Experiment2: Preparation of Dibenzalacetone
Using the cabon-cabon bond making ability in carbonyl chemistry, Dibenzalacetone is synthesized from 2 equivalent of benzaldehyde and 1 equivalent of acetone in a base catalyzed reaction.
Physical Data1: *detailed risk and safety phrases are attached. substance
Hazards, risks and safety practices
R11, R36, R67, S9, S25, S26
R11, R36, R66, R67, S16, S26, S33
2 ml per gram
R35,S22, S26, S38, S45, S62, s24/25
R11, S2, S7, S16
Limiting reagent: acetone (0.004 mol)
Presuming 100 % of limiting agent makes dibenzalacetone
Dibenzalacetone (100% yield) = 0.004 mol * 234 g/mol = 0.936 gram The theoretical yield of dibenzalacetone is 0.936 gram
In a 50 ml conical flask sodium hydroxide (0.4g, 0.01 mol), distilled water (2 ml) and ethanol (2ml, 95%) were mixed into a clear solution. The solution was then cooled to room temperature. Benzaldehyde (0.8ml; 9.82g, 0.008mol) was then added to the solution followed by addition of acetone (0.3ml; 0.24g, 0.004mol) and formed into a thick yellow solution. The flask was then swirled gently and constantly for 5 minutes. This turned into a fluffy precipitate as the flask was swirled. After 5 minutes of constant swirling, the flask was swirled once or twice every minute for 10 minutes thereafter. Ethanol (95%) was cooled in ice bath while the fluffy precipitate in the 50 ml conical flask was collected using a small buchner funnel. The fluffy precipitate was washed with distilled water (approximately 500 ml) followed by ethanol (approximately 2ml, 95%). The washing produced a clear filtrate solution and a yellow precipitate. The washed precipitate was then left to air dry for a week in a clean 50 ml beaker forming a lumpy yellow solid. Which was then weighted and recrystallised in ethyl acetate (approximately 2ml) to afford dibenzalacetone, a shiny powedery yellow solid ( 0.4377g, 46.8%, m.p 107-109, literature m.p. 110-1112).
Product calculations for Adol formation of Dibenzalacetone
Weight of the receiver flask = 16.2662 g
Received flask + product = 16.7039 g
Nett weight = 0.4377 g
Theoretical yield =0.936 g
Percentage yield = 46.76%
BP = 107 – 109 (Celsius)
Lit. BP = 110 – 111 (Celsius)2
Infrared spectrum table3:
*the IR spectrum of dibenzalacetone is attached
Absorption (per cm)
very strong, sharp
very strong, very sharp
all strong and sharp Description
sp and sp2 C-H streches, alkene, arene. This confirms the two rings and 2 double bonds in our molecule
aldehyde C-H strech, aldehyde shouldn't be present but aldehydes are very similar to ketone which is present.
C=O stretch. This is a very useful peak as it is very diagnostic which also confirms the presence of ketone.
C=C stretch, This could be from the alkene and benzene ring in the molecule. A very strong intensity indicates presence.
A lot of different things are absorbed at this region thus although the signals are strong, it's best ignored.
The key to this experiment is the aldol reaction4 that results in a C-C bond forming reaction. From observation it seems this reaction can be used to synthesis very large organic molecules. The concept of this reaction revolves around the idea having the α-carbon of an aldehyde or ketone attacking the carbonyl carbon of another aldehyde or ketone. The result of this attack is a new C-C bond being formed.
The α-carbon of the acetone in our experiment gets deprotonated easily in NaOH revealing an α-carbon with a lone pair of electron...
Please join StudyMode to read the full document