Transcript
Multistep Synthesis of Acetylsalicylic Acid with TLC and IR Analysis
TA:
Section: 022
CHY224
Introduction:
The purpose of the experiment in the following report is to carry out a multistep synthesis of acetylsalicylic acid, which is an ingredient in modern medicines Aspirin.1 The first week of the experiment involved carrying out the hydrolysis of methyl salicylate, thus creating salicylic acid. The second week of the experiment involved the acetylation of methyl salicylate, creating acetylsalicylic acid. The third week of the experiment involved the analysis and purification of the acetylsalicylic acid created in the second week of the experiment.
In the first part of the experiment, methyl salicylate was treated with an aqueous base. This process is otherwise known as hydrolysis.2 The constituents of the following products of hydrolysis included: methanol, water, and disodium salicylate. After this, the reaction mixture is acidified with sulphuric acid. Thus, the overall organic products of the reaction consists of salicylic acid and methanol. The chemical equations that describe this reaction is shown below:
The resulting salicylic acid can then be isolated and purified by crystallization. During the hydrolysis, the phenolic hydroxyl group is converted to the corresponding sodium salt because it’s acidic. The group also becomes reprotonated in the subsequent acidification.
In the second part of the experiment, the synthesis of acetylsalicylic acid occurred. This involved an acid catalyzed reaction between the phenolic OH of salicylic acid and the acetylating agent acetic anhydride, resulting in acetylsalicylic acid. The acetic anhydride acts as both a reactant and a solvent in the reaction. In order for this reaction to occur, sulphuric acid is used as a catalyst and when the reaction is over, water is added in order to destroy the excess acetic anhydride. The chemical equations that describe this reaction is shown below:
In this reaction, the phenol is considered as a nucleophile and thus causes a substitution reaction at one of the carbonyl groups of the anhydride.
This multistep synthesis process is very useful in the chemical industry, especially in regards to industrial scale preparation of drugs.3 Basically, compounds are purchased and then a reaction is carried out with these compounds.3 The products of the reaction is then used in another reaction, creating another product.3 This process is repeated until the desired product has been formed. Due to the nature of multistep synthesis, it is important that efficiency is as high as possible. In other words, the percent yield in each of the reactions is maximized in order to get as much desired product as possible.3 This multistep synthesis process is used in this experiment as well as the consideration of maximum percent yield.
The analysis of the products in this experiment is done using several different lab techniques. These lab techniques included: melting point analysis, recrystallization, vacuum filtration, reflux, ferric chloride tests, thin layer chromatography and infrared spectroscopy.
A melting point analysis is done usually in order to determine the purity of a compound by comparing the measured melting point range to a literature value. A pure organic compound has a sharp melting point, which means it melts within the range of 1.0 degrees Celsius or less. A less pure organic compound would exhibit a broader melting point, such as a melting point range between 3.0 to 10.0 degrees Celsius. In addition to a broader melting point, a less pure organic compound would exhibit a lower melting point in general as well. The technique in order to determine the melting point is to gradually heat a small sample of the solid material until the first signs of melting occurred. When the first sign of melting has occurred, this is called the lower temperature of the melting range. When the sample has completely become a clear liquid, that temperature is called the upper temperature of the melting range.
Recrystallization is a technique used to purify a solid compound. When a solid organic compound is prepared in the laboratory, it is most likely impure. Thus, the recrystallization technique is important. The compound is dissolved in a minimum amount of hot solvent. After this, the hot, saturated solution is cooled slowly so that the desired compound crystallizes at a moderate rate. When the crystals are fully formed, they are isolated from the mother liquor by vacuum filtration.
A vacuum filtration is done by connecting a Buchner funnel to a side arm flask and a vacuum. This process is required in order to separate crystals from the mother liquor. If this was not done, specific crystals would not be able to be measured. An important aspect to vacuum filtration is allowing the crystals to dry afterwards. If the mass is measured right after the vacuum filtration process, a lot of the mass measured would consist of water weight, which would cause an error in the percent yield aspect of the experiment.
