ULTRASONIC IRRADIATION AND THE HOMO- AND HETERO-DIELS-ALDER REACTION

The effects of ultrasound on the hetero- and homo-Diels- Alder reactions have been investigated varying ultrasonic source and solvent. Irradiation enhances both reactions minimally; however, while this appears to be due to cavitation in the homo Diels-Alder reaction, mechanical mixing appears to be the cause in the hetero-Diels-Alder reaction.     

PHOTO-INDUCED INTERMOLECULAR AND INTRAMOLECULAR ELECTRON-TRANSFER REACTIONS BETWEEN XANTHENE DYES AND DONORS/ACCEPTORS

A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced electron transfer reactions were determined and calculated. It is found that the photo-induced electron transfer reactions occurred between xanthene dyes and many, including very weak donors or acceptors. The rate constants of intermolecular reactions were controlled by diffusion, and influenced by the reactant concentrations. The laser flash experiments showed that for low reactant concentrations, this kind of reactions took place mainly via the triplet excited state of the dyes. If different electric charges exist with dyes and donors/acceptors, there will be static quenching of the dyes' fluorescence. The intramolecular electron transfer reactions are independent of the solution concentrations, and they may directly proceed via the singlet excited state of the dyes effectively.     

PHOTOCHEMICAL REACTIONS OF CYTOSINE AND 5-METHYLCYTOSINE WITH METHYLAMINE AND n-BUTYLAMINE

Abstract The photoinduced exchange reactions of cytosine ( la ) and 5-methylcytosine (IIa) with two primary amines have been studied. The reactions of Ia and IIa with methylamine lead, respectively, to 1-methylcytosine ( Ib ) and 1,5-dimethylcytosine (IIb) as final products; the reactions of the same two starting materials with n -butylamine gives the corresponding n -butyl compounds. The reactions of IIa with the two amines also gave small amounts of 1-methylthymine and 1- n -butylthymine. An opened ring intermediate, N-(N'-methylcarbamoyl)-3-arnino-2-methylacrylamidine ( IVa ), was isolated from the IIa -methylamine system irradiated at pH 7 and shown to be a precursor of both IIb and 1-methylthymine. The pH profiles for rate of production of IIb , 1-methylthymine and IVa in the reaction of IIa with methylamine were determined and found to be similar in shape. All three profiles show a maximum in reactivity at about pH 8.7 with some reactivity being detectable at pH values as low as 5.     

METALLAPHOSPHENES AND DIPHOSPHENES

Abstract

Transient metallaphosphenes (rbnd2;M[dbnd]P[sbnd]) have been obtained by exchange reactions between disilylphosphines and organometaldihalides (M = Ge, Sn), or by thermolysis of 2-metallaphosphetanes (M = Si, Ge). They are characterized by trapping reactions with strained heterocycles. The first stable germaphosphene 12 has been synthesized by dehydrohalogenation from the parent halogermylphosphine and isolated in form of orange crystals. It is very reactive toward compounds with active hydrogen.

Transient diphosphenes ([sbnd]P[dbnd]P[sbnd]) have been prepared by the same type of exchange reactions between disilylphosphines and dichlorophosphines and characterized by trapping reactions on dienes. The second stable diphosphene 18 has been obtained by addition of t-BuLi on trisyldichlorophosphine. Its structure has been determined by X-ray diffraction and some aspects of its reactivity are described. The reaction of bisyltrichlorogermylphosphine with DBU affords the new stable and potentially reactive diphosphene 30.     

SOME SULFUR AND NITROGEN SUBSTITUTED XYLOQUINONES

Abstract

This paper reports reactions of dihalogeno-xyloquinone with sulfur and nitrogen nucleophiles, leading to the di-and mono-substituted derivatives, respectively. The mixed nitrogen-sulfur and carbon-nitrogen derivatives were also synthesized. New reactions, oxidation of dimethylthioxyloquinone to yield a mono-sulfinyl derivative and treatment of the latter with thionyl chloride, are described.

Although dihalogeno-xyloquinones are known compounds^{2a, b} their reactions with sulfur and nitrogen nucleophiles have not been reported. These reactions seemed to be of interest in view of potential biological activity of the expected thio-and amino-substituted xyloquinones, in comparison with the naphthoquinone and benzoquinone analogues.³     

化学反应的选择性和金属有机化学

本文是对旨在提高合成效率的化学反应选择性和金属有机化学关系的综述,按金属有机化合物的基元反应进行讨论。     

PHOTOSENSITIZED OXYGENATION OF CARBONYL STABILIZED SULFUR AND PYRIDINIUM YLIDS, AND RELATED DIAZO COMPOUNDS. CARBON-SULFUR AND NITROGEN BOND CLEAVAGES

