Oxidation Reactions of 1- and 2-Naphthols: An Experimental and

Subscriber access provided by Colorado State University | Libraries

Article

Oxidation Reactions of 1- and 2-naphthols: An Experimental and Theoretical Study Nair R Sreekanth, Kavanal P Prasanthkumar, Menachery Mathew Sunil Paul, Usha Kulangara Aravind, and Charuvila T Aravindakumar J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp4081355 • Publication Date (Web): 06 Oct 2013 Downloaded from http://pubs.acs.org on October 8, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Oxidation Reactions of 1- and 2-Naphthols: An Experimental and Theoretical Study R. Sreekanth1, Kavanal P. Prasanthkumar1†*, M. M. Sunil Paul2, Usha K. Aravind3, C. T. Aravindakumar2, 4* 1

School of Chemical Sciences, 2School of Environmental Sciences, 3Advanced Centre of

Environmental Studies and Sustainable Development, 4Inter University Instrumentation Centre, Mahatma Gandhi University, Kottayam 686560, India ABSTRACT The transients formed during the reactions of oxidizing radicals with 1-naphthol (1) and 2naphthol (2) in aqueous medium has been investigated by pulse radiolysis with detection by absorption spectroscopy and DFT calculations. The transient spectra formed on hydroxyl radical (•OH) reactions of 1 and 2 exhibited λmax at 340 nm and 350 nm at neutral pH. The rate constant of the •OH reactions of 1 (2) were determined from build-up kinetics at λmax of the transients as (9.63 ± 0.04) × 109 M-1s-1 ((7.31 ± 0.11) × 109 M-1s-1). DFT calculations using B3LYP/631+G(d,p) method have been performed to locate favorable reaction sites in both 1 and 2 and identification of the pertinent transients responsible for experimental results. Calculations demonstrated that •OH additions can occur mostly at C1 and C4-positions of 1, and at C1 and C8-positions of 2. Among several isomeric •OH adducts possible, the C1 adduct, was found to be energetically most stable both in 1 and 2. TDDFT calculations in solution phase have shown that

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 35

experimental spectrum of 1 was mainly attributed by 1a4 (kinetically driven •OH-adduct) formed via the addition of •OH at C4 position which was 0.73 kcal/mol endergonic than 1a1 (thermodynamic •OH-adduct); whereas 2a1 (thermodynamic/kinetic •OH-adduct) was mainly responsible for the experimental spectrum of 2. Naphthoxyl radicals of 1 and 2 have been predicted as the transient formed in the reaction of •OH at basic pH. In addition, the same transient species resulted from the reactions of oxide radical ion (O•–) at pH~13 and azide radical (N3•) at pH 7 with 1 and 2. Further, UV photolysis of aqueous solutions of 1 and 2 containing H2O2 (UV/H2O2) were used for the •OH induced oxidation product formations up on 60% degradations of 1 and 2; profiling of the oxidation products were performed by using an ultraperformance liquid chromatography quadrupole time of flight mass spectrometry (UPLC–QTOF-MS) method. According to the UPLC–Q-TOF-MS analyses, the preliminary oxidation products are limited to dihydroxy naphthalenes and naphthoquinones with N2-saturation while some more additional products (mainly isomeric mono hydroxy naphthoquinones) have been observed in the degradations of 1 and 2 in presence of O2. We postulate that, dihydroxy naphthalenes are derived explicitly from the most favorable •OH-adducts speculated (preference is in terms of kinetic/thermodynamic dominancy of transients) by using theoretical calculations which in turn substantiate the proposed reaction mechanisms. The observations of •OH-adducts for an aromatic phenol (herein for both 1 and 2 at pH 7) rather than phenoxyl type radical in the pulse radiolysis experiments is a distinct and unique illustration. The present study provides a meaningful basis for the early stages associated with the •OH initiated advanced oxidation processes of 1- and 2-naphthols.


2

Page 3 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Key words: Hydroxyl radical, transient absorption, rate constant, DFT, phenol, UPLC–Q-TOF MS.

AUTHOR INFORMATION Corresponding Author [email protected] (KPP), Tel: +91-487-2334144, Fax: +91-487-2334590 [email protected] (CTA), Tel: +91-481-2732120, Fax: +91-481-2731009. †Present Address Department of Chemistry, Government Engineering College, Thrissur 680009, India

INTRODUCTION 1-Naphthol and 2-naphthol (designated as 1 and 2, Scheme 1) are isomeric hydroxyarenes, has been the subject of several experimental and associated theoretical studies. Basically 1 and 2 are released into the environment through manufacture, handling, use and disposal in the context of their use in dye and pesticide industries1-3. Further they entered into the environment owing to the oxidation of naphthalene (the major constituent of coal tar) or as metabolites of carbamate pesticides like sevin or carbaryl (1-naphthyl-N-methylcarbamate) by chemical and biological processes

4-12

. The presence of hydroxyl group in 1 and 2 leads to their increased solubility and

portability in natural aquifers and is considered as more toxic than naphthalene and other polycyclic aromatic hydrocarbons13. Both 1 and 2 are used as biomarkers for livestock and humans exposed to polycyclic aromatic hydrocarbons4, 14, 15. Remarkably, molecules 1 and 2 are regarded as archetypes of ‘photoacids’ and exhibit major difference in pKa between the ground


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 35

and excited states due to the dependence of dissociation constant on electronic state of the molecule16-23.

Scheme 1: Structures of 1- and 2-naphthols with atomic numbering. Several comprehensive experimental/theoretical studies have been reported for the •OH induced oxidation reactions of phenolic compounds in view of their so-called antioxidant or freeradical scavenging propertie24-36. In the case of phenol (C6H5OH), the •OH reacts by addition to the aromatic ring that lead to the formation of the •OH-adduct as the preferred transient at neutral pH as demonstrated by ESR and pulse radiolysis studies25,

26

. However, the •OH addition

essentially leads to the formation of isomeric adduct species. Acids and bases catalyze the dehydration of the primary •OH-adduct(s) to the formation of phenoxyl radical26-28,

31

.

