V O L U M E 22, NO. 4, A P R I L 1 9 5 0
585
2.37 and 3.32, respectively, from the data of Figure 1. The mean values for C obtained from five other elutions are 2.39 for sodium and 3.28 for potassium, with mean deviations of 0.03 and 0.05, respectively. CONCLUSION s
precipitation techniques, indicates possible application 01 this: method to the determination of these alkalies in silicates such as glasses, clays, and feldspars.
A simple, accurate method for the separation and deterinination of sodium and potassium is described. The ion-exchange elution curves of sodium and potassium, under the recommended conditions, follow closely the theoretical curves based on the normal curve of error. The effects of some variables such as flow rate and temperature are shov-n. The relation t)etn-een distribution coeffirient’s and column behavior and the observed and calculated points of maximum cross contamination have been found to check the predictions of other authors. The success of these separations, dorig with t,he absence of tedious
The authors expms:: thrir inc1el)tcdness t o the Office of S:iv;il Research for fin:incial support during the latter part of this i r i vestfigation.
.A Cli\lOWLEI)C, A 1ENT
LITERATURE CITED
(1) Raunian, XT. C., (1947).
and Eichhom, ,J., J . A m . Chem.
Soc., 69, 2k30
(2) Cohn, IT.E., and Kohn. H. IV..Ihid., 70, 1986 (1938). (3) Kayas, 11.G., C o m p t . rend., 228, 1002 (1949). (4) Mayer, S. IT.,and Tompkins, E. R.. J . Am. Chem. Soc., 69, 2859, 2866 (1947); J . Chcm. Education, 26, 32, 92 (1949). RECEIVEDAuguEt 19, 1949.
lodometric Determination of Resorcinol lIOB.-IKT 13. WlLL-IKD
AND
A . I,. WOOTEN’, Z’nirersity of Michigun. Ann Arbor, Mich.
This ~olumetriemethod f o r resorcinol is based on selective iodination in a buffered solution. Kelatibely few other phenols are reactive under the conditions chosen. An iodination time of 1 minute at pH 5.0 is used. Fift? millip r a m s of resorcinol ma: he determined with an accuracy of 5 parts per 1000 or 1 nip. with an accuracj of 10 parts per 1000.
ETHODS ior t l w mnc.rodeterIiiiriation of resorcinol have been based principalll- on bromination ( 2 , S ,5-7) or iodination reactions (1, 4 , 6), but :is used do not distinguish resorcinol from any of the other phenols. Methods based on the oxidation of resorrinol by slkaline permanganate are even less selective. The resinous precipitate formed by the reaction of resorcinol and furfural in an acid solution forms the basis of a selective method (9). Phloroglucinol, pyrogallol, cresol, sj-lenol, and orcinol interfere. The method is not adapted to rapid determinations and requires an empirical factor. This determination may be concluded gravimetrically or volumetrically. Resorcinol may be titrated in very dilute solutions with nitrous acid. Phenol does not interfere. The titration is continued until a permanent (30-minute) end point is obtained with starchiodide paper. The product is 2,4dinitroresorcinol. The present procedure is based on the selective iodination of resorcinol in a buffercd solution. Soper and Smith (8) have investigated the iodination of phenol as a function of pH, and conclude that the phenate ion is very much more readily iodinated than the nonionized phenol molecule. It is probable that the present method is possible because of the large ionization constant of resorcinol. Very fe\v of the common phenols interfere with this procedure. m-Dihydroxy phenols, such as phloroglucinol and orcinol, also absorb iodine and thus interfere. o-Dihydroxyphenols, such as catechol, interfere by the formation of exceedingly dark flocculent precipitates which obscure the end point. Catechol may be removed by the lead acetate method of Jones et al. ( 5 ) . Resorcinol samples of 50 mg. may be determined with an error of less than 5 parts per 1000 and samples of 1 mp. n-ith an error of less than 10 parts per 1000. REAGENTS
Iodine. .4 0.1 N iodine solution was prepared by weighing 6.5 grams of iodine and 10 grams of potassium iodide into a beaker and adding 20 ml.of water. The mixturo was st,irred until solution was complete and then was diluted to 1 liter. The iodine solution was standardized against arsenious oxide using starch as an indicator. 1
Present address, Reichhold Cheiniralr;, Inc., I‘erndale, hlich.
