Nucleophilic substitutions at the pyridine ring. Conformational preference of the products and kinetics of the reactions of 2-chloro-3-nitro- and 2-chloro-5-nitro-pyridines with arenethiolates †

Hamed, Ezzat A.; El‐Bardan, Ali A.; Saad, Esmat F.; Gohar, Gamal A.; Hassan, Ghada M.

doi:10.1039/a701902e

Cited by 33 publications

(30 citation statements)

References 23 publications

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“…6 kJ. Previous kinetic results have confirmed that the transition state for ortho substitution is less extensively solvated than the transition for para substitution [2,16].…”

Section: The Ortho/para Ratiosupporting

confidence: 57%

“…Hence, in the absence of steric encumbrance, the activating power of a 6-nitro group is greater than that of a ring nitrogen. This was attributed to the more efficient delocalization of the negative charge with a nitro group than with a ring nitrogen in the transition state [2,16].…”

Section: Comparison Relative Activation Of a Ring Nitrogen And 6-nitrmentioning

confidence: 99%

“…In 2-chloro-3-5-dinitropyridine, the ring nitrogen occupies one of the ortho position and its lone electron pair takes the place of the 6-nitro group in 1-chloro-2,4,6-trinitrobenzene. This lone electron pair is less bulky than even a hydrogen substituent [2, 16,18].…”

Section: Comparison Relative Activation Of a Ring Nitrogen And 6-nitrmentioning

confidence: 99%

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Nucleophilic heteroaromatic substitution: Kinetics of the reactions of nitropyridines with aliphatic amines in dipolar aprotic solvents

Isanbor¹,

Emokpae²

2008

Int J of Chemical Kinetics

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Rate data are reported for the reactions of 2-chloro-5-nitropyridine 2a, 2-chloro-3-nitropyridine 2b, and the corresponding 2-phenoxy derivatives 2c with n-butylamine, pyrrolidine and piperidine and 2d with n-butylamine and pyrrolidine in dimethyl sulfoxide (DMSO) as solvent. The same reactions in acetonitrile had been reported earlier (Crampton et al., Eur J Org Chem 2007, 1378-1383. Values in these solvents are compared with those of 2,4-dinitrochlorobenzene 3a, 2,6-dinitrochlorobenzene 3b, and the corresponding nitroactivated diphenyl ethers 3c and 3d. Reactions with n-butylamine in both solvents gave values of k obs , which increase linearly with amine concentration indicating that nucleophilic attack is rate limiting. The only exception is the reactions in acetonitrile with 2c where base catalysis was observed. Values of k 1 , the rate constant for the nucleophilic attack, decrease in the order pyrrolidine > piperidine > n-butylamine. In acetonitrile, kinetic data show that kratios are more than unity while the inverse is the case in DMSO. With the phenoxy derivatives, substitution was the only process observed. Base catalysis detected in the reactions of the 1-phenoxy derivatives is attributed to rate-limiting deprotonation of the initially formed zwitterionic intermediate. Our results shed more light on fundamental aspects of activation, hydrogen bonding, and steric effects associated with an aza or a nitro group in the molecules investigated as it affects the nucleophilic aromatic substitution (S N Ar) reaction pathways.

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“…6 kJ. Previous kinetic results have confirmed that the transition state for ortho substitution is less extensively solvated than the transition for para substitution [2,16].…”

Section: The Ortho/para Ratiosupporting

confidence: 57%

Section: Comparison Relative Activation Of a Ring Nitrogen And 6-nitrmentioning

confidence: 99%

See 1 more Smart Citation

Nucleophilic heteroaromatic substitution: Kinetics of the reactions of nitropyridines with aliphatic amines in dipolar aprotic solvents

Isanbor¹,

Emokpae²

2008

Int J of Chemical Kinetics

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“…This agrees with the rate determining formation of the zwitterionic intermediate I., Scheme 4. This is in line with the nucleophilic aromatic displacements of a good leaving group in polar and dipolar solvents (Khattab, Hamed, Albericio, & El-Faham, 2011;El-Mallah, Nabil, Senior, Ramadan, & Hamed, 2010;Asghar, Fathalla, & Hamed, 2009;Fathalla, Kassem, & Hamed, 2008;Khattab, Hassan, Hamed, & El-Faham, 2007;Al-Howsaway, Fathalla, El-Bardan, & Hamed, 2007;Fathalla & Hamed, 2006;Fathalla, Ibrahim, & Hamed, 2004;El-Hegazy, Abdel-Fathah, Hamed, & Sharaf, 2000;Hamed, El-Bardan, Saad, Gohar, & Hassan, 1997;Hamed, 1997aHamed, , 1997b. The plot of H # against log -S # for the reaction of 2 with hydrazine in MeOH, MeCN and DMSO gave straight line (r = 0.99) indicating a common mechanism for the reaction of 2 with hydrazine in these solvents.…”

