lab Flashcards
How did you remove the majority of the triphenylphosphine oxide byproduct of the Wittig reaction from your desired alkene?
Filtration - triphenylphosphine oxide is poorly soluble in ether
What byproducts were removed from your Wittig reaction product by the column chromatography and
recrystallization steps?
Triphenylphosphine oxide.
Why did you use potassium tert-butoxide as the base, as opposed to the “usual” Wittig base nbutyllithium?
all of the above
The NMR spectrum of the product from the Wittig reaction is given to the
right. Use it to answer the following questions:
Measure the coupling constant between HC and HD
16.2 Hz
There is a small peak at δ 7.15. To what does it correspond?
A small amount of cis isomer as byproduct.
Which frequency corresponds to the C=O stretch in the ethyl-4-nitrocinnamate IR spectrum?
1711 cm-1
Vanillin has an acidic OH and an electrophilic aldehyde group that could conceivably react with sodium
hydroxide. However, in the aldol reaction, you added the NaOH directly to the solution of vanillin and
acetone, rather than pre-treating acetone with base. Why could you do this successfully?
The reaction of NaOH with phenol OH groups and aromatic aldehydes is reversible, and the
reaction is driven to the most stable product.
Your aldol condensation procedure calls for refluxing vanillin in acetone and NaOH for an hour. What
might happen if you didn’t heat the reaction, or heated it for too short a time?
A mixture of aldol products and hydroxyketone intermediates would form.
You used a 1:1 mixture of hexane and ethyl acetate for your aldol TLC, which allowed you to separate
the vanillin from the product. What would happen if you used hexane as elution solvent?
The polar vanillin and product would stay at the baseline of the plate
The downfield (double bond) region of the NMR spectrum of the product from the aldol reaction is given below. Use it to answer the following questions: Measure the coupling constant between HE and HF (labelled on the spectrum).
16.2 Hz
What is the expected coupling pattern for HC, and where can its peak be found on the NMR spectrum?
Doublet of doublets, 7.07 ppm
What would be the major difference between the IR spectrum of your aldol product and an IR
spectrum of a mixture of vanillin and acetone?
Both a) and b)
a) There would be two C=O stretches in the starting mixture, but not in the product.
b) The C=O stretch in the product would be at lower frequency than acetone, as it is a highly
conjugated ketone.
You’re performing your esterification, and you lose your strip of Nafion. What could you use as a
substitute that would still give good ester yield?
conc. H2SO4.
In the esterification experiment, the organic phase of diethyl ether is washed with 2 portions of 5%
NaOH. Where would you discard these washings?
Aqueous waste container.
In the esterification experiment, the organic phase of diethyl ether is washed with 2 portions of 5%
NaOH. Why did you wash with aqueous base?
To remove unreacted acetic acid from the mixture.
Glacial acetic acid is (as the name suggests) an acid. Why did you need the Nafion strip to perform
the esterification reaction?
AcOH isn’t a sufficiently strong acid to drive the equilibrium forward.
Why can you not use this reaction to make a secondary amine?
The secondary amine product is more nucleophilic than the primary amine reactant, so
over-reaction will occur
Why do you wash the dichloromethane solution of your reductive amination product with sodium
bicarbonate, rather than dilute aqueous HCl?
The amine product will be protonated by acid and remain in the aqueous layer as a salt.