In this experiment, the technique reflux is used to induce an organic reaction. Basically, the reaction is cooked at a constant temperature without letting the solvent escape into the lab. The solvent is chosen so that the reactants will dissolve in it when it is hot, and the boiling point of the solvent is high enough for the reaction to occur quickly.
Ferric chloride tests will also be conducted in this experiment. When a solution of FeCL3 is mixed with a solution containing compounds such as enols, phenols or carboxylic acids, a colour change reaction occurs.4 From this colour change, the identity and purity of the compounds can be determined.4
Thin layer chromatography is used to separate and identify mixtures of compounds. There are two phases consisted in thin layer chromatography: the stationary phase and the mobile phase. The stationary phase absorbs the compounds whereas the mobile phase moves the substances along the stationary phase. In regards to this experiment, thin layer chromatography was used to chromatograph the acetylsalicylic acid as well as the other reactants and intermediates. This is done by using the samples obtained in the experiment as well as reference samples and spotting them onto the surface of one end of the plate. The spots are allowed to dry and then the plate is placed into a developing tank that contains a small amount of developing solvent. Via capillary action, the solvent will move up the length of the plate, varying in length for each of the compounds.
Infrared spectroscopy is a laboratory technique which measures the absorbance of energy. This is done by putting together absorbance’s to form a fingerprint which can identify the compound. The frequency that this absorbance occurs is indicative of vibrations between atoms within a molecule. In the experiment, the spectra of the reactants will be compared in order to determine the purity.
After the TLC analysis has been conducted, the retention factor for the various compounds can then be calculated. The formula for retention factor is:
Rf = ?dsubstance / ?dsolvent ; where ?dsubstance and ?dsolvent are the distance the substance and the solvent travelled across the chromatography card.5 The retention factor is a constant that is calculated and used to determine the identity of solutes that travel across the chromatography card.
Experimental:
Week 1
5.0 g of methyl salicylate was first weighed into a 250 ml round-bottom flask, making sure that the flask was tarred. Next, 50 mL of 20% NaOH solution was added to the flask. A reflux condenser was then attached to the flask and the ground glass joints was lightly greased. Approximately 2-3 boiling chips was added to the reaction mixture in order to prevent bumping when the solution is heated. The solution was heated at boiling point for about 20 minutes. After heating the mixture, the solution was allowed to cool to room temperature. The solution was then transferred to a 600 mL beaker and 250 mL of 1 M sulphuric acid was added. A litmus test was conducted to ensure the solution was acidic. The mixture was further cooled in an ice-water bath for approximately 10 minutes. After this, the product was collected by vacuum filtration, using a Buchner funnel. The crude salicylic acid that was produced was weighed and then a small amount of crystals was set aside for a melting point determination, infrared analysis, feral chloride test, and TLC.
The crude salicylic acid was then recrystallized using a minimum amount of hot solvent in a 250 mL beaker. This was done by bringing the solution to a boil until the crystal dissolved, then removing the beaker from heat and placing it on the bench. A watch glass was placed on top of the beaker in order to cover it and the solution was allowed to cool to room temperature. It was made sure that the beaker was not moved, jiggled, or in any way disturbed during the cooling process. Once the filtrate was relatively cool and the crystals had started to form, the beaker was placed in an ice-water bath in order to aid recrystallization. After 10 minutes, the remaining crystals of salicylic acid was collected via vacuum filtration. The crystals were then washed with small amounts of ice-cold distilled water and remaining liquid was suctioned away. The crystals were then weighed and given to the teaching assistant for storage until the following week.
Week 2
The pure salicylic acid produced in the week 1 experimental procedure was weighed. The melting point of both the crude and pure salicylic acid was taken using melting point determination. Some crude and pure salicylic acid was retained for ferric chloride tests, TLC, and IR analysis.
