[mana]

hi all

when we want to recrystalize with two solvent, first we have to prepare a saturated solution with solvent 1 with heating the solution and then solvent 2 is added to solution dropwise until the solution become cloudy and it must be continued until cloudiness would persist in solution. then solvent 1 must be added to return to a clear solution. then the solution is cooled to r.t to achieve the participate.

now my question is why I have to add solvent 1 at the end to return to a clear solution? the resulted cloudy solution is my pure participate so why I have to dissolve it again by adding the solvent 1?

[clarkstill]

Because the material you gain initially after adding the antisolvent is triturated, not recrystallized.

Although you can purify by trituration, the purity will generally be lower than that obtained by a true recrystallization, since impurities may crash out alongside your desired product.

You should isolate a sample at both stages and take an NMR of each - if it's pure at the trituration stage then you can save yourself some time in the future.