Showing papers on "Benzophenone published in 2006"

New Static Apparatus and Vapor Pressure of Reference Materials: Naphthalene, Benzoic Acid, Benzophenone, and Ferrocene

Abstract: A new static apparatus, capable of measuring vapor pressures in the range (0.4 to 133) Pa and in the temperature range (243 to 413) K, is fully described. The performance of the new apparatus was checked by measuring the vapor pressures of four compounds recommended as reference materials for the measurement of vapor pressurenaphthalene, benzoic acid, benzophenone, and ferrocene. A recommended value for the enthalpy of sublimation of benzophenone, (298.15 K) = (95.1 ± 1.9) kJ·mol-1, is suggested.

Aqueous oxidation of phenylurea herbicides by triplet aromatic ketones.

Abstract: Excited triplet states of dissolved natural organic matter (DOM) are important players for the transformation of organic chemical contaminants in sunlit natural waters. The present study focuses on kinetics and mechanistic aspects of the transformation of phenylurea herbicides induced by well-defined excited triplet states, which have been chosen to model DOM triplet states having oxidative character. The aromatic ketones benzophenone, 3‘-methoxy- acetophenone, and 2-acetonaphthone were used to photogenerate their triplet states and oxidize a series of eleven substituted phenylureas. Quenching of the excited triplet states by the phenylureas was measured using laser flash photolysis in the microsecond time domain, while the oxidation kinetics of the phenylureas was followed under steady-state irradiation. Second-order rate constants for quenching and oxidation were largely identical for a given pair of ketone and phenylurea. They reached the diffusion-controlled limit (≈4 × 109 M-1 s-1) and decreased with...

Determination of ionic liquids solvent properties using an unusual probe: the electron donor-acceptor complex between 4,4'-bis(dimethylamino)-benzophenone and tetracyanoethene.

Abstract: Michler's ketone (MK) and tetracyanoethene (TCNE) may be used as a UV-vis probe to investigate the solvent properties of ionic liquids (ILs). In molecular solvents, MK and TCNE give an electron donor-acceptor (EDA) complex, a zwitterionic species or a radical ion pair, depending on the aprotic or protic nature of the solvent and on its ionizing power. In agreement with the behavior observed in aprotic solvents, only the EDA complex was detected in ILs bearing low donor anions (beta < 0.7). The formation constant determined in [bmim][Tf(2)N] (K(c) = 5.6 (0.5) M(-1)) is similar to that measured in 1,2-dichloroethane at 25 degrees C. The visible absorption maximum (nu(max,CTC)) of the EDA complex is quantitatively described by a multiple correlation using the Kamlet-Taft pi, beta, and alpha parameters of the solvents. The H-bond donating capacity of ILs is not sufficient to determine the transformation of the EDA complex into the zwitterionic species, but the Kamlet-Taft alpha parameter seems to affect the position of the absorption band. The high ionization power of ILs, moreover, favors the slow dissociation of the EDA complex into its corresponding radical ion pair; this behavior generally characterizes highly polar and highly ionizing protic solvents, such as TFE and HFI. Finally, since the formation of the EDA complex is strongly affected by the presence of impurities, traces of nucleophiles (chloride or amines) or water may be easily detected through the change of the solution color.

N-phenyl-3-substituted 5-pyrazolone derivatives as organic stabilizers for rigid poly(vinyl chloride) against photodegradation

Abstract: N-Phenyl-3-substituted 5-pyrazolone derivatives were investigated as organic photostabilizers for rigid poly(vinyl chloride) (PVC). Their stabilizing efficiency was evaluated by the determination of the weight loss of the polymer after irradiation for different periods and by the determination of the amount of gel formation as well as the intrinsic viscosity of the soluble fraction of the degraded polymer. Moreover, the efficiency was evaluated from the extent of the discoloration of the degraded polymer. This was attributed not only to the radical trapping potency of the pyrazolone derivatives, which intervened with the radical degradation species in the degradation process of PVC, but also to the blocking of the newly formed radical sites on the polymeric chains. Their stabilizing efficiencies were compared with those of phenyl salicylate and 2-hydroxy-4-(octyloxy)phenyl benzophenone, industrially known UV absorbers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1543–1555, 2006

A well-defined hydrocarbon-soluble calcium hydroxide: synthesis, structure, and reactivity.

