核磁気共鳴法によるナフタリンスルホン酸異性体の簡易定量

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It was difficult to determine naphthalenesulfonic acid isomers in the form of the acids because of their strong polar effects and high boiling points. A method for the determination of peak area ratios of naphthalenesulfonic acid isomers by nuclear magnetic resonance technique was investigated. The NMR measurements were made by a JNM-C-6OHL spectrometer (60 MHz) and the intensities of peak areas were measured by an integrator. From the NMR spectrum of an equimolar mixture of α- and β-naphthalenesulfonic acids dissolved in D2O, the doublet of 2-position proton for α-naphthalenesulfonic acid appears at 8.69 and 8.84 ppm and the singlet of 1-position proton for β-naphthalenesulfonic acid appears at 8.37 ppm (Fig. 4). The area intensities of these characteristic peaks were used for the determination of naphthalenesulfonic acid isomers. The well-resolved spectra were obtained in the concentration range 8 to 15%, where the OH proton peak in D2O did not overlap with the aromatic ring proton peaks. The area intensities were measured by alterations in the compositions for the preparation of the calibration curve. The mixed ratios agreed well with the area ratios of their peaks (Table I). Since naphthalenesulfonic acids contained sulfuric acid, the OH proton peak of SO3H was appreciably shifted to a low field. However the OH proton peak did not shift up to the peaks of the aromatic ring proton, even if samples contained about 2-fold weight of sulfuric acid. Therefore the method was free from the effect of sulfuric acid remaining in naphthalenesulfonic acids. By this method, the ratio of naphthalenesulfonic acid isomers produced by sulfonation of naphthalene was determined (Table II). The method is rapid and easy with an average error of about 1%.
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核磁気共鳴法によるナフタリンスルホン酸異性体の簡易定量

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