ALDOL REACTION. SYNTHESIS OF TRANS-p-ANISALACETOPHENONE

1. Weigh 1 g of sodium hydroxide1 and place it in a test tube. Add 1 mL of water, stopper the

test tube, and gently swirl the tube until complete dissolution of solid is achieved. As sodium

hydroxide dissolves, the solution may become hot. Allow the solution to cool to room

temperature.

2. Place 1.0 mL of p-anisaldehyde and 1.0 mL of acetophenone in a 25 mL pear shape flask,

and add 3 mL of 95% ethanol. Place a stir bar in the flask and stir the solution for 1 min. Using

a Pasteur pipet, add to the flask 5-7 drops of the 50% sodium hydroxide solution. Stir the

resulting mixture for 30 min at room temperature (Fig. A).

A. B.

3. Transfer the solution into a 25 mL Erlenmeyer flask and cool it in an ice bath. If crystals do

not form, scratch the liquid-air interface with a spatula to induce crystallization. It can take up

to 20 min for crystals to form. Collect the product by vacuum filtration, wash it with 1-2 mL of

cold ethanol, and air-dry the crystals (Fig. B).

1 Sodium hydroxide is hygroscopic, so avoid unnecessary exposure of the pellets to air.

4. Transfer the crude product into a clean, dry 25 mL Erlenmeyer flask, add 5-6 mL of methanol

and heat the mixture to just below boiling point. All solid should dissolve upon heating (Fig.

C).

C. D.

5. Cool the solution in ice. Isolate the obtained crystals by vacuum filtration on a Hirsch funnel

and rinse them with 1.5-2 mL of cold methanol. Air-dry the product, calculate the percent yield,

and determine the melting point (Fig. D).

6. Perform the test for unsaturation using bromine in dichloromethane and the Baeyer test.

Obtain IR spectrum for the product. To prepare the IR sample, dissolve a few milligrams of the

product in dichloromethane (about 0.5 mL), load 2-3 drops of this solution onto Teflon tape,

and allow the solvent to evaporate.

The following is to be included in your laboratory report, along with your response to the

exercises below:

IR Exercise

On the IR spectrum of the product provided below (Fig. 1), identify the following signals:

C=C stretching of aromatic rings;

C=O carbonyl stretching (hints: Carbonyl group signal is one the most intense. C=O absorption

occurs at lower frequency in conjugated systems);

Ar-O stretching.

Figure 1. IR-spectrum of trans-p-anisalacetophenone.

NMR Exercise

Below is a 400 MHz 1H NMR spectrum of the expected product of your aldol reaction (Fig. 2).

1) On the spectrum, label the signals arising from the alkene protons. Calculate the J coupling constant for the signals. Does the calculated coupling constant meet with your

predictions?

2) On the spectrum, label the signals arising from the protons on the para-disubstituted phenyl ring of the product. Calculate the J coupling constant for the signals.

You should be able to identify the signals using the integration trace on the spectrum, and from

your prediction of splitting patterns.

Equation for calculating coupling constant:

J = distance between split peaks (in ppm) times 400 Hz/ppm

500750100012501500175020002500300035001/cm

15

30

45

60

75

90

105

%T

16

58

.67

15

91

.16

15

71

.88

15

10

.16

12

57

.50

12

11

.21

11

70

.71

11

53

.35

FTIR Measurement

Fig

ure

2.

1H

NM

R S

pec

tru

m o

f trans-p

-an

isal

acet

op

heno

ne.

9.5

9.0

8.5

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

Chem

ical S

hift (p

pm

)

3.0

011.1

0

3.841

6.9296.9517.4137.4527.5027.5217.5617.5797.5957.6177.7867.8258.0218.040

Me

O

O

8.0

7.5

7.0

Chem

ical S

hift (p

pm

)

11.1

0

6.9296.951

7.4137.4527.502

7.521

7.5797.595

7.617

7.7867.825

8.0188.0218.040