1
|
Kao MH, Orr-Ewing AJ. Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution. J Phys Chem A 2022; 126:6934-6943. [PMID: 36148486 PMCID: PMC9549464 DOI: 10.1021/acs.jpca.2c05327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Although ultraviolet
(UV)-induced photochemical cleavage of carbon–halogen
bonds in gaseous halocarbons is mostly homolytic, the photolysis of
chlorobenzene in solution has been proposed to produce a phenyl cation,
c-C6H5+, which is a highly reactive
intermediate of potential use in chemical synthesis and N2 activation. Any evidence for such a route to phenyl cations is indirect,
with uncertainty remaining about the possible mechanism. Here, ultrafast
transient absorption spectroscopy of UV-excited (λ = 240 and
270 nm) chlorobenzene solutions in fluorinated (perfluorohexane) and
protic (ethanol and 2,2,2-trifluoroethanol) solvents reveals a broad
electronic absorption band centered at 540 nm that is assigned to
an isomer of chlorobenzene with both charge-separated and triplet-spin
carbene character. This spectroscopic feature is weaker, or absent,
when experiments are conducted in cyclohexane. The intermediate isomer
of chlorobenzene has a solvent-dependent lifetime of 30–110
ps, determined by reaction with the solvent or quenching to a lower-lying
singlet state. Evidence is presented for dissociation to ortho-benzyne, but the intermediate could also be a precursor to phenyl
cation formation.
Collapse
Affiliation(s)
- Min-Hsien Kao
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| |
Collapse
|
2
|
Hong ZS, Kao SC, Cheng YT, Chen CJ, Wu YK. Photoinduced arylation of chloroarenes in flow: synthesis of unsymmetrical biaryls. Org Biomol Chem 2022; 20:8212-8216. [DOI: 10.1039/d2ob01710e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A photoflow cross-coupling reaction of unactivated arenes and aryl chlorides is developed for the synthesis of unsymmetrical biaryl products.
Collapse
Affiliation(s)
- Zih-Siang Hong
- Department of Applied Chemistry, National Yang Ming Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan
| | - Shih-Chieh Kao
- Department of Applied Chemistry, National Yang Ming Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan
| | - Yu-Tsen Cheng
- Department of Applied Chemistry, National Yang Ming Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan
| | - Chun-Jen Chen
- Department of Applied Chemistry, National Yang Ming Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan
| | - Yen-Ku Wu
- Department of Applied Chemistry, National Yang Ming Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan
| |
Collapse
|
3
|
Photolysis of polychlorobiphenyls in the presence of nanocrystalline TiO2 and CdS/TiO2. REACTION KINETICS MECHANISMS AND CATALYSIS 2019. [DOI: 10.1007/s11144-019-01543-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
4
|
Raviola C, Chiesa F, Protti S, Albini A, Fagnoni M. On the Route to the Photogeneration of Heteroaryl Cations. The Case of Halothiophenes. J Org Chem 2016; 81:6336-42. [PMID: 27383725 DOI: 10.1021/acs.joc.6b00978] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
2-Chloro-, 2-bromo-, and 2-iodothiophenes undergo photochemical dehalogenation via the triplet state. In the presence of suitable π-bond nucleophiles, thienylation occurs with modest yield from chloro and bromo derivatives (via photogenerated triplet 2-thienyl cation). Specific trapping by using oxygen along with computational analysis carried out by means of a density functional method support that, in the case of iodo derivatives, homolytic thienyl-I bond fragmentation occurs first and heteroaryl cations are formed by electron transfer within the triplet radical pair, thus opening an indirect access to such cations.
Collapse
Affiliation(s)
- Carlotta Raviola
- PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy
| | - Francesco Chiesa
- Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy
| | - Stefano Protti
- PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy
| | - Angelo Albini
- PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy
| | - Maurizio Fagnoni
- PhotoGreen Lab, Department of Chemistry, University of Pavia , Viale Taramelli 12, 27100 Pavia, Italy
| |
Collapse
|
5
|
Raviola C, Ravelli D, Protti S, Albini A, Fagnoni M. Conditions and Edges for the Photochemical Generation of Short-Lived Aryl Cations: A Computational Approach. Synlett 2015. [DOI: 10.1055/s-0034-1379945] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A DFT investigation on the conditions required for the photochemical generation of triplet aryl cations from differently para-substituted aryl halides has been carried out. The results showed a correlation between the energy change associated with the Ar–X bond heterolytic cleavage and the substituent Hammett–Brown constant (σp
+). The method provides a means to predict the viability of the ArSN1 photosubstitution reaction.
