食用黄色5号製造時における副成色素Trisodium salt of 6-hydroxy-7-(4-sulfophenyl)-5-(4-sulfophenylazo)-2-naphthalenesulfonic acidの生成条件

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  • The Generative Condition of the Trisodium salt of 6-hydroxy-7-(4-sulfophenyl)-5-(4-sulfophenylazo)-2-naphthalenesulfonic acid, a Subsidiary Color Formed in the Production of Food Yellow No.5 (Sunset Yellow FCF)
  • ショクヨウ キイロ 5ゴウ セイゾウジ ニ オケル フクセイシキソ Trisodium salt of 6 hydroxy 7 4 sulfophenyl 5 4 sulfophenylazo 2 naphthalenesulfonic acid ノ セイセイ ジョウケン

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In our previous report, we described the isolation of two unknown subsidiary colors from commercial Sunset Yellow FCF (Y5) and the identification of their chemical structures. The trisodium salt of 6-hydroxy-7-(4-sulfophenyl)-5-(4-sulfophenylazo)-2-naphthalenesulfonic acid (Y5-SA) is one of the subsidiary colors isolated and it has a sulfonatophenyl moiety located at the 7-position of Y5. As it was thought that Y5-SA is generated under the reaction conditions used in Y5 production, we investigated its mechanism of generation. The experimental synthesis of Y5-SA clarified the following points: 1) When a ratio of the the sulfanilic acid diazonium salt and the Schaeffer's salt were changed and then reacted, the quantity of Y5-SA that was generated increased when the quantity of the sulfanilic acid diazonium salt was increased. 2) When the sulfanilic acid diazonium salt was added to Y5, the amount of Y5-SA that was generated depended on time and the quantity of the sulfanilic acid diazonium salt. 3) There was little generation of Y5-SA at pH 8.0 〜 pH 10.0, and generation peaked at pH 12.0, and then decreaced at pH 13.0. Fig.5 shows the reaction pathways of Y5-SA. According to Mazzola et al, Y5 is balanced as shown in Fig.5-A. They also proved that the pKa of phenol is 12.0 by potentiometric titration and from the chemical shift change of 13C-NMR. We concluded as follows: ・Y5 at pH 12.0 is balanced as shown in Fig.5-B. Phenoxide ions that are generated are delocalized and stabilized on the naphthalene ring. ・The anion localized at the 7-position of the naphthalene ring is highly reactive. ・This anion reacts with the cation generated by the decomposition of the sulfanilic acid diazonium salt (Fig. 5-C) to produce Y5-SA (Fig. 5-D). When Y5 is manufactured, Schaeffer's salt and sulfanilic acid diazonium salt are coupled in equal amounts. Therefore, to reduce the amount of Y5-SA in Y5, it is necessary to carry out the reaction at pH 10.0, which is the optimum pH for the coupling reaction used in the generation of Y5. Based on these reacts, Y5-SA can be used as a GMP marker during Y5 production.

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