Kinetics and mechanism of the addition of benzylamines to β-nitrostyrenes in acetonitrile

Abstract

The kinetics and mechanism of the addition of benzylamines to β-nitrostyrenes in acetonitrile at 25.0 °C have been investigated. The addition reaction proceeds by two pathways, uncatalyzed (k₂) and catalyzed (k₃) paths. The kinetic isotope effects (k_H/k_D) involving deuterated benzylamine nucleophiles support the proposal that proton transfer from the amine to the β-carbon occurs concurrently with addition of the amine to the α-carbon. The transition state is predicted to have four- (I) and six-membered (II) cyclic structures for the k₂ and k₃ paths, respectively, with a tighter and more rigid structure for the uncatalyzed process. The cross-interaction constants, ρ_XY, are negative (−0.90 and −0.54 when the fall-off factor is taken into account) and the magnitude is larger for the uncatalyzed path than for the normal backside attack S_N2 reaction of benzyl derivatives with anilines (−0.6 to −0.8).

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Introduction

In our endeavors to establish the cross-interaction constants, ρ_ij and β_ij in eqns. (1) and (2) (where i and j can be any two fragments X, Y or Z, involved in a transition state (TS), e.g. Scheme 1), as a mechanistic tool for organic reactions,¹ we have shown that the sign of ρ_XY and β_XY (Scheme 1) for the bond-making step is negative while that of ρ_YZ and β_YZ for the bond-breaking step is positive in normal backside attack S_N2 reactions.^1,2 In general, the magnitude of ρ_ij (and β_ij) represents a change in the strength of interaction between the two fragments, i and j, on going from the reactants to the TS.³ Thus the magnitude of ρ_XY is greater while that of ρ_YZ is smaller, when the TS is tighter with a larger degree of bond making (shorter r_XY) and a smaller degree of bond cleavage (shorter r_YZ).³

log (k_ij/k_HH) = ρ_iσ_i + ρ_jσ_j + ρ_ijσ_iσ_j (1)

log (k_ij/k_HH) = β_ipK_i + β_jpK_j + β_ijpK_ipK_j (2)

Scheme 1 Typical S_N2 transition state. R and σ represent reaction center and substituent on each fragment, r is the distance between fragments.

In the limiting case in which only bond cleavage occurs in the TS, i.e., in the S_N1 TS, ρ_YZ was indeed positive and large.⁴ In this work, we have studied the other limiting case, in which only bond formation takes place in the TS, using the nucleophilic addition reactions of benzylamines to (E )-β-nitrostyrenes.

Although mechanistic studies of nucleophilic additions to an activated olefins including β-nitrostyrene have been reported,⁵ we have found no examples of reactions in which the structures (or substituents) of both the nucleophile (X) and the olefin (e.g. substituent Y in the β-nitrostyrene) are varied simultaneously.

We have carried out kinetic studies of addition reactions of benzylamines (BA) to (E )-β-nitrostyrenes (NS) in acetonitrile at 25.0 °C, eqn. (3). The main aim of this paper is to examine the substituent effects (both X and Y) on this addition reaction, and to determine the cross-interaction constant, ρ_XY, for the exclusive addition step in the TS. The sign and magnitude of ρ_XY are expected to provide a useful guide for predicting the TS structure.

Results and discussion

The pseudo-first order rate constants (k_obs) for all reactions studied in this work obeyed eqn. (4), indicating that the addition of BA to NS is catalyzed by a second BA molecule. The k₂ (uncatalyzed) and k₃ (catalyzed) values were determined as the intercept and slope, respectively, of a linear plot of k_obs/[BA] vs. [BA]. The details of the experimental conditions, i.e., [BA], [NS], ranges of k_obs and extinction coefficient changes at λ_max, are given in the Experimental section (vide infra). The k₂ and k₃ values are summarized in Tables 1 and 2, where the Hammett (ρ_X and ρ_Y) and Brønsted (β_X) coefficients are also shown. Jalani et al. reported ^5c the k₂ and k₃ values with 28 X substituents but with Y = H only in eqn. (3). Comparison of their values at 25.0 °C with our k₂ and k₃ values in Tables 1 and 2 shows that our values are consistently greater, by a factor of 1.7. In their experimental section, they report that the k_obs values were evaluated from the linear plot of log[NS] vs. time. The slope of this plot is actually smaller by a factor of 2.303 than the true k_obs value, since k_obs is the slope of a linear plot of ln[NS] (=2.303 log [NS]) vs. time.⁶ If we multiply their k_obs value (and hence k₂ and k₃ values) by 2.303, our k₂ and k₃ values are consistently smaller by a factor of 1.2–1.3, which, we consider, is more appropriate since the difference in the temperature control may allow such small, but consistent, differences.