Furthermore, the base catalyzed dehydration is reported to be faster than the acid catalyzed dehydration27. Indeed, it was recognized that thermodynamically the formation of phenoxyl radical is more favorable than •OH additions37. Moreover, in substituted phenols the substituent have marked influence on directing the incoming •OH30,

32, 38

. A number of techniques which

essentially comprise of chemical, biological, catalytic, and electrochemical procedures were reported for the •OH induced degradation of naphthols in waste water39-51. Also, the free electron transfer phenomena of naphthols, their analogues and derivatives has been extensively studied by


4

Page 5 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


fluorescence, laser flash as well as pulse radiolysis techniques in organic solvents52-59. To our knowledge there has not been any comprehensive report of the kinetics, mechanism and intermediate species produced during the one-electron oxidations of both naphthol molecules with •OH in aqueous medium. The main interest of the present study is accordingly to understand the mechanism of primary oxidation reactions of isomeric naphthol molecules with •OH. In order to further understand the oxidations of naphthols, two other oxidizing inorganic radicals (O•– and N3•) were also selected and their reactions were compared with •OH reactions. We used pulse radiolysis technique with optical absorption detection as direct, convenient and reliable method to portrait the reactions of oxidizing radicals produced in aqueous medium with naphthols. The advantage of pulse radiolysis method is that, it offers a clean source for the selective generation of a particular radical like •OH under suitable experimental conditions to probe its reactions with a substrate. DFT calculations were carried out to locate the most probable reaction sites and to evaluate the preferred kinetic/thermodynamic transient(s) that would be formed in the pulse radiolysis experiments. Additionally, analysis of the oxidation products resulting from the reactions of •OH (generated via UV/H2O2 method) with 1 and 2 has been carried out using UPLC-Q-TOF-MS technique to elucidate the primary radical intermediates in the pulse radiolysis studies.

EXPERIMENTAL AND THEORETICAL METHODS Materials 1- and 2-naphthols were purchased from Sigma and were used as received. All other chemicals were of purest commercially available grade. Solutions were prepared in water purified by a Millipore Milli-Q system; freshly prepared solutions were used for day-to-day experiments. The


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 35

pH adjustments were done with NaOH or HClO4. All experiments were carried out at room temperature. Pulse radiolysis Pulse radiolysis experiments were performed using a 7 MeV linear accelerator delivering electron pulse with duration of 50 ns. Further details of the pulse radiolysis and optical absorption detection setup have been described elsewhere60. Thiocyanate dosimetry using N2O saturated aqueous solutions of KSCN (0.01 M) were used to determine the dose per pulse by monitoring the formation of (SCN)2•– at 480 nm61. The impact of high energy radiation on N2saturated water leads to the formation of highly reactive radicals such as •OH, hydrated electron (eaq–), hydrogen atom (H•), molecules like H2O2 and H2, and some H3O+ (eq 1). High yield of oxidizing hydroxyl radicals during radiolysis is achieved by saturating the solution with nitrous oxide (N2O), which converts eaq– into •OH (eq 2). H2O → •OH, eaq–, H•, H2O2, H2, OH–, H3O+ H2O + eaq– + N2O → •OH + OH– + N2

(1)

(2)

The reactions of O•–, the conjugate base of •OH (pKa of •OH is 11.9)62 were conducted in N2O saturated solutions at pH~13. Radiolysis of N2O-saturated aqueous solution that contained NaN3 was used to produce N3•. N3– + •OH → N3• + OH–

(3)

Computational methods All the electronic structural calculations were performed with Gaussian 03 suite of program63. Geometry optimizations and harmonic vibrational frequency analysis both in gas and solution phases were performed with the B3LYP method64, 65 using 6-31+G(d,p) basis set. The absence of imaginary frequencies in the calculated vibrational spectra demonstrated that the optimized


6

Page 7 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


structures represent minima in the potential energy surface. Inclusions of solvent effects were done by using the PCM method66-68. The spin densities of the transients were calculated by means of Mulliken population analysis. The interaction energies (Eint) of the •OH adducts were calculated in the gas phase at B3LYP/6-31+G(d,p) level with correction for the basis set superposition error (BSSE) using the Boys-Berrnardi counterpoise method69,

70

. The TDDFT

method71 has been adopted for the evaluation of optical absorptions of the transients in solution phase. Oxidation products analyses Reactions of •OH with 1- and 2-naphthols at pH 7 were carried out using UV irradiation in the presence of H2O2 (UV/H2O2), which provides a continuous supply of •OH. Photo-irradiations were carried out using a medium pressure high intensity (254 nm) mercury lamp. Approximately 60% degraded sample solutions of 1 and 2 were subjected to product analysis (with and without N2-saturation). N2-saturation creates an identical reaction environment used for •OH reactions by pulse radiolysis experiments. Products were analyzed using a Waters ACQUITY UPLC H-Class system coupled with a Waters Xevo G2 quadrupole-time-of-flight (Q-TOF) high resolution mass spectrometer which uses electrospray ionization (ESI) technique. The samples were introduced into the mass spectrometer through a BEH C18 column (50 mm × 2.1 mm × 1.7 µm). A gradient elution of methanol and water (flow rate 300 µL/min) was used as the mobile phase. All the spectra were recorded in both positive and negative ionization mode in the mass to charge (m/z) range of 50-600 Da.

RESULTS AND DISCUSSION Pulse radiolysis studies


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 35

(A) Reactions with •OH The transient absorption spectra formed on the reactions of •OH with 1 and 2 at pH 7 and 10.5 are presented in Figure 1. The ordinate in all these plots represents the product of G-value72 and absorption coefficient (ε) of the transient at a particular wavelength. It should be noted that, the ground state pKa values of 1 and 2 are respectively 9.3 and 9.673, therefore their anionic forms are reacting at higher pHs. The spectrum measured after 5 µs shows λmax 340 nm for 1 at pH 7 (Figure 1A), whereas at pH 10.5 the transient absorption shows λmax 410 nm and a broad but minor absorption centered around 540 nm (Figure 1B). The transient spectrum produced in the reaction of •OH with 2 (Figure 1C) showed λmax 350 nm at pH 7, whereas the same reaction at pH 10.5 is characterized by three absorptions with λmax 330 nm, 370 nm and 480 nm (Figure 1D). In all these cases we have observed no change in the spectral maxima with time except the decrease in signal intensities. Subsequently, from time resolved spectral studies we postulate the formations of relatively long-lived transient(s) in the reactions of •OH with 1 and 2 in neutral and alkaline solutions. Further, it has been found that, the transient with absorptions at either 340 or 350 nm in the reactions •OH with 1 or 2 at pH 7 decayed via second order kinetics. The second order rate constants for the reactions of •OH with 1 and 2 were determined from the slope of the plot of observed rate constant (kobs) as a function of concentrations of naphthols measured at their transient λmax at 340 nm and 350 nm respectively. The slopes of these plots (Figure 2) gave rate constants of (9.63 ± 0.04) × 109 M-1s-1 and (7.31 ± 0.12) × 109 M-1s-1 for 1 and 2 respectively; these values indicate that the reactions of •OH with 1 and 2 are nearly diffusion controlled. Also, these values are exceptionally not far-off to reported rate constant of 1.4 × 1010 M-1s-1 for the •OH additions to phenol24; hence the observed rate coefficients are consistent with the

well-known

electrophilic

addition

nature

of

•

OH


to

aromatic

rings.

The

8

Page 9 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydroxycyclohexadienyl-type radical formed via the addition of •OH to the benzenoid unit of phenol and a number of benzene derivatives

24, 28, 74

were reported to have λmax around 330 nm.

Obviously, a number of competent •OH addition sites are present in benzenoid units of both naphthol molecules. However, the prosperity of •OH addition to a particular ring atom is highly dependent upon the electron density on that carbon atom.

