Showing papers on "Benzophenone published in 1991"

Highly conjugated π-electron donors for organic metals: synthesis and redox chemistry of new 1,3-dithiole and 1,3-selenathiole derivatives

Abstract: The bis(1,3-dithiolium) dication salts 8a–c have been synthesised in three steps (31–51% overall yields) starting from 1,4-bis(bromomethyl)naphthalene, 9,10-bis(chloromethyl)anthracene and 4,4′-bis(chloromethyl)biphenyl, respectively. The bis(halogenomethyl) compounds 5 were converted into the dipiperidiniumbis(dithiocarboxylate) salts 6, which on alkylation with 3-chlorobutane-2-one yielded bis(dithioesters)7; cyclisation of 7 occurred on treatment with concentrated sulphuric acid to give dication salts 8. Dimethyl 1,3-dithiol-2-ylphosphonate 20, dimethyl 4,5-dimethyl-1,3-dithiol-2-ylphosphonate 21 and dimethyl 1,3-selenathiol-2-ylphosphonate 22 were treated with butyllithium in the presence of a range of carbonyl compounds and quinones, e.g., cyclopentanone, cyclohexanone, benzophenone, acetophenone, benzaldehyde, thioxanthen-9-one, anthraquinone, bianthrone and naphthacene-5,12-quinone to yield Wittig–Horner products, e.g., alkenes 26–34 and the anthracenediylidene derivatives 35, 36, 40–43 and 53. Unsymmetrical derivatives 37–39 were prepared in two steps as follows: anthrone reacted with 2-methylthio-1,3-dithiolium iodides 45 and 46 in pyridine-acetic acid to yield ketones 48 and 49 which were then treated with the Wittig–Horner reagents 23–25. Cyclic voltammetric data for the new tetrathiafulvalene, selenatrithiafulvalene and diselenadithiafulvalene derivatives 35–43and 53, show that these systems undergo two-electron redox behaviour which is observed as a single wave. Complexes of these donors with electron acceptors, e.g. 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), have been obtained, some of which are organic semiconductors.

Picosecond and nanosecond studies of the photoreduction of benzophenone by N,N-diethylaniline and triethylamine

Abstract: The photoreduction of benzophenone by N,N-diethylaniline and triethylamine has been examined in a number of solvents by both nano- and picosecond laser photolysis. With diethylaniline, electron transfer is the primary step and the spectrum of the ion pair has been detected even in nonpolar solvents such as benzene and cyclohexane. Rapid proton transfer then takes place to form a high yield of the ketyl radical. The lifetime of the ion pair in benzene is about 900 ps. In acetonitrile, the ion pair dissociated into individual ions which then decay by back electron transfer and proton transfer. A spectral shift to the red occurs over 100 ps as the contact ion pair dissociated. In acidic alcohols such as methanol and trifluoroethanol, proton transfer from the alcohol occurs to produce the ketyl radical. In the case of triethylamine, no distinct absorption band for benzophenone anion was seen in picosecond experiments but difference spectra, which removed much of the spectrum of benzophenone triplet, clearly showed some contribution from the anion. For this compound, it is likely that electron transfer occurs first followed by very fast proton transfer.

Degradation of crystal violet by Bacillus subtilis

Abstract: Crystal Violet (BV3), a typical triphenylmethane dye, was degraded by growing cells of Bacillus subtilis IFO 13719 in 802 medium, although their growth was inhibited at an initial stage of incubation. The compound was degraded at a low concentration below 7 × 10‐6 mol dm‐3 which brought about the inhibition of the growth The major degradation product of BV3 was extracted with benzene from the reaction mixture and identified as 4,4'‐bis(dimethylamino)benzophenone (Michler's keton ; MK) by GC‐MS. In addition to BV3, two other triphenylmethane dyes (Para rosanillne and Victoria blue) were shown to be degraded by growing cells of B. subtilis IFO 13719.

Vibrational spectra of para‐disubstituted benzophenones

Abstract: Raman (3500-20 cm −1 ) and IR (4000-80 cm −1 ) spectra of benzophenone and a series of its para-disubstituted derivatives (substituents F, Cl, Br and CH 3 ) as melts and in solution were recorded. A complete empirical assignment of the measured spectra was made and the influence of para substitution on the normal modes was investigated

Benzophenone derivatives and their preparation

Abstract: UV-crosslinkable materials based on (meth)acrylate copolymers and containing special modified unsaturated benzophenone derivatives as copolymerized units are used as hotmelt adhesives, for coating sheet-like mineral substrates and as surface coatings.

