Showing papers on "Benzophenone published in 1989"

Rate-determining step of the reactions of benzophenone with various Grignard reagents

Abstract: Effets des substituants de la benzophenone et effets isotopique cinetique pour la reaction de la benzophenone-14C-7 avec divers reactifs de Grignard

Time-resolved laser spectroscopy of the sensitized photolysis of iodonium salts

Abstract: Laser flash photolysis of thioxanthone derivatives in the presence of substituted iodonium salts gives rise to an electron transfer process. Rate constants are measured and the cation radical of the thioxanthone is determined. Other results obtained with anthracene, pyrene, benzophenone and ruthenium tris-2,2′-bipyridine are discussed.

Study of the long-lived intermediate formed in the photoreduction of benzophenone by isopropyl alcohol

Abstract: The formation, structure and decay kinetics of the long-lived intermediate formed in the photoreduction of benzophenone by isopropyl alcohol in acetonitrile has been investigated. Laser flash photolysis and transient absorption measurements carried out with the benzophenone—isopropyl alcohol—acetonitrile and benzophenone—benzhydrol—acetonitrile systems indicated that the intermediate, generally called a “light-absorbing transient” (LAT), is formed by coupling of a diphenylketyl with a dimethylketyl radical. Dimerization of diphenylketyl radicals appeared to contribute very little to LAT formation. Study of the decay kinetics of the intermediate revealed that LAT actually consisted of a mixture of an ortho and a para isomer for which absorption spectra could be obtained. The ortho-LAT isomer decomposed faster, mainly by a benzophenone-enhanced process, and absorbed at longer wavelengths with a maximum at 358 nm, while para-LAT isomer decayed more slowly and had an absorption maximum at 317 nm. Additional investigations supplied absolute spectra for short-lived transients, i.e. for benzophenone and acetone triplet states and diphenylketyl and dimethylketyl radicals.

Geminate recombination kinetics of triplet radical pairs in glycerol: magnetic field effect

Abstract: Les radicaux [BH • , PhO • ] sont produits par la photoexcitation de la benzophenone(B) en presence du p-cresol (PhOH)

Light-induced polymer and polymerization reactions XXXIII: direct photoinitiation of methyl methacrylate polymerization by excited states of ketones

Abstract: The S 1 and T 1 excited states of several aromatic ketones (benzophenone, xanthone, fluorenone, thioxanthone, acridone, N -methylacridone) are quenched by methyl methacrylate (MMA). The rate constants of T 1 quenching ( k 3 q ) measured by means of flash experiments show a linear log k 3 q vs. E T relationship. Results of kinetic treatment agree with the formation of 1,4-diradicals which decompose mainly into the starting materials, whilst some initiate the polymerization of MMA. Data of the kinetic experiments of polymer formation (monomer exponents, light intensity exponents) accord with such a mechanism. The polymers obtained contain the corresponding ketone moiety, identified by absorption and fluorescence measurements.

Quenching of ketone triplet states by silanes

Abstract: Triplet state quenching of the ketones benzophenone, p -methylbenzophenone, p -phenylbenzophenone and benzil by silanes containing an SiH bond was investigated in a 9:1 (v/v) mixture of acetonitrile and acetone. It was found that both the n,π* and n,π*−π,π* triplet states are quenched if their energies are above 280 kJ mol −1 . Quenching rate constants k H were determined using steady state phosphorescence quenching and the time-resolved measurement of the triplet—triplet absorption. From an analysis of the behaviour of the triplet—triplet absorption of benzophenone as a function of time at variable silane concentrations, a reaction scheme was derived which includes the combination reactions of diphenyl ketyl, solvent and silyl radicals and the addition of silyl radical to the ground state of benzophenone. k H values obtained in this way agree with the phosphorescence quenching data and are of the order of 3 × 10 6 to 3.4 × 10 8 dm 3 mol −1 s −1 . Furthermore, it was found that the log k H values depend on the magnitude of the wavenumber of the SiH vibration of the silanes.

Photo-polymerizable composition

Abstract: A photo-polymerizable composition is disclosed, which comprises a thermoplastic polymeric binder; a non-gaseous ethylenically unsaturated compound; a photo-polymerization initiator system composed of 4,4'-bis(dialkylamino)benzophenone, aromatic ketone and lophine dimer; an organic halogen compound; and a leuco dye.

Radical processes in lipids. Selectivity of hydrogen abstraction from lipids by benzophenone triplet.

