NaBH4 Reduction of Vanillin

Spring 2015 CH 421 Name ________________________________________ Section ________ Post‐lab 1: NaBH4 Reduction of Vanillin (to be completed and handed one week after the experiment was conducted) 1. Synthetic vanillin can be prepared from eugenol, an essential oil found in cloves. Transition‐metal catalyzed isomerization of eugenol provides isoeugenol. What specific reagents are required to convert isoeugenol to vanillin? (NOTE: we learned two different methods in CH250 that could work for this transformation. Just provide one.) 2. When humans consume alcoholic beverages, the enzyme alcohol dehydrogenase catalyzes the conversion of ethanol to acetaldehyde. Acetaldehyde is then metabolized to acetate, catalyzed by the aldehyde dehydrogenase enzyme. The coenzymes NAD+/NADH are required for both steps (NAD = nicotinamide adenine dinucleotide). The two‐step conversion of ethanol to acetate is shown below. Considering the structures shown, answer the following questions. (HINT: refer to Chapter section 10.8 in McMurry on oxidation‐reduction in organic molecules.) a. Is ethanol oxidized or reduced when it is converted to acetaldehyde? b. Is acetaldehyde oxidized or reduced when it is converted to acetate? c. Is NAD+ oxidized or reduced when converted to NADH? 3. The coenzymes discussed in Problem 2 (NAD+/NADH) perform redox chemistry in our bodies. Draw arrows to show the flow of electrons in the following NADH ketone reduction mechanism. NOTE: only the nicotinamide fragment of the NADH molecule is shown below; and H‐Enz+ represents a proton source from another enzyme involved in this biochemical reduction reaction. H Enz+
O
R1
OH
R2
R1
H
Enz
R2
O
O H H
H2N
H2N
N
N
(NADH)
(NAD+)
4. Considering what we know about the mechanism of a NaBH4 reduction (either from the lab handout and/or from McMurry 17.4), draw the products of the following benzaldehyde reductions, indicating specifically where deuterium is incorporated in each of the molecules. 5. The NaBH4 reduction of (R)‐3‐methylcyclohexanone, shown below, generates two products. a. Draw the structures of the products. b. What is the relationship between the two products – are they enantiomers, diastereomers, or the same? 6. Once the reduction is complete as judged by TLC, you add dilute HCl to the reaction mixture. Besides quenching any excess NaBH4 remaining, the HCl also reacts with your product in solution. a. Draw the structure of the product of the reaction above. b. In the procedure, it states to acidify your reaction mixture and collect the resulting solids. If you did not add the dilute HCl, would you expect the product to precipitate from solution (YES or NO)? c. Why or why not? (HINT: think about the acid/base forms of your product and their water solubilities.) 7. In the lab introduction, it states that LiAlH4 is a more reactive (i.e. stronger) reducing agent than is NaBH4. In one or two sentences, explain WHY this is true. HINT: think about bond strength and how that is influenced by electronegativity and/or atomic size.