Fisher Esterification Lab Report
April 04, 2014 Fisher Esterification
Introduction:
Esters are one of the most common derivatives of carboxylic acids and are widely distributed in both nature and industry. A Fischer Esterification is the formation of an ester and water from alcohol and an acid. It is the simplest means of synthesizing an ester and requires the reaction of a carboxylic acid and an alcohol. The general reaction of Fischer esterification is, CH3CO2H + ROH ↔ CH3CO2R + H2O (reaction1)
CH3COOH + ROH ↔ CH3COOR + H2O (reaction2) An alcohol (ROH in reaction 1) is a functional group containing a hydrogen, oxygen bond. Carboxylic acids (CH3CO2H in reaction 1) are characterized by a carbon, oxygen double bond, with one alcohol group and an alkyl or …show more content…
aromatic side chain. Esters (CH3CO2R in reaction 1) are identified by a carbon, oxygen double bond and an oxygen alkyl or aromatic group. Carboxylic esters often have pleasant odors and are used in foods and beverages to create flavors mimicking fruit. Depending on the ester synthesized smells such as banana, pineapple, or orange can be obtained. Reaction is a double displacement reaction. Carboxylic esters can be made by a variety of methods from the corresponding carboxylic acids. The simplest method to synthesize an ester is to react a carboxylic acid with an alcohol. This reaction is called Fischer esterification.it is a nucleophillic acyl substitution reaction carried out under acidic conditions. Carboxylic acids alone are not reactive enough to be attacked by neutral alcohols, but they can be made much more reactive in the presence of a strong acid, such as sulfuric acid. The mineral acid protonates the carbonyl group oxygen atom and gives the carboxylic acid a positive charge. Now positively charged, the carboxylic acid is much more reactive toward a nucleophillic attack by the alcohol. 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. They also have important medical uses. Ethyl nitrite is a diuretic and an antipyretic. Amyl nitrite is used in the treatment of asthma and epileptic convulsions as an antispasmodic. The reaction of a carboxylic acid with an alcohol is equilibrium, and therefore governed by the equilibrium constant. The equilibrium constant for esterification with primary alcohols is usually very close to unity; the equilibrium constant for the reaction shown below for the synthesis of ethyl acetate is 3.38.The equilibrium should be shifted to the right, namely to completion, by applying Le Chateliar’s principle. Keq = [Ester]/ [Acid] [ROH] = 3.38
Mechanism of the Fischer Esterification
Addition of a proton (e.g.: p-TsOH, H2SO4) or a Lewis acid leads to a more reactive electrophile. Nucleophilic attack of the alcoholgives a tetrahedral intermediate in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester.
Materials:
Unknown alcohol # 41, acetic acid, concentrated sulfuric acid, NM spectroscopy Saturated aqueous sodium carbonate (Na2CO3 (aq)), Granular sodium sulfate Hickman still head, Boiling chips, 25 ml round bottom flask, Assembled reflux apparatus, Stir glass rod, IR spectroscopy, Pasteur pipette
Procedure:
1. An empty 25 ml round-bottom flask was weighed.
2. Approximately 1.5ml of the alcohol was placed in the flask, and the flask was reweighed.
3. ~ 3ml of glacial acetic acid was added to occur the esterification reaction.
4. Three boiling chips were placed in the flask then 2 drops of concentrated sulfuric acid was added, which act as catalyst.
5. A reflux apparatus was assembled.
6. The assembly was places in the heating mantle and the reflux was heated for 70 minutes.
7. Then the reaction mixture was cooled down.
8. While stirring, 3 ml of 5% aqueous sodium bicarbonate was added.
9. The solution was stirred until the CO2 formation ceases.
10. The reaction mixture was shook gently, let that settled, and the lower aqueous layer was removed with a Pasteur pipet.
11. As much as of water as possible was removed with a Pasteur pipet, leaving the ester at bottom, and then a small amount of granular sodium sulfate was added to remove the water from organic layer. Then capped and let stand for 10-15 minutes.