Figure 1: Transient spectra for •OH reactions with 1- and 2-naphthols (0.1 mM) recorded at 5 µs after irradiation. (A) 1-naphthol at pH 7, (B) 1-naphthol at pH 10.5 (C) 2-naphthol at pH 7 and (D) 2-naphthol at pH 10.5. Dose = 15.4 Gy/pulse


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 35

As the spectral features (in terms of both λmax and G × ε values) are apparently different at neutral and basic pH for •OH reactions of both naphthol molecules, one can presume that different transient species are observed at neutral and basic pH. One probable mechanism would be the formation of an •OH adduct radical at neutral pH; naphthoxyl radical formation via •OH attack to the naphthoxide ion followed by rapid elimination of OH– from the so-formed adduct at basic pH. The due reason for the supposition of •OH addition followed by OH– elimination at basic pH can be well admired on the basis of similar type of reactions studied by Roder and coworkers on phenol27. Their studies have revealed that phenoxyl radical formation through the OH– elimination of •OH adduct of phenol (pKa = 9.9) at pH 11 is almost 6-8 times faster than the H2O-elimination of the •OH adduct in highly acidic medium. Therefore in the present case (at basic pH), the initial reaction is expected to be an addition of •OH to naphthoxide ion followed by a rapid elimination of OH– to give naphthoxyl radical. Demonstration of naphthoxyl radical formation will be more obvious when we look at the O•– and N3• reactions of naphthols.


10

Page 11 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2: Plots of kobs as a function of concentrations of 1- and 2-naphthols at the λmax of the transients formed on their reactions with •OH at pH 7. It can be noted that, under the pulse radiolysis time scale, the naphthols at neutral pH can react with •OH according to three possible pathways as depicted in Scheme 2. In one mechanistic pathway, the electrophilic additions of •OH can occur to either benzenoid units of naphthol molecules which lead to the formations of so-called •OH-adducts. There could be two types of •

OH addition to hydroxyl group bearing (i.e. phenolic) benzenoid unit, one is addition to ipso-

position and the other being addition at un-substituted carbon atoms. The quantification of isomeric •OH-adducts formed in the case of phenol has been reported on the basis of product analysis and pulse radiolysis data26. The ipso- as well as meta- additions accounts 8% each, whereas 48% and 36% accounts for the •OH additions at ortho- and para- positions of phenol26. The relative yields for addition of •OH to ipso-, meta-, ortho-, and para- positions of phenol reported recently by Albarran and Schuler are 8%, 25%, 4% and 34% respectively34. The direct outer-sphere electron transfer reactions can lead to the formations of radical cations of 1 and 2.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 35

The third possibility is the H-abstractions from the phenolic OH units leading to naphthoxyl radicals. The differentiation of these three competing mechanistic pathways (viz. •OH-adducts formations, direct electron transfer and H-abstraction) is rather very difficult; however, the reactions of specific one-electron oxidants such as O•– and N3• would rather eliminate the possibility of one or two pathways.

Scheme 2: Possible reaction channels for •OH interaction with 1- and 2-naphthols. (B) Reactions with O•– and N3• The transient spectra (panel A and B in Figure 3) obtained for O•– reactions with anionic forms of 1 and 2 are identical to that generated from their •OH reactions at pH 10.5. Moreover, it was found that spectra shown in Figure 3 are in good agreement with the spectra reported for the naphthoxyl radicals in the reactions of 1 and 2 with N3• in aqueous solutions53, 73. Apparently, we


12

Page 13 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


could also reproduce identical spectra (not shown herein) for N3• reactions with 1 and 2 in aqueous solutions at pH 7 and 10.5. As N3• reacts with aromatic compounds mainly via direct electron transfer pathway, the results presented above clearly establish identical transient (i.e. naphthoxyl radical) formations in the reactions of •OH at pH 10.5 and of O•– at pH~13. Concomitantly, the possibility of electron transfer and thereby the formations of radical cations of 1 and 2 can also be ruled out. Therefore, the spectral data presented herein infer the operation of two different mechanisms under the experimental conditions used (neutral and basic pH) for •

OH reactions of 1 and 2. If one considers an addition of •OH at neutral pH (for both 1 and 2) as

in the case of phenol, then the chances of H-abstraction from phenolic OH (thereby naphthoxide radical) of naphthols can easily be precluded.

Figure 3: Transient spectra for O•– reactions with 1- and 2-naphthols (0.1 mM) recorded at 5 µs after irradiation at pH~13. (A) 1-naphthol and (B) 2-naphthol. Dose = 15.4 Gy/pulse.

The reactions of O•– and N3• with 1 and 2 underlined our previous hypothesis of naphthoxyl radical formations in the reaction of •OH at basic pH. Therefore, the observed experimental data


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 35

in combination with the results of O•– and N3• reactions unequivocally establish the formation of •

OH-adduct(s) at pH 7. However, there are many possible •OH addition sites in naphthol

skeleton and hence the experimental observations alone are unable to resolve the question of the most probable adduct(s) and is the rationale for DFT studies. DFT calculations were unfailingly supported us in previous studies by resolving the otherwise complicated pulse radiolysis experimental results and serves well in assigning the exact transient(s) formed therein 75-78. Theoretical studies We have carried out theoretical modeling mainly to find the reactive sites in naphthol molecules for •OH additions and as an alternate tool to predict the most probable experimental transient(s) by exploring the formation energies and predictions of λmax of •OH-adducts. The gas phase optimized geometries of the isomeric naphthols are depicted in Figure 4 along with selected bond lengths. Essentially several orientations of phenolic hydrogens are possible for both naphthols and we have presented the most stable conformations. It was found that both benzenoid rings of 1 and 2 are in the same plane and also phenolic hydroxyl units are positioned in the same molecular plane. Calculations showed that, the interaction takes place between the LUMO of •OH, located at -5.05 eV, and the HOMOs of 1 located at -5.77 eV and of 2 located at −5.92 eV. HOMOs of both naphthol molecules color mapped onto van der Waal's surfaces are presented in Figure 4. The contribution of each atom towards the HOMO may be considered as an indicator for the electrophilic addition of •OH towards that site. It can be seen from the MO plot (Figure 4) that, C4 and C1 positions formulate larger contribution towards the HOMO for compound 1; whereas C1 and C8 are the major contributors for the HOMO of compound 2. Other key contributors for the HOMO of 1 are phenolic O, C2, C5, and C8, similarly for the HOMO of 2 are phenolic O, C2, C4, C5, and C6. The interaction of •OH with the phenolic


14

Page 15 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxygen in both naphthols would primarily result in direct one-electron oxidation as well as Habstraction reactions and these possibilities are ruled out while discussing the experimental results at neutral pH. Therefore, we have theoretically modeled the •OH additions at vulnerable sites C1, C2, C4, C5 and C8 of 1 and the corresponding adducts are represented as 1a1, 1a2, 1a4, 1a5, and 1a8. Similarly, the •OH additions at C1, C2, C4, C5, C6 and C8 of 2 lead to adduct molecules represented as 2a1, 2a2, 2a4, 2a5, 2a6, and 2a8. Attempts to find pre-complexes for the •

OH-adduct formations lead product-like (i.e. adduct) structures for both 1 and 2. Therefore, it

seems that •OH-additions are very fast and occurs via energy free or they are barrier-less processes.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 35

Figure 4: Optimized geometries of (a) 1-naphthol and (b) 2-naphthol with selected bond lengths in Å unit. HOMO of (c) 1-naphthol and (d) 2-naphthol are color-mapped onto van der Waal's surfaces and the MO coefficients of major donor atoms are also shown.

