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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?
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.
