Two Step Synthesis of Cinnamate Ester Sunscreen
Analog
4/3/2008Chem 213Joshua Bailey
Introduction
Esters derived from trans-4-methoxycinnamic acid are effective absorbers of UV
radiation. These types of compounds are highly conjugated, absorb UVB radiation between 290
– 320 nm, and are oil soluble. UVB radiation can cause dermal cell DNA damage, which causes
skin cancer. There are to objectives to this experiment. The first is to synthesize trans-4-
methoxycinnamic acid. Synthesis of ethyl trans-4-methoxycinnamate is the second objective of
the experiment. Trans-4-methoxycinnamic acid will be analyzed by melting point, infrared
spectroscopy, and nuclearmagnetic resonance. Ethyl trans-4-methoxycinnamate will be analyzed
by infrared spectroscopy.
2
Data Analysis
Mass of trans-4-methoxycinnamic acid: 0.85 g
Mass of ethyl trans-4-methoxycinnamate: 0.20 g
MELTING POINT
Compoundmp (°C) Literarure melting point (°C)
Trans-4-methoxycinnamic acid 173 173-175
IR of Trans-4-methoxycinnamic acidPeak (cm -
1 ) Represents Lit Value Peak (cm -1 ) 1702 C=O (carboxylic acid) 1700-17252848 O-H (carboxylic aid) 2500-32001633 C=C 1620-16801260 C-O (ester) 1000-13001601 C=C (aromatic) 1440-1625
IR of Ethyl trans-4-methoxycinnamate
Peak (cm -1 ) Represents Lit Value Peak (cm -1 ) 1703 C=O (esters) 1715-17301603 C=C 1600-16501260 C-O (ester) 1000-13001601 C=C (aromatic) 1440-1625
3
H+ NMR of Trans-4-methylcinnamic acid
Shift (ppm) Represent
0 HA
3.876 HC and HE
6.982 HB
7.003 HB
7.816 HD
7.837 HD
9.87 HF
4
5
6
Discussion
Benzaldehyde and malonic acid were dissolved in pyridine and heated to give the product
trans-4-methoxycinnamic acid. The reactants underwent a Verley-Doebner modification of the
Knoevenagei condensation, the reaction is shown in (figure 1).
The first step is the deprotonation of malonic acid by pyridine (figure 2).
After malonic acid has been deprotonated three different resonance structures can be drawn
displacing the negative charge over the molecule (figure 3).
7
Attack of benzaldehyde by the deprotonated malonic acid can now occur. Benzaldehyde bonds
to the middle carbon, and a proton transfer occurs (figure 4).
8
The Verley-Doebner modification of the Knoevenagei condensation reaction occurs in refluxing
pyridine. Carbon dioxide and the hydroxide are both expelled from the molecule to give trans-4-
methoxycinnamic acid (figure 5).
9
Trans-4-methoxycinnamic acid was converted to ethyl trans-4-methoxycinnamate in the
second part of the lab by the process of esterification. The net reaction is shown in figure 6.
The first step that occurs is the iodoethane is attacked by a lone electron pair on trans-4-
methoxycinnamic acid. If two electrons come in two must leave which results in I- being
expelled from the molecule (figure 7).
10
Oxygen now has a positive charge so the base, cesium carbonate, comes in and deprotonates
the compound to give ethyl trans-4-methoxycinnamate (figure 8).
All of the results obtained in lab suggests that both trans-4-methoxycinnamic acid and
ethyl trans-4-methoxycinnamate were successfully synthesized in lab. The melting point of
trans-4-methoxycinnamic acid was found to be 173°C and the accepted literature value is 173°C
- 175°C. The IR obtained for trans-4-methoxycinnamic acid showed the following peaks: C=O
(carboxylic acid), O-H (carboxylic aid), C=C, C-O (ester), C=C (aromatic). All of these
11
functional groups are present on trans-4-methoxycinnamic acid The H+ NMR obtained for
trans-4-methoxycinnamic acid showed the correct structure of the molecule (see data section).
The IR for ethyl trans-4-methoxycinnamate showed the following peaks: C=O (esters), C=C, C-
O (ester), and C=C (aromatic). Using all this data it was determined that the desired product
were successfully obtained.
Conclusion
The compounds trans-4-methoxycinnamic acid and ethyl trans-4-methoxycinnamate were
successfully synthesized. The melting point of of trans-4-methoxycinnamic acid was 173°C and
the literature value is 173°C - 175°C. The IR of both -4-methoxycinnamic acid and ethyl trans-
4-methoxycinnamate suggested that the desired products were obtained. The H+ NMR obtained
for trans-4-methoxycinnamic acid suggested that structure of the product was correct (see data
section).
References
Smith, Janice G. Organic Chemistry. 1st ed. New York: McGraw-Hill, 2006. 801.
Mohrig, Jerry R., Christina N. Hammond, and Paul F. Shatz. Techniques in Organic Chemistry. 2nd ed. New York: Craig Bleyer, 2006. IR table.
12
13