why not distill off all the solvent first then separate the solid residue of benzoin and benzoic acid by recrystallization

Distilling off the solvent first before separating the solid residue of benzoin and benzoic acid by recrystallization may not be the most efficient or effective approach. Here's an explanation of why:

1. Nature of the compounds: Benzoin and benzoic acid have different physical properties, including different boiling points. Benzoin has a significantly higher boiling point than benzoic acid. Distilling the solvent first will mainly result in the evaporation of benzoin, while benzoic acid will remain in the solution.

2. Solubility: Benzoin and benzoic acid have distinct solubility characteristics. Benzoin is sparingly soluble in hot water, while benzoic acid is highly soluble in hot water. By distilling off the solvent first, you will lose the opportunity to utilize the solubility difference for separation.

A more suitable approach would be to perform recrystallization directly without distilling off the solvent. Here's how you can do it:

1. Dissolve the mixture of benzoin and benzoic acid in a suitable solvent. Ethanol or a mixture of ethanol and water is commonly used.

2. Heat the solution to dissolve both compounds completely. This step is done to ensure that all the components are in a dissolved state.

3. Allow the solution to cool down slowly. As the solution cools, solid crystals will form.

4. Filter the solution to separate the solid crystals from the remaining solution. The solid crystals will contain a mixture of benzoin and benzoic acid.

5. Wash the crystals with a small amount of cold solvent to remove any impurities.

6. Air dry the crystals or use a desiccator to remove any remaining solvent and obtain the pure crystals of benzoin and benzoic acid.

Recrystallization is a separation technique based on differences in solubility. It allows the separation of compounds based on their different solubility characteristics, making it a more effective approach for separating benzoin and benzoic acid in this case.