Synthesis of Dibenzalacetone by Aldol Condensation of Benzaldehyde and Lab Report

Synthesis of Dibenzalacetone by Aldol Condensation of Benzaldehyde and Acetone - Lab Report Example Under basic conditions, the carbonyl group of acetone having an alpha hydrogen atom is converted to an enolate ion (Mc Murry, 1999, pp. 939). The enolate ion thus produced is a strong nucleophile and attacks the carbonyl group of the â€Å"accepting partner†, which in this case is benzaldehyde (Mc Murry, 1999, pp. 939). An alkoxide is formed as a result of this nucleophilic attack. The alkoxide then undergoes protonation by H2O, forming a â€Å"neutral condensation product†, hydroxyketone. This undergoes dehydration in presence of NaOH, forming an enolate ion, hydroxyenolate, which then forms Benzalacetone by loss of a hydroxyl group. Benzalacetone also has alpha hydrogen, which again forms enolate ion under basic conditions, similar to the first step. This enolate nucleophilically attacks another Benzylaldehyde molecule. Subsequent reactions are similar to those already discussed, leading to the formation of dibenzalacetone, the final product. Thus, two molecules of be nzaldehyde and one molecule of acetone are required to form one molecule of dibenzalacetone. O O O CH3 – C – CH2 – H CH3 – C– CH2 – H – C – OH- Acetone Enolate ion- nucleophilic attack on benzaldehyde O OH O O- CH3 – C – CH2 – CH – CH3 – C – CH2 – CH – OH- ?-Hydroxyketone Alkoxide O OH O CH3 – C – CH- – CH – CH3 – C – CH = CH – Hydroxyenolate Benzalacetone O – CH = CH – C – CH = CH – Dibenzalacetone (iii) Experimental: Benzaldehyde (80  µl), acetone (29  µl), and ethanolic NaOH (1.0 ml) were used in this experiment. The reaction was carried out in a conical vial containing a magnetic spinvane, according to the procedure specified in the SC214 practical manual, page 41. Filtration of the product was done using a Hirsch funnel, and the Craig tube method was used for purification and recrystalliz ation of the product as per the SC214 practical manual, page 42. Melting point and IR spectrum were also obtained for the characterization of the product. (iv) Results: The weight and yield of the product (dibenzalacetone) are calculated as follows: (1) Calculation of mass of the product: Weight of glass= 37.458 g Weight of glass along with Dibenzalacetone crystals= 37.502g Therefore, mass of Dibenzalacetone crystals= 37.502 – 37.458 = 0.044g (2) Calculation of yield of the product: % Yield of Dibenzalacetone = Benzaldehyde is the limiting reactant in this experiment No. of moles of Dibenzalacetone= = = 0.001877 = 1.87 ? 10-4 moles No. of moles of Benzaldehyde= = = 0.000784 =7.84 ? 10-4 moles Since 2 benzaldehyde molecules are involved in each reaction, =7.84 ? 10-4/2 = 3.92 moles % yield of Dibenzalacetone= = = 0.477?100 = 47.7% Therefore, % yield of Dibenz