Photoreduction of 9,10-anthraquinone derivatives: transient spectroscopy and effects of alcohols and amines on reactivity in solution

The photoreduction of 9,10-anthraquinone (AQ), the 2-methyl, 2-ethyl, 2,3-dimethyl, 1,4-difluoro, 1-chloro and 1,8-dichloro derivatives as well as 1,4,4a,9a-tetrahydroanthraquinone, 1,2-benzanthraquinone and 6,13-pentacenequinone in nonaqueous solution at room temperature was studied by time-resolved UV-visible spectroscopy. Upon 308 nm excitation of AQ the triplet state reacts with alcohols and triethylamine (TEA). The rate constant of triplet quenching by amines is close to the diffusion-controlled limit. The semiquinone radical *QH/ Q*- is the main intermediate, and the half-life of the second-order decay kinetics depends significantly on the donor and the medium. Photoinduced charge separation after electron transfer from amines to the triplet state of AQ in acetonitrile and the subsequent charge recombination or neutralization also were measured by transient conductivity. The maximum quantum yield, lambdairr = 254 nm, of photoconversion into the strongly fluorescing 9,10-dihydroxyanthracenes is close to unity. The fluorescence with maximum at 460-480 nm and a lifetime of 20-30 ns disappears as a result of a complete recovery into AQ, when the dihydroxyanthracenes are exposed to oxygen. The mechanisms of photoreduction of parent AQ in acetonitrile by 2-propanol and in benzene and acetonitrile by TEA are discussed. The effects of AQ follow essentially the same pattern. The various functions of oxygen, e.g. (1) quenching of the triplet state; (2) quenching of the semiquinone radical, thereby forming HO2*/O2*- radicals; and (3) trapping of the dihydroxyanthracenes are outlined.     

Photoreduction of benzophenones by amines in room-temperature ionic liquids

[reaction: see text] The amine-mediated photoreduction of benzophenones in room temperature ionic liquids was investigated. Unlike the analogous reaction in organic solvents, the photoreduction produces mainly the corresponding benzhydrol in most cases. Because the reaction consumes only 1 equiv of amine and the solvent can be easily recycled, the photoreduction allows a very clean method for the conversion of benzophenones to benzhydrols.     

Photoreduction of oxoisoaporphine dyes by amines: transient-absorption and semiempirical quantum-chemical studies

Photoreduction by amines of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the metastable N-hydrogen oxoisoaporphine anion. During photoreduction that occurs from the triplet manifold of the oxoisoaporphine, a radical ion A(-)(*), a neutral-hydrogenated radical A-NH(*), and the metastable ion A-NH(-) of the oxoisoaporphine are formed. We present time-resolved spectroscopic data and quantum mechanical semiempirical PM3 and ZINDO/S results for the transient species formed during the flash photolysis of oxoisoaporphines in the presence of amines. These calculations reproduce adequately the experimental spectra of the triplet-triplet absorption near 450 nm, and that of neutral hydrogenated radical of the studied oxoisoaporphines centered at 390 nm. A transient absorption observed near 490 nm, for all of the studied systems, was explained by considering the formation of radical ion pair between the radical anion of the oxoisoaporphine, A(-)(*), and the radical cation of the amine, whose ZINDO/S calculated spectra generate the strongest transition near the experimentally observed absorption maximum at 490 nm, supporting the formation of a radical ion pair complex as the first step of the photoreduction.     

Dual-function of alcohols in gold-mediated selective coupling of amines and alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol.     

Concentration effects in the nucleophilic reactions of tertiary amines in aqueous solutions: Alkylation of amines with chloroacetic acid

In alkylations of tertiary amines with chloroacetic acid in aqueous solutions, an increase in the initial concentrations of reagents to a certain level led to an abrupt increase in the initial rates and conversions attained during the control time. Viscosimetric and refractometric data showed that association with reagents occurred in these systems. The structures of associates that determine the character of the concentration effects of the Menschutkin reaction in water were suggested.     

Photoreduction of 4,4'-bipyridine by amines in acetonitrile-water mixtures: influence of H-bonding on the ion-pair structure and dynamics

The photoreduction of 4,4'-bipyridine (44BPY) by diazabicyclo[2.2.2]octane and triethylamine (TEA) is investigated by using picosecond transient absorption and time-resolved resonance Raman spectroscopy in various acetonitrile-water mixtures. The results are interpreted on the basis of a preferential solvation effect resulting from the presence of a specific interaction between 44BPY and water by hydrogen bonding. Below 10% water, the free 44BPY species is dominant and leads upon photoreduction to a contact ion pair that undergoes efficient intrapair proton transfer if TEA is the amine donor. Above 10% water, most of the 44BPY population is H-bonded and leads upon photoreduction to a hydrated ion pair in which the intrapair proton transfer is inhibited. Instead, the 44BPY(-*) species is protonated by water through the hydrogen bond with a rate constant that increases by more than 3 orders of magnitude on going from 10% to 100% water. The dependence of this rate constant on the solvent mixture composition suggests that the reaction of intracomplex proton transfer is controlled by the hydration of the residual OH(-) species by three molecules of water, leading to a trihydrated HO(-)(H(2)O)(3) species.     

