last updated Friday, December 11, 2015

1. General

a. Make sure that you get all the assigned texts and that you read them as thoroughly asap. If you have questions, please consult your TA or the instructor before you attend the lab to get through the lab more efficiently.

b. You also should start writing the introduction for your formal report. It could not hurt either to write up the experimental and the discussion part as you go along with the project. There are no post-labs due for this project because the formal report replaces those.

c. Review the following subjects in the Survival Kit Reader (=SKR): recystallization, polarimetry

d. Organizational skills: The ability to set priorities to certain tasks at a given time i.e., getting a reaction started instead of wasting time cleaning every piece of glassware in the drawer, which is not needed to run the reaction. It might also be advisable to pick up glassware needed for the reaction before you go to the lab.

2. Experimental (Resolution of the Diamine)

a. It is important that the diamine is added slowly. Why?

b. If the salt does not precipitate upon addition of glacial acetic acid, check the pH-value. It should be pH= 3-4. If this is not the case, add a little bit more glacial acetic acid to lower the pH-value. The addition of small amounts of methanol can also help to initiate precipitation.

c. The desired product crystallizes together with some trapped material, hence you will need to recrystallize the crude product.

d. The Hanson paper suggests to recrystallize the crude product from hot water (1:10 w/v = 1 g dry material/10 mL water=). The isolated crude product is not completely dry when the student proceeds with the recrystallization. Thus, a ratio of ~1:2-1:3 (w/v) might be more appropriate because it is easier to add water than removing it. Note that the solubility of the salt increases dramatically towards the boiling point of the solution. It is important to bring the suspension to a boil before adding additional solvent. Sometimes a small amount of foam is observed on the top which is fine. The amount of water used in the recrystallization should not exceed 30 mL.

e. If the product does not crystallize upon cooling, a small amount of methanol (~ up to 2 mL dropwise) can be added while stirring the solution.

f. It is crucial that the pure product is isolated before leaving for the day. Why?

g. The final product should be a white or off-white solid after recrystallization.

h. The characterization (i.e., infrared spectrum, melting point), has to be performed after the product has been properly dried and not with the wet product. The GC/MS sample can be prepared from the wet sample.

i. The tartrate salt is treated with sodium hydroxide to release the free diamine, which is extracted into ethyl acetate (hexane cannot be used as solvent because the diamine does not dissolve well in it (log Kow= 0.09)). After drying the organic layer over potassium carbonate, 1.5 mL of the solution is submitted in the GC vial (don't forget to sign in!).

3. Things to think about

a. How could you isolate the (S, S)-form of the diamine mixture provided in the lab?

b. What is the maximum yield (in % and grams) for the tartrate salt assuming that you use the commercially available mixture described in the reader?

c. Suggest a different way to separate the different enantiomeric forms in preparative scale.

d. How can the optical purity of the tartrate salt be determined?

e. Why is a high degree of optical purity of the salt desirable for the rest of the project?

f. Why is the value for the optical rotation of the free (R,R)-1,2-diaminocyclohexane different from the one for the tartrate salt isolated in the lab?