Introduction
Recrystallization is the primary method for purifying solid organic compounds. Compounds obtained from natural sources or from reaction mixtures almost always contain impurities. The impurities may include some combination of insoluble, soluble, and colored impurities. To obtain a pure compound, these impurities must be removed. Each is removed in a separate step in the recrystallization procedure. [8]
Acetylation of aniline by acetic anhydride was performed to synthesize the crude acetanilide. The obtained crude acetanilide contained acetic acid as well as unreacted acetic anhydride. The said impurities of the crude acetanilide were removed using activated charcoal, filtration and recrystallization.
EXPERIMENTAL
A. Compounds tested
Aniline
Aniline is a clear to slightly yellow liquid with a characteristic odor. It does not readily evaporate at room temperature. Aniline is slightly soluble
in water and mixes readily with most organic solvents. Aniline is used to make a wide variety of products such as polyurethane foam, agricultural chemicals, synthetic dyes, antioxidants, stabilizers for the rubber industry, herbicides, varnishes and explosives. [2] Aniline is prepared commercially by the catalytic hydrogenation of nitrobenzene or by the action of ammonia on chlorobenzene. The reduction of nitrobenzene can also be carried out with iron borings in aqueous acid. [6] Preparation of Aniline:
The Essay on Recrystallization of Acetanilide Using Water as Solvent
... tripod, wire gauze, beaker, filter paper, aniline compound, hexane compound, acetic anhydride and methanol. The experiment began ... followed by the compound being dissolved in a minimum solvent. Insoluble impurities are removed and crystallization follows ... synthesis of acetanilide. Pure acetanilide was collected after recrystallizing the crude acetanilide. Quantitative Analysis of Acetanilide thru ...
C6H5NO2 + 3 H2 → C6H5NH2 + 2 H2O
(a)
(b)
Figure 1. (a) Hydrogenation of nitrobenzene (b) Bechamp reduction
Acetic anhydride
Acetic anhydride is clear, colorless liquid with a strong, pungent, sour vinegar-like odor, lachrymator. [5] Acetic anhydride is an important solvent and acetylation agent. [4] It is used in the manufacture of acetyl compound, cellulose acetates, acetylizer and solvent in examining wool fat, glycerol, fatty and volatile oils, resins, detection of rosin, in organic synthesis, such as dehydrating agent in nitrations, sulfonations and other reactions where removal of water is necessary. [5] Acetic anhydride is prepared by the carbonylation of methyl acetate. There is a two-stage process for the preparation of acetic anhydride, in which, in a first step, methyl bromide or, preferably, iodide is carbonylated to provide the corresponding acetyl halide, such acetyl halide in turn being reacted with methyl acetate, in a second step, to provide acetic anhydride, which corresponds to the following reaction scheme, in the event that methyl iodide is the starting material: [7] Step 1:
CH3I + CO → CH3COI
Step 2:
CH3COI + CH3COOCH3 → (CH3CO)2O + CH3I
Figure 2. Carbonylation of methyl acetate
B. Procedure
1. Choosing the Recrystallizing Solvent
A corn-grain amount of pure acetanilide was placed into each of three test tubes. Methanol, hexane, and water were added to each test tube respectively. Each was shaken and was placed in a warm bath (37oC-40oC) for 1-5 minutes and then was cooled.
Figure 3. Pure acetanilide in test tubes containing different solvents – methanol, hexane, water respectively.
2. Acetylation of Aniline by Acetic Anhydride
Aniline solution was made by mixing 2mL of aniline with 20mL of distilled water. 3mL of acetic anhydride was then added to the solution to form acetylation. The over-all solution was then placed in an ice bath to form crystals of crude acetanilide.
The Essay on Safety Precautions For Synthesis Of Acetic Anhydride
Acetic anhydride is an irritant and also flammable, therefore gloves and goggles should be worn at all times during the experiment. It is reactive to water, so in the case of fire, alcohol foam or carbon dioxide is preferred to use as an extinguisher. This chemical has harmful fumes and use of a fume hood is strongly recommended. Sulphuric and Salicylic Acid These acids may irritate the skin in ...
Figure 4. 2mL of aniline mixed with 20mL of distilled water
Figure 5. 3mL of acetic anhydride added to the aniline solution
Figure 6. Crystallization of crude acetanilide in an ice bath 3. Purification of Crude Acetanilide by Recrystallization
The crude acetanilide crystals were filtered through a wet filter paper. The residue was then dried and weighed. In a separate Erlenmeyer flask, the crude acetanilide residue was placed and 20mL of the recrystallizing solvent was added. The solution was then heated on a hot plate until the entire solid dissolved completely. When the solution became colored, it was removed from the heat and enough amount of activated charcoal was added. The heating process continued until the solution became colorless. While the solution was still hot, it was quickly filtered using a fluted filter paper. Its filtrate was then cooled by placing the receiver in a beaker with cold water. The crystals that formed were collected and were washed. When the
crystals completely dried up, it was then weighed.
