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<p>This study successfully explains the kinetic and thermodynamic behavior of oxidative coupling reactions between 4-amino-<i>N</i>,<i>N</i>-dimethylaniline and various para-substituted phenol derivatives using potassium dichromate in alkaline medium. All reactions were confirmed to follow first-order kinetics. The comprehensive determination of activation parameters (E<sub>a</sub>, k, ΔH*, ΔS*, and ΔG*) for each derivative, revealing clear trends based on electronic effects. Electron-withdrawing groups (F, Cl, Br, I) significantly reduced activation energies, with 4-bromophenol exhibiting the lowest E<sub>a</sub> (11.02 kJ/mol), while electron-donating substituents raised the activation energy, with 4-methoxyphenol showing the highest (29.32&#xa0;kJ/mol). Notably, 4-iodophenol presented an exceptional combination of low ΔH* (8.357&#xa0;kJ/mol) and highly negative ΔG* (− 65.07 kJ/mol), attributed to favorable entropy contributions, indicating strong spontaneity. Complementary DFT calculations using the 6-311G(d,p) basis set confirmed these results, showing consistent trends with experimental data, while highlighting differences in energetic magnitudes. Theoretical analysis confirmed the influence of substituent electronics on reactivity and intermediate stability.</p> Graphical abstract <p></p>

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Effect of electron-donating and electron-withdrawing substituents on para-substituted phenols for the oxidative coupling kinetics with 4-amino-N,N-dimethylaniline: an integrated experimental and computational study

  • 期刊论文

  • 发表日期：

    2025年8月28日

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  • Kareem Jumaah Al-Salihi,
  • Mohammad Tahir Kareem,
  • Sirwan Abdallah Ahmed

摘要

This study successfully explains the kinetic and thermodynamic behavior of oxidative coupling reactions between 4-amino-N,N-dimethylaniline and various para-substituted phenol derivatives using potassium dichromate in alkaline medium. All reactions were confirmed to follow first-order kinetics. The comprehensive determination of activation parameters (Ea, k, ΔH*, ΔS*, and ΔG*) for each derivative, revealing clear trends based on electronic effects. Electron-withdrawing groups (F, Cl, Br, I) significantly reduced activation energies, with 4-bromophenol exhibiting the lowest Ea (11.02 kJ/mol), while electron-donating substituents raised the activation energy, with 4-methoxyphenol showing the highest (29.32 kJ/mol). Notably, 4-iodophenol presented an exceptional combination of low ΔH* (8.357 kJ/mol) and highly negative ΔG* (− 65.07 kJ/mol), attributed to favorable entropy contributions, indicating strong spontaneity. Complementary DFT calculations using the 6-311G(d,p) basis set confirmed these results, showing consistent trends with experimental data, while highlighting differences in energetic magnitudes. Theoretical analysis confirmed the influence of substituent electronics on reactivity and intermediate stability.

Graphical abstract