Sample pre-lab quiz for Reduction of Ketones experiment.

1) How much hot solvent should be used to dissolve a solid that is to be recrystallized?

  1. 10 mL
  2. just as much as it takes to dissolve the compound
  3. enough to dissolve the compound, then an additional 10 mL
  4. a little less than it takes to dissolve the compound

2) The solubility of a compound with a melting point of 70 degrees is as follows: 8 g/100 mL hexanes (70 degrees C); 1 g/100 mL hexanes (0 degrees C). If you tried to recrystallize 1 g of this compound from 10 mL of hexanes, you would notice an oil forming in the hot mixture. What is this oil? What would you do to correct the problem so that the compound will recrystallize properly?

  1. I know the answer, but tell me anyway
  2. I don't know the answer: tell me?

3) If you have a compound with an amide group at one end and a ketone group at the other end, what will you use to reduce the ketone only, NaBH4 or LiAlH4?

  1. NaBH4
  2. LiAlH4

4) The filtrates from recrystallization of the product contain hexanes as well as small amount of benzhydrol. Where do they go at the end of the experiment, as directed in the Lab Manual?

  1. aqueous
  2. organic
  3. recovery jar for benzhydrol
  4. down the drain
  5. recovery bottle for recycled hexanes

5) If you run an IR of your product and see a broad peak at 3500 cm-1, you can conclude that:

  1. there is starting material in the product
  2. the product contains an alcohol group, as expected
  3. there is an aromatic ring in the product
  4. the product is contaminated with NaB(OH)4

6) The study problems in the Lab Manual include assigning the IR and NMR spectra of benzhydrol and benzophenone. Make sure you are able to do these.

Answers.