The Aldol Condensation Reaction: Preparation of Benzalacetophenones

...

= 0.618g

Mol of acetophenone = 0.618/120

= 0.00515 mol

1 mol of acetophenone react with 1 mol of 3-nitrobenzaldehyde

0.00515 mol of acetophenone react with 0.00515 mol of 3-nitrobenzaldehyde

Therefore, 3-nitrobenzaldehyde is limiting reagent.

Theoretical yield = 5.1026x10-3 x 253

= 1.2910g

=

Percentage yield = (actual/theoretical) x100

= (3.0807/1.2910)x100

= 238.63%

After recrystallization,

Percentage yield= (1.2575/1.2910) x 100

= 97.41%

Melting point

1st trial = 146.0°C

2nd trail = 146.0°C

3rd trail = 146.0°C

Average = 146.0°C

DISCUSSION:

From the experiment, the limiting reagent is the 3-nitrobenzaldeyde. The theoretical mass is calculated by referring to the mole of the 3-nitrochalcone. From the result obtained, the product seems to be pure enough by comparing the actual melting point, 146°C with the theoretical melting point that around 146°C. Errors may occur during the filtration process by using the Buchner funnel vacuum filtration. The pressure used to collect the solid is too high until the filter paper form holes that can pass through the solid with the liquid into the conical flask. This then will make the actual yield mass will decrease. To make sure there is no error in weighing the product, the solid must be dry at least overnight to evaporate all the water moisture. From the NMR result the 1H doublet signal was observed with frequency of 8.55Hz. From the literature review, the frequency of signal for trans compound is between 8.10-7.85Hz, so that it is proven that the compound yield is that trans-compound. This frequency is compared to cis-compound frequency that is lower, 7.55Hz

Conclusion:

The aldol condensation was successful done with the percent yield is 97.41% and from the NMR result the 1H doublet signal was observed with frequency of 8.55Hz. the melting obtained is 146°C which the same with the theoretical value.

Questions:

1. Write the mechanism of the reaction.

2. How do you confirm that the product is pure? Explain.

To confirm the purity of the product yield, the melting point of the product were taken and been compared with the theoretical value. The closer the value of actual melting point to the theoretical value, the higher the purity of the product. The confirmation also been done by H1 NMR spectrum that will give the structure of the compound.

3. Why the ethanol is used during crystallization?

Ethanol was used because it has lower boiling point than the water and the by-product with impurities can dissolve in ethanol. When the ethanol is vaporized, the by-product together with the impurities will evaporate too and leaving only the pure product.

References:

1)Retrieve from http://en.wikipedia.org/wiki/File:Vanillin2.svg

2) Donal L . Pavia ; Gary M. Lampman;George S Kriz;Randall G Engel , A microscale approach to organic laboratory techniques , fifth edition , published by Belmont/Cole , Cengage Learning ,[2013] , page : 863

3) T.W.Graham Solomons and Craig B.Fryhle;Organic Chemistry,tenth edition,published by Wiley[2011],page:744,746 and 749.

Pre-laboratory preparation:[pic 2]

Laboratory techniques:

The techniques involves in this experiment is filtration and Crystallization.