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ORGANIC CHEMISTRY ============
Organic Chemistry Laboratory - CH 201 (2010-2011) Experiment 2
Synthesis of Octyl Acetate Wilmer Patrick Bareng, Maria Kristine L. Bautista*, Kevin Arven Benin Department of Chemistry, College of Science University of Santo Tomas, Espana Street, Manila 1050 Date Submitted: August 09, 2010
________________________________________________________________________ Abstract: 1.3329 g of octyl acetate was synthesized synthesized from the Fischer reaction reaction process process using 2.0 ml of acetic anhydride and and 2.5 ml of n-octanol n-octanol alcohol. alcohol. The theoretical theoretical yield yield was 2.58 2.58 g of octyl acetate. acetate. The percent percent yield was 51.66%. It was a colorless liquid that had a fragrance of orange.
Keywords: Keywords: Esters, Esterification, Esterification, octyl acetate, acetic anhydride, systhesize, n-octanol alcohol ____________________________________________________________________________
1. Introduction
The tart taste of citrus was due to citric acid. The vinegar used in adobo was acetic acid. Both acids were carboxylic acids. When an acid combines with alcohol, an ester was formed. Esters have pleasant odors. The natural fragrance and flavor of many fruits are due to the presenc presencee of mixture mixture of esters esters.. Artifi Artificial cial flavoring flavoring essence essencess were were compos composed ed of mixt mixtur ures es of este esters rs sele select cted ed so as to dupl duplic icate ate the the flav flavor or and arom aromaa of natura naturall frui fruits ts (Mendoza, Religioso, 2001). Esters were among the widespread of all naturally occurring compounds. The chemical industry uses esters for a variety purposes. Ethyl acetate, for instance, was commonly used solvent (McMurry, 2008).
2 A type of esterification and the process of forming an ester by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst were called Fischer esterification. RCO2H + HOR′ carboxylic acid alcohol
RCO2R′ + ester
H2O water
Carboxylic acids are organic acids characterized by the presence of a carboxyl group. Carboxylic acids include formic acid, aceitc acid, benzoic acid, butyric acid, salicylic acid and anthranilic acid. An alcohol was any organic compound in which a hydroxyl group (OH) is bound to a carbon atom of an alkyl or substituted alkyl group. Alcohols include isopropyl alcohol, ethanol, octyl alcohol and methyl alcohol. Most alcohols can be refluxed with carboxylic acids in the presence of sulfuric acid to produce an ester. Esters of acetic acid can be prepared in a more efficient manner by using acetic anhydride, rather than acetic acid, as the non-alcohol reactant shown in the equation below, CH3C(O)OC(O)CH3 + HOR′ acetic anhydride alcohol
→
CH3CO2R′ acetate ester
+ CH3CO2H acetic acid
In this experiment, n-octanol alcohol and acetic anhydride will be used to prepare an ester, octyl acetate via the Fischer reaction and calculate its percent yield.
2. Experimental Section
Two dry test tubes labeled A containing octyl alcohol and B containing anhydride were placed in an ice-water bath. A concentrated H2SO4 was added continuously in test tube B and well mixed using a dropper. While keeping both tubes in an ice bath, the contents of the test tube B was added slowly to test tube A. The tube was constantly swirled. The resulting mixture was transferred in a reflux set-up. Boiling chips were added to it and the
3 water bath was heated at 80oC for 15 minutes. After heating, the hot bath was removed, cool for a minute and the contents were poured in a small beaker containing a cube of crushed ice.
Figure1. Reflux set-up The resulting mixture was transferred in a separatory funnel containing 15mL saturated NaHCO3 solution. The cease forming of bubbles were waited and the funnel was secured with the cap, then it was turned upside down. The stopcock was opened to prevent the formation of the gas inside. Gently swirled and the two layers were allowed to separate. Turn upside right and removed the cap. The lower layer which is the aqueous layer was discarded. The extraction was repeated with another 15mL NaHCO3. After that, the extraction was repeated again but with 15mL saturated NaCl solution. The organic layer was transferred into a clean, dry beaker with half spatula of anhydrous Na2SO4 and decanted. The final product was weighed and the percent yield was calculated.
