Highly Chemoselective Allylic Reductions with Silicon Hydrides and Palladium Catalyst

Novel reducing systems, comprising various silicon hydrides and a soluble palladium(0) catalyst, allow very mild and chemoselective reductive cleavage of allylic heterosubstituents. Other easily-reducible functionalities such as ketones, aldehydes and Michael-acceptors are not affected under these conditions. The relative reactivities of twelve commercially available silanes towards allylic reduction were determined using ¹H NMR techniques. Similarly, the role of various reaction parameters such as temperature, solvent and concentration of reactants, and the effect of added water and zinc chloride on the reduction rate have been studied.     

氯铬酸吡啶/硅胶载体氧化剂的制备及其对醇的氧化研究

利用二氧化硅作载体，负载氯铬酸吡啶制备了一种新的载体氧化剂，研究了该氧化剂的氧化性。该试剂制备简单，性质稳定，应用于各种醇的氧化，能高收率得到相应的醛（酮），反应操作简单，提纯方便。     

New progress in the chemistry of stable metallaaromatic compounds of heavier group 14 elements

By taking advantage of kinetic stabilization afforded by introduction of an efficient steric protection group, several kinds of silaaromatic compounds, such as silabenzene, 1- and 2-silanaphthalenes, and 9-silaanthracene, were successfully synthesized and isolated as stable compounds. The first stable germaaromatics, such as germabenzene and 2-germanaphthalene, were also synthesized by the use of a similar synthetic approach. Most of their molecular structures were definitively determined by X-ray crystallographic analysis. The novel molecular structures and unique reactivities of these metallaaromatic species are discussed on the basis of the experimental results together with those obtained by theoretical calculations, focusing on their aromaticity.     

辅酶NADH模型物还原α,β-环氧酮为β-羟基酮反应活性的研究

在光照条件下,辅酶NADH模型物可以直接还原α,β-环氧酮为β-羟基酮,并且活性强弱顺序为：AcrH2〉BNAH〉HEH。     

Schiff bases and their complexes: Recent progress in thermal analysis

Schiff bases are versatile compounds synthesized from the condensation of primary amino compounds with aldehydes or ketones. The high thermal of many Schiff base and their complexes were useful attributes for their application as catalysts in reactions involving at high temperatures. This thermal behavior of Schiff bases and their complexes was evaluated by TGA/DTG and DTA curves with mass losses related to dehydration and decomposition. This review summarizes the developments in the last decade for thermal analysis of Schiff bases. Therefore, synthesis of Schiff bases and their complexes are reviewed.     

Stable silyl, germyl, and stannyl cations, radicals, and anions: heavy versions of carbocations, carbon radicals, and carbanions

The rapidly growing chemistry of the cations, radicals, and anions based on the group 14 elements heavier than carbon (Si, Ge, Sn, and Pb) is one of the most important organometallic fields. Recent developments in this research area moved such species from the class of short-lived reactive intermediates to the class of easily accessible, isolable, and fully characterizable compounds. In this Account, we deal with the major accomplishments in the field of the stable representatives of "heavy" cations, radicals, and anions.     

Combustion of toluene-hexane binary mixtures in a reverse flow catalytic reactor

This work is focused on the application of reverse flow reactors to the combustion of lean mixtures of aliphatic and aromatic hydrocarbons in air. For this purpose, hexane and toluene were chosen as model compounds. The combustion of binary mixtures of these compounds (up to 500 ppmV total hydrocarbon concentration) over a commercial Pt/Al₂O₃ catalyst in reverse flow reactors has been studied both experimentally, in a bench-scale unit, and by simulations, using a heterogeneous mono-dimensional dynamic model, good correspondence being observed between both approaches.As general trend, it was observed that the behaviour of the reactor is determined mainly by the combustion enthalpies and reactivities of toluene and hexane. Hence, increasing total concentration and increasing fraction of toluene (the most reactive compound) lead to more stable operation. Regarding the kinetic inhibition effects, in the conditions studied no influence on the reactor performance was observed, probably because the hydrocarbons combust in different reactor zones. This behaviour can be extended to the combustion of aromatic and C₅-C₈ alkanes, characterised by their relatively low concentrations (determined by their vapour pressure) and high reaction rates.     

