Spectroscopic and Theoretical Study of the “Azo”-Dye E124 in Condensate Phase: Evidence of a Dominant Hydrazo Form

• DOI: 10.1021/jp907473d
• Publication Date: 2009-10-23T16:00:42Z
• Authors: Mariana R. Almeida; Rodrigo Stephani; Hélio F. Dos Santos; Luiz Fernando C. ...
• Keywords: 02 engineering and technology; 0210 nano-technology

Spectroscopic techniques, including Raman, IR, UV/vis, and NMR were used to characterize the samples of azo dye Ponceau 4R (also known as E124, New Coccine; Cochineal Red; C.I. no. 16255; Food Red No. 102), which is 1,3-naphthalenedisulfonic acid, 7-hydroxy-8-[(4-sulfo-1-naphthalenyl) azo] trisodium salt in aqueous solution solid state. In addition, first principle calculations carried out for (OH) hydrazo (NH) tautomers order assist assignment experimental data. The two intense bands observed UV/vis spectrum, centered at 332 507 nm, can be compared calculated values 296 474 nm 315 500 isomer, with latter closer agreement experiment. Raman spectrum quite sensitive tautomeric equilibrium; state solution, three around 1574, 1515, 1364 cm(-1), assigned mixed modes deltaNH + betaCH nuCC, nuC horizontal lineO lineN nuCC vibrations, respectively. These assignments are predicted only NH species 1606, 1554, 1375 cm(-1). tautomer showed strong 1468 (nuN = N deltaOH) 1324 cm(-1) (nuCC nuC-N), not obtained experimentally. (13)C a very characteristic peak 192 ppm carbon bound oxygen naphthol ring; 165 OH 187 supporting once again predominance solution. Therefore, all theoretical results strongly suggest food or E124 has major contribution structure instead form most abundant condensate phase.