Showing papers on "Benzophenone published in 1997"

Transient Intermediates in the Laser Flash Photolysis of Ketoprofen in Aqueous Solutions: Unusual Photochemistry for the Benzophenone Chromophore

Abstract: The transient intermediates in the nanosecond laser flash photolysis of ketoprofen, an aryl propionic acid, show the formation of a carbanion in aqueous solutions at pH 7.1. This carbanion incorporates spectroscopic properties from both a ketyl radical anion and a benzylic radical. The ketoprofen carboxylate undergoes biphotonic photoionization, a process that contributes less than 10% to its photodecomposition and leads to a benzylic-type radical after decarboxylation with a rate constant ≥1 × 107 s-1. On the other hand, the carbanion forms monophotonically and the unsuccessful attempts to sensitize the formation of the ketoprofen triplet excited state in aqueous solutions suggest that the carbanion precursor is either an excited singlet state or an extremely short-lived triplet. In organic solvents of lower polarity, the excited triplet state is readily detectable.

Infrared Approach to the Study of Adsorption on Cellulose: Influence of Cellulose Crystallinity on the Adsorption of Benzophenone

Abstract: The structures of different celluloses (microcrystalline and native) were characterized by diffuse reflectance infrared spectroscopy (DRIFT), analyzing the bands due to O−H stretching, C−O stretching, and C−H bending modes. The respective crystallinities were determined as 73 ± 2% and 40 ± 2%, and the crystalline structure in both was characterized as type Iβ. A comparative study of adsorption of an aromatic ketone, benzophenone, on these two substrates was made, using the same technique. Through the modifications observed in the carbonyl stretching band of benzophenone, it was possible to distinguish adsorption in three different environments: entrapped between the glycosidic chains in crystalline domains, in amorphous domains, and as crystallites adsorbed at the cellulose surface. By deconvolution of spectra and subsequent analysis of the main components' relative intensities, it has been possible to calculate the approximate amounts of entrapped molecules per gram of cellulose as a function of total b...

External skin treatment composition

Abstract: An external skin treatment composition containing (I) vitamin A (retinol) and (II) as a stabilizer, a chelating agent/a polysaccharide, an oil, polyethylene (propylene) glycol, a hydroxy carboxylate, a neutral amino acid salt, an oil-soluble antioxidant/EDTA/a benzophenone compound, an oil-soluble antioxidant/an acid/a benzophenone compound, an inclusion compound of cyclodextrin including an antioxidant and/or an ultraviolet absorber, butanediol and/or an oil-soluble antioxidant, a water-soluble benzophenone compound, a basic amino acid and the salt thereof, an acidic amino acid and the salt thereof, a polar oil, a water-swellable clay mineral.

Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

Abstract: Cationic organic dyes (phenosafranine, safranine T (ST + ), thiopyronine, and methylene blue) are efficient quenchers of the triplet states of aromatic ketones. The triplets of benzophenone (BP), xanthone, thioxanthone, benzil, and N-methylacridone are quenched by the dyes via energy transfer, generating triplet excited dyes (typically kq ) 5.5 10 9 M -1 s -1 for 3 BP * + ST + in acetonitrile solution). Regarding Michler’s ketone, p-(dimethylamino)benzophenone, and 3,6-bis(dimethylamino)thioxanthone, the mechanism of triplet quenching is solvent-dependent. Electron transfer occurs in polar solvents like acetonitrile, and energy transfer is the dominant reaction pathway in less polar solvents, such as dichloromethane. Delayed fluorescence of the dye caused by heterotriplet-triplet annihilation involving ketone and dye was detected upon studying the reaction of the dyes with triplet excited ketones (BP, xanthone, thioxanthone, and benzil). By applying two successive laser pulses (Iex ) 532 and 308 nm, respectively), the rate constant of the reaction 3 BP * + 3 (ST + ) * was determined: kht ) 1.1 10 10 M -1 s -1 .

Preparation of Primary Amines by the Copper(I) Catalyzed Reaction of 4,4′-Bis(trifluoromethyl)benzophenone O-Methylsulfonyloxime and Alkyl Grignard Reagents

Abstract: Primary amines are prepared by the reaction of 4,4′-bis(trifluoromethyl)benzophenone O-methylsulfonyloxime and alkyl Grignard reagents in the presence of a catalytic amount of CuCN•2LiCl and the successive acid hydrolysis of the resulting N-alkylimine derivatives.