k_obs = k₂[BA] + k₃[BA]² (4)

Table 1 Second order rate constants (k₂/10⁻² dm³ mol⁻¹ s⁻¹) for the addition reactions of β-nitrostyrenes with X-benzylamines in acetonitrile at 25.0 °C. [NS] = 8.0 × 10⁻⁵ M and [BA] = 1.5–25 mM. ρ_X and ρ_Y are the Hammett coefficients for X and Y. β_X is the Brønsted coefficient for X

	Y
X	p-Me	H	p-Cl	p-NO2	ρY^a
a  The σ values were taken from J. A. Dean, Handbook of Organic Chemistry, McGraw-Hill, New York, 1987, Table 7-1. Correlation coefficients were better than 0.998 in all cases.b  At 15 °C.c  At 5 °C.d  The σ values were taken from D. H. McDaniel and H. C. Brown, J. Org. Chem., 1958, 23, 420. Correlation coefficients were better than 0.985 in all cases.e  Correlation coefficient was 0.997.f  The pKa values were taken from A. Fischer, W. J. Galloway and J. Vaughan, J. Chem. Soc., 1964, 3588. Correlation coefficients were better than 0.991 in all cases. X = p-CH3O were excluded from the Brønsted plot for βX (benzylamine) due to unreliable pKa value listed.
p-OMe	2.55	4.46	15.2	128	1.82 ± 0.09
	2.40 ^b			118 ^b
	2.24 ^c			108 ^c
p-Me	1.92	3.86	11.9	86.2	1.74 ± 0.08
H	1.42	2.63	7.78	61.4	1.73 ± 0.06
p-Cl	0.649	1.12	3.02	20.6	1.60 ± 0.05
	0.605 ^b			18.9 ^b
	0.562 ^c			17.1 ^c
ρX^d	−1.17 ± 0.11	−1.22 ± 0.15	−1.41 ± 0.14	−1.55 ± 0.19	ρXY^e = −0.41
βX^f	1.20 ± 0.16	1.36 ± 0.14	1.51 ± 0.15	1.59 ± 0.29

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Table 2 Third order rate constants (k₃/dm⁶ mol⁻² s⁻¹) for the addition reactions of β-nitrostyrenes with X-benzylamines in acetonitrile at 25.0 °C. [NS] = 8.0 × 10⁻⁵ M and [BA] = 1.5–25 mM. ρ_X and ρ_Y are the Hammett coefficients for X and Y. β_X is the Brønsted coefficient for X

	Y
X	p-Me	H	p-Cl	p-NO2	ρY^a
a  Same as the footnotes for Table 1, except correlation coefficients, r: r ⩾ 0.994.b  Same as the footnotes for Table 1.c  Same as the footnotes for Table 1.d  Same as the footnotes for Table 1, except correlation coefficients, r: r ⩾ 0.995.e  Same as the footnotes for Table 1, except correlation coefficients, r: r ⩾ 0.996.f  Same as the footnotes for Table 1, except correlation coefficients, r: r ⩾ 0.995.
p-OMe	1.51	4.46	11.0	88.3	1.81 ± 0.13
	1.15 ^b			67.0 ^b
	0.867 ^c			49.9 ^c
p-Me	1.33	3.21	8.30	64.1	1.75 ± 0.08
H	0.833	2.33	5.84	40.3	1.72 ± 0.14
p-Cl	0.481	1.15	2.76	20.0	1.67 ± 0.08
	0.351 ^b			15.7 ^b
	0.254 ^c			12.1 ^c
ρX^d	−1.04 ± 0.06	−1.15 ± 0.08	−1.19 ± 0.08	−1.29 ± 0.02	ρXY^e = −0.24
βX^f	1.10 ± 0.08	1.13 ± 0.11	1.21 ± 0.11	1.26 ± 0.01