Figure 7. Filtration of the crude acetanilide crystals
Figure 8. Crude acetanilide residue mixed with the recrystallizing solvent
Figure 9. Heating process of the solution
Figure 10. Addition of the activated charcoal to the solution
Figure 11. Continued heating process of the solution until colorless
Figure 12. Filtration and recrystallization of the acetanilide
Figure 13. Weighing of the dried acetanilide crystals
RESULTS AND DISCUSSION
1. Choosing the Recrystallizing Solvent
Among the three recrystallizing solvents – methanol, hexane, and water, water was chosen to be used in the recrystallization of the acetanilide. Table 1. Solubility of pure acetanilide in various solvents
| At room temp.| During heating| Upon cooling|
Water| Insoluble| Soluble| Insoluble|
Methanol| Soluble| Soluble| Soluble|
Hexane| Insoluble| Insoluble| Insoluble|
2. Acetylation of Aniline by Acetic Anhydride
The crude acetanilide was obtained by the acetylation of the aniline. The crude acetanilide obtained was 7.2 grams in its weight. 3. Purification of Crude Acetanilide by Recrystallization
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The Problems and Solutions in Building an Age-friendly City The Problems and Solutions in Building an Age-friendly City: Economic Conditions for the Elderly in Singapore Prepared By: Tang Jiahui & Qian Ziyuan NUS SM2 Batch 16, Group 1 Prepared For: Dr. Lira Dumaguing April 7, 2013 1 The Problems and Solutions in Building an Age-friendly City 2 Table of Contents List of Tables &# ...
Pure acetanilide was obtained by the recrystallization of the crude acetanilide. From the 7.2 grams of crude acetanilide, 1.2 grams of pure acetanilide was gathered.
Theoretical Yield:
Aniline
2mL x 1.0217 g/mL = 2.0434 g
2.04 g x 1 mol x 135.17 g =
93.13 g 1 mol
2.96 g Acetanilide
Acetic Anhydride
3mL x 1.082 g/mL = 3.246 g
3.246 g x 1 mol x 135.17 g =
102.09 g 1 mol
4.30 g Acetanilide
∴ Aniline is the limiting reagent.
Percentage Yield:
= Actual Yield x 100
Theoretical Yield
= 1.20 grams x 100
2.96 grams
= 40.54 %
The experiment conducted was able to perform different chemical processes. In choosing the recrystallizing solvent, solubility test was conducted among various solvents – methanol, hexane, and water. The solubility test resulted to the conclusion of choosing water as the recrystallizing solvent. The experiment also included the acetylation of aniline by acetic anhydride to
form the crude acetanilide. In the experiment, 7.2 grams of crude acetanilide was obtained. Since the crude acetanilide has impurities, it was purified by several processes – heating of solution, activated charcoal addition, and recrystallization. When recrystallization has already occurred in the solution, the pure acetanilide was then obtained. 40.54% of the pure acetanilide was gathered with its weight of 1.2 grams.
References
[1] Acetylation of Aniline using Acetic Anhydride. http://prolabscientific.com/Acetylation-of-Aniline-using-Acetic-Anhydride-p-23917.html. [2] Agency for Toxic Substances & Disease Registry: Toxic Substances Portal – Aniline. http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=449&tid=79. [3] Bayquen, A. V., Cruz, C. T., de Guia, R. M., Lampa, F. F., Peńa, G. T., Sarile, A. S., & Torres, P. C. (2009).
Laboratory Manual in Organic Chemistry. 839 EDSA, South Triangle, Quezon City: C & E Publishing, Inc. [4] Chemical Book: Acetic Anhydride. http://www.chemicalbook.com/ChemicalProductProperty_EN_CB2852742.htm. [5] Chemical Book: Acetic anhydride (108-24-7).
http://www.chemicalbook.com/ProductMSDSDetailCB2852742_EN.htm. [6] Encyclopædia Britannica: Aniline. http://global.britannica.com/EBchecked/topic/25473/aniline. [7] Gauthier-Lafaye et al. Carbonylation of methyl acetate. http://www.google.com.ph/patents?hl=en&lr=&vid=USPAT4500474&id=ymY2AAAAEBAJ&oi=fnd&dq=carbonylation+of+methyl+acetate&printsec=abstract#v=onepage&q=carbonylation%20of%20methyl%20acetate&f=false. [8] Recrystallization. http://www.chem.umass.edu/~samal/269/cryst1.pdf.
The Essay on Bromination of Acetanilide
The objective of this experiment was to use melting point and NMR to determine which of two isomers, ortho or para, would most likely form after brominating Acetanilide through electrophilic aromatic substitution. Procedure/Observations: 1. Weigh out ~280 mg of acetanilide in a 10 mL r. b. flask with a stir bar. 2. Then, add 2. 0 mL of glacial acetic acid using a calibrated Pasteur pipet. 3. Stir ...