Femtosecond-Picosecond Laser Photolysis Studies on Reduction Process of Excited Benzophenone with Tertiary Aromatic Amines in Acetonitrile Solution.

Abstract: Photoreduction processes of benzophenone (BP)-N,N-diethylaniline (DEA) system in acetonitrile solution were studied by means of femtosecond–pecosecond laser photolysis and time resolved transient absorption spectroscopy. The reaction processes including the formation of geminate ion pairs (IP) by electron transfer (ET) between BP* and DEA at encounter followed by intra-IP proton transfer giving the ketyl radical (BPH·) were clearly observed in both triplet and singlet excited state, while the IP produced by excitation of the CT complex between BP and amine formed easily in more or less concentrated solutions did not give BPH·. In addition to the detailed investigations on the BP-DEA system, we made comparative studies on BP–tertiary aromatic amine systems including N,N-diethyl-p-toluidine, N,N-dimethylaniline, and N-methyldiphenylamine. We observed clearly the characteristic tendency that the proton transfer rate in the 3IP decreased with decrease of the oxidation potential of the amine. This result was i...

PHOTOCHEMISTRY ON SURFACES: TRIPLET-TRIPLET ENERGY TRANSFER ON MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE REFLECTANCE TRANSIENT ABSORPTION and EMISSION SPECTROSCOPY*

Abstract: Triplet-triplet energy transfer has been studied between benzophenone and an oxazine dye (2,7-bis(diethyl-amino)-phenazoxonium chloride) co-adsorbed on the surface of microcrystalline cellulose Ground state absorption and fluorescence measurements provide evidence for dimer formation of the oxazine dye when adsorbed on cellulose in contrast to the behaviour in ethanol solution where no dimerization is observed The equilibrium constant for dimerization, which is found to be (10 × 01) × 106 mol−1 g (2560 × 250 dm3 mol−1) for oxazine alone on cellulose decreases in the presence of co-adsorbed benzophenone Fluorescence is detected from excited monomeric but not from excited dimeric oxazine The absorption spectrum of the triplet state of oxazine adsorbed on cellulose was obtained and its extinction coefficient evaluated relative to that of triplet benzophenone which was used as a sensitizer The lifetime of adsorbed triplet oxazine is 43 ms which is 300 times longer than that in acetonitrile solution The efficiency of energy transfer from triplet benzophenone to oxazine on cellulose was studied using both time resolved sensitized absorption and phosphorescence intensity measurements as a function of oxazine concentration Lifetime measurements show that the energy transfer process involves static quenching since the benzophenone lifetime is independent of oxazine loading at the surface A mechanism is proposed to explain the results in which one oxazine molecule is suggested as being able to quench phosphorescence from a “pool” consisting of 2 to 3 benzophenone molecules

Ion-forming processes on 248 nm laser excitation of benzophenone in aqueous solution: a time-resolved absorption and conductivity study

Abstract: The laser flash photolysis (excitation at 248 nm) of benzophenone in aqueous solution was investigated using absorption and conductivity measurements. In addition to intersystem crossing to the ground state, benzophenone triplets undergo triplet—triplet (T—T) annihilation partly by an electron transfer reaction leading to cation and anion radicals. A second ion-forming process is two-photon photoionization which leads to radical cations and hydrated electrons. Secondary reactions, involving the protolytic equilibrium between ketyl radicals and anion radicals, are observed and discussed.

PHOTOCHEMISTRY IN A CYCLODEXTRIN CAVITY. PRIMARY PROCESSES IN THE PHOTOREDUCTION OF 3- and 4-BENZOYLPYRIDINE STUDIED BY LASER FLASH-PHOTOLYSIS*

Abstract: The photochemistry of 3- and 4-benzoylpyridine-cyclodextrin inclusion complexes (BPyCDx) was examined by nanosecond laser flash-photolysis and stationary techniques. The lifetimes of the triplet complex and of the triplet radical pair, formed by H-abstraction from a glucose unit of the CDx, have been measured in β-CDx complexes. The reactivity of the heterocyclic ketones with CDx is higher than that of benzophenone, but the lower binding ability of the macrocycle toward these more hydrophylic molecules induces faster separation of the geminate radicals. The quantum yields of the escaped radicals and their decay kinetics have been determined. The β-CDx cage favours geminate recombination reactions, while α- and -γ-CDx tend to release the guest molecule. Cage products have been spectroscopically characterized in the case of the 3-BPy-β-CDx system.

