Stereoelectronic Inhibition of Deprotonation in the Radical Cation ofN-Benzylpiperidine: a Contribution to the Debate on the Mechanism ofN-Dealkylation of Tertiary Amines

Bietti, Massimo; Cuppoletti, Andrea; Dagostin, Claudio; Florea, Cristina; Galli, Carlo; Gentili, Patrizia; Petride, Horia; Russo, C.

doi:10.1002/(sici)1099-0690(199811)1998:11<2425::aid-ejoc2425>3.0.co;2-m

Cited by 13 publications

(8 citation statements)

References 23 publications

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“…At the same time, on keeping constant the pH value, a linear dependence of k exp with the amine concentration was observed. It follows that the ET-reaction is first-order in both [4A] and [1], as expected. 7a,8 As no significant differences were observed between the k exp values determined in this way (with extraction; ~ 3 half-lives) and those obtained directly on the somewhat cloudy reaction mixture (no extraction; ~ 1 half-live), the more easy direct method was adopted to determine k exp at other pH values.…”

Section: Methodssupporting

confidence: 82%

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Electron transfer vs. heterolytic reactions. Behaviour of N-benzyl aziridine towards (aqua)xCuII and batho2CuII ions

Drăghici¹,

Florea²,

Galli³

et al. 2002

Arkivoc

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Treatment of N-benzylaziridine (1) with (aqua) x Cu 2+ yields tetrabenzylcyclen 3 by a metalassisted heterolytic (HETERO) pathway. Conversely, 1 is oxidised by the batho 2 Cu II ion (batho:2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline disulfonate) to afford benzaldehyde, dibenzylpiperazine 2 and 3, according to an electron-transfer mechanism (ET). Actually, evidence is presented for a competition between the ET and HETERO routes leading to 3. This competition is modulated by the pH of the solution, and experimental conditions are found where the contribution of the ET route unambiguously prevails.

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Section: Methodssupporting

confidence: 82%

“…Starting from [1] 0 = 0.03 M, the same concentration of the kinetic experiments to be reported below, a detailed search revealed that [1] ] 0 ratio was twice the generally accepted 16 stoicheiometric value (i.e., 1:2). On the other hand, blank and oxidation experiments showed both the HETERO and ET rates decreasing with increasing pH value.…”

Section: Methodsmentioning

confidence: 99%

Electron transfer vs. heterolytic reactions. Behaviour of N-benzyl aziridine towards (aqua)xCuII and batho2CuII ions

Drăghici¹,

Florea²,

Galli³

et al. 2002

Arkivoc

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“…The UV spectrum is similar to that of CpQ; therefore, the modification in the molecule should be away from the chromophores. The chemistry of amine oxidation is well-known, − and it is widely accepted to occur by either hydrogen atom transfer (HAT) or single-electron transfer (SET) mechanisms. Secondary amines oxidize to hydroxylamine that leads to loss of water and are further oxidized to nitrone [CpQ-nitrone (Scheme )].…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Degradation Mechanism of Adrenaline Derivative CpQ in Diluted Aqueous Solutions

et al. 2018

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The degradation kinetics of an adrenaline (epinephrine) derivative, CpQ, was studied in solution in the pH range of 1-12 at 40-80 °C by high-performance liquid chromatography and ultraviolet-visible spectroscopy. The pH-rate profile exhibits a bell-shaped curve with two sigmoidal regions in the specific acid-catalyzed and specific base-catalyzed regions. The pH range of maximum stability was 2.5-4.5 with the main degradation pathway being the oxidative N-dealkylation of the aliphatic amino moiety followed by fast interconversion of the resulting fragments to stable degradation products. The autoxidation reaction was slower than the reaction of the oxygen reactive species. The chiral center underwent R to S racemization by a polar reaction mechanism under acidic conditions with a rate minimum at pH 4. The rates of degradation of the R and S enantiomers were similar across all pHs. CpQ degradation in the presence of hydrogen peroxide at 40 °C was significantly faster, and the extent of increases with pH. Metal ions bind to CpQ and catalyze its hydrolysis in the order Fe > Fe > Mg > Mn > Ti > Sr > Zn, with a rate enhancement of ≤1 order of magnitude at the studied pH values of 1 and 5. There was no buffer catalysis observed in the hydrolysis of the studied compound for maleate and phosphate but significant buffer catalysis in the case of citrate and malate.

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“…Several possibilities might be advanced for the formation of iminium cations, but we cite only three: (i) hydrogen-atom-transfer (HAT), (ii) electron-transfer (ET), or, by analogy with the RuO 4 -oxidation of esters, 11 (iii) a concerted mechanism with an S E 2-like transition state. We discovered previously 12 that 1B undergoes oxidation to 8B and 11 in bona fide HAT or ET conditions with regioselectivities (alkyl/benzyl) of 0.7 and 0.4, respectively. These values are significantly different from that of 2.1 found for 1B in the present paper.…”

Section: A-bmentioning

confidence: 96%

RuO4-mediated oxidation of N-benzylated tertiary amines. 2. Regioselectivity for N,N-dimethyl- and N,N-diethylbenzylamine as substrates

Petride¹,

Costan²,

Drăghici³

et al. 2005

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N, and N,N-diethylbenzylamine (1B) underwent RuO 4 -mediated oxidation by attack at both types of (N-α)C-H bonds (i.e., alkyl and benzyl) to yield the corresponding Nalkyl-N-benzylamides [and N-methyl-(8A) or N-ethylbenzylamine (8B), resp.] and benzaldehyde (and N,N-dialkylbenzamides), respectively. Oxidation of 8A-B occurred also, as well as their reaction with formaldehyde or acetaldehyde, respectively, equally formed during the oxidation of 1A-B or 8A-B. Initial formation of the iminium cations from 1A-B was proved by their capture as nitriles. The statistically corrected alkyl/benzyl regioselectivity of the oxidation reaction was 4.1 for 1A and 2.1 for 1B. Comparison with the results obtained on Nbenzylpiperidine showed that RuO 4 does not discriminate axial and equatorial CH bonds in the piperidine ring. The N-α-C . carbon-centered radical and the amine cation radical seem not to be involved as precursors of the iminium cations.

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Stereoelectronic Inhibition of Deprotonation in the Radical Cation ofN-Benzylpiperidine: a Contribution to the Debate on the Mechanism ofN-Dealkylation of Tertiary Amines

Cited by 13 publications

References 23 publications

Electron transfer vs. heterolytic reactions. Behaviour of N-benzyl aziridine towards (aqua)xCuII and batho2CuII ions

Electron transfer vs. heterolytic reactions. Behaviour of N-benzyl aziridine towards (aqua)xCuII and batho2CuII ions

Kinetics and Degradation Mechanism of Adrenaline Derivative CpQ in Diluted Aqueous Solutions

RuO4-mediated oxidation of N-benzylated tertiary amines. 2. Regioselectivity for N,N-dimethyl- and N,N-diethylbenzylamine as substrates

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