Abstract: Controlled hydrolysis of a (β-diketiminate)calcium-amide gave a heteroleptic (β-diketiminate)calcium-hydroxide complex that is remarkably stable against ligand exchange and formation of Ca(OH)2 The structure of this dimeric complex shows OH- units that symmetrically bridge the Ca2+ ions This hydrocarbon-soluble calcium hydroxide reacted rapidly with CO2 to produce a gel from which amorphous CaCO3 slowly separated This reaction behavior allows for sol−gel coating with CaCO3 from an organic solvent Reaction with benzophenone did not lead to nucleophilic attack of OH- to the carbonyl but gave a red benzophenone adduct instead

Magnetic field control of photoinduced silver nanoparticle formation.

Abstract: The micellar photoreduction of benzophenone in the presence of Ag+ leads to very rapid and efficient formation of silver nanoperticles. External magnetic fields can be used to control the rate of formation and properties of silver nanoparticles generated by reaction of ketyl radicals formed in the photoreduction of benzophenone in surfactant micelles. The effect is attributed to Zeeman splitting of the triplet sublevels of the confined radical pair that causes a reduction in the rate of geminate processes and increases the availability of ketyl radicals (through escape processes) for metal ion reduction.

Photobiodegradation of low‐density polyethylene/banana starch films

Abstract: The effects of the starch content, photosensitizer content, and compatibilizer on the photobiodegradability of low-density polyethylene (LDPE) and banana starch polymer blend films were investigated. The compatibilizer and photosensitizer used in the films were PE-graft-maleic anhydride (PE-g-MA) and benzophenone, respectively. Dried banana starch at 0–20% (w/w) of LDPE, benzophenone at 0–1% (w/w) of LDPE, and PE-g-MA at 10% (w/w) of banana starch were added to LDPE. The photodegradation of the blend films was performed with outdoor exposure. The progress of the photodegradation was followed by determining the carbonyl index derived from Fourier transform IR measurements and the changes in tensile properties. Biodegradation of the blend films was investigated by a soil burial test. The biodegradation process was followed by measuring the changes in the physical appearance, weight loss, and tensile properties of the films. The results showed that both photo- and biodegradation rates increased with increasing amounts of banana starch, whereas the tensile properties of the films decreased. The blends with higher amounts of benzophenone showed higher rates of photodegradation, although their biodegradation rates were reduced with an increase in benzophenone content. The addition of PE-g-MA into polymer blends led to an increase in the tensile properties whereas the photobiodegradation was slightly decreased compared to the films without PE-g-MA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2725–2736, 2006

Radical-induced generation of small silver particles in SPEEK/PVA polymer films and solutions: UV-Vis, EPR, and FT-IR studies.

Abstract: The present study is centered on the processes involved in the photochemical generation of nanometer-sized Ag particles via illumination at 350 nm of aqueous solutions and cross linked films containing sulfonated poly(ether ether ketone) and poly(vinyl alcohol). Optical and electron paramagnetic resonance experiments, including electron nuclear double resonance data, proved conclusively that the photogenerated chromophore exhibiting a band with λmax = 565 nm is an α-hydroxy aromatic (ketyl) radical of the polymeric ketone. This reducing species was produced by illumination of either solutions or films, but the radical lifetime extended from minutes in the fluid phase to hours in the solid. Direct evidence is presented that this long-lived chromophore reduces Ag(I), Cu(II), and Au(III) ions in solution. A rate constant of k = 1.4 × 103 M-1 s-1 was obtained for the reduction of Ag+ by the ketyl radical from the post-irradiation formation of Ag crystallites. FTIR results confirmed that the photoprocess yield...

