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Page 1
Effect of Reaction Conditions on the Aldol Reaction
Question:
How do reaction conditions of temperature and choice of base affect the
outcome of an aldol reaction?
Background
The aldol reaction is a very important means of making carbon-carbon bonds.
Under
basic conditions, the
protons of ketones, aldehydes, and esters may be removed to form
strong nucleophiles that can then add to another compound containing a carbonyl.
While
this can lead to a mixture of products, there are ways to favor formation of one product.
For example, if a ketone is mixed with an aldehyde containing no
protons, there is only
one possible nucleophile.
Furthermore, the aldehyde is a much better electrophile than a
ketone under these conditions, so the aldehyde serves as the electrophile.
An example of
such a “crossed Aldol” reaction is shown below:
N
O
+
H
O
NO
2
catalytic base
?
The outcome of any reaction depends on the reaction conditions.
Choices of solvents,
temperatures, and bases can lead to an effective or ineffective reaction.
In some cases,
these changes can even lead to different products being formed.
For example, in the
reaction above, there is the possibility that the product formed will be the aldol product; it
is also possible that the reaction will continue on to form the condensation product.
Your team will investigate two parameters:
temperature and choice of base.
You should
run the reaction at room temperature and 60
o
C, and you should compare the reaction
using sodium carbonate to the reaction with sodium hydroxide.
Based on your
knowledge of the aldol reaction, you should have a prediction of the expected product or
products.
After the reaction is complete, you should characterize the resulting compound
to determine its actual identity.
You might, for instance, choose to use any or all of the
characterizations that you learned throughout the course.
Pre-lab
:
Come up with a team plan for how to investigate reaction condition effects of the
aldol reaction. (Assume four people on your team.)
Draw the structures of the aldol product and the condensation product that would
form in this reaction.
Predict the proton NMR for each compound.
Re-write this general procedure below into a specific procedure you will follow,
including calculation of mass or volume for each reactant.


Page 2
Procedures
:
In a 25 mL roundbottom flask equipped with a spin bar, add 0.0010 mole
(___g, ___mL
given density=1.08g/mL) of 2-acetylpyridine and 10 mL of water.
(Always work with 2-
acetylpyridine in the hood.
Strong odor—do you recognize it?)
Stir the mixture
vigorously.
(Use a flat stirbar, not the triangular stirbar, for best stirring.)
In a separate
vial, dissolve 0.0010 mole (___g) nitrobenzaldehyde in a minimum amount of hot
methanol.
While still hot, add the solution of aldehyde into the vigorously stirring
mixture in the roundbottom flask.
Add 0.00025 mol (___g) of base (either sodium
carbonate or sodium hydroxide) dissolved in 5 mL of water.
Stir for one hour.
(If
heating, attach a reflux condenser to the reaction flask and heat in a hot water bath.
Do
not allow the water bath to exceed 65
o
C.)
Cool the reaction in an icebath and collect the
precipitate by suction filtration.
Wash the solid with water (3x 10mL.)
Allow the
product to dry for one week, and then obtain characterization data.
Results:
All characteristic data you obtained to determine the structure and purity of each product.
Yield data
Comments:
What product was isolated for your set of reaction conditions (or was only starting
material isolated?)
What data supports this conclusion?
Ask other students who used
different conditions about their conclusions.
How did the choice of temperature and base affect the outcome of the reaction?
Give a
rational explanation of these outcomes.
Calculate a theoretical yield of your product and determine the % yield of your reaction.
Conclusions:
The outcome of this aldol reaction is/is not affected by changing
temperature and base.


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