Photochemical hydrolysis of some nitrophenyl acetates

1986 ◽  
Vol 51 (6) ◽  
pp. 1293-1300 ◽  
Author(s):  
Petr Kuzmič ◽  
Libuše Pavlíčková ◽  
Milan Souček
Keyword(s):  
Aqueous Solution ◽  
Excited State ◽  
Triplet State ◽  
Quantum Yields ◽  
Ester Bond ◽  
Acidic Media ◽  
Effective Lifetime ◽  
Product Molecule ◽  
Neutral Aqueous Solution ◽  
Hydrolysis Of

Nitro substituent exhibits a meta-activating effect on the course of photochemical hydrolysis of phenyl acetates since UV photolysis of isomeric 4- and 3-nitrophenyl acetates in neutral aqueous solution leads to the formation of the corresponding phenols with quantum yields 0.002 and 0.006, respectively; 2-methoxy-4-nitro- and 2-methoxy-5-nitrophenyl acetates showed still greater difference in their photochemical reactivity (Φr 0.002 and 0.129, respectively). Quenching of the photohydrolysis of the latter compound with 2,4-hexadienoic acid indicates the participation of a triplet state with the effective lifetime of 0.15 μs. The photoreaction is accelerated in acidic media which means that one of the early photochemical steps is the protonation of the excited state. No incorporation of 18O into the product molecule was observed after the photolysis of 2-methoxy-5-nitrophenyl acetate in H218O, which is an unambiguous evidence that the photoreaction proceeds as a light-induced hydrolysis of the ester bond.

THE CHEMISTRY OF ETHYLENE OXIDE: V. THE REACTION OF ETHYLENE OXIDE WITH HALIDE IONS IN NEUTRAL AND ACID SOLUTION

1952 ◽  
Vol 30 (3) ◽  
pp. 169-176 ◽  
Author(s):  
A. M. Eastham ◽  
G. A. Latremouille
Keyword(s):  
Aqueous Solution ◽  
Ethylene Oxide ◽  
Acid Solution ◽  
Activation Energies ◽  
Hydrogen Halide ◽  
Halide Ions ◽  
Neutral Aqueous Solution ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The rates of reaction of halide ions with ethylene oxide in neutral aqueous solution and the rate of hydrolysis of ethylene oxide in acid solution have been measured and the activation energies determined. From these data and from the ratio of glycol to chlorohydrin formed when ethylene oxide reacts with excess aqueous hydrogen halide, the rates of the acid-catalyzed addition of halide ions to ethylene oxide at 25 °C. have been estimated.

Photooxygenation of nitrobenzyl derivatives. Mechanisms of photogeneration and hydrolysis of α-hydroperoxy nitrobenzyl ethers

1987 ◽  
Vol 65 (8) ◽  
pp. 1775-1783 ◽  
Author(s):  
Peter Wan ◽  
S. Muralidharan ◽  
Iain McAuley ◽  
Christopher A. Babbage
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Acid Hydrolysis ◽  
Quantum Yields ◽  
Acid And Base ◽  
Hydrolysis Of

The photooxygenation of nitrobenzyl derivatives 1–10 has been studied in aqueous solution as a function of pH. For m-nitrobenzyl ethers 2–4 and 9, stable α-hydroperoxy ethers (11–13) are the primary photochemical products. Acid hydrolysis of 11–13 gives m-nitrobenzaldehyde and hydrogen peroxide. Quantum yields for photooxygenation are reported for a number of derivatives as a function of pH. Acid and base catalyses of photooxygenation are observed for several compounds. A mechanism involving photogenerated nitrobenzyl carbanion intermediates is proposed.

