Fischer Esterification of Acetic acid with Isopentyl Alcohol PDF

Preview

Summary

lab report...

Description

Experiment IX: Fischer Esterification of Acetic acid with Isopentyl Alcohol

Abstract: The purpose of this experiment was to form the carboxylate ester isopentyl acetate (the smell of bananas and honey bee pheromone) by separating the organic compound of a carboxylic acid through the Fischer Esterification process. In this process, the carboxylic acid used, Acetic acid, reacted with an alcohol, Isopentyl alcohol, and an acid catalyst of sulfuric acid to produce the ester, Isopentyl Acetate, and the byproduct water. Within the reaction vial, blue silica beads were added to absorb the water during esterification through the water-jacketed reflux condenser. The experiment utilized a hot sand bath that heated the reaction for 90 minutes. The reaction was then removed to cool down and went through liquid-liquid extraction with the addition of diethyl ether to obtain the organic layer. The organic layer was then placed through gravity filtration with anhydrous sodium sulfate. The product was obtained and massed after the culture tube was left to dry and evaporate in the hot sand bath. The remaining product of isopentyl acetate had a final mass of 451mg and a 47 percent yield. Procedure: The use of the water-jacketed reflux condenser, liquid-liquid extraction, and gravity filtration was completed with the given steps from the Poulos, Z.J., “Fischer Esterification of Acetic acid with Isopentyl Alcohol37,” in Organic Chemistry I- A Laboratory Manual for the Health Science Major,” Fall 2019; Hayden-McNeil: Plymouth, MI, 2019, pp 143-150. There were no changes made to this experiment. Reactions:

Acetic acid

Isopentyl Alcohol

Isopentyl Acetate

Data and Calculations: Mass of Culture Tube

11.557g

Mass of Culture Tube w/ Product

(11.557x1000)= 11557mg 12.008g

Isopentyl Acetate

(12.008x1000)= 12008mg (12008mg – 11557)=

Theoretical Yield

451mg 800L x (0.8104mg/ 1L)= 648mg 648mg x (1mol/ 88.15mg) x 1000 = 7.35mmol 7.35mmol x (130.1mg/ mmol)=

Actual Yield (%)

956mg (451mg / 956mg) x 100 = 47%

Discussion and Conclusion: Fisher esterification was the main method used in this experiment. The initial step is having an active catalyst generated, the carboxylic acid is protonated, so that the carbonyl becomes more electrophilic. In this experiment, the isopentyl alcohol transferred its electrons to the hydrogen of the carboxyl group in the acetic acid. Water leaves the group, since there is an intermolecular proton transfer after the nucleophilic addition of alcohol occurred. Due to the loss of water, it breaks the tetrahedral intermediate, where Csp2 becomes Csp3, causing the non-nucleophilic acid catalyst to regenerate, resulting in a hydronium ion and carboxylate ester, isopentyl acetate, to form. In this experiment, the reaction vial containing a mix of acetic acid and isopentyl alcohol, had to be submerged in a hot sand bath and connected to a water-jacketed reflux condenser, that was also connected to the sink where water was slowly dripped out of. Within the reaction, 8-10

blue silica gel beads impregnated with anhydrous cobalt (II) chloride CoCl2, was added. With the beads absorbing the water, the equilibrium can be pushed to the right, favoring the ester formation. The reaction took 90 minutes, and by the time of completion, the blue beads were now clear and the mixture remained a clear color throughout the reflux. After cooled in a beaker of room temperature water, the reaction mixture was transferred and rinsed with diethyl ether. 2mL of saturated sodium bicarbonate solution was added to the reaction to neutralize the acid catalyst and forms sodium acetate. Two layers were formed, where the bottom aqueous layer was removed through liquid-liquid, leaving the top ethereal organic layer in the culture tube. Another 2mL of aqueous bicarbonate was added to the organic phase, and the extraction was repeated for a total of 3 extractions. After the organic layer was washed with deionized water and transferred, it was gravity filtered and dried through a column of anhydrous sodium sulfate. After left to dry and evaporate in the hot sand bath, the product had a mass of 451mg with a percent yield of 47%. Due to a low percent yield, there could have been many sources of errors throughout this experiment. One of the errors, could be the amount of blue silica beads added. It is possible that not enough beads were used, so that not many could absorb all the water, resulting in a lower final mass. Another error could have been that during the esterification, the reaction was not ran for a total of 90 minutes or more. When analyzing the IR spectrum of Acetic acid, there are three significant peaks. At peak 1288cm-1, there is a Carbon Oxygen Hydrogen bond (C–OH) of the hydroxyl group. There is a Carbon Oxygen double bond (C=O) from the aldehyde bond at peak 1705cm-1 and at 3038cm-1, there is a Carbon Hydrogen Bond (C–H). The IR spectrum of Isopentyl alcohol has an Oxygen Hydrogen bond stretch at 3323cm-1 for the alcohol functional group. There is also at peak at 1057cm-1, showing a Carbon Oxygen (C–O) bond. For Isopentyl Acetate, the structure is very

similar to acetic acetate with similar bonds of Carbon Hydrogen (C–H) and Carbon Oxygen double bond (C=O) at peaks 2958cm-1 and 1739cm-1. At 1232cm-1 however, there is a strong Carbon Oxygen bond (C–O) in the ester....