Abstract— The dye sensitized photooxygenation of sulfur and pyridinium ylids proceeds by way of singlet oxygen under the reaction conditions studied. The most remarkable results were that dimethyl sulfoxide and pyridine were obtained in the photooxygenations of oxosulfonium and pyridinium methy-lids, respectively. as the major cleavage products. These results suggested that the 1,2-dioxetane like intermediates were not significant ones in these reactions. The oxygenation reactions in the presence of diphenyl sulfide which was known as the most unreactive one to singlet oxygen afforded diphenyl sulfoxide efficiently. A new type of intermediate instead of 1,2-dioxetane. that can monooxygenate the substrate may be formed. Photosensitized oxygenations of corresponding diazo compounds were also studied.     

菁染料和份菁染料的合成及其溶液的光稳定性研究

利用UV-Vis吸收光谱仪和光化学反应器,研究了菁染料和份菁染料的光降解动力学.研究结果表明,染料在乙腈溶液中的光褪色反应遵循假一级或零级动力学衰减.与相应的份菁染料相比,携带正电荷的菁染料具有相对较好的光稳定性.     

REACTIONS OF THIOPHENES AND ACETYLENES IN POLAR AND APOLAR SOLVENTS

Abstract

Although the aromatic 6π-electron system of thiophenes is rather unreactive in cycloaddition reactions we have found that several thiophene derivatives react with acetylenes. Alkylthiophenes undergo (2+2)-cycloaddition reactions with electron-deficient acetylenes in apolar solvents in the presence of Lewis acids to give 2-thia-bicyclo [3. 2. 0] hept-3, 6-dienes (1). These compounds show isomerization via an a, a-Cope rearrangement at temperatures of 100 to 150°C.     

TETRAPHOSPHORUS TRISULFIDE IN REACTIONS WITH THIOACETALS,AMINALS, SULFENAMIDES AND DISULFIDES. INFLUENCE OF AMINES AND BENZOYL PEROXIDE

Abstract

The reactions of tetraphosphorus trisulfide with thioacetals, aminals, sulfenamides and disulfides were studied. The reactions were found to give organothiophosphorus compounds and to be facilitated by organic amines and benzoyl peroxide.     

THE FORMATION OF FREE RADICALS AND THE CONSEQUENCES OF THEIR REACTIONS IN VIVO

Abstract— Mechanisms for the initiation of free radical reactions in vivo are reviewed, including ozone and ¹O₂ reactions, radiation, one-electron transfer processes, and enzymatic reactions. The roles that radical reactions might play in aging processes and in carcinogenesis are discussed.     

THE PHOTOREDUCTION OF FLAVINS BY AMINO ACIDS AND EDTA. A CONTINUOUS AND FLASH PHOTOLYSIS STUDY

Abstract— Primary and secondary photochemical processes in oxygen-free aqueous solution have been characterised for FMN alone and in the presence of EDTA and four amino acids using nanosecond and microsecond flash photolysis and continuous photolysis techniques. The relative contributions of oneelectron and two-electron (group or hydride transfer) reactions to the deactivation of the triplet has been determined by comparing the radical concentration (560 nm) with the bleaching of the ground state (446 nm). It was concluded that one-electron reactions (hydrogen atom or electron abstraction) are the major mode of reactivity of the flavin triplet state with all the suhstrates studied.
The nature of the reactions of the flavin semiquinone radical have been studied quantitatively by microsecond flash photolysis. These secondary reactions consist of either a 'back reaction' between the flavin and substrate radicals (tryptophan or glycyl-tyrosine) or the transfer of a second electron (or hydrogen atom) from the substrate radical to the flavin radical (EDTA, methionine and possibly cysteine) to form reduced flavin and oxidised substrate. From a comparison of the quantum yields of formation of reduced flavin using 'flash' and continuous irradiation, an additional pathway for the decay of the flavin radical is suggested to occur at low light intensities in the presence of glycyl-tyrosine or histidine.     

煤中腐植酸与尿素相互作用机理的研究

采用化学法和波谱分析法对泥炭、褐煤、风化煤腐植酸（ＨＡ）与尿素的相互作用机理进行了研究。结果表明,ＨＡ与尿素之间发生了极其复杂的反应,包括离子化、络合配位、亲核加成、自由基反应及氢键缔合等,形成不同的化学键。羧基对反应深度的影响最大;含官能团（特别是羧基）最多的风化煤ＨＡ反应性最高。本项研究为有机长效尿素的研制提供了理论依据     

