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3.3D: Using Solubility Data

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    95752
  • If you are not following a procedure where a crystallization solvent has been specified, it may be helpful to consult solubility data for the desired compound. Qualitative (and sometimes quantitative) solubility data can be found for many compounds in the CRC\(^5\) and Merck Index.\(^6\)

    If the goal is to use just one solvent for crystallization, it's best to look for a solvent in which the desired compound is slightly soluble. Although the percent recovery will be less than \(100\%\) (a portion will remain in the mother liquid), there is a good chance that a slightly soluble solid will dissolve when heated. It is possible that solvents listed as insoluble will not dissolve the compound at any temperature.

    For example, below are entries in the CRC and Merck Index for the compound 1,4-dinitrobenzene:

    • CRC Handbook: "i \(\ce{H_2O}\); sl \(\ce{EtOH}\), chl; s ace, bz, tol" Translation: The compound is insoluble in water; slightly soluble in ethanol and chloroform; and soluble in acetone, benzene, and toluene.
    • Merck Index: "White crystals. . . one gram dissolves in \(12,500 \: \text{mL}\) cold water, \(555 \: \text{mL}\) boiling water, \(300 \: \text{mL}\) alcohol; sparingly soluble in benzene, chloroform, ethyl acetate." Translation: The compound is very insoluble in cold water, but much more soluble in hot water. It is slightly soluble in ethanol, and basically insoluble in benzene, chloroform, and ethyl acetate.

    1,4-dinitrobenzene is slightly soluble in ethanol, making it a good "first guess" as a crystallization solvent. Indeed Perrin's Purification of Organic Chemicals\(^7\) recommends crystallization of 1,4-dinitrobenzene using ethanol or ethyl acetate.

    \(^5\)Handbook of Chemistry and Physics, CRC Press, 84^\text{th}\) edition, 2003-2004.

    \(^6\)The Merck Index, Merck Research Laboratories, 12\(^\text{th}\) edition, 1996.

    \(^7\)D.D. Perrin, W.L.F. Armarego, Purification of Organic Chemicals, Pergamon Press, 3\(^\text{rd}\) edition, 1988.

    Contributor

    Lisa Nichols (Butte Community College). Organic Chemistry Laboratory Techniques is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Complete text is available online.