12. A distillation apparatus was assembled using the Hickman still head.
13. The distillation assembly was paced in the heating mantle and was heated to ~180 degree Celsius. The acetate was distilled.
14. After the distillation, the acetate was transferred to a tared vial, and weighed.
15. The percent yield of ester from unknown was calculated.
16. An IR spectrum was obtained of a product. A sample for NMR analysis was submitted to instructor.
Table of Reagents
Compound
Molecular Weight (g/mol)
Density (g cm−3)
Structure
Melting Point (ºC)
Boiling Point (ºC)
1-pentanol
88.15
.811
-78
137-139
2-pentanol
88.148
.812
-73
119.3
Isopentanol
88.148
.8104
-
-117.2
131.1
Sulfuric Acid
98.087
1.84
10.0
290.0
Hexanol
102.17
.8136
-53 - 41
155 - 159
Sodium Bicarbonate
84.007
2.20
50.0
4-methyl-2-pentanol
102.174
.8075
-90
131.6
1,3-dimethylbutyacetate
144.21
.86
144
Anhydrous Sodium sulfate
142.04
2.664
884
1429
Acetic Acid
60
.8136
-53 - 41
158
Data
Unknown #21
Initial Weight
Final Weight
% Recovery of Ester
1.215 gram
0.67 gram
~55%
RESULTS
Weight of vial and unknown #41 = 30.01g
Weight of flask = 28.85g
Weight of product produced = 0.67g
Volume of unknown alcohol started = 1.5mL
Boiling Chips = 3 pieces
Density of alcohol (4-methyl-2-pentanol) = .8075 g/cm3
The mass (wt.) of 4-methyl-2-pentanol alcohol = 0.811.5 = 1.215g
% Recovery = (0.67g 1.215g) 100 = 55%
First, a 1.215 gm. of unknown alcohol #21 was obtained along with three boiling chips and flask weighing about 28.85gm. The 1.215 gm. sample of unknown # 41 was placed into a 25ml round bottom flask, and ~ 3 ml of was added into the flask to occur the reaction. Then the three pieces of boiling chips was added, then 2 drops of concentrated sulfuric acid was added to catalyze the reaction. The reflux apparatus was assembled, and then solution was heated on the heating mantle for 70 minutes. After the reaction occurred, the flask was removed from the heat and cooled down in room temperature and the 2ml of 5% aqueous sodium bicarbonate was added. The reaction mixture was stirred until the CO2 formed, then small amount of sodium sulfate was added to remove water from organic layer. The dry ester was then collected in the Hickman still head. The IR spectrum was obtained from the final product and Dr. Houston provided the NMR. The ester recovered weighed 0.67g and the percent recovered was ~ 55%. The percent yield may have been low because the entire condensed product could not be removed from the Hickman still. Although most of it could be removed using the bent Pasteur pipette, some may still have been stuck inside the still. The IR and NMR spectra was analyzed, the final product was identified as (1,3-dimethylbutyl) acetate and the unknown alcohol # 21 as 4-methyl-2-pentanol.