OPTICALLY PURE CHALCOGENURANES: SYNTHESIS AND STEREOCHEMISTRY OF THEIR REACTIONS

Abstract

An overview of our recent studies on the asymmetric syntheses, stereochemical studies, reactions and applications of chiral chalcogenuranes is described. Chiral chalcogenuranes, including halooxachalcogenuranes and spirooxachalcogenuranes, have been synthesized by highly diastereoselective oxidation of the 2-exo-hydroxy- 10-bornyl chalcogenides. The stereochemistry of chalcogenuranes have been confirmed as with a trigonal bipyramidal (TBP) geometry. Nucleophilic substitution reactions of these compounds provided a good method to prepare the chiral chalcogenonium (IV) compounds with excellent diastereoselectivity. Our results indicated that the reactivity of the axial bonds of chalcogenuranes plays an important role in the control of the stereochemistry of the reactions. The mechanistic and stereochemical research on the nucleophilic substitution reactions have been carried out which indicated that two kinds of pathways, dissociative and associative routes, might exist. The applications of the reactions through the asymmetric [2, 3] sigmatropic rearrangement and enantioselective protonation with optically active selenonium (IV) compounds have been investigated to give good to high selectivities.     

PHOTOCHEMICAL REACTIONS OF AROMATIC KETONES WITH NUCLEIC ACIDS AND THEIR COMPONENTS I—. PURINE AND PYRIMIDINE BASES AND NUCLEOSIDES*.

Abstract— The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady-state experiments. Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H-atom abstraction from the purines. Steady-state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts. All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers.     

THE PHOTOPHYSICS AND PHOTOCHEMISTRY OF THE NEAR-UV ABSORBING AMINO ACIDS–I. TRYPTOPHAN AND ITS SIMPLE DERIVATIVES

Abstract— The photophysics and photochemistry of tryptophan and its simple derivatives is comprehensively reviewed with special emphasis on excitation by near-UV radiation. Topics explicitly discussed include the origins of large Stokes shifts in the fluorescence spectra, photoionization, the puzzle of multiple tryptophan fluorescence decay time, photochemical reactions in the presence and absence of oxygen, and the possible mechanisms of these reactions. A separate section reviews the photosensitizing properties of N-formylkynurenine, an important photooxidation product of tryptophan.     

ASPECTS OF CHEMICAL DAMAGE IN RADIATION AND PHOTO-BIOLOGY

Abstract— The reactions of oxidizing free radicals produced by the action of ionizing radiation on aqueous solutions with molecules of biological interest are discussed. In particular the reactions of inorganic radical anions with proteins are considered and their use as selective probes described by example.     

ADDITION AND SUBSTITUTION REACTIONS OF ACETYLENIC AND ETHYLENIC SULPHONES WITH CUPRATES

Abstract

Synthetic, mechanistic, and stereochemical aspects of the reactions of cuprates with various systems are being investigated in these laboratories⁽¹⁾. The series of substrates includes several sulphonyl-activated compounds.     

PREPARATION AND PHOTOSENSITIVITY OF WATER SOLUBLE PHENOLIC RESINS CONTAINING ACRYLOYL AND QUATERNARY AMMONIUM CHLORIDE GROUPS

New water soluble and photocrosslinkable prepolymers colltaining acrylate and quaternary ammonium salt groupswere synthesized from epoxy phenolic resin via ring-opening reaction with acrylic acid and with aqueous solution oftriethylamine hydrochloride successively. The second reaction needs no phase transfer catalyst to accelerate, since theproduct formed can act as a phase transfer catalyst. The prepolymer obtained contains both photocrosslinkable acrylategroups and hydrophilic quaternary ammonium salt groups. Optimum conditions for these reactions were studied. Thephotosensitivity of the prepolymer was also investigated. The effects of different photoinitiators, different crosslinkablediluent monomers and amine accelerator on the photosensitivity of the prepolymer were compared. The photoinitiator ofhydrogen abstraction type is still effective without using amine or alcohol as accelerator, because the prepolymer containsα H beside the OH groups formed in the ring-opening reactions     

OH+C2H2与OH+C2H4加成反应的热力学和动力学

OH基与乙炔(乙烯)的反应是控制大气中OH基浓度的重要化学反应。对反应OH+C_2H_2,1975年Davis等用FP-RF技术测定了反应的速率常数。1977年,Perry又用同样方法对该反应作出了研究;结果表明,此反应的速率常数强烈地依赖于压力,与Davis等人的实验结果不符。对反应OH+C_2H_4,Atkinson等人的实验研究表明,压力在30.0kPa以下,反应的速率常数随压力而改变;而在30.0—88.4 kPa之间,与压力无关.这与前人的结果不同。两个反应的产物也因温度不同而异.此外,上述反应一般是在近101kPa下发生的,而实验结果大多是在低压下获得的。且目前尚无直接的理论计算结果。为此,我们在从头算水平上用统计热力学方法,对反应