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2. once the two pure melting points have been determined find a partner and together prepare 3 samples: one of 1:9 urea : cinnamic acid, one of 1:1 urea : cinnamic acid, and one of 9:1 urea : cinnamic acid. take the melting point of each of these mixtures. plot the graph of melting point vs. the composition of the sample. note: you can prepare a large batch of sample and share the materials among yourselves (take 10mg urea and 90 mg cinnamic acid for 1st sample and mix it together, ratio should be same).

Part ii. determination of an unknown substance

In this portion of the lab you cannot determine the identity of an unknown by comparing its melting point with the melting point of the three possible compounds. Mixing characteristics will be used instead to determine the identity.

1. Prepare three capillary tubes in the following manner. Take a piece of weighing paper and mix a small amount of the unknown with a small amount of the sample of diphenylacetic acid (1:1). Place this in a capillary tube. Then on a new piece of weighing paper, weigh a small amount of the unknown and mix it with a small amount of adipic acid. Place this in a capillary tube.

2.Place these three capillary tubes in the melting point apparatus and record in detail what occurs to each tube and at what temperature. Using this knowledge determine the identity of the unknown.

Experimental procedure for diels-alder

Cyclopentadiene dimerizes at ambient conditions. Because of this cyclopentadiene is purchased as the stable dimer dicyclopentadiene. In order to be of any use, the dimer must be cracked and distilled. Due to time constraints you will be given the cyclopentadiene that has been prepared by your TA.

Part iii. diels alder reaction

1.       Dissolve 0.20 g of powdered maleic anhydride in 1 mL of ethyl acetate in a test tube and then add 1 mL of petroleum ether. This combination of solvents is used because the product is too soluble in pure ethyl acetate and not soluble enough in pure petroleum ether.

2.To the solution of maleic anhydride add 200 mL (0.160 g) of cyclopentadiene and mix the reactants. Mixing can be accomplished by tapping the bottom of the test tube back and forth with your finger.

Safety: Be careful when injecting the cyclopentadiene into the test tube and make sure the test tube points away from you.

3.Crystals should begin to form, if no crystals begin to form scratch the inside of the tube with a pipette to initiate growth. The scratch marks on the inside of the tube often form the nuclei on which crystallization starts.

4.Should crystallization occur too rapidly at room temperature the crystals will be very small. If so, save a seed crystal, heat the mixture until the product dissolves, seed it and allow it to cool slowly to room temperature. You will be rewarded with large plate-like crystals.

5.Remove the solvent from the crystals with a pipette forced to the bottom of the tube. Wash the crystals with one portion of cold petroleum ether then again remove the solvent. Scrape the product onto a piece of filter paper, allow the crystals to dry in air, determine their weight, and calculate the yield of the product.

6.Take the melting point of the product.

7.Take and analyze an IR and NMR spectrum of your compound.

 Waste disposal

All capillary tubes are to be disposed of in the GLASS CONTAINER and NOT in the trash can!! Dispose organic substances in their proper containers.

Approximate lab time 2-2.5 hours

Report1: Diels-Alder and Melting Point(Total 30 points)

Here for the Report

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’work or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

1. Draw the reaction and mechanism of maleic anhydride and cyclopentadiene. (4 points)

 

 

 

2. Show theoretical and percent yield calculations of the reaction between maleic anhydride and cyclopentadiene. (2 points)

 

 

3. What are the important IR frequencies and the functional group they correspond to? (2 points)

 

4. Analyze the NMR spectrum of the product. Draw the structure and assign each peak to the correct proton on the NMR spectrum. Are there any impurities? If yes, what are they? (4 points)

5. Write the major product of the following reactions with proper stereochemistry if required. (8 points)

Part 2: melting point (total 10 points)

1. Fill in the blanks: (5 points)

Melting Points of: Temperature in°C
Urea _________________________
Cinnamic acid _________________________
1:9 mixture _________________________
1:1 mixture _________________________
9:1 mixture _________________________

2. Draw a Plot of melting point versus composition of the mixture. (2 points)

 

3. Your explanation as to why your measured melting points do not match those in literature. (1 point)

4. Identity the unknown (Part II) product. (1 point)

5. Melting point of the DA product is: ____ (1 point)

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Source:  OpenStax, Chem217labsfall07. OpenStax CNX. Oct 16, 2007 Download for free at http://cnx.org/content/col10463/1.4
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