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UNIVERSITI SAINS MALAYSIASCHOOL OF CHEMICAL ENGINEERING
EKC 107/3 – ORGANIC CHEMISTRY
LABORATORY COURSE
Name of student : Chin Jin Wei
Matrix Num : 108223
Name of partner : Nor Hasni Binti Abdul Saat
Matrix Num : 108250
Group : B2
Instructor : Prof. Madya Dr. Mashitah Mat Don
EXPERIMENT: SYNTHESIS OF ASPIRIN
Experiment 2: Purification Test
Test Tube Observation/ExplanationWater + salicylic acid + ferric chloride Dark purple colouration formed. Ferric chloride
reacts with the phenol group on the salicylic acid to form a purple complex.
Water + product of experiment + ferric chloride
The solution turn light purple. There is no phenol group presents in the product of the experiment. The aspirin synthesized does not contain a phenol group. However, since aspirin is added to 0.5ml of water, it will undergo hydrolysis, forming salicylic acid and acetic acid (vinegar).therefore, light purple complex formed since salicylic acid from the hydrolysis of aspirin is of lower concentration.
Water + ferric chloride The solution remains colourless due to the absence of salicylic acid. This is act as a control sample.
QUESTION:
1. The important material for preparation of aspirin is salicylic. Preparation process of salicylic acid using phenol is known as Kolbe-Schmitt Reaction. Discuss this reaction process in details.
The Kolbe-Schmitt Reaction is a carboxylation chemical reaction that proceeds by heating sodium phenolate with carbon dioxide under pressure 100 atm at 125°C. The product is then treated with sulfuric acid. The final product obtained is an aromatic hydroxy acid which is also known as salicylic acid, the precursor to aspirin.
Mechanism:
This reaction undergoes the aromatic electrophilic substitution reaction between carbon dioxide and sodium phenoxide. Then it will form three transition states and three intermediates. In the first step of the reaction, a polarized O-Na bond of sodium phenoxide is attacked by the carbon dioxide molecule and the intermediate NaPh-CO2 is formed. Then, the electrophilic carbon atom attacks the ring primarily at the ortho position, it forms two new intermediates. Sodium salicylate is then formed by a 1, 3-proton shift from C to O atom. Salicylic acid can then be obtained through acidification.
2. Salicylic acid is one of the phenol groups while acetylsalicylic acid is not a phenol group. Explain this statement.
Salicylic acid is one of the phenol groups because it contains a benzene ring which has hydroxyl group (-OH). The presence of the phenol group can be tested by using ferric chloride. When salicylic acid react with ferric chloride, purple colouration will be formed, then it has been proven that salicylic acid is
one of the phenol groups.
Aspirin is not a phenol because it does not contain any hydroxyl group that is attached directly to the benzene ring. It is a kind of ester. Hence, aspirin react with ferric chloride, there is no purple solution form. Then we can say that aspirin is not a phenol. This is because aspirin will not reacted with ferric chloride. However, once aspirin has been hydrolysed, salicylic acid and acetic acid (vinegar) will be formed. Thus, reaction with ferric chloride will form light purple complex.
References: http://en.wikipedia.org/wiki/Kolbe–Schmitt_reaction Hermann Kolbe (1860). "Ueber Synthese der Salicylsäure". Annalen der Chemie und
Pharmacie 113 (1): 125–127 http://www.organic-chemistry.org/namedreactions/kolbe-schmitt-reaction.shtm
http://www.chymist.com/DRUG%20TESTING.pdf