Determination of Resorcinol in Solutions Containing Phenol, Hydroquinone, and Catechol MAURICE CODELL and LEONARD TEITELL Research and Development Group, Frankford Arsenal, Philadelphia 37, Pa. EDGAR HOWARD, Jr. Temple Universify, Philadelphia, Pa. A colorimetric method was developed for the determination of resorcinol in the mixture of phenolic compounds that i s obtained upon gamma irradiation of phenol in dilute sulfuric acid solution. This method is based upon extraction, with butyl acetate, of the colored product obtained by addition of iodine to a buffered mixture of resorcinol and catechol. The method can be applied over the range 1 to 14 kg. per ml. of sample. Phenol, hydroquinone, and catechol do not interfere.
A
method was needed for the determination of resorcinol in a mixture of compounds obtained upon gamma irradiation of phenol in aqueous solutions containing 0.1 mole of sulfuric acid per liter of solution. ilmong other compounds, the irradiated solutions contained hydroquinone and catechol as products and a relatively large amount of unchanged phenol. Sensitive analytical procedures were used by Stein and Weiss (4) in their study of X-irradiated aqueous phenol solutions, but they did not observe the presence of resorcinol in their solutions. I n the present work resorcinol was detected in the gamma-irradiated phenol solutions by paper chromatography, but quantitative methods based upon this technique are, besides being tedious, unsatisfactory because of the nearly identical Rf values of hydroquinone and resorcinol in the solvent systems described (1-3) for separating the dihydroxybenzenes. Resorcinol was determined spectrophotometrically, a t 275 mp, by eluting with ethyl alcohol the resorcinol-hydroquinone spot from a paper chromatogram. Hydroquinone interferes, but can be corrected for by determining it independently a t 292 mp. The method fails when the ratio of hydroquinone to resorcinol is large, The quantities of resorcinol to be determined ranged from l to 100 pg. per ml., depending upon the radiation dose given to the aqueous solutions of phenol. Volumetric and gravimetric methods for determining resorcinol RELIABLE
were not considered practical for quantities as low as 1 fig. per ml., and methods such as polarographic, that are based upon the measurement of the oxidation potential of resorcinol, do not differentiate between resorcinol and its isomers. A preferred method would be one which could be directly applied to the aqueous solution and in which no interference is encountered from phenol, hydroquinone, catechol, dihydroxydiphenol, and quinones obtained from the oxidation of phenol. A gravimetric method for resorcinol was developed by Willard and Wooten ( 5 ) , based upon iodination. C&(oH)z
+ 312
+
CaHIdOH)*
+ 3HI
The ability of resorcinol to undergo this reaction is attributed to its large ionization constant; several other phenolic compounds are also capable of undergoing this reaction. Phenol, which has a low ionization constant, is not iodinated under these conditions. Willard and MTooten noted that when this reaction was carried out in the
presence of catechol, a blue-violet precipitate was formed which was soluble in acetone, and they utilized this reaction for a colorimetric determination of resorcinol and catechol (6). The method was shown to be satisfactory in the presence of up to a 50 to 1 ratio of many phenolic compounds. Attempts to apply this method, without modification, to the determination of resorcinol in irradiated phenol mixtures were unsuccessful for several reasons. The solutions were strongly acid and neutralization with sodium hydroxide or ammonium hydroxide produced inconsistent results. The irradiated solutions exhibited various shades of yellow or brown which absorbed strongly a t wavelengths that could be used for the determination. The irradiated solutions contained compounds which gave colored products with iodine. The method was not sufficiently sensitive for the quantities of resorcinol to be determined. These limitations were overcome by changing the conditions for the reaction and by extracting and concentrating the colored products. The changes eliminated or decreased the criticalities of the iodination period, the buffer adjustment, and the bleaching effect of thiosulfate. Extraction of the colored product increased the sensitivity and separated colored products that arise from interfering substances originally present. EXPERIMENTAL
a3
MO
600
700
800
WAV€ LENGTH-mp
Figure 1. Spectrophotometric curves for n-butyl acetate-ethyl alcohol solutions of resorcinol-catechol-iodine product. Upper. lower.