Photochemistry and photopolymerization activity of perester derivatives of benzophenone

Abstract: The spectroscopic properties and photopolymerization activities of a mono- and tetraperester derivative of benzophenone are examined and compared with those of benzophenone. Their photopolymerization activity in methyl methacrylate (MMA) and an ethoxylated bis-phenol-A diacrylate have been studied using a combination of gel permeation chromatography (GPC), and real time Fourier transform infrared spectroscopy (RTFTIR) as well as the commercial pendulum hardness test. Using GPC analysis on the poly(methyl methacrylate) samples the tetra--t-butyl perester derivative of benzophenone is found to give a higher weight average (Mw) and number average (Mn) molecular weight polymer than that produced using the mono perester. For the two peresters of benzophenone photopolymerization efficiency using real time FTIR increases with increasing initiator concentration, and no self-termination is observed up to 0.75% w/w concentration with the mono perester derivative being the more efficient initiator. Similar results were obtained using the commercial pendulum hardness tester with a triacrylate/epoxyurethane acrylate resin with benzophenone exhibiting the lowest activity. Photopolymerization activities of the initiators correlate well with their spectroscopic properties. The phosphorescence quantum yield is higher for the monoperester than the tetraperester derivative and is consistent with a shorter lifetime and lower photolysis quantum yields in 2-propanol. Compared with benzophenone, phosphorescence analysis indicates that the perester groups impart a degree of charge-transfer content to the molecule which is consistent with the degree of substitution. Ketyl radical formation on microsecond flash photolysis follows the order benzophenone > mono- > tetraperester derivative and is consistent with the phosphorescence quantum yields. On nanosecond laser flash photolysis in nitrogen-saturated acetonitrile, triplettriplet absorption is extremely weak for both the perester derivatives, being stronger for the monoperester.

Quenching of triplet benzophenone by 1,4-diazabicyclo[2.2.2]octane in acetonitrile revisited

Abstract: In conditions of laser flash photolysis, the kinetics of decay of the absorption of the benzophenone radical anion show that free, solvated ions are formed after electron transfer between the title compounds in neat, dry acetonitrile. Furthermore, it is shown that the opposite conclusion claimed by Devadoss and Fessenden (J. Phys. Chem., 1990, 94,4540), Le., no ion pair dissociation, results from a misinterpretation of the transient decay rate.

Method for making organic carbonates

Abstract: A method for making diphenyl carbonate free of color bodies is provided by reacting an organic hydroxy compound, such as phenol with carbon monoxide and oxygen in the presence of an effective amount of a palladium catalyst, in the form of a palladium material which is used in combination with a quaternary ammonium salt, an inorganic cocatalyst, such as cobalt diacetate and an organic cocatalyst such as benzophenone or 1,10-phenanthroline. Recycling of catalyst values is also provided.

Zinc-promoted reactions. 1. Mechanism of the Clemmensen reaction. Reduction of benzophenone in glacial acetic acid

Abstract: The mechanism of the Clemmensen reduction of diaryl ketones was investigated by reducing benzophenone, benzhydryl chloride, and dichlorodiphenylmethane in AcOH under a variety of conditions. Besides diphenylmethane, dimeric products were isolated that were indicative of the formation of radical species. Different product distributions were obtained from reactions run under different conditions. The reduction of deuteriated benzhydryl chloride was also performed. A quite complicated mechanistic pattern, involving ionic and nonionic reactions, emerged from the experimental picture. Two pathways, connected through the protonated substrate, were recognized. According to the first pathway the reduction is promoted by a SET from Zn to the substrate, leading to the formation of a carbon radical having one zinc atom bound to the oxygen of the carbonyl group

Second-harmonic generation in derivatives and analogs of benzophenone and chalcone

Abstract: The second harmonic generation efficiencies of some derivatives and analogs of benzophenone and chalcone are presented. Several of these compounds have potential as diode laser doublers. In particular, (4-bromobenzal)-3-acetylpyridine has an SHG efficiency 10 times that of urea and a cutoff wavelength of 398 nm.

Mixture of photoinitiators

Abstract: Photoinitiator mixtures comprising a) 100 parts by weight of a mono- or diacylphosphine oxide, b) 10-70 parts by weight of an alpha -hydroxyacetophenone and c) 10-70 parts by weight of a benzophenone, are effective initiators for photopolymerisations of ethylenically unsaturated compounds. They are particularly suitable for the photocuring of white paints.