The optimized geometries of adduct molecules 1a1, 1a2, 1a4, 1a5, and 1a8 in solution phase are illustrated in Figure 5 with selected bond lengths. The BSSE corrected Eint values of the adduct systems in gas phase are also depicted in Figure 5. The Eint values illustrate that the adduct systems are much more stable than the separate entities viz., 1 and •OH. Also, the 1a8 is more stable than other available adduct molecules. However, the solution phase studies point at the influence of solvation on the stabilities of the radicals. The relative electronic energies (∆E0), enthalpies (∆H), and free energies (∆G) of •OH adduct molecules of 1 in solution phase are listed


16

Page 17 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in Table 1. It can be found that, formations of all adducts systems are likely due to negative values of enthalpy and free energy of formations. The difference in free energy between the most stable 1a1 and the least stable 1a2 accounts for 3.92 kcal/mol. However, the formations of 1a1 and 1a4 (via additions at C1 and C4) are thermodynamically more feasible than other adduct molecules. Interestingly, the high electron density reserves at C1 and C4 positions are also in favor of the formations of 1a1 and 1a4 as obvious from the HOMO picture (Figure 4). Therefore, adducts 1a1 and 1a4 arises by the kinetic/thermodynamic harmony of •OH reaction with 1. It can also be noted from Table 1 that, except in 1a2 the unpaired electron spin is confined to the same benzenoid ring to which •OH gets added. The fewer stability associated with 1a2 can be attributed as a result of unpaired electron spin delocalization onto both benzenoid units which renders the reduction of inherent aromaticity of both the •OH added and spectator benzenoid ring. The solution phase optimized geometries of adduct molecules 2a1, 2a2, 2a4, 2a5, 2a6, and 2a8 are presented in Figure 6 with selected bond lengths. The calculated Eint values (with BSSE correction) showed that 2a1 is the most stable adduct molecule in gas phase. The Eint values of 2a2, 2a4, 2a5, and 2a8 are found to be lower than that of 1a2, 1a4, 1a5, and 1a8. The solution phase ∆E0, ∆H, and ∆G value of •OH adducts of 2 are presented in Table 1. The addition of •OH at C1position of 2 results in the formation of most stable radical 2a1 followed by the addition at C8position leading to 2a8. The stabilities of the •OH adducts follows the order 2a1 > 2a8 > 2a5 > 2a4 > 2a2 > 2a6. The difference in free energy between the most stable 2a1 and the least stable 2a6 accounts for 5.37 kcal/mol. Interestingly, the ipso-addition of

•

OH leads to the

thermodynamically most stable adduct (i.e. 1a1) in 1 in contrast to 2 where the ipso-addition causes the formation of one of the least stable adduct (i.e. 2a2). Also it can be noted from Table 1


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 35

that, for all •OH-adducts of 2 the odd electron spin density is mainly dispersed onto the carbon atom adjacent to the •OH added carbon. As noted in the case of 1a2, there is marked odd electron spin delocalization into both benzenoid units of 2a2 and 2a6 and which accounts for the fewer stabilities associated with these two species. Also it seems that the stabilities of the •OH adducts of 2 in solution are lower than that of 1. Albeit, the stabilities of 2a1 and 2a8 are consistent with the intuitive reactivity of C1 and C8 positions and therefore we can conclude that formations of 2a1 and 2a8 occur via the kinetic/thermodynamic control of •OH reaction with 2.


18

Page 19 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5: Solution phase optimized geometries of adducts formed via •OH additions at C1, C2, C4, C5, and C8 positions of 1-naphthol. Bond lengths are in Å unit. BSSE corrected Eint values (in kcal/mol) in gas phase are shown in parenthesis.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 35

Figure 6: Solution phase optimized geometries of adducts formed via •OH additions at C1, C2, C4, C5, C6 and C8 positions of 2-naphthol. Bond lengths are in Å unit. BSSE corrected Eint values (in kcal/mol) in gas phase are shown in parenthesis.


20

Page 21 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Calculated relative electronic energies (∆E0), enthalpies (∆H), free energies (∆G), Mulliken spin densities, λmax and corresponding oscillator strengths (ƒ) of the •OH adducts of 1and 2-naphthols in solution phase at B3LYP/6-31+G(d,p) level of theory.

Transient

∆E0 (kcal/mol)

∆H (kcal/mol)

∆G (kcal/mol)

Spin density (a.u.)

λmax (nm)

ƒ

1a1

-20.477

-21.440

-11.647

C2(0.56), C4(0.62)

328

0.130

1a2

-16.483

-17.431

-7.729

C1(0.58),C6(0.29), C8(0.30)

300

0.106

1a4

-19.600

-20.520

-10.913

C1(0.48), C3(0.59)

336

0.145

1a5

-18.583

-19.517

-9.951

C6(0.57), C8(0.65)

347

0.197

1a8

-17.638

-18.864

-8.400

C5(0.66), C7(0.61)

343

0.146

2a1

-19.78

-20.701

-11.264

C2(0.46), C4(0.62)

344

0.174

2a2

-16.000

-16.939

-7.130

C1(0.66), C6(0.29)

280

0.070

2a4

-17.692

-18.52

-9.146

C1(0.66), C3(0.58)

305

0.182

2a5

-18.244

-19.168

-9.558

C6(0.59), C8(0.64)

321

0.133

2a6

-14.678

-15.617

-5.886

C5(0.73), C2(0.26)

313

0.056

2a8

-18.701

-19.611

-10.078

C5(0.64), C7(0.57)

347

0.238

Calculated λmax and corresponding oscillator strengths of •OH adducts of 1 and 2 by the application of TDDFT method on solution phase optimized geometries are also presented in Table 1. The λmax 336 nm calculated for the adduct 1a4 agrees well with the experimentally observed transient λmax 340 nm in the reaction of •OH with 1 at neutral pH. Obviously, in terms of free energy, the stability of this kinetic adduct is only 0.74 kcal/mol less than the thermodynamic adduct 1a1. The thermodynamic adduct 1a1 can also contribute towards the


