of hypophosphorous acid under the described conditions are scandium(III), zirconium(IV), hafnium(IV), thorium(IV), and tantalum(V). Tin, silica, and germanium are not soluble in this medium. Copper, silver, gold, mercury, antimony, arsenic, selenium, tellurium, and palladium are reduced to an insoluble form, usually the element. In separate experiments, 100 mg. of bismuth was determined in the presence of equal amounts Of lithiuni(I), Sodium(I), potassium(I), magnesium(I1).
calcium(II), zinc(II), barium(II), aluminum(III), lead(II), N(NH+), chromium(III), manganese(II), iron(II), eobalt(II), and nickel(III), which did not interfere. The solutions containing iron, manganese, and chromium were treated with 5 ml. of 6% sulfurous acid before addition of hypophosphcr o w acid to remove higher oxidation states. Perchloric acid concentration of 0.1N was used when potassium was present, to prevent precipitation Of potassium perchlorate.
LITERATURE CITED
(1) Cousin, J., J . p h a n . chzm. 28, 179
w,,
(2) &lawrow, ( 1923). Muthman, F., z, anorg, Chem. 13, 209 (1897). '3) Silverman, I,., Shideler, M., ANAL. CHEW26, 911 (1954). (4) Vaninop L., Truebert~F.l Ber. 31, 1303 (1898).
for December 1' 1957. Accepted March 24, 1958. Work performed under auspices of ~ 1 .S. -4tomic Energy Commission.
Detection of Phthalic Acid Isomers and Benzoic Acid in Alkyd Resins by Infrared Absorption Spectrometry M. 1. ADAMS and M. H. SWANN Coating and Chemical laboratory, Aberdeen Proving Ground, Md. The three isomeric phthalic acids and benzoic acid can usually be detected in alkyd resins from the infrared absorption spectra of dried films. Preliminary identification of one or more of these acids improves the speed and accuracy of subsequent quantitative analysis.
I
spectrometric analysis has been investigated for the detection of the three isomeric phthalic acids and benzoic acid in alkyd resins. Such information is particularly valuable for increasing both the speed and accuracy of subsequent quantitative analysis by existing methods. The quantitative method for determining the phthalic acid isomers involves separation from the oils and benzoic acid, if present, by saponification, followed by multiple-component ultraviolet absorption technique (3). If the absence of any of these acids could be established prior to the quantitative determination, the number of points at which ultraviolet absorbances are measured would be reduced. More important, the accuracy of the determination would be increased through the use of feRTer linear equations in the calculation of acid concentrations. The quantitative determination of benzoic acid in alkyd resins (4) involves separation of the acid from the oil acids by a special extraction technique followed by a one-component ultraviolet absorption procedure. If the absence of benzoic acid could be established in advance, much time would be saved by avoiding the quantitative determination entirely. As indicated by Shreve (I), the use NFRARED
1322
ANALYTICAL CHEMISTRY
of isophthalic or terephthalic acid in place of phthalic anhydride in alkyd resins produces specific changes in the infrared absorption spectra of the resins. The presence of benzoic acid, a monosubstituted benzene, gives characteristic absorption differing from that of the disubstituted acids. Absorption characteristics in the 11to 15-micron region by which each of the four acids may be identified in the presence of each or all of the other acids, are illustrated, tabulated, and discussed. PROCEDURE
A double-beam infrared spectrophotometer (Perkin-Elmer Model 21) with sodium chloride optics was used. A thin film of the resin solution is spread evenly on a polished rock salt plate and the solvent is removed by vacuum drying in an oven a t 60" C. for 1 hour. The spectrum from 11 to 15 microns is scanned using instrument settings designed to give ample resolution for qualitative analysis. The spectrum is then examined for characteristic points of absorption ns indicated in Table I. DISCUSSION
The points of specific absorption used to identify the isomeric phthalic acids and benzoic acid are illustrated in Figure 1 and tabulated in Table I. Figure 2 represents the absorption spectra in this same region of various alkyd resins. The compositions and concentrations of these resins and the interpretation of the absorption curves are given in Table I. The actual concentrations were determined by applying the ultraviolet quantitative techniques mentioned.
Spectra 1, 2, and 3 in Figure 1 are from dried films of alkyds containing phthalic anhydride, isophthalic acid, and terephthalic acid, respectively. The terephthalic acid alkyd was prepared in the laboratory especially for this purpose. Because a resin was not available in which benzoic acid was present without a phthalic acid isomer, the spectrum of ethyl benzoate is illustrated in spectrum 4 of Figure 1. Diethyl and dibutyl esters of phthalic anhydride produce spectra shoning the same points of absorption as an o-phthalic alkyd. Both ethyl benzoate and diethyl phthalate produce additional weak absorption bands from their ethyl group in the 11.4- to 11.5-micron region. Such absorption does not appear in a phthalic anhydride alkyd resin film and should not appear in an alkyd containing benzoic acid. The spectra of several commercially available isophthalic-benzoic acid alkyds were examined. I n all cases, strong absorption a t 14.06 to 14.16 microns occurred because of the monosubstitution on the benzene ring. This corresponds to the absorption produced by ethyl benzoate. There mas no absorption from 11.4 to 11.5 microns. I n alkyd resins containing combinations of the isomeric phthalic acids and/or benzoic acid, the points of specific absorption indicated in Table I and spectra 1 through 4 in Figure 1 remain well defined except for ophthalic acid. T h e n it is present with isophthalic acid (Figure 2, spectrum 6), the absorption a t 13.45 to 13.50 microns shows only as a shoulder on the isophthalic acid band. The 14.16 to 14.20 peak also will appear only as
Table 1.
