Photolysis Of Benzene Research Articles

Aluminum sheet-based S-doped TiO2 for photocatalytic decomposition of toxic organic vapors

S-doped TiO2 (S-TiO2) films were immobilized on flexible low-cost aluminum sheets (S-TiO2-AS) using a sol-gel dipping process and low post-processing temperatures. The photocatalytic degradation of toxic organic vapors using the prepared films was evaluated using a continuous-flow glass tube under visible light exposure. The surface properties of the S-TiO2-AS and TiO2-AS films were examined by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and ultraviolet-visible spectroscopy. The photolysis of benzene, toluene, ethyl benzene, and xylene (BTEX) did not occur on the bare AS. In contrast, the photocatalytic degradation efficiencies of the target pollutants using S-TiO2-AS were higher than those obtained using reference TiO2-AS photocatalyst. In particular, the average photocatalytic degradation efficiencies of BTEX using S-TiO2-0.8-AS (S/Ti ratio = 0.8) over a 3-h process were 34%, 78%, 91%, and 94%, respectively, whereas those of TiO2-AS were 2%, 11%, 21%, and 36%, respectively. The photocatalytic decomposition efficiencies of BTEX under visible irradiation using S-TiO2-AS increased with increasing S/Ti ratios from 0.2 to 0.8, but decreased when the ratio further increased to 1.6. Thus, S-TiO2-AS can be prepared using optimal S/Ti ratios. The degradation of BTEX over S-TiO2-AS depended on the air flow rates and initial concentrations of the target chemical. Overall, under optimal conditions, S-TiO2-AS can be effectively applied for the purification of toxic organic vapors.

ChemInform Abstract: Matrix-Controlled Photochemistry of Benzene and Pyridine.

Dewar benzene has been shown to be a primary product from the photolysis of benzene in low temperature argon matrices at 253.7 nm. This is the first observation of Dewar benzene product at this wavelength and a mechanism is proposed that involves benzene S{sub 1}-S{sub 2} state mixing induced by the matrix environment. Analogous experiments on the photolysis of pyridine show that the only primary products are isomeric species derived at least in part from a triplet state of pyridine, probably T{sub 1}. This is the first observation of photochemistry from the T{sub 1} state and may be the process responsible for the small values of {tau}{sub p} and {phi}{sub p} in pyridine. Analysis of the IR spectral bands points to the main product being Dewar pyridine although other isomers cannot be ruled out. In contrast to the gas phase, no decomposition of pyridine was found in matrices producing compounds such as acrylonitrile, ethyne, and hydrogen cyanide.

Quenching of poly(vinyl phenyl ketone) photolysis by energy transfer in solution

The Stern-Volmer constant of 40 quenchers was determined at 366 nm for poly(vinyl phenyl ketone) photolysis in benzene and dioxane solution at room temperature. Aromatic hydrocarbons, dienes and olefins were used as quenchers. A procedure for quantitative separation of the screening effect of quenchers absorbing at irradiation wavelength was elaborated. The correctness of this procedure was checked using 2-hydroxy-5-methyl benzophenone over the concentration range 0-10−3 mole/1. The values of the Stern-Volmer constants lay within the range 0-250 1./mole, expressing changes of the rate constant of quenching. Stern-Volmer constants were found to be constant for naphthalene, its alkyl, halogen derivatives and esters at about 70 1./mole, that of 1-naphtyl amine 1- and 2-naphtol being, however, substantially higher. Electron-deficient olefins were equally effective as dienes. There has not so far been found a parameter to characterize unambiguously the quenching efficiency of the compounds investigated.

Photoinduced intramolecular hydrogen atom transfer in 2-(2-hydroxyphenyl)benzoxazole and 2-(2-hydroxyphenyl)benzothiazole studied by laser flash photolysis

2-(2-Hydroxyphenyl)benzoxazole (HBO) and 2-(2-hydroxyphenyl)benzothiazole (HBT) underwent hydrogen atom transfer to give the tautomer in both the singlet excited state and the triplet excited state. In the singlet excited state, the keto form produced by excited state hydrogen atom transfer underwent isomerization around the quasi-double bond to give the trans-keto form. In the triplet excited state, HBO and HBT were equilibrated between the enol form and the cis-keto form and the equilibrium constant was determined by triplet sensitization and quenching experiment by using laser flash photolysis in benzene at room temperature. From these results, we have revealed the energy diagram of the hydrogen atom transfer reaction of HBO and HBT both in the singlet excited state and the triplet excited state.