A warm bath was prepared by heating approximately 100 mL of distilled water in a 400 mL beaker containing about 3-4 boiling chips to about 45-50 degrees Celsius. 3.0 g of salicylic acid was weighed into a clean, dry 100 mL beaker using a top-loading balance. 5.0 mL of acetic anhydride was then measured and added to a 10 mL graduated cylinder while the salicylic acid was added to the beaker. Next, approximately 5 drops of concentrated sulphuric acid was added cautiously to the beaker containing salicylic acid and acetic anhydride. The mixture was then stirred with a glass rod. The mixture was then warmed gently in the warm bath, and was continuously stirred until the solid dissolved. Once the solid had dissolved, the mixture was further warmed for about 10 minutes. The reaction vessel was removed from the water bath and the reaction mixture was allowed to cool to room temperature while not being disturbed. During the cooling process, crystals of the acetylsalicylic acid started to form and then the vessel was placed in an ice bath until a semi-solid mass had formed. Once the crystallization was complete, 50 mL of ice-cold distilled water was added to the beaker. The crude aspirin was then separated from the mother liquor via vacuum filtration and after, the crystals were washed several times with chilled distilled water. The suction from the vacuum was allowed to continue for 5 minutes to aid in drying as well as fluffing of the crystals. The crude aspirin, now dry, was then weighed using a weigh dish and top-loading balance. A small sample of the crude aspirin was taken for a melting point determination test, ferric chloride test, TLC, and IR analysis.
Using a minimum amount of hot solvent, the crude aspirin was then recrystallized. This was done by starting with 20 mL of water to which dissolved the crude aspirin in a 250 mL beaker. The beaker was covered in a watch glass and allowed to cool to room temperature undisturbed. After this, the beaker was transferred to an ice bath and was allowed to cool further for about 5 minutes. Next, the pure aspirin was washed using ice-cold solvent and then a vacuum filtration technique was utilized to separate the pure aspirin crystals from the mother liquor. Once the crystals were dry, they were transferred to a pre-weighed weigh dish and handed to the TA for storage until the next week.
Week 3
The pure aspirin produced in the week 2 experimental procedure was weighed and a melting point determination test was performed for both the crude and pure aspirin that was collected.
To start the TLC test, the plate was inscribed very lightly with a pencil so that the start line was approximately 2 cm from the bottom of one end of the plate. This line was where the standards and the produced acetylsalicylic acid was spotted. A map of the order in which the spots were applied on the plate was recorded in the lab notebook. Seven lanes were formed for each of the compounds produced as well as the standards: pure methyl salicylate, salicylic acid, acetylsalicylic acid, crude and pure salicylic acid that was produced, and the crude and pure acetylsalicylic acid that was produced. At the stations for the standards, a capillary was used to draw up 4 microliters of solution. The capillary, now with the drawn up solutions, was gently touched on the surface of the plate where the corresponding lanes were drawn. After spotting all the seven lanes with their corresponding solutions, the plate was allowed to dry for 2-3 minutes. Next, the plate was then gently placed into the tank so the bottom end with the spotted samples touches the solvent. A thin layer of tin foil was covered on the top so that gas was not released into the lab room. Once the solvent had moved approximately 80% of the distance of the plate, the plate was removed carefully from the tank. Immediately after being removed, the solvent front was traced onto the plate. The plate as then placed in the fume hood and was allowed to dry for approximately 10 minutes. After the plate was allowed to dry in the fume hood, any spots visible to the naked eye were traced with a pencil. Next, the plate was taken to the UV light and the fluorescent spots were then traced. The distance from the start line to the leading edge of each spot was then measured.
To start the ferric chloride test, seven small test tubes were obtained and labelled #1-#7. About 0.5 mL of methanolic ferric chloride solution was added to each test tube. A different sample in each tube was tested by adding a few drops of the sample, swirling the liquids together, and then noting any colour change. These seven samples for the tests were: pure methyl salicylate, salicylic acid, acetylsalicylic acid, crude and pure salicylic acid that was produced, and the crude and pure acetylsalicylic acid that was produced. After the ferric chloride test concluded, the test solutions were disposed of in the designated waste container and the test tubes were thoroughly cleaned.
