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

Abstract

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 -NO(2) groups which form an extended conjugated pi-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.

pH-dependent, thermosensitive polymeric nanocarriers for drug delivery to solid tumors

“…[36] However, after incorporation into polymers, the p K a of acids have been shown to increase due to changes in the microenvironment that reduce the acidity of the acid groups. [37, 38] Based on the pH-responsive LCST curves, the p K a of βA and ACA are also increased to greater than 6.0 when they were incorporated in polymers (Figure 1A). Protonation of the acid groups at pH below their p K a increases the hydrophobicity of the polymer and shifts the LCST to a lower temperature.…”

Molecule motion at polymer brush interfaces from single‐molecule experimental perspectives

“…Furthermore, it was observed that poly(acrylic acid) brushes had an even higher pKa than that of the polymer in the bulk, due to the high osmotic pressure causing a strong condensation of counterions on polyelectrolyte chains. In a similar manner, the pKa of PSSNa brushes could be much higher than that of its sulfonic acid monomer (pKa = 1) . When the pH was below 3.5, PSSNa brushes became less ionized, which can promote the diffusion of R6G molecules inside less charged PSSNa brush layers.…”

Competitive adsorption of cadmium and aluminum onto fresh and oxidized biochars during aging processes

“…These results are attributed to the lower pK a of oxidized sample (RS350-NS60) than those of primary biochar (RS350). The lower pK a of oxidized samples is mainly attributed to the nitro groups added to biochar surface (Dong et al 2009;Evanko and Dzombak 1998), as nitro groups can form an extended conjugated π system with the benzene ring, and exhibits strong enhancement of the acidity (Dong et al 2009;Evanko and Dzombak 1998). Because the carboxylic groups of oxidized samples were dissociated at relatively low pH values , the electrostatic bonding of Cd to biochars was reasonable.…”