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The magnitudes of ρ_X for k₂ (−1.2 to −1.6, which corresponds to −2.7 to −3.4 if the fall-off factor of 2.19 ^1a,7 is taken into account for the CH₂ group between substituent X and the functional center N) and β_X (1.2–1.6) are relatively large, compared to the corresponding values of ρ_X (−1.89 ± 0.13) and β_X (0.68) ⁸ for the addition of anilines.^5b This is an indication of a greater degree of bond formation in the TS for the BA relative to aniline addition. The magnitude of ρ_Y is also large (ρ_Y = 1.6–1.8) suggesting that negative charge development at the C_α[double bond, length half m-dash]C_β moiety should be large, which is consistent with the tight bond formation predicted by the large magnitude of ρ_X and β_X. In agreement with these trends, the cross-interaction constant, ρ_XY, is also large and negative (ρ_XY = −0.41, which corresponds to −0.90 when the fall-off factor is taken into account). The corresponding values for the normal backside attack S_N2 reaction of benzyl derivatives with anilines are ca. −0.6 to −0.8.^1,2

Surprisingly, our k₃ values give very similar, only slightly smaller, magnitudes of ρ_X, β_X, ρ_Y and ρ_XY (−0.24, corresponding to −0.54 taking into account fall-off) to those for aniline addition. This may be taken as evidence for a slightly looser bond-making structure in the catalyzed TS. This is supported by the smaller k_H/k_D (>1.0) values for the catalyzed (k₃) process in Tables 3 and 4. The normal kinetic isotope effects (k_H/k_D > 1.0) involving deuterated benzylamines (XC₆H₄CH₂ND₂) provide evidence for partial N–H(D) bond cleavage in the TS.^1b We presume that proton transfer to C_β occurs concurrently with the C_α–N bond formation in the TS, I and II. In the k₂ path, relatively greater stretching of the N–H bond is required than in the k₃ path, so the k_H/k_D values are greater in general. This is consistent with a lesser degree of bond formation in the catalyzed path, as indicated by the smaller magnitude of the selectivity parameters, ρ_X, β_X and ρ_XY. For both paths, the largest k_H/k_D value is obtained for the X = p-OMe and Y = p-NO₂ set. This is quite reasonable, since for this set of substituents the extent of bond formation in the TS is the greatest with the largest magnitude of ρ_Y and ρ_X (β_X) values (Tables 1 and 2).

Table 3 Kinetic isotope effects on the second-order rate constants for the reactions of β-nitrostyrenes with deuterated X-benzylamines in acetonitrile at 25.0 °C ^a

X	Y	kH/10^−2 M^−1 s^−1	kD/10^−2 M^−1 s^−1	kH/kD
a  Concentrations of NS and BA are the same as in Tables 1 and 2.b  Standard deviations.
p-OMe	p-Me	2.55 (±0.03)	0.992 (±0.002)	2.57 ± 0.06 ^b
p-OMe	H	4.46 (±0.06)	1.56 (±0.03)	2.86 ± 0.06
p-OMe	p-Cl	15.2 (±0.2)	5.18 (±0.06)	2.93 ± 0.05
p-OMe	p-NO2	128 (±3)	41.5 (±0.1)	3.08 ± 0.06
p-Cl	p-Me	0.649 (±0.005)	0.282 (±0.002)	2.30 ± 0.02
p-Cl	H	1.12 (±0.02)	0.420 (±0.006)	2.67 ± 0.04
p-Cl	p-Cl	3.02 (±0.04)	1.10 (±0.02)	2.74 ± 0.06
p-Cl	p-NO2	20.6 (±0.4)	7.43 (±0.07)	2.77 ± 0.06

