74 ml., compared with an actual value of 62 ml. While these predictions are not exact, the agreement with the actual values is good enough to be quite useful. The predicted retention volume depends on V,, which is not easy to measure with high precision. I t may be of interest to mention that for the column separation just described, calculations based on plate theory indicate that the column has 20 theoretical plates. Thus the height equivalent of a theoretical plate is approximately 0.6 em. During part of this research, our results for most phenols tended to be high. This difficulty was caused by our use of surgical rubber tubing on the column exit, which introduced significant amounts of ultraviolet-ab-
sorbing immrities into the test solutions. +he use of Teflon capillary tubing to connect the to the flow monitor and from the flow monitor to the receiving - vessel avoids this source of error. A standard o-cresol solution in 0.5M aqueous sodium chloride which stood in contact for 0.5 hour with surgical rubber showed a significant increase in absorbance; no change in absorbance was found when this solution was in contact with silicone stopcock grease or the solid support for similar iime periods. ACKNOWLEDGMENT
The authors thank Jack Horowitz for making available the ultraviolet flow monitor used in part of this work.
LITERATURE CITED
( 1 ) cerrai, E.,Testa, c., J . Chromatog. 9, 216 (1962). ( 2 ) Chen, P. S., Jr., Terepka, A. R., Remaen, Tu'., AXAL.CHEM.35, 2030 (1963). ( 3 ) Frevtacr. W.,Fette, Seifen. Anstrichtmitted 65;'603'(1963); C.A.' 60, 2310a (1964). ( 4 ) Fritz, J. S., Hedrick, C. E., A N ~ L . cHEM. 36, 1324 (19641, ( 5 ) Hamlin, A. G., Roberts, B. J., Loughlin, W., Walker, S. G., Z b d . , 33, 1547 (1961). (6) Hayes, T. J., Hamlin, A. G., Analyst 87, 770 (1962). ( 7 ) Rindi, G., Perri, V,,A n d . Biochem. 5, 179 (1963). (8) Sara, S . C., Bhattacharjee, A., Basak. X . G.. Lahiri., 8.. , J. Chem. E m . Data 8 , 405 (1963). ( 9 ) Schwab, H., Rieman, W., Vaughan, P. A., ANAL.CHEM.29, 1357 (1957).
R~~~~~~~for review J~~~~~~13, 1965. Accepted May 24, 1965.
Empirical Formulae of Some Alcohol Complexes of Quad rivalent Ceriu m from Spectrometric Measurements H. G. OFFNER' and D. A. SKOOG Chemistry Department, Stanford University, Stanford, Calif.
b The
empirical formulae of the quadrivalent cerium complexes of n-, sec-, and tert-butanol and ethylene glycol were determined from spectrometric measurements, and in all cases a 1 : 1 ratio of cerium to alcohol in the complexes was observed. The ethylene glycol complex was the most stable, possibly because of formation of a chelated five-membered ring structure. Experiments were carried out in both nitric and perchloric acid solutions, and the effect of acid and nitrate concentrations on the observed "instability" constants was examined.
Q
cerium ion forms adducts with many anions such as sulfate (Z), chromate ( 8 ) , nitrate (9),oxalate ( 5 ) , and hydroxyl (6) in aqueous solution. Highly colored complexes are also formed with aliphatic alcohols, and analytical procedures have been developed for the determination of methanol, ethanol, and ethylene glycol by absorbtion spectrometry ( 3 , 4). Although the composition of some of the inorganic complexes has been determined, similar work on the organic complexes has not been reported. Consequently, it was considered of interest to further investigate this problem. UADRIVALEST
1 Present address, Rocketdyne, A Division of Xorth American Aviation, Inc., Canoga Park, Calif.
1018
ANALYTICAL CHEMISTRY
The determination of the combining ratios of quadrivalent cerium with n-, sec-, and krt-butanol and ethylene glycol by a spectrometric method is described in this report.
