Download   Spring 2015 CH 421  Name ________________________________________    1. Consider the structures of vanillin and vanillyl alcohol.  

 Spring 2015 CH 421 Name ________________________________________ Pre‐lab 1: NaBH4 Reduction of Vanillin (to be completed and handed in prior to the start of lab) 1. Consider the structures of vanillin and vanillyl alcohol. a. Which compound do you expect to be more polar? b. Which compound do you expect to have a higher Rf value by silica gel TLC? 2. In this week’s lab, you will determine an optimal mobile phase with which to monitor your reaction. Consider the two mobile phases 1:1 hexanes:ethyl acetate and 4:1 hexanes:ethyl acetate. a. Which is mobile phase is more polar? b. If you wanted to achieve the highest Rf for your vanillyl alcohol product, which would you choose? 3. Alcohols are the most common solvents for a NaBH4 reduction. However, the solvent used in this week’s experiment in 1M NaOH. Considering the functional groups present on vanillin, draw the production from the reaction of vanillin and NaOH. The pKa of the phenol in vanillin is ~10, and the pKa of water is 15.74. 4. The sodium borohydride (NaBH4) should be added in small portions to the reaction mixture since the reduction of carbonyls with this reagent is: a. Endothermic b. Exothermic 5. Borohydride acts as a(n): a. Nucleophile b. Electrophile 6. If the reduction reaction went to about 90% completion (i.e. about 10% of vanillin is still left), both vanillin and vanillyl alcohol would be isolated by precipitation from water, since they are both insoluble in water. Considering their physical properties and the methods of purifying compounds that you learned last semester, list two different methods that could potentially be employed to purify vanillyl alcohol from vanillin: a. b. 7. If the progress of this reduction reaction was monitored by IR, which of the following would be observed? a. Disappearance of a peak at 3300 cm‐1 and appearance of peaks at 1030 cm‐1 and 1720 cm‐1 b. Disappearance of a peak at 1720 cm‐1 and appearance of a peaks at 1030 cm‐1 and 3300 cm‐1 c. Disappearance of a peak at 1030 cm‐1 and appearance of peaks at 1720 cm‐1 and 3300 cm‐1 d. None of the above 8. Which peak from the 1H NMR of vanillin will disappear upon its conversion to vanillyl alcohol? Indicate the chemical shift rounded to the tenths digit. (Note the other peaks may be shifted, but they are still present in the product.) 9. Complete the table below. Where a line is drawn through a box, you do not need to include that information. Name
formula
MW
(g/mol)
vanillin
500.
NaBH4
_____
1M
NaOH
_____
vanillyl
alcohol
mass
(mg)
1M aq.
solution
_____
Theor.
mass =
mmol
equiv
d (g/mL)
vol
(mL)
mp
(°C)
bp
(°C)
1.0
_____
___
0.50
_____
___
___
___
1.2
_____
4.0
___
___
_____
_____
___
Lit. mp
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