Kamis, 17 Mei 2012

Synthesis of Salicylic Acid


Throughout history, botanical extracts have been used as medicines. Approximately 30% of all medicines have a plant origin. This number increases to 60% if you consider medicines that at one time were derived from plants, but have more recently been synthesized in the laboratory. Salicylic acid is a white crystalline compound that can be isolated from the bark of birch trees. Since it is a valuable substance that can be isolated from nature, it is called a "natural product". Although it was used historically as an analgesic (pain reliever), today it is commonly used in ointments and plasters for the removal of warts from the skin. 
In this experiment you will synthesize salicylic acid from methyl salicylate. In this synthesis, methyl salicylate is the “starting material” or “precursor” and salicylic acid is the “synthetic target.” If the procedure goes well, we’ll be able to refer to salicylic acid as the “product.” Examine the structures pictured in Figure 1.  The difference in the two structures is a single functional group. In methyl salicylate (on the left) the benzene ring is substituted by two functional groups, a hydroxyl group (-OH) and an ester group (-COOCH3). In salicylic acid (on the right), the ester group has been replaced by a carboxylic acid group (-COOH).











In this experiment to analyze the crystal we have gotten, we need to test. is it the crystal formed really salicylic acid compound or not, by using IR and UV instrumental. 
IR instrumental is a way to analyze the compound from the chemical structure not the chemical composition by figuring out the arrangement of each species in the compound. 
in this experiment, organic compound is not as difficult as inorganic compound. when the experiment was ongoing, we did recrystallization to make sure the compound really pure or the opposite and in the elucidation structure to analyze the matter, it has to be pure. if its not pure the others species will appear in the band of IR or UV (it affects the frequency of species).
Crystal is a form of solid to analyze with IR, it has to use Kbr pellet to triturate the sample.Trituration of Kbr is followed to avoid light scattering due to the large size of KBr crystal. KBr is an alkyl halide which doesn't show any absorption spectrum in infrared region. we also can use KCl. KBr doesn't absorb the infrared radiation in the region 4000-400 cm-1. 
The typical sample to KBr ratio used is 1 mg sample/900 mg KBr. This ratio was chosen so that the absorption bands are in the linear region of Beers Law, and so that the signal-to-noise ratio is maximized. Reliable quantitative analysis of samples depends on precise and reproducible sample preparation.



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