Week 7 Problem Set 30 BL (Esterification Reaction)
Useful Link: Refractometer
ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up.
1. Reaction planning of esterification carried out in the lab
a. In this week's experiment an unknown carboxylic acid is reacted with an unknown alcohol to form an ester. Which compound is used in excess here? Why is this approach necessary?
b. The procedure also asks to add a few drops of concentrated sulfuric acid to the reaction mixture. Why is this necessary and how much should be used here? Show the appropriate key intermediate assuming benzoic acid was used as unknown acid.
c. Why is it important to reflux the mixture? What does this mean and how is this accomplished in the lab?
d. After the reaction is terminated, the reaction mixture is chilled. Cold water is added at this point. Which purpose does this step serve? What should student observe at this point?
e. Why is the aqueous layer extracted with diethyl ether? How much should be used here?
f. Why is the organic layer extracted with sodium bicarbonate during the work-up? Show pertinent chemical equations. How does the student know that he is done with this step?
g. During the vacuum distillation, the procedure asks to apply the vacuum to the setup before heating the mixture. Explain briefly why.
2. A student refluxes a mixture of 2.72 g of p-toluic acid, 4.00 mL of propanol and a few drops of concentrated sulfuric acid for several hours. After the work-up, the student isolated 3.20 g of a liquid product.
a. Show a balanced chemical equation for the reaction.
b. Determine the yield of the reaction. Show all calculations.
c. Predict the boiling point of the product at p = 40 torr.
d. The student observes refractive index of nD20= 1.5030. Which conclusion can he draw from this observation?
e. How many signals does the product exhibit in the H-NMR and the C-NMR, respectively?
3. After reviewing the UV-Vis chapter in the reader, take the online quiz
(http://bacher.chem.ucla.edu/TakeQuiz/?id=c20ad4d76fe97759aa27a0c99bff6710). The quiz is worth 10 points, and has to be taken until 1 hour prior to the in-lab meeting 7. (Hint: In some cases more than one answer is correct!) Even though you can take the quiz until one hour prior to meeting 7 of your section, you should not delay taking it since there might be some problems with the server. There seem to be problems with some MAC systems as well. After you submit the answers, your score should appear on your screen. If this does not happen, you will have to retake the quiz. (There will not be any possibility to retake the quiz weeks later!). In order to take the quiz, you have to go through a UCLA ICP address. This means that you either have to use your Bruin-Online account or go through the VPN (Vitual Private Network, software can be found here: http://www.bol.ucla.edu/services/vpn/) to have this UCLA ICP address. To log in, use your last name and your student ID. If you are experiencing problems, contact the instructor via email and include your full name (indicated which one is your last name), your student ID and section .