Diels-alder and melting point  (Page 3/4)

In this lab we will be studying the reaction of cyclopentadiene with maleic anhydride. From previous knowledge of Diels Alder reactions you should be able to predict the stereochemistry of the products. Cyclic dienes can give stereoisomeric products depending on whether the dienophile lies under or away from the diene in the transition state. The endo product is usually the major product (due to kinetic control).

In Figure 12, the diene and dienophile are aligned directly over each other which yields the endo product(dienophile under or in = endo).In Figure 13, the diene and dienophile are staggered with respect with to each other which yields the exo product(dienophile exposed or out = exo).

Pre-Lab 1: Diels-Alder and Melting Point (Total 10 points)

Here for the Pre-Lab

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

This assignment must be completed individually and turned in to your TA at the beginning of lab. Usually, you will not be allowed to begin the lab until you have completed this assignment–allowance made for the first week.

1. The reaction, as you will notice, occurs very rapidly. State two characteristics of the starting materials that make them ideal coupling partners for this reaction (i.e. what are good characteristics for reactants in Diels Alder reactions). (2 points)

2. Write the major product of the following reactions, if there is no product specify why. (4 points)

3. a) Which of these dienes gives the FASTEST reaction with maleic anhydride, why? (2 points)

(b) Which of these dienophiles gives the FASTEST reaction with cyclopentadiene and why? (2 points)

Grading

You will be assessed on:

• Pre-Lab assignment completed prior to lab, TA will check
• Melting points of urea, trans-cinnamic acid, of their mixture in different ratios and of the Diels-Alder reaction product
• Graph of melting point versus composition of the mixture urea/trans-cinnamic acid
• Your explanation as to why your measured melting point ranges do not match those in literature
• IR spectrum of product
• Write-up in your Lab Notebook
• Answers to post-lab questions
• TA evaluation of lab procedure.Material Required

Equipment Chemicals

• Capillary tube Cinnamic acid, urea
• Test tubes Diphenyl acetic acid
• Round bottom flask (5 mL) Dicyclopentadiene
• Beaker Maleic anhydride, Ethyl acetate
• Glass rod (for recrystalisation) Petroleum ether
• Filter paper

SAFETY

Wear gloves all the time, especially when you are working with NaOH, HCl. Keep safety glasses on all the time.

Experimental procedure for melting point

Part i. the effect of purity on melting point

In this section you will take two compounds (cinnamic acid and urea) and create mixtures of them to determine what effect this will produce, as well as the extent of this effect depending on the composition of the sample.

1.Prepare a capillary tube containing urea as well as one containing cinnamic acid. Take the melting point of each and compare it to the "Houston" values (which your TA will have). Repeat if the values are not correct.