[Puresimple]

Hi All,

I did a lab on synthesis of cyclohexene and was a bit curious as to what is going on that is causeing my product to be impure. It seems as if we did a lot in order to maximize yield and still get a pure cyclohexene so I am a bit confused. The expected yield was 5.0g (61%). My actual results was 59.83% with a refractive index of 1.4455 compared to the literature of 1.4465. We started with 10.0g of cyclohexanol and added 2.5 mL of 85% phosphoric acid and 1 mL of sulfuric acid and ran through a simple distillation. we than drained the aqueous layer with 3mL of water and 3mL of saturated NaCl. Then as the final drying step we put in calcium chloride and a week later we distilled it once again through simple distillation.

is the drying steps not sufficient for eliminating the cyclohexanol and water that are formed even after distillation? are there other impurities I should think about?

[kriggy]

So you get 59,8 instead of 61%? That is pretty good IMO. The thing that comes to my mind is that the sample is not dry enough. But the difference in yields is almost nothing so not a big deal imo

[sjb]

A difference of 1.2% in yield, and very similar refractive index isn't that much to worry about really. How accurate were you weighing out reagents etc? Where have you got your "expected" yield from? Is this just one reaction, or an average of several runs?

[kriggy]

A difference of 1.2% in yield, and very similar refractive index isn't that much to worry about really. How accurate were you weighing out reagents etc? Where have you got your "expected" yield from? Is this just one reaction, or an average of several runs?

Indeed.
Just to show out:
yesterday I got not more than 5% from reaction which was supposed to give over 93 or smthing (according to the paper).

[Puresimple]

I know the yield is not that bad... I was actually surprised that I got only 1.2% difference. I was more interested (for my own sanity) as to why the product was impure. I know refractive index is sensitive to some physical properties, but something tells me that there was other things going on in the distillation and drying steps thats contributing to having an impure product. I don't know why this is bugging me, but i guess it's just my curiosity coming into play. I actually researched some and was thinking that maybe some dicyclohexyl ether may be an impurity formed? I wasn't too sure though, as distilling the product as its being formed should have eliminated this no? the only impurities i can think off are water and cyclohexanol (due to reverse reaction), but the drying agents should have taken care of that.

O and to answer your question sjb, i was pretty accurate as my partner double checked all of my work for me and I got the expected yield from my lab manual. This was only one reaction and not an average of several runs.