Showing papers on "Benzophenone published in 1990"

Femtosecond-picosecond laser photolysis studies on photoreduction process of excited benzophenone with N,N-dimethylaniline in acetonitrile solution.

Abstract: Photoreduction processes of excited benzophenone (BP) by N,N-dimethylaniline (DMA) in acetonitrile solution were studied by means of picosecond-femtosecond laser photolysis and time resolved transient absorption spectroscopy as well as transient photoconductivity measurement. Proton transfer process in the triplet ion pair formed by electron transfer (ET) at encounter between 3BP* and DMA, competing with the ionic dissociation process was observed. It was clearly demonstrated that, in addition to the triplet ion pair, the ion pair produced by the excitation of the CT complex between BP and DMA formed in the ground state and that produced by ET reaction between 1BP* and DMA played important roles in the reaction processes of excited benzophenone. The behaviors of the three kinds of ion pairs were investigated in detail, leading to the elucidation of reaction mechanism of each ion pair. The reactivity characteristic of each kind of the ion pair and its relation to the structure of the ion pair were discussed.

Excited states of ketones as electron donors—ketone—iodonium salt systems as photoinitiators for radical polymerization

Abstract: The excited states of the aromatic ketones benzophenone, 4,4′-bis(dimethylamino)benzophenone (Michler's ketone), xanthone, thioxanthone, acridone and 10-methylacridone sensitize the decomposition of diphenyl-iodonium salts via electron transfer processes. Owing to the long lifetime of the excited singlet state, at high concentrations of iodonium salts both the singlet and triplet states can function as electron donors. In the presence of methylmethacrylate an additional quenching takes place. Determination of the processes which occur in the excited states allows the photoinitiation step of the reaction to be discussed. The quantum yields of the sensitized photolysis of diphenyliodonium salts and of the polymerizations initiated by the ketone—iodonium salts systems have been determined. Some of these systems are effective photoinitiators for radical polymerization.

Picosecond and nanosecond studies of the photoreduction of benzophenone by 1,4-diazabicyclo(2. 2. 2)octane: Characterization of the transient

Abstract: The transient that is produced in the quenching of triplet benzophenone by 1,4-diazabicyclo(2.2.2)octane (DABCO) has been examined by use of nano- and picosecond laser photolysis. The initial step in all solvents, both polar and nonpolar, is electron transfer to form a triplet contact ion pair. In nonpolar solvents, the ion pair remains in this form until it decays. For polar solvents, the spectra change somewhat over the first 100 ps showing that the solvation changes and the ion pair becomes solvent separated. The lifetime of the ion pair varies greatly with the solvent. In saturated hydrocarbons it is about 80 ps. Nonpolar solvents with either {pi} electrons or a lone pair of electrons stabilize the ion pair on the nanosecond to microsecond time scale. A small amount of alcohol in benzene also stabilizes the ion pair by hydrogen bonding. A shift in the peak position with time toward the blue accompanies the formation of hydrogen bonds in this case.

Picosecond Laser Photolysis Studies on the Photoreduction of Excited Benzophenone by Diphenylamine in Solutions

Abstract: The mechanism of photoreduction of benzophenone (BP) by diphenylamine (DPA) in isooctane as well as acetonitrile and other polar solvents has been investigated by means of picosecond laser photolysis and time-resolved transient absorption spectral measurements. The results of measurements have demonstrated clearly that the hydrogen abstraction and charge transfer (CT) or ion pair (IP) state formation by electron transfer are competing at encounter between triplet benzophenone (3BP*) and DPA both in nonpolar and polar solvent, and the CT or IP state relaxed with respect to the donor acceptor configurations and solvation does not contribute to the ketyl radical formation. It has been concluded that the very short-lived CT state at encounter between 3BP* and DPA plays a crucial role in the hydrogen abstraction reaction, i.e. the mutual orientation of 3BP* and DPA in this very short-lived CT state at encounter will determine the successive process, the formation of the ketyl radical or relaxed CT or IP state.