Effect of photosensitizer and hydrogen peroxide on desulfurization of light oil by photochemical reaction and liquid-liquid extraction

Abstract: A desulfurization process for dibenzothiophene (DBT) by a combination of photochemical reaction and liquid-liquid extraction has been investigated. The DBT dissolved in tetradecane was photodecomposed by the use of a high-pressure mercury lamp and removed into the water phase at conditions of room temperature and atmospheric pressure. The addition of benzophenone (BZP), a triplet photosensitizer, enhanced the removal of DBT from tetradecane. This reaction, however, hardly proceeded in the presence of naphthalene (NP), probably because of triplet energy transfer from photoexcited DBT or BZP to ground-state NP. The addition of hydrogen peroxide enhanced the desulfurization of commercial light oil as well as the removal of DBT from tetradecane, since H{sub 2}O{sub 2} acted as a weak oxidizing agent for photoexcited DBT and interrupted the energy transfer from excited DBT to NP to some extent. In the case using a 30% H{sub 2}O{sub 2} solution, the desulfurization yield of commercial light oil was 75% following 24 h of photoirradiation and the sulfur content in the light oil was reduced from 0.2 wt % to less than 0.05 wt %.

Triplet quenching by onium salts in polar and nonpolar solvents

Abstract: The triplet quenching of several sensitizers (thioxanthone (TX), 2-chlorothioxanthone (CTX), xanthone (X), benzophenone (BP), pyrene (PY), benzil (BZ), and phenothiazine (PT)) was investigated with lipophilic substituted onium salts (iodonium I(1) and sulfonium salts S(1)) in benzene, n-heptane, and mixtures of these. Moreover, the triplet quenching of these sensitizers was also studied in acetonitrile with onium salts I(2) and S(2) with a similar pattern of substitution to the lipophilic salts. Using the determined half-wave reduction potential of the onium salts, one can show that an efficient triplet quenching by electron transfer is possible with the exception of BP and BZ. The quenching constants obtained fit the theoretical Rehm-Weller plot. The quality of the fit is better in acetonitrile than in n-heptane. Using TX and CTX cation radicals are detectable, which support a triplet quenching by electron transfer. Nevertheless, the triplets of BP and BZ were also efficiently quenched by the onium salts. The quenching reaction by sulfonium salt is hardly influenced from the polarity of the solvent used. However, the iodonium salt shows a strong dependence on the polarity: for instance in benzene the rate is one order of magnitude higher than in n-heptane. Moreover, the magnitude of triplet quenching in benzene is for the iodonium salt one order higher than for the sulfonium salt. Surprisingly, we found (with exception of PT and PY) in n-heptane no strong differences in quenching between iodonium and the sulfonium compounds.

Total Synthesis of (-)-Balanol

Abstract: The efficient total synthesis of (−)-balanol, a potent inhibitor of the protein kinase C, is described. (−)-Balanol consists of a chiral hexahydroazepine-containing fragment and a benzophenone fragment, both of which were prepared via novel synthetic routes. The hexahydroazepine fragment was prepared in racemic form through either Bu3SnH- or SmI2-promoted radical cyclization of oxime ethers 2ab intramolecularly connected with the formyl group. SmI2-promoted radical cyclization of 2b was found to be particularly successful in the selective synthesis of the seven-membered trans-amino alcohol 8b. Preparation of the enantiomerically pure hexahydroazepine-containing fragment was achieved through the enantioselective enzymatic acetylation of racemic alcohol 9, employing the immobilized lipase from Pseudomonas sp. The benzophenone fragment was prepared in short steps through a biomimetic oxidative anthraquinone ring cleavage starting from commercially available natural chrysophanic acid 15c. This reaction procee...

Surface modification of poly(tetrafluoroethylene) with benzophenone and sodium hydride by ultraviolet irradiation

Abstract: Poly(tetrafluoroethylene) (PTFE) films were surface modified in a solution of benzophenone and sodium hydride in dry dimethylformamide by ultraviolet (UV) light irradiation. The extent of surface modification was characterized after durations of UV light irradiation from 5-20 min at temperatures from 19-60°C. The modified films were analyzed by electron spectroscopy for chemical analysis, diffuse reflectance ultraviolet-visible light spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, dynamic contact angle measurement, and low-voltage scanning electron microscopy. PTFE surfaces produced by this modification demonstrated extensive defluorination, oxygen incorporation, surface unsaturation, and reduction in both advancing and receding dynamic water contact angles in a manner that was more extensive at long durations of irradiation and at high temperatures. Morphological damage depended upon treatment conditions, but extensive surface modification could be obtained without substantial morphological damage to PTFE films. Control experiments indicated that the surface modification proceeded by photoexcitation of either diphenyl ketyl radical anion or benzhydrol anion, the products of reaction of benzophenone with sodium hydride.

