The Effects of Chemical Substitution and Polymerization on the pKa Values of Sulfonic Acids

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• 作者：Haitao Dong ; Hongbo Du ; Sumith Ranil Wickramasinghe ; Xianghong Qian
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：October 29, 2009
• 年：2009
• 卷：113
• 期：43
• 页码：14094-14101
• 全文大小：182K
• 年卷期：v.113,no.43(October 29, 2009)
• ISSN：1520-5207

文摘

The effects of ring substitution on the pK_a value of benzenesulfonic acid (BSA) were investigated using a combined quantum mechanical and classical approach. Ring substitution with strong electron-withdrawing elements such as F, Cl, and Br is found to enhance the acidity of the BSA. More importantly, ring substitution with −NO₂ groups which form an extended conjugated π-system with the benzene ring exhibits the strongest enhancement of the acidity. The effects of polymerization on the styrenesulfonic acid (SSA) were also investigated by solving the classical Poisson−Boltzmann equation. It is found that polymerization significantly decreases the acidity of SSA due to the alteration of the electrostatic environment surrounding the acid group upon polymerization. The average pK_a value converges to 2.9 from the corresponding monomer value of −0.53 at a degree of polymerization of 8−12. These results shed significant light on how to design sulfonic-acid-based solid acid catalysts to achieve desired catalytic properties.