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Synthesis Of Dibenzalacetone

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Autor:   •  March 7, 2011  •  1,231 Words (5 Pages)  •  1,644 Views

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Experiment2: Preparation of Dibenzalacetone

Aim:

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 MW (g/mol) Amt. Used Mol. mp (K) bp (K) density(g/cm^3)

acetone R11, R36, R67, S9, S25, S26 58.08 0.24 g 0.004 178.2 329.4 0.79

benzaldehyde R22, S24 106.13 0.82 g 0.008 247 451.1 1.0415

ehtyl acetate R11, R36, R66, R67, S16, S26, S33 88.11 2 ml per gram n/a 189.55 350.25 0.897

NaOH R35,S22, S26, S38, S45, S62, s24/25 39.997 0.4 g 0.01 591 1663 2.1

Ethanol R11, S2, S7, S16 46.07 2 ml n/a 158.8 351.6 0.789

Dibenzalacetone n/a 234 g/mol n/a n/a 379 unknown unknown

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

Procedures:

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 вЂ" 109 (Celsius) Lit. BP = 110 вЂ" 111 (Celsius)2

Infrared spectrum table3:

*the IR spectrum of dibenzalacetone is attached

Absorption (per cm) 3024 2363 1649 1600 1338-981

Intensity medium, sharp medium, sharp 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.

Discussion

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 О±-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 О±-carbon of the acetone in our experiment gets deprotonated easily in NaOH revealing an О±-carbon with a lone pair of electron attached to it. This О±-carbon is a very good nucleophile, a very good lewis acid and is extremely reactive. In other word we have turned our acetone into an anion. This anion likes to attack and form a covalent bond with a carbonyl carbon. This is due to the positive nature of carbonyl carbon and the electronegativity of the oxygen , most of the electron in a carbonyl molecule is around the oxygen thus leaving the carbon bare and susceptible to nuecleophilic attack. As a result of this attack, a molecule is yielded with both aldehyde and alcohol functional groups, hence the name aldo reaction. The product

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