Synthesis, photophysicochemical studies of adjacently tetrasubstituted binaphthalo-phthalocyanines

2005 ◽  
Vol 09 (05) ◽  
pp. 316-325 ◽  
Author(s):  
Itumeleng Seotsanyana-Mokhosi ◽  
Ji-Yao Chen ◽  
Tebello Nyokong
Keyword(s):  
Excited State ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet Oxygen ◽  
Photophysical Properties ◽  
Zinc Phthalocyanine ◽  
Quantum Yields ◽  
Triplet Excited State ◽  
General Increase ◽  
Photochemical Behavior

Adjacent binaphthalo-phthalocyanines tetra-substituted with phenoxy (4a), 4-carboxyphenoxy (4b) and 4-t-butylphenoxy (4c) groups, as well as the di-substituted 4-carboxyphenoxy (5b) have been synthesized and characterized. The photophysical and photochemical behavior of 4a-c, were compared with those of the corresponding di-substituted derivatives, (5a-c). The secondary substituents on the phenoxy ring have an influence on the aggregation of the molecules and hence on their photophysical properties. All of the complexes exhibit a relatively good conversion of energy from the triplet-excited state to the singlet oxygen. The less aggregated molecule (4c), has the highest singlet oxygen quantum yield. For all the molecules, fluorescence yields are low and they all have relatively shorter triplet lifetimes compared with the unsubstituted zinc phthalocyanine. Increasing the number of ring substituents on these rigid MPc complexes (from complexes 5 to 4) showed a general increase in the triplet state lifetimes and singlet oxygen quantum yields, and a decrease in stability.

scholarly journals The Influence of Detergents on the Bleaching Process, Laser Properties of Rhodamine 6G and B in Aqueous Solution

1979 ◽  
Vol 34 (5) ◽  
pp. 551-556
Author(s):  
Z. Konefał
Keyword(s):  
Aqueous Solution ◽  
Triplet State ◽  
Rhodamine 6G ◽  
Quantum Yields ◽  
Generation Efficiency ◽  
Bleaching Process ◽  
Relative Quantum ◽  
Aqueous Detergent ◽  
Detergent Solutions

Abstract The bleaching and the laser properties of Rhodamine 6G and B in aqueous detergent solutions have been studied. The rate of bleaching depends on the concentration of the detergent. The relative quantum yields of the bleaching process for these solutions have been determined. It is found that the influence of detergents on the generation efficiency depends on the type of dye employed. From the results obtained it is concluded that the detergents influence the population of the triplet state of the lasing dye.

scholarly journals The behavior of 1,4-benzodiazepine drugs in acidic media. V. Kinetics of hydrolysis of flutazolam and haloxazolam in aqueous solution.

1986 ◽  
Vol 34 (1) ◽  
pp. 320-326 ◽  
Author(s):  
TOMONARI KUWAYAMA ◽  
YUKIHISA KURONO ◽  
TSUYUKO MURAMATSU ◽  
TAMOTSU YASHIRO ◽  
KEN IKEDA
Keyword(s):  
Aqueous Solution ◽  
Acidic Media ◽  
Kinetics Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Benzodiazepine Drugs

scholarly journals Excited States of Gold(I) Compounds, Luminescence and Gold-Gold Bonding

1994 ◽  
Vol 1 (5-6) ◽  
pp. 459-466 ◽  
Author(s):  
John P. Fackler ◽  
Zerihun Assefa ◽  
Jennifer M. Forward ◽  
Richard J. Staples
Keyword(s):  
Aqueous Solution ◽  
Excited State ◽  
Triplet State ◽  
Excited States ◽  
Ground State ◽  
Superoxide Anion ◽  
Direct Interaction ◽  
Water Soluble ◽  
State Behavior ◽  
Β Carotene

It has long been established by Khan that the superoxide anion, O2-, generates singlet oxygen, O21Δg, during dismutation. Auranofin, gold-phosphine thiols, β-Carotene, and metal-sulfur compounds can rapidly quench singlet O2. The quenching of the O21Δg, which exists at 7752 cm-1 above the ground state triplet, may be due to the direct interaction of the singlet O2 with gold(I) or may require special ligands such as those containing sulfur coordinated to the metal. Thus we have been examining the excited state behavior of gold(I) species and the mechanisms for luminescence. Luminescence is observed under various conditions, with visible emission ranging from blue to red depending on the ligands coordinated to gold(I). Triplet state emission can be found from mononuclear three coordinate Au(I) species, including species which display this behavior in aqueous solution. A description is given of the luminescent three coordinate TPA (triazaphosphaadamantane) and TPPTS (triphenylphosphine-trisulfonate) complexes, the first examples of water soluble luminescent species of gold(I).