Discussion The product (Ester) was found to be (1-3-dimethylbutyl) acetate and the unknown alcohol #41 found to be 4-methyl-2-pentanol. The objective of this experiment was to efficiently perform a Fischer esterification of provided unknown alcohol # 41 and acetic acid to form water and ester, and to identify the ester using IR spectroscopy and NMR spectrum analysis and unknown alcohol #41. It was found that 0.67 grams of unknown ester was formed with a percent yield of 55%. This may have been low because not the entire condensed product could be removed from the Hickman still. Although most of it could be removed using the Pasteur pipette, some may still have been stuck inside the still. Also, some product may have lost when the liquid was transferred from the Hickman still into the vial. Some of the product may have also evaporated during the distillation. Some of the product could have been lost during the reflux process if the heat was too high, since the heat was continuously being adjusted during the process due to the mantles being old, hence the vapors would go past the condenser part and product would be lost decreasing the yield. To decrease this sort of error the heat should be kept at a low level. The product was confirmed by using IR and NMR spectroscopy. The reaction mechanism for this specific reaction was as follows: First the protonation of a carbonyl oxygen activates the carboxylic acid towards nucleophillic attack by the alcohol yielding a tetrahedral intermediate, in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester. The reaction is a nucleophillic acyl substitution carried out under acidic conditions of acetic acid. The alcohol used was 4-methyl-2-pentanol, which limits the ester to a side. After completing the esterification, it was found that 0.67 grams of (1-3-dimethylbutyl) acetate was formed with a percent yield of 55%. The product was confirmed as (1-3-dimethylbutyl) acetate using IR and NMR spectroscopy; therefore, the unknown alcohol # 41 is 4- methyl-2-pentanol. An ester normally has a carbonyl at 1740 cm-1. One of the really useful absorptions, found in the range 1680 - 1750 cm-1, the other really useful bond is the C-O bond also has an absorption in the fingerprint region varying between 1000 and 1300 cm-1. The strong and wide peak at 1165.4 cm-1 showed the carbon-oxygen single bond present in the compound. A strong peak at 1740 cm-1 implies the carbonyl (C=O) group. The IR spectroscopy graph of the final product of the unknown #41showed the characteristic of Ester at 1714.4 cm-1 (C=O), which was (20-40 cm-1) less than the normal peak of ester at 1740 cm-1, which was caused because of the presence of a broad alcohol (O-H) peak at 3300-2500 cm-1. The presence of O-H in final product was occurred due to contamination. The another source of error that caused the present of O-H peak was during the extraction of organic layer with bicarbonate, the water was not removed as much as possible. The extraction of organic layer was taken only once, which was supposed to extract two more times with bicarbonate to yield the more pure acetate. This may cause the more deposition of O-H on the final product. NMR spectroscopy is another great technique for determining the structure of organic compounds.
There were four signals present in the H1 spectrum at high field (right). The integration of protons was 1:3:2+1:3:6 (2+1 overlapping) in H1 spectrum, which implies there were 16 hydrogen present in the compound. Two signals were present at 0.9 and at 2 (singlet). The other two signals were present at 4.9 (multiplet) and 1.5 (looks multiplet because 2+1 integration was overlapping). The multiplicities of all signal clusters of H1 spectrum helped in determining the structure of compound. The signal at 4.9 indicates that the alkane group must be attached with electronegative compound that shifted alkane group by “2”, and the signal at 2 indicate the alkane group must be attached with carbonyl group. Thus, all the information collected from NMR suggested that the product of fisher esterification was (1,3-dimthylbutyl) acetate. A number of errors could have occurred in this experiment, which could have limited the amount of desired product yield. First, if not enough acid catalyst was used, protonation of the carbonyl group on the carboxylic acid would have been difficult to obtain. Second, if the temperature was too high in heating the mixture, some of the product could have been lost during the reflux
process.
