏响应特性:好的线性响应关系、灵敏度和响应速度.用硅微机械加工技术批量构制的薄膜微电极器件,既保持了微电极的全部优点,又实现了微电流器件结构的一体化,电流响应异常稳定和重现.     

Direct Observation of Radical Intermediates While Investigating the Redox Behavior of Thiamin Coenzyme Models

The redox behavior of “active aldehydes” 1 ⁻ derived from 3-benzylthiazolium salts and simple aldehydes in the presence of a base has been examined with low-temperature cyclic voltammetry and EPR spectroscopy. The highly negative oxidation potentials of 1 ⁻ and the spin distribution of the intermediate radicals 1 ^. indicate that the active aldehyde can act as an efficient electron mediator in thiamin-dependent enzymatic redox systems.     

过氧亚硝酸盐的化学发光反应与测定

过氧亚硝酸盐是一氧化氮衍生物,由一氧化氮和超氧阴离子反应生成,它是很强的生物氧化剂,具有很高的反应活性和不稳定性。本文详细介绍了ONOO-的化学发光分解、ONOO-与二氧化碳的化学发光反应、ONOO-化学发光测定和应用,并展望了其发展前景。引用参考文献54篇。     

二氧化碳多相催化加氢的新进展

就近年来关于ＣＯ２活化、几个重要的ＣＯ２多相催化加氢反应及廉价氢的供给的研究进展进行综述。参考文献３４篇。     

钴(Ⅱ)配合物与卟啉在超临界二氧化碳中的反应动力学研究

用紫外-可见光谱研究了1,1,1,5,5,5-六氟-2,4-戊二酮-钴(Ⅱ)二水[Co(hfac)2(H2O)2]与5,10,15,20-四(五氟苯基)卟啉(H2tpfpp)在超临界二氧化碳中反应生成钴卟啉[Co(tpfpp)]的反应动力学.在钴(II)配合物大大过量时,此反应对卟啉为一级,且其表观一级速率常数随钴(Ⅱ)配合物的浓度增加先增加、而后趋于稳定.根据实验事实,讨论了此反应的机理,得到了相应的热力学和动力学参数.     

Reaction of Proposed Phosphorothiolate S-Oxide Intermediates with Alcohols

Abstract

S-Oxide 2 is an extremely reactive intermediate. Its phosphorylation vs rearrangement rates, strongly depend upon the nature of the nucleophile.     

Mild, Reversible Reaction of Iridium(III) Amido Complexes with Carbon Dioxide

Unlike some other Ir(III) hydrides, the aminopyridine complex [(2-NH(2)-C(5)NH(4))IrH(3)(PPh(3))(2)] (1-PPh(3)) does not insert CO(2) into the Ir-H bond. Instead 1-PPh(3) loses H(2) to form the cyclometalated species [(κ(2)-N,N-2-NH-C(5)NH(4))IrH(2)(PPh(3))(2)] (2-PPh(3)), which subsequently reacts with CO(2) to form the carbamato species [(κ(2)-O,N-2-OC(O)NH-C(5)NH(4))IrH(2)(PPh(3))(2)] (10-PPh(3)). To study the insertion of CO(2) into the Ir-N bond of the cyclometalated species, a family of compounds of the type [(κ(2)-N,N-2-NR-C(5)NH(4))IrH(2)(PR'(3))(2)] (R = H, R' = Ph (2-PPh(3)); R = H, R' = Cy (2-PCy(3)); R = Me, R' = Ph (4-PPh(3)); R = Ph, R' = Ph (5-PPh(3)); R = Ph, R' = Cy (5-PCy(3))) and the pyrimidine complex [(κ(2)-N,N-2-NH-C(4)N(2)H(3))IrH(2)(PPh(3))(2)] (6-PPh(3)) were prepared. The rate of CO(2) insertion is faster for the more nucleophilic amides. DFT studies suggest that the mechanism of insertion involves initial nucleophilic attack of the nitrogen lone pair of the amide on CO(2) to form an N-bound carbamato complex, followed by rearrangement to the O-bound species. CO(2) insertion into 1-PPh(3) is reversible in the presence of H(2) and treatment of 10-PPh(3) with H(2) regenerates 1-PPh(3), along with Ir(PPh(3))(2)H(5).     

Photocatalytic Reaction of Sulfur Dioxide with Heptane in the Gas-phase Over Titanium Dioxide

IntroductionA broad range of orgainc compounds[1 ,2 ]can be oxidized by means of semiconductor pho-tocatalysis with a primary focus on Ti O2 as a durable photocatalyst in recent years.WhenTi O2 is illuminated with the light of energy greater than the semiconductor band gap,elec-tron- hole pairs(e-- h ) are formed in the conduction and thevalence bandsof thesemiconduc-tor,respectively.These charge carriers,which migrate to the semiconductor surface,are ca-pable of activating oxygen species,et…     

Promoter Effect of Potassium on an Iron Catalyst in the Carbon Dioxide Hydrogenation Reaction

Catalysts containing copper, zinc and aluminium oxides are used extensively in hydrogenation reactions, low temperature water-gas shift and low pressure methanol synthesis processes. In the present study, the effects of certain pertinent preparation parameters on catalysts' activity have been studied, applying the saturated fractional factorial experimental design method. The influence of time and temperature of calcination, aging time, the method of mixing of reactant solutions, the nature of the precipitant and the molar ratio of the latter to metal nitrates have been investigated. The catalysts prepared, using sodium carbonate showed higher activities relative to those synthesized by applying sodium hydrogen carbonate. Higher temperatures and longer time of calcination have profound effects on the activity of catalysts prepared, using sodium hydrogen carbonate. Shorter aging times and higher molar ratios of precipitant to metal nitrates promoted the activity of catalysts prepared by sodium carbonate. In case of catalysts synthesized, using sodium hydrogen carbonate as the precipitant, the aging time should be maintained as short as possible in order the catalysts to acquire higher activities.     

KI-醚类催化剂催化二氧化碳和环氧乙烷合成碳酸乙烯酯反应研究

合成了５个含有金属铁的环醚Ｆｅ（ＣＯ）３Ｌ（Ｌ１＝Ｐｈ２Ｐ（ＣＨ２ＣＨ２Ｏ）２ＣＨ２ＣＨ２ＰＰｈ２，Ｌ２＝Ｐｈ２Ｐ（ＣＨ２ＣＨ２Ｏ）４ＣＨ２ＣＨ２ＰＰｈ２，Ｌ３＝ＯＰｈ［（ＯＣＨ２ＣＨ２）ＰＰｈ２］２，Ｌ４＝ＯＰｈ［ＯＣＨ２ＣＨ２）２ＰＰｈ２］２）和［Ｆｅ（ＣＯ３）］２Ｌ５（Ｌ５＝［Ｐｈ２ＰＣＨ２ＣＨ２ＯＣＨ２ＣＨ２ＰＰｈ２］２）．对它们进行了元素分析，并用红外光谱和核磁共振谱进行了结构表征．用ＫＩ＋醚类为催化剂，催化二氧化碳与环氧乙烷反应生成碳酸乙烯酯，反应选择性大于９６．９％．催化机理为碱催化，催化剂的活性受醚的影响．能和Ｋ＋形成稳定配合物的醚可提高催化剂的活性．含金属铁的环醚和普通醚类相似，可以和钾离子作用，提高阴离子的亲核催化性能．