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Table 4 Kinetic isotope effects on the third-order rate constants for the reactions of β-nitrostyrenes with deuterated X-benzylamines in acetonitrile at 25.0 °C ^a

X	Y	kH/10^−2 M^−2 s^−1	kD/10^−2 M^−2 s^−1	kH/kD
a  Concentrations of NS and BA are the same as in Tables 1 and 2.b  Standard deviations.
p-OMe	p-Me	1.51 (±0.04)	1.17 (±0.02)	1.29 ± 0.04 ^a
p-OMe	H	4.46 (±0.06)	3.41 (± 0.05)	1.31 ± 0.03
p-OMe	p-Cl	11.0 (±0.2)	7.96 (±0.07)	1.38 ± 0.03
p-OMe	p-NO2	88.3 (±0.9)	46.5 (±0.6)	1.90 ± 0.03
p-Cl	p-Me	0.481 (±0.004)	0.333 (±0.003)	1.44 ± 0.02
p-Cl	H	1.15 (±0.02)	0.650 (±0.001)	1.77 ± 0.04
p-Cl	p-Cl	2.76 (±0.05)	1.50 (±0.02)	1.84 ± 0.04
p-Cl	p-NO2	20.0 (±0.3)	10.6 (±0.2)	1.87 ± 0.04

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Finally, the activation parameters in Table 5 support the proposed mechanism. We note that in general the ΔH ^‡ values are higher but the negative ΔS^‡ values are, in general, large. This is in accord with the greater degree of bond formation (exoergic) leading to less energy being required to break the π bond (endoergic) on C[double bond, length half m-dash]C but more rigid four-membered TS, I, for the k₂ path. For the k₃ path, the six-membered TS, II, has a looser (than I) structure with smaller negative ΔS^‡.

Table 5 Activation parameters ^a for the reactions of β-nitrostyrenes with X-benzylamines in acetonitrile at 25.0 °C ^b

X	Y	Reactionpath	ΔH ^‡/kcalmol^−1	−ΔS^‡/ calmol^−1 K^−1	ΔG ^‡/kcalmol^−1
a  Calculated by the Eyring equation. The maximum errors calculated (by the method of K. B. Wiberg, Physical Organic Chemistry, Wiley, New York, 1964, p. 378) are ±0.5 kcal mol^−1 and ±2 eu for ΔH^‡ and ΔS^‡, respectively.b  Concentrations of NS and BA are the same as in Tables 1 and 2.
p-OMe	p-Me	k2	0.5	64	19.6
p-OMe	p-NO2	k2	0.9	55	17.3
p-Cl	p-Me	k2	0.5	61	18.7
p-Cl	p-NO2	k2	1.0	58	18.3
p-OMe	p-Me	k3	4.0	44	17.1
p-OMe	p-NO2	k3	4.6	32	14.1
p-Cl	p-Me	k3	4.6	44	17.7
p-Cl	p-NO2	k3	3.8	41	16.0

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It is well known that there is a charge imbalance in the TS for the addition reactions of amines to activated olefins such as β-nitrostyrenes,^5a,10eqn. (5). The TS “imbalance” was attributed to a lag in the charge delocalization into the NO₂ moiety behind C–N bond formation in the TS.^5b,10 This sort of imbalance leads to an extreme structure in which negative charge builds up on the C_β carbon, as in III, instead of delocalizing onto the NO₂ group, as in IV,¹⁰ in the TS. Since the negative charge transferred from the amine to the substrate is practically localized on C_β in the TS, the proton transfer to C_β from the amine should become viable, and our proposal of the proton transferred TS structures, I and II, is supported. The low cost of energy (ΔH ^‡) required for the π-bond cleavage in the TS may also be partly attributable to the concurrent proton transfer. In view of the results of Bernasconi et al.,^5a that there is considerable positive charge development on the amine nitrogen in the TS, the positive charge carried away by the transferring proton should be small, i.e., the N ⋯ H bond stretching should be in its early stage in I and II.

