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Which is best solvent for recrystallization of benzoic acid?

  • Water
  • $\ce{CH3Cl}$
  • $\ce{CCl3COOH}$
  • $\pu{0.1 M}\ \ce{NaOH}$

I understand the solute/solvent should be soluble at high temperature, and insoluble at room temperature. But how to make the specific arguments for eliminating the alternatives?

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It can be difficult to guess at what a given compound will crystallise out from, and often there is a lot of trial and error involved.

Generally, the most 'common' type of recrystallisation involves finding a solvent in which the compound of interest is sparingly soluble at room temperature, but highly soluble at elevated temperature such that slow cooling of a saturated solution affords recrystallised material.

If you look up the entry for benzoic acid in Purification of Laboratory Chemicals, Armagero and Perrin, several solvents are suggested:

Benzoic acid has been crystallised from boiling water (charcoal), aqueous acetic acid, glacial acetic acid, benzene, aqueous EtOH, petroleum ether (b 60-80C), and from EtOH solution by adding water.

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