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Experiment 4: Heating Under Reflux- Synthesis of Salicylic Acid from Wintergreen Oil

Precious Ahmed
ID# 6463614
Section 07, Friday afternoon

Lab experiment performed on: Friday, January 19, 2013
Lab report submitted on: Friday, January 24, 2013
Introduction
Before the synthetic aspirin of today, salicylic acid, which is the important ingredient found in aspirin, was extracted naturally from methyl salicylate found in Wintergreen oil, which could be found in certain plants. The purpose of this lab experiment is to prepare salicylic acid from the natural starting material, methyl salicylate, and compare it with the salicylic acid produced from the artificial compound benzene (obtained through petroleum refining). Based on the two reactions of aspirin synthesis shown below, methyl salicylate and benzene share a common intermediate which is salicylic acid:

In order to prepare salicylic acid from wintergreen oil, an organic synthesis must be carried out. This is done first by separating salicylic acid from methyl salicylate, followed by its purification. The separation can be done by performing a reflux of a solution of methyl salicylate and sodium hydroxide. After the reflux is complete, sulphuric acid will be added to the refluxed solution, which will cause the salicylic acid to precipitate. This will then be filtered through suction filtration. Once the product has dried, purification must be done by recrystallization; dissolving the product in a minimum amount of hot solvent (water), and then filtering once again through suction filtration. Finally, to complete the main purpose of the experiment, which is to compare the prepared product with a standard (salicylic acid from benzene), an analysis must be done by measuring the melting point of the crystals and of the standard. This is fulfilled by using capillaries opened at one end containing a very small amount of both samples (dried product and a 1:1 mixture of the dried product with standard), and inserting them into the melting-point apparatus, where their melting point can be read on the thermometer. Results:

Physical Properties:
| Molecular weight (g/mol)| Melting point (oC)| Boiling point (oC)| Density (g/mL)| Methyl salicylate| 152.1| -8| 223| 1.174|
Salicylic acid| 138.1| 159| -| -|

Raw data:
Mass of watch-glass (g)| Mass of watch-glass + initial product (g)| Mass of watch-glass + crystals (g)| Melting point range of crystals (oC)| Melting point range of 1:1 mixture (oC)| 29.677| 30.808| 30.876| 154-157| 158-159|

Observations:
* Precipitation of salicylic acid occurring from addition of sulphuric acid * crystals appearing on the surface while cooling in ice-bath
Data:

Mass of product, actual yield (g)| Percent yield (%)| Melting point range (oC)| 1.199| 86.82| 154-157|

Calculations:
Theoretical yield
*Methyl salicylate =MS, Salicylic acid= SA
1.521g MS x (1mol MS/152.1g MS) x (1mol SA/1mol MS) = 0.01 mol SA Mass of SA:
0.01mol SA x (138.1g SA/1mol SA) = 1.381g Salicylic acid
Percent yield
Percent yield = (actual yield/ theoretical yield) x 100%
= (1.199g/ 1.381g) x 100% = 86.82 %
Percentage error
Percentage error = [(Actual yield – theoretical yield)/ theoretical yield] x 100% = [(1.199g – 1.381g)/ 1.381g] x 100% = 13.18% Mechanism:

Discussion and conclusion

Methyl salicylate (which comes from wintergreen oil) and benzene are two compounds from which salicylic acid can be obtained from. The difference between the two is that one can be found naturally in plants (methyl salicylate) and the other is artificially produced (benzene). The question is do they yield the same desired product (salicylic acid)? This lab experiment consisted of preparing salicylic acid from a methyl salicylate sample and, and comparing it with salicylic acid made from benzene by measuring their melting points at the same time. In order to do so,...
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