Showing papers on "Benzophenone published in 1972"
148 citations
TL;DR: The photoreactivity of benzophenone in water has been reinvestigated in this article, where it is suggested that hydrogen abstraction from water occurs to give free OH radicals which then attack benzphenone to give a cyclohexadienyl radical.
Abstract: Phosphorescence has been observed from oxygen-free aqueous solutions of benzophenone and acetophenone. In the case of benzophenone the phosphorescence is strongly self-quenched. Rate constants for quenching of triplet benzophenone by various species have been measured.The photoreactivity of benzophenone in water has been reinvestigated. Photolysis does occur, the quantum yield being low and somewhat irreproducible. Benzopinacol is a product of the photolysis in oxygen-free solution, while in aerated solution hydroxybenzophenones are formed with a very low quantum yield.Flash photolysis experiments have characterized the triplet-triplet absorption of benzophenone in aqueous solution and show that the ketyl radical and another radical are intermediates in the reaction. It is suggested that hydrogen abstraction from water occurs to give free OH radicals which then attack benzophenone to give a cyclohexadienyl radical. The energetics of this process are considered.
82 citations
TL;DR: 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.
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.
65 citations
TL;DR: In this paper, the authors studied the energy-resolved decay of benzophenone in the gas phase at various pressures and showed that it exhibits the characteristics of strong coupling between the S1 and T1 vibronic levels.
Abstract: We have studied the energy‐resolved decay of benzophenone in the gas phase at various pressures. In the ``isolated‐molecule'' case benzophenone is shown to exhibit the characteristics of strong coupling between the S1 and T1 vibronic levels. A small contribution from weakly coupled vibrational levels may also be present and is discussed in the context of a weak coupling model.
61 citations
TL;DR: In this article, semi-empirical calculations of zero-field-splitting parameters have been performed for the lowest triplet states of aromatic ketones, the mixing between the nearly degenerate n, π* and ππ,π* triplets states through the vibronic and spin-orbit interactions being considered.
Abstract: Semi-empirical calculations of zero-field-splitting parameters have been performed for the lowest triplet states of aromatic ketones, the mixing between the nearly degenerate n, π* and π, π* triplet states through the vibronic and spin-orbit interactions being considered. The results show that the mixing through the spin-orbit interaction is important to explain the absolute values and signs of the zero-field-splitting parameters observed for acetophenone, p-chlorobenzaldehyde, and benzophenone. The observed and calculated D values are -0·1943 cm-1 and -0·180 cm-1 for the lowest triplet state of p-chlorobenzalhyde in p-dibromobenzene.
61 citations
TL;DR: In this paper, the electron transfer complex between photoactivated benzophenone and ground-state amine was found to be the chain-initiating species for methyl acrylate.
Abstract: Benzophenone-sensitized photopolymerization of methyl acrylate was shown to be remarkably enhanced by the addition of small amounts of triethylamine. This was attributed to the efficient formation of an electron-transfer complex between photoactivated benzophenone and ground-state amine. Ketyl and amine free radicals derived from this complex were postulated to be the chain-initiating species. Quantum yield experiments indicated that methyl acrylate itself was also a quencher of the benzophenone triplet state.
60 citations
TL;DR: A black man with a broad-spectrum light sensitivity simultaneously showed an urticarial and contact sensitivity to a preparation containing 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (sulisobenzone).
Abstract: A black man with a broad-spectrum light sensitivity simultaneously showed an urticarial and contact sensitivity to a preparation containing 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (sulisobenzone). Both the benzophenone and sulfonic acid parts of the molecule were required for elicitation of the contact reaction, while benzophenone alone elicited the urticarial reaction.
55 citations
TL;DR: In this paper, the photo-oxidation products of EPC were identified as ethyl o-aminobenzoate, ethyl n-phenyl-carbamate (EPC), aniline, water, carbon dioxide, azo compounds, and other colored material.
Abstract: The photo-oxidation products of ethyl N-phenyl-carbamate (EPC) were identified as ethyl o-aminobenzoate, ethyl p-aminobenzoate, aniline, water, carbon dioxide, azo compounds, and other colored material. The ethylaminobenzoates, formed by intramolecular rearrangement of EPC, were precursors of the azo and colored products. Diethyl 4,4′-azobenzenedicarboxylate was produced by the ultraviolet irradiation of the precursor, ethyl p-aminobenzoate, in the presence of oxygen. Benzophenone and anthraquinone, as the triplet donors, sensitized the photo-oxidation of EPC. Quantum yields of photolysis of EPC were measured. The photorearrangement reaction was inhibited by the polar solvent (ethanol). The presence of metal ions and phenyl isocyanate in EPC showed no effect on the oxygen consumption rate.
