Conclusion questions Organic Chemistry Laboratory I1 OXIDATION OF AN ALKYL SIDE
ID: 1080524 • Letter: C
Question
Conclusion questions Organic Chemistry Laboratory I1 OXIDATION OF AN ALKYL SIDE CHAIN The purpose of this experiment is to enable the student to learn about oxidation reactions. In an effort aimed at illustrating such reactions, the permanganate oxidative degradation of the alkyl side chain of an unknown aromatic compound to yield a carboxylic acid will be performed. SCHEME 1. General equation of the permanganate oxidative degradation of an alkyl side chain on an aromatic ring COOH CHR2 1)KMnO4 / OH . / 2) H X- H or alkyl group X--F, -CI, -Br, -I,-NO2, -OCR3,.... X -OH,-NR2 where, RExplanation / Answer
a) The purity of the product obtained in the reaction can be checked by employing chromatographic techniques. TLC can be used to check if the reaction mixture (after 1 and half hours) contain the starting material or not. In TLC, a spot of the reaction mixture is placed near the bottom of a silica/alumina plate and the plate is introduced in a developing chamber containing a suitable solvent. A similar set-up must be set for the pure starting material (toluene in this case). After a certain amount of time, when the plate has developed (a TLC separation is usually complete when the sample spot has travelled almost to the top of the silica plate), we need to check for the number and the position of the sample spot on both the plates. If the reaction is complete and contain the pure product, then the spots on the two plates will move up to different positions. In case the mixture contains only the product, there will be no spot for the reactant (this can be checked on the second plate). However, if the mixture contains both the reactant and the product, then the plate will contain two separate spots for the reactant and the product. Thus, TLC is a simple but powerful tool for deciding the purity of the product.
b) TLC may be used to check for the purity of the reaction mixture at the end of 1 and half hours. A small volume of the sample may be withdrawn from the reflux flask and the TLC run as noted in part (a) above. If the TLC plate contains a single spot (this spot must be different from that of the reactant), then the reaction is complete (check for the purity of the product by IR and NMR). However, if the reactant spot is still present, the reflux needs to be carried on longer and samples must be withdrawn from the reflux flask at regular intervals to check for the purity of the product. At all times, it must be remembered that the TLC for the reactant (toluene) must be run for comparison purposes.
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