Solution containing 87 pg. of resorcinol Solution containing 20 pg. of resorcinol
Apparatus. Universal Coleman Model 14 Spectrophotometer with 1-inch matched cells. Reagents. Standard Resorcinol Solution (1 ml. = 10 pg. of resorcinol). Dissolve 1.0000 gram of resorcinol in 0.2N sulfuric acid and dilute to 1000 ml. with 0.2N sulfuric acid. Dilute 10 ml. of this solution to 1000 ml. with 0.2N sulfuric acid. Catechol Reagent (1000 pg. per ml.). Dissolve 1.0 gram of catechol 1 ~ .0.2N sulfuric acid and dilute to 1 liter with 0.2N sulfuric acid. Iodine Solution, 0.15N. Dissolve 19.5 grams of iodine and 30 grams of potasVOL 34, NO. 1, JANUARY 1962
a
157
Table 1. Effects of pH and Phenol on Color Formation (50 pg, of resorcinol present in each sample) 0 1M Phenol HzSO, XaC2H302 (in 0 2.L’ HzSO~), Absorbance (750 M p ) ( 0 2 X ) , M1. (4 O A T ) , 111. Ml. pH 10 1 0.0 4.58 0 1.5 0.0 4.74 0.079 2.0 0.0 4.89 0.187 0.0 2.5 5.14 0.280 0.0 3.0 5.30 0,285 0.0 4.0 5.60 0.286 0.0 5.0 5.76 0.288 9.5 5.0 5.72 0.287 0.5 9.0 5.76 0.288 5.0 1.0 5.61 0,286 8.0 5.0 2.0 5.67 0,281 5.0 5.0 5.0
sium iodide in water and dilute to 1 liter. Sodium Thiosulfate Solution, 0.3iv. Dissolve 75 grams of sodium thiosulfate in 1 liter of freshly boiled cool water. Sodium Acetate Solution, 4N. Dissolve 300 grams of anhydrous sodium acetate in water and dilute t o 1 liter. Butyl Acetate-Ethyl Alcohol Solution (1 t o 1). Mix equal volumes of butyl acetate and ethyl alcohol, 95%. Preparation of Calibration Curve. Transfer quantities of standard resorcinol solution containing 10 to 100 pg. of resorcinol to 100-ml. separatory funnels. Add sufficient 0.2N sulfuric acid to bring the volume to 10 ml. From a pipet add 1 ml. of catechol solution and 5 ml. of sodium acetate solution. From a buret add 5 ml. of iodine solution, swirl for about 15 seconds, and add from a buret sufficient sodium thiosulfate solution to discharge the iodine color, adding 1 or 2 drops in excess. Immediately add 20 ml. of
the butyl acetate-ethyl alcohol solution and shake vigorously for about 20 seconds. Allow the layers t o separate, then draw off and discard most of the water layer. Let stand about 0.5 minute, then draw off the remainder of the water layer. Transfer the extract from the top of the funnel to a 25-ml. volumetric flask, rinse the funnel with 5 ml. of ethyl alcohol, and add it t o the flask. Finally dilute the solution in the flask to the mark with ethyl alcohol. Determine the absorbance at 750 mp against a reagent blank which has been carried through all steps of the procedure. Procedure. Transfer t o a 100-ml. separatory funnel a sample in 0.2N sulfuric acid not exceeding 10 ml. containing 10 to 100 pg. of resorcinol. If less than 10 ml. of sample has been taken, add sufficient 0.2N sulfuric acid to bring the volume to 10 ml. Follow the procedure used for the preparation of calibration curve and determine the concentration of resorcinol by consulting the curve or from the relationship:
diluted to 25 ml. with ethyl alcohol. The absorbance was determined at 750 m p . It can be seen from Figure 1 that the complex exhibits maxima a t 515 and 750 mp, but the latter was preferred because of a light yellow color in the extract from samples which have undergone intense irradiation, and this solution absorbs somewhat a t 515 mfi, The colored complex obeys Beer’s law, and is stable for a t least a week. Phenol and catechol mere found to interfere slightly with this method in the presence of ammonium salts, because of the formation of a yellow coloration, and it would be necessary to apply correction curves in their presence. Attempts to eliminate this interference by neutralization with sodium hydroxide were unsuccessful because a t the high p H values obtained with sodium hydroxide, catechol is oxidized fairly rapidly and errors from tm-o effects may be introduced. The quantity of catechol can be reduced below that required for the comples formation, resulting in lower absorbance, and the greenish yellow color of oxidized catechol can result in increased absorb-
Table IV.
