Showing papers on "Benzophenone published in 1995"

Transformation kinetics of phenols in water: photosensitization by dissolved natural organic material and aromatic ketones.

Abstract: Different dissolved natural organic materials photosensitize the transformation of a series of methyl and methoxy phenols at pH 8 with a very similar high selectivity (reactivity range 50). This selectivity falls in the range of that achieved using the aromatic ketones benzophenone (BP), 3'-methoxyacetophenone (3'-MAP), and 2-acetonaphthone (2-AN) as model photosensitizers. For both natural and model sensitizers, the photooxidation at pH 8 is not controlled by singlet oxygen. Deuterium isotope effects (k H /k D ) of different phenols are 0.7-1.3 for humic and fulvic acids and 1.1-1.7 for BP, suggesting an electron transfer mechanism. In contrast, the isotope effect for 2-AN of 4 indicates an H-atom abstraction reaction. The results show that reactive excited triplet states are important photooxidants in natural waters and should be considered for assessing the abiotic degradation of chemicals. The reactive triplet state concentration is estimated to be 10 -14 M in the top meter of Lake Greifensee under summer noon sunlight, and this leads to a half-life of 7 h for 2,4,6-trimethylphenol. Further still uncharacterized photooxidants derived from the dissolved organic material are also involved in the phototransformation of the phenols.

Deuteration of acetanilides and other substituted aromatics using [Ir(COD)(Cy3P)(Py)]PF6 as catalyst

Abstract: Deuterium exchange labelling using [Ir(COD)(Cy 3 P)(Py)]PF 6 as catalyst and deuterium gas was studied on a number of substituted acetanilides. In most cases products containing deuterium ortho to the anilide group were obtained with a high degree of enrichment. With one exception no evidence for meta, para or anilide methyl labelling was seen. The catalyst was also effective in the ortho deuteration of acetophenone, benzophenone and the β-lactam containing compound Sch 48461

Exploratory laser flash photolysis study of free radical reactions and magnetic field effects in melatonin chemistry

Abstract: Melatonin is an excellent free radical scavenger, reacting with tert-butoxyl and cumyloxyl radicals with rate constants of 3.4 x 10 7 and 6.7 x 10 7 M -1 s -1 , respectively. Reaction with benzophenone triplet occurs with a near-diffusion-controlled rate constant of 7.6 x 10 9 M -1 s -1 in acetonitrile and probably involves charge transfer. When the radical pair formed by reaction of benzophenone triplet and melatonin is sequestered in a micelle, it is subject to extensive magnetic field effects that can be readily interpreted by the radical pair model.

Benzophenone derivatives: a novel series of potent and selective inhibitors of human immunodeficiency virus type 1 reverse transcriptase.

Abstract: A series of benzophenone derivatives has been synthesized and evaluated as inhibitors of HIV-1 reverse transcriptase (RT) and the growth of HIV-1 in MT-4 cells. Through the use of the structure-activity relationships within this series of compounds and computational chemistry techniques, a binding conformation is proposed. The SAR also indicated that the major interactions of 1h with the RT enzyme are through hydrogen bonding of the amide and benzophenone carbonyls and pi-orbital interactions with the benzophenone nucleus and an aromatic function separated from the benzophenone by a suitable spacer group. The crystal structure of compound 1h has been determined. A number of compounds with potent inhibitory activity against HIV-1 RT and HIV in cellular assays at levels comparable with AZT and our efforts to identify a metabolically stable analogue are described.

Photochemistry on Surfaces: Matrix Isolation Mechanisms Study of Interactions of Benzophenone Adsorbed on Microcrystalline Cellulose Investigated by Diffuse Reflectance and Luminescence Techniques

Abstract: The swelling of microcrystalline cellulose by the use of polar protic solvents such as ethanol or methanol enables the penetration of benzophenone into submicroscopic pores of the natural polymer, while solvents such as benzene or dichloromethane do not open the polymer chains, thus not producing any entrapped benzophenone. Ground-state diffuse reflectance studies revealed a dramatic blue shift in the 350-nm absorption of benzophenone in the former case, in accordance with a strong interaction of the hydroxyl groups of cellulose with the ketone. Diffuse reflectance laser flash photolysis studies of benzophenone adsorbed on microcrystalline cellulose showed, in cases where benzophenone is entrapped in the polymer chain, the formation of a transient which decays nonexponentially and exhibits a maximum absorption at about 530 nm, assigned to triplet benzophenone. After ca. 25 μs, this transient generates another species with an absorption maximum at 545 nm. We assigned this new species to the diphenylketyl radical. In all cases where the solvent does not swell cellulose, a different behavior was observed typical forbenzophenone microcrystals triplet decay. The ketyl radical formation is greatly reduced in this case. Triplet benzophenone decays by complex kinetics and lives about 10 μs when adsorbed onto microcrystalline cellulose, while the ketyl radical, when formed, lives 1 order of magnitude longer than the triplet. Samples which exhibit a high yield of ketyl radical formation also have a smaller phosphorescence emission in accordance with the fact that large amount of triplet molecules were consumed in the process of hydrogen abstraction from the matrix, involving hydrogens linked to carbons bearing a hydroxyl group