Enamides and enecarbamates as nucleophiles in stereoselective C-C and C-N bond-forming reactions

Because the backbone of most of organic compounds is a carbon chain, carbon-carbon bond-forming reactions are among the most important reactions in organic synthesis. Many of the carbon-carbon bond-forming reactions so far reported rely on nucleophilic attack of enolates or their derivatives, because those nucleophiles can be, in general, readily prepared from the corresponding carbonyl compounds. In this Account, we summarize the recent development of reactions using enamide and enecarbamate as a novel type of nucleophile. Despite their ready availability and their intrinsic attraction as a synthetic tool that enables us to introduce a protected nitrogen functional group, enamide and enecarbamate have rarely been used as a nucleophile, since their nucleophilicity is low compared with the corresponding metal enolates and enamines. A characteristic of enamides and enecarbamates is that those bearing a hydrogen atom on nitrogen are relatively stable at room temperature, while enamines bearing a hydrogen atom on nitrogen are likely to tautomerize into the corresponding imine form. Enamides and enecarbamates can be purified by silica gel chromatography and kept for a long time without decomposition. During the investigation of nucleophilic addition reactions using enamides and enecarbamates, it has been revealed that enamides and enecarbamates bearing a hydrogen atom on nitrogen react actually as a nucleophile with relatively reactive electrophiles, such as glyoxylate, N-acylimino ester, N-acylimino phosphonate, and azodicarboxylate, in the presence of an appropriate Lewis acid catalyst. Those bearing no hydrogen atom on nitrogen did not react at all. The products initially obtained from the nucleophilic addition of enamides and enecarbamates are the corresponding N-protected imines, which can be readily transformed to important functional groups, such as ketones by hydrolysis and N-protected amines by reduction or nucleophilic alkylation. In the nucleophilic addition reactions of enamides and enecarbamates to aldehydes, it was unveiled that the reaction proceeds stereospecifically, that is, (E)-enecarbamate gave anti product and (Z)-enecarbamate afforded syn product with high diastereoselectivity (>97/3). This fact can be rationalized by consideration of a concerted reaction pathway via a hydrogen-involved cyclic six-membered ring transition state. In the addition reactions to N-acylimino phosphonates, much higher turnover frequency was observed when enamides and enecarbamates were used as a nucleophile than was observed when silicon enolates were used. When silicon enolates were used, the intermediates bearing a strong affinity for the catalyst inhibited catalyst turnover, resulting in low enantioslectivity because of the dominance of the uncatalyzed racemic pathway. In the case of nucleophilic addition of enamides and enecarbamate, however, a fast intramolecular hydrogen transfer from the enecarbamate nitrogen may prevent the intermediate from trapping the catalyst for a long time, to afford the product with a high enantioselectivity. In conclusion, enamides and enecarbamates, although originally employed as just N-analogues to silicon enolates, have emerged as remarkably useful nucleophiles in a variety of Lewis acid-catalyzed reactions.     

Liquid phase oxidation of the light ketones

Acetone, methyl ethylketone, methyl isopropylketone and toluene were oxidized separately in the liquid phase by oxygen at 140°C, under 15 atm partial pressure of oxygen with 1 wt % di- ter- butylperoxide. The main product is acetic acid. Acetone is much less reactive than the other two ketones. Cooxidations of binary mixtures composed of a ketone and toluene were performed under the same experimental conditions. In these cooxidation systems, the three ketones have similar reactivities. The discrepancy between the relative reactivities of the ketones oxidized alone or with toluene is interpreted by the theory of the branched chain oxidations, and indicates the great influence of the chain branching coefficients and the stability of the free peroxy radicals on the total rate of oxidation of the ketones.     