In summary, the addition of benzylamines to (E )-β-nitrostyrenes in acetonitrile proceeds by two pathways, the uncatalyzed (k₂) and catalyzed (k₃) paths. Furthermore, the reaction is a one-step process, in which the proton transfer from benzylamine to the β-carbon occurs concurrently with the addition of benzylamine to the α-carbon. This assertion is supported by the observation of relatively large primary kinetic isotope effects, k_H/k_D > 1.0, for deuterated nucleophiles, XC₆H₄CH₂ND₂. The charge imbalance leading to a practically localized negative charge on C_β in the TS, III, seems to provide support for the proposed concurrent proton transfer. Bond formation in the TS is more advanced in the k₂ (larger negative ρ_XY) than k₃ path, so that the k₂ path has a more rigid (more negative ΔS^‡) four-membered structure with a greater degree of proton transfer.

Experimental

Materials

Solvent, acetonitrile (Merck GR) was used after three distillations. Benzylamines (Aldrich GR) were used after recrystallization. The β-nitrostyrenes were prepared by the literature method of Worrall.¹¹ The analytical data are as follows (IR: NICOLET 5BX FTIR; NMR: JEOL 400 MHz).

(E )-p-Methyl-β-nitrostyrene.. Mp 97–99 °C; λ_max 324 nm; IR(KBr) ν_max/cm⁻¹ 3100 (C–H, alkene), 1636 (C[double bond, length half m-dash]C, alkene), 1595 (C[double bond, length half m-dash]C, aromatic), 1431 (–CH₂ bend); ¹H NMR (400 MHz, CDCl₃) 2.41 (3H, s, –CH₃), 7.26 (2H, d, m-H, J 7.81 Hz), 7.44 (2H, d, o-H, J 8.31 Hz), 7.57 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz), 7.99 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz); ¹³C NMR (100.4 MHz, CDCl₃) 143.1, 139.2, 136.3, 130.2, 129.2, 127.3, 100.6, 21.7.

(E )-β-Nitrostyrene.. Mp 58–60 °C; λ_max 311 nm; IR(KBr) ν_max/cm⁻¹ 3113 (C–H, alkene), 1629 (C[double bond, length half m-dash]C, alkene) 1582, 1475 (C[double bond, length half m-dash]C, aromatic), 1448 (–CH₂ bend); ¹H NMR (400 MHz, CDCl₃) 7.45 (2H, d, m-H, J 6.84 Hz), 7.55 (2H, d, o-H) 7.59 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz), 8.01 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz); ¹³C NMR (100.4 MHz, CDCl₃) 139.1, 137.1, 132.2, 130.1, 129.4, 129.2.

(E )-p-Chloro-β-nitrostyrene.. Mp 102–104 °C; λ_max 314 nm; IR(KBr) ν_max/cm⁻¹ 3107 (C–H, alkene), 1636 (C[double bond, length half m-dash]C, alkene), 1589 (C[double bond, length half m-dash]C, aromatic), 1441 (–CH₂ bend); ¹H NMR (400 MHz, CDCl₃), 7.43 (2H, d, m-H, J 8.79 Hz), 7.49 (2H, d, o-H, J 8.79 Hz), 7.57 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz), 7.97 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz); ¹³C NMR (100.4 MHz, CDCl₃) 137.7, 137.4, 130.0, 129.8, 129.3, 128.5, 127.3.

(E )-p-Nitro-β-nitrostyrene.. Mp 194–196 °C; λ_max 307 nm; IR(KBr) ν_max/cm⁻¹ 3101 (C–H, alkene), 1635 (C[double bond, length half m-dash]C, alkene), 1594 (C[double bond, length half m-dash]C, aromatic), 1431 (–CH₂ bend); ¹H NMR (400 MHz, CDCl₃) 7.64 (1H, d, [double bond, length half m-dash]CH, J 13.7 Hz), 7.73 (2H, d, m-H, J 8.79 Hz), 8.04 (1H, d, CH, J 13.7 Hz), 8.32 (2H, d, o-H, J 8.79 Hz); ¹³C NMR (100.4 MHz, CDCl₃) 136.7, 135.0, 129.7, 128.9, 128.3.