Conclusion The purpose of this lab was to use the alcohol and acetic acid to produce an ester and then identify the unknown alcohol and the ester by IR and NMR spectrum analysis. Ester can be formed from both organic and inorganic acids and the process of producing ester is called an esterification. In the first part of experiment, the unknown alcohol #41 was mixed with acetic acid in 25ml round bottom flask, which was catalyzed by concentrated sulfuric acid to produce the desired ester and water. After the ester was isolated, a percent yield was calculated from the ester recovery. Then the unknown ester was identified as (1,3-dimethylbutyl) acetate by analyzing the IR and NMR spectrum, thus the unknown alcohol #41 was identified as 4-methyl-2-pentanol. It was found that 0.67 grams of unknown acetate was formed with a percent yield of 55%. The percent yield of ester was low because the entire condensed product may not be removed from the Hickman still. However most of ester was removed using the Pasteur pipette, some may still have been stuck inside the still. Some of the product may have also evaporated during the distillation. Some of the product could have been also lost during the reflux process if the heat was too high, hence the vapors would go past the condenser part, and product would be lost, decreasing the percent yield. To reduce this kind of error the heat should be kept at a low level and constant. After completing the esterification, the structure of ester was confirmed using IR spectrum that obtained from IR analysis lab and NMR spectra of ester from unknown alcohol provided by Dr. Houston. The IR spectroscopy graph showed the characteristic of carbonyl at 1714.4 cm-1 (C=O) strong absorption, and a broad O-H peak at 3300-2500 cm-1 decreasing the strong peak of normal ester by 20-40 cm-1, confirming the product as an ester that contained lost of alcohol. The presence of O-H in final product was occurred might be due to contamination. The another source of error that caused the present of O-H peak was during the extraction of organic layer with bicarbonate, the water might not remove as much as possible. The solubility of alcohol in water was not checked before the experiment, so the other reason for the O-H absorption in IR may be the alcohol soluble in water, which present in the final product. To avoid this kind of mistake, student should check the solubility of alcohol before the esterification reaction. The NMR spectroscopy have four signals and the integration of protons was 1:3:2+1:3:6. All this information suggested that the ester yielded was (1,3-dimethylbutyl) acetate; therefore, the unknown alcohol # 41 was 4-methyl-2-pentanol. The quantitative error was most likely due to product getting stuck in the apparatus. These errors most likely caused the change in end result (percent yield, IR spectrum). Different sources of error may have prevented a pure ester from being produced from unknown alcohol.
The experiment was successful with percent yield ~55% of ester from unknown alcohol, although the 100% yield of ester from the esterification reaction was not successful. The values of the major peaks on the IR spectrum, and the four signals and the integration of protons (1:3:2+1:3:6) present in NMR spectrum also corresponded to the theoretical values of the ester 1,3-dimethylbutyl. Therefore, it was concluded that this was the ester formed and the experiment was a success, because even though there was error, this was only for the percent yield of ester, not in its identity.
Introduction:
Esters are one of the most common derivatives of carboxylic acids and are widely distributed in both nature and industry. A Fischer Esterification is the formation of an ester and water from alcohol and an acid. It is the simplest means of synthesizing an ester and requires the reaction of a carboxylic acid and an alcohol. The general reaction of Fischer esterification is, CH3CO2H + ROH ↔ CH3CO2R + H2O (reaction1)
CH3COOH + ROH ↔ CH3COOR + H2O (reaction2) An alcohol (ROH in reaction 1) is a functional group containing a hydrogen, oxygen bond. Carboxylic acids (CH3CO2H in reaction 1) are characterized by a carbon, oxygen double bond, with one alcohol group and an alkyl or …show more content…
aromatic side chain. Esters (CH3CO2R in reaction 1) are identified by a carbon, oxygen double bond and an oxygen alkyl or aromatic group. Carboxylic esters often have pleasant odors and are used in foods and beverages to create flavors mimicking fruit. Depending on the ester synthesized smells such as banana, pineapple, or orange can be obtained. Reaction is a double displacement reaction. Carboxylic esters can be made by a variety of methods from the corresponding carboxylic acids. The simplest method to synthesize an ester is to react a carboxylic acid with an alcohol. This reaction is called Fischer esterification.it is a nucleophillic acyl substitution reaction carried out under acidic conditions. Carboxylic acids alone are not reactive enough to be attacked by neutral alcohols, but they can be made much more reactive in the presence of a strong acid, such as sulfuric acid. The mineral acid protonates the carbonyl group oxygen atom and gives the carboxylic acid a positive charge. Now positively charged, the carboxylic acid is much more reactive toward a nucleophillic attack by the alcohol. 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. They also have important medical uses. Ethyl nitrite is a diuretic and an antipyretic. Amyl nitrite is used in the treatment of asthma and epileptic convulsions as an antispasmodic. The reaction of a carboxylic acid with an alcohol is equilibrium, and therefore governed by the equilibrium constant. The equilibrium constant for esterification with primary alcohols is usually very close to unity; the equilibrium constant for the reaction shown below for the synthesis of ethyl acetate is 3.38.The equilibrium should be shifted to the right, namely to completion, by applying Le Chateliar’s principle. Keq = [Ester]/ [Acid] [ROH] = 3.38
Mechanism of the Fischer Esterification
Addition of a proton (e.g.: p-TsOH, H2SO4) or a Lewis acid leads to a more reactive electrophile. Nucleophilic attack of the alcoholgives a tetrahedral intermediate in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester.