Temperature-driven oxygenation rate control by polymeric photosensitizer.

Abstract: A polymeric photosensitizer, poly(NIPAM-co-BP), consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, demonstrates a temperature-controlled oxygenation activity in water. The system promotes a heat-induced oxygenation enhancement at 22 °C. This unprecedented photo-oxygenation activity is triggered by a heat-induced phase transition of the polymer from coil to micelle, and then to globule state, cleverly controlling the stability and diffusion of singlet oxygen and the location of substrate.

Intramolecular interactions in the triplet excited states of benzophenone-thymine dyads.

Abstract: Time-resolved and product studies on the synthesized dyads 1 and 2 have provided evidence that the benzophenone-to-thymine orientation strongly influences intramolecular photophysical and photochemical processes. The prevailing reaction mechanism has been established as a Paterno-Buchi cycloaddition to give oxetanes 3-6: however, the ability of benzophenone to achieve a formal hydrogen abstraction from the methyl group of thymidine has also been evidenced by the formation of photoproducts 7 and 8. These processes have been observed only in the case of the cisoid dyad 1. Adiabatic photochemical cycloreversion of the oxetane ring is achieved upon direct photolysis to give the starting dyad 1 in its excited triplet state. The photobiological implications of the above results are discussed with respect to benzophenone-photosensitized damage of thymidine.

A triethylenetetramine bearing anthracene and benzophenone as a fluorescent molecular logic gate with either-or switchable dual logic functions.

Abstract: Fluorescence behaviors of a triethylenetetramine bearing anthracene (AN) and benzophenone (BP) fragments at the respective ends, L1, have been studied in water, where effects of pH (H+) and metal cations on the emission properties have been studied in detail. L1 behaves as a fluorescent molecular logic gate driven by H+ (Input1) and metal cations (Input2) as input chemicals. The most notable feature of L1 is that this molecule expresses the “either−or” switchable dual logic functions. Operation of L1 with Cu2+ as Input2 expresses the INHIBIT logic function, where a strong AN fluorescence appears only at pH 4 (with H+) without Cu2+ [Input1(1)-Input2(0)]. In contrast, operations of L1 with all other metal cations as Input2 express the TRANSFER logic function, where the presence of H+ allows strong AN fluorescence regardless of whether the metal cation exists or not [Input1(1)-Input2(0); Input1(1)-Input2(1)]. These emission switching behaviors of L1 are driven by the difference in the coordination stability ...

Use of a new methacrylic monomer, 4,4′-di(2-hydroxy-3-methacryloyloxypropoxy)benzophenone, in the synthesis of porous microspheres

Abstract: A new aromatic, tetrafunctional methacrylate monomer, 4,4'-di(2-hydroxy-3-methacryloyloxypropoxy)benzophenone, and its application to the synthesis of porous microspheres are presented. This new monomer was copolymerized with divinylbenzene in the presence of pore-forming diluents. The properties of the obtained highly crosslinked microspheres were investigated as column packing for high-performance liquid chromatography. Their porous structures in both dry and wet states were studied and compared with those of poly(divinylbenzene) and the less crosslinked copolymer of 2,3-epoxypropyl methacrylate and divinylbenzene.

Benzophenone-functionalized, starlike polystyrenes as organic supports for a tridentate bis(imino)pyridinyliron/trimethylaluminum catalytic system for ethylene polymerization

Abstract: Starlike polystyrenes composed of a microgel core and arms terminated with benzophenone groups were used as organic supports for a tridentate bis(imino)pyridinyliron catalyst for ethylene polymerization in the presence of trimethylaluminum as a cocatalyst. The microgels were synthesized by the atom transfer radical polymerization of styrene initiated by 4-(1-bromoethyl)-benzophenone, with divinylbenzene as the crosslinker. The bromine polystyrene chain ends prevented the ethylene polymerization reaction and had to be removed. This was readily achieved with Cu0 together with dodecanethiol as a transfer agent. When used as supports in the presence of trimethylaluminum and 2,6-bis[1-2,6(diisopropylphenyl)imino]ethylpyridynyl iron, these bromine-free, functionalized polystyrene stars enabled the production of polyethylene beads of a spherical morphology and high bulk density with a catalytic activity similar to that under homogeneous reaction conditions. Moreover, the molar mass distribution of the polyethylene was narrow, suggesting limited transfer to trimethylaluminum. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6997–7007, 2006