Abstract: Laser photolysis techniques have been used to measure the reactivity of benzophenone triplet (3BZP) toward various fatty acids and two glycerides in benzene solution. Eight compounds varying both in number and in the configuration of olefinic bonds have been examined. It has been found that the rate constant for hydrogen abstraction from these compounds by 3BZP may be related to the number of secondary, allylic and doubly allylic hydrogens in each molecule by the equation: kH = [0.023[H sec] + 0.112[H allylic] + 1.78[H doubly allylic]] x 10(7) M-1s-1

Positive type photoresist composition

Abstract: PURPOSE:To improve the stability of application ability, the sensitivity, the film retention ratio and the resolution of the titled composition by incorporating a 1,2-naphthoquinone diazide sulfonate of 2,3,4-trihydroxy-2'-methyl benzophenone as a guinone diazide type photosensitive component. CONSTITUTION:The titled composition comprises the 1,2-naphthoquinone diazide sulfonate of 2,3,4-trihydroxy-2'-methyl benzophenone as the quinone diazide type photosensitive component. The trihydroxy benzophenone is necessary to have a methyl group at 2'-position thereof, and said 2,3,4-trihydroxy benzophenone having the methyl group at 3' or 4' position is useless. And, the quinone diazide type photosensitive component is preferably used as a solution by dissolving said component together with an alkaline soluble resin in a suitable solvent. Additionally, the titled composition may compound an additive such as a surfactant, a dyestuff, a stabilizer and a sensitizer, etc. Thus, the stability of application ability, the sensitivity, the film retention ratio and the resolution of the titled composition are improved.

Study of polymeric photosensitizers. 5. Synthesis of multifunctional photosensitizers bonded on cross-linked polymer beads and their application for photoisomerization of potassium sorbate

Abstract: Preparation des photosensibilisants par substitution de poly(chloromethylstyrene) reticule par le benzoyl-4 phenolate de potassium suivie de l'addition d'amine ou le phosphine tertiaire, ou par copolymerisation radicalaire du chloromethylstyrene avec la vinyl-4 benzophenone suivie de l'addition d'amine ou de phosphine. Le pouvoir photosensibilisant des copolymeres dans la photoisomerisation du sorbate de potassium en solution aqueuse depend de la teneur en groupes benzophenone, de l'encombrement et de l'hydrophilie des groupes ammonium et phosphonium, et du milieu reactionnel

The mechanism of photocure of inherently photosensitive polyimides containing a benzophenone group

Abstract: The photochemistry of an appropriately substituted bisimide has been studied in solution by conventional means and time resolved laser techniques as a model for the behavior of inherently photosensitive solvent soluble polyimides, whose photochemistry are not well understood A mechanism for the photochemical insolubilization of the polymer systems is suggested based on the results for the model system, which is confirmed by time resolved laser studies of polyimide solutions Phosphorescence quenching rate constants for the model compound indicate that the triplet excited state is about one order of magnitude more reactive than triplet benzophenone, an increase most likely due to the inductive effect of the imide moieties

Sensitized and heavy atom induced production of acenaphthylene triplet: a laser flash photolysis study

Abstract: The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.

A laser flash photolysis study of the behaviour of polyfluorophenyl ketones in solution

Abstract: Decafluorobenzophenone triplets, which have a triplet energy very close to that of benzophenone, are much more reactive than benzophenone in quenching reactions that involve hydrogen transfer and/or charge transfer. An excellent correlation has been observed between the rate constants for charge transfer quenching and the oxidation potential of the substrate. In the case of 2-propanol, where the reactivity can be fully accounted for by hydrogen transfer, decafluorobenzophenone is 35 times more reactive than benzophenone. Pentafluorobenzophenone shows intermediate behaviour. Keywords: laser photolysis, benzophenones, triplet states, charge transfer, photoreduction.

Hotmelt contact adhesives which can be crosslinked with ultraviolet radiation in the presence of oxygen

Abstract: Hotmelt contact adhesives which are crosslinkable with UV light in the air are based on copolymers which contain tetrahydrofurfur-2-yl (meth)acrylate and/or N-2-tetrahydrofurfuryl (meth)-acrylamide and/or alkoxyalkyl (meth)acrylates and/or N-alkoxyalkyl (meth)acrylamides as copolymerized units and added benzophenone and/or benzophenone derivatives as photosensitizers.