Sodium Thiosulfate. A 0.1 sodium thiosulfate solution wa.; prepared by dissolving 24.85 grams of sodium thiosulfate i n 1 liter of freshly boiled water containing 0.1 gram of sodinin carbonate. It was allowed to stand in a stoppered bottle for 2 days before being standardized against pot,assiuni iodate. Starch Solution. A 1% starch solution in distilled water coiltaining 2y0 potassium iodide. Buffer. The buffer was acetic acid-sodium acetate and wa5 1molar in acetate ion. A solution of 120 nil. of acetic acid in about 1700 ml. of water was neutralized with concentrated sotliuin hydroxide until the pH rose to about 1.5. The solution \ \ a \ cooled to room temperature and the neutralization wab (wntinued with dilute sodium hydroxide until the pH rose to 5.0. The buffer is stored in a rubber-stoppered bottle and the pH should be frequently rccliecked. PROCEDURE
-1saniple containing about 0.05 gram of resorcinol is dissolved
i n a little water and 50 1n1. of buffer are added. Fifty milliliters of 0.1 Ai iodine are added from a pipet. After 1 minute the excess iodine is titrated with st,andard 0.1 &Vsodium t.hiosulfatr :iiid starch. . CALCULATIONS
Because the reartion is
+
CsH,(OH)> + 3 I ~ + C ~ s l l I ~ ( O F I ) ~ 3HI the equivalent \wight of re € I of Buffer
2.P 2.0 2.0 3.5 3 .5 3.5 3.6 3.5 4.0 4.0 4.0
Reartion Time, 11inutp.e 1.00 2.00 4.00 0.30 1 .oo 2.00 4.00
7 ,oo
Resorcinol Reacted, c&, 11.4 16.0 24.8 37.5 41.3 48.2 55.7 65.9
58.5 70.8 81.1
0.60 1 .oo
2 .00 4.00
4.0 4.0
94.0
7 ... no 0,50
4.5 4.5
98.6
89.1
1 .oo
97.2 100.0 100.0 100.4
2.00 6.00 0.50
4.5 4.5 5.0
The amount of resorcinol taken remained fixed a t 2.725 milliequivalents. The temperature \vas 25.0' * 0.1" C. The iodine added was 5.450 me., an excess of 100%. Results of these experiments (Table I, Figure 1 ) show that an iodination time of 30 seconds a t pH 5.0 is sufficient. The iodination time of 1minute, suggested in the procedure, was chosen to eliminate the neressity of actually timing the reaction. Effect of Temperature on Rate of Iodination of Resorcinol. A pH of 4 0 was chosen for this series in order to show the effect of temperature over a wider range. The resorcinol used was 2.725 me. An iodination time of 1.00 minute and a 100% escess of iodine Tvere used. The results are found in Table 11. Effect of Other Phenols. tTsing the suggested procedure determinations were made in the presence of an equal amount of the second phenol (Table 111).
Table 11. Effect of Temperature on Rate of Iodination of Resorcinol Temp, C . 12 0 25 0 28 5 39 5
Reqorcinol Reacted, % 41 6 72 5 77 4 99.5
- ~ _
Table 111. Effect of Certain Other Phenols on Determination of Resorcinol Other Phenol Resorcinol Reacted, % Phenol 99 8 Mixed cresols 100.0 o-Phenylphenol 99.9 p-Phenylphenol 100.0 o-tert-Butylphenol 100.0 p-tert-Butylphenol 100.0 p-terf-.4mylphenol 100.0 Catechol Color too dark to see end point 100.4 Hydroquinonea Pyrogallol Color too dark to see end point Phloroglucinol Color too dark to see end point ' Alodifiration desrribed in discubsiun \vas i i s ~ d .