General method for the asymmetric synthesis of anti-diastereoisomers of β-substituted L-2-aminobutanoic acids via chiral nickel(II) Schiff's base complexes of dehydroaminobutanoic acid. X-Ray crystal and molecular structure of the nickel(II) complex of the Schiff's base from [(benzylprolyl)amino]benzophenone and dehydroaminobutanoic acid

Abstract: An efficient approach to the asymmetric synthesis of (L)-allo-isomers of β-substituted α-aminobutanoic acid is described. The chiral NiII complex of a Schiff's base derived from (S)-o-[N-(N-benzylprolyl)amino]benzophenone (BBP) and glycine was treated with acetaldehyde in MeOH. The addition proceeds with high diastereoselectivity to give, if catalysed by MeONa, the corresponding complex of (R)-threonine, and, if catalysed by Et3N, the corresponding complex of (S)-allo-threonine. The (R)-threonine complex was converted into the chiral NiII complex of dehydroaminobutanoic acid, and a X-ray diffraction structural study of its major isomer showed that the dehydroaminobutanoic acid moiety was in the E-configuration. The complex, in turn, entered into Michael addition reactions with nucleophiles, including MeOH, EtOH, PhSH, and PhCH2SH. The reaction proceeded with high diastereoselectivity, producing predominantly complexes of the allo-threonine derivatives (d.e. > 90%). Diastereoisomerically and enantiomerically pure α-amino acids were obtained after chromatographic purification, decomposition of the complexes, and recovery of the initial chiral auxiliary, BBP. The thiol addition reaction is accompanied by a side reaction leading to the formation of sizeable amounts of the vinylglycine complex. An approach to the synthesis of optically active vinylglycine starting with racemic methionine is described.

Hydrogen abstraction from lipids by triplet states of derivatized benzophenone photosensitizers.

Abstract: Laser photolysis techniques have been used to characterize the reactivity of triplet state lipoidal benzophenone derivatives toward fatty acids and glycerides in benzene solution. The reactivities of benzophenone-4-heptyl-4'-pentanoic acid (BHPA) toward fatty acid compounds having different configurations of olefinic bonds have been determined. The rates of hydrogen abstraction are found to be lower when compared with similar measurements using benzophenone alone. However, the contribution of physical quenching of the triplet derivative by double bonds also appears to be slightly lower than that found with benzophenone itself. The hydrogen abstraction efficiencies of three other benzophenone derivatives toward linoleic acid in benzene have also been measured. For benzophenone incorporated into a fatty acid molecule, there is a limited relationship between structure and photoreactivity. Finally, these sensitizers have been incorporated into mixed SDS/linoleate micelles to determine the effects of molecular organization on photochemical behavior of the sensitizer and lipid.

Excited-state calorimetry studies of triplet benzophenone using time-resolved photothermal beam deflection spectroscopy

Abstract: Etude de la chaleur de reaction liberee par l'etat triplet de la benzophenone et mesure des constantes de vitesse de l'enlevement d'hydrogene de l'ethanol par la benzophenone a l'etat triplet

Method of gas separation and membranes therefor

Abstract: An improved method of gas separation and novel polyimide membranes are disclosed and claimed. Membranes in accordance with the present invention include the condensation product of fluorinated diamines such as 2,2′-bis 3-aminophenyl)hexafluoro­propane, 2,2′-bis(4-aminophenyl)hexafluoropropane and 2-(3-amino­phenyl)-2′-(4-aminophenyl)hexafluoropropane with aromatic dian­hydrides such as 3,3′, 4,4 benzophenone tetracarboxylic acid dianhydride.

Benzophenone dicarboxylic acid antagonists of leukotriene B4. 2. Structure-activity relationships of the lipophilic side chain.

