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SYNTHESIS OF ESTERS USING GREEN AND NON-GREEN CHEMISTRY Abstract Esters are a class of organic compounds with the general formula RCOOR’. Ester also contributes the flavor and aromas in fruits and flowers.
The esterification reactions will use in the procedure, which are the interaction of a carboxylic acid with an alcohol, aided by an inorganic acid catalyst (H2SO4).
Moreover, the green method will not use any catalyst but using heating source instead (microwave).
Based on the comparison of two methods, green chemistry is the effective method because reduce the consumption energy and less time consuming than the non-green chemistry preparation. Introduction Esters are among the most widespread of all naturally occurring compounds. Many simple esters are pleasant-smelling liquids that are responsible for the fragrant odors of fruits and flowers. Examples are benzyl acetate, which is finding in orange oil, and isopentyl acetate, which is the part of banana oil.
The ester linkage is also present in animal fats and in many biologically important molecules. Esters can be formed from both organic and inorganic acids and the process of producing an ester is called an Esterification. Esters of organic acids are usually colorless, neutral liquids, pleasant-smelling and generally insoluble in water but readily soluble in organic solvents. Esters are prepared synthetically in large quantities for commercial use as artificial fruit essences and other flavorings and as components of perfumes.
Esterification is used to derivatize carboxylic acids and other acidic functional groups. In a typical reaction, Esterification involves the condensation of the carboxyl group of an acid and the hydroxyl group of an alcohol, with the elimination of water (Konwar, 2008). Many Esterification reactions are slow and elevated temperatures are frequently used. Since the Esterification reaction is an equilibrium reaction, it may be necessary to remove the water generated during the reaction. The chemical industry uses esters for a variety of purposes.
Ethyl acetate, for example, is a common solvent found in nail-polish remover, and dialkyl phthalates are used as plasticizers to keep polymers from becoming brittle (Wilkes, 2005). They also have important medical uses. Ethyl nitrite is a diuretic and an antipyretic. The aim of this experiment is to compare the effectiveness between green and non-green chemistry of esterification by using the infrared spectroscopy and each percentage yield. Non-green chemistry will use acid catalyst in the reaction, but green chemistry will use microwave radiation instead of the acid-catalyst.
The preparation of banana oil will perform in this experiment to determine the effectiveness of green and non-green chemistry. Below is the general mechanism of esterification: Experiment Details A. Non Green method of preparation of Banana Oil Isopentyl alcohol was used to synthesize the banana oil. 15-mL of isopentyl alcohol was placed in a 100-mL round-bottom flask and 20 mL of glacial acetic acid was added. Then, swirl the flask and 4 mL of conc. H2SO4 was added carefully to the flask. A reflux condenser was set up to reflux the mixture for one hour, and then cool down the mixture to room temperature.
After the mixture was cooled down, the reaction mixture was placed in a separatory funnel followed by 55 mL of cold water to separate the lower aqueous layer. Then, extract the organic layer (upper layer) with 25 mL of 5% sodium bicarbonate solution twice and also extract the organic layer with 25 mL of water. Finally, add 5 mL of saturated aqueous sodium chloride to aid in layer separation which removes traces of water from the organic layer. Then, Draw off the lower aqueous layer and Pour the top organic layer into an Erlenmeyer flask and dry with 2 g of anhydrous magnesium sulfate. UOregon) The distillation was performed after the substance dried. Collect all distilled material but collect the fraction between 134 and 143 oC in a separate tared flask. Keep the receiver flask cold to reduce the vapor escaping into the lab environment. Finally, the product was weighed and the IR was obtained. (Umsl) First Process: Reflux CondenserSecond Process: Titration Third Process: Distillation B. Green method of preparation of Banana Oil Under the hood, 7. 0 mL of acetic anhydride was mixed with 8. 0 mL of 3-methylbutanol in the microwave.
Then, the sample was heated constantly at 100oC for 8 minutes. After that, the product was poured into a 100 mL beaker under the hood. Then, slowly add 25 mL of water and Titrate with 40. 0 mL of 2. 0 M NaOH. Finally, the product was weighed and the IR was obtained. Result Below is the table 1 that illustrates the data obtained from synthesis of banana oil using green and non-green chemistry followed by each percentage yield. Table 1: Data Obtained From Synthesis of Banana Oil Using Green and Non-Green Method | Green Method| Non-green Method|
Theoretical Yield (g)| 6. 26| 17. 966| Mass Obtained (g)| 9. 63| 8. 769| Percent Yield (%)| 65%| 49%| Figure 1 illustrates the reference IR of isopentyl alcohol was attached. Figure 2 and Figure 4 illustrate the first trial IR of non-green chemistry of banana oil were attached. Figure 5 illustrates the second trial IR of non-green chemistry of banana oil was attached. Lastly, Figure 3 illustrates the IR of banana oil in green chemistry was attached. Discussion/Analysis The preparation of banana oil was done by using non-green chemistry and green chemistry.