Spectrum
T
0
Film Phthalic anhydride alkyd
2
Isophthalic acid alkyd5
3
Terephthalic acid alkyd
4
Ethyl benzoateb Alkyd Composition, yo Phthalic Isomer Is0 Ortho Tere
5
27
0
0
9
G
10
14
0
3
7
25
0
4c
0
S
11
6c
2
Z
F t z cn Z Q
E
Z
W
0 QI W
a
11
1
SO.
W
-i t-
Data Obtained from the Spectra of Dried Films of Alkyd Resins and Ethyl Benzoate
Sd
Wave Length, Microns 12 13 14 15
Benzoic
Weak absorption at 12.1 microns does not always appear. Absorption at 14.06 - 14.12 microns is due to monosubstitution on the benzene ring and will occur in the same region for ester and acid. c Butyl ester of terephthalic acid added. d Presence of isophthalic acid is in doubt. Absorption strength: S = strong; ;11 = medium; IT = weak; Sh = shoulder (approximate position and band width as illustrated). a
b
4 Figure 1. 1. 2. 3.
4.
Spectra of alkyds
Containing o-phthalic anhydride Containing isophthalic acid Containing terephthalic acid Spectrum of ethyl benzoate
a shoulder or not a t all, the latter being the case when benzoic acid is present as in spectrum 6. If the presence of o-phthalic acid should be in doubt as in the unlikely mixture containing a large excess of isophthalic acid, the qualitative test for the ortho isomer using hydroquinone should be applied ( 2 ) . However, the resin mixtures available for analysis offered no difficulty.
4 Figure 2. 5. 6.
7. 8.
Spectra of alkyds containing:
Isophthalic and benzoic acids o-Phthalic, isophthalic, and benzoic acids Isophthalic acid with butyl terephthalate a d d e d o-Phthalic, isophthalic, and benzoic acids with butyl terephthalate a d d e d
Although one of the points of ophthalic acid absorption (14.16 to 14.20 microns) is adjacent to that of benzoic acid (14.06 to 14.12 microns), even 1% benzoic acid showed as a peak. I n mixtures high in o-phthalic
acid, the absorption band from 14.16 to 14.20 microns appeared only as a shoulder on the isophthalic acid band. Terephthalic acid appears in alkyd resins only in very small quantities. Efforts to formulate a terephthalic alkyd had minor success in the form of a small yield and an unstable product. An attempt to prepare 1,4-dibutyl phthalate produced an ester that was analyzed to contain 32% terephthalic acid rather than the theoretical 60%; apparently the half ester was formed. To test the possibility of detecting terephthalic acid, this half ester wab added to two commercial alkyds, one containing isophthalic acid only (Figure 2 , spectrum 7) and one containing o-phthalic, isophthalic, and benzoic acids (Figure 2, spectrum 8). Ir! spectrum 7, the terephthalic acid band a t 11.43 to 11.45 microns is clearly resolved as is the weak isophthalic acid band a t 12.05 to 12.15 microns. Both acids show absorption a t 13.72 microns. I n spectrum 8, however, the presence of isophthalic acid is not established because the 12.05- to 12.15micron band does not appear. If terephthalic acid were used appreciably in alkyd resins, it could be identified by its specific absorption a t 11.43 t o 11.45 microns. If a t the same time there were a weak peak a t 12.05 to 12.15 microns, the presence of isophthalic acid could be confirmed. The absence of absorption a t 12.05 to 12.15 microns under these circumstances does not necessarily indicate the absence of isophthalic acid, and it VOL. 30,
NO. 8, AUGUST 1958
1323
would have t o be included in the subsequent quantitative determination.
Chemical Laboratory, is acknowledged and appreciated.
ACKNOWLEDGMENT
LITERATURE CITED
The advisory assistance of C. F. Pickett, Director of the Coating and
( 1 ) Shreve, 0. D., in “Organic Analysis
A . Weissberger, eds., Interscience, Sew York, 1956. (2) Swann, RI. H., ANAL. C H m . 29, 1352 (1957). (3) Swann, M. H., Adams, If. L., Weil, D. J., Ibid., 27, 1604 (1955). (4) Ibid., 28, 7 2 (1956).
