Essay, Pages 5 (1064 words)
The name of this reaction is called the Perkin’s reaction. The reaction was first used by William Perkin to create phenylcinnamic acids (Johnson). It is very similar to the aldol condensation which is followed by elimination. In this reaction E and Z isomers of phenylcinnamic acid are created using benzaldehyde and acetic anhydride. The intermediate product is acetic phenyl acetic anhydride. Benzaldehyde is an aromatic compound that
The reaction involves the use of benzaldehyde with acetic anhydride which gave the phenylacetic acid which would be used with in the farther steps of the reaction to produce the E and Z phenylcinnamic acid.
The mechanism for this reaction can be seen in figure 1. Table 1 includes all spectroscopic values for both E and Z isomers of phenylcinnamic acid. The IRs for both E and Z can be seen in figure 2 and 3. The NMR can be seen in figure 4 and 5, while the mass spec can be seen in figure 6. According to the experimental IR spectroscopy for the E isomer of phenylcinnamic acid the peaks of the wavenumber were at 2952, 2518 1672 and 1426 cm-1.
The peak at 2952 presents the double bond CH stretch for the alkene carbon. The peak at 2518 presents the carboxylic acid –OH peak. The peak at 1672 could present the carbonyl group.
The aromatic ring peaks are around 1600 and 1426-1492. Different values could be seen for the z isomer. The wavenumbers for the IR spectroscopy are 3412, 3247, 1687 and 1552 cm. The value at 3412 presents the carboxylic acid –OH peak. The peak at 3247 presents the –CH that is part of the double bond.
The value at 1687 presents the carbonyl group. The aromatic ring has two peaks at around 1600 and 1552. The H NMR peaks for the E-phenylcinnamic acid is at 7.05, 7.20, 7.37 and 7.76. The peak at 7.05 is a triplet, this represents the presents the proton c that is attached to the benzene that is being split by protons B, which have equal energy and resonance.
The peak at 7.20 is the proton attached to the carbon with the double bond. It is been split by multiple protons in near it. The 7.37 peak is the other aromatic ring hydrogens. And finally the 7.76 peak is the proton attached to the Oxygen is being split by the nearby aromatic ring hydrogens. The NMR peaks for Z-phenylcinnamic acid is at 2.58, 7.09, 7.40, and 7.54. 2.58 may be an impurity or the NMR solvent. 7.09 is the proton attached to the carbon with the double bond. 7.40 is a multiplet which means the benzene ring hydrogens are splitting each other and the 7.54 is a multiplet which is the carboxylic proton that is being split by the nearby aromatic group. The M/Z spectra for both E and Z isomers the base peak is 179 and the molecular ion peak is 224
The synthesis of E and Z phenylcinnamic acid had been created somewhat successfully. The theoretical yield was supposed to be a total of 2.22 g for both the E and Z isomers together. The experimental was determined to be 1.30g and 0.03g. The total was 1.5 grams, which let the yield to be 60.4%. Even though there was a decent yield most of the product was impurities. There were a few concerns that would make a compound not as pure as it should be. The first indicator that the showed the compound was not pure was the melting point. The theoretical melting point for the E isomer was 172-174oC and the melting point of the Z isomer was 162-164. The experimental melting points were found to be 164-168 for the E isomer and 155-160 for the Z isomer. Another reason why the melting points may be lower is because the products may not have been dried for allotted time therefore the melting point was affected by the moisture still in the products.
The IR spectra did not show much in interferences, perhaps it was a small contributor to lowering the melting point and the overall yield. However there was an issue with the peak for the OH of the carboxylic acid and the –CH peak of the double bond not being as broad and strong compared to the literature. This could possibly because the entire product was not completely converted to the phenylcinnamic acid. The reactants or intermediates may have been still present in the product because after recrystallization of E product white clumps of were found and the theoretical product of E was to look like sharp crystals. The NMR values showed that the peaks were around 7.0-7.8. These are confirmed by comparing them to the theoretical NMR spectra. However for both E and Z there were peaks at the around the 3.0 range which was not present in the theoretical NMR spectra. The peaks at around 2.0 are solvents used to run the NMR.
This could confirm that the impurities were in fact present in synthesis, which confirms why the melting point is not closer to the theoretical value and why certain peaks on the IR spectra are not as what they should be. The impurities could be possibly being water because that is a common impurity that occurs around the 3.0 range. This could have been prevented by drying the products for longer times than suggested and then taking an accurate reading on the melting point and yields. Other techniques could have been employed to insure that the product is not carrying any water. The use of flash chromatography could help separate the products. Another technique that could bused to remove the impurities is the rotary evaporator which can remove the solvents and impurities leaving behind the product.
In this experiment two compounds were successfully synthesized. The products were E and Z phenylcinnamic acids and synthesized using the Perkin reaction. However due to impurities the yield and purity of these two products was high enough. The Yield of this reaction was 60.4% and the melting point for the E product was 164-168 and Z product was 155-160. To confirm the successful synthesis of the product IR, NMR and GCMS were used. These spectra confirmed the existence of the products however they also showed the impurities that were present which caused them to look slightly different than the theoretical spectra.