As said above, sulfuric acid was used for non-green while the green chemistry was only used the microwave to prepare the banana oil. There are three methods for non-green method, which are reflux condenser, titration, and distillation. First trial, the preparation was stopped after reflux the mixture and it was kept in the refrigerator for one week. After one week, the preparation was continued until the distillation and the IR was obtained also. According to the IR, Figure 2, it showed that lots of water contamination in the product compared to the reference IR (isopentyl acetate).
By knowing that, my group decided to do the second trial of banana oil preparation with non-green method and we put more drying agent in the first trial product. When the preparation was repeated, we stopped after titration process and kept in the refrigerated with drying agent for one week. And, the drying agent was also added in the first trial of banana oil preparation. In the 3rd week of experiment, the second trial of preparation was continued to the distillation process and followed by obtaining the IR of second trial preparation and the IR of product in the first trial with more drying agent.
According to those IR, it really showed the significant differences between first trial and second trial. Figure 5 showed less absorption of water contamination compared to the Figure 2 in the first trial. Even though we added more drying agent in the first trial product, the IR still showed more water contamination than the second trial preparation but the water got reduced when we kept the product with drying agent for one week (Figure 3).
By comparing these two trials, discontinue the preparation in the middle of the process had affect in the product which is water contamination. Due to the amount of time that we have in the lab, we couldn’t finish all steps for banana oil preparation with non-green method in one day. Therefore, the preparation of banana oil should be done in one day experiment for the future experiment to avoid lots of water contamination in the product and would have the better yield than this experiment (49%).
For green chemistry, the banana oil was prepared under the hood and using the microwave radiation. Within 8 minutes in constant temperatures (110oC) and titration with sodium hydroxide, the preparation of banana oil was done successfully. Figure 3 showed the evidence that the banana oil was prepared effectively because the IR was closed to the reference IR (isopentyl acetate). The percentage yield was 65% which higher than the non-green chemistry’s percentage yield.
The low percentage was due to the evaporation some the products when heating the substance in the regular microwave. If we used the microwave reaction vessel, maybe the mixture will not evaporate as much as we used the regular microwave. But, the IR really showed that the product was pure. Based on the result of two methods in preparation of banana oil, the green chemistry was really effective to use in real life. Beside is green, the process was done really fast compared to the non-green chemistry which can take more than one day if we use the large scale.
The benefits for using green chemistry are eliminated the need for using sulfuric acid as a catalyst, and ether for the extraction, eliminates the need for the distillation, and also reduces energy consumption. Performing the experiment using green chemistry also enabled easy product recovery, easy recycling, microwave-promoted heating, completion of the chemical reaction in a matter of minutes, compared to the hour of reflux required with conventional heating (Sanghi, 2003) After doing this experiment, the limitation of directions should provide for the future experiments.
The experiment time should be longer to finish the preparation of banana oil in non-green chemistry in order to have the high yield and pure products. For green chemistry, I believe that we should prepare in microwave that has temperature control and pressure inside which can reduce the evaporation when the mixture heated. Source possible of error that can be thinks of is the mixture was not reflux enough (less than 1 hour), Conclusion Isopentyl acetate was prepared by refluxing isopentyl alcohol with excess acetic acid and sulfuric acid.
The acetate was obtained by distillation in 49 percent yield and a boiling point of 134-143oC. The acetate’s structure was confirmed using IR spectra. The IR spectrum (Figure 5) shows a strong absorption at 1740 cm-1 consistent with a C=O stretching vibration. Isopentyl acetate was successfully synthesized using microwave radiations instead of sulfuric acid. The acetate was obtained by titration in 65 percent yield. Upon examination of the IR spectrum, it was found out that the product spectrum had similarities with the reference IR.
This indicated that the product obtained was in fact isopentyl acetate. References Konwar, Dilip. Esterification of Carboxylic Acids by Acid Activated Kaolinite Clay. Indian Journal of Chemical Technology: Vol. 15, January 2008: pp. 75-78. Retrieved June 9, 2010. <http://nopr. niscair. res. in/bitstream/123456789/872/1/IJCT%2015%281%29%20%282008%29%2075-78. pdf> Preparation of 3-Methylbytylacetate (Banana Oil) in the Microwave Oven. Uoregon. Retrieved April 10, 2010