Strukturchemie ungesättigter Siliciumverbindungen: Kristall- und Molekülstrukturen des stabilen Silanimins ′Bu2Si=N—Si′Bu3 und von Silanimin-Donoraddukten (Donor = Tetrahydrofuran, Benzophenon) / Structural Chemistry of Unsaturated Silicon Compounds: Crystal and Molecular Structures of the Stable Silaneimine ′Bu2Si=N—Si′Bu3 and of Silaneimine Donor Adducts (Donor = Tetrahydrofuran, Benzophenone)

Abstract: The structure of the first stable silaneimine ′Bu2Si=N—Si′Bu3 (1) (i.e. a compound containing a silicon nitrogen double bond) has been determined by X-ray crystallography (monoclinic, space group P21/n, a = 8.962(1), b = 18.361(1), c = 14.658(1) Å, β = 90.98(1)°, V = 2411.6 Å3.Z = 4, wR = 0.043, w = 1/σ2(Fo) for 208 refined parameters and 2610 observed structure factors. It is monomeric in the solid state and has a nearly linear Si=N—Si skeleton (Si—N—Si 177.8(2)°) with drastically different Si=N and Si—N bond lengths (1.568(3) and 1.695(3) A, respectively). The benzophenone adduct of ′Bu2Si=N—Si′Bu3 and the tetrahydrofuran (THF) adduct of the closely related silaneimine Me2Si=N—Si′Bu3 contain the donor molecules being coordinated exclusively to the unsaturated silicon atoms, which adopt a distorted tetrahedral coordination geometry upon coordination with characteristically elongated Si=N double bonds. The solid state structure of the benzophenone adduct strongly suggests that [2+2] cycloadditions of Si=N double bonds with aldehydes or ketones proceed in a non-concerted manner via prior formation of donor-Si bonds. ((THF) • Me2Si=N—Si′Bu3 (2): P21/n, a = 18.480(4), b = 14.209(2), c = 18.683(5) Å, β = 115.11(2)°, V = 4442.2 Å3, Z = 8, wR = 0.094 for 397 parameters and 3432 observables; (Ph2C=O) · ′Bu2Si=N—Si′Bu3 (3): P21,/n, a = 13.247(2), b = 15.689(2), c = 17.073(2) Å. β = 110.53(1)°, V = 3323.0 Å3, Z = 4, wR = 0.039 for 379 refined parameters and 3789 observables.)

Nonmetallised CdS-catalysed photoreduction of aromatic ketones to alcohols and/or pinacols

Abstract: In acetonitrile containing triethylamine as a sacrificial electron donor, non-metallized CdS shows photocatalytic activity for reduction of benzophenone derivatives whose reduction potentials are larger than –1.90 V vs. standard calomel electrode (SCE), giving alcohols and/or pinacols under visible light irradiation.

Chemically induced dynamic nuclear polarization in the photo-oxidation of benzylic acid with uranyl nitrate

Abstract: The photo-oxidation of benzylic acid and benzhydrol by uranyl nitrate was studied using the 1 H chemically induced dynamic nuclear polarization technique. The photo-oxidation of both compounds leads to the formation of a polarized reaction product, i.e. benzophenone. The signs of polarization are the same in both cases. It is concluded that the reactions proceed via triplet radical pairs.

Uv-light stabilized polyester molding compositions

Abstract: Polyester molding compositions include an effective amount of a triazine-based antioxidant and a benzophenone ultraviolet light absorber sufficient to achieve a clor difference, as calculated in CIELab units under illuminant "D-65" according to ASTM Standard D-2244, of less than about 10,0, when exposed in a Xenon arc weather-ometer operated according to SAE J1885 for 315 Kj/sq.m. The triazine-based antioxidant is of the formula: ##STR1## wherein R is a phenolic group attached to the triazine ring via a C1 to C5 alkyl or an ester substituent. Preferably, the triazine-based antioxidant is 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester with 1,3,5-tris-(2-hydroxyethyl)-s-triazine-2,4,6-(1H, 3H, 5H) trione. The benzophenone UV-absorber is of the general formula: ##STR2## where R' is hydrogen or an alkyl radical.

CIDEP study of the photoreduction of aromatic ketones with alkoxides in alcohols.

Abstract: The photoreductions of xanthone and benzophenone with alkoxides in several alcohols were studied by observing CIDEP. The total emission spectra, observed after the photoexcitation, were assigned to the ketone anion radicals having TM spin polarization. The dependence of the spectral line width upon alkoxides indicates the existence of a hyperfine interaction between the ketone anion radical and the alkali metal cation, even in the early stage of the photochemical reaction in an alcoholic media. A careful analysis of the spectral pattern leads to the conclusion that the counter radical of the ketone anion interacting as a geminate pair which is responsible for the RPM polarization, is other than a methoxyl radical in these systems.