Solution and Nujol Matrix Photochemistry of (η5-C5H5)2Os2(CO)4 and Nujol Matrix Photochemistry of (η5-C5H4CH3)2Ru2(CO)4 and (η5-C5H5)M(CO)2H, Where M = Ru and Os

Lowering the temperature of a Nujol solution of (η5-C5H4CH3)2Ru2(CO)4 containing bands of the trans- and cis-bridging and trans-nonbridging isomers from room temperature to ca. 90 K results in complete disappearance of the bands of the trans-terminal isomer. The photochemistry of (η5-C5H4CH3)2Ru2(CO)4 in frozen Nujol at 90 K differs subtly from that of (η5-C5H5)2Ru2(CO)4 in inert gas matrixes at 12 K in that the trans-bridging isomer is found to undergo photolysis at high energy (λirr > 250 nm) to yield both the triply bridged carbonyl-loss species, (η5-C5H4CH3)2Ru2(μ-CO)3, and the cis-bridged species isomer. There is no evidence for formation of the trans-nonbridged isomer upon photolysis as observed for (η5-C5H5)2Ru2(CO)4. The solution photochemistry of (η5-C5H5)2Os2(CO)4 is shown to closely parallel that of (η5-C5H5)2Ru2(CO)4. Photolysis of (η5-C5H5)2Os2(CO)4 in CHCl3 yields (η5-C5H5)Os(CO)2Cl, while photolysis in benzene yields hydride products believed to arise from metal-to-ring coupling of radicals. Photolysis of (η5-C5H5)2Os2(CO)4, which exists only in a nonbridged form, in frozen Nujol (90 K) results in CO loss and formation of (η5-C5H5)2Os2(μ-CO)3 as the only photoproduct. Photolysis of (η5-C5H5)M(CO)2H, where M = Ru or Os, in frozen Nujol yields (η5-C5H5)M(CO)H and a second product that appears to be either (η5-C5H6)M(CO)2 or the (η5-C5H5)M(CO)2 radical.

Photoinduced substitution reaction in halothiophenes. Quantum-mechanical and photochemical studies on nitro- and cyano-derivatives

2-Iodo-5-nitrothiophene, 2-iodo-5-cyanothiophene, 2-bromo-5-cyanothiophene and 4-iodo-nitrobenzene were studied by steady state and pulsed techniques and by semi-empirical quantum-mechanical calculations. The quantum yields for the direct and sensitized photoarylation of these haloaromatics following the photocleavage of the carbon–halogen bond were measured in benzene. The transient species (triplet states and free radicals) originated by direct and sensitized laser excitation were investigated by nanosecond laser flash photolysis in benzene and methylcyclohexane. The transients were characterized in terms of absorption spectra and decay lifetimes. The triplet states were also characterized by phosphorescence measurements in rigid matrices at low temperature. The quenching rate constants of the triplet states and the quantum yields for singlet oxygen production were determined in methylcyclohexane. The results obtained with sensitizers of different triplet energy indicate that an upper triplet state is involved in the photocleavage of the carbon–halogen bond.

New results on the atmospheric photooxidation of simple alkylbenzenes

A study of the photolysis of two postulated intermediates in the OH initiated photooxidation of aromatic hydrocarbons, benzene oxide/oxepin and toluene-1,2-oxide/2-methyloxepin, has been conducted under the real light conditions of a large volume outdoor reaction chamber. The main focus of the study was on the formation of the hydroxylated aromatic hydrocarbons, i.e., phenol from benzene oxide/oxepin and the cresol isomers from toluene-1,2-oxide/2-methyloxepin. Photolysis frequencies were measured relative to that of NO 2, which was determined with a filter radiometer. A linear dependency was found within the experimental errors, the ratios of the photolysis frequencies of the arene oxides to that of NO 2 were found to be (4.41±0.44)·10 −2 and (3.99±0.48)·10 −2 for benzene oxide/oxepin and toluene-1,2-oxide/2-methyloxepin, respectively. The yield of phenol in the photolysis of benzene oxide/oxepin was found to be (43.2±4.5)%, independent of the light intensity. For toluene-1,2-oxide/2-methyloxepin, an o-cresol yield of (2.7±2.2)% was determined, the formation of other cresol isomers was not observed. The results obtained are in agreement with arene oxides being intermediates in the atmospheric photooxidation of benzene and toluene, they are discussed with regard to their implications for the formation of hydroxylated aromatics in the OH initiated photooxidation of benzene and toluene.

