chemsample-lab1-discussion

Conducted by: Student A + B
 * __Microscale Dehydration of Cyclohexanol (Using Glassware with Elastomeric Connectors) – Regular Quantities__**

Distillation of 1.5 mL 85 % Phosphoric acid, 1.422 g (1.5 mL) cyclohexanol, and approx. 3 drops of concentrated Sulfuric acid over 25 minutes yielded 0.474 g of isolated Cyclohexene product. Dividing the actual yield by our original calculated (theoretical yield) of 1.422 g yielded our distillation with a recovery percent (or, percentage yield) of 33.33 %. This is a low percent of distilled product—however, a few factors can be taken into account for this value. First, our distillation was stopped as a result of excess temperature (in excess of 85 deg C), which left much of the solution within the 5 mL distilling flask untapped. If this solution was distilled completely, our results would most certainly have reflected a higher ​yield. Also, before separating the layers from one another, we could have dried our product a few more times with Calcium Chloride. Even though it is tedious, there could have been traces of water in our product which would explain the low yield we obtained. The reason for water not leaving during the distillation is because cyclohexanol has strong intermolecular forces that take place in the bond between oxygen and the hydrogen. This force is known as hydrogen bonding. Its important to understand that there is always room for error in the process of pipetting away one of two layers, as we did with the organic and acidic layer in the distilled receiver vial. This error could have occured because we pipetted the desired layer along with the undesired. Thus, correcting for the first (not error, but) limiting process, possibly finding a more precise method of layer separation, and getting rid of any possible water traces, would likely result in greater yield during another trial of this experiment.

After the calculation of percent yield, it was important to test the sample we distilled for the presence of alcohol for two reasons: 1) we could determine whether or not our distillation occurred properly—i.e., did the alcohol groups actually undergo elimination, leaving the cyclohexane rings to form double bonds (thus cyclohexene). 2) Testing them gave us some insight into the purity of our sample—i.e., how definitively did the distillation run, and to what degree is the cyclohexene sample “pure” (containing no alcohol). Testing our sample with Ammonium Cerium (IV) Nitrate did not give us any insight either way. Adding cyclohexene to the Ammonium Cerium (IV) Nitrate / 1,4 – dioxane solution was supposed to render the solution clear (indicating a strong presence of double bonds capable of soaking up reagents—i.e. bonding them). Instead, the solution remained full of color … red / orange / yellow. In contrast, however, testing the sample with Bromine proved successful. Bromine added to cyclohexanol reacted to yield a clear solution; added to our sample resulted only in a seeming liquid separation. The color associated with Bromine remained in the solution (dark red / brown) and gave us an idea as to the condition of the sample. The lack of reaction between the two, Bromine and isolate (//assumed// to be cyclohexene) lead us to the conclusion that our sample was in fact highly pure—i.e., that very little alcohol was present in our distilled sample. Conducting our Infrared analysis and refractive index measurements will give us an even better idea as to the purity of our distillate.

Conducted by: Student C + D We were not able to calculate a yield, or run any tests on our sample due to lack of distillation. There are several reasons why we got the results we did. First, the apparatus itself may have had a leak. This could be fixed in the future by applying a sealant or plastic to all joints in the apparatus. Another possibility is that the liquid never got hot enough, for a long enough period of time, to evaporate. Because we had double the quantity of the other (more successful) pair, it might have been more effective to get the heat above the recommended 85 degrees for longer. We did get the temperature up to over a hundred, but only for about twenty minutes. Finally, the double quantities did not seem to work very well. Other than our group, several other groups had problems getting results with these amounts. However, we do know there was some amount of dehydration occurring, because two layers did appear in the initial flask. Unfortunately, there was no way to abstract the liquid to test for cyclohexene because it was very contaminated. In the future, running the microscale dehydration at the recommended quantities seems to be a better procedure.
 * __Microscale Dehydration of Cyclohexanol- Double Quantities__**

Conducted by: Student E + F
 * __Semi-microscale Dehydration of Cyclohexanol__**

We got a product yield of 1.091g, which is a 37.80% yield. THis is a small amount of product that was obtained through the reaction, but it could have been because of human error- we had never used the apparatus of a semi-microscale, and this could have simply been a matter of practice. Also, all of the reactants in the flask were not distilled because we reached 85 degrees C, therefore the experiment was not carried out to its highest potential. When testing the product with Bromine, it turned out the same as the Bromine test on stock cyclohexene, which means that the product is cyclohexene. Both solutions were clear after this test. Cyclohexanol changed to a light yellow color.


 * After you synthesize it, here is** [|**something else**] **you can do with cyclohexene! Check it Out!!!**

Return to Dehydration Lab __Chem Kids Home __