Preparation of Fruit Flavors (Pear) Abstract. In this experiment an assigned Ester is prepared, particularly n-Propanol. The Preparation was done via Fischer reaction. In this reaction, a reflux set-up is required. The reflux set-up was used in the liquid-liquid extraction. After adding an immiscible solution to the compound containing n-Propanol, the mixture now will have two layer: the Organic and Aqueous layer. The organic layer is the extract needed and its % yield is computed resulting to 58. 3% INTRODUCTION
Many of the processed foods that you buy today come with an ingredient label that lists “artificial flavors” as one of the key ingredients. Artificial flavors are simply chemical mixtures that mimic a natural flavor in some way. Anything that we smell has to contain some sort of volatile chemical — a chemical that evaporates and enters a person’s nose (The evaporated chemical comes in contact with sensory cells in the nose and activates them. In the case of taste, a chemical has to activate the taste buds.
Taste is a fairly crude sense — there are only four values that your tongue can sense (sweet, salty, sour, bitter) — while the nose can sense thousands of different odors. Therefore most artificial flavors have both taste and smell components. Any natural flavor is normally quite complex, with dozens or hundreds of chemicals interacting to create the taste/smell. But it turns out that many flavors — particularly fruit flavors — have just one or a few dominant chemical components that carry the bulk of the taste/smell signal. Many of these chemicals are called esters.
Esters have the structure of -COOR. Instead of the alcohol portion of thecarboxylic acid (-COOH), there is an ether portion. The low boiling, volatile esters are known for their “fruity” smell and flavor. They are used in artificial flavorings. (Operational Organic Chemistry, John W. Lehman, Third Edition, Prentice Hall, 1999). The preparation of the food flavours are done with the use of Fischer reaction or Fischer Esterification. Fischer Esterification is a special type of esterification by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction was irst described by Emil Fischer and Arthur Speier in 1895. In this experiment, the Fischer esterification will make the acid and alcohol reactants to be in equilibrium with the assigned ester, n-Propanol, to prepare an artificial Pear flavoring. The n-Propanol will be refluxed with acetic anhydride and with concentrated Sulfuric acid as the catalyst. The product is isolated using a combination of techniques. EXPERIMENTAL A. Preparation Two dry test tubes labeled A and B, containing 2. 5 mL n- Propanol and 4. 0 mL acetic anhydride respectively, were placed in an ice-bath.
Concentrated sulfuric acid was cautiously added into test tube B. While both test tubes are in the ice-bath, the contents of test tube B were added drop-wise into test tube A. The test tube was swirled constantly. The resulting mixture was transferred into a reflux set-up. Boiling chips were added and heated in a water bath at 80°C for 15 minutes. After 15 minutes, the hot bath was removed, cooled for a minute and the contents were poured in a small beaker containing a cube of crushed ice. B. Work up The resulting mixture was transferred in a separatory funnel containing 15 mL saturated NaHCO3 solution.
The bubbles were waited to cease then the funnel was secured with the cap. The funnel was gently swirled to avoid forming emulsion. The two layers were allowed to separate. The cap was removed and the lower layer was discarded. The extraction was repeated with another 15 mL NaHCO3. After the lower layer was discarded again, a 15mL saturated NaCl solution was added into the remaining layer. The organic layer was transferred into a clean, dry beaker with half spatula of anhydrous Sodium Sulfate. The final product was decanted and the final product was weighed. The % yield was calculated and sealed.
RESULTS AND DISCUSSION Before the experiment, the Limiting reactant was computed between n- Propanol and acetic anhydride to obtain the theoretical yield: n- Propanol + Acetic Anhydride ——– Propyl Acetate + Acetic Acid With corresponding densities n- Propanol: 0. 8035 g/mL; Acetic Anhydride: 1. 081g/ mL; Propyl Acetate: 0. 886 g/mL; Acetic Acid: 1. 049 g/mL. Now for the computation of Limiting reactant: ? mol of n- Propanol = 2. 5 mL n-Propanol x (0. 8035g/ml n-propanol) x 1mol/60g = 0. 0335 mol ? mol of Acetic Anhydride = 4. 0 mL Acetic Anhydride x (1. 081 g/mL Acetic Anhydride) x 1mol/ 102g = 0. 424 mol The Limiting reactant is n- Propanol. (0. 00335 mol) For the Theoretical yield: ? Theoretical yield = 0. 0335 mol n-Propanol x (1mol propyl acetate/ 1 mol n- propanol) x 102g/mol propyl acetate = 3. 417g This means that the Ester obtained will most likely have a weight of 3. 417g. Now to compare with the actual Ester obtained from the experiment. Weight of Ester (Obtained with the use of Analytical balance): 1. 9935g ? % Yield = (Actual yield/ Theoretical yield) x 100% ? % Yield = (1. 9935g/ 3. 417g) x 100% = 58. 3% In the experiment, the n-Propanol underwent Fischer esterification to prepare an artificial fruit extract.
The reaction mixture was refluxed in order to thermally accelerate the reaction by conducting it at an elevated temperature. The addition of concentrated sulfuric acid is important in Fischer reaction because, it acts as an acid and dehydrating agent which is important in protonation of Oxygen atoms present in the mixture. The swirling of the separatory funnel must be done gently because too hard will cause the mixture to emulsify. The mixture should create two layers as the funnel is swirled gently. The extraction with saturated NaCl is to remove the bulks of water remaining in the mixture.
The extraction with sodium bicarbonate is to remove the excess acids from the mixture. The mixing with anhydrous sulfate is to dry the mixture from the water. CONCLUSION The Lewis or Bronsted acid-catalyzed esterification of carboxylic acids with alcohols (n – Propanol) to give esters is a typical reaction in which the products and reactants are in equilibrium. The equilibrium may be influenced by either removing one product from the reaction mixture (in the experiment, removal of the water by liquid-liquid distillation or absorption by molecular sieves) or by employing an excess of one reactant (Acetic Anhydride).
At the start of Fischer reaction, a proton transfer from sulfuric acid (acid catalyst) to the carbonyl group of acetic anhydride, making it electrophilic (electron-loving). The oxygen atom from n-Propanol (alcohol) attacks the electrophilic Carbon of the carbonyl group creating a tetrahedral intermediate. A proton transfer from the oxonium ion to second moldcule of n- Propanol gives an activated complex. Protonation of one of the hydroxyl groups in the activated complex gives a new oxonium ion (removing of OH).
Through several extractions with the use of sodium bicarbonate and saturated sodium chloride will remove the neutral water molecules from the oxonium ion. After the water loss and subsequent deprotonation, the reaction will give its product, the Ester.
REFERENCES Lehman, J. (2001). Operational Organic Chemistry, Third Edition. Prentice Hall: USA. Solomons, G. ;amp; Fryhle, C. (2008. Organic Chemistry, 9th Ed. Wiley India: USA. Atkins, P. (2007). Physical Chemistry. Oxford Publishing: New York, USA. Morrison, R. , ;amp; Boyd, R. (1992). Organic Chemistry, 6th Ed. Prentice Hall of India: India.