Section: Reactions Of 1-chloro-24-dinitrobenzene 2 With Hydrazine Inmentioning

confidence: 54%

Nucleophilic Substitution Reactions of 2,4-Dinitrobenzene Derivatives with Hydrazine: Leaving Group and Solvent Effects

Ibrahim¹,

Abdel-Reheem²,

Khattab³

et al. 2013

IJC

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The hydrazinolysis of 2,4-dinitrophenyl acetate in methanol proceed exclusively through acyl-oxygen scission by a concerted mechanism. The reaction of 1-chloro-2,4-dinitrobenzene with hydrazine in methanol, acetonitrile and dimethyl sulfoxide undergo uncatalyzed substitution and the formation of the zwitterionic intermediate is the rate-determining step. While 2,4-dinitrobenzene derivatives 1, 2, 3, 4, 5a-i, 6 with hydrazine in DMSO undergo uncatalyzed substitution and the departure of the leaving group is the rate-determining step. The process depends on the basicity of the leaving group and its steric hindrance as well as the possible intramolecular hydrogen bond in the transition state. The reactivity of compounds 5a-i depends on the substituent of the thioaryl ring while the small ρ Y value is due to the sulfides existing preferentially in the skew conformation. The small β lg value (-0.18, r = 0.99) indicated that the reaction of sulfides with hydrazine proceeds with advanced bond formation to the nucleophile and the bond cleavage proceed in a slow extent in the transition state.

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“…The present kinetic results shows difference in rates with changing in the nature of the leaving group from OBt to Cl, I, O-N = C(COOEt) 2 , O-N = C(CN)COOEt, O-N = C(CN) 2 [36,37,[51][52][53].…”

Section: Kinetics and The Reaction Mechanismmentioning

confidence: 99%

Aminolysis of 1-(1-Hydroxybenzotriazolyl)-2,4-dinitrobenzene and 2-(1-Hydroxybenzotriazolyl)-5-nitropyridine

Khattab¹,

Kharaba²,

El-Hawary³

et al. 2012

OJPC

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The reaction 1-(1-hydroxybenzotriazolyl)-2,4-dinitrobenzene 1 and 2-(1-hydroxybenzotriazolyl)-5-nitro-pyridine 2 with amines undergoes amination followed by elimination of the 1-hydroxyl benzotriazolyl anion. The kinetic data for the reaction of 1 and 2 with Mo, CHA and An in MeOH and AN proceeded by uncatalysed mechanism in which the rate limiting step is the leaving group departure, whereas the reaction with Mo in toluene proceeded by uncatalysed mechanism in which the formation of the zwitterionic intermediate is the rate determining step. While the reactions of 1 with CHA and An and the reaction of 2 with CHA in toluene proceeded by SB mechanism in which the rate determining step is the proton transfer process. The reactions of 1 and 2 with Mo in the three solvents and with CHA and An in MeOH and AN is greatly depended on the stability of the zwitterionic intermediate. The effect of ring activation is due to the ground state stabilization and the more efficient delocalization of the negative charge with a nitro group than with a ring-nitrogen in the transition state. The low activation enthalpies ΔH # and the highly negative activation entropies ΔS # are due to the intramolecular hydrogen bonding with the ammonio hydrogen present in the transition state.

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Nucleophilic substitutions at the pyridine ring. Conformational preference of the products and kinetics of the reactions of 2-chloro-3-nitro- and 2-chloro-5-nitro-pyridines with arenethiolates †

Cited by 33 publications

References 23 publications

Nucleophilic heteroaromatic substitution: Kinetics of the reactions of nitropyridines with aliphatic amines in dipolar aprotic solvents

Nucleophilic heteroaromatic substitution: Kinetics of the reactions of nitropyridines with aliphatic amines in dipolar aprotic solvents

Nucleophilic Substitution Reactions of 2,4-Dinitrobenzene Derivatives with Hydrazine: Leaving Group and Solvent Effects

Aminolysis of 1-(1-Hydroxybenzotriazolyl)-2,4-dinitrobenzene and 2-(1-Hydroxybenzotriazolyl)-5-nitropyridine

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