Free-radical reductions of arenediazonium ions in aqueous solution. Part I. Toluene-p-diazonium ions reduced with methanol

Packer, J. E.; House, D. B.; Rasburn, Eric J.

doi:10.1039/j29710001574

Cited by 25 publications

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“…aqueous methanol as the solvent, where reduction occurs with F ≈ 3.5-8. 13 Furthermore, the present reactions involve attack to nucleophilic, not electrophilic, olefins. We checked that generating the 4-nitrophenyl radical from 1a under the classical Meerwein conditions (CuCl 2 ) leads to arylation of acrylonitrile (forming the 3-phenyl-2-chloropropionitrile) but not of ATMS (product 6a 10%) and conversely photodecomposition of 1a in the presence of acrylonitrile does not lead to arylation, contrary to the case of ATMS.…”

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confidence: 92%

Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations

2002

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The photodediazoniation of some 4-X-phenyldiazonium tetrafluoborates in MeCN leads to the singlet phenyl cations (X = H, tert-butyl, NMe2, CN), which add to the solvent yielding the corresponding acetanilides. Triplet sensitisation, however, leads to the triplet phenyl cation, which is reduced in neat solvent and is trapped by pi nucleophiles (allyltrimethylsilane and benzene), resulting in an ionic analogue of the Meerwein or Gomberg arylations. With the 4-nitro derivative intersystem crossing prevails over dediazoniation from the singlet and with the 4-cyano competes with it, so that in those cases the triplet phenyl cation is formed also upon direct irradiation.

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confidence: 92%

Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations

2002

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“…CH 2 OH radical [18] . As this particular radical is known to be capable of reducing diazonium ions to aryl radicals and dinitrogen along with the formation of formaldehyde, an undesired reduction of the diazonium salt to the parent aromatic compound can basically occur in the presence of alcohols via these two steps in the sense of a chain reaction [27] …”

Section: Resultsmentioning

confidence: 99%

“…[18] As this particular radicali sk nown to be capable of reducing diazonium ions to aryl radicals and dinitrogen along with the formation of formaldehyde, an undesired reductiono ft he diazonium salt to the parenta romatic compound can basically occur in the presence of alcohols via these two steps in the sense of ac hain reaction. [27] Results from initial experiments are summarized in Table 2, at which the optimized conditions from Table 1( entry 6) were only varied in the wayt hat water was replaced by methanol, and the effect of potassium acetate was studied in thise arly stage.…”

Section: Entrymentioning

confidence: 99%

Visible Light Promoted, Catalyst‐Free Radical Carbohydroxylation and Carboetherification under Mild Biomimetic Conditions

Altmann

Zantop

Wenisch

et al. 2020

Chemistry A European J

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Metal and catalyst‐free carbohydroxylations and carboetherifications at room temperature have been achieved by a combination of beneficial factors including high aryl diazonium concentration and visible light irradiation. The acceleration of the reaction by visible light irradiation is particularly remarkable against the background that neither the aryldiazonium salt nor the alkene show absorptions in the respective range of wavelength. These observations point to weak charge transfer interactions between diazonium salt and alkene, which are nevertheless able to considerably influence the reaction course. As highly promising perspective, many more aryldiazonium‐based radical arylations might benefit from simple light irradiation without requiring a photocatalyst or particular additive.

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“…Incorporating a figure of 1·4 ϫ 10 5 dm 3 mol -1 [70] for the rate constant for attack of p-methylphenyl radical upon MeOH as approximately equal to k 59 , one obtains k 58 = 1·2 ϫ 10 7 dm 3 mol -1 s -1 at 298 K. Similar consideration of the decomposition of PAT in benzene, combined with the value of k 58 , yields a rate constant for the phenylation of benzene, eqn (61), of 7·8 ϫ 10 4 dm 3 mol -1 s -1 [69]: (61) These data, in turn, combined with earlier data concerning the spin trapping of radicals produced in the decomposition of benzoyl peroxide in benzene [71] yields a figure of 4 ϫ 10 7 dm 3 mol -1 s -1 for the trapping of PhCO 2 • by PBN at 313 K. A similar competition method was utilised in determining spin-trapping rates by tert-butoxyl radicals [72].…”

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confidence: 99%

Kinetic Aspects of Spin Trapping

Kemp

1999

prog. rct. kin. mech.

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288 1. 3·2·4 Rate constants of dimerization 330 3·2·5 Induced decomposition of spin adducts 334 3·3 Rates of isomerization reactions from spin trapping 336 3·4 Rates of radical abstraction reactions 341 3·5 Rates of radical addition reactions 345 3·6 Rates of polymerisation processes 345 3·7 Rates of reactions of excited states 349 3·7·1 Rates of abstraction reactions by excited states 349 3·7·2 Interactions of excited states with spin adducts 350 3·8 Reaction rates of transient radicals with stable aminoxyls 350 3·9 Radical traps as mediators in electron-transfer reactions 352 4. ACKNOWLEDGEMENTS 353 REFERENCES 353ABSTRACT Kinetics are described of the spin-trapping process itself, based on indirect methods such as radical clocks and other competition methods, and also direct methods based on flash photolysis and pulse radiolysis. The stability of spin traps and their dimerization are discussed, as is the stability of spin adducts, once formed. Caution is given over the utilisation of spin traps in photo -and redox systems where the spin trap can undergo excitation and/or dissociation to lead to radicals which undergo trapping processes to give potentially misleading spectral data. The use of well-authenticated spin trapping kinetic data to examine rates of ringopening and -closing and isomerization reactions is covered. The role of spin trapping as a probe of biochemical processes is also included, with particular reference to the trapping of hydroxyl and superoxide radicals. GLOSSARYBPG alkyl tert-butyl peroxyglyoxalates DMPO 5,5-dimethyl-1-pyrroline-N-oxide DMSO dimethyl sulfoxide epr electron paramagnetic resonance HFCC hyperfine coupling constant MBN methylene-N-tert-butylnitrone MNP 2-methyl-2-nitrosopropane NB nitrosobenzene ND nitrosodurene NM nitromethane PBN phenyl tert-butyl nitrone PMNB pentamethylnitrosobenzene SOD superoxide dismutase TBNtri-tert-butylnitrosobenzene TEMPO 2,2,6,6-tetramethylpiperidine N-oxyl 1.

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Free-radical reductions of arenediazonium ions in aqueous solution. Part I. Toluene-p-diazonium ions reduced with methanol

Abstract: M13 9PL 6oCo y-Radiation has been used to initiate the free-radical reduction reaction (i) and the mechanism is shown to be as in reactions (ii)-(iv), where reactions (ii) and (iii) are the propagating steps and reaction (iv) the terminating

Cited by 25 publications

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Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations

Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations

Visible Light Promoted, Catalyst‐Free Radical Carbohydroxylation and Carboetherification under Mild Biomimetic Conditions

Kinetic Aspects of Spin Trapping

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