long a time the precipitate becomes dark red through aristol formation and the end point is difficult to see. In the presence of hydroquinone a modification in the procedure is necessary. The hydroquinone consumes iodine under these conditions. This iodine, hoNever, may be recovered by making the sample strongly acid with hydrochloric acid after the normal iodination period. llfter 1 minute's contact with the acid the sample is titrated in the normal manner. Phloroglucinol, pyrogallol, orcinol, and the other nt-dihydroxyphenols interfere through iodination and usually through aristol formation also. In the presence of catechol a different type of interference occurs. A blue-black precipitate forms when resorcinol is iodinated in the presence of catechol. The catechol may be removed prior to iodination by the lead acetate method of Jones et al. ( 5 ) . Ten milliliters of freshly filtered 4% lead acetate are added to a sample containing not more than 0.05 gram of catechol. After 30 minutes the precipitate is filtered on a fine paper and washed five times with small portions of distilled water. The filtrate is buffered and iodinated in the normal manner. Ten milliliters of concentrated hydrochloric acid are added just prior to titration and a correction of 0.05 ml. is subtracted from the titration. With this procedure i t is possible to determine resorcinol in the presence of an equal amount of catechol with an error of less than 1 part per 100. Milligram samples of resorcinol may be determined by this method using 0.01 N iodine and thiosulfate. Five milliliters of buffer are used and a 10-ml. buret is used for the thiosulfate. The error on a 1-mg. sample is less than 1part per 100. Erratic r e s u l t s obtained with any of these procedures usually mean incomplete reaction. This may be caused by too low a pH, too little buff e r , t o o 8 Ismall an excess of iodine, or too short an iodination period. A very red a precipitate m e a n s too high a pH, too long an iodination time, or too high a 0 temperature. 0 2 4 6 This method has TIME MINUTES been used for 2 Figure 1. Effect of pH on years in an indusIodination trial laboratory as a routine control method where it has proved to be of satisfactory valuP in the hands of experienced analysts.
8
8
5
p
8
a
ACKNOWLEDGMENT
One of the authors wishes to express thanks to Reichhold Chemicals, Inc., for the financial aid that made this workpossible. DISCUSSION
LITERATURE CITED
.h shown in Table I, iodination is complete in 1 minute a t any pH over 4.5. The p H 5.0 was selected for two reasons. Small changes in p H of the buffer in general cause large changes in the rate of reaction, but this is not true a t 5.0. The iodination time is less critical a t pH 5.0. As shown in Table 11, a change in temperature of 10" C. causes a change in the rate of reaction of about 25% under these conditions. Because a 1-minute iodination time is used, which is twice as long as is necessary, any room temperature should be suitable. The iodination time need not be mcasured, but it is advisable not to allow much more than 1 minute. At too high a pH or t 10
Degener, P., J . prakt. Chem. (21, 20, 320 (1879). Francis, A. W., J . Am. Chem. Soc., 48, 1631 (1926). Francis, A. W., and Hill, A. J., Ibid., 46, 2498 (1924). Gardner, W. M., and Hodgson, H. H., J . Chem. SOC.,95, 1824 (1909). I. CHEM., Jones, D. O., Prahl, M. A., and Taylor, J. R., IND.ENG
ANAL.
ED.,4, 84 (1932).
Pence, C. M., J . I n d . Eng. Chem., 3,820 (1911). I b i d . , 7, 2030 (1913). Soper, F. G., and Smith, G. F., J . Chem. Soc., 1926, 1582. Votocek, E., Ber., 49, 2546 (1916). RECEIVED hiigii-t 31, 1949. From a dissertation submitted by A. L. Wooten the Graduate School of tlie IJniverrtit,y of Michigan in partial fulfillment of the requirements for the degree nf doctor of philosophy in chemiatry. tq