Kinetic measurements

The reaction was followed spectrophotometrically by monitoring the decrease in the concentration of β-nitrostyrene, [NS], at λ_max of the substrate to over 80% completion. The reaction was studied under pseudo-first-order conditions, [NS] = 8.0 × 10⁻⁵ M⁻¹ and [BA] = (1.5–25) × 10⁻³ M⁻¹ at 25.0 ± 0.1 °C. The pseudo-first-order rate constant, k_obs, was determined from the slope of the plot (r > 0.993) ln[NS] (2.303 log [NS]) vs. time. The uncatalyzed (k₂) and catalyzed (k₃) rate constants were determined by fitting the k_obs data to a parabolic curve, Fig. 1, of the k_obsvs. [BA] plot, eqn. (4), which corresponded to a linear plot of k_obs/[BA] vs. [BA] with an intercept of k₂ and slope of k₃. The two methods gave the same results within an experimental error of ±3%. The ranges of [BA] (1.5–25 mM] and the concentration of [NB] (8.0 × 10⁻⁵ M) were fixed in all cases. The ranges of k_obs and extinction coefficients changes at λ_max are summarized in Table 6. Representative data are shown in Table 7.

Table 6 The λ_max (nm) ranges of extinction coefficient (ε/dm³ mol⁻¹ cm⁻¹) and (k_obs/10⁻⁴ s⁻¹) and percentage completion of reactions. [NS] = 8.0 × 10⁻⁵ M and [BA] = 1.5–25 mM

X	Y	λmax/nm	ε/dm^3 mol^−1cm^−1	kobs/10^−4s^−1	Completion (%)
p-OMe	p-Me	324	1.60–0.20	0.406–15.5	87.5
	H	311	1.50–0.18	0.751–37.1	88.0
	p-Cl	314	1.70–0.21	2.49–108	87.6
	p-NO2	307	1.90–0.23	15.5–878	88.4
p-Me	p-Me	324	1.80–0.21	0.364–13.5	88.3
	H	311	1.55–0.19	0.579–29.4	87.7
	p-Cl	314	1.75–0.22	1.88–82.0	87.4
	p-NO2	307	1.90–0.25	14.9–637	86.8
H	p-Me	324	1.42–0.17	0.224–8.93	88.0
	H	311	1.50–0.15	0.344–20.1	90.0
	p-Cl	314	1.20–0.15	1.30–56.1	87.5
	p-NO2	307	1.75–0.20	9.47–385	88.6
p-Cl	p-Me	324	1.50–0.18	0.108–4.83	88.0
	H	311	1.75–0.22	0.180–9.78	87.4
	p-Cl	314	1.25–0.15	0.283–22.8	88.0
	p-NO2	307	1.65–0.20	3.02–195	87.8

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Table 7 The k_obsversus [BA] (benzylamine concentration/M) data in acetonitrile at 25.0 °C

X	Y	[BA] M	kobs/10^−4 s^−1	k2/10^−2 M^−1 s^−1	k3/M^−2 s^−1	R corr. coeff.
p-OMe	p-Me	0.0015	0.406	2.55 ± 0.04	1.51 ± 0.03	0.999
		0.0030	0.975
		0.0045	1.47
		0.0060	1.96
		0.0075	2.74
		0.0100	4.03
		0.0150	7.34
		0.0200	11.32
		0.0250	15.55
p-OMe	p-Cl	0.0015	2.49	15.2 ± 0.3	11.0 ± 0.2	0.999
		0.0030	5.76
		0.0045	9.21
		0.0060	13.3
		0.0075	17.3
		0.0100	25.6
		0.0150	47.1
		0.0200	74.7
		0.0250	108
p-Me	p-Cl	0.0015	1.88	11.9 ± 0.4	8.30 ± 0.03	0.994
		0.0030	4.18
		0.0045	7.17
		0.0060	10.2
		0.0075	14.7
		0.0100	20.6
		0.0150	34.8
		0.0200	57.0
		0.0250	82.0
p-Me	p-NO2	0.0015	14.9	86.2 ± 0.3	64.1 ± 0.2	0.996
		0.0030	32.7
		0.0045	52.2
		0.0060	74.4
		0.0075	98.8
		0.0100	147
		0.0150	264
		0.0200	420
		0.0250	637

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Fig. 1 The plot of k_obsvs. concentration of benzylamine for the reaction of (E )-p-chloro-β-nitrostyrene in MeCN at 25.0 °C.