Materials:
Unknown alcohol # 41, acetic acid, concentrated sulfuric acid, NM spectroscopy Saturated aqueous sodium carbonate (Na2CO3 (aq)), Granular sodium sulfate Hickman still head, Boiling chips, 25 ml round bottom flask, Assembled reflux apparatus, Stir glass rod, IR spectroscopy, Pasteur pipette
Procedure:
1. An empty 25 ml round-bottom flask was weighed.
2. Approximately 1.5ml of the alcohol was placed in the flask, and the flask was reweighed.
3. ~ 3ml of glacial acetic acid was added to occur the esterification reaction.
4. Three boiling chips were placed in the flask then 2 drops of concentrated sulfuric acid was added, which act as catalyst.
5. A reflux apparatus was assembled.
6. The assembly was places in the heating mantle and the reflux was heated for 70 minutes.
7. Then the reaction mixture was cooled down.
8. While stirring, 3 ml of 5% aqueous sodium bicarbonate was added.
9. The solution was stirred until the CO2 formation ceases.
10. The reaction mixture was shook gently, let that settled, and the lower aqueous layer was removed with a Pasteur pipet.
11. As much as of water as possible was removed with a Pasteur pipet, leaving the ester at bottom, and then a small amount of granular sodium sulfate was added to remove the water from organic layer. Then capped and let stand for 10-15 minutes.
12. A distillation apparatus was assembled using the Hickman still head.
13. The distillation assembly was paced in the heating mantle and was heated to ~180 degree Celsius. The acetate was distilled.
14. After the distillation, the acetate was transferred to a tared vial, and weighed.
15. The percent yield of ester from unknown was calculated.
16. An IR spectrum was obtained of a product. A sample for NMR analysis was submitted to instructor.
Table of Reagents
Compound
Molecular Weight (g/mol)
Density (g cm−3)
Structure
Melting Point (ºC)
Boiling Point (ºC)
1-pentanol
88.15
.811
-78
137-139
2-pentanol
88.148
.812
-73
119.3
Isopentanol
88.148
.8104
-
-117.2
131.1
Sulfuric Acid
98.087
1.84
10.0
290.0
Hexanol
102.17
.8136
-53 - 41
155 - 159
Sodium Bicarbonate
84.007
2.20
50.0
4-methyl-2-pentanol
102.174
.8075
-90
131.6
1,3-dimethylbutyacetate
144.21
.86
144
Anhydrous Sodium sulfate
142.04
2.664
884
1429
Acetic Acid
60
.8136
-53 - 41
158
Data
Unknown #21
Initial Weight
Final Weight
% Recovery of Ester
1.215 gram
0.67 gram
~55%
RESULTS
Weight of vial and unknown #41 = 30.01g
Weight of flask = 28.85g
Weight of product produced = 0.67g
Volume of unknown alcohol started = 1.5mL
Boiling Chips = 3 pieces
Density of alcohol (4-methyl-2-pentanol) = .8075 g/cm3
The mass (wt.) of 4-methyl-2-pentanol alcohol = 0.811.5 = 1.215g
% Recovery = (0.67g 1.215g) 100 = 55%
First, a 1.215 gm. of unknown alcohol #21 was obtained along with three boiling chips and flask weighing about 28.85gm. The 1.215 gm. sample of unknown # 41 was placed into a 25ml round bottom flask, and ~ 3 ml of was added into the flask to occur the reaction. Then the three pieces of boiling chips was added, then 2 drops of concentrated sulfuric acid was added to catalyze the reaction. The reflux apparatus was assembled, and then solution was heated on the heating mantle for 70 minutes. After the reaction occurred, the flask was removed from the heat and cooled down in room temperature and the 2ml of 5% aqueous sodium bicarbonate was added. The reaction mixture was stirred until the CO2 formed, then small amount of sodium sulfate was added to remove water from organic layer. The dry ester was then collected in the Hickman still head. The IR spectrum was obtained from the final product and Dr. Houston provided the NMR. The ester recovered weighed 0.67g and the percent recovered was ~ 55%. The percent yield may have been low because the entire condensed product could not be removed from the Hickman still. Although most of it could be removed using the bent Pasteur pipette, some may still have been stuck inside the still. The IR and NMR spectra was analyzed, the final product was identified as (1,3-dimethylbutyl) acetate and the unknown alcohol # 21 as 4-methyl-2-pentanol.
