Final Project Spring 2011: Part IV

The third project started with the synthesis of an azo dye that we had performed earlier in the semester. The combination of 4-aminosulfonic acid and 2-naphthol yields 4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid which is also known as acid orange 7. The phenolic hydroxyl group was acetylated with acetic anhydride in a reaction which is similar to the one used in the synthesis of aspirin. Then we attempted to reduce the azo nitrogen-nitrogen double bond with sodium dithionite (Na2S2O4). This last reaction works on paper, but I was not absolutely sure that this reaction would not completely reduce the azo bond to two primary amines. Interestingly, the reaction seemed to work well in the lab. The acetylated azo dye was dissolved in water and a small amount of potassium carbonate was added. Solid sodium dithionite was added with stirring. The orange solution bleached somewhat and a precipitate formed with continued stirring and cooling in an ice. The precipitate could be easily recovered by filtration. IR showed that the nitrogens were indeed reduced (doublet at 3386 & 3314 1/cm). The UV-vis lambda max was shifted from 484 to 345 nm. NMR of the product was inconclusive since the two structures are pretty close – the only difference being two new N-H hydrogens.

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