ceric ion or the alcohol concentrations are in large excess in the solution. The following chemical equilibria are considered to exist in a perchloric acid solution containing an alcohol:
p Ce+'
THEORY
Experiments were carried out in both perchloric and nitric acid solutions. The mathematical equation used to reduce the data obtained in the perchloric acid series of experiments is derived in detail, while the equation applicable to the nitric acid experiments, being of the same form, is only indicated. The regions of absorption in the spectra of the aquo-ceric ion overlap those of the ceric alcohol complex; therefore, the equations are derived with an appropriate correction term. The following theoretical treatment parallels the method of Bent and French ( I ) . The several equilibria existing in solution are first specified. Then a rigorous expression is derived relating the observed absorbance values to the concentrations of the various species in solution. This expression, containing unknown terms, is not in a usable form; however, approximate relations are developed, based on selected experimental conditions, from which the combining ratio may be calculated from experimentally measurable quantities. The experimental conditions include the cases where the
Ce+'
+
?a
+ ROH = Cep (ROH) HzO = Ce (OH).+('--))
+'p
+ n H+
The molar concentrations are denoted as follows: co = Ce+' c o = Ce (OH).+(4-.)
co = CeP(ROH)+'p Also, let A be the observed absorbance and eo, e., and e, the corresponding molar absorptivities. ch
c t = co
=
H30f
+ c. + p c ,
(total cerium concentration)
cI = ROH
c,
= c,
+ cc
(total alcohol concentration)
The stability constant equations are:
'.Ch" CO
=
K,
0
ceric-alcohol complex), an analogous equation can be derived. If the chemical equation is written in the form
1.340
-
1.320
-
1.300
-
then all subsequent mathematical manipulations are the same as above to obtain the corresponding approximate equation (Equation 9).
1.280
-
where
1.260
-
?.
l / p ROH = Ce (ROH)1,p+4
This expression is in terms of the total alcohol concentration c,, which may be varied to determine the combining ratio p , as before. I n the presence of nitrate ion, the additional chemical equilibrium exists :
4
1.240
1.220
+
Ce+4
-
CeS4
+ p N O 3 - = Ce ( X O ~ ) ~ + ( ~ - V )
Equation 9 then becomes 1.200
1.180
-
LI
where
I
I
0.400
0.600
0.800
I
1.OOO
I
I.=
CC
CONCENTRATION, M
HC IO,
c,"p
Figure 1 .
and
= 5lOrns
L'
Absorbance as function of acid concentration fort-Butanol concn. = 0.541 OM; Cs" concn. = 0.05502M; wavelength
=
Ec
- E & . ' ' eoK, f ebKbChnCnn ~
ch"
it follows from Equation 4 and Equation 1 that for 1-cm. path length. From Equation 2 and the definition of c , :
(7) where
A
=
A,
+ Lc,
where
L = t , - p
Ch"
(6)
+ EX, + Ka
and
which is the absorbance of the solution in the absence of alcohol. If experimental conditions exist, such that c t >> p c , and, therefore, c , = co c.,
+
The total acid concentration will be equivalent to the equilibrium acid concentration if it is in large excess over the cerium concentration; also, if it is held constant as the ceric concentration is varied, then L and K , also remain constant. I t follows from Equation 8 that a plot of A vs. A - AojctP a t constant total alcohol concentration will be linear, thus defining the combining ration, p . The value of Kc', the slope, should be a function of acid concentration, and this was experimentally demonstrated. If the alcohol concentration is made in large excess over the ceric ion (and
Kb~h''~n''
In these relations Kb is the stability constant of the ceric-nitrate complex; c , is the NO3- concentration; and Eb equals molar absorptivity of the ceric-nitrate complex. From Equation 10, a plot of A us. A Ao/csl'p,at constant total ceric and nitrate concentrations, will be linear, and the combining ratio p may be then calculated.
From Equations 6 and 7 :
Substituting and collecting in Equation 3:
+ + Ka
(c* - c,)
EXPERIMENTAL
Apparatus. A Beckman DU spectrophotometer with matched 1-cm. silica cells was used for all absorbance measurements. Reagents. Ceric perchlorate, 0.5M in 6.M perchloric acid, was obtained from the G. F. Smith Chemical Co. The ceric concentration was determined with standard ferrous sulfate ( 7 ) . The acid concentration was determined with standard base following removal of the cerium as the oxalate. Sodium oxalate was added in excess and the solution was digested for 30 minutes at 90" C. to obtain an easily filterable precipitate of cerous oxalate. Ammonium hexanitrato cerate, primary standard grade from G. F. Smith Chemical Co., was used to prepare the nitric acid solutions of the alcohols. VOL. 37,
NO. 8, JULY 1965
1019
Table 1.