(Samples prepared from stock solution 0.1N in phenol, 0.2.V in and containing 100 pg./ml. of resorcinol, hydroquinone, and catechol, respectively. Stork solution diluted with 0.2.V H2S04to provide resorcinol contents listed below) Resorcinol Resorcinol Content, Found, pg. Absorbance !4. 2
sg. of resorcinol = absorbance X 173 Table II. Effect of Catechol on Absorbance
(Each sample contained 50 pg. of resorcinol) CateAbsorbCateAbsorbchol ance chol ance Added, (750 Added, (750 PLg.
Ab)
PLg.
M/.l)
100 200 300 400 1000
0.158 0.220 0.280 0.282 0.284
2000 4000 5000 6000
0.283 0.222 0.182 0.124
Table 111.
Effect of Hydroquinone
(Each sample contains 30 pg. of resorcinol) Hydro- Absorb- Hydro- Absorbance ance quinone quinone (750 Added, (750 Added, Pg. hb) M. 1000 2000 3000 4000 5000
158
0.176 0.174 0.179 0.178 0.178
10,000 15,000 20,000 30,000 50,000
ANALYTICAL CHEMISTRY
0.173 0.069 0.033 0.015 0.008
RESULTS A N D DISCUSSION
All of the irradiated phenol mixtures were present in aqueous 0.2iV sulfuric acid solution. It was therefore necessary to adjust the p H of the solution to a value which permitted full color development. A method was first developed in which the solution, containing sufficient catechol to form the resorcinol-catechol-iodine complex, was neutralized with ammonium hydroxide to phenolphthalein and the color of the indicator just discharged with sulfuric acid. Sodium acetate was added, producing a solution of p H 7 . 8 . Iodine solution was then added and the excess iodine destroyed with sodium thiosulfate. The colored complex was estracted with a mixture of ethyl alcohol and butyl acetate. The complex mas extractable with butyl acetate alone, but its low solubility resulted in incomplete recoveries when high concentrations of resorcinol were involved. After extraction, the solution was
Determination of Resorcinol in Synthetic Mixture
10 20
30 40
50
80
100
140
0 017 o.oi7 0.018 0.058 0.057 0.055 0.125 0.122 0.118 0.117 0.180 0.178 0.176 0.237 0.235 0.238 0.238 0.290 0.294 0.288 0,292 0.295 0.462 0.462 ~._. 0.457 0.465 0.459 0.570 0.570 0.790 0.800
2 9 2.9 3.1 10.0 9.8 9.5 21.5 21.0 20.3 20.1 30.9 30.6 30.2 40.7 40.4 40.9 40.9 49.8 50.5 49.5 50.2 50.7 79.4 79.4 78.5 79.9 78.9 97.9 97.9 135.7 137.5
ance. To eliminate the difficulties encountered upon neutralizing the solutions, the addition of a carefully calculated quantity of sodium hydroxide iollowed by the addition of sodium acetate resulted in a solution of approximately pH 6.5 and produced satisfactory results. However, this procedure was not dependable because of the required careful control of acid and base. The addition of a sufficient quantity of sodium acetate to the sample solution resulted in solutions of pH values sufficient for color development. To determine the optimum quantity of sodium acetate, the effect of increasing quantities upon pH and absorbance was determined (Table I). pH values above approximately 5.2 are satisfactory and the addition of 5 ml. of 4N sodium acetate provides a safe excess. That phenol has no appreciable effect is also shown in Table I. The effect of catechol is shown in Table I1 and the effect of hydroquinone is shown in Table 111. For a sample containing 50 pg. of resorcinol a t least 300 pg. of catechol must be present. A lesser amount of catechol is used for samples containing less than 50 pg. of resorcinol. Interference is encountered from quantities of catechol in excess of 3000 pg, or a ratio of catechol to resorcinol of 60 to 1. The quantity of hydroquinone in the sample must not exceed 10,000 fig. Results for a svnthetic mixture are s h o m in Table