环氧硅酸酯的合成研究

直接从SiO2 (白炭黑 )制备了高活性的五配位硅化合物 ,并用带环氧官能团的含卤化合物与活性五配位硅作用 ,衍生出带有环氧官能团的硅酸酯。借助于X 衍射法测试手段 ,对合成产物进行了分析。结果表明 ,高活性的五配位硅呈强碱性 ,吸水性强 ,吸收水分后很快分解还原成SiO2 和有机物。而在含卤化合物与活性五配位硅化合物作用生成硅酸酯后 ,即控制和消除了这种可逆反应 ,制备出了稳定的环氧硅酸酯。     

Determination of heavy hydrocarbon contamination using supercritical fluid extraction with infrared detection

Supercritical fluid extraction (s.f.e.) conditions to extract heavy hydrocarbons quantitatively from soil were developed, using high temperature (150 °C) and an infrared-clear organic solvent. S.f.e. with pure CO₂ at 65 °C gave good recovery of light crude oil components ( C25 alkanes) but did not efficiently extract heavier components. An increase in temperature during s.f.e. to 150 °C increased the recovery of the heavier hydrocarbons, but the best recoveries were achieved by extraction at 150 °C after addition of perchloroethylene as a modifier. Under these conditions s.f.e. (15 min static followed by 15 min dynamic extraction) gave recoveries 5–45% higher than did 4 h of Soxhlet extraction for soils contaminated with light to heavy crude oils, motor oil and heavy residual oil. Adsorption of the extracted polar compounds on silica indicated that both polar and non-polar organics were more efficiently extracted by s.f.e., Since the modifier is added directly to the soil sample, the method does not require either dual pumps or premixed fluids.     

Deep desulfurization of full range and low boiling diesel streams from Kuwait Lower Fars heavy crude

Information on feed quality and, in particular, various types of sulfur compounds present in the diesel (gas oil) fractions produced form different crudes and their HDS reactivities under different operating conditions are of a great value for the optimization and economics of the deep HDS process. This paper deals with deep desulfurization of gas oils obtained from a new heavy Kuwaiti crude, namely, Lower Fars (LF) which will be processed in the future at Kuwaiti refineries. Comparative studies were carried out to examine the extent of deep HDS, and the quality of diesel product using two gas oil feeds with different boiling ranges. The results revealed that the full range diesel feed stream produced from the LF crude was very difficult to desulfurize due to its low quality caused by high aromatics content (low feed saturation) together with the presence of high concentrations of organic nitrogen compounds and sterically hindered alkyl DBTs. The low-boiling range gas oil showed better desulfurization compared with the full range gas oil, however, deep desulfurization to 50 ppm sulfur was not achieved even at a temperature as high as 380 °C for both feeds. The desulfurized diesel product from the low-boiling gas-oil feed was better in quality with respect to the S, N and PNA contents and cetane index than the full-range gas-oil feed.     

粉煤灰碱熔-水热合成沸石用于水溶液中汞的吸附

汞被认为是危害最为严重的重金属之一。目前虽已有大量水处理技术可用于水中汞的去除,但由于成本较高等原因均未实现大面积的工业化应用。以工业固废粉煤灰为原料通过碱熔-水热法合成了沸石,可将其应用于水溶液中汞的吸附。结果表明:碱熔活化可以使得粉煤灰中稳定的莫来石、石英及非晶相矿物转变为钠铝硅酸盐、硅酸钠和钠霞石等矿物;这些矿物可溶于氢氧化钠溶液中,形成富含钠、铝、硅的碱性溶液;在适宜的水热条件下,通过调配铝硅比,可合成纯度较高的NaA型沸石;该法合成的粉煤灰基沸石可有效吸附水溶液中的Hg(II),去除率可达95%左右,吸附过程符合拟二级吸附动力学模型,反应速率同时受到内外扩散影响。     