Abstract: A series of lipophilic benzophenone dicarboxylic acid derivatives were found to inhibit the binding of the potent chemotaxin leukotriene B4 (LTB4) to its receptor on intact human neutrophils. Activity at the LTB4 receptor was determined by using a [3H]LTB4-binding assay. The structure-activity relationship for the lipophilic side chain was systematically investigated. Compounds with n-alkyl side chains of varying lengths were prepared and tested. Best inhibition of [3H]LTB4 binding was observed with the n-decyl derivative. Analogues with alkyl chains terminated with an aromatic ring showed improved activity. The 6-phenylhexyl side chain was optimal. Substitution on the terminal aromatic ring was also evaluated. Methoxyl, methylsulfinyl, and methyl substituents greatly enhanced the activity of the compound. For a given substituent, the para isomer had the best activity. Thus the nature of the lipophilic side chain can greatly influence the ability of the compounds to inhibit the binding of LTB4 to its receptor on intact human neutrophils. The most active compound from this series, 84 (LY223982), bound to the LTB4 receptor with an affinity approaching that of the agonist.

Photochemistry of novel 4-alkylamino benzophenone initiators: a conventional laser flash photolysis and mass spectrometry study

Abstract: Conventional microsecond and nanosecond laser flash photolysis studies have been carried out on 15 novel 4-alkylamino-substituted benzophenone photoinitiators. Using the microsecond technique, ketyl radical formation is observed from all 15 photoinitiators with a half-life longer than that for the ketyl radical of benzophenone. The formation of the radical anion through an intramolecular exciplex is considered to be an important precursor to this reaction. Triplet-triplet absorption decays by a first-order process; this decay is independent of the ground state concentration of the initiator when intramolecular hydrogen atom abstraction is structurally feasible. The solvent is also seen to influence intramolecular hydrogen atom abstraction and it dominates in acetonitrile where pseudo-first-order hydrogen atom abstraction does not occur. Photolysed product analysis using mass spectrometry complies with the conclusions from laser flash photolysis.

Photochemistry of diphenylketyl radicals in polar solvents

Abstract: The photolysis of diphenylketyl radicals in acetonitrile leads to their photobleaching with a quantum yield of 0.10. The decay of the excited radicals occurs by four different pathways: (a) doublet-doublet fluorescence; (b) radiationless decay; (c) electron photoejection, which accounts for 20% of the observed bleaching; and (d) O-H bond cleavage leading to benzophenone, which is presumed to account for the remaining 80% of the bleaching

Reactions of pyridin-3-ol with pulse-radiolytically generated reducing species

Abstract: Rate constants for reactions of hydrated electron, hydrogen atom, and other reducing radicals such as (CH3)2COH and CO2– with pyridin-3-ol at different values of pH have been determined using the pulse-radiolysis technique. The absorption spectra of the transient product species and kinetic parameters pertaining to them have been investigated. Of the above reducing species all except e–aq lead to transient species other than the one-electron reduction product of pyridin-3-ol. (CH3)2ĊOH and CO2– radicals are found to add on to the pyridin-3-ol ring. Pyridin-3-ol radicals formed by reaction with e–aq are found to be highly reducing in nature and transfer electrons to thionine, methylene blue, safranine, anthraquinone 2-sulphonate, paraquat, and benzophenone with almost diffusion-controlled rate constants.

Benzophenone dicarboxylic acid antagonists of leukotriene B4. 1. Structure-activity relationships of the benzophenone nucleus.

Abstract: A series of lipophilic benzophenone dicarboxylic acid derivatives was prepared which inhibited the binding of the potent chemotaxin leukotriene B4 to its receptor(s) on intact human neutrophils. With a radioligand-binding assay as a measure of receptor affinity, a structure-activity relationship for this series was investigated. Both acidic residues were required for receptor-binding activity. The relative orientation of the two acidic groups was important for optimal binding. Replacement of the carbonyl group of the benzophenone with a variety of polar and nonpolar linking groups led to only small changes in binding affinity, indicating the linking group may not be involved in receptor recognition. Further structure-activity relationships within this series are reported in an accompanying paper.

