An organic conversion
He underwent a few purification steps; the first was recrystallization, where he added boiling water to the solid, and heated it to evaporate some of the water off. The saturated solution, when cooled back to room temperature, formed crystals which were then filtered. The second purification step was to dissolve the anthranilic acid crystals in methanol. The solid was far more soluble in the similarly organic liquid, and then when cold water was added, the 2 solutions hydrogen-bonded and mixed, which therefore lowered the solubility of the solution and kicked out the acid solid, while retaining some of the impurities; this left a relatively pure solid. The final step was to convert the anthranilic acid into the final product, methyl anthranilate. The acid was dissolved in methanol, before adding concentrated sulfuric acid, which reacted with the other acid to form anthranilic acid sulfate. The solubility of the acid sulfate is very low in methanol, and so it gets kicked out of the solution. To combat this, the solution is heated up to increase the solubility of the methanol, and then it is refluxed with the sulfuric acid as a catalyst, so that a Fischer Esterification reaction can occur. In this mechanism, the electropositive hydrogens from the sulfuric acid are donated a lone pair of electrons from the double-bonded carbon, leaving sulfate ions and a positively charged oxygen. Then, the electrons from the pi-bond relocate to become a lone pair on the oxygen atom to neutralize this charge, and leaving the carbon with a positive charge. This carbon is attacked by the lone pair of electrons on the oxygen from the methanol, which joins the structure and inherits the positive charge. Next, the hydroxyl group deprotonates the O + ion, inheriting another hydrogen, and then being eliminated as a water molecule. This occurs while the original oxygen re-donates its lone pair to the carbon atom to restore the pi bond, and regain a positive charge; the sulfate ion can then deprotonate it to reform the sulfuric acid. Overall, the methyl anthranilate sulfate would be formed.
Fischer Esterification Mechanism
To isolate the methyl anthranilate from the reaction mixture, it was all poured into a beaker of water, to which sodium carbonate solution was added, which both neutralized the sulfuric acid in the mixture, and also reacted with the sulfate salt to free the methyl anthranilate from its sulfate salt form. The mixture was then poured into a separatory funnel and shaken with dichloromethane, a solvent which could mix with the methyl anthranilate due to their organic nature, but not with the solution due to its inability to hydrogen bond. After the aqueous layer was discarded, the DCM was shaken with water in the funnel, to remove any water-soluble impurities.
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