Recrystallisation of dibenzylideneacetone Recently, I carried out the synthesis of dibenzylideneacetone. I had a lot of problems with the purification process, especially the part involving recrystallisation. I was instructed to carry out the recrystallisation using an "ethanol/water" pair. That means to say, I was supposed to dissolve the crude product in ethanol until just enough dissolved, then add a small volume of water until some of the non-polar dibenzylideneacetone precipitated out of the solution and lastly, add another small volume of ethanol to re-dissolve the precipitate that had just formed. Once done, the beaker is removed from the hotplate and left to cool at room temperature. Subsequently, the crystals were washed with cold ethanol to finally obtain the final product. It is similar to what was done in this video.

During the practical I had to repeat the recrystallisation step multiple times for a variety of reasons. Firstly, there were some instances when the dibenzylideneacetone melted to form a yellow oily liquid. Secondly, there were also some instances when the crystals "crashed out" of solution upon cooling. This resulted in poor-quality crystals which clumped together. I am just wondering if anyone has any tips on how I could have improved my procedure so that I don't have to perform recrystallisation multiple times and yet still obtain poor-quality crystals.
Armarego's Purification of Laboratory Chemicals suggests using dichlormethane–hexane pair instead of ethanol–water; it also lists crystallization from warm ethyl acetate, ethanol or petroleum ether as alternative [1, p. 342]. 


  Dibenzalacetone [DBA, bda, trans-trans-1,5-diphenyl-1,4-dien-3-one, 1,5-(bisphenyl)-penta-1E,4E-diene-3-one] [538-58-9] $\ce{C17H14O}$, $M~234.3$, $m~107°$, $111°$, $112°$, $113°$, $120-122°$.
  Purify the ketone by flash chromatography (150 mesh $\ce{Al2O3}$ deactivated with $6\%$ v/w $\ce{H2O}$) using  petroleum ether $40-60°/\ce{EtOAc}$ ($4/1$, v/v), and the yellow solid is recrystallised by layering a concentrated $\ce{CH2Cl2}$ solution with hexane (i.e. $\ce{CH2Cl2}$/hexane, $1:4$, v/v).
  Also recrystallise the ketone from hot ethyl acetate $(\pu{2.5 ml/g})$ or $\ce{EtOH}$.
  It has been also crystallised from petroleum ether b $30-60°$. 


References


Armarego, W. L. Purification of Laboratory Chemicals; Elsevier: Boston, MA, 2017. ISBN 978-0-12-805457-4.