Quenching of triplet benzophenone by methyl and methoxy benzenes : are triplet exciplexes involved?

Abstract: The quenching of triplet benzophenone by methyl and methoxy substituted benzenes in acetonitrile was investigated. For both series of donors the quenching rate constants are considerably higher than expected from the Rehm-Weller relationship, which could be explained by a mechanism involving a (triplet) exciplex intermediate. Two corresponding models from the literature were chosen for simulating the experimental data. The results are in accord with the exciplex proposal. For a given driving force the quenching rate constants differ substantially for the two kinds of donor employed. Together with the free ion yields, obtained by transient photoconductivity measurements, this confirms the important role of the chemical structure of the donors which determines the stability of the exciplexes.

Radiation Chemical Oxidation of Benzaldehyde, Acetophenone, and Benzophenone

Abstract: Radiation chemical reactions of •OH, O•-, and SO4•- with benzaldehyde, acetophenone, and benzophenone have been studied using both pulse and steady-state radiolysis techniques. The observed rates for the •OH addition (k = (2.6−8.8) × 109 M-1 s-1) are higher than those found for the SO4•- reaction (k = (0.7−4.0) × 109 M-1 s-1). The rate for the reaction of O•- with benzaldehyde is higher than that found for •OH, while a reverse trend is observed in the case of the two ketones. Optical absorption spectra of the intermediate transients formed in the reactions of •OH and SO4•- with all three compounds are similar with a peak around 370−380 nm. The absorption spectra from the O•- reaction have shown a major peak at 310 nm and are somewhat different from those obtained in the reaction of •OH. The yields of the phenolic products formed in the reaction of •OH with benzaldehyde and acetophenone in the presence of 0.1 mM ferricyanide corresponded to only 30% and 50% •OH yields, respectively. Benzoic acid is a major...

Photoresponsive functionalized vinyl cinnamate polymers: Synthesis and characterization

Abstract: A series of functionalized vinyl cinnamate monomers were synthesized by the reaction of hydroxyethylmethacrylate and various substituted cinnamoyl chlorides. Electron donating and accepting functional groups such as-OCH 3 , -Cl and -NO 2 were introduced at the para position of cinnamoyl chloride. Homopolymerization of the synthesized monomers were carried out in dimethylformamide using azobisisobutyronitrile as a free radical initiator at 80°C for 12h. The structures of the synthesized monomers and their polymers were characterized using Fourier transform infrared (FTIR), 1 H and 13 C nuclear magnetic resonance spectroscopic techniques. Solid-state crosslinking of the above photosensitive polymers was studied by UV and FTIR spectroscopic techniques. The effects of various functional groups and the addition of sensitizer (benzophenone) on the photocrosslinking nature of the polymers were studied. The mechanism of photocrosslinking is a (2 + 2)π electron cycloaddition and not cis-trans isomerization in the functionalized polyvinylcinnamates.

Ultraviolet-visible and Fourier transform infrared diffuse reflectance studies of benzophenone and fluorenone adsorbed onto microcrystalline cellulose

Abstract: Benzophenone and fluorenone, which have a nonrigid and a rigid structure, respectively, were used as probes to study the nature of the adsorption process onto microcrystalline cellulose. Diffuse reflectance techniques were used in the UV−vis and infrared regions. Luminescence studies revealed that whenever fluorenone or benzophenone are entrapped into the natural polymer chains and in close contact with the substrate, a strong quenching effect exists for both probe's luminescence at room temperature. For fluorenone, the fluorescence quantum yields (ΦF) determined were about 0.10 when dichloromethane, cyclohexane, and benzene (solvents which do not swell cellulose) were used for sample preparation, while for dioxane, acetone, ethanol, and methanol (solvents which efficiently swell cellulose) ΦF was approximately 0.01. These values are about 1 order of magnitude higher than those obtained in solution, showing the importance of the rigid dry matrix in reducing the nonradiative pathways of deactivation of the...

