The Rate of Reaction of Piperidine with Piperonal in Methanol

Crowell, Thomas I.; O'Brien, Daniel H.; Neveu, Maurice C.

doi:10.1021/jo01030a524

Cited by 3 publications

(3 citation statements)

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“…The present report describes the base-catalyzed equilibrium addition of alcohols to benzylideneanilines [1][2][3][4][5][6][7][8][9][10][11]…”

Section: Equilibrium Additionsmentioning

confidence: 99%

Equilibrium additions of carbon-nitrogen double bonds in nonaqueous solutions. Addition of alcohols to substituted benzylideneanilines

Ogata¹,

Kawasaki²

1974

J. Org. Chem.

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0.05, Le., indistinguishable from I. For the system of eq 1 a similar inversion plot in 65% DMSO had afforded an intercept of 1.35 from which K2 was ~alculated.~ We now have serious reservations about this value because of a possibly erroneous extinction coefficient ( € 3 ) . For lack of any better value we were forced to use €3 determined in 85% DMSO. Our present study indicates that € 6 decreases from 32,200 in 80% DMSO to 21,000 in 50% DMSO. If c3' depends in a similar way on the solvent as does € 6 , the true intercept of said inversion plot would become indistinguishable from 1. Though the pKa values of compounds like RN(CH3)CHzCH20H (R (1971). = alkyl) have to t h e best of our knowledge not been reported, we expect such compounds to be slightly less acidic than compounds like ROCHzCH20H (pKa = 14.8 for R = methyl17) on the basis of a somewhat higher inductive effect in the latter. With R = 2,4-dinitrophenyl, resonance which is more important for the nitrogen analog (2a, 2b) would tend to counteract the inductive effect. I f the K , values were still substantially different, the more weakly basic anion (higher K1) would also be a weaker nucleophile (lower K 2 ) ; thus even in this worst case K I K~ would still be a reasonably good comparative measure for the stabilities of the two u complexes.Rate and equilibrium constants for the base-catalyzed addition of methanol to benzylideneanilines in methanol-acetonitrile (9O:lO v/v) were determined by means of spectrophotometry. The equilibrium constant increases by electron-withdrawing substituents in the aniline ring as well as in the benzylidene ring, showing a correlation with the u+ constants. Also the rate constant increases by electron-withdrawing groups, showing a Correlation with u in this case. The solvent deuterium isotope effects are 0.98 for KoM-H/KoMeOD and 0.60 for kfMeoH/kfMeoD. The structural change of alcohol leads to the Taft equation for equilibrium constant, KO: log (KoX/KoMe) = -8 . 2~~ + 0.48E,. The rate decreases in the order n-BuOH > EtOH > MeOH > sec-BuOH > t-BuOH > i-PrOH, showing no simple correlation. The observed base catalysis, substituent effect, and solvent isotope effect are best explained by a mechanism involving a rate-determining attack by the alkoxide ions on the imino carbon atom. Thermodynamic parameters are calculated. Equilibrium additions of nucleophiles to ( 3 0 bonds have been extensively studied1 but the studies on the additions to C!== N bonds are few except for the hydrolysis of Schiff and for the additions of amines5 and of hydrogen ~y a n i d e .~,~ Only a few reports have paid attention to the addition of alcohols to C=N.2383 Because of the higher b a s i c i t i e~~-~ and lower electrophilicity of C=N than those of (30,l these reactions involve the protonated Schiff bases, where negative p values have been observed.2-7 The present report describes the base-catalyzed equilibrium addition of alcohols to benzylideneanilines 1-1 1 in which no subsequent reactions such as C-N cleavage in hydrolysis occur. R'C,H&H=N C,...

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“…The present report describes the base-catalyzed equilibrium addition of alcohols to benzylideneanilines [1][2][3][4][5][6][7][8][9][10][11]…”

Section: Equilibrium Additionsmentioning

confidence: 99%

Equilibrium additions of carbon-nitrogen double bonds in nonaqueous solutions. Addition of alcohols to substituted benzylideneanilines

Ogata¹,

Kawasaki²

1974

J. Org. Chem.

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“…10 3 times faster (intramolecular catalysis) than the imine-AE equilibration process in DMEDA buffer, and since 6 does not absorb at the wavelengths at which the measurements were conducted, ′ A 0 and ′ ∞ A can be expressed by eqs. [5] and [6], and K is given by eq. [7].…”

Section: Equilibrium Constantsmentioning

confidence: 99%

“…Until 1974, only a few reports had paid attention to α-AE formation (4,5). At that time, Ogata and Kawasaki (6) examined the addition of methanol and other aliphatic alcohols to benzylideneanilines, 1, and to N-(4-nitrobenzylidene)-anilines, 2, both essentially substituted at the aniline residue.…”

Section: Introductionmentioning

confidence: 99%

General acid-catalyzed addition of methanol to (E)-N-benzylideneanilines

Bennour¹,

Toullec²

1999

Can. J. Chem.

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The reaction of equilibrium addition of methanol (α-amino ether formation) to benzylideneanilines (C 6 H 5 CHϭNC 6 H 4 Y, with Y = H (1a), 3-Cl (1b), 3-NO 2 (1c), 4-CN (1d), and 4-NO 2 (1e)) in methanol is shown to be general acid-catalyzed in carboxylic acid buffers. The mechanism involves fast iminium ion formation followed by base-assisted addition of methanol. The α Brønsted exponents are in the 0.67-0.88 range, and α increases with the electron-withdrawing ability of Y. The same mechanism is valid for MeOH 2 + -catalysis, meaning that two solvent molecules are involved in the addition process, one of them playing the role of base. The equilibrium constant, K, is increased by electron-withdrawing substituents, log K depending linearly on the σ -substituent parameters. The substituent effects on the forward and reverse catalytic rate constants are analyzed by means of the log k = ρ n σ n + ρ r (σ --σ n ) + constant (Young-Jencks) equation. For carboxylic acid catalysis, the ρ n and ρ r parameters are in keeping with ca. half C-O bond forming or breaking at the transition state. The catalytic rate constants and α exponent for elimination of ClCH 2 CH 2 OH in methanol from the C 6 H 5 CH(OCH 2 CH 2 Cl)NH(4-CNC 6 H 4 ) chloroethyl adduct are compared with those for the elimination of methanol from C 6 H 5 CH(OCH 3 )NH(4-CNC 6 H 4 ). The chloromethyl group makes the reaction slower and α lower. This indicates that proton transfer is a little ahead of C-O bond cleavage at the transition state. Y substituent effects, α values, and the effects of the CH 2 Cl group are interpreted on the basis of a More O'Ferrall -Jencks diagram.

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