Photochemical displacement of co-ordinated ethene from [Rh(η5-C5H5)(PPh3)(C2H4)

The rhodium (triphenylphosphine)(ethene) complex [Rh(η5-C5H5)(PPh3)(C2H4)], was synthesized by reaction of [{Rh(C2H4)2Cl}2] with triphenylphosphine and thallium cyclopentadienide. Like in [Rh(η5-C5H5)(PMe3)(C2H4)], the co-ordinated ethene ligand may be displaced photochemically. Photoreaction of [Rh(η5-C5H5)(PPh3)(C2H4)] with SiR3H (R = Pri or Et) and hexafluorobenzene yielded [Rh(η5-C5H5)(PPh3)(SiR3)H] and [Rh(η5-C5H5)(PPh3)(η2-C6F6)], respectively. Oxidative addition of the C–H bonds of partially fluorinated arenes, C6F5H and 1,3-C6F2H4, was demonstrated by NMR spectroscopy to result in formation of [Rh(η5-C5H5)(PPh3)(R)H] (R = C6F5 or 2,6-C6F2H3). Oxidative addition of benzene may be detected following photolysis in benzene–thf mixtures at 233 K, but the product decomposes on warming. The molecular structure of [Rh(η5-C5H5)(PPh3)(SiPri3)H] has been determined crystallographically. The disorder of the isopropyl groups was modelled with two orientations of the SiPri3 with equal occupancies. The Rh–Si bond length is 2.386(2) A, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).

Laser photolysis of liquid benzene and toluene: Graphitic and polymeric carbon formation at ambient temperature

ArF laser photolysis of liquid benzene and toluene yields hydrogen, methane, ethene, ethyne, aromatic hydrocarbons and carbon. The preponderance of biphenyl among the aromatic products from photolysis of benzene, and that of bibenzyl among those from photolysis of toluene reveals the importance of the phenyl and benzyl radical combinations in the initial stages of photolysis. XPS and Raman spectroscopies showed the carbon to contain both sp 3 and sp 2 components and to consist of graphitic and polymeric constituents. The remarkable feature is that the carbon formation occurs at ambient temperature of the irradiated liquids; photolytic graphitization modes must therefore be different from those involved in thermally-induced graphitization which takes place at temperatures above 2500.

Tetrahydrofuran Derivatives from Epoxides via Group Transfer Cyclization or Reductive Radical Cyclization of Organotellurium and Organoselenium Intermediates

Monosubstituted epoxides were regiospecifically ring-opened from the sterically least hindered side by benzenetellurolate and benzeneselenolate reagents to afford aryl beta-hydroxyalkyl tellurides and selenides, respectively. These materials were O-allylated by treatment with allylic bromides/sodium hydride in tetrahydrofuran and O-prop-2-ynylated when reacted with propargyl bromide/sodium hydride. On photolysis in benzene containing 40 mol % of hexabutylditin, the beta-(allyloxy)alkyl aryl tellurides were found to undergo group transfer cyclization to afford 2-substituted 4-[(aryltelluro)methyl]tetrahydrofurans (cis/trans = 1/3-1/10). The aryl beta-(prop-2-ynyloxy)alkyl tellurides similarly afforded 2-substituted 4-[(aryltelluro)methylene]tetrahydrofurans with an E/Z-ratio close to unity. The beta-(allyloxy)alkyl aryl selenides and aryl beta-(prop-2-ynyloxy)alkyl selenides failed to undergo group transfer cyclization. In the presence of tributyltin hydride and 2,2'-azobisisobutyronitrile, the former compounds were found to undergo reductive radical cyclization in high yields to afford 2-substituted 4-methyltetrahydrofurans (cis/trans = 1/3-1/10). Aryl beta-(prop-2-ynyloxy)alkyl selenides similarly afforded 2-substituted 4-methylenetetrahydrofurans. 2-Alkoxy-2-(allyloxy)ethyl phenyl selenides, prepared by allyloxyselenenation of vinyl ethers, were found to undergo reductive radical cyclization to afford 2-alkoxy-4-methyltetrahydrofurans (cis/trans = 1/3-1/4). The preference for formation of trans-2,4-disubstituted tetrahydrofurans in the group transfer and reductive radical cyclizations was rationalized assuming a chairlike transition state with a preferred adoption of a pseudoequatorial position of the 2-substituent. By carrying out the reactions at lower temperatures (ambient or -45 degrees C), using triethylborane as an initiator, it was possible to further increase the trans selectivity in the reductive cyclizations.