Laser flash photolysis study on antioxidant properties of hydroxycinnamic acid derivatives

Abstract: The antioxidant properties of hydroxycinnamic acid derivatives (HCA) were studied by laser flash photolysis. The transient species with maximum absorption at 360 nm were assigned to the phenoxyl radical of HCA. The SO 4 •− induced oxidation of HCA was also investigated. It was shown that the interaction of SO 4 •− with HCA resulted in the formation of HCA phenoxyl radicals with rate constants of 2.0–3.9×109 M−1 s−1. The reactions of HCA with triplet state of benzophenone were analyzed and quenching rate constants of 4.3–7.8×109 M−1 s−1 were determined.

Oxygen uptake and involvement of superoxide radicals upon photolysis of ketones in air-saturated aqueous alcohol, formate, amine or ascorbic acid solutions.

Abstract: The photolysis of acetophenone, benzophenone, 4-carboxybenzophenone and benzil was studied in air-saturated aqueous solution in the presence of alcohols. The overall reaction is an oxidation of 2-propanol to acetone. The quantum yield of oxygen uptake (Φ−O2) increases with increasing 2-propanol concentration up to 0.9. The photoreaction can also be initiated by quenching of the ketone triplet state by ascorbic acid, formate or an amine e.g. triethylamine. Subsequent reactions of the involved radicals with oxygen yield the superoxide radical and eventually hydrogen peroxide. For the ketones in the presence of 3–30 mM ascorbic acid or triethylamine Φ−O2 = 0.3–0.9. The specific properties of ketones, including 4-methoxyacetophenone and 2-acetonaphthone, the radicals involved and the pH and concentration dependences of Φ−O2 are discussed.

Using silica films and powders modified with benzophenone to photoreduce silver nanoparticles

Abstract: Porous silica (SiO2 films and powders), modified with benzophenone (BP), facilitates the formation of stable sliver nanoparticles by taking advantage of the solid supported photosensitizer. The silica serves as a carrier for the BP into an aqueous solution and its subsequent removal. Benzophenone, bound to a silica film, was able to reduce silver ions to generate nanoparticles in solution, while silica powder with bound BP generates silver nanoparticles that are attracted to the silica. Silver nanoparticles are also fabricated in porous silica films by incorporating silver ions into the films before casting and then irradiating the film in a solution containing BP. From pH studies, it is concluded that the ketyl-radicals and anion-radicals of BP and IPA both take part in the reduction of silver ions. These synthetic studies provide a new photochemical reduction method by immobilizing the reactant on a silica surface allowing generation of silver nanoparticles in solution attached to powders or inside a film for catalytic applications or increased conductivity of silica films.

Highly efficient, polymerizable, sulfur‐containing photoinitiator comprising a structure of planar N‐phenylmaleimide and benzophenone for photopolymerization

Abstract: In a continuation of research on chemically bonded photoinitiators comprising a structure of planar N-phenylmaleimide (NPMI) and benzophenone (BP), a novel, highly efficient, polymerizable, sulfur-containing photoinitiator, 4-[(4-maleimido) thiophenyl]benzophenone (MTPBP), was synthesized by the introduction of an NPMI group into BP. Another chemically bonded photoinitiator, 4-[(4-maleimido)phenoxy] benzophenone (MPBP), was selected to evaluate its photoefficiency. The results showed that MTPBP possessed a greatly redshifted UV maximal absorption and a very weak fluorescence emission. Electron spin resonance spectra indicated that the C-S bond in its molecule underwent photolysis reactions to generate radicals to initiate the polymerization. Three representative types of different functionality monomers-methyl methacrylate, 1,6-hexanediol diacrylate, and trimethylolpropane triacrylate-were chosen to be initiated through dilatometry and differential scanning photocalorimetry with unsaturated tertiary amine N,N-dimethylaminoethyl methacrylate as the coinitiator. The results showed surprisingly high efficiency of MTPBP due to the mutual influence between NPMI and BP as in their physical mixtures and photolysis reactions at the C-S bond. Both MPBP and MTPBP behaved with similar regularity toward different monomers.

