Abstract
In the manufacture of the food colorants Food Blue No. 1 (B1) and Food Green No. 3 (G3), various sulfonated aromatic
intermediates and their regioisomers, [N-ethyl-N-(sulfophenyl)amino]methylbenzenesulfonic acids (ESBSAs), are potentially
generated as impurities. Determining how well these ESBSAs are detected under HPLC analysis conditions for B1 and G3, in
accordance with Japan’s Specifications and Standards for Food Additives, provides useful insights for updating quality control
procedures. Although m,p-ESBSA (7), m,m-ESBSA (8), and m,o-ESBSA (9) have previously been synthesized and analyzed,
other regioisomers remain unidentified. In this study, three other isomers that can theoretically be generated as impurities in the
preparation process̶ p,p-ESBSA (10), p,m-ESBSA (11), and p,o-ESBSA (12)̶were synthesized, and their molecular structures
were rigorously assigned using 1D/2D-NMR spectroscopies, including COSY, NOESY, HMQC, and HMBC. The chromatographic
retention times and photodiode array spectra of the three new compounds 10–12, along with those of the previously synthesized
compounds 7–9, were also determined under the HPLC conditions specified in the purity test of B1 and G3. Among the newly
synthesized compounds, 10 was identified as an impurity in commercial B1 samples. These findings expand the impurity profile
associated with B1 production and provide essential data for establishing higher-level quality control and safety assessments of tar
dye products.
