TITLE: PREPARATION AND PURIFICATION OF ACETANILIDE
AIM:
To synthesis acetanilide by reaction of aniline and acetic anhydride
To purify acetanilide by crystallization method from water
Purity check by melting point
INTRODUCTION:
Acetanilide is an odourless solid chemical of leaf or flake-like appearance. It is also known as N-phenylacetamide, acetanil, or acetanilind and was formerly known by the trade name Antifebrin.
Acetanilide can be produced by reacting acetic anhydride with aniline:
C6H5NH2 + (CH3CO)2O C6H5NHCOCH3 + CH3COOH
Acetanilide is formed when aniline reacts with acetic anhydride. Another product, acetic acid, is also formed. In this reaction, the acetic anhydride is broken between the center oxygen and is connected carbon. A proton breaks off the amine group of the aniline. The electrons from this separation form a bond with a secondary carbon in the acetic anhydride. When the bond is broken between the secondary carbon and the center oxygen of the acetic anhydride, the electrons are used to attach the broken off proton to that oxygen. This forms acetanilide and acetic acid
The preparation used to be a traditional experiment in introductory organic chemistry lab classes, but it has now been widely replaced by the preparation of either paracetamol or aspirin both of which teach the same practical techniques (especially recrystallization of the product) but which avoid the use of aniline, a suspected carcinogen.
Acetanilide is commonly used today as an intermediate product of several pharmaceutical products, including sulfa drugs, pencillin, camphor, certain dyes, and other medications.
Acetanilide is slightly soluble in water, and stable under most conditions. Pure crystals are plate shaped and colorless to white. In this experiment acetanilide is synthesized from aniline, acetic anhydride and acetic acid.
PROCEDURE
In a 500ml beaker, 200cm3 of water, 6.75cm3 of hydrochloric acid, and 7.75cm3 of aniline was added. This mixture was then stirred until the aniline has been completely dissolved. To this solution, acetic anhydride of 10.25g was then added. It was stirred to dissolve the solid particles and then immediately a solution of sodium acetate(13g) in 37.4cm3 of water.
The mixture was stirred vigorously and then cooled in an ice-water bath. The solid acetanilide which got separated by suction filtration was filtered out and the solid in the funnel was washed with ice-cold distilled water to get rid of soluble impurities. It was then drained well under suction. The product obtained was then left in the oven at 500C for about 15 minutes to get dry. After 15 minutes the product was then used to obtain the melting point and the yield was recorded.
REACTION
CALCULATION
LIMITIMG REACTANT
C6H5NH2 + (CH3CO)2O C6H5NHCOCH3 + CH3COOH
1 : 1
moles of aniline moles of acetic anhydride
n = mmr n = mmr
=7.75g93.13g/mol =10.25g102.09g/mol
= 0.08 mol = 0.10 mol
Hence the limiting reactant in this reaction is aniline since it has moles of 0.08, that is less than the moles of acetic anhydride.
THEORITICAL YIELD
0.08 mol 0f aniline x 1 mol of acetanilide x 135.16g
= 10.82g acetanilide
Therefore, in a perfect experiment, 10.28g of acetanilide will be synthesized.
ACTUAL YIELD
Mass of acetanilide = Mass of vial + lid + acetanilide - Mass of vial + lid
= 30.56g - 19.97g
= 10.59g
PERCENT YIELD
Percentage Yield = Actual YieldTheoretical Yield X 1001
=10.59g10.82g x 1001
= 97%
MELTING POINT
Melting point of crystallized Acetanilide : 112 – 1150C
DATA ANALYSIS
After completing the synthesis of acetanilide from aniline and acetic anhydride, a sample of acetanilide was collected with a mass of 10.59g. Theoretical yield, based on the limiting of aniline (based on the smaller molar mass and the ratio of 1:1 ratio of the two reactants in the balanced equation) is 10.82g of acetanilide. Actual yield was 10.59g acetanilide. Therefore, percent yield for this synthesis is 97%.
The melting point, measured at 112-1150C, is within the literature range of acetanilide. This shows that the acetanilide produced is of an extremely pure quality, and little to no impurities exist.
POST LAB QUESTIONS
1. Aniline is insoluble in water because it does not under hydrogen bonding. This is because of the presence of the benzene ring which is highly hydrophobic. Whereas despite the fact that aniline is only a weak base, with a strong acid like hydrochloric acid the reaction is very straight forward. Aniline is only slightly soluble to insoluble in water, but freely dissolves in dilute hydrochloric acid as the lone pairs on the nitrogen forms bond with molecules in HCL.
2. Sodium acetate is added to the reaction mixture when synthesizing acetanilide so that it can act as a base with the hydrochloric acid present in the mixture to produce acetic acid.
3. Recrystallization is a purification process used to remove impurities from the organic compounds that are solid at room temperature. The process is based on the premises that the solubility of a compound in a solvent increases with temperature. Solubility of a compound decreases as the solution cools and crystals form. An appropriate solvent is that in which acetanilide is soluble at high temperature and insoluble in cold solvent. Acetanilide itself is non-polar solvent whereas ethanol on the other hand is polar; therefore ethanol when singly used is not a good solvent.
EXPERIMENTAL LIMITAIONS
The acetanilide produced in this experiment from the synthesis of aniline and acetic anhydride was a good amount. Likewise, the quality of the product was greater than anticipated. The quality was achieved likely due to the care in ensuring all glassware and instruments were clean and each step of the progress was done with careful precision.
However, if was possible to attain a lower yield of acetanilide than the one achieved. This is because the aniline we achieved at the end of experiment was low in yield and therefore commercial aniline was mixed with the crude aniline.
The lost aniline is likely to be the result of mixture not being stirred vigorously enough to produce all the crystals that could have been produced.
Therefore, it can be concluded purification by recrystallization allows for the purification of the crude material. The small loss in yield is made up by the high gain in purity. The purity of the material obtained can be correlated to the sharpness and veracity of the melting point data and this was observed.
REFERENCE:
Klein. Organic Chemistry, 1st edition, John Wiley & Sons, Inc, United States
Pavia, D, L, Lampman, GM, Kritz, G. S. and Angel, RG. (2005'), Introduction to organic laboratory techniques: a small-scale approach, United States, Brooks/ Cengage Learning
2. http://chem.chem.rochester.edu/~chem201/Recrystallization.pdf
http://science.csustan.edu/russel/Courses/Chem3012/Lab%20Procedures/Recrysatllization.pdf
University of the South Pacific, CH201, Organic Chemistry, laboratory manual, pg, 32 & 33.