The photomediated reaction of alkynes with cycloalkanes.

Abstract: In the presence of a photomediator such as benzophenone, alkynes with electron-withdrawing groups react with cycloalkanes to give vinyl cycloalkanes. The reaction involves the regiospecific addition of a photochemically generated cycloalkyl radical to the β-carbon of the alkyne. The stereochemical outcome of the reaction depends on the nature of the photomediator and alkyne used.

Surface photochemistry: benzophenone as a probe for the study of silica and reversed-phase silica surfaces

Abstract: This work reports the use of benzophenone, a very well characterized probe, to study new hosts: two reversed-phase silicas. Laser-induced room temperature luminescence of argon purged solid powdered samples of benzophenone adsorbed onto the two different reversed-phase silicas, RP-18 and RP-8, revealed the existence of a low energy emission band in contrast with the benzophenone adsorbed on 60 A pore silica, where only triplet benzophenone emits. This low energy emission band was identified as the fluorescence of the ketyl radical of benzophenone, which is formed as the result of a hydrogen atom abstraction reaction of the triplet excited benzophenone from the alkyl groups of the surface of the reversed silicas. Such emission does not exist for benzophenone adsorbed onto 60 A pore silica. Room temperature phosphorescence was obtained in argon purged samples for all the surfaces under use. The decay times of the benzophenone emission vary greatly with the alkylation of the silica surface when compared with “normal” silica surface. A lifetime distributions analysis has shown that the shortest lifetimes for the benzophenone emission exist in the former case. Triplet–triplet absorption of benzophenone was detected in all cases and is the predominant absorption in the case of 60 A pore silica, while benzophenone ketyl radical formation occurs in the case of the reversed silicas. Diffuse reflectance laser flash photolysis and gas chromatography-mass spectrometry techniques provided complementary information, the former about transient species and the latter regarding the final products formed after laser irradiation, both at 266 nm or 355 nm. Product analysis and identification show that the degradation photoproducts are dependent on the excitation wavelength, the photochemistry being much more rich and complex in the 266 nm excitation case, where an α-cleavage reaction occurs. A detailed mechanistic analysis is proposed.

Structural Characterization and Properties of Organo-soluble Polyimides, Bismaleimide and Polyaspartimides Based on 4,4′-Dichloro-3,3′-Diamino Benzophenone:

Abstract: A novel chlorinated diamine monomer with keto group, 4,4′-dichloro-3,3′-diamino benzophenone (DADCB) was prepared through the nitration of dichloro benzophenone (DNDCB) followed by catalytic reduction with SnCl4 and HCl. Chlorinated polyimides (IVa-e) were synthesized from the above diamine with various commercially available dianhydrides via one-step and two-step methods. Polyimides IVa-e have inherent viscosity in the range 0.98–1.42 dL g° 1 in the one-step method and 0.70–0.95 dL g° 1 (thermal imidization) and 0.84–1.33 dL g° 1(chemical imidization) in the two-step method. The polyimidesprepared by the one-step method and chemical imidization method exhibited excellent solubility, but those prepared via thermal imidization exhibited limited solubility. Polyimide° lms exhibited tensile strength 95–121MPa, percentage elongation 8–13% and tensile modulus 1.6–2.4 GPa. The T g of the polyimides are in the range 272–297° C and T10 values are in the range 510–542° C in N2 and 460–498° C in air with more than ...