44 citations
TL;DR: In this paper, a compound was identified as Na-[Co(I)TPP]·5THF (tetraphenylporphin is abbreviated to TPP).
Abstract: Cobalt(I) tetraphenylporphin was prepared by reduction of tetraphenylporphinatocobalt(II) with sodium benzophenone ketyl in tetrahydrofuran (THF) and was purely isolated. The compound was identified as Na-[Co(I)TPP]·5THF (tetraphenylporphin is abbreviated to TPP). On the basis of electronic absorption spectrum, magnetic circular dichroism, magnetic susceptibility and NMR spectrum, the complex formed was concluded to be a complex of cobalt(I). Although some part of cobalt electron is migrated into the conjugated system of porphin, an electron furnished by the reducing reagent is mainly trapped by the central cobalt. The compound should be named sodium tetraphenylporphinatocobaltate(I).
34 citations
TL;DR: Two main reactions are observed: thymine dimerization and chain break formation in benzophenone in the presence of calf thymus and E. coli DNA, which leads to photosensitized damages to the macromolecule.
Abstract: — Excitation of benzophenone in the presence of calf thymus and E. coli DNA leads to photosensitized damages to the macromolecule. Two main reactions are observed: thymine dimerization and chain break formation. Benzophenone photosensitized chain breaks are also observed in polyadenylic acid.
The melting temperature of DNA decreases with the duration of irradiation.
Under our experimental conditions, the ratio of the yields of dimers and single-chain breaks produced in DNA is about 1. Photosensitized damage to deoxyribose residues leading to chain breakage is shown to be similar to that produced by X or γ ray irradiation. The oxygen effect upon chain break production is studied and discussed in relation with its effect upon intermediate species.
Thymine dimers are formed following energy transfer from benzophenone in its triplet state. In previous flash-photolysis studies we showed that benzophenone in its triplet state reacts with water molecules to give ketyl and OH radicals. Ketyl radicals are not involved in reactions with DNA. It is proposed that OH radicals produced in the above reaction are responsible for the production of single-chain breaks by attack on the deoxyribose residues.
33 citations
TL;DR: In this article, it was shown that tertiary aromatic amines can donate an electron to triplet benzophenone, and lend some credence to the previous postulate that amines react with triplet ketones by an electron-transfer process.
Abstract: Triphenylamine and tri-p-tolylamine quench the photoreduction of benzophenone by diphenylmethanol and in the case of triphenylamine, the quenching effect is substantially increased by a change of solvent from benzene to acetonitrile. Flash photolysis of nitrogen-flushed acetonitrile solutions of tri-p-tolylamine containing benzo-phenone, produced the amine radical cation and the radical anion of the ketone. When oxygenated solutions of either the amine alone of amine plus benzophenone were flash-photolysed, only the radical cation of the amine was observed. The lifetime and concentration of the radical cation is increased as the concentration either of oxygen or of benzophenone is increased. One of the modes of decay of the radical cation appears to be reaction with tri-p-tolylamine and a rate constant of 3·5 × 103 l mol–1 s–1 was determined for this process. Nitrogen-flushed acetonitrile solutions of triphenylamine gave, on flash photolysis, an intermediate (λmax. 610 nm) identified, from previous work, as cyclisation product, whereas when benzophenone is present in solution, the amine radical cation is produced. These results support the conclusion that tertiary aromatic amines can donate an electron to triplet benzophenone, and lend some credence to the previous postulate that amines react with triplet ketones by an electron-transfer process.
TL;DR: In this article, the ESR spectra of the mixtures of benzophenone and aromatic amines have been studied in rigid solutions, and it has been concluded that benzphenone as an acceptor forms the molecular complexes with various aromatic amine as donors.
Abstract: Electronic absorption and emission spectra of the mixtures of benzophenone and aromatic amines have been studied in rigid solutions. From absorption spectral measurements, it has been concluded that benzophenone as an acceptor forms the molecular complexes with various aromatic amines as donors. Emission spectra different from those of the component molecules were observed at longer wavelengths in the same systems. The maxima of the anomalous emission spectra of these systems were found to shift slightly to lower frequencies with the decrease in the ionization potentials of donor molecules. On account of their decay times, the emissions may be ascribed to the phosphorescence of benzophenone-aromatic amine complexes. Photolysis of benzophenone-aromatic amine complexes in rigid matrices always resulted in the appearance of the visible absorption spectrum of benzoketyl radical, together with ESR spectra, the analysis of which indicated that there is an interacting pair of radicals which is in the combined tr...