Paramagnetic intermediates in the photolysis of 2-methylpropanoyltripropylstannane studied by means of multinuclear CIDNP

1 H, 13C and 119Sn CIDNP studies of 2-methylpropanoyltripropylstannane Pr3SnC(O)Pri 1 photolysis in benzene have shown that its photodecomposition occurs from the triplet excited state via Sn–C (tin–carbonyl) bond cleavage. Formation of Pr3Sn˙, ˙COCHMe2 and ˙CHMe2 free radicals has been observed. Possibilities of their reactions with initial ketone and main reaction products have been discussed.

Excited state properties of 4-bromo- and 4,4'-dibromobiphenyl

The triplet-triplet absorption spectra for 4-bromobiphenyl and 4,4'-dibromobiphenyl have been determined by pulse radiolysis and laser flash photolysis in benzene, cyclohexane, isopropanol, ethanol and methanol. The extinction coefficient for the triplet-triplet absorption of 4-bromobiphenyl and 4,4'-dibromobiphenyl in benzene was calculated to be 32,000 ± 500 dm 3 mol −1 cm −1 and 39,500 ± 500 dm 3 mol −1 cm −1, respectively. The quenching of triplet by ground state molecules was not very significant. The energy transfer rate constants from benzene to 4-bromobiphenyl and 4,4'-dibromobiphenyl were found to be diffusion controlled. The quenching of naphthalene fluorescence by biphenyl was also found to be diffusion controlled.

Acoustic Monitoring of Carbon Film Formation by Laser-Induced Chemical Vapor Deposition

Acoustic signals generated by the deposition of carbon thin films were monitored in situ by a microphone. Photolysis of benzene or adamantane vapor in the presence of helium buffer gas of 5 to 100 Torr by an ArF excimer laser formed several kinds of carbon films (e.g., polymeric, amorphous, and graphitic films), depending on the optical configuration, the ambient pressure, the laser fluence, and the reagent pressure. Analysis of the acoustic signal offers some insight into the mechanism of the deposition processes, which include the graphitization of the deposited films and the role of energetic particles, such as vibrationally excited benzene, in the deposition of amorphous hydrogenated carbon film. Also, the acoustic signal clearly showed the presence of surface-related processes in the course of film deposition.

Analogues of Sialic Acids as Potential Sialidase Inhibitors Synthesis of 2‐C‐Hydroxymethyl Derivatives of N‐Acetyl‐6‐amino‐2,6‐dideoxy‐neuraminic Acid

AbstractThe intramolecular cycloaddition of the previously described azidoalkene 16, the related diacetates 7 and 13, and the monoacetate 8 led diastereoselectivity to the (2R)‐ and (2S)‐configurated hydropyridotriazoles 17, 9 and 11, 14 and 15, and 10 and 12, respectively (Scheme 1). Thermolysis of 16 gave also the aziridine 18, its proportion increasing with reaction time. The diastereoselectivity of the cycloaddition‐ is rationalized on the basis of steric interactions and of Hbonds in the transition state. Photolysis in benzene partially transformed 9 into the aziridine 19. Treatment of 9 with aqueous AcOH gave 19 and the tetrahydrofuran 20, with AcOH in benzene 20 and the triacetate 23, and with aqueous H2SO4 in THF, the primary alcohol 22 (room temperature) or 19 and 22 (0°). Deacetylation of 9 followed by reaction with pyridinium hydrochloride led to the tetrahydrofuran 21 and the chloride 24 (Scheme 2). The diacetate 22 and the triacetate 23 gave the tripl 25 which was deprotected to 26. Reduction of the keto‐aziridine 18 (NaBH4) gave the alcohols 27 and 29 which were acetylated to give 28 and 19, respectively (Scheme 3). Treatment of the aziridine 28 with AcOH in benzene followed by deacetylation gave 30 and hence 31. AcOH in benzene transformed the triazoline 15 first into the aziridine 32 and hence into 33, which was deprotected to give the triol 34 and hence 35. The 2‐(hydroxymethyl)piperidines 26, 31, and 35 inhibited Vibrio cholerae sialidase with K1 = 3.8 · 10−2 M, 3.4 · 10−3 M, and 1.5 · 10−4 M, respectively. The conformation of the glycerol side chain of these compounds and of the unbranched piperidines 2–4 deviates from the one of Neu5Ac (and Neu2en5Ac). This finding is rationalized by an H‐bond between OHC(8) and NHC(6). The conformations and the K1 values of 26, 31, and 35 correlate with each other.