Product analysis

β-Nitrostyrene (0.05 mol) and benzylamine (0.5 mol) were reacted in acetonitrile at 25.0 °C. After more than 15 half lives, solvent was removed under reduced pressure and product was separated by column chromatography (silica gel, 20% ethylacetate–n-hexane). Analytical data are as follows.

C₆H₅CH(NHCH₂C₆H₄OCH₃)CH₂NO₂.. Liquid; IR(KBr) ν_max/cm⁻¹ 2993 (C–H, CH₂), 2958 (N–H, stretch), 2946 (C–H, CH₃), 1460 (C[double bond, length half m-dash]C, aromatic), 1448 (C–H, CH₂); ¹H NMR (400 MHz, CDCl₃) 3.82 (3H, s, OCH₃), 4.30 (1H, t, CH, J 6.90 Hz), 4.76 (2H, d, benzylamine CH₂, J 3.01 Hz), 4.78 (2H, d, benzyl CH₂, J 6.10 Hz), 6.88–7.53 (9H, m, aromatic ring); ¹³C NMR (100.4 MHz, CDCl₃) 134.0 130.7 129.4 128.9, 128.6, 128.5, 128.3, 127.2, 114.1, 113.8, 64.9, 55.2, 41.7.

Acknowledgements

The authors wish to acknowledge the financial support of the Korea Research Foundation made in the program year of 1998.

References

1. (a) I. Lee, Adv. Phys. Org. Chem., 1992, 27, 57; (b) I. Lee, Chem. Soc. Rev., 1995, 24, 223.
2. I. Lee, C. S. Shim, S. Y. Chung, H. Y. Kim and H. W. Lee, J. Chem. Soc., Perkin Trans. 2, 1988, 1919.
3. I. Lee, J. Phys. Org. Chem., 1992, 5, 736.
4. I. Lee, M. S. Choi and H. W. Lee, J. Chem. Res. (S), 1994, 92; I. Lee, M. S. Choi and H. W. Lee, J. Chem. Res. (M), 1994, 568.
5. (a) C. F. Bernasconi, R. A. Renfrow and P. R. Tia, J. Am. Chem. Soc., 1986, 108, 4541; (b) B. Varghese, S. Kothari and K. K. Banerji, J. Chem. Res. (S), 1998, 422B. Varghese, S. Kothari and K. K. Banerji, J. Chem. Res. (M), 1998, 1853; (c) N. Jalani, S. Kothari and K. K. Baneryi, Can. J. Chem., 1996, 74, 625.
6. F. Ruff and I. G. Csizmadia , Organic Reactions. Equilibria, Kinetics and Mechanism, Elsevier, Amsterdam, 1994, p. 62..
7. C. Hansch, D. Hoekman and H. Gao, Chem. Rev., 1996, 96, 1045.
8. Estimated by ρ_X/ρ^e = β_X,^1a where ρ^e is the Hammett coefficient for dissociation of anilinium ions (pK_a) vs.σ, which is ρ^e = 2.77.⁹.
9. C. D. Johnson , The Hammett Equation, Cambridge University Press, Cambridge, 1993, p. 30..
10. (a) C. F. Bernasconi, Acc. Chem. Res., 1987, 20, 301; (b) C. F. Bernasconi, Tetrahedron, 1989, 45, 4017.
11. D. E. Worrall , in Organic Synthesis, H. Gilman and A. Blatt, eds., Wiley, New York, 1941, Coll. Vol. 1, p. 413..

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