Spectrophotometric Determination of I-Naphthol GEORGE A. PEARSE, Jr. Chemistry Department, leMoyne College, Syracuse 3, N . Y.
b A method was developed for the determination of 1-naphthol in the presence of 2-naphthol and other phenolic compounds. This method is based upon the simultaneous development and extraction of the colored product obtained by shaking 1 -naphthol in the presence of iodine, sodium hydroxide, and a water-immiscible solvent. The absorbance of the nonaqueous system is measured at 528 mp. The method can be applied over the concentration range of 5 to 35 p.p.m. Phenol, 2,4-dichlorophenol, picric acid, thymol, catechol, resorcinol, hydroquinone, and phloroglucinol do not interfere.
A
some methods have been published for the determination of 1-naphthol, the literature contains very few direct spectrophotometric procedures which are fast, accurate and free from interferences by phenols. Svailable procedures include the direct fluorometric measurement of I- and %naphthol (4) and the potentiometric titration of 1- and 2-naphthol with iodine monobromide in glacial acetic acid ( 8 ) . 1-Naphthol can be determined gravimetrically as the dinaphtholcarbinol (2). The spectrophotometric LTHOUGH
Table 1.
Stability of the 1-Naphthol Color
Time, hr. (after addition of NaOH)
0.00 0.25 0.50 0.75 1.00 1.50 2.00 4.00
Absorbance 0.00
0.73
0.72
0.70 0.69 0.66 0.62 0.57
Table II.
a
Effect of Iodine Concentration" 0 l,jS ioditie solution, nil. Absorbmce 0.00 0.00 0.05 0.50 0.34 1.00 0.68 2.00 0.73 3.00 0.73 5.00 0.73 10.00 1-Yaphthol concent,rntion of S X 1 0 - 5
mole/liter. 1954
ANALYTICAL CHEMISTRY
procedures include the reaction of 1-naphthol with benzene diazonium chloride (3), with X-chloro-p-toluenesulfonamide ( I ) , with sodium nitrite (6), and with tetramethylaminobenzophenone (6) followed by the measurement of the colored system produced. These procedures suffer froin either interference by 2-naphthol (7') requiring prior removal or a relatively large average error. A study of the reaction of a number of phenols with iodine and sodium hydroxide accompanied by extraction of the colored species showed that only 1-naphthol undergoes a color formation under these conditions and does so in the presence of any or all of the phenols tested. The l-naphtholiodine-sodium hydroxide system \vas investigated thoroughly, and a spectrophotometric procedure for the determination of 1-naphthol was developed. EXPERIMENTAL
Apparatus and Reagents. -111 spectrophotometric measurements mere made a t 25' C. n-ith a Beckman DU or a Uau-.ch and Lomb Spectronic 505 spectrophotometer using 1-em. matched silica cells. A11 phenol and naphthol compounds were Eastman Kodak white label and were recrystallized just prior t o use. Stock solutions of all compound- were prepared by diasolution of a weighed amount of the solute in the solvent under investigation just prior to being used. The 0.15N iodine stock solution was prepared by dissolving 19.5 grams of iodine and 30 grams of potassium iodine in water and diluting to 1 liter. Xylene, chloroform, nitrobenzene, and carbon tetrachloride were reagent grade solvents and were used without further purification. Recommended Procedure. The sample containing 1-naphthol is dissolved in xylene and diluted to a known volume. An aliquot containing 1 to 25 mg. of 1-naphthol is pipetted into a 125-inl. separatory funnel, and sufficient xylene added t o make the volume about 25 ml. Stock 0.15.Y iodine solution ( 5 ml.) iq added and shaken to ensure distribution between the organic and aqueous layers. To this solution is added 5 ml. of 1 S sodium hydroxide wlution, : L I I ~the mixture ia shaken for 1 minute. The color is extracted into the xylene layer and the excess iodine is decolorized by the sodium hydroxide (Table I). Sodium chloride ( l N , 10 ml.) is added to the separatory funnel to assist in breaking the emulsion formed at
the liquid interface. The organic layer is washed three times with distilled water, transferred to a 50-ml. volumetric flask, and brought to volume with xylene. The absorbance is measured a t 528 mp against a reagent blank, and the amount of 1-naphthol is determined from a previously prepared calibration curve. DISCUSSION AND RESULTS
The 1 - naphthol - iodine - sodium hydroxide system is not sensitive to excess iodine over and above that necessary for maximum color development (Table 11) eliminating the necessity of carefully controlling the amount of reagent added. However, the greater the excess of iodine, the more sodium hydroxide solution is necessary to discharge the color due to excess iodine. Similarly, excess sodium hydroxide is not a critical factor (Table 111),but it does contribute to the emulsion which forms between the organic and aqueous phases. The colored species has a fairly high absorptivity, 9000, which is enhanced by estraction. Several common waterimmiscible organic solvents u-ere investigated including xylene, chloroform, nitrobenzene, and carbon tetrachloride. All except carbon tetrachloride extracted the colored species, but xylene is the most advantageous because of its density, lack of absorbance in the visible region of the spectra, and its insolubility in water. Solvents such as chloroform, having a density greater than water, complicate the washing of the absorbing species in the organic phase, and 1 cm. of nitrobenzene is opaque to radiant energy below 435 mp. Data concerning the effect of 2naphthol and other phenols on the determination of 1-naphthol were ob-
Table 111.
Effect of Sodium Hydroxide Concentration" 1.O S SaOH, ml. Absorbance 0.00 0.00 0.45 0.25 0.63 0.50 I .oo 0.r 6 2 00 0.70 :