In the method developed by U’illard and Wooten, the thiosulfate used to destroy excess iodine must be carefully titrated, using a starch solution as indicator, because excess thiosulfate has a bleaching effect on the color. The pH of the buffer solution which they used was 5.7 and was found to be critical. Frequent checking and adjustment of the pH of this solution were necessary. KO bleaching effect could be tolerated with the irradiated solutions because the amounts of resorcinol to be determined were so small. I n the extraction procedure, no interference is encountered from a few drops of excess thiosulfate solution, because the colored complex is immediately removed from the aqueous solution with butyl acetate-ethyl alcohol mixture. However, a large escess of thiosulfate has an immediate bleaching effect and must be avoided. No control of the pH of the buffer solution is required with the extraction procedure. Willard and Wooten were able to obtain full color development with slightly more catechol than a 1 to 1 ratio and an iodination period of one minute was required for full color development. With the extraction procedure, a catechol-resorcinol ratio of 6 to 1 is required, but the iodination period is not critical. Iodination periods ranging from 10 seconds to 5 minutes produced equivalent results. The sensitivity of the extraction procedure is increased by two effects. The color intensity of the extracted com-
plex is greater than that in the aqueous solution, and the solution of the coniplex can be concentrated by estraction with a small volume of solvent. The application of the estraction procedure to the determination of catechol in irradiated phenol mixtures was not very successful, because the resorcinol which must be present in excess forms a colored complex with iodine and a correction curve would have to be applied. Also an iodination period of approximately 5 minutes was required for full color development. X serious effort toward applying the method to the determination of catechol did not appear warranted because the titanium (111) method used by Stein and Weiss (4) for irradiated phenol solutions was found satisfactory. LITERATURE CITED
(1) Bray, H. G., Thorpe, I?. V., “Uethods of Biochemical Analysis,” D. Click, ed., Chap. 2, Vol. 1, p. 37, Interscience,
New York, 1954. R. W., LeTourneau, D., Mahlum., D.., J. Chromatoa. 1. 534 (1958). (3) .Reio:, L., “Chromatographic Remews, M. Lederer, ed., p. 39, Elsevier, Amsterdam, 1959. (4) Stein, G., Weiss, J., J. Chem. SOC. 1951,3265. (5) Willard, H. H., Wooten, A. L., ANAL. CHEW22, 585 (1950). (6) Ibid., p. 670. (2) Keith,
1
for revie’v
“9
.
lg6“
Accepted November 8, 1961. Division of Analytical Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961.
Identification of Sensitizers in Diazotype Products by Conversion to Azides W. 1. EVANS,’ R. G. D. MOORE, and J. E. REDDING Research and Development laborafory, Ozalid Division, General Aniline and Film Corp., Johnson City,
,A positive, rapid method for identifying unknown arenediazonium ions b y conversion to the corresponding azidoarenes has been developed. Its application to the identification of diazotype sensitizers is discussed.
P
information on diazonium salts describes various methods of quantitative estimation of known compounds-e.g., nitrometric assay after thermal or photolytic decomposition ( I , 6, 16), formation of azo dyes (2, 4 , I d , 15), reduction ( I , I I ) , halometric titration (IQ), and a spectral method based on the absorptivity a t a UBLISHED
suitable absorption peak (14). Literature on characterization of these relatively infrequently isolated, rather unstable compounds, on the other hand, is very meager. Conversion to simpler or more complex, but more stable, derivatives such as phenols, halobenzenes, hydrazines, or azo dyes is the usual procedure (20). This laboratory has repeatedly been faced with the task of identifying the cationic part of the diazonium salts in unknown diazotype products. Drydeveloping diazotype coatings are complex mixtures containing a photosensitive diazonium salt, usually derived from a substituted p-phenylenediamine,
N. Y.
an azo dye coupler, stabilizing metal salts and organic acids to prevent premature dye formation, sometimes white pigments for smoothness and contrast, and possibly adjuvants such as thiourea or antioxidants to restrain yellowing of the white background after development. Since formulations for diazotype coatings on paper, representing by far the largest production volume in the industry, are usually aqueous solutions, 1 Present address, Eastern Laboratory, Explosives Department, E. I. du Pont de Nemours & Co., Inc., Gibbstown, N. J.
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