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.

Administrative Issues

1. Please consult your TA directly in order to find out when a particular postlab report is due. The red reader outlines the tentative schedule which has to be adjusted from time to time depending on how the section proceeds with the in-lab work.

2. If you have questions of general nature, please post them on the course discussion board instead of sending it to the instructor. Answering the same question several times is not productive for anybody.

3. The report for the project will be due by Wednesday, November 26, 2014 at 12:00 pm (in paper) and on the same day by 1 pm (on www.turnitin.com, CourseID: 8192874, Password: Chem30BL).

1. Please watch the following video (MP4-format), review the TLC chapter in the reader and the TLC lecture module (PP and lecture), take the online quiz read the appropriate chapter in the "Survival Kit Reader".

Quiz: (http://bacher.chem.ucla.edu/TakeQuiz/?id=d3d9446802a44259755d38e6d163e820). The quiz is worth 10 points, and has to be taken until one 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 .

2. Reaction planning of esterification carried out in the lab

a. Which compound is used in excess in this reaction? Why is this approach necessary?

b. What is used as catalyst in the reaction? Show the appropriate key intermediate assuming the student uses benzoic acid for the reaction.

c. Why is it important to reflux the mixture properly? Which observations should the student make?

d. After the completion of the reaction, the mixture is chilled. Upon cooling, the student observes the formation of a large amount of oil. How should he proceed?

e. The combined organic layers are extracted with saturated sodium bicarbonate solution. How does the student know that he is done with this step? Show pertinent balanced chemical equations.

f. The crude ester is distilled in vacuo. The student observes that some of his liquid collects in the Hickman head while some of it remains in the conical vial. Rationalize this observation. How should the student proceed?

3. A student refluxes a mixture of 2.74 g of m-methoxybenzoic acid, 3.00 mL of methanol and 0.30 mL of concentrated sulfuric acid for three hours. After the work-up, the student isolated 2.05 g of the product.

a. Show a balanced chemical equation for the reaction.

b. Determine the percentage 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 n_D²⁴= 1.5120. Which conclusion can he draw from this observation?

e. How many signals does the product exhibit in the ¹H-NMR and the ¹³C-NMR, respectively? How do these signals look like? In which range do they fall?

f. On a non-polar stationary phase, what would be the sequence of elution of the alcohol, ester and the carboxylic acid used in this experiment? Explain briefly.