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 35

experimental spectrum even though the calculated λmax 328 nm differs by 12 nm (blue shift) with respect to the experimental λmax; a difference (12 nm) which is in the acceptable limit by considering the uncertainty in the experimental transient absorption spectroscopy and the TDDFT theoretical calculations. Although, the calculated λmax values of 1a5 and 1a8 are coinciding with the experimental λmax, the feasibility of the formations of these adducts are less in accordance with their enthalpy and free energy formations as compared to 1a1 or 1a4. Therefore, with the aid of the prevailing theoretical results, the experimental spectrum in the reaction of •OH with 1 at neutral pH is assigned as a result of adducts 1a1 and 1a4. The optical absorptions calculated for the most stable thermodynamic adduct 2a1 with λmax 343 nm and the next stable thermodynamic adduct 2a8 (λmax 347 nm) agrees well with the experimental λmax of 350 nm observed in the reaction of •OH with 2 at neutral pH. Moreover, 2a1 and 2a8 are produced as a result of •OH additions to the leading contributors of the HOMO of 2 (Figure 4). Thus, the λmax calculations are also in favor of the formations of kinetic/thermodynamic driven products (viz., 2a1 and 2a8) of •OH reaction with 2. Accordingly, on the basis of theoretical calculations it can be perceived that the experimental spectrum for •

OH reactions of 2 at neutral pH is attributed due to 2a1 and 2a8 formations.

Product analyses Further insights of •OH reaction mechanisms of 1 and 2 were obtained by the evaluation of preliminary oxidation products derived from UV/H2O2 method. Table 2 summarizes the results (the retention time and m/z values of the major products) of the analyses by using UPLC–QTOF-MS technique performed on degraded samples solutions of 1 and 2 via the UV/H2O2 method. Three major products were identified in the •OH reactions of 1 with N2-saturation; two


22

Page 23 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of them have an [M-H]– value of 159.04 with retention time (RT) at 2.5 and 2.9 min while the third one possess an [M+H]+ value of 159.04 with RT at 2.1 min. Based on the analyses of MS/MS fragmentation patterns and also taking account of the feasibilities of initial •OH attack to the ring of 1 (based on our theoretical studies as shown above), we have deduced the structures of the degradation products as the dihydroxy naphthalenes 1p1 and 1p4 and the naphthoquinone 1q4 (Scheme 3). The product 1p1 results from the ipso-addition of •OH (most stable thermodynamic transient) while 1p4 results from the initial •OH attack at C4 (next stable thermodynamic but the most feasible kinetic transient). Obviously, Scheme 3 represents one of the possible mechanistic pathways for product formations. However, in the presence of oxygen (O2) additional peaks have been observed in the total ion chromatogram (TIC) besides 1p1, 1p4 and 1q1. The TIC in the presence of oxygen in the negative ionization mode have species with identical [M-H]– mass of 159.04 observed at RT 1.9, 2.5, and 2.9 min; these peaks were assigned as due to the formations of isomeric dihydroxy naphthalenes 1p5, 1p4 and 1p1. The TIC in the positive ionization mode has a peak with an [M+H]+ value of 159.04 at RT 2.1 min and the product is identified as 1q4. Products with identical [M-H]– mass of 173.02 were observed at RT 1.0, 1.5 and 2.0 min; which is consistent with hydroxylation of 1q4 and the isomeric products were assigned as 1q41, 1q42 and 1q43 (Scheme 4).


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 35

Table 2. The retention time and m/z values obtained from UPLC-Q-TOF-MS analyses of the UV/H2O2 treated 1- and 2-naphthols and the identified products based on Scheme 3 to 6. Parent Molecule

Retention Time (min)

1-Naphthol

A. With N2-saturation 2.1 159.04 2.5 2.9 B. Without N2-saturation 1.0 1.5 1.9 2.0 2.1 159.04 2.5 2.9

2-Naphthol

Experimental (m/z)

Assigned Product

[M+H] +

[M-H]–

Designation

Mass

159.04 159.04

1q4 1p4 1p1

158.04 160.05 160.05

159.04 159.04

1q41 1q42 1p5 1q43 1q4 1p4 1p1

174.03 174.03 160.05 174.03 158.04 160.05 160.05

159.04 159.04

2q1 2p1 2p8

160.05 160.05 158.04

2q11 2q12 2q13 2q1 2q14 2p1 2p8 2p5

174.03 174.03 174.03 158.04 174.03 160.05 160.05 160.05

A. With N2-saturation 2.1 159.04 2.6 3.0 B. Without N2-saturation 1.1 1.4 1.6 2.1 159.04 2.2 2.6 3.0 3.1

173.02 173.02 159.04 173.02

173.02 173.02 173.02 173.02 159.04 159.04 159.04


24

Page 25 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 3: A possible route of product formations in the oxidation of 1-naphthol by UV/H2O2 method with N2–saturation.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 35

Scheme 4: Proposed channels for oxidation product formations from 1-naphthol by UV/H2O2 method without N2-stauration. As in the case of 1, three major products were obtained for the degradation of 2 by the UV/H2O2 method in the presence of N2-saturation. As can be seen from Table 2 that, two of them have an [M-H]– value of 159.04 with retention time (RT) at 2.6 and 3.0 min while the third one possess an [M+H]+ value of 159.04 with RT at 2.1 min. One possible mechanism that accounts the formations of these oxidation products is shown in Scheme 5. The product 2p1 and 2p8 arises from the initial •OH attack at C1 (the most feasible kinetic site for •OH addition that leads to the most stable thermodynamic adduct) and at C8 (the next feasible kinetic site for •OH addition that leads to the second stable thermodynamic adduct). Further oxidation of 2p1 results in the formation of 2q1. The degradation of 2 in the presence of O2 renders more products compared to N2-saturation; at the same time the number is higher than that of 1 under similar experimental conditions. In addition to the peaks of 2q1, 2p1 and 2p8 (RT respectively 2.1, 2.6


26

Page 27 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and 3.0 min) the TIC comprise of additional peaks at RT 1.1, 1.4, 1.6 and 2.2min (all having identical mass 173.02) and another one at 3.1 min (mass 159.04). The peaks at 1.1, 1.4, 1.6 and 2.2 min are considered as the mono hydroxy naphthoquinones via the hydroxylation of 2q1 and these products are designated as 2q11, 2q12, 2q13, and 2q14, while the 3.1 min peak with mass 159.04 is regarded as 2p5 (Scheme 6).

Scheme 5: A possible route of product formations in the oxidation of 2-naphthol by UV/H2O2 method with N2–saturation.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 35

Scheme 6: Proposed channels for oxidation product formations from 2-naphthol by UV/H2O2 method without N2-stauration. Therefore, the evaluation of the preliminary degradation products of 1 and 2 by the UV/H2O2 method in the presence of N2-saturation provides complementary data for the pulse radiolysis experiments.

