Dealkylation kinetics

The propensity of S-S dications to undergo dealkylation was found to decrease in the order of methyl > ethyl > benzyl. This order of reactivity parallels the increase in the stability of the corresponding carbocations.94 Dealkylation of dication 77 affords thiosulfonium salt 78 in quantitative yield.95 Kinetic studies suggest SN1 mechanism of dealkylation. In addition, reaction of sulfoxide 79 with a substituent chiral at the a-carbon results in racemic amide 80 after hydrolysis. 

The use of an anionic reagent for addition at carbonyl carbon rather than a fully esterified form of a trivalent phosphorus acid obviates a troublesome aspect of the Abramov reaction. Specifically no dealkylation step is required. Mechanistic investigations257 258 indicate that the reaction proceeds much as a simple "aldol"-type reaction in which the anionic phosphorus site adds directly to the carbonyl center. While the initial efforts concerned with the "Pudovik reaction"259 were directed toward the use of sodium salts of the simple dialkyl phosphites, as shown in Equation 3.17,260 266 with a, 5-unsaturated carbonyl systems (vide infra) competition between sites for addition can occur. Addition at the carbonyl carbon site is the kinetically favored route.267-270... 

The relative extent of alkylation of 10, R = H, at N2 and N3 has been observed to vary substantially with the reaction conditions employed, and it now appears likely that the Nj-alkylated compound is the product of kinetic control. The betaines (79) are reasonably stable compounds and can readily be isolated they do, however, undergo both dealkylation (with regeneration of 10, R = H) and rearrangement to the 3-isomers on... 

Kinetic parameters of metabolism of fluorinated analogues of propanolol by a cytochrome enzyme (recombinant CYP1A2) have been determined. They clearly indicate that the A/-dealkylation was almost tenfold lower for the A/-CH2CF3... 

Kinetic parameters of metabolism of fluorinated analogues of propanolol by cytochrome enzyme (recombinant CYP1A2) have been determined. They clearly indicate that the A-dealkylation process was 10-fold lower for the N—CH2CF3 compound with respect to propanolol itself. Hydroxylation of the naphthalene ring process is not observed in the case of propanolol but it becomes the major process with the fluoro analogue (Figure 3.13)." The same decreased metabohsm trend has also been observed with lower pKa values for CYP2D6 cytochrome enzyme." ... 

Tauber A, von Sonntag C (2000) Products and kinetics of the OH-radical-induced dealkylation of atrazine. Acta Hydrochim Hydrobiol 28 15-23... 

Reaction of 9-chloroacridine with aryl sulfonyl hydrazides results in aminodechlo-rination to give the corresponding A-acridinylbenzenesulfonyl hydrazides kinetic studies in methanol and DMSO have been reported.44 Reaction of electron-deficient heteroaryl chlorides with tertiary amines may proceed by quaternization and dealkylation, as shown in Scheme 3. These reactions occur under mild conditions, e.g. acetonitrile solvent at room temperature, and in THF may be accelerated by the addition of lithium chloride.45... 

The cracking of cumene has received considerable attention in recent years as a reaction typical of one class of cracking reactions, namely dealkylation of aromatics. Among the studies of cumene cracking found in the literature there are several attempts to determine the kinetics of... 

Since the N(5)-methylflavinium cation undergoes general-base-catalyzed dealkylation (Equation 36) (31) with a deuterium kinetic isotope effect (N(5)—CH3/N(5)—CD3) of greater than 10, we chose —CD3 and more simply —CH2CH3 as the N(5)-blocking groups. The compound 4a-FlEtOOH is prepared routinely in our laboratory in... 

Guengerich FP, Yun CH, Macdonald TL. Evidence for a 1-electron oxidation mechanism in N-dealkylation of N,N-dialkylanilines by cytochrome P450 2B1. Kinetic hydrogen isotope effects, linear free energy relationships, comparisons with horseradish peroxidase, and studies with oxygen surrogates. J Biol Chem 1996 271 27321-9. 

Silverman s studies on mechanism based MAO inactivation have provided overwhelming support for the role of electron transfer in the MAO catalyzed dealkylation of amines. It must be mentioned however that spectroscopic attempts for detecting the radical ion intermediates have hitherto been unsuccessful. Yasanobu and coworkers could not find EPR spectral evidence for radical intermediates in MAO-catalyzed oxidation of benzylamine [205]. Miller et al. failed to observe the flavin semiquinone or an amine-flavin adduct in rapid-scan-stopped flow spectroscopy [206]. The only time-dependent absorption change observed in this study was the bleaching of the oxidized flavin. Furthermore, no influence of a magnetic field up to 6500 G was observed on the rate of MAO B reduction. The reaction rates of systems with kinetically significant radical pair intermediates are known to be altered... 

As mentioned earlier, transalkylation, measured both by band width and A.I., was most extensive in the sample from —4.93 m (Table IV). No kinetic data for the transalkylation reaction are available however, intuitively a maximum in the range of 100°-150°C seems reasonable. Below that range the alkylation reaction is noncompetitive with other diagenetic reactions and above that range dealkylation and destruction predominate. 

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