Photoreduction of benzophenone by dimethylaminoethyl methyacrylate in solutions

The photoreduction of benzophenone by dimethylaminoethyl methacrylate was investigated under the conditions of stationary and pulsed irradiation. With stationary irradiation of this system in benzene an intermediate photoproduct is formed, and its destruction is described by a kinetic equation of second order. By irradiation under pulsed conditions it is possible to detect the formation of the ketyl radicals of benzophenone, the yield and destruction of which depend substantially on the nature of the medium. The relationship between the destruction constant and the concentration of the aminomethacrylate and butyl methacrylate was examined and explained; the constant increases with decrease in the aminomethacrylate concentration and with increase in the butyl methacrylate concentration. The mechanism of the photoreduction of aromatic carbonyl compounds by aminomethacrylates is described.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, 56–62, January–February, 1990.     

Microheterogeneity in aqueous-organic solutions: Heat capacities,volumes and expansibilities of some alcohols,aminoalcohol and tertiary amines in water

The heat capacities per unit volume and the densities of aqueous solutions of 2-propanol, neopentanol, tert-amylalcohol, 2-amino-2-methylpropanol, triethylamine and diethylmethylamine were measured, in many cases as a function of temperature, over the whole mole fraction or solubility range. Apparent and partial molal heat capacities, volumes and expansibilities were derived. The concentration dependence of these functions suggest the existence of transitions in some of these systems, in the water-rich region, qualitatively similar to micellization. The large relaxation contribution observed with some of the thermodynamic functions of hydrophobic alcohols and amines suggests a reinforcement of hydrophobic hydration due to strong hydrogen-bonding interactions of the polar groups with water.     

Acetylenic alcohols and amines of the diphenyl oxide series

Conclusions A number of alcohols and amines-derivatives of 4-ethynyldiphenyl oxide and 4,4 -diethynyldi-phenyl oxide-were synthesized. Important differences in the reactivity of the starting mono- and diacetylenes in the Favorskii and Mannich reactions were not detected.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 905–908, April, 1967.     

Electrochemical acylation and alkylaminocarbonylation of amines and alcohols

Electrochemical acylation and ethylaminocarbonylation of amines and alcohols are performed by anodic oxidation of the hydroxamic acids and N-ethyl-N′hydroxyurea, respectively, in acetonitrile at a glassy-carbon electrode.     

Ruthenium catalyzed synthesis of secondary or tertiary amines from amines and alcohols

Unsymmetrical secondary and tertiary amines are prepared by the ruthenium catalyzed reaction of alcohols with amines, which provides highly efficient method for synthesis of cyclic amines.     

Benzofuran derivatives. Part 3 On the reactivities of the intermediates in benzofuran synthesis

3-Methyl-5-nitrobenzofuran ( 2 ) and 3-methyl-5-nitrobenzofuran-2-carboxylic acid ( 3 ) were obtained by heating 2-acetyl-4-nitrophenoxyacetic acid ( 1 ) with various bases in acetic anhydride. It appeared that 3-hydroxy-3-methyl-5-nitro-2,3-dihydrobenzofuran-2-carboxylic acid ( 4 ) was the intermediate in the benzofuran synthesis. The properties of 4 were examined under various conditions. Using strong bases such as triethyl-amine in place of sodium acetate, 3-methyl-5-nitrobenzofuran-2-carboxylic acid ( 3 ) was obtained exclusively. However, in the presence of acetic acid in the reaction mixture 3-methyl-5-nitrobenzofuran ( 2 ) was obtained in good yield. The reaction pathways for the formation of 2 and 3 are discussed.     

Concentration effects in the nucleophilic reactions of tertiary amines in aqueous solutions. Alkylation of amines with ethylene chlorohydrin

During the alkylation of tertiary amines with ethylene chlorohydrin in aqueous solutions, the initial rates and degrees of conversion attained within control periods of time showed nonstandard dependences on the initial concentrations of reagents. The character of the concentration dependences depended on the structure of the hydrocarbon fragments and the available sets of functional groups in amines. On the basis of our results and viscosimetric data for the model systems, we assumed that these effects were due to pre-reaction association involving the reagents and products.     