CONCLUSIONS The present study using pulse radiolysis technique, allows the qualitative understanding of the preliminary oxidation products (the transient species) formed during the reaction of •OH with 1 and 2. Absorption spectra of the transients produced for •OH reactions at pH 7 exhibited very close λmax for these isomeric naphthol molecules. Rate constant determinations demonstrated the diffusion controlled nature of •OH reactions of 1 and 2. Results of DFT calculations for •OH


28

Page 29 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reactions of both naphthols provide a conceptual framework of the most applicable reaction mechanism. The preferential attack of •OH at C4 site of 1 is mainly responsible for the experimental spectrum, whereas addition at C1 is dictated in the case of 2; agreement between experimental and theoretical λmax of the kinetic transients in both 1 and 2 validate this possibility again. However, naphthoxyl radical was proposed as the transient observed at pH 10.5 via the •

OH induced oxidation of 1(2). Moreover, the reactions of 1 and 2 with specific one-electron

oxidants O•– (at pH~13) and N3• (at pH 7) also point at naphthoxyl radical formations. We suggest that, in addition to •OH, the other radicals viz. O•– and N3• used in the present study are also effective for the degradation of naphthols, but comprehensive experimental studies are required to determine their effectiveness in advanced oxidation processes. The formations of isomeric dihydroxy naphthalenes as products in the oxidation via UV/H2O2 treatment clearly demonstrate the selective addition of •OH at C1, C4 & C5 of 1 and at C1, C5 & C8 of 2. Our present experimental and theoretical results along with UPLC-Q-TOF-MS data should serve as useful guides to the understanding of •OH induced oxidation of naphthols.

ACKNOWLEDGMENT The authors are thankful to NCFRR, Pune for extending pulse radiolysis facility. RS is thankful to UGC, New Delhi for a research fellowship. CTA would like to thank BRNS, Mumbai and DST, New Delhi (Purse programme) for financial support. ASSOCIATED CONTENT


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

Supporting Information: Calculated thermodynamic parameters of naphthols and transients & first stage ESI-MS spectra of oxidation products analyzed by using the UPLC-Q-TOF-MS technique. This material is available free of charge via the Internet at http://pubs.acs.org.

REFERENCES 1. 2. 3. 4. 5.

6. 7.

8. 9.

10.

11.

12. 13.

14.

Zollinger, H., Color Chemistry, Syntheses, properties and applications of organic dyes and pigments. VCH: New York, 1991. Freeman, J. P.; Mock, G. N., In Handbook of Industrial Chemistry and Biotechnology, Kent, J. A., Ed. Springer: New York, 2007. Kuhr, R. J.; Dorough, H. W., In Toxicology biochemistry and chemistry, Kuhr, R. J., Ed. CRC Press: Cleveland, Ohio, USA, 1976. Preuss, R.; Angerer, J.; Drexler, H. Naphthalene - An Environmental and Occupational Toxicant. Int. Arch. Occup. Environ. Health 2003, 76, 556-576. Atkinson, R.; Arey, J.; Zielinska, B.; Aschmann, S. M. Kinetics and Products of the GasPhase Reactions of OH Radicals and N2O5 with Naphthalene and Biphenyl. Environ. Sci. Technol. 1987, 21, 1014-1022. Crosby, D. G.; Leitis, E.; Winterlin, W. L. Photodecomposition of Carbamate Insecticides. J. Agric. Food Chem. 1965, 13, 204-207. Karinen, J. F.; Lamberton, J. G.; Stewart, N. E.; Terriere, L. C. Persistence of Carbaryl in the Marine Estuarine Environment - Chemical and Biological Stability in Aquarium Systems. J. Agric. Food Chem. 1967, 15, 148-156. Bollag, J.-M.; Czaplicki, E. J.; Minard, R. D. Bacterial Metabolism of 1-Naphthol. J. Agric. Food Chem. 1975, 23, 85-90. Wolfe, N. L.; Zepp, R. G.; Paris, D. F. Carbaryl, Propham and Chlorpropham: A Comparison of the Rates of Hydrolysis and Photolysis with the Rate of Biolysis. Water Res. 1978, 12, 565-571. Cerniglia, C. E.; Freeman, J. P.; Evans, F. E. Evidence for an Arene Oxide-NIH Shift Pathway in the Transformation of Naphthalene to 1-Naphthol by Bacillus Cereus. Arch. Microbiol. 1984, 138, 283-286. Allen, C. C. R.; Boyd, D. R.; Larkin, M. J.; Reid, A. K.; Sharma, D. N.; Wilson, K. K. Metabolism of Naphthalene, 1-Naphthol, Indene, and Indole by Rhodococcus Spp. Strain NCIMB 12038. Appl. Env. Microb. 1996, 63, 151-155. Cho, T. M.; Rose, R. L.; Hodgson, E. In Vitro Metabolism of Naphthalene by Human Liver Microsomal Cytochrome P450 Enzymes. Drug Metab. Dispos. 2006, 34, 176-183. Croera, C.; Ferrario, D.; Gribaldo, L. In Vitro Toxicity of Naphthalene, 1-Naphthol, 2Naphthol and 1,4-Naphthoquinone on Human CFU-GM from Female and Male Cord Blood Donors. Toxicol. In Vitro 2008, 22, 1555-1561. Smith, C. J.; Walcott, C. J.; Huang, W.; Maggio, V.; Grainger, J.; Patterson, D. G. Determination of Selected Monohydroxy Metabolites of 2-, 3- and 4-Ring Polycyclic Aromatic Hydrocarbons in Urine by Solid-Phase Microextraction and Isotope Dilution Gas Chromatography–Mass Spectrometry. J. Chromatogr.B 2002, 778, 157-164.


30

Page 31 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15.

16. 17. 18.

19.

20.

21.

22. 23.

24.

25.

26.

27.

28.

29.

30. 31.