Comparative mechanistic study of the reactions of benzophenone with n-butylmagnesium bromide and n-butyllithium

Abstract: Substituent effects on reactivity and product distribution (addition vs reduction) were determined for the reactions of benzophenones with n-BuMgBr and n-BuLi at 0 o C. In case of the reaction with n-BuMgBr, meta and para-substituted benzophenones gave a reasonably linear Hammett plot, from which the ρ value of 1.45 was calculated, while ortho-substituted derivatives deviated downward from the correlation line. In contrast, the reaction with n-BuLi exhibited very small substituent effects on reactivity. The product distribution is highly dependent on substitutents in the n-BuMgBr reaction, whereas it is essentially independent of substituents in the n-BuLi reaction. Mechanistic differences between the reactions of these two reagents are discussed on the basis of these experimental results

Cyclization Reactions in Azole Chemistry: The Reaction of Some Azoles With o-Fluoroacetophenone, o-Fluorobenzaldehyde and o-Fluorobenzophenone

Abstract: The reactions of some azoles with o-fluoro-acetophenone , -benzaldehyde and -benzophenone in dimethyl sulfoxide solution in the presence of anhydrous potassium carbonate have been investigated. In addition to the expected substitution products, cyclization reactions frequently occurred to give carbinols in the case of the reactions of o-fluoro-acetophenone and -benzophenone, and cyclic ketones in the case of the reactions with o-fluorobenzaldehyde . Fluoren-9-ol and related carbinols containing heteroaromatic nuclie are readily converted in dimethyl sulfoxide solution into the corresponding ketones by treatment with anhydrous potassium carbonate. When treated with ethanolic alkali, 2′-(benzimidazol-1′-yl) acetophenone undergoes a remarkable transformation to give 1-(2𔈊-aminophenyl)quinolin-4(1H)-one.

Homogeneous rate constants for coupling between electrochemically generated aromatic anion radicals and alkyl radicals

Abstract: Rate constants have been measured for the coupling between hexenyl radicals and 2,2-dimethylhexenyl radicals and electrogenerated anion radicals of anthracene, 9,10-diphenylanthracene, benzophenone and quinoxaline. The rate constant for all four reactions in N,N-dimethylformamide is log k 2 =9.1(5), which is in accordance previous results in 1,2-dimethoxyethane for naphthalene and benzophenone anion radicals and 1-hexenyl radicals. The conclusion is that the coupling reaction between aromatic anion radicals and alkyl radicals has all the characteristics of a radical-radical coupling

Tetrapolyimide film containing benzophenone tetracarboxylic dianhydride

Abstract: Tetrapolyimide films derived from 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic acid dianhydride, p-phenylene diamine and 4,4'-diaminodiphenyl ether, and their preparation, are described. The tetrapolymer films have low water absorption, low coefficients of thermal and hygroscopic expansion, high modulus and are caustic etachable and can be used in flexible printed circuit and tape automated bonding applications.

Benzophenone sensitization of triplet oxazine and of delayed fluorescence by oxazine in acetonitrile solution

Abstract: Benzophenone has been used as a triplet energy donor to sensitize the production of the triplet state of the oxazine, 2,7-bis (diethylamino)-phenazoxonium chloride, in dilute acetonitrile solution. This enabled the spectrum, lifetime (14.5 µs) and absorption coefficient (1.6 × 104 dm3 mol–1 cm–1 at 830 nm) of the triplet oxazine to be determined. The quantum yield of triplet–state production for this oxazine by direct excitation was shown to be < 0.01 but addition of ethyl iodide quenched the oxazine fluorescence by induced intersystem crossing as confirmed in nanosecond laser photolysis experiments in which the oxazine triplet-state transient absorption spectrum was detected in the presence but not in the absence of ethyl iodide. Quenching of triplet benzophenone by oxazine was investigated by means of steady-state luminescence and also transient emission and absorption techniques in deaerated acetonitrile solution at room temperature. A rate constant for triplet-triplet energy transfer of 0.9 ± 0.1 × 1010 dm3 mol–1 s–1 was obtained. Delayed fluorescence was detected, which like the prompt fluorescence exhibits a slight red shift of the maximum owing to increasing reabsorption when the concentration of oxazine increases. The mechanism for this delayed fluorescence is established as involving an interaction between the triplet state of the donor (benzophenone) and the triplet state of the oxazine, i.e. mixed triplet–triplet annihilation.