Discussion The product (Ester) was found to be (1-3-dimethylbutyl) acetate and the unknown alcohol #41 found to be 4-methyl-2-pentanol. The objective of this experiment was to efficiently perform a Fischer esterification of provided unknown alcohol # 41 and acetic acid to form water and ester, and to identify the ester using IR spectroscopy and NMR spectrum analysis and unknown alcohol #41. It was found that 0.67 grams of unknown ester was formed with a percent yield of 55%. This may have been low because not the entire condensed product could be removed from the Hickman still. Although most of it could be removed using the Pasteur pipette, some may still have been stuck inside the still. Also, some product may have lost when the liquid was transferred from the Hickman still into the vial. Some of the product may have also evaporated during the distillation. Some of the product could have been lost during the reflux process if the heat was too high, since the heat was continuously being adjusted during the process due to the mantles being old, hence the vapors would go past the condenser part and product would be lost decreasing the yield. To decrease this sort of error the heat should be kept at a low level. The product was confirmed by using IR and NMR spectroscopy. The reaction mechanism for this specific reaction was as follows: First the protonation of a carbonyl oxygen activates the carboxylic acid towards nucleophillic attack by the alcohol yielding a tetrahedral intermediate, in which there are two equivalent hydroxyl groups. One of these hydroxyl groups is eliminated after a proton shift (tautomerism) to give water and the ester. The reaction is a nucleophillic acyl substitution carried out under acidic conditions of acetic acid. The alcohol used was 4-methyl-2-pentanol, which limits the ester to a side. After completing the esterification, it was found that 0.67 grams of (1-3-dimethylbutyl) acetate was formed with a percent yield of 55%. The product was confirmed as (1-3-dimethylbutyl) acetate using IR and NMR spectroscopy; therefore, the unknown alcohol # 41 is 4- methyl-2-pentanol. An ester normally has a carbonyl at 1740 cm-1. One of the really useful absorptions, found in the range 1680 - 1750 cm-1, the other really useful bond is the C-O bond also has an absorption in the fingerprint region varying between 1000 and 1300 cm-1. The strong and wide peak at 1165.4 cm-1 showed the carbon-oxygen single bond present in the compound. A strong peak at 1740 cm-1 implies the carbonyl (C=O) group. The IR spectroscopy graph of the final product of the unknown #41showed the characteristic of Ester at 1714.4 cm-1 (C=O), which was (20-40 cm-1) less than the normal peak of ester at 1740 cm-1, which was caused because of the presence of a broad alcohol (O-H) peak at 3300-2500 cm-1. The presence of O-H in final product was occurred due to contamination. The another source of error that caused the present of O-H peak was during the extraction of organic layer with bicarbonate, the water was not removed as much as possible. The extraction of organic layer was taken only once, which was supposed to extract two more times with bicarbonate to yield the more pure acetate. This may cause the more deposition of O-H on the final product. NMR spectroscopy is another great technique for determining the structure of organic compounds.
