REG NO.: 21519648
DATE PRAC DONE: 20/03/2018
DATE SUBMITTED: 03/04/2018


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AIM: To synthesize dibenzalacetone from benzaldehyde and acetone by aldol condensation.

INTRODUCTION:Aldol condensation is characteristic reaction of aldehydes and ketones having Alpha hydrogen atom. In this reaction, aldehydes or ketones are warmed with dilute NaOH or Na?CO?.Alpha hydrogen atom in carbonyl compounds is acidic in nature, as enolate is resonance stabilized. Hence base removes Alpha hydrogen atom in carbonyl compound to form enolate, which attacks on carbonyl carbon of other molecule to form intermediate. This is further protonated to form ?-hyroxy aldehyde or ketone, which on heating loses water molecule to form ?, ?-unsaturated aldehyde or ketone.


Sodium hydroxide (NaOH) Ethanol (C2H5OH) Benzaldehyde (C7H6O) Acetone (C3H6O) Benzaldehyde-Acetone (C17h14O) PROCEDURE:
In a 250 mL beaker, 4g of solid NaOH was dissolved in 40mLof water.

30 mL of 95% ethanol was added.

The solution was stirred and let to cool down.

4.0380g of benzaldehyde and 1.5 mL of acetone was placed in 100 mL beaker, content were mixed to obtain a homogeneous solution.

Approximately half of the benzalaldehyde-acetone solution was then added to the hydroxide solution and the solution was stirred for 10 minutes, the remaining benzaldehyde-acetone solution was added and the solution was stirred for another 20 minutes.

Using the vacuum filtration, the yellow solid was filtered, press dried and transferred to a clean beaker.

The solid was transferred into a beaker and 20mL of 95% ethanol.

To dissolve the solid, the beaker was placed on water bath, then in ice bath to recrystallize the product.

The crystals were filtered and weighed in an analytical balance, and the mass was recorded.

The percentage yield was calculated to be 67.88%


Calculation of the number of moles of acetone and benzaldehydeBenzaldehyde
Mole of C7H6O = 4.2 g C7H6O × 1 mol C7H6O106.13 g C7H6O
= 0.03958 mol C7H6O
Mole of C3H6O = 0.79 g C3H6OmL × 1.5 mL× 1 mol C3H6O58.08 g C3H6O =0.0204 molDetermination of the limiting reagent:
For benzaldehyde: 0.03958 mol2 = 0.01979
For acetone: 0.02040 mol1 = 0.02040
Therefore the limiting reagent is benzaldehyde, because it is used up completely in the reaction.

Calculation of the theoretical yield
Mass of C17H14O = 0.03958 C7H6O × 1 mol H17H14O2 mol C7H6O × 234.31 g C17H14O1 mol H17H14O = 4.6370 g C17H14O
Percent yield
% yield = Actual yield Theoritical yield × 100 % = 3.0257g4.6370 g × 100 % = 65.25 %
In this experiment aldehyde reacts with itself in the presence of acetone and the base NaOH. Acetone is used as the enolate forming a compound, adding to the benzaldehyde followed by the dehydration to form a benzal group. As for the low yield (65.25%), it was caused by the crystals being wasted in the beaker and some in the filter paper used to dry them. The NaOH (catalyst) and aldehyde should be added first, then the acetone. If the acetone goes in first, it could do aldol condensation on itself, in which enolate anions of acetone just attack neutral acetone carbonyls. This would yield a different product.

The aim for the experiment was to synthesize dibenzalacetone from benzaladehyde and acetone by aldol condensation. From the results obtained, they show that dibenzalacetone was successfully produced in this experiment. From the calculated number of moles of both reactants, the limiting reagent (benzaldehyde) was determined by dividing each moles by coefficient of each reactant. Moles of benzaldehyde were used find the moles of dibenzalacetone. By multiplying these moles by the molar mass of dibenzalacetone the mass of dibenzalacetone (which is the theoretical yield) was obtained to be 4.6370 g. By dividing the actual mass (3.0257g) of dibenzalacetone weighed and multiplying by 100, the percentage yield was calculated to be 65.25 %.

Organic Chemistry Portal. Aldol Condensation. (Accessed 23 March 2018).

Studymoose. Aldol synthesis of dibenzalacetone. (Accessed 23 March 2018).


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