Reversible photodimerization of coumarin derivatives dispersed in poly(vinyl acetate)

Abstract: Four photoreactive coumarin derivatives were successfully synthesized from 7-hydroxy-coumarin and 7-hydroxy-4-methylcoumarin, i.e., 7-propionyloxy-4-methylcoumarin (M1), 7-palmitoyloxy-4-methylcoumarin (M2), 7-propionyloxycoumarin (M3), and 7-palmitoy-loxycoumarin (M4). Reversible photodimerization (350 or 300 nm) and photocleavage (254 nm) of these coumarin derivatives dispersed in poly(vinyl acetate) (PVAc) were investigated by tracing their UV absorbance variations at 310 nm. The M2 and M4 with long palmitoyl chain show much better photoreaction reversibility than M1 and M3 with short propionyl chain. Moreover, photodimerization rate (under 350 nm) of M2 is greater than 200 times of that of M1. This has been explained by the formation of suitable conformation for revers-ible photodimerization due to the hydrophobic interactions. Photodimerization of M2 is ca. 3 times quicker than that of M4, indicating 4-methyl substitution enhances pho-todimerization. The influence of photodimerization wavelength (350 and 300 nm) and photosensitizer (benzophenone) have also been investigated in detail. © 1995 John Wiley & Sons. Inc.

Functionalized polysiloxanes with thioxanthone side groups : a study of their reactivity as radical polymerization macroinitiators

Abstract: Functionalized silicone copolymers containing thioxanthone side groups were prepared and evaluated as radical polymerization photoinitiators in the presence of 4-(dimethylamino)benzoate ester derivatives as coinitiators and acrylic esters as monomers. Compared to low molecular weight thioxanthone analogues, the functionalized polysiloxanes exhibit a polymer effect similar to that observed with polysiloxanes containing benzophenone side groups : the photoinitiating efficiency is enhanced when thioxanthone chromophores are present as pendant groups on polymer chains and when the tertiary amine is a free reactant in the medium. This effect disappears when the chromophores and the amino groups are attached to the same chains. Time-resolved spectroscopy was used to compare the quenching of thioxanthone triplets in several systems where the ketone and the amine reactants are present in the form of pendant groups in copolymers or as low molecular weight reactants. The photophysical study performed in media different in their nature and viscosity indicates that the polymer effect is not to be found in the efficiency of the primary deactivation process.

Type I benzophenone-mediated nucleophilic reaction of 5'-amino-2',5'-dideoxyguanosine. A model system for the investigation of photosensitized formation of DNA-protein cross-links.

Abstract: 5'-Amino-2',5'-dideoxyguanosine has been synthesized in order to investigate the intramolecular reactivity of an amino group toward the guanine radical produced by type I photosensitization mechanism. Benzophenone-mediated photosensitization of 5'-amino-2',5'-dideoxyguanosine in aerated aqueous solution results in the formation of a predominant cyclic nucleoside together with an unstable nucleoside precursor. The two modified nucleosides have been isolated by reverse phase high performance liquid chromatography and characterized by spectroscopic measurements including 13C and 1H NMR, fast atom bombardment mass spectroscopy, and UV absorption. The stable photoproduct has been identified as 9-oxa-2,4-diazabicyclo[4.2.1]non-2-en-7-ol, 3-amino- (1R-exo), whereas its precursor has been assigned as acetic acid, [(7-hydroxy-9-oxa-2,4-diazabicyclo[4.2.1]non-2-en-3-yl)amino]oxo- (1R-exo). A reaction mechanism, involving nucleophilic addition of the sugar amino group to guanine radical intermediates, is proposed to explain the formation of the two photoproducts.