Collapse
|
6
|
Qrareya H, Protti S, Fagnoni M. Aryl Imidazylates and Aryl Sulfates As Electrophiles in Metal-Free ArSN1 Reactions. J Org Chem 2014; 79:11527-33. [DOI: 10.1021/jo502172c] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Hisham Qrareya
- Photogreen
Lab, Department
of Chemistry, University of Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Stefano Protti
- Photogreen
Lab, Department
of Chemistry, University of Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Maurizio Fagnoni
- Photogreen
Lab, Department
of Chemistry, University of Pavia, Via Taramelli 12, 27100 Pavia, Italy
| |
Collapse
|
7
|
Young RB, Chefetz B, Liu A, Desyaterik Y, Borch T. Direct photodegradation of lamotrigine (an antiepileptic) in simulated sunlight--pH influenced rates and products. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2014; 16:848-857. [PMID: 24448325 DOI: 10.1039/c3em00581j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Lamotrigine is an antiepileptic and mood stabilizing drug that has been detected in wastewater, groundwater, surface water and drinking water, at frequencies in surface water ranging from 47 to 97%. Because lamotrigine is a weak base (pKa = 5.7) that appears in two protonation states in natural waters, this study examined the direct photodegradation of lamotrigine (11.4 to 12.0 mg L(-1)) in simulated sunlight using liquid chromatography-UV diode array detection and buffered aqueous solutions at pH 3.3, 5.3, and 7.7. Lamotrigine's half-life varied little (100 ± 3 to 112 ± 2 h) with solution pH, but its specific light absorption rate was 12 times higher, and its reaction quantum yield was 13 times lower, at pH 7.7 versus pH 3.3. In the estimated midday, midsummer sunlight in Denver, CO, USA (latitude 39.8617 °N), lamotrigine's estimated photodegradation rate was more than twice as fast at pH 7.7 versus pH 3.3. Lamotrigine's photoproducts were detected by liquid chromatography-UV diode array detection and time-of-flight mass spectrometry. Solution pH was shown to affect the identities and relative abundances of lamotrigine's photoproducts. Some photoproducts appeared only in solutions containing protonated lamotrigine, and others appeared only in solutions containing neutral lamotrigine. As a result, different reaction mechanisms were proposed. Finally, lamotrigine's reaction quantum yield (2.51 ± 0.07 × 10(-5) mol einstein(-1) at pH 7.7) and other results suggested that lamotrigine and three photoproducts are approximately as resistant to direct photodegradation as carbamazepine, a frequently detected pharmaceutical in surface waters.
Collapse
Affiliation(s)
- Robert B Young
- Department of Soil and Crop Sciences, Colorado State University, Fort Collins, Colorado 80523-1170, USA.
| | | | | | | | | |
Collapse
|
8
|
Qrareya H, Raviola C, Protti S, Fagnoni M, Albini A. Transition-Metal-Free Arylations via Photogenerated Triplet 4-Alkyl- and 4-Trimethylsilylphenyl Cations. J Org Chem 2013; 78:6016-24. [DOI: 10.1021/jo4007046] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hisham Qrareya
- PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia,
Italy
| | - Carlotta Raviola
- PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia,
Italy
| | - Stefano Protti
- PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia,
Italy
| | - Maurizio Fagnoni
- PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia,
Italy
| | - Angelo Albini
- PhotoGreen Lab, Department of Chemistry, University of Pavia, V. Le Taramelli 12, 27100 Pavia,
Italy
| |
Collapse
|
9
|
Raviola C, Protti S, Ravelli D, Mella M, Albini A, Fagnoni M. Acetalization allows the photoheterolysis of the Ar-Cl bond in chlorobenzaldehydes and chloroacetophenones. J Org Chem 2012; 77:9094-101. [PMID: 22963457 DOI: 10.1021/jo3016264] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nonaccessibility of phenyl cations by irradiation of electron-poor aryl chlorides was circumvented by transforming the carbonyl group of aromatic ketones or aldehydes into the corresponding 1,3-dioxolanes and the carboxyl group of benzoate ester into an orthoester functionality. This transformation allowed the heterolytic photoactivation of the Ar-Cl bond in protic media and the generation of phenyl cations. In the presence of π-bond nucleophiles, arylated products were obtained in good to excellent yields.
Collapse
Affiliation(s)
- Carlotta Raviola
- PhotoGreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
| | | | | | | | | | | |
Collapse
|