Wikipedia lists chlorobenzene's solubility in water at 0.5 g/L at 20C, and benzene's at 1.79 g/L in 15C and 1.84g/L at 30C.
Chlorobenzene is very slightly polar, shouldn't it be more soluble? What other effects are taking place here?
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$\begingroup$ For that you need to know how interactions between aromatics and water work. For starters why benzene is much better soluble, than for ex. hexane. $\endgroup$– MithoronCommented Dec 6, 2023 at 20:20
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$\begingroup$ Solubility is one of the parameters that have never been perfectly explained and understood. A lot of different theories have been proposed to explain this or that solubility. These theories explain correctly plenty of substances. But not all. Never all. From time to time a new theory is published in the Journal of Chemical Education to explain solubility in term of electronegativity, dipole moments, entropies and other parameters. But there are always plenty of exceptions. If you discover the final solution of this problem, tell it quickly : it will be the next Nobel prize in chemistry. $\endgroup$– MauriceCommented Dec 6, 2023 at 21:27
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1 Answer
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Determining solubility is more complex than just evaluating interactions of a solute with the solvent at infinite dilution. If that were all that is required - if solubility depended only on enthalpy of solvation, then chlorobenezene would indeed be more soluble. The free energies of solvation are -0.87 kcal/mol for $\ce{C6H6 }$ and -1.12 kcal/mol for $\ce{C6H5Cl}$, from the Minnesota solvation database (Ref 1).
The free energy of solvation describes only the first step in the process of solubilization up to the solubility limit. As more solute is added, second-order effects that include solute-solute interactions and changes to the solvent structure must be considered. See eg Ref 3 on the range of intermolecular interactions possible between chlorobenzene molecules.
Predicting solvation free energy values accurately is not simple either, see for instance Ref 2.
References
Marenich, A. V.; Kelly, C. P.; Thompson, J. D.; Hawkins, G. D.; Chambers, C. C.; Giesen, D. J.; Winget, P.; Cramer, C. J.; Truhlar, D. G. Minnesota Solvation Database – version 2012, University of Minnesota, Minneapolis, 2012.
Sergei F. Vyboishchikov and Alexander A. Voityuk. Solvation Free Energies for Aqueous and Nonaqueous Solutions Computed Using PM7 Atomic Charges. Journal of Chemical Information and Modeling 2021 61 (9), 4544-4553. DOI: 10.1021/acs.jcim.1c00885
Lloyd Muzangwa, Silver Nyambo, Brandon Uhler, Scott A. Reid; On π-stacking, C-H/π, and halogen bonding interactions in halobenzene clusters: Resonant two-photon ionization studies of chlorobenzene. J. Chem. Phys. 14 November 2012; 137 (18): 184307. https://doi.org/10.1063/1.4765102
answered Dec 7, 2023 at 9:04