There were four signals present in the H1 spectrum at high field (right). The integration of protons was 1:3:2+1:3:6 (2+1 overlapping) in H1 spectrum, which implies there were 16 hydrogen present in the compound. Two signals were present at 0.9 and at 2 (singlet). The other two signals were present at 4.9 (multiplet) and 1.5 (looks multiplet because 2+1 integration was overlapping). The multiplicities of all signal clusters of H1 spectrum helped in determining the structure of compound. The signal at 4.9 indicates that the alkane group must be attached with electronegative compound that shifted alkane group by “2”, and the signal at 2 indicate the alkane group must be attached with carbonyl group. Thus, all the information collected from NMR suggested that the product of fisher esterification was (1,3-dimthylbutyl) acetate. A number of errors could have occurred in this experiment, which could have limited the amount of desired product yield. First, if not enough acid catalyst was used, protonation of the carbonyl group on the carboxylic acid would have been difficult to obtain. Second, if the temperature was too high in heating the mixture, some of the product could have been lost during the reflux
process.
Conclusion The purpose of this lab was to use the alcohol and acetic acid to produce an ester and then identify the unknown alcohol and the ester by IR and NMR spectrum analysis. Ester can be formed from both organic and inorganic acids and the process of producing ester is called an esterification. In the first part of experiment, the unknown alcohol #41 was mixed with acetic acid in 25ml round bottom flask, which was catalyzed by concentrated sulfuric acid to produce the desired ester and water. After the ester was isolated, a percent yield was calculated from the ester recovery. Then the unknown ester was identified as (1,3-dimethylbutyl) acetate by analyzing the IR and NMR spectrum, thus the unknown alcohol #41 was identified as 4-methyl-2-pentanol. It was found that 0.67 grams of unknown acetate was formed with a percent yield of 55%. The percent yield of ester was low because the entire condensed product may not be removed from the Hickman still. However most of ester was removed using the Pasteur pipette, some may still have been stuck inside the still. Some of the product may have also evaporated during the distillation. Some of the product could have been also lost during the reflux process if the heat was too high, hence the vapors would go past the condenser part, and product would be lost, decreasing the percent yield. To reduce this kind of error the heat should be kept at a low level and constant. After completing the esterification, the structure of ester was confirmed using IR spectrum that obtained from IR analysis lab and NMR spectra of ester from unknown alcohol provided by Dr. Houston. The IR spectroscopy graph showed the characteristic of carbonyl at 1714.4 cm-1 (C=O) strong absorption, and a broad O-H peak at 3300-2500 cm-1 decreasing the strong peak of normal ester by 20-40 cm-1, confirming the product as an ester that contained lost of alcohol. The presence of O-H in final product was occurred might be due to contamination. The another source of error that caused the present of O-H peak was during the extraction of organic layer with bicarbonate, the water might not remove as much as possible. The solubility of alcohol in water was not checked before the experiment, so the other reason for the O-H absorption in IR may be the alcohol soluble in water, which present in the final product. To avoid this kind of mistake, student should check the solubility of alcohol before the esterification reaction. The NMR spectroscopy have four signals and the integration of protons was 1:3:2+1:3:6. All this information suggested that the ester yielded was (1,3-dimethylbutyl) acetate; therefore, the unknown alcohol # 41 was 4-methyl-2-pentanol. The quantitative error was most likely due to product getting stuck in the apparatus. These errors most likely caused the change in end result (percent yield, IR spectrum). Different sources of error may have prevented a pure ester from being produced from unknown alcohol.
The experiment was successful with percent yield ~55% of ester from unknown alcohol, although the 100% yield of ester from the esterification reaction was not successful. The values of the major peaks on the IR spectrum, and the four signals and the integration of protons (1:3:2+1:3:6) present in NMR spectrum also corresponded to the theoretical values of the ester 1,3-dimethylbutyl. Therefore, it was concluded that this was the ester formed and the experiment was a success, because even though there was error, this was only for the percent yield of ester, not in its identity.