To start the Infrared Spectroscopy test, the instructions on the correct usage of the spectrometer was referred to appendix B-3 of the lab manual.5 The spectra for the crude and purified salicylic acid as well as the spectra for the crude and purified acetylsalicylic acid was obtained.
Results and Calculations:
Table of Reactants
Compound
Formula
Molecular Weight gmol
Melting Point °C
Methyl Salicylate
C8H8O3
152.148
-8.5
Sodium Hydroxide
NaOH
39.997
323
Water
H2O
18.015
0.00
Methanol
CH3OH
32.042
-97.5
Acetic Anhydride
C4H6O3
102.089
-73.4
Sulfuric acid
H2SO4
98.079
10.31
Reference.7
Table of Products
Compound
Formula
Molecular Weight gmol
Melting Point °C
Salicylic Acid
C7H6O3
138.121
158.6
Sodium Bisulfate
NaHSO4
120.061
58.5
Methanol
CH3OH
32.042
-97.5
Acetylsalicylic Acid
C9H8O4
180.158
136
Acetic
Acid
C2H2O2
60.052
17
Reference.7
Compound
Amount created (g)
Melting point range (°C)
Crude Salicylic acid
8.8
152-158
Pure Salicylic acid
3.2
159-161
Crude Acetylsalicylic acid
4.4
128-135
Pure Acetylsalicylic acid
2.4
134-135
Table 1.1: Quantitative results pertaining to both crude and pure salicylic acid and acetylsalicylic acid
Compound
Colour
Compound description
Crude Salicylic Acid
A mix of yellow and white
Pasty
Pure Salicylic acid
Almost completely clear with a tint of white
Thin crystals, similar to snowflakes
Crude Acetylsalicylic acid
A mix of yellow and white
Pasty
Pure Acetylsalicylic acid
Very white
A combination of powder and needle-like thin crystals
Table 1.2: Qualitative results pertaining to both crude and pure salicylic acid and acetylsalicylic acid
Compound
Distance between reference line (solvent front)
(cm)
Solvent front distance
5.7
Methyl salicylate
5.6
Salicylic acid standard
5.0
Acetylsalicylic acid standard
4.5
Crude salicylic acid standard
5.5
Purified salicylic acid
1.9
Crude acetylsalicylic acid
5.3
Purified acetylsalicylic acid
5.0
Table 1.3: Quantitative results of TLC analysis
Tube number
Compound
Observations
1
Standard methyl salicylate
Dark purple/black, very dark
2
Standard salicylate acid
Dark purple/black
3
Standard acetylsalicylic acid
Hints of yellow, dark brown/black, solid not fully dissolved
4
Pure Asa
Hints of yellow, still dark brown/black, darker than standard.
5
Crude Asa
More yellow than black, lighter than standard Asa.
6
Pure Sa
Dark purple/black, very similar to standard Sa.
7
Crude Sa
Dark purple, darker than pure and standard Sa.
Table 1.4: Qualitative results of Ferric Chloride test
Figure 1.1: Infrared Spectroscopy analysis of Crude Salicylic acid
Figure 1.2: Infrared Spectroscopy analysis of crude acetylsalicylic acid
Figure 1.3: Infrared Spectroscopy analysis of pure salicylic acid
Figure 1.4: Infrared Spectroscopy analysis of pure acetylsalicylic acid
Figure 1.5: Reference spectra for salicylic acid.6
Figure 1.6: Reference spectra for acetylsalicylic acid.6
Figure 1.7: TLC plate after tracing the solvent front and points.
Figure 1.8: Ferric chloride test for standard methyl salicylate.
Figure 1.9: Ferric chloride test for standard salicylic acid.
Figure 1.10: Ferric chloride test for acetylsalicylic acid.
Figure 1.11: Ferric chloride test for pure acetylsalicylic acid.
Figure 1.12: Ferric chloride test for crude acetylsalicylic acid.
Figure 1.13: Ferric chloride test for pure salicylic acid.
Figure 1.14: Ferric chloride test for crude salicylic acid.
