with 2% sodium nitrite solution in all cases. Clear and quantitative separations were possible with 75, 50, 33.33, and 16.67% silver in the mixtures with cobalt. After silver elution cobalt could be completely eluted with 200 to 350 ml. of 5% sodium nitrate solution. SEPARATION OF SILVER FROM NICKEL. Similar studies with silver and nickel mixtures were repeated. Sodium nitrite (2%) was used as the eluting agent. It was possible to separate silver completely by a similar procedure from mixtures containing 75, 50, 25, and 10% silver with nickel as nitrates. Only in the last mixture, which contained 90% nickel, the last fraction (6th 20-ml. fraction) contained traces of nickel. Nickel in all cases could be eluted later by the same eluent (200 to 350 ml.). MODIFICATION OF VOLHARD METHOD. I n all the above methods a rapid volumetric method such as the Volhard method was needed for the estimation of silver. The elution by sodium nitrite caused difficulty in the estimation because the indicator, ferric nitrate, failed in presence of the nitrite ion in the solution. Hence a process similar to one given below was employed. The solution containing silver ion in the presence of excess nitrite ion (forming probably the complex ion [Ag (NO&]-) was acidified with a few milliliters of dilute acetic acid. About 1 gram of urea was then added to it and the solution boiled to destroy free nitrous acid so formed. The solution was then cooled and acidified with dilute nitric acid until the effervescence (which was started by its addition) ceased. The solution was boiled for a
few minutes more, cooled, and titrated with ammonium thiocyanate solution using ferric nitrate as indicator. The precipitation of silver thiocyanate was satisfactory and the appearance of end point was sharp. If this procedure is not used, the titer continues to decompose. At the same time, ferric indicator changes to the ferrous state and hence does not give the end point. This procedure was also used for silver titrations in the presence of the colored ions of cobalt and nickel after their removal by the ion exchange technique detailed above. The percentage error in all the cases was less than *0.5. DISCUSSION
Detailed studies with 2% sodium nitrite as eluting agent indicated the quantitative separation of silver from cobalt as well as from nickel with a fast flow rate of 8 ml. per sq. em. per minute 011 Amberlite IR-120 (Na+) in all cases. The use of sodium nitrite as an eluting agent for silver a t first appeared to be unusual. But it was possible, probably because of the formation of the complex ion [Ag(NO&]- whose formation has been suggested by Abegg from electrometric studies as cited by Remy (6) and also by Nardelli, Cavalca, and Brailanti (6). I n an excess of sodium nitrite silver nitrite remains as a soluble complex and hence the eluted silver remains in the effluent solution. It can easily be titrated by the modified Volhard method as described. The use of a complex formation for the separation of cobalt from silver before
the sorption step was also successful. Cobalt as the complex, nitrocobaltate (111) ion, was not retained by the cation exchanger and hence separated. Although the process was effective, it was not quantitative, as separated cobalt as well as silver solutions were contaminated with traces of impurities. The applicability of such a separation as a modification of Volhard’s method for estimating silver volumetrically was equally successful. Standard books on quantitative analysis suggest that the presence of colored ions (as cobalt and nickel) interfere with the Volhard method. The present studies show that the method can be used, after the separation of ions of cobalt and nickel by ion exchange chromatography, to obtain the desired accuracy. LITERATURE CITED
(1) Atteberry, R. W., Larson, Q. V., Boyd, G. E., Abstracts, 118th Meeting,
ACS, p. 8G, Chicago, Ill., September 1950. ( 2 ) Blasius, E., Kegwer, N., Naturwissenschaften 39,257 (1952).