Synthetic applications of nonmetal catalysts for homogeneous oxidations

Nonmetal oxidation catalysts have gained much attention in recent years. The reason for this surge in activity is 2-fold: On one hand, a number of such catalysts has become readily accessible; on the other hand, such catalysts are quite resistant toward self-oxidation and compatible under aerobic and aqueous reaction conditions. In this review, we have focused on five nonmetal catalytic systems which have attained prominence in the oxidation field in view of their efficacy and their potential for future development; stoichiometric cases have been mentioned to provide overview and scope. Such nonmetal oxidation catalysts include the alpha-halo carbonyl compounds 1, ketones 2, imines 3, iminium salts 4, and nitroxyl radicals 5. In combination with a suitable oxygen source (H2O2, KHSO5, NaOCl), these catalysts serve as precursors to the corresponding oxidants, namely, the perhydrates I, dioxiranes II, oxaziridines III, oxaziridinium ions IV, and finally oxoammonium ions V. A few of the salient features about these nonmetal, catalytic systems shall be reiterated in this summary. The first class entails the alpha-halo ketones, which catalyze the oxidation of a variety of organic substrates [figure: see text] by hydrogen peroxide as the oxygen source. The perhydrates I, formed in situ by the addition of hydrogen peroxide to the alpha-halo ketones, are quite strong electrophilic oxidants and expectedly transfer an oxygen atom to diverse nucleophilic acceptors. Thus, alpha-halo ketones have been successfully employed for catalytic epoxidation, heteroatom (S, N) oxidation, and arene oxidation. Although high diastereoselectivities have been achieved by these nonmetal catalysts, no enantioselective epoxidation and sulfoxidation have so far been reported. Consequently, it is anticipated that catalytic oxidations by perhydrates hold promise for further development, especially, and should ways be found to transfer the oxygen atom enantioselectively. The second class, namely, the dioxiranes, has been extensively used during the last two decades as a convenient oxidant in organic synthesis. These powerful and versatile oxidizing agents are readily available from the appropriate ketones by their treatment [figure: see text] with potassium monoperoxysulfate. The oxidations may be performed either under stoichiometric or catalytic conditions; the latter mode of operation is featured in this review. In this case, a variety of structurally diverse ketones have been shown to catalyze the dioxirane-mediated epoxidation of alkenes by monoperoxysulfate as the oxygen source. By employing chiral ketones, highly enantioselective (up to 99% ee) epoxidations have been developed, of which the sugar-based ketones are so far the most effective. Reports on catalytic oxidations by dioxiranes other than epoxidations are scarce; nevertheless, fructose-derived ketones have been successfully employed as catalysts for the enantioselective CH oxidation in vic diols to afford the corresponding optically active alpha-hydroxy ketones. To date, no catalytic asymmetric sulfoxidations by dioxiranes appear to have been documented in the literature, an area of catalytic dioxirane chemistry that merits attention. A third class is the imines; their reaction with hydrogen peroxide or monoperoxysulfate affords oxaziridines. These relatively weak electrophilic oxidants only manage to oxidize electron-rich substrates such as enolates, silyl enol ethers, sulfides, selenides, and amines; however, the epoxidation of alkenes has been achieved with activated oxaziridines produced from perfluorinated imines. Most of the oxidations by in-situ-generated oxaziridines have been performed stoichiometrically, with the exception of sulfoxidations. When chiral imines are used as catalysts, optically active sulfoxides are obtained in good ee values, a catalytic asymmetric oxidation by oxaziridines that merits further exploration. The fourth class is made up by the iminium ions, which with monoperoxysulfate lead to the corresponding oxaziridinium ions, structurally similar to the above oxaziridine oxidants except they possess a much more strongly electrophilic oxygen atom due to the positively charged ammonium functionality. Thus, oxaziridinium ions effectively execute besides sulfoxidation and amine oxidation the epoxidation of alkenes under catalytic conditions. As expected, chiral iminium salts catalyze asymmetric epoxidations; however, only moderate enantioselectivities have been obtained so far. Although asymmetric sulfoxidation has been achieved by using stoichiometric amounts of isolated optically active oxaziridinium salts, iminium-ion-catalyzed asymmetric sulf-oxidations have not been reported to date, which offers attractive opportunities for further work. The fifth and final class of nonmetal catalysts concerns the stable nitroxyl-radical derivatives such as TEMPO, which react with the common oxidizing agents (sodium hypochlorite, monoperoxysulfate, peracids) to generate oxoammonium ions. The latter are strong oxidants that chemoselectively and efficiently perform the CH oxidation in alcohols to produce carbonyl compounds rather than engage in the transfer of their oxygen atom to the substrate. Consequently, oxoammonium ions behave quite distinctly compared to the previous four classes of oxidants in that their catalytic activity entails formally a dehydrogenation, one of the few effective nonmetal-based catalytic transformations of alcohols to carbonyl products. Since less than 1 mol% of nitroxyl radical is required to catalyze the alcohol oxidation by the inexpensive sodium hypochlorite as primary oxidant under mild reaction conditions, this catalytic process holds much promise for future practical applications.     

