In today experiment you will perform the reduction of 4- t -butylcyclohexanone t

Question

In today experiment you will perform the reduction of 4-t-butylcyclohexanone to synthesize a mixture of cis- and trans- 4-t-butylcyclohexanol. Answer the following questions regarding this reaction:

1.The reduction of 4-tert-butylcyclohexanone with sodium borohydride is a stereoselective reaction. What does this mean, in terms of the products that were isolated?

2. Why the reduction is done in methanol and not in water?

3. Why in the reaction a very big excess of NaBH4 will be used?

4.Compare and contrast the (A) reductive abilities of LiAlH4 with those of NaBH4, and, (B) compatibility of the two reducing agents with protic solvents (water, alcohols). Use as reference internet sources and your lecture manual. After the comparison, decide why NaBH4 was used in the reduction of 4-t-butylcyclohexanone (your experiment) rather than LiAlH4.

5.After the reduction the product mixture is quenched with cold dilute HCl. Why do we do that?

6.To isolate the reaction product you will perform an extraction. What solvent will be used for extraction and what layer is on the bottom? Circle the correct response:   Et2O,   H2O,   CH2Cl2, pentane.

7. What is the purpose of adding anhydrous Na2SO4 in step 8 of the procedure, before the filtration of the combined CH2Cl2 extracts?

8. Why do you expect cis- and trans-4-t-butylcyclohexanol to be separable by GC? Do you expect more cis- or trans-4-t-butylcyclohexanol?

9. Is the reaction thermodynamically or kinetically controlled?

10.Calculate the theoretical and actual % yield for the reduction of 50.0 mg 4-t-butylcyclohexanone (MW = 154.3 mg/mmol) with excess NaBH4 to obtain 30.0 mg of product (MW = 156.3 mg/mmol). Show your calculations with the proper units.

Explanation / Answer

1. In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during the non-stereospecific creation of a new stereocenter or during the non-stereospecific transformation of a pre-existing one. Thus, the reduction of 4-tert-butylcyclohexanone with sodium borohydride is a stereoselective reaction, wherein, it forms a mixture of cis- and trans- 4-t-butylcyclohexanol.

2. The reduction is done in methanol and not in water, because the compound is soluble in alcohols and certain ethers but reacts violently with water in the absence of a base.

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