Nucleophilic Acyl Substitution: the Synthesis of Esters

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Nucleophilic Acyl Substitution: The Synthesis of Esters
Razon, Valjean Paulo Mella
Rico, Fatima Sarah Rogel
Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines
Department of Food and Nutrition, College of Home Economics, University of the Philippines, Diliman, Quezon City 1101 Philippines


------------------------------------------------- The purpose of this experiment is to observe the synthesis of esters (also known as esterification), to understand the chemical processes that ester synthesis undergoes, and to know the optimum conditions needed for high yields. Esterification is a Nucleophilic Acyl Substitution Reaction
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However, the proton that left replenishes that acid catalyst to help repeat the mechanism for other molecules. The general mechanism of Nucleophilic Acyl Substitution could be simplified and shown by Figure 3 and the specific mechanism of the Fischer Esterification reaction that ensues in the experiment is portrayed by figure 4. (John McMurry, 2007) Figure 3 Nucleophylic Acyl Substitution Reaction Mechanism

Figure 4 Fischer Esterification Mechanism (Gunawardena, 2009) Practically, the procedure involves the heating a mixture of an alcohol and a carboxylic acid in the presence of an acid catalyst to yield an ester and water as end product. The reaction is reversible and the position of equilibrium depends on the reaction conditions. An excess of the alcohol favor the formation of the ester. While the presence of water drives the reaction backwards. (John McMurry, 2007) This concept of driving thereaction forward makes use of Le Chatelier’s principle states that “When an equilibrium system is subjected to change in temperature, pressure, or concentration of reacting species, the system responds by attaining a new equilibrium that partially offsets the impact of change.” (Petrucci, 2010) The structure of the reagents greatly affects the rate of Esterification. Presence of bulk groups on the alpha carbon or the site of the reaction causes esterification to slow
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