Synthesis of Dibenzalacetone

Topics: Aldehyde, Carbonyl, Aldol reaction Pages: 5 (1396 words) Published: May 21, 2008
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. substanceHazards, risks and safety practicesMW (g/mol)Amt. (K)bp (K)density(g/cm^3) acetoneR11, R36, R67, S9, S25, S2658.080.24 g0.004178.2329.40.79 benzaldehydeR22, S24106.130.82 g0.008247451.11.0415

ehtyl acetateR11, R36, R66, R67, S16, S26, S3388.112 ml per gramn/a189.55350.250.897 NaOHR35,S22, S26, S38, S45, S62, s24/2539.9970.4 g0.0159116632.1 EthanolR11, S2, S7, S1646.072 mln/a158.8351.60.789

Dibenzalacetonen/a234 g/moln/an/a379unknownunknown

Theoretical Yield:
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%

Product characteristics
BP = 107 – 109 (Celsius) Lit. BP = 110 – 111 (Celsius)2

Infrared spectrum table3:
*the IR spectrum of dibenzalacetone is attached
Absorption (per cm)30242363164916001338-981
Intensitymedium, sharpmedium, sharpvery strong, sharpvery strong, very sharpall strong and sharp Descriptionsp and sp2 C-H streches, alkene, arene. This confirms the two rings and 2 double bonds in our moleculealdehyde 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...
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