Solid-phase synthesis of bicyclic dipeptide mimetics by intramolecular cyclization of alcohols, thiols, amines, and amides with N-acyliminium intermediates

A general strategy for the solid-phase synthesis of structurally diverse bicyclic dipeptide mimetics is presented. Depending on the amino acid side-chain (R(1)), peptide-derived N-acyliminium intermediates may undergo nucleophilic attack from either side-chain functional groups (-OH, -NH(2), -SH, and -CONH(2)) or the amide backbone (-CONH-) of the peptide, thus affording a range of aza-, thia-, and oxabicycloalkanes in excellent purity and diastereoselectivity. [reaction: see text]     

Ethyl pentafluoropropanethioate: A useful pentafluoropropionylating agent for amines and alcohols

Ethyl pentafluoropropanethioate, prepared by treating ethanethiol with hexafluoro-1, 2-epoxypropane in the presence of triethylamine, was found to be a convenient pentafluoropropionylating agent for amines and alcohols.     

纳米二氧化铈催化制备亚胺

近年来,金属氧化物的晶面效应及其独特的催化性能引起研究者的广泛关注.其中,二氧化铈(CeO2)因具有储放氧性质、易于形成氧空位等特点,在诸多领域得到应用,尤其是作为催化剂,可用作活性相、载体、复合催化材料等. CeO2的晶面效应主要由于晶面上氧空位的性质引起的.目前,这方面的研究主要集中在高温条件下氧空位的动态转化过程,如水汽变换反应、有机物脱除等.但是高温下CeO2中氧空位的活泼性,增加了晶面效应的复杂性.因此,利用低温液相有机反应作为探针,研究晶面效应是一种可靠的解决方案.我们近些年的工作研究了CeO2不同晶面上的酸性及催化水解性能,在本研究中,我们提出在温和条件下, 采用有机探针反应,研究不同晶面的氧化还原性质.亚胺类化合物作为一类重要的含氮有机中间体,在生物、农药、医药等领域中具有重要应用.传统的亚胺合成方法是将醛类化合物或酮类化合物与胺类在酸催化剂的作用下直接缩合.近年来出现了新的亚胺合成方法,例如通过胺类氧化脱氢、炔烃的氢胺化、醇胺脱氢/氧化偶联等,其中醇胺脱氢/氧化偶联的方法因具有原料廉价易得、过程清洁等优点,而成为研究热点.最近, Masazumi Tamura等研究发现CeO2能够在温和条件下高效催化醇胺氧化偶联制亚胺,通过一系列表征发现CeO2的高活性主要由于其氧空位中存在丰富的活性氧物种.然而, CeO2的晶面效应及其在此反应中的催化性能,以及不同晶面上的氧化还原性质还有待进一步的研究.本文研究了CeO2的晶面效应及其在醇胺氧化偶联制亚胺反应中的催化性能.在温和的反应条件下(60 oC), CeO2能够高效催化苯甲醇与苯胺反应制备亚胺,并且对底物具有很好的普适性,在催化一系列醇与胺氧化偶联制亚胺的反应中,对于大部分底物,醇类化合物的转化率可达89%以上,亚胺类化合物的选择性可达90%以上.通过水热合成法分别制备了棒状CeO2、立方体CeO2和八面体CeO2,并通过X射线衍射、透射电子显微镜和高分辨透射电子显微镜确证了其结构和形貌,结果表明三种形貌的CeO2均为纯相的CeO2,其中棒状CeO2暴露(110)和(100)晶面,立方体CeO2暴露(100)晶面,八面体CeO2暴露(111)晶面.并以苯甲醇氧化反应和苯甲醇与苯胺反应为探针研究了其催化性能.结果发现：不同形貌的CeO2具有显著不同的催化活性,其中棒状CeO2表现出最优异的催化性能,立方体CeO2和八面体CeO2次之.通过Raman光谱表征了不同形貌CeO2的氧空位性质并比较了它们的氧空位浓度.结果发现：棒状CeO2的氧空位浓度相对值(A595/A462)为0.077,高于立方体CeO2和八面体CeO2.通过比较分析计算可知,在CeO2(110),(100)和(111)三种晶面中,(110)晶面因其具有最多的氧空位而表现出最高的催化活性和优异的氧化还原性质,(110)晶面上亚胺的生成速率为4.618 mmol/(g·h),分别为(100)晶面和(111)晶面上的32倍和49倍.该研究有助于提高认识CeO2基催化材料的低温氧化还原性质.