Benzoylation of benzene to benzophenone over zeolite catalysts

Abstract: The liquid phase benzoylation of benzene with benzoyl chloride (BOC) to benzophenone is catalyzed by various zeolites at 353 K. Zeolite H-beta is found to be more active than the other zeolites. The conversion of benzoyl chloride to benzophenone over H-beta increases significantly with increase in the reaction time, temperature, catalyst/BOC (wt/wt) and benzene/BOC (mole) ratios. The yield of benzophenone decreases with increase in SiO2/Al2O3 ratio and isomorphous substitution of Al-by Ga- and Fe-in zeolite H-Al-beta in the following order: Al-> Ga-> Fe-H-beta suggesting that high density of acidic centers along with strong acid sites are required for the reaction.

Photo-initiated and thermal curing of epoxides by the use of photo-base generators bearing acyloxyimino groups

Abstract: The formation of amines by the photolysis of O-acyloximes derived from acetophenone oxime, benzophenone oxime, fluorenone oxime, and 2-acetonaphthone oxime and the curing of epoxides by the resulti...

Solvation effects on reactions of triplet benzophenone in supercritical fluids

Abstract: Laser flash photolysis of the hydrogen abstraction reaction of triplet benzophenone ({sup 3}BP) from 2-propanol and 1,4-cyclohexadiene in supercritical ethane and fluoroform was investigated. Bimolecular rate constants based on bulk concentrations decrease with an increase in pressure along both isotherms studied. These results corroborate previous studies in CO{sub 2} that show increased reaction rates due to enhanced local compositions of cosolvent around the {sup 3}BP solute. Analysis of the results includes prediction of the thermodynamic pressure effect on the rate constant, which suggests an increase in the rate constant with pressure, as well as the effects of increased local cosolvent concentrations about {sup 3}BP. Spectroscopic measurements of the local composition of 2-propanol about a solute in supercritical CO{sub 2} are used to explain the apparent discrepancy between experiment and prediction, providing reasonable evidence that the local environment can influence kinetically controlled reactions in supercritical fluids.

Photoinduced transient phenomena in cyclodextrin solid complexes: photochemistry of aromatic ketones

Abstract: — The photochemistry of benzophenone (BP) in cyclodextrin (α-, s- and γ-CD) solid complexes has been examined by time-resolved diffuse reflectance laser-flash photolysis techniques. Benzophenone is photoreduced as a consequence of hydrogen abstraction from the CD cavity. Both BP phosphorescence and diphenylketyl radical fluorescence spectra in CD solid complexes were recorded at room temperature. Lifetime distribution analysis is used in order to describe the dynamics of triplet decay. The most probable BP triplet lifetime is found to decrease as the size of the CD cavity decreases (α-CD = 0.3 (µs, s-CD = 0.5 µs and γ-CD = 1.2 (µs). This observation contrasts with that for xanthone, a more rigid, yet structurally related ketone (α-CD = 8 µs, s-CD = 3 µ.s and γ-CD = 0.6 (µs) studied previously. The differences are interpreted in terms of changes in triplet reactivity and of restrictions on molecular mobility.

Picosecond Transient Thermal Phase Grating Study of a Photoinduced Electron Transfer Reaction in Solution

Abstract: A study of the dynamics and thermodynamics of the photoinduced electron transfer reaction between benzophenone and 1,Cdiazabicycl0[2.2.2]octane in acetonitrile using picosecond transient thermal phase grating spectroscopy is reported. Two heat releases were observed within the time window of the experiment (0-4 ns): a fast one corresponding to the formation of a benzophenone lower triplet state and a slow one due to the electron transfer reaction. The observed dynamics is in agreement with earlier studies using transient absorption spectroscopy. The quenching of benzophenone in the first singlet excited state at high concentration of quencher and the very rapid decay of the resulting singlet geminate ion pair are confirmed. The enthalpy of formation of the geminate ion pair was determined by comparing the amounts of heat released in the fast and slow processes. The electron transfer is more exergonic by 0.23 eV than calculated from the Rehm- Weller equation, assuming spherical ions with point charges in their centers. The difference is tentatively ascribed to the electrostatic interaction within the ion pair.

A new series of type II (benzophenone) polymeric photoinitiators

Abstract: Polyimides derived by the reaction of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) with amino-terminated polyethers have been used as photoinitiators in conjunction with tertiary amine synergists for the polymerization of acrylates. The performance of the new, fully characterized materials was compared with that of benzophenone and BTDA. The performance of the novel photoinitiators was assessed by their ability to cure thin films of multifunctional acrylates. Real time IR spectroscopy and photo-differential scanning calorimetry were used to assess the cure rate and extent of photopolymerization. Cured films were subjected to solvent extraction to determine the level and nature of the extractable components and these were shown not to contain any of the photoinitiator. The polyimide photoinitiators were found to be absent in the extracts. The polymeric photoinitiators were shown to have lower reactivities than benzophenone and BTDA. The reactivity of the new photoinitiators is affected by such factors as the composition of the polyimide and molecular weight (which markedly changes the viscosities of the formulations).