Functional Group
Bond
Position (wavenumber cm-1)
Alkane
CH3
-CH2-
2960
2930
Alkene
C-H
C=C
3050
1640 (1670 for trans)
Aromatic
C-H
Mono
Ortho
Meta
Para
750
750
782
817
Alcohol
C-O
O-H
1100
3350 (very broad)
Ether
C-O
1100
Aldehyde
C-H,
C=O
2700
1730
Ketone
C=O
1700
Ester
C-O
C=O
1200
1740
Carboxylic Acid
O-H
C=O
3100
1720
Table 1.5: Reference IR analysis.5
Peak Number
Point
Associated Functional Group
1
(3229.875, 8.038)
Alcohol (O-H)
2
(2996.734, 2.870)
Alkane (CH3)
3
(2849.315, 3.540)
Alkane (-CH2-)
4
(2590.317, 1.401)
Aldehyde (C-H)
5
(2532.030, 0.359)
Aldehyde (C-H)
6
(2087.644, 1.554)
Ester (C=O)
7
(1865.056, 1.144)
Ester (C=O)
8
(1655.281, 25.044)
Alkene (C=C)
9
(1439.583, 21.346)
Ester (C-O)
10
(1290. 274, 30.061)
Ester (C-O)
11
(1235. 564, 15.266)
Ester (C-O)
12
(1150.372, 2.769)
Ester (C-O)
13
(1028.572, 6.520)
Alcohol (C-O)
14
(994.835, 3.474)
Ether (C-O)
Table 1.6: IR analysis of pure salicylic acid
Peak Number
Point
Associated Functional Group
1
(2962.724, 0.410)
Alkane (CH3)
2
(2828.925, 1.504)
Alkane (-CH2-)
3
(2655.926, 1.099)
Alkane (-CH2-)
4
(2545.280, 2.235)
Aldehyde (C-H)
5
(2098.938, 3.735)
Ester (C=O)
6
(1837.111, 0.348)
Ester (C=O)
7
(1748.111, 28.994)
Ester (C=O)
8
(1676.665, 40.932)
Ketone (C=O)
9
(1603.038, 9.997)
Alkene (C=C)
10
(1455.516, 10.910)
Alkene (C=C)
11
(1416.690, 9.495)
Alkene (C=C)
12
(1367.467, 18.676)
Ester (C-O)
13
(1287.124, 39.480)
Ester (C-O)
14
(1181.266, 23.555)
Ester (C-O)
15
(1088.170, 16.258)
Ether (Alkene (C-O)
Alcohol (C-O)
16
(1009.871,12.097)
Ether (Alkene (C-O)
Alcohol (C-O)
Table 1.7: IR Analysis of Pure Acetylsalicylic acid
Compound
Retention Factor
Methyl salicylate
0.98
Salicylic acid standard
0.88
Acetylsalicylic acid standard
0.79
Crude salicylic acid
0.96
Pure salicylic acid
0.33
Crude Acetylsalicylic acid
0.93
Pure acetylsalicylic acid
0.88
Table 1.8: Retention factors of the various compounds based off a solvent of a distance of 5.7 cm. Refer to appendix for sample calculation.
Compound
Melting Point Range (°C)
Literature Melting Point (°C)
Theoretical Yield (g)
Actual Yield (g)
Percent Yield (%)
Crude salicylic acid
152-158
N/A
N/A
8.8
N/A
Pure salicylic acid
159-161
159
4.54
3.2
70.48
Crude acetylsalicylic acid
128-135
N/A
N/A
4.4
N/A
Pure acetylsalicylic acid
134-135
135
4.54
2.4
52.86
Table 1.9: Quantitative results of theoretical, actual and percent yield. See appendix for sample calculation. Literature melting point reference.7
Discussion:
There were several tests conducted in the experiment to determine compound purity on the different compounds used throughout the laboratory: melting point determination, thin layer chromatography (TLC), ferric chloride test, and the infrared spectroscopy analysis.