Determination of forms of organic sulfur in coal by step-wise oxidation with perchloric acid-ferric perchlorate mixture

Differentiation of organic sulfur forms in coal by step-wise oxidation with a mixture of perchloric acid (HClO₄) and ferric perchlorate (Fe(ClO₄)₃) was studied. Various organic sulfur compounds were oxidized with HClO₄ solution containing Fe(ClO₄)₃, and the amounts of sulfate formed during reaction were measured. The compounds can be grouped into three categories according to their reactivities as follows: (1) easily oxidized ones, i.e. disulfides, for which almost all of the sulfur was converted to sulfate after oxidation, (2) less reactive ones including aliphatic sulfides, aliphatic and aromatic thiols (20–30% of sulfur in these compounds was oxidized to sulfate), and (3) relatively stable ones, i.e. thiophenes and aromatic sulfides, from which no sulfate was formed. Samples of Illinois No. 6 and Bevier coals were also reacted with HClO₄ solutions containing increasing concentration of Fe(ClO₄)₃. The organic sulfur in these coals could be differentiated into various groups according to their reactivities.     

Allylic polymers from resin acids. Monomer synthesis at high temperature

New chemical compounds, i. e. ketones of the abietic acid-diallyl maleate Diels-Alder adduct, have been synthesized when the reaction of abietic acid and diallyl maleate was carried out at high temperatures (up to 250°C). Having unsaturated groups in their structure, they are polymerizable substances. The monomers and the polymers have been investigated by commonly used chemical and physical methods. The polymers are soluble in polar organic solvents only at low molecular weights. The behavior of these compounds as crosslinking monomers in copolymer systems has been examined.     

有机锆络合物在高选择性催化反应中的应用

有机锆络合物可以高选择性地催化环辛二烯加氢、烯烃与２－甲基吡啶偶合反应、环酮与醛、醇交叉缩合反应、ＭＰＶ型酮还原和ＯＰＰ型醇氧化反应及多羟基化合物酰基化等反应．这些反应在有机合成中具有应用价值。     

Condensation Reactions of Softwood and Hardwood Lignin Model Compounds Under Organic Acid Cooking Conditions

In order to examine the condensation reactions of softwood and hardwood lignin during organic acid cooking, mixtures of benzyl alcohol type lignin model compounds with guaiacyl and syringyl units as the sources of benzyl cations and creosol and 5-methoxycreosol as the sources of electron-rich aromatic carbons were cooked under acidic pulping conditions.

From the yield of the condensation products in the initial reactions, it was shown that the carbonium cations of guaiacyl nuclei were more reactive than those of syringyl nuclei.

Syringyl type aromatic ring carbons had higher reactivities than guaiacyl type ones.

The cleavage of the benzyl ether bond in syringyl compounds was slower than that of guaiacyl compounds.

The diphenylmethane structures formed by the condensation reaction between veratryl alcohol and 5-methoxycreosol were found to be unstable under the strong acidic cooking conditions.

It is concluded that the condensation reactions between benzylic cations from the guaiacyl compounds and the electron rich aromatic ring carbons of syringyl ones are very fast, but the condensation products are unstable under the strong acidic pulping conditions.

When the guaiacyl nuclei react as an electron-rich aromatic carbon, the reaction is slower but the condensation product is much more stable.

These differences in reactivities, and the stabilities of the condensation products, may contribute to the resistance of softwood toward complete delignification on acid pulping.     

不同ZSM-5分子筛对增产低碳烯烃的性能对比及改性研究

低硅择形分子筛在增产液化气和丙烯方面优于高硅择形分子筛,但加入低硅择形分子筛助剂后汽油收率降低幅度较大。改性后ZSM-5分子筛制备的催化剂与未改性ZSM-5分子筛制备的催化剂相比,液化气和丙烯产率均有明显提高,重油产率明显降低,转化率升高,总液收基本不变,汽油中烯烃含量有所降低,芳烃含量提高。