Chemistry of photogenerated α-phenyl-substituted o-, m-, and p-quinone methides from phenol derivatives in aqueous solution

2008 ◽  
Vol 86 (2) ◽  
pp. 105-118 ◽  
Author(s):  
Li Diao ◽  
Peter Wan
Keyword(s):  
Aqueous Solution ◽  
Excited State ◽  
Intramolecular Proton Transfer ◽  
Quinone Methide ◽  
Quantum Yields ◽  
Biological Applications ◽  
Substituted Phenols ◽  
Quinone Methides ◽  
Phenol Derivatives ◽  
Related Compounds

The enhanced photochemical reactivity of o-substituted phenols in its propensity to give o-quinone methide (o-QM) intermediates via excited state intramolecular proton transfer (ESIPT) was uncovered by Keith Yates as part of his now classic studies of photohydration of aromatic alkenes, alkynes, and related compounds. Photogeneration of QMs and the study of their chemistry along with potential biological applications are the focus of many groups. In this work, photochemical precursors to o-, m-, and p-QMs based on substituted phenols (hydroxybenzyl alcohols) and related compounds have been studied in aqueous solution as a function of pH and water content. The focus will be on QMs that are stabilized by an α-phenyl substituent, which enhances quantum yields for their formation, with the resulting QMs having longer lifetimes and easier to detect. Noteworthy is that all QM isomers can be photogenerated with the o and m isomers being the most efficient, consistent with the Zimmerman “ortho-meta” effect. m-QMs have formal non-Kekulé structures, and although they can be routinely photogenerated, are found to be most reactive. One m-QM was found to undergo a photocondensation reaction at high pH giving rise to m-substituted oligomers. The mechanism of QM formation in aqueous solution is believed to involve singlet excited phenols that undergo adiabatic deprotonation to give the corresponding photoexcited phenolate ion, which subsequently expels the hydroxide ion (photodehydroxylation). A pathway involving direct loss of water for the o-isomers is also possible in organic solvents.Key words: quinone methides, phenols, excited state acidity, solvolysis, carbocations, meta effect, photopolymerization, non-Kekulé intermediates.

Photocyclization of 2-vinylbiphenyls: stereochemistry of the triplet state cyclization

1985 ◽  
Vol 63 (8) ◽  
pp. 2192-2196 ◽  
Author(s):  
René Lapouyade ◽  
Claude Manigand ◽  
Aziz Nourmamode
Keyword(s):  
Excited State ◽  
Triplet State ◽  
Trans Isomer ◽  
Singlet State ◽  
Membered Ring ◽  
Quantum Yields ◽  
Triplet States ◽  
Singlet Excited State ◽  
Singlet And Triplet States ◽  
Cis Isomer

The photochemistry of five- to eight-membered ring containing 2-cycloalkenyl biphenyls was examined under direct and sensitized irradiation. From the singlet excited state only trans 9,10-cycloalkyl-9,10-dihydrophenanthrenes were obtained. From the triplet state the trans isomer was exclusively formed from 2-cyclopentenyl and 2-cyclohexenyl biphenyls while the cis isomer also appeared with 2-cycloheptenyl and 2-cyclooctenyl biphenyls. We propose that the cis isomers resulted from the cyclization of the perpendicular triplet of cycloheptenyl biphenyl and from the perpendicular and trans triplet of cyclooctenyl biphenyl. Whereas the photocyclization of 2-vinylbiphenyls was regarded as a singlet-state reaction, the quantum yields of reaction of 2-cycloalkenyl biphenyls, from both singlet and triplet states, were high (ΦS = 0.20–0.26; ΦT = 0.15–0.46).

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