Why use petroleum ether to wash caffeine crystals after toluene recrystallization

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soundlover
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lo all, i´m having a small prob here
-extract the caffein of the tea leaves with CH2Cl2 + NaOH

- after the liquid-liquid extraction the organic phase (that contains the caffeine) was evaporated. then i joined some hot "toluen" (C6H5CH3) to the caffeine to occur a cristalization by slow evaporation of the solvent..
ok,i understand that but why the heck should i join some PETROLEUM ETHER to the cristals?

good lord,my english is painfull,sry

tks for any tip
 
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I believe it is used in this case as a transfer/rinse solvent, in which caffeine is moderately soluble. Usually the crude caffeine is dissolved in acetone, to remove the impurities and subsequently the former is used.