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Figure2. Adding the mixture.
Figure3. The separated mixture in the separatory funnel
3. Results and Discussion
The first objective of this work was to prepare octyl acetate via the Fischer reaction, by mixing together the 2.5mL octyl alcohol and 2.0 acetic anhydride with 5 drops of concentrated H2SO4 as catalyst, it was heated at constant 80 o C for 15 minutes using a reflux set-up. The concern was to keep the reaction at reflux temperature to prevent it from evaporating. The group, then, poured the contents in a small beaker with a cube of crushed ice which purposed was to hydrolyze any excess unreacted acetic anhydride remaining after the esterification was completed. The resulting mixture was transferred to a separatory funnel to enable the group to visually see the separation between two immiscible liquid phases and due to differences in their densities, the group can separate the lower layer from upper layer. The organic layer was extracted twice with 15ml NaHCO3. The base neutralizes remaining acids and helps to remove traces of acetic acid. Then, the organic layer was extracted with 15ml saturated NaCl solution. The salt helps to break emulsions. If water alone were used, the two layers would not separate easily. The upper layer was the
5 ester, which was a water-insoluble volatile liquid. The lower layer was a water solution of sulfuric and acetic acids, and should be removed and discarded. The organic layer was transferred to a clean, dry beaker with half spatula of anhydrous Na2SO4 which purposed was to dry an organic liquid. It was decanted, placed in a clean vial and weighed.
The final objective of this experiment was to determine the percent yield of the obtained ester. The reaction below shows that, A + B C + D, which C represents the ester and D represents the carboxylic acid. CH3(CH2)6CH2OH + (CH3CO)2O CH3CO2C8H17 + CH3COOH
Density
n-octanol
Acetic
Octyl
alcohol
anhydride
acetate
0.8270
1.081
0.885
Acetic acid
1.049
(g/ml) Table 1. Density of each compound.
To obtain the limiting reagent, the n-octanol alcohol and acetic anhydride were computed. The computation shows that, 0.8270 g/ml CH3(CH2)6CH2OH
x 2.5 ml CH3(CH2)6CH2OH
x 1 mol/ 130 g
CH3(CH2)6CH2OH = 0.015 mol CH3(CH2)6CH2OH 1.081 g/ml (CH3CO)2O x 2.0 ml (CH3CO)2O x 1 mol/ 102 g (CH3CO)2O = 0.021 mol (CH3CO)2O which represents that the n-octanol alcohol was the limiting reagent because it has the smallest value of mole. To calculate the theoretical yield of octyl acetate,
6 0.015 mol CH3(CH2)6CH2OH x 1 mol CH3CO2C8H17 / 1 mol CH3(CH2)6CH2OH x 172g CH3CO2C8H17 / 1 mol CH3CO2C8H17 = 2.58 g CH3CO2C8H17
Wt. of vial w/ cap
Wt. of vial w/ cap Wt. of octyl acetate and octyl acetate
14.9128g
16.2457g
1. 3329g
Table 2. Weight of the vial and octyl acetate
The percentage yield of octyl acetate was 51.66% based on the obtained and calculated data which, 1.3329g/ 2.58g x 100 = 51.66%.
4. Conclusion
The final product which was octyl acetate was obtained and the final product yielded 1.3329 g of octyl acetate. The theoretical yield of octyl acetate from 172 g/mole at 0.015 moles would have been 2.58 g octyl acetate. Therefore, the percentage yield of octyl acetate was 51.66%.
5. References For Books 1. E.E., Mendoza, T.F., Religioso. Chemistry 2nd edition. SIBS Publishing House Inc.: Philippines (2001) p. 387-388.
2. J., McMurry. Organic Chemistry 7th edition. Brooks/Cole: USA (2008) p. 808