Alcohol tert-Butanol sec-Butanol n-Butanol Diethylene glycol
absorbance values (at zero time) were extrapolated from the observed values by measuring the rate of fading. The ionic strength of the solutions was maintained constant as the ceric concentration was varied by addition of sodium perchlorate. The values for A , were obtained from absorbance measurements in the absence of alcohol.
Color-Fading Rates
Fading Ce(C10a)4 Alcohol after 1 concn., concn., minute, M x 102 M x 102 % 22.00 10.00 0 16.39 2.943 5.2 16.39 3.051 7.3 16.39 2.033 3.2
("4)Z-
Ce(XO& concn., M x 102 21 .oo 22.65 22.65 22.50
Alcohol concn., M x 102 9,695 8.911 9.079 7.637
Fading after 1 minute,
yo
0
0.1 0.3 0.6
RESULTS AND DISCUSSION
tert-Butanol was purified by distillation followed by fractional crystallization: m.p., 25.5" C.; b.p., 82.8" C. The sec- and n-butanols were fractionally distilled: b.p. for sec-butanol, 98-99' C.; and for n-butanol, 116-117" Table 11. Absorbance Values (A,) of Ceric Solutions (540 mp)
HClO4 concn. = 1.690M CeC4concn., Absorbance ( A , ) M x 103 x 10s 23.4 27.5' 46.8 44.0 58.0 70.2 93.6 70.2 117.0 83.7 140.4 96.3 163.9 119.0
C. Ethylene glycol, Eastman yellow label, was used without further purification. Procedures. Absorbance measurements were made at 540 mp using slit widths of 0.015 to 0.020 mm. Although the measurements were not made a t the absorbance maximum, a convenient range of absorbance values was obtained with the reagent concentrations used. I n one set of experiments the alcohol concentration was varied in a nitric acid solution of quadrivalent cerium, and in the second set of experiments, the ceric concentration was varied in a perchloric acid solution of the alcohol. The oxidation of all the alcohols except tert-butanol was noticeable in the perchloric acid solution, as would be expected from the high redox potential of the ceric-cerous couple, so the true
Typical data on the oxidation rates of the alcohols in perchloric and nitric acid solutions are shown in Table I, and from such data, the corrected absorbance values were calculated by extrapolation. Some absorbance values of ceric perchlorate solutions in perchloric acid, a t 540 mp, are shown in Table 11, and these represent the A , values used in Equations 8 and 9. The absorbance term A - A , is shown to be a function of acid concentration for a particular solution (Figure I), as predicted from the definitions of K,' and
K,". A plot of the data from experiment 2 (Table HI), in which the alcohol concentration was varied using Equation 9, with p = 1 was linear throughout the entire concentration range. Using the same data, but taking l i p = 2, the plot
630
540
n
450
0 X
w
0
z
3a 360
m U
270
I80 1
600
I
I
I
I
I200
I600
2400
3000 200
I
I
I
3.W
4.00
5.00
ct
600
7.00
A-A,
Figure 2.
1
Data from experiment 2 plotted using - = 2 P Ce+'concn. = 0.02086Mj HNOa concn. = 2.OM
1020
ANALYTICAL CHEMISTRY
Figure 3. Absorbance as function of ceric concentration (experiment 1 ) fed-Butanol concn. = 0.1 OOOMJ HClOc concn. = 1.62M
shown in Figure 2 is obtained. I n this case the combining ratio is 1. Data from experiment 1 in which the ceric concentration is varied are shown in Figure 3, plotted from Equation 8, taking p = 1. The curve is linear except for the two lower poinib a t ceric concentrations less than 3.86 X 10-2M. At these lower concentrations, the assumption that c, >> cc is not valid, and, therefore, the curve deviates from linearity. Details of experiments are summarized in Table 111. I n all cases (except experiment I ) , a linear plot was obtained over the entire concentration ranges shown, using unity as the combining ratio. Values of K for every alcohol were considerably lower in the solutions containing nitric acid, and this is the result of the formation of ceric nitrate complex ions, which reduce the concentration of the complexing species (see equation defining K”’). ,4comparison of the K values obtained for the three butanols shows that they are all of the same magnitude. Ethylene glycol, however, presents a definite anomaly, as the K values in both perchloric and nitric acid solutions are considerably larger than the corresponding values for the
Table 111.