The first test was a melting point determination. In the laboratory a melting “point” is referred to as a melting “range” where the lower limit of the range is the temperature at which the first droplet of liquid is observed and the upper limit of the range is the temperature at which the sample becomes a clear liquid throughout. A melting point determination helps determine a compounds purity because a pure organic compound has different melting point characteristics than an impure organic compound. A pure organic compound has a sharp melting point – meaning the sample, given a certain temperature range, will melt within a 2°C range. On the other hand, an impure organic compound has a depressed and broader melting range.
When referring to Table 1.9, the melting rage of the pure salicylic acid was observed to be 159-161°C. The known melting range of salicylic acid is 159°C. Because these two have a discrepancy of 0-2°C, it can be said that the experimental pure salicylic acid is pure. Discrepancies come from small impurities which may have been added to the sample during the synthesis or during a container transfer or while being placed on the hot stage of the melting point determination apparatus. In addition to the comparison to the known melting point, the experimental pure salicylic acid sample could be identified as a pure organic compound because it has a sharp melting range – it melts within a range of 2°C. Conversely, the melting range of the crude salicylic acid was observed to be 152-158°C. This range is not as close to the known range and thus is it impure. In addition, this crude melting range carries the two characteristics of an impure organic compound: it has a depressed and broader melting range – the lower end of the range is 152°C and the range itself spans 6°C.
The melting rage of the pure acetylsalicylic acid was observed to be 134-135°C. The known melting range of acetylsalicylic acid is 135°C. Because these two have a discrepancy of 0-1°C, it can be said that the experimental pure acetylsalicylic acid is pure. Discrepancies come from small impurities which may have been added to the sample during the synthesis or during a container transfer or while being placed on the hot stage of the melting point determination apparatus. In addition to the comparison to the known melting point, the experimental pure acetylsalicylic acid sample could be identified as a pure organic compound because it has a sharp melting range – it melts within a range of 1°C. Conversely, the melting range of the crude acetylsalicylic acid was observed to be 128-135°C. This range is not as close to the known range and thus is it impure. In addition, this crude melting range carries the two characteristics of an impure organic compound: it has a depressed and broader melting range – the lower end of the range is 128°C and the range itself spans 7°C.
The percent yield of the synthesis of salicylic acid and acetylsalicylic acid were also calculated. The percent yield is a comparison between the theoretical yield of a product and the actual, experimental yield of a product. If the percent yield is 100%, that means that the same amount of theoretically calculated product yield was actually yielded in the lab. Given the procedure for this laboratory, that would have been very difficult to achieve a 100% percent yield. In the lab, it was determined that the percent yield of the synthesis of salicylic acid was 70.48%. It was determined that the percent yield of the synthesis of acetylsalicylic acid was 52.86%. These two yields are not 100% because some experimental mass was lost due to a number of factors like transferring substances from one container to another causes a small loss of substance during each transfer, less than ideal crystallization formation, and mass loss during vacuum filtrations.
The second test for purity in the laboratory was a thin layer chromatography (TLC) analysis for seven samples: methyl salicylate, standard salicylic acid, standard acetylsalicylic acid, crude salicylic acid, pure salicylic acid, crude acetylsalicylic acid, and pure acetylsalicylic acid. Looking at Figure 1.7 for the TLC plate, it is obvious that each sample lane has its own individual height and no multiple heights/dots were noted. This mean that all samples were pure compounds because had there been a lane where there were multiple dots, that means the sample was composed of different substances and was not pure.
The third test for purity was the ferric chloride test which analyzed the same seven compounds that were analyzed in the TLC. The ferric chloride test determines, in the case of this laboratory, the presence of phenols in a substance. When a phenol is detected, a coloured complex turns the mixture solution purple. Out of the seven substances that were tested, the only substances which had a phenol group were methyl salicylate, and the salicylic acid compounds (crude, pure, standard). This means the methyl salicylate and salicylic acid compounds should have turned purple when under the ferric chloride test. When looking at Table 1.4, it was observed as predicted: the methyl salicylate and the salicylic acid compounds were the only compounds which had a purple colour to them – the acetylsalicylic acid compounds were more of a yellow colour than purple. Thus, since the acetylsalicylic acid compounds were not purple, the acetylsalicylic acid synthesis created a pure sample.