TL;DR: The first complete spectral distribution of the benzophenone fluorescence was presented in this article, where a pulsing nitrogen laser (3371 A, ≈ 6 nsec) was used to induce the fluorescence.
TL;DR: An investigation of benzophenone phosphorescence in water, and of its quenching by pyrimidine and purine derivatives, was undertaken to overcome the abovementioned difficulties.
Abstract: BENZOPHENONE has been used in aqueous solution to photosensitize the formation of cyclobutane dimers of pyrimidine derivatives (Charlier and Helene, 1967; Von Wilucki et af., 1967; Greenstock and Johns, 1968). This photosensitized reaction is assumed to involve energy transfer from the benzophenone triplet state, thus populating the triplet state of the pyrimidine derivative, which then reacts with a ground-state molecule to give a cyclobutane dimer. In order to provide evidence for the energy-transfer step, we studied the transient species produced during flash excitation of benzophenone and their subsequent reactions with pyrimidine and purine derivatives (Charlier and Helene, 1972). Two transient species (triplet-state molecules and ketyl radicals) were identified on the basis of different decay kinetics and different spectra. The benzophenone triplet-' state lifetime in water was determined to be 65 psec from the decay of the triplet-triplet absorption (A,,,= = 525 nm). However, overlap of the triplet-triplet and ketyl radical absorption spectra prevents accurate determination of the triplet-state lifetime in the presence of quenchers, especially in the case of purine derivatives, which do not affect markedly the yield of ketyl radicals (Charlier and Helene, 1972). Since phosphorescence emission from the benzophenone triplet state has already been observed in organic solvents at room temperature (Parker, 1968; Clark et al., 1969; Saltiel et al., 1970), an investigation of benzophenone phosphorescence in water, and of its quenching by pyrimidine and purine derivatives, was undertaken to overcome the abovementioned difficulties.
TL;DR: In this article, the rate constants for decarboxylation of several acids of the type RXCH2CO2H (X = O, S, and NH), sensitised by benzophenone and tetrachloro-p-benzoquinone have been determined.
Abstract: The rate constants for the decarboxylation of several acids of the type RXCH2CO2H (X = O, S, and NH), sensitised by benzophenone and tetrachloro-p-benzoquinone have been determined. The reactions are considered as occurring via exciplex formation between the carbonyl compound and the acid, and in agreement with this hypothesis, the published values of rate constants for the reaction of triplet benzophenone with substituted hydrocarbons (RXCH3) are very similar to those determined for reaction with the corresponding carboxylic acid. In addition, the rate constants for decarboxylation are in the order expected from a consideration of the ionisation potentials of their corresponding substituted hydrocarbon (RXCH3). The rate constants for reaction with the quinone are higher than those for the corresponding reactions with benzophenone. Decarboxylation of (phenylthio)acetic acid in acetonitrile solution is acid catalysed whereas in benzene solution, acids slightly retard the reaction. This reaction is also quenched by methyl phenyl sulphide. Attention is drawn to the fact that the inefficiency of photoreduction of benzophenone by substituted hydrocarbons (RXCH3) can stem from the hydrogen abstraction reaction being reversible, as well as being due to exciplex formation.
TL;DR: The mechanism of the benzophenone-photosensitized degradation of films of poly(vinyl chloride) was studied in this paper, both under vacuum and in the presence of oxygen.
Abstract: The mechanism of the benzophenone-photosensitized degradation of films of poly-(vinyl chloride) was studied, both under vacuum and in the presence of oxygen. Initial rapid increases in absorption in the 340 nm region strongly implicate the ketyl radical in the initiation process which involves the abstraction by triplet benzophenone of a methylenic hydrogen from poly(vinyl chloride). Dehydrochlorination then occurs by a chain mechanism, and the conjugated polyene structure produced photosensitizes further initiation and, in the presence of oxygen, photo-oxidation of the polymer.
TL;DR: In this paper, a refined calculation that accounts for molecular polarizabilities, crystal reaction fields and resulting field induced moments in polar molecular crystals allows excited-state dipole moments and polarizability to be derived from optically determined Stark splitting versus applied electric field results.
