Proton transfer reaction of 4-hydroxy-1-naphthalenesulphonate in methanol-water and ethanol-water mixtures

Htun, M. Than; Suwaiyan, A.; Klein, U.

doi:10.1016/0009-2614(95)00786-4

Cited by 26 publications

(5 citation statements)

References 14 publications

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“…Robinson et al − , suggested that a water tetramer is an effective proton acceptor for both weak (2OH) and strong (1OH) photoexcited acids. Klein et al have found that the a water dimer is an effective proton acceptor for the dissociation of 4S1OH in alcohol−water mixtures. Agmon et al suggested that the proton is solvated in the water-rich region by a single water molecule, with either water or methanol in the H 3 O + solvation shell.…”

Section: Resultsmentioning

confidence: 99%

“…The influence of water structure on the PTTS kinetics is most conspicuous in the investigation of proton transfer in mixed water/organic solvents. Protolytic photodissociation of various hydroxyaromatic compounds was studied in series of mixtures of water with alcohols − and other solvents. ,, In all cases PTTS rates were found to decrease with decreasing molar fraction of water in the mixture. This was accompanied by an increase of excited ROH (R*OH) fluorescence decay times and quantum yields, and a reduction of R*O - emission.…”

Section: Introductionmentioning

confidence: 99%

“…Klein et al11c suggested that protolytic photodissociation of 1-hydroxy-4-naphthalenesulfonate (4S1OH) (p K a * ≈ −0.1 in water) in propanol/water mixtures requires a critical water concentration (4.1 ± 0.3 M at 25 o C). Above this critical value, only two water molecules are needed to sustain the proton-accepting cluster.…”

Section: Introductionmentioning

confidence: 99%

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Photochemistry of “Super” Photoacids. 2. Excited-State Proton Transfer in Methanol/Water Mixtures

et al. 2000

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Excited-state proton transfer to solvent (PTTS) of 5-cyano-2-naphthol was investigated in methanol/water mixtures. We have found that the time-resolved fluorescence data fit the solution of the Debye−Smoluchowski equation for the reversible geminate recombination of ions over the whole range of methanol/water concentration ratios. The rate constants of the elementary protolytic photochemical processes and their isotope effects were determined by a simultaneous analysis of the time-resolved fluorescence of the photoacid and its conjugated anion. The competition between adiabatic protonation and quenching of the excited naphtholate anion by the geminate proton was observed to diminish sharply near pure methanol. The dissociation rate coefficient near pure methanol depends on a power of the water concentration, which appears to decrease from 2 (for “ordinary” photoacids) to below 1 for “super” photoacids.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photochemistry of “Super” Photoacids. 2. Excited-State Proton Transfer in Methanol/Water Mixtures

et al. 2000

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“…For 2OH, water is the only solvent that promotes appreciable dissociation with subsequent ion separation. It was suggested that proton transfer to solvent depends crucially on the availability of “water cluster” proton acceptors. − The dominance of the acceptor properties of water has been questioned before. , Indeed, water is not the best solvent for proton solvation. Proton free energies of transfer from water to various solvents, Δ G t (H + ), have been compiled in ref (see Table ).…”

Section: Discussionmentioning

confidence: 99%

Solvatochromism of β-Naphthol

1998

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Excitation and emission fluorescence spectra of 2-naphthol and 2-methoxynaphthalene were measured in a series of pure solvents. The spectral shifts are correlated by the Kamlet−Taft parameters (π*, β, and α). As judged from the π* dependence, both molecules have a negligibly small dipole moment in their ground electronic state, which increases in the excited (S 1) state. However, the majority of the Stokes shift is due to hydrogen-bonding rather than to dipole−dipole interactions. By comparing the shifts for the two compounds, it is demonstrated that the β dependence in 2-naphthol is due exclusively to a hydrogen bond donated from its hydroxylic hydrogen atom to the solvent. This bond becomes stronger upon excitation and hence produces a bathochromic shift. We find α dependence only in the excitation spectrum, indicating that protic solvents stabilize the ground state by donating a hydrogen bond to the hydroxylic oxygen. This bond breaks following excitation to S 1 but re-forms following proton transfer.

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“…For strong photoacids, water dimers can be effective proton acceptors. Than Htun et al came to a similar conclusion after studying the dissociation of the strong photoacid 4-hydroxy-1-naphthalenesulfonate in alcohol/water mixtures. − In the investigation of the proton transfer to solvent from the cyano naphthols in nonaqueous solvents and water, Agmon et al. and Tolbert et al found the existence of reversible proton geminate recombination processes and proton-transfer rates controlled by the solvent motion in many instances. ,− …”

Section: Introductionmentioning

confidence: 88%

Role of Hydrogen-Bonded Adducts in Excited-State Proton-Transfer Processes

2000

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The protonated cation of 2-(2‘-hydroxyphenyl)benzimidazole becomes a very strong acid in its first excited singlet state (C*). We studied the proton-transfer process from C* to the bases water, methylurea (MU), and dimethyl sulfoxide (DMSO) in acetonitrile solution by means of fluorescence and UV−vis absorption spectroscopy. We found that the process occurs via a 1:1 hydrogen-bonded adduct between the photoacid C* and the base. We determined the photophysical properties of the adducts with the three bases and the equilibrium constants of formation of various adducts in the ground and excited states. The proton transfer takes place by dissociation of the adduct, in a unimolecular or bimolecular process involving a second molecule of the base. The unimolecular dissociation takes place for the adducts formed with DMSO and MU, but not for the adduct formed with water. The bimolecular dissociation occurs for the adducts formed with water and MU. In this process, the entity that finally accepts the proton is a cluster of two molecules of the base. We conclude that only one molecule of water is not able to accept the proton donated by the photoacid, a cluster of two molecules of water being required. This cluster is formed in two consecutive steps. First the adduct between the photoacid and one molecule of water is formed, subsequently followed by the reaction of the adduct with a second molecule of water.

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Proton transfer reaction of 4-hydroxy-1-naphthalenesulphonate in methanol-water and ethanol-water mixtures

Cited by 26 publications

References 14 publications

Photochemistry of “Super” Photoacids. 2. Excited-State Proton Transfer in Methanol/Water Mixtures

Photochemistry of “Super” Photoacids. 2. Excited-State Proton Transfer in Methanol/Water Mixtures

Solvatochromism of β-Naphthol

Role of Hydrogen-Bonded Adducts in Excited-State Proton-Transfer Processes

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