I have a question concerning dibenzalacetone and recrystallization using ethanol and 2 other things.?

Question

I did an organic chem lab this week and I had to recrystallize .30g of dibenzalacetone with ethanol, weigh the crystals I got which came to be .08g and take the melting point which I recorded as 115-177. Does this sound right?

Also, we had to do the same experiment using 2-propanol and the crystals weighed .22g and the mp was 92-95. This makes no sense to me.

The third time we used 80% ethanol and 20% water. The mp was 100-105.

Can someone please tell me if this sounds about right and why the melting points are what they are. I need a good grade on this.

Thanks!

Answer 1

Simple, the dibenzalacetone is impure. The more pure the sample is, the higher and sharper the melting point. When you used ethanol, you removed the largest amount of product AND the impurities. When you used isopropanol, you removed less material and less of the impurities, therefore the mp was lower and broader.