Abstract: A refined calculation that accounts for molecular polarizabilities, crystal reaction fields and resulting field induced moments in polar molecular crystals allows excited‐state dipole moments and polarizabilities to be derived from optically determined Stark splitting versus applied electric field results. The determination of these excited‐state properties in a dipolar lattice is particularly dependent on the evaluation of the local field at a molecular site. For this case, the local field is evaluated by introduction of an ellipsoidal cavity approximation and by using the Ewald‐Kornfeld lattice summation method for dipolar arrays. The dipolar benzophenone crystal was chosen to demonstrate this method. The dipole moments of the lowest 1nπ* and 3nπ* states of benzophenone have been determined and are 1.23 D and 1.72 D, respectively; these are the zero field values and refer to the benzophenone molecules in the absence of the crystal environment. The polarizabilities of benzophenone in its ground, 1nπ* and...
TL;DR: In this article, it was suggested that the deactivation of triplet ketones may be a result of either electron transfer and hydrogen-atom transfer, and the conclusion was reached that deactivation may result from either or both electron transfer or hydrogen atom transfer.
Abstract: Triplet benzophenone does not react efficiently with aniline, o-toluidine, and diphenylamine to give isolable products However, flash-photolysis studies showed that the ketone quite efficiently abstracts hydrogen from the amines From a consideration of the kinetics of decay of the α-hydroxydiphenylmethyl radical, pathways were suggested whereby the radicals may react so as to produce the starting compounds These results lead to a questioning of the assumption that primary and secondary aromatic amines act purely as physical quenchers for triplet ketones and the conclusion is reached that deactivation may be a result of either or both electron transfer and hydrogen-atom transfer 9,10-Dihydroacridine reacts with excited benzophenone, benzylideneacetophenone, and benzylideneacetone to give isolable reduction products
TL;DR: In this paper, three types of T → S emission were detected and the importance of vitreous defects in crystalline benzophenone was examined, as a function of temperature between 7 and 77°K.
Abstract: The phosphorescence from benzophenone crystals has been investigated as a function of temperature between 7 and 77°K. Three types of T → S emission are detected and the importance of vitreous defects in crystalline benzophenone is examined.
TL;DR: The efficiency of transfer from the triplet of polymethylvinylketone (PMVK) to naphthalene has been measured at 77°K as mentioned in this paper, which is the usual value of Ro for exchange interaction without migration.
TL;DR: In this article, photolysis of ethyl diazoacetate in the presence of benzophenone gave an oxazoline incorporating the eleme-means of the EDE.
Abstract: Photolysis of ethyl diazoacetate and of ethyl diazomalonate in acetonitrile gave oxazoles. Photolysis of ethyl diazoacetate in the presence of benzophenone gave an oxazoline incorporating the eleme...
TL;DR: In this article, the photochemical reduction of azobenzene in isopropyl alcohol has been investigated and it was shown that the π,π* excited triplet state (T2) abstracts a hydrogen atom.
Abstract: The photochemical reduction of azobenzene in isopropyl alcohol has been investigated. The n-π* transition of azobenzene caused only the cis-trans photoisomerization, while the n-π* transition caused both photoisomerization and photoreduction. The reduction product was hydrazobenzene. The photoreduction was accelerated by a small amount of oxygen and was quenched by 1,3-pentadiene. The photoreduction was sensitized by fluorene and the aromatic carbonyl compounds (benzophenone, benzaldehyde, and acetophenone). These results suggest that the π,π* excited triplet state (T2) of azobenzene abstracts a hydrogen atom.
TL;DR: In this article, a high pressure 100-W mercury lamp was used to photolyze polyoxime-urethane, and the rate of decomposition of the NO bond was determined by use of ultraviolet and infrared spectra.
Abstract: Polyoxime-urethanes have been synthesized from dioximes and diisocyanates, and their structures have been ascertained by elemental analysis and infrared spectroscopy. They can be represented by the general formula:
These polymer films were photolyzed by using a high-pressure 100-W mercury lamp, and the rate of decomposition of the NO bond was determined by use of ultraviolet and infrared spectra, or comparing the photochemical behavior with that of corresponding model compounds. Upon irradiating these polymers in the presence or absence of sensitizers or a hydrogen donor, there were obtained photolyzed polymers of low molecular weight, of which the molecular weights were estimated by observing the viscosity changes. To deduce the mechanism of photodegradation of polyoxime-urethane, photolysis of benzophenone oxime-phenyl urethane was investigated as a model compound.
TL;DR: In this article, the zero-field splitting parameters of the triplet ground state of carbene anthronylidene were determined for two cases: in the parent matrix of (I), and in a benzophenone glass.
TL;DR: In this article, the direct and sensitized photoisomerization of the two isomers of 2-carbomethoxy-but-2-ene, methyl tiglate and methyl angelate, has been studied in solutions in cyclohexane and ethanol.