Photoinduced graft polymerization of styrene onto polypropylene substrates

Abstract: The photochemical grafting of styrene onto polypropylene (PP) using benzophenone (BP) and benzoin ethyl ether (BEE) as photosensitizers is described. The effects of various parameters (such as monomer and photosensitizer concentration, reaction time, and solvent) on percent grafting were studied. We found that BP is a very efficient photosensitizer for the grafting of styrene onto PP surfaces. Unlike BEE, BP does not initiate nongrafting homopolymerization reactions in solution which compete with grafting reactions. This is advantageous over other photosensitizers since homopolymer formed in solution can interfere with the grafting reaction as well complicate sample preparation and purification. The graft copolymers obtained using both BP and BEE were characterized by high resolution 1H-NMR, optical microscopy and swelling studies. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 883–889, 1997

Intrazeolite Photochemistry. 19. Effect of the “Spectator” Pyridine on the Behavior of Carbonyl Triplet States in the Zeolite NaY

Abstract: “Spectator” molecules, which do not participate directly in the photochemistry of organic molecules included in zeolites, can be used to “tune” their photochemistry and photophysics. Such control can be exerted through changes in the diffusional behavior, spatial restrictions, or modification of the acid−base properties of the zeolite. In the case of the faujasite NaY, we have employed pyridine as a “spectator” to alter the behavior of xanthone, p-methoxy-β-phenylpropiophenone, and benzophenone which provide examples of the three mechanisms mentioned above. These processes were examined with laser flash photolysis techniques employing diffuse reflectance detection. For example, the lifetime of triplet xanthone is enhanced nearly 2 orders of magnitude when a small amount of pyridine is included, showing that a small number of acid sites in NaY may severely quench the excited triplet. In the case of p-methoxy-β-phenylpropiophenone, incorporation of large concentrations of pyridine restricts the motions requ...

Photoinduced charge transfer processes of triplet benzophenone in acetonitrile

Abstract: Photoconductivity experiments of benzophenone in acetonitrile under nanosecond laser flash photolysis conditions result in the production of ions. Irradiation with laser energies of 3.5 eV and 4.7 eV reveals different ionization mechanisms. On excitation at 355 nm, the photocurrents are observed on the microsecond timescale. Energetic considerations and comparison of the experimental traces (variation in the ground state benzophenone concentration, laser pulse intensity and oxygen concentration) with simulations indicate that the ion-generating process at 355 nm is due to triplet-triplet annihilation. On excitation at 266 nm, a monomolecular biphotonic process is operative, resulting in the observation of photocurrents within the laser pulse. This difference is explained by the energy requirements of these processes, taking into account the dipole-induced dipole solvation interaction.

Benzophenone as a probe of local cosolvent effects in supercritical ethane

Abstract: The n → π* shift of benzophenone has been used to quantify solute−cosolvent interactions in supercritical ethane. Dilute solutions of benzophenone in cosolvent/supercritical ethane mixtures were st...

Synthesis and Antitumor Activity of Novel Benzophenone Derivatives

Abstract: Novel benzophenone derivatives were synthesized and screened for cytotoxic and antitumor activity. Friedel-Crafts condensation was employed to construct the benzophenone skeleton. Among the compounds synthesized, morpholino and thiomorpholino benzophenones 3a-d exhibited potent cytotoxic activity against P388 murine leukemia and PC-6 human lung carcinoma cells in vitro, and compounds 3a, 3c, and 3j, when administered intraperitoneally, showed significant antitumor activity against the malignant ascites caused by intraperitoneal inoculation of P388 cells in mice.

Photopolymerization of 7,7′‐coumarinyl polymethylene dicarboxylates: Fluorescence and kinetic study

Abstract: All eight 7,7′-(4-methylcoumarinyl) polymethylene dicarboxylates (3, 4) containing terminal photoreactive coumarin chromophores show strong fluorescence intensities at room temperature in dimethyl sulfoxide (DMSO) and CH2Cl2. After irradiation with 350 nm light for 2 h, the fluorescence characteristics of the dicarboxylates reveal their photopolymerization paths. On irradiation of the unsubstituted dicarboxylates (3) in DMSO, singlet excited state excimers are formed, leading to syn head-to-head coumarin dimer configuration. However, for all dicarboxylates in CH2Cl2, the dimerization of the coumarin chromophore proceeds via a triplet excited state in the presence of benzophenone to form the anti-configuration photoproducts. Further confirmations of the reaction mechanism are made by kinetic studies. At high concentration, photopolymerization of 7,7′-(4-methylcoumarinyl) polymethylene dicarboxylate (4c) obeys zero-order and first-order kinetics for coumarin chromophore and benzophenone, respectively. This is a powerful proof of the proposed mechanism of a triplet excited state reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2999–3008, 1997