The fourth test for purity was the infrared (IR) spectroscopy. This test uses the fact that different molecules of different bonds and functional groups absorb different wavelengths of infrared energy. The two samples for which the IR analysis was done on were the pure salicylic acid and pure acetylsalicylic acid samples. When comparing the pure salicylic spectra in Figure 1.3 and the reference spectra in Figure 1.5, they are very similar in general patterns. For example, from wavelengths between 4000 and 3500 cm-1, both graphs increase at a similar rate and both graphs have a drop around 1600 cm-1 with a succeeding increase. Since both graphs were visually similar, that means the purified salicylic acid was pure. When comparing the pure acetylsalicylic spectra in Figure 1.4 and the reference spectra in Figure 1.6, they are very similar in general patterns. For example, from wavelengths between 3000 and 2500 cm-1, there is that area of low % transmittance with a successive increased area. It is obvious there are some discrepancies like the peak in the pure spectra at wavelength 2098.938 cm-1 which does not appear in the reference spectra. A peak like that would be considered an impurity because impurities are added onto the experimental spectra. These impurities come from several places: like when transferring substance containers as said above or from not cleaning the IR analysis stage well enough.
Conclusion:
In conclusion, the experiment could be considered somewhat a success. The percent yield of pure salicylic acid turned out to be approximately 70%, which is good, whereas the percent yield of acetylsalicylic acid turned out to be around 53%, which is mediocre results. The reason these yields are not 100% is due to the errors within the experiment. The melting point range test concluded that our salicylic acid and acetylsalicylic acid were pure, in addition to the TLC analysis as well as the IR analysis, since there were few deviations to the standard.
Appendix-Common Calculations:
A1- Calculating the retention factor for methyl salicylate
Rf = ?dsubstance/ ?solvent
=5.6 cm /5.7 cm
=0.98
A2- Calculating the theoretical yield of Salicylic acid
First, find the moles of Methyl Salicylate involved in the reaction and the moles of NaOH in order to figure the limiting reactant:
nMethyl Salicylate =(5.0g )/ (152.148g/mol)
= 0.03286mol
nNaOH = (50mL)(2.13g/mL) / (39.997g/mol)
= 2.662mol
Therefore, methyl salicylate is the limiting reactant. The theoretical yield of sodium salicylate is equal to the theoretical yield of salicylic acid. Thus:
Theoretical Yield= (0.03286mol) (138.121g/mol)
= 4.54g
A3- Calculating Percent Yield of Salicylic acid
% yield= (Actual yield)/ (Theoretical yield) x 100
= (3.2 g)/ (4.54 g) x 100%
= 70.48%
References:
Williams AN, Simon RA, Woessner KM, Stevenson DD. The relationship between historical aspirin-induced asthma and severity of asthma induced during oral aspirin challenges. J.Allergy Clin.Immunol. 2007;120(2):273-277.
Hussain A, Schurman P. Thiol esters II: A kinetic study of hydrolysis and aminolysis of propionyl thiocholine iodide and 2?dimethylaminoethanethiol propionate. J.Pharm.Sci. 1969;58(6):687-693.
Phimister JR, Fraga ES, Ponton JW. The synthesis of multistep process plant configurations. Comput.Chem.Eng. 1999;23(3):315-326.
Soloway, S., Wilen, S.H. “Improved Ferric Chloride Test for Phenols”, Analytical Chemistry, 1952, 24(6), 979-983,
Johnson, A., McFadden, S., Viirre, R. “Organic Chemistry Laboratory Manual”, 2015, 89-94.
NIST Chemistry WebBook. (n.d.). Retrieved from http://webbook.nist.gov/chemistry/
The PubChem Project. (n.d.). Retrieved from https://pubchem.ncbi.nlm.nih.gov/
