Abstract
In the previous papers, the characters of the hydroxyl derivatives of chromone, benzo-1, 4-pyrone, as an analytical reagent have been reported. Similar studies were carried out on the hydroxyl derivatives of xanthone, dibenzo-1, 4-pyrone or 2, 3-benzochromone. The present paper deals with the reaction of 1-hydroxy- xanthone, 2, 3-benzo derivative of 5-hydroxychromone which is an useful reagent for the spectrophotometric or fluorometric determination of some cations, with about forty metallic ions.
The reagent was prepared by fusing resorcinol with salicylic acid in the presence of zinc chloride. The investigations were carried out on the solutions ranging in pH from 1 to 12, which contained 1 × 10-6 mol of metallic ion, 1.5 × 10-5 mol of reagent and 50 vol% of metanol in 25 ml. When precipitation or coloration was observed, extraction with the organic solvents was attempted. Thirteen ions react with this reagent. The following ions give the precipitates which are insoluble in the organic solvents: magnesium, yellow, pH>10; titanium, pale yellow-green, pH>5 ; zirconium, yellow, pH>4 ; cerium(IV), yellow, pH>8; thorium, yellow, pH>7. Aluminum reacts to form a soluble yellow-brown complex in the range of pH 210 with a maximum absorbance at pH about 5 and uranium to form a yellow-brown complex in the range of pH711 with a maximum absorbance at pH about 9. These can not be extracted. Nickel and cobalt react to form yellow precipitates at pH>7. These can be extracted, but they are very unstable. Palladium forms a yellow precipitate at pH>2. It can be extracted, but the organic phase become slightly turbid. Iron(III) gives dull green in the range of pH 14 with a maximum absorbance at pH about 2.5 and a red-brown precipitate at pH>8.The latter complex can be extracted with the organic solvents, but it is unstable. Beryllium and copper react to form yellow precipitates at pH>5 which can be extracted and they are stable. The beryllium complex shows a strong fluorescence in ultraviolet radiation similarly to its 5-hydroxychromone complex. The number of reacting cations is less than that reacts with 5-hydroxychromone and the complexes extracted are very unstable except those of beryllium and copper. These effects may be attributed to the steric hindrance deu to two benzene rings on both sides of pyrong ring.
Beryllium and copper can be determined spectrophotometrically. An analytical procedure is as follows: To a sample solution containing up to 7 μg of beryllium or 40 μg of copper, are added 10 ml of 3 × 10-3 M methanol solution of the reagent, 2.5 ml of methanol, 5ml of buffer solution (boric acid-sodium hydroxide, 0.25 M in boric acid, pH 8 for beryllium, pH 11 for copper), and it is made up to 25 ml with water. After about one hour, the solution is shaken for thirty seconds with 10 ml of benzene. The organic phase is separated and dried over sodium sulfate. Its absorbance is measured at 430 mμ for beryllium or 440 mμ for copper. Both analytical curves are linear.