”
Vol. 111, p. 485, John Mitchell, Jr., I. bI. Kolthoff, E. S. Proskauer, and
R E C E I ~ Efor D review Sovember 8. 1957. Accepted March 6, 1958.
Performance of a Wide-Range High-Frequency Titration Apparatus ARTHUR H. JOHNSON’ and ANDREW TIMNICK Kedzie Chemical Laboratory, Michigan State University, East lansing, Mich.
b In a high-frequency titration apparatus, when the usual multiturn coil, into which the titration vessel is introduced, is replaced b y a singleturn loop, the distributed capacity associated with the inductance is reduced to a minimum and the instrument appears to respond only to changes in the solution conductivity. Practical instrument response is observed with aqueous solutions in the titration cell varying in concentration from 0.003 to 5.OM in sodium chloride. Direct titration of 3N hydrochloric acid solution with 4N sodium hydroxide was accomplished.
R
ELATIVELY FEW high-frequency
instruments have been constructed in which the solution was placed in a vessel in the field of the coil of a parallel resonant circuit. The few that have been developed have been of two types: those in which the parallel resonant circuit was a part of the circuit of a radio-frequency oscillator (5, 8-1 1 , I S ) , and those of the wavemeter type-i.e., parallel resonant circuit excited by radio-frequency energy from an external oscillator (3, 4,l a ) . All the instruments used coils of the multiturn type, which have associated with them relatively high values of distributed capacity. The distributed capacity shunts the inductance of the coil, making the coil equivalent to a parallel resonant circuit having a natural resonant frequency. The natural resonant frequency of the coil sets an upper limit to the frequency a t which the coil is useful in providing an inductive reactance. Inserting a solution of high dielectric constant within the coil markedly affects the natural resonant frequency of the coil. Thus, the response of a n instrument of this 1 Present address, Bauer and Black, Chicago, 111.
1324
ANALYTICAL CHEMISTRY
type is a function of at least tn-o variables, the dielectric constant of the solution and the high-frequency conductivity of the solution, as the inductance of the coil is not a constant and the conductivity of the solution varies with the addition of reagent. The instrument described (6) is of the loaded coil type, in which part of the tank circuit is a rigid single-turn loop constructed of 3/16-inch copper tubing. The diameter of the loop is substantially larger than the diameter of the polyethylene titration vessel that is inserted into the loop along its axis. The tank circuit is a partially distributed and partly lumped constant system, and has some of the characteristics of a quarter wave length line shorted at one end. The vessel and its contents are inserted near the closed end of the line (the loop) where the effect of changes in dielectric constant-that is, changes in lumped tuning capacity-have a minimum effect on the resonant frequency of the line. At the closed end of the line, changes in solution conductivity-that is, changes in load-have the maximum effect on the Q of the resonant circuit. Thus, a practical separation of two variables, which contributed to highfrequency titration instrument response, has been attained. The instrument responds only to changes in the solution conductivity for all practical purposes. Loading of the oscillator by the solution is controlled in three ways: by withdrawing the titration vessel vertically along the axis of the loop-Le., controlling the volume of the solution in the field of the loop; by increasing the diameter of the loop-Le., reducing the coupling between the solution and the oscillator; and by varying the feedback to the grid of the oscillator tube by changing the ratio of the capacities of the feedback capacitors, C1 and C?.
INSTRUMENT CONSTRUCTION
The instrument is a modified version of the 120-mc. instrument using a capacitative-type cell ( 7 ) . The loop and its shield have been substituted in the position previously occupied by the capacitative cell. The loop leads are terminated in banana plugs, which in turn are plugged into insulated banana jacks, in the side of the chassis, that serve as terminals to the grid and plates of the 955 tube. The feedback and tuning capacitors, C1 and Cz, are short lengths of Amphenol RG 8/U coaxial cable with one end terminated in Amphenol-type PL-259 male coaxial cable connectors. A range of capacity of C1 and Cz is obtained by simply varying the length of the coaxial cable attached to the male connectors. The male connectors plug into the female coaxial cable connectors mounted on the top of the chassis used to receive the ends of the 120-mc. half-wave line when the capacitative cell is employed. The interchangeable parts (feedback capacitors and half-wave line, loop shield assembly, and capacitative cell) make rapid conversion from one type of instrument to another a simple process. KO changes in the oscillator wiring are required-it., no soldered connections need to be broken.
d schematic diagram of the circuit of the instrument is shown in Figure 1. Figure 2 is a photograph of the instrument with the cover plate removed from the loop shield assembly to show the position of the polyethylene titration vessel relative to the loop. The loop shown is 7.5 cm. in diameter. and the titration vessel, 6 cm. in diameter. The diameter of the shield assembly is 17 cm., and the spacing between the cover plate and the bottom plate of the shield assembly is 7 cm. Concentrically secured around the aperture in the cover plate is a ring 2 cm. wide, having a n inside diameter of 6 cm. One and one-half cm. of the ring protrudes below the plane of the cover