HClOi HNOs concn., concn.,
M
Experiment tert-Butanol
M
1.62
1
2 sec-Butanol 3 4 n-Butanol 5 6 Diethylene glycol 7 8
1,69 1,69 1.69
2.00 2.00 2.00 2.00
Summary of Experiments
concn., M x 102 2.750-22.00
3.277-16.39 2.341-16.39
I’ \ \
II
Ce LITERATURE CITED
(1) Bent, H. E., French, C. L., J. Am. Chem. SOC.63, 588 (1941). (2) Moore, R. L., Anderson, R. C., Ibid., 67, 167 (1945).
R
2.086
10.00 17.01-123.7
13 0.6
1.982
2.943 4.025-64.40
11 1
1.982
3.051 3.400-54.40
16 1
1.982
2.033 3.680-58.88
40 3
2.341-16.39
butanols. This may be because of the formation of a stable chelated ring, as the disposition of the electron donor oxygen atoms are such that a fivemembered ring may form (OHCHzOCHzCHZOH) + 4 ,\
concn., Alcohol concn., M x 102 M x 102
(3) Reid, V. W., Truelove, R. K., Analyst 77, 325 (1952). (4) Reid, V. W., Salmon, D. G., Ibid., 80. 704 (1955). (5) Ross, ‘S.P:, Swain, C. G., J . Am. Chem. soc. 69, 1325 (1947). (6) Sherrill, M. S., King, C. B., Spooner, R. C., Ibid., 65, 170 (1943). ( 7 ) Smith, G. F., “Cerate Oxidimetry,” G. F. Smith Chemical Co., Columbus, Ohio. 1942. ~(8) Tong, J. Y-P., King, E. L., J. Am. Chem. SOC.76, 2132 (1954). (9) Wylie, A. W., J . Chem. SOC.1951, p. 1475. - I
~
RECEIVEDfor review January 25, 1965. Accepted April 27, 1965.
Quantitative Gas Liquid Chromatography of Mono nuc Iea r Hy d roxymet hy Ipheno Is as Acetate Este rs HAROLD P. HIGGINBOTTOM, HARRY M. CULBERTSON,’ and JAMES C. WOODBREY Plastics Division, Monsanto
Co., Springfield,
A new method for analyzing complex resole prepolymer systems is presented. Under anhydrous conditions, phenol and hydroxymethylated phenol derivatives are quantitatively converted to the acetate esters by treatment with acetic anhydride in the presence of an organic base at room temperature. All of the acetylated mononuclear resole components are sufficiently stable and volatile to permit their separation by gas liquid chromatography. The complex acetylated mixtures are resolved using temperature-programming techniques in conjunction with an ionization detector. Certain aspects of the quantitative method are discussed in detail, and special emphasis is given to sample preparation procedures. Proton magnetic resonance is used to confirm the validity of the method.
R
as a type of phenolic prepolymer (141, have many industrial uses since they can be crossESOLES,
Mass.
linked to give thermoset plastics with desirable properties. These prepolymers are usually prepared by reaction of one mole or more of formaldehyde per mole of phenol under base-catalyzed conditions (IO). The reaction is complex, since a multitude of mono- and polynuclear hydroxymethylated phenols can be formed, However, many commercially important resole prepolymers are mainly composed of mononuclear components. The problem of analyzing these prepolymers has been formidable because of their complexity and instability. A number of analytical procedures have been applied to determining the prepolymer structure, but only a small percentage of the methods provides a quantitative (or even qualitative) determination of one or more of the individual components present. Unreacted formaldehyde in a resole can be accurately determined chemically (18). Unreacted phenol has been determined by methods employing steam distillation (8), infrared spec-
trometry (16), and, more recently, gas liquid chromatography (GLC) (I 7 ) . Thus far, the only successful method for the individual hydroxymethylated phenols has been the use of paper chromatographic techniques, as applied by Freeman (5), Reese (IS), and others (IO). The latter method makes possible the determination of the common mononuclear and many of the dinuclear components of the resole system. Although the methods reported in the literature are successful to varying degrees, some are limited in applicability and many have inherent limitations with respect to rapidity and accuracy of the measurements. The fact that resole systems are usually reactive and heat-sensitive has prevented their direct analysis by a number of otherwise potentially useful techniques. Derivative formation may impart the required stability and convert the resoles to a highly desirable Present address, Monsanto Chemicals (Australia), Ltd., Melbourne, Australia. VOL. 37, NO. 8, JULY 1965
1021