Yanga, H.; Wang, Y.; Wang, Y.; Li, J.; Xiao, X.; Tan, X. Study on the Interaction Among Pyronine Y, Potassium Bromate and Naphthols by Absorption, Three-Dimension Fluorescence and Resonance Light Scattering Spectra and Their Application. Spectrochim. Acta A 2008, 71, 1290-1295. Weller, A. Fast Reactions of Excited Molecules. Prog. React. Kinet. 1961, 1, 187-214. Ireland, J. F.; Wyatt, P. A. H. Acid-Base Properties of Electronically Excited Stated of Organic Molecules. Adv. Phys. Org. Chem. 1976, 12, 131-160. Arnaut, L. G.; Formosinho, S. J. Excited-State Proton Transfer Reactions. I. Fundamentals and Intermolecular Reactions. J. Photochem. Photobiol. A: Chem. 1993, 75, 1-20. Barroso, M.; Arnaut, L. G.; Formosinho, S. J. Intersecting-State Model Calculations on Fast and Ultrafast Excited-State Proton Transfers in Naphthols and Substituted Naphthols. J. Photochem. Photobiol. A: Chem. 2002, 154, 13-21. Tolbert, L. M.; Solntsev, K. M. Excited-State Proton Transfer: From Constrained Systems to "Super" Photoacids to Superfast Proton Transfer. Acc. Chem. Res. 2002, 35, 19-27. Webb, S. P.; Philips, L. A.; Yeh, S. W.; Tolbert, L. M.; Clark, J. H. Picosecond Kinetics of the Excited-State, Proton-Transfer Reaction of 1-Naphthol with Water. J. Phys. Chem. 1986, 90, 5154-5164. Agmon, N. Elementary Steps in Excited-State Proton Transfer. J. Phys. Chem. A 2005, 109, 13-35. Premont-Schwarz, M.; Xiao, D.; Batista, V. S.; Nibbering, E. T. J. The O–H Stretching Mode of a Prototypical Photoacid as a Local Dielectric Probe. J. Phys. Chem. A 2011, 115, 10511-10516. Land, E. J.; Ebert, M. Pulse Radiolysis Studies of Aqueous Phenol. Water Elimination from Dihydroxycyclohexadienyl Radicals to Form Phenoxyl. Trans. Faraday Soc. 1967, 63, 1181-1190. Klein, G. W.; Bhatia, K.; Madhavan, V.; Schuler, R. H. Reaction of Hydroxyl Radicals with Benzoic Acid. Isomer Distribution in the Radical Intermediates. J. Phys. Chem. 1975, 79, 1767-1774. Raghavan, N. V.; Steenken, S. Electrophilic Reaction of the Hydroxyl Radical with Phenol. Determination of the Distribution of isomeric Dihydroxycyclohexadienyl Radicals. J. Am. Chem. Soc. 1980, 102, 3495-3499. Roder, M.; Wojnarovits, L.; Foldiak, G.; Emmi, S. S.; Beggiato, G.; D'Angelantonio, M. Addition and Elimination Kinetics in OH Radical Induced Oxidation of Phenol and Cresols in Acidic and Alkaline Solutions. Radiat. Phys. Chem. 1999, 54, 475-479. Mvula, E.; Schuchmann, M. N.; von Sonntag, C. Reactions of Phenol-OH-Adduct Radicals. Phenoxyl Radical Formation by Water Elimination vs. Oxidation by Dioxygen. J. Chem. Soc., Perkin Trans. 2001, 2, 264-268. Albarran, G.; Schuler, R. H. Micellar Electrophoretic Capillary Chromatographic Analysis of the Products Produced in the Radiolytic Oxidation of Toluene and Phenol. Radiat. Phys. Chem. 2002, 63, 661-663. Tripathi, G. N. R. Electronic Structure of Para Aminophenoxyl Radical in Water. J. Chem. Phys. 2003, 118, 1378-1391. Tripathi, G. N. R.; Su, Y. The Origin of Base Catalysis in the •OH Oxidation of Phenols in Water. J. Phys. Chem. A 2004, 108, 3478-3484.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

32. 33. 34. 35.

36. 37.

38. 39. 40.

41. 42.

43.

44. 45.

46.

47.

48.

49.

Page 32 of 35

Albarran, G.; Schuler, R. H. Concerted Effects of Substituents in the Reaction of •OH Radicals with Aromatics: The Cresols. J. Phys. Chem. A 2005, 109, 9363-9370. Bonin, J.; Janik, I.; Janik, D.; Bartels, D. M. Reaction of the Hydroxyl Radical with Phenol in Water Up to Supercritical Conditions. J. Phys. Chem. A 2007, 111, 1869-1878. Albarran, G.; Schuler, R. H. Hydroxyl Radical as a Probe of the Charge Distribution in Aromatics: Phenol. J. Phys. Chem. A 2007, 111, 2507-2510. Singh, U.; Barik, A.; Priyadarsini, K. I. Reactions of Hydroxyl Radical with Bergenin, a Natural Poly Phenol Studied by Pulse Radiolysis. Bioorg. Med. Chem. 2009, 17, 60086014. Das, T. N. Hidden Chemistry in Phenoxyl Radical (C6H5O•) Coupling Reaction Mechanism Revealed. J. Phys. Org. Chem. 2009, 22, 872-882. Lundqvist, M. J.; Eriksson, L. A. Hydroxyl Radical Reactions with Phenol as a Model for Generation of Biologically Reactive Tyrosyl Radicals. J. Phys. Chem. B 2000, 104, 848855. Peller, J.; Kamat, P. V. Radiolytic Transformations of Chlorinated Phenols and Chlorinated Phenoxyacetic Acids. J. Phys. Chem. A 2005, 109, 9528-9535. Matthews, R. W. Photo-Oxidation of Organic Material in Aqueous Suspensions of Titanium Dioxide. Water Res. 1986, 20, 569-578. Mihelcic, J. R.; G., L. R. Degradation of Polycyclic Aromatic Hydrocarbon Compounds Under Various Redox Conditions in Soil-Water Systems. Appl. Environ. Microbiol. 1988, 54, 1182-1187. Armbrust, K. L.; Crosby, D. G. Fate of Carbaryl, l-Naphthol, and Atrazine in Seawater Pacific Sci. 1991, 45, 314-320. Karthikeyan, K. G.; Chorover, J.; Bortiatynski, J. M.; Hatcher, P. G. Interaction of 1Naphthol and Its Oxidation Products with Aluminum Hydroxide. Environ. Sci. Technol. 1999, 33, 4009-4015. Karthikeyan, K. G.; Chorover, J. Effects of Solution Chemistry on the Oxidative Transformation of 1-Naphthol and Its Complexation with Humic Acid. Environ. Sci. Technol. 2000, 34, 2939-2946. Panizza, M.; Cerisola, G. Electrochemical Oxidation of 2-Naphthol with in situ Electrogenerated Active Chlorine. Electrochimi. Acta 2003, 48, 1515-1519. Qourzal, S.; Tamimi, M.; Assabbane, A.; Ait-Ichou, Y. Photocatalytic Degradation and Adsorption of 2-Naphthol on Suspended TiO2 Surface in a Dynamic Reactor. J. Colloid Interf. Sci. 2005, 286, 621-626. He, Y.; Lv, Y.; Hu, J.; Qi, L.; Hou, X. Simple, Sensitive and on-line Fluorescence Monitoring of Photodegradation of Phenol and 2-Naphthol. Luminescence 2007, 22, 309316. Qourzal, S.; Barka, N.; Tamimi, M.; Assabbane, A.; Ait-Ichou, Y. Photodegradation of 2Naphthol in Water by Artificial Light Illumination Using TiO2 Photocatalyst: Identification of Intermediates and the Reaction Pathway. Appl. Catal. A: Gen 2008, 334, 386-393. Qourzal, S.; Barka, N.; Tamimi, M.; Assabbane, A.; Nounah, A.; Ihlal, A.; Ait-Ichou, Y. Sol–Gel Synthesis of TiO2–SiO2 Photocatalyst for β-Naphthol Photodegradation. Mat. Sci. Eng. C 2009, 29, 1616-1620. Qourzal, S.; Tamimi, M.; Assabbane, A.; Ait-Ichou, Y. Photodegradation of 2-Naphthol Using Nanocrystalline TiO2. M. J. Condensed Mater. 2009, 11, 55-59.