(3) Jentzsch, Doe, Chem. Tech. (Berlin) 6. (1954). - ,339 --.- - ~ (4) Kraus, K. ’A.,Moore, G. E., J. Am. Chem. SOC.75, 1460 (1953). ( 5 ) Nardelli, M., Cavalca, L., Brailanti, A.. Gazz. chim. ital. 82,413 (1952). (6) Remy, H;, “Treatise on Inorganic Chemistry, Vol. 11, p. 440, Elsevier, New York, 1956. ( 7 ) Samuelson, O., Sachhram, K., unpublished (cited in “Ion Exchangers in Analytical Chemistry,” p. 156, Wiley, New York, 1953). RECEIVED for review November 10, 1959. Accepted February 12, 1960.
Pa per Chro mCI tog ra p hy of Bis phe no1 A G. CHALLA and P. H. HERMANS Institute for Cellulose Research, Achter St. Piefer 6B,Utrecht, Netherlands
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b 2,2 Bis(4 -hydroxy phenyl) p r o p a ne and three principal impurities occurring in commercial bisphenol A have been separated by paper chromatography in an atmosphere of ammonia using a mixture of 1 -propanol and kerosine as eluent. In the case of fairly pure samples the impurities are preconcentrated by fractional vacuum sublimation. On commercial bisphenol A samples, the method gives purity data which agree with freezing point depression values.
I
recent article, Anderson, Carter, and Landua (1) described a paper chromatographic method for the quanN A
778
ANALYTICAL CHEMISTRY
titative analysis of commercial grades Some years ago the authors developed of bisphenol A. The main constituent, a method primarily intended for qualitap,p’-BPA [2,2-bis(4-hydroxyphenyl)pro- tive and semiquantitative analysis of pane], and the principal impurities, bisphenol -4. It involved simple oneo,p‘-BPA [2-(2-hydroxyphenyl)-2-(4 dimensional paper chromatography and, hydroxyphenyl) propane], codimer [4, when necessary, preconcentration of 4‘ - hydroxyphenyl - 2,2,4 - trimethylthe impurities by vacuum sublimation. chroman], and BPX [2,4-bis(a,a-diThe authors’ procedure appears to niethyl-4-hydroxybenzyl)phenol], Lvere have advantages over that of Anderseparated on two one-dimensional paper son, Carter, and Landua because of its chromatograms using as eluents water simplicity and because it is also easily and carbon tetrachloride, respectively. adaptable to quantitative work. Preconcentration of the impurities in the mother liquor from a recrystallizaEXPERIMENTAL tion of bisphenol A was necessary, when the amounts of the impurities in Paper Chromatography. From B the original sample were less than 1%. micropipet 5 p l . of 5% solutions in
alcohol (250 y of bisphenol A) were applied to a sheet of Whatman No. 1 paper (25 X 32 cm.). The sheet was rolled into a cylinder and kept in shape by strands of sewing thread. This paper cylinder was placed in a cylindrical glass jar containing a dish with 25% ammonium hydroxide and a dish with a 45 to 55 (v./v.) mixture of 1-propanol and kerosine (b.p. 100" to 140" C.). The paper cylinder dipped into the latter dish, permitting the solvent mixture to ascend into the paper. The glass jar was covered with a glass lid and the elution was continued for 7 hours a t about 20" C. Then the paper cylinder was taken out of the jar and allowed to dry a t room temperature. After unrolling, it was sprayed first with a 5% aqueous sodium carbonate solution and then with a 0.5y0 aqueous solution of diazotized sulfanilic acid. This reagent coupled with the various phenolic components and formed separate yellow to brown spots of the corresponding azo compounds.