Silicon Compounds with Strong Intramolecular Steric Interactions. LVII. Oxidation and Cycloaddition Reactions of an Unsymmetrically Substituted Disilene

Abstract: Reaction of the unsymmetrically substituted disilene R2Si=SiR′2 (4; R = 2,4,6-Me3C6H2, R′ = 2,4,6-iPr3C6H2) with m-chloroperbenzoic acid (mCPBA) or oxygen furnished the correspondingly substituted 1,2,3-oxadisilirane 5 or 1,3,2,4-dioxadisiletane 6, respectively. The [2 + 2] and [2 + 4] Cycloaddition reactions of 4 with benzophenone and 3,5-di-tert-butyl-1,2-benzoquinone, respectively, proceeded with a high degree of regioselectivity to yield the 1,2,3-oxadisiletane 9 and the 2,3-dihydro-1,4,2,3-benzodioxadisiline 7. The latter product was isolated together with a small amount of an isomeric compound 8 in which the substituents at the silicon atoms are reversed. The molecular structures of the products 5, 6, and 7 were determined by X-ray crystallography.

Investigation of the Redox Couple Benzophenone/Benzophenone Anion Radical in Acetonitrile and N,N-Dimethylformamide by Electrochemical and Spectroelectrochemical Methods

Abstract: Diffusion layer imaging (DLI), time-resolved spectroelectrochemical methods and electrochemical impedance spectroscopy (EIS) were applied to determine the influence of the solvent and the supporting electrolyte on reaction parameters for the benzophenone/benzophenone radical anion redox couple (BP/BP*−) formed at a Hg-covered Au wire in aprotic solvents. Results are reported for the solvents acetonitrile (AN) and N,N-dimethylformamide (DMF) using two different tetraalkylammonium salts as supporting electrolytes. Heterogeneous rate constants for the electron transfer reaction and diffusion coefficients of the neutral BP and the radical anion BP*− obtained with the different methods are discussed and compared.

Photo-initiator composition and coating composition

Abstract: PURPOSE:To obtain an initiator composition having less smelling trouble during printing and of printed matter and excellent hardness of cured coating and capable of being prevented from the deterioration of curability by compounding a specific propyl ketone with a phosphineoxide. CONSTITUTION:This initiator composition is obtained by compounding 10-90wt.% of a compound of formula I [R1 is H or methyl; R2 is H or CH2=CR1CO; PHIis p-phenylene; (n) is 1-5] or a polymer of the compound with 90-10wt.% of 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 or 2,4,6- trimethylbenzoyldiphenylphosphineoxide. Further, 1-10wt.% of 4,4-bis(di-lower alkylamino)benzophenone is optionally incorporated. The coating composition is obtained by compounding a radically polymerizable double bond-containing compound with 0.1-20wt.% of the initiator composition.

Picosecond Laser Photolysis Studies on Chain-Length, Solvent and Temperature Dependences of the Intramolecular Photoreduction Process of Benzophenone by Diphenylamine

Abstract: Photoinduced hydrogen abstraction (HA) processes of 1-(4-anilinophenyl)-2-(4-benzophenoxy)ethane, 1-(4-anilinophenyl)-3-4-benzophenoxy)propane, and 1-(4-anilinophenyl)-8-(4-benzophenoxy)octane (BP–O–(CH2)n–O–DPA: n = 2, 3, and 8) in benzene, acetonitrile, and N,N-dimethylformamide solutions were investigated by means of picosecond transient absorption spectroscopy. In benzene solution, apparent mechanism of the hydrogen abstraction reaction was “direct” process and no absorption spectrum of the charge separated state was observed. The decay of triplet benzophenone moiety (3BP*) was regulated by the dynamic rearrangement process of the mutual geometry between 3BP* and DPA to a more compact one. In polar solutions, the electron transfer (ET) from DPA to 3BP* moiety took place in addition to the direct HA from DPA by 3BP*. The rate of the ET reaction was regulated mainly by the distance between the reactant moieties. Moreover, the intra-ion pair (IP) proton transfer (PT) resulting in the HA product formation...

Type II polymeric photoinitiators (polyetherimides) with built-in amine synergist

Abstract: In this work, a photoinitiating system is described where both the benzophenone chromophore and the tertiary amine synergist are attached to a polymer backbone (i.e. amine-terminated polyetherimides).