The Aldol Condensation: Synthesis of Dibenzalacetone Research

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Aldol condensation is an necessary organic synthesis since the method leads to the formation of carbon-carbon bonds. The reaction mechanism involves a nucleophilic addition of enol or enolate ion to a carbonyl compound to structure a β-hydroxyaldehyde or β-hydroketone. Hydration follows to give a conjugated enone (Loudon).
In some cases, an aldehyde or ketone is reacted with an aromatic carbonyl compound which lacks an alpha-hydrogen in the presence of sodium hydroxide as a base. This outcomes in double mixed-aldol condensation commonly referred to as Claisen-Schmidt condensation. This is the process that is used to put together dibenzalacetone where there is condensation of acetone with two equivalent of benzaldehyde (Holleman).
Aim of the experiment

The objective of this experiment is to synthesis m-Aminoacetophenone from m-Nitrocetophenone.

Procedure

Part I Synthesis of Dibenzalacetone

Safety measures were put in place. The experiment was to be performed in a fume hood.

Ice water bath was prepared in a 250ml beaker.

The reaction mixtures were prepared using acetone, benzaldehyde, ethanol, and NaOH as the raw materials and following the procedure provided.

The reaction in (3) above was stirred while the flask open to air.

A yellow precipitate was formed from the reaction.

The mixture was warmed in 500C water bath for 10 min to increase yield.

The flask was placed in an ice water bath after formation of the precipitate.

The solids were collected using vacuum filtration.

The solid was washed using cold distilled water and rinsed with 8 drops of ethanol. The solid was after that dried using the vacuum for 10 minutes.

The dried solid was weighed and mass recorded.

Part II Recrystallization

60-700C hot-water bath was prepared in a 250 mL beaker. The temperature was monitored using a thermometer.

The crude product was transferred into a test tube, and 5 mL of ethanol added.

The solution was stirred using a glass rod until all the solids dissolved.

The solution was after that cooled in an ice-water bath for crystallization to occur.

The solids were collected using a vacuum filtration and mass recorded.

The solid was allowed to air dry for 15 minutes.

Mass of the dry crystalline products was recorded.

Part III: Testing the Melting Temperature of Dibenzalacetone.

A small amount of the powdered sample was obtained and packed in a capillary tube.

The Melt Temp was adjusted and connected to the power supply.

The capillary tube was inserted into one of the sample holders in the Melt Temp.

Melting temperature was recorded.

Data Table

Part I Synthesis of Dibenzalacetone

Mass of acetone

0.250g

Mass of benzaldehyde

1.000g

Mass of filter paper and funnel

7.660g

Mass of filter paper and product

9.399g

Mass of crude product

1.739g

Part II Recrystallization

Mass of filter paper and funnel

7.667g

Mass of filter paper and product

9.816g

Mass of recrystallized product

2.149g

Part III Melting Temperature of Dibenzalecetone: 90.30C

Theoretical Yield of the reaction: 1.007 g

Response to Questions

a. Mono-substitution will occur leading to formation of benzylideneacetone.

b. Mesityl oxide will be formed due to self-condensation of acetone.

c. Addition of high (50%) concentration of sodium hydroxide increases formation of

Sodium by-products due to side reactions.

d. Dibenzalacetone will dissolve since ethanol is a solvent.

a. AC15H12O

b. BC8H7NO2

c. DC10H9NO DC10H10O3

d. EC6H10O3FC7H10O2

f. GC8H12O3

Discussion

The reaction between the benzaldehyde and acetone catalyzed by sodium hydroxide is an example of Claisen- Schmidt reaction. Acetone has α-hydrogens on either side thus deprotonates to form a nucleophilic enolate anion. A β-hydroxyketone is after that formed after protonation of the alkoxide above through a base-catalyzed dehydration by the solvent. Since the benzaldehyde used is in excess, the condensation occurs on both sides resulting to formation of dibenzalacetone. This reaction is exothermic thus carried out in an ice-water bath. Lastly, ethanol is used in amount sufficient to dissolve the starting materials, benzaldehyde and benzalacetone formed as an intermediate (Haynes).

Conclusion

The aim of the experiment was achieved since yellow crystals of dibenzalacetone were obtained as the end product. Sources of error in the experiment could be from not following the steps provided carefully.

Works Cited

Haynes, William M. CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press, 2011.

Holleman, A.F., Wiberg, E. Inorganic Chemistry. San Diego: Academic Press, 2001.

Loudon, G. Marc. Organic Chemistry. 3rd ed. Redwood City, CA: Benjamin/ Cummings, 1992.

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