Organoruthenium sulfur complexes. Synthesis of (μ-S 5) [RuCp(CO) 2] 2 and its reaction with acid chlorides. Preparation of RuCp(CO) 2SCOR and molecular structure of RuCp(CO) 2SCO(2-O 2NC 6H 4)

The binuclear pentasulfur bridged organoruthenium complex, (μ-S 5) [RuCp(CO) 2] 2 (I), and other organoruthenium polysulfanes have been prepared by reaction of [RuCp(CO) 2] 2 with elemental sulfur upon refluxing or photolysis in benzene. These organoruthenium sulfanes readily react with acid chlorides, RCOCl, to give the S-bonded monothiocarboxylate derivatives, RuCp(CO) 2SCOR (R = 1-C 10H 7 (II), 2-FC 6H 4 (III), 4-O 2NC 6H 4 (IV), 3,5-(O 2N) 2C 6H 3 (V), 2-O 2NC 6H 4 (VI), C 6H 4COSFeCp(CO) 2 (VII)). The crystal structure of VI has been determined. Compound VI crystallizes in the monoclinic system, space group C2/ c with a 1488.0(5), b 1359.4(3), c 1651.6(5) pm; β 115.68(2)°: Z = 8; R 1 = 0.027; R 2 = 0.027.

ChemInform Abstract: Photochemical and Thermal Reactions of 2‐Aryloxybenzohydroxamic Acids.

AbstractPhotolysis of the hydroxamic acids (III) derived from the acids (I) leads to the salicylamides (IV).

Photochemical and thermal reactions of 2-aryloxybenzohydroxamic acids

2-Aryloxybenzohydroxamic acids 1–7 were subjected to photolysis in benzene or methanol. In each case corresponding N-arylsalicylamides 8–10 were obtained in good yields. Compounds 1–7 on thermolysis in decaline also produced 8–10.

Consequences of hydrophobic association in photoreactions: photodimerization of alkyl cinnamates in water

Photolysis of alkyl cinnamates in water gave δ-truxinates in near quantitative yields. Dimerization of alkyl cinnamates at low concentration (about 10 −4 M) in water is attributed to hydrophobic association of these solutes. At such low concentrations, photolysis in benzene and methanol yields only geometric isomers. This study illustrates the potential of water as a solvent for photoreactions and stresses the need for increased appreciation of its utility.

Photolysis of 2,3-epoxy-7,7-diphenylbicyclo[3.2.0]heptan-6-ones and 2-exo, 3-exo-dihydroxy-7,7-diphenylbicyclo[3.2.0]heptan-6-one

Photolysis of 2,3-endo-epoxy-7,7-diphenylbicyclo [3.2.0] heptan-6-one (2) in methanol gave products (4), (8) derived from an oxacarbene intermediate and the products (5)–(7), (9) derived from an initially formed alkenylketene. Photolysis of the same epoxide in benzene containing methanol (0.2M) gave the oxo-ester (10) as a major product whilst photolysis of (2) in benzene alone gave the lactone (11). The isomeric epoxide (3) behaved in a similar fashion giving the oxo-ester (10) on photolysis in benzene–methanol and the lactone (11) on photolysis in benzene alone. The homologous epoxide (13) gave products (14), (15) resulting from photon-induced ring-expansion. The dihydroxy ketone (16) gave the hydroxy lactone (17) in 66% yield by intramolecular trapping of the intermediate ketene.

Ftir photoacoustic investigation of the surface species resulting from the photochemical reaction of Re 2(CO) 10 with silica and alumina

The photolysis of Re 2(CO) 10 in the presence of Cab-O-Sil silica and alumina has been investigated by FTIR/PAS methods. The formation of tricarbonyl species on the surface of both oxides has been observed. The formation of tetracarbonyl and pentacarbonyl surface species during photolysis in THF slurries has also been postulated. A comparison of the photolysis in benzene and THF has been undertaken, and benzene appears to promote tricarbonyl formation.