exp 13- fr 2 nucleuphilic acyl substitution,the synthesis of esters

EXPERIMENT 13- NUCLEUPHILIC ACYL SUBSTITUTION: THE SYNTHESIS OF ESTERS HONEYLYN A. HERBIETO Department of Mining, Metallurgical and Materials Engineering, University of the Philippines, Diliman, Quezon City FEBRUARY 6 AND 11, 2014 FEBRUARY 21, 2014 Abstract Esters are known to be compounds that yield odor. They are made from the reaction of alcohols and carboxylic acids in a reaction known as Fischer Esterification Reaction which involves nucleuophilic acyl substitution. The carbonyl carbon is first protonized with acid allowing the alcohol to attack it. The objective of this experiment is to synthesize 2- pentyl ethanoate from acetic acid and excess amount s of 2-pentanol. Laboratory expe rimental procedures such as reflux and distillation are done I order to obtain a crude ester which should be clear indicating loss of contamination . The result of the experiment yielded 0% ester and 100% alcohol after distillation. 2-pental has a lower boiling point than 2-pentyl ethanoate allowing it evaporate first and be contained on the receiving flask of the distillation set-up. The lack of ester can be accounted by non-completion of the reaction, presence of water or contaminants. Keywords: ester, Fischer Esterification Reaction, 2-pentyl et hanoate I. Introduction Ester, compounds who have pleasing aromas, is known to be a derivative of carboxylic acid [3] . It can be synthesized from the reaction of a carboxylic acid and an alcohol with the addition of a catalyst like heat and highly concentrated acids like H 2 SO 4 . The reaction is known as the Fischer Esterification Reaction, where the oxygen of the alcohol is added to the carbonyl group making an ester however, the reaction is reversible, allowing the reaction to reach equilibrium with unreacted reactants [1] . The esterification reaction involves nucleuophilic acyl substitution reaction where a nucleophile is added to a polar C=O bond and having the intermediate of the reaction to eliminate one of the substituents bonded to the carbonyl atom [2] . The objective of this experiment is to synthesize an ester specifically 2-pentyl ethanoate which yields a strong banana odour. II. Methodology From the list of reactants found at the laboratory manual table, to synthesize 2-pentyl ethanoate, 6.57 mL of 0.06 mol 2-pentanol and 3.43 mL of 0.06 mol acetic acid were mixed in a 25-mL round bottom flask. Boiling stones should then be added to the solution, avoiding the use of calcium carbonate boiling stones as it reacts with the acidic medium of the solution. 2-3 drops of concentrated H 2 SO 4 should then be added while swirling the round bottom flask gently. The mixture should then be refluxed for 45-60 min by attaching it to a reflux condenser (Fig. 1); the mixture was then cooled to room temperature and transferred to a 30-mL separatory funnel. The round bottom flask was rinsed with cold water, adding the washings to the separatory funnel. The flask was again washed with water, adding the washings to the separatory funnel, repeating the procedure until the aqueous layer is twice that of the organic layer. The mixture was then shaken and allowed to stratify. To hasten separation, saturated NaCl solution was added. Solid NaHCO 3 was added until the acid was removed completely which was indicated by the lack of effervescence.

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