Vacuum Sublimation. Preliminary experiments showed t h a t the impurities o,p'-BPA and codimer can be removed from samples of commercial bisphenol A by vacuum sublimation. At temperatures around 95' C. (vapor of boiling 1-propanol) and a pressure of 1 mm. of mercury the rate of sublimation of p,p'-BPA is small as compared n-ith those of the two impurities. This was utilized to effect preconcentration of these impurities when the original sample was relatively pure. The rate of sublimation depends on the construction of the sublimation apparatus and the quantity of volatile impurities in the sample. The authors used an apparatus designed for quantitative work as developed in this laboratory by Heikens ( 2 ) . It has a horizontal cold finger about 1 cm. from the small sublimation boat carrying the weighed sample (about 100 mg.). The sublimate is caught on a thin-walled removable glass tube which fits the cold finger and is tared in advance. X i t h this apparatus the sublimate received in 11/2 hours contained the major part of the impurities. The sublimate was weighed and tested by chromatography. It contained o,p'BPA4, codimer, and but a relatively small quantity of p,p'-BPA. Complete sublimation of o,p'-BPA and codimer can be achieved in about 6 hours. Finally, the remaining p,p'-
1.0-
K- O ' 0.6 *:
a2 OL:
0-
c;3
P
a 0
0
Codirner (orange, faint)
Codirner (faint)
A
0,P'-BPA (red.brown,
m o derate)
P, P'.BPA (yellow, intensive) 0.2
1
"i
BPX? (reddish, very faint)
1
Figure 2. Paper chromatogram for 125 y of sublimate ofcommercial grade bisphenol A
BPA can be sublimed rather quickly a t 156" C. and is then received in a very pure state. All our samples of bisphenol A left behind a small residue (0.5 to 1.5% by weight) representing, perhaps, the impurity BPX, identified by Anderson et d.(1). This residue was not an artifact because pure p,p'BPA did not leave a sublimation residue. RESULTS AND DISCUSSION
A normal paper chromatogram of commercial bisphenol A is shown in Figure 1, which indicates the R / values, the colors, and the intensities of the spots for the various components. The resolution and R/ values depend critically on the volume ratio of 1propanol and kerosine in the eluent, For a volume ratio of 50 to 50, the spots of p,p'-BPA and o,p'-BPA are shifted toward higher R/ values yielding less resolution. For a volume ratio of 40 to 60 the Rfvalues are lower and the o,p'-BPA spot becomes much less sharp, The same effect is observed when pre-equilibration between the eluent and the vapor of the ammonia is omitted before elution starts. Figure 2 illustrates the efficiency of preconcentration of contaminants by vacuum sublimation a t 96" C. and 1 mm. of mercury for l 1 / 2 hours. I n this chromatogram the spot of p,p'-BPA is reduced considerably in intensity and 0 has completely the spot a t R? disappeared. The supposition that the original very faint spot a t R / 0 is related to the sublimation residue is consistent with the observation that such a residue itself exhibited only one reddish spot of moderate intensity a t Rt-0.
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To check the quantitative aspects of the chromatographic method the redbrown spots for o,p'-BPrl in four commercial bisphenols -4were compared with those for approximately known quantities of o,p'-BPA present in some primary sublimates (these sublimates had high o,p'-BPA contents and were previously standardized by running parallel spots of pure p,p'-BPA and neglecting the small amounts of codimer). The o,p'-BPA contents of the bisphenols A, so estimated, ranged from 1 to 6% by weight. Further, the freezing point depression of these samples relative to a bisphenol -4 freed from o,p'-BPA by recrystallization was determined. The results of these quantitative assays show that there is a linear relationship between o,p'-BPA content and freezing point depression for the commercial samples of bisphenol A. From the linear slope it was calculated that the molar freezing point depression for p,p'-BPA amounts to roughly 170" C. per mole in 100 grams of p,p'-BPA. A combination of the sublimation and chromatographic procedures may yield a suitable method for quantitative analysis of bisphenol A. LITERATURE CITED
(1) Anderson, W. M., Carter, G. B., Landua., A. J.. - , AXAL. CHEM.31, 1214 ~~
(1959).
(2) Heikens, D., Rec. trav. chim. 75,
1199 (1956).
N
RECEIVED for Review October 30, 1959. Accepted February 18, 1960. Communication No. 104 from the Institute for Cellulose Research of the AKU and affiliated companies, Utrecht, Ketherlands.
VOL. 32, NO. 7, JUNE 1960
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