vishesh

Yes its 2-amino-4-nitrophenol and was wrongly mentioned in paper I am using ethanol. For extracting precipitate I am doing vacuum filtration. I am not monitoring reaction progress using TLC. Thanks for clearing many of my doubts. I guess I'll monitor my reaction using TLC next time and see if I can get complete diazotization and if that solves the problem. I'll come back to this forum if I face any problem during synthesis. Also I see a clear rationale about why I can not use basic conditions for precipitation. Thanks a lot once again

I am using RB flasks for synthesis and I am currently doing synthesis in a chemical hood. Protocol stated here is taken ad verbum from the paper. I also wear protective clothing and eye protection during synthesis. I have done some very basic functional group analysis in organic chemistry. So I don't have an experience in handling such compounds. I keep mixture cold by keeping it in ice bath. Although I did not stirred the reaction mixture vigorously during diazonation. As soon as sodium nitrite is added to the mixture it forms a solid yellow colored precipitate. Also I am adding sodium nitrite very slowly to the reaction mixture.

Dear forum members I am a biologist who is trying to synthesize an organic compound. I am trying to synthesize an organic compound 5-(2-hydroxy-5-nitrophenylazo)rhodanine using a protocol stated in article "Zaijun, L. et al. (2003). Analytical and Bioanalytical Chemistry 375, 408-413." The protocol states that - Transfer 1.54 g of 4-nitro-2-aminophenol dissolved in 45 mL of 95% alcohol into a 100 mL beaker, add 12.0 mL of 6.0 mol L–1 HCI then cool the solution to 0 °C, and add 7 mL of 10% NaNO2 slowly. In another 200 mL beaker, 1.34 g of rhodanine and 14mL of 7.5 mol L–1 ammonia were added. After the solution has been cooled to 0 °C, add the above diazotized solution dropwise and leave the mixture overnight. The solution is then acidified to pH 1 with concentrated HCI and the precipitate was isolated and dried. The crude product was re-crystallized from alcohol, giving pure 5-(2-hydroxy-5-nitrophenylazo)rhodanine (HNAR) in 65% yield. When I acidify the reaction mixture I get yellow precipitate which are not soluble in ethanol. But when NaOH solution is added to these ppt. they solubelize just fine. According to authors this compound has three dissociation constants and it appears yellow in acidic conditions and red in basic conditions. As the compound has three states of pKa (2.75, 6.88, 10.91) can I precipitate this compound by using alkaline conditions? Also how can I check the purity of the compound formed? Also I figured that this synthesis is a two step process which involves diazotization of 2-amino-4-nitrophenol followed by its addition to the solution of rhodanine. Can incomplete/inefficient diazotization be a problem in this synthesis? Is water essential for diazotization? Can I take conc. HCl or higher concentration of Sodium Nitrite to increase the efficiency of diazotization reaction? Thanks.