Synthesis of 1-(2,6-Dihydroxyphenyl)-1-alkanones and Benzophenone by Aromatization of 2-Acyl-3-hydroxy-2-cyclohexene-1-ones with Mercuric Acetate

Abstract: 1-(2,6-Dihydroxyphenyl)-1-alkanones, natural products identified from insects and from medicinal plants, are readily prepared from 1,3-cyclohexanedione and appropriate carboxylic acids. The final step involves aromatization using mercuric acetate

Electron-transfer-induced photoarrangements and photooxygenations of 1,1,2,3-tetraarylcyclopropanes

Abstract: 1,1-Diaryl-trans-2,3-diphenylcyclopropanes and trans-2,3-diaryl-1,1-diphenylcyclopropanes were prepared by di-π-methane rearrangement of 1,1-diaryl-3,3-diphenylpropenes and 3,3-diaryl-1,1-diphenylpropenes, respectively. In nonpolar and in polar solvents, tetraarylcyclopropanes are inert toward singlet oxygen. In the presence of 9,10-dicyanoanthracene (DCA), irradiation of cyclopropanes in O 2 -saturated acetonitrile (MeCN) solutions yield oxygenation products; benzophenone and benzaldehyde as main products and 1,2-dioxolanes

Benzophenone ether esters, processes for their preparation, and their use for improving the light stability of polyester dyeings

Abstract: The present invention relates to compounds of the general formula I ##STR1## in which R1, R2, R3, R4, R5, x and y are defined as in the description, processes for their preparation, their use for improving the light stability of polyester dyeings and a dyeing process and dye preparations.

Reactions of triplet carbonyl compounds and nitro derivatives with silanes

Abstract: The photoinduced reactions of aromatic and aliphatic carbonyl compounds and nitro derivatives with tetramethylsilane, hexamethyldisilane, and tetrakis(trimethylsilyl)silane were investigated by EPR spectroscopy. The photoreaction of benzophenone with the three silanes was also studied by time-resolved optical techniques. Triplet ketones and quinones reacted with Me 3 SiSiMe 3 and with (Me 3 Si) 4 Si by a radical-like displacement mechanism

Photochemistry in cyclodextrins

Abstract: The photochemistry of two ketones with contrasting excited state reactivity (benzophenone and 4-phenylbenzophenone) incorporated into β-cyclodextrin (β-CD) was investigated. The formation of a 1:1 benzophenone-β-CD complex was demonstrated by UV spectroscopy and the association constant K was determined to be 670 ± 60 mol −1 dm 3 . However, the reactive ketone triplet state was quenched by the carbohydrate, preventing the observation of room temperature phosphorescence (RTP). The possibility that the 3 n,π* state was self-quenched in a 2:1 complex was ruled out on the basis of the observed photochemistry and the temperature dependence of the quenching. In contrast, the RTP of the related compound, 4-phenylbenzophenone, in β-CD solution was demonstrated for the first time.

Thermal diffusivity measurements in benzophenone crystals using photoacoustic techniques

Abstract: The amplitude of the photoacoustic signal is measured as a function of chopping frequency for thin benzophenone polycrystalline samples in the temperature range 100–300 K. Analysis of experimental results, obtained by rear surface illumination, allows us to determine the thermal diffusivity of benzophenone crystals in the whole temperature range.

Effect of the nitrogen position on the excited state properties of the six isomeric di-pyridyl-ketones

Abstract: The properties of the excited states of the six isomeric di-pyridyl-ketones have been investigated in acetonitrile solution. Triplet lifetimes and yields were obtained by pulsed techniques and/or by phosphorimetric quenching and sensitization measurements. By comparison with benzophenone, the effect of the heterocyclic nitrogen atom is seen to produce a shortening of triplet lifetime and a decrease in the intersystem crossing and emission yields. Even though all of these molecules are characterized by the lowest excited states of n π* configuration localized on the carbonyl, their deactivation pathways were found to be mainly determined by the position of the nitrogen atoms in the aromatic rings.

A laser flash photolysis study of di-pyridyl ketones

Abstract: The effects of solvent and structure on the photophysical properties of the six isomeric di-pyridyl ketones have been investigated by nanosecond laser flash photolysis. Triplet-triplet absorption spectra and triplet lifetimes have been determined in benzene and acetonitrile. Ketyl radicals formed by hydrogen abstraction from the solvent have been identified in isobutyl alcohol from their doublet-doublet absorption and slow decay. Radicaloid transients, other than ketyls, have also been detected on flashing some of the isomers in both polar and hydrogen donating solvents. Structure and solvent effects on photochemistry of these molecules are discussed in the light of the photophysical results.