32

Page 33 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50.

51. 52.

53.

54.

55.

56.

57.

58.

59.

60. 61. 62.

63.

64. 65. 66.

Karunakaran, C.; Narayanan, S.; Gomathisankar, P. Photocatalytic Degradation of 1Naphthol by Oxide Ceramics with Added Bacterial Disinfection. J. Hazard Mater. 2010, 181, 708-715. Zang, S.; Lian, B.; Wang, J.; Yang, Y. Biodegradation of 2-Naphthol and its Metabolites by Coupling Aspergillus Niger with Bacillus Subtilis. J. Env. Sci. 2010, 22, 669-674. Sinha, S.; De, R.; Ganguly, T.; De, A. K.; Nandy, S. K. Studies on Quenching Reactions in the Excited Electronic States of Tetrahydronaphthols Both at the Ambient Temperature as well as at 77 K. J. Lumin. 1997, 75, 99-116. Mohan, H.; Hermann, R.; Naumov, S.; Mittal, J. P.; Brede, O. Two Channels of Electron Transfer Observed for the Reaction of n-Butyl Chloride Parent Radical Cations with Naphthols and Hydroxybiphenyls. J. Phys. Chem. A 1998, 102, 5754-5762. Hermann, R.; Dey, G. R.; Naumov, S. Thiol Radical Cations and Thiyl Radicals as Direct Products of the Free Electron Transfer from Aromatic Thiols to n-Butyl Chloride Radical Cations. Phys. Chem. Chem. Phys. 2000, 2, 1213-1220. Hermann, R.; Naumov, S.; Brede, O. Electron Transfer From Phenolic Compounds to Parent n-Butyl Chloride Radical Cations - A Quantum Chemical Study of Product Transient Formation and Stability. J. Mol. Struct. (Theochem) 2000, 532, 69-80. Mohan, H.; Brede, O.; Mittal, J. P. Radiolytically Generated Benzene Triplets as Sensitizers for Energy and Combined Electron/Proton Transfer Processes. J. Photochem. Photobiol. A 2001, 140, 191-197. Baidak, A.; Naumov, S.; Hermann, R.; Brede, O. Ionization of Amino-, Thio- and Hydroxy-naphtalenes via Free (Unhindered) Electron Transfer J. Phys. Chem. A 2008, 112, 11036- 11043. Riyad, Y. M.; Naumov, S.; Hermann, R.; Brede, O.; Hermann, R.; Abel, B. Structure Dependence of the Photogeneration of Thionaphthol Triplets. Chem. Phys. Lett. 2009, 447, 290-297. Riyad, Y. M.; Naumov, S.; Hermann, R.; Abel, B. Shedding Light into the Detailed Excited-State Relaxation Pathways and Reaction Mechanisms of Thionaphthol Isomers. J. Phys. Chem. A 2011, 115, 718-725. Gaikwad, P.; Priyadarsini, K. I.; Rao, B. S. M. Radiation Chemistry Research Using PULAF. Radiat. Phys. Chem. 2008, 77, 1124-1130. Buxton, G. V.; Stuart, C. R. Re-evaluation of the Thiocyanate Dosimeter For Pulse Radiolysis. J. Chem. Soc. Faraday Trans. 1995, 91, 279-281. Alam, M. S.; Janata, E. UV Absorption Spectrum, Formation and Disappearance of The Oxide Radical Ion O•− in Aqueous Solution: A Pulse Radiolysis Study. Chem. Phys. Lett. 2006, 414, 363-366. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J., J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; et. al Gaussian 03, Revision C. 02.; Gaussian, Inc.: Wallingford C T, 2004. Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785-789. Becke, A. D. Density-functional thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648-5652. Miertus, S.; Scrocco, E.; Tomasi, J. Electrostatic Interaction of a Solute with a Continuum. A Direct Utilizaion of ab initio Molecular Potentials for the Prevision of Solvent Effects. J. Chem. Phys. 1981, 55, 117-129.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

67. 68.

69.

70.

71.

72. 73. 74.

75.

76.

77.

78.

Page 34 of 35

Tomasi, J.; Persico, M. Molecular Interactions in Solution: An Overview of Methods Based on Continuous Distributions of the Solvent. Chem. Rev. 1994, 94, 2027-2094. Cossi, M.; Scalamni, G.; Rega, N.; Barone, V. New Developments in the Polarizable Continuum Model for Quantum Mechanical and Classical Calculations on Molecules in Solution. J. Chem. Phys. 2002, 117, 43-54. Boys, S. F.; Bernardi, F. The Calculation of Small Molecular Interactions by the Differences of Separate Total Energies. Some Procedures with Reduced Errors. Mol. Phys. 1970, 19, 553-566. Simon, S.; Duran, M.; Dannenberg, J. J. How Does Basis Set Superposition Error Change the Potential Surfaces for Hydrogen-Bonded Dimers? J. Chem. Phys. 1996, 105, 1102411031. Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An Efficient Implementation of TimeDependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules. J. Chem. Phys. 1998, 109, 8218-8224. Spinks, J. W. T.; Woods, R. J., Introduction to Radiation Chemistry. Wiley: New York, 1990. Das, T. N.; Neta, P. Reduction Potentials of Naphthoxyl and Pyridoxyl Radicals in Aqueous Solutions. J. Phys. Chem. A 1998, 102, 7081-7085. Fang, X.; Pan, X.; Rahmann, A.; Schuchmann, H.-P.; von Sonntag, C. Reversibility in the Reaction of Cyclohexadienyl Radicals with Oxygen in Aqueous Solution. Chem. Eur. J. 1995, 1, 423-429. Pramod, G.; Prasanthkumar, K. P.; Mohan, H.; Manoj, V. M.; Manoj, P.; Suresh, C. H.; Aravindakumar, C. T. Reaction of Hydroxyl Radicals with Azacytosines: A Pulse Radiolysis and Theoretical Study. J. Phys. Chem. A 2006, 110, 11517-11526. Prasanthkumar, K. P.; Mohan, H.; Pramod, G.; Suresh, C. H.; Aravindakumar, C. T. Anomalous Reaction of Oxide Radical Ion with 5-Azacytosines: An Experimental and Theoretical Study. Chem. Phys. Lett. 2009, 467, 381-286. Prasanthkumar, K. P.; Suresh, C. H.; Aravindakumar, C. T. Theoretical Study of the Addition and Abstraction Reactions of Hydroxyl Radical with Uracil. Rad. Phys. Chem. 2012, 81, 267-272. Prasanthkumar, K. P.; Suresh, C. H.; Aravindakumar, C. T. Oxidation Reactions of 2Thiouracil: A Theoretical and Pulse Radiolysis Study J. Phys. Chem. A 2012, 116, 10712-10720.


34

Page 35 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


64x47mm (300 x 300 DPI)


Oxidation Reactions of 1- and 2-Naphthols: An Experimental and

Recommend Documents