Dete rminat io n of Pyrid ine- 2-aIdoxi me Methio d ide a nd Its Corresponding Stereoisomer by Ultraviolet Analysis ROBERT I. ELLIN and ALBERT A. KONDRITZER Physiological Chemistry Brunch, Physiology Division, U. S. Army Chemical Wurfare Laborafories, Army Chemical Center, Md. An ultraviolet spectrophotometric method has been developed for the quantitative estimation of pyridine-2aldoxime methiodide (PAM), in the presence of its acid hydrolytic products. A similar procedure was applied to the quantitative determination of the syn and anti configurations of PAM. The method i s based on the fact that the anti configuration of PAM has absorption maxima at 292 mp in acid solution and 333 mp in alkaline solution. Neither the syn configuration nor acid hydrolytic products of PAM absorb at these wave lengths. The method i s simple and rapid and adheres to the usual absorption laws.
A related feature of this study deals with the stereoisomers of PAM. Oximes of aldehydes and unsymmetrical ketones of both the aromatic and aliphatic series may exist in two geometrically isomeric forms. The double bond between the carbon and nitrogen atoms of the oximes accounts for the existence of these substances in the s p and anti forms, which correspond to the cis and trans forms, respectively,
of the olefins. The syn configuration generally has the lower melting point, higher pK, value, greater water solubility, and is lighter in color than the anti form. Ginsburg and Wilson (2) described and tentatively characterized the sj-n and anti configurations of PAM. Unless otherwise indicated, PAM is assumed to have the anti configuration. APPARATUS
.
7
5
i
All absorbance measurements were made with a Beckman Model DU spectrophotometer and 1.00-em. silica cells. A Beckman Model G pH meter was used for pH determinations. EXPERIMENTAL AND RESULTS
YRIDINE-%ALDOXIME methiodide P ( P A M ) is an effective chemical for overcoming the neuromuscular block that occurs in nerve gas poisoning. The treatment of nerve gas poisoning in laboratory animals has been more successful with a combination of PAM and atropine than with either compound alone (3, 6). Because the physicochemical factors governing the stability of atropine toward hydrolysis in aqueous solution have been reported (4, 7), a similar investigation of the stability of PAM was desirable. For a study of the chemical kinetics of the breakdown of PAM in solution a simple quantitative assay procedure for either the compound itself or its deterioration products was needed. A colorimetric procedure (1) based on the determination of hydroxylamine, which is produced in the acid hydrolysis of PAM, was investigated and used initially. I n this method the hydroxylamine is oxidized by iodine to nitrous acid, reacted with sulfanilic acid to form the diazonium salt, which is then coupled with l-naphthylethylenediamine dihydrochloride to produce a purple color. Because PAM yields hydroxylamine on acid hydrolysis, the formation of pyridine-2-carboxaldehyde methiodide (PCAM) was indicated. The ultraviolet absorption spectra of PAM and PCAM were investigated over a wide pH range to determine the suitability of this technique for a simple, rapid assay procedure. 200
ANALYTICAL CHEMISTRY
Preparation of Pyridine-2-carboxIn general, aldehyde Methiodide.
220
250 300 350 WAVE LENGTHlmu) Figure 1. Ultraviolet spectra
A. 6. C.
Pyridine-2-aldoxime methiodide, 3.8 X 1 O-bM in 0.1 N acid solution Pyridine-2-aldoxime methiodide, 3.8 X 1 0 a M in 0.1N basic solution Pyridine-2-carboxaldehyde methiodide, 3.8 X 1 Od5Min 0.1 N acid solution
Table 1.
Molar Extinction Coefficients
Wave Length,
Molar Extinction Coefficient
Compound &Ic, x 103 Pyridine-2225 max.) 18.75 aldoxime 262 [min.) 3.75 methiodidea 292(max.) 12.20 Pyridine-2226(max.) 12.50 carbox247 (rnin.) 3.41 aldehyde 263 (max.) 6.18 methiodidea Pyridine-% 226 (max.) 14.22 carbox248 (min.) 3.66 aldehyde 4.53 258(max.) methiodideb Pyridine-2225(max.) 17.11 aldoxime 253.5 (min.) 2.48 methiodideb 333 (max.) 18.27 a I n neutral or 0.1N acid solution. b In 0.1N alkaline solution.
methiodides of pyridine-like compounds are crystalline, yellow solids. Lenart (6) described pyridine-2-carboxaldehyde methiodide as a liquid; however, his product may have been impure. The authors have prepared the compound as follows: Pyridine - 2 - carboxaldehyde (10.7 grams, 0.1 mole) was placed in a 100ml. round-bottomed flask and dissolved in an excess of methyl iodide (28 grams), The solution was refluxed for 2 hours. A double condenser was used to prevent methyl iodide from escaping. The orange crystals which formed were filtered, washed with ether, and dried. A 50% yield of light orange crystals melting a t 178-9" C. was obtained. Ginsburg and Wilson (6)described the above compound as having a melting point of 174' C. They prepared it by allowing the corresponding aldehyde to react for several days a t room temperature, with methyl iodide in a nitrobenzene solvent. The procedure described herein produces the compound in good yields in a much shorter time. Ultraviolet Spectra of PAM, Syn PAM, and Possible Hydrolytic Products. Ultraviolet absorption spectra
of PAM and PCAM were determined in distilled water and in solutions of varying p H values. Figure 1 illustrates the spectrum of each compound in distilled water, in acid solution, and in basic solution. No differences in the spectrum of any of the compounds were observed when a sample was dissolved in either distilled water or in acid solu-
tion. At p H values 8 to 13, the spectrum of PCAM does not noticeably change; whereas the absorption maximum of PAM a t 292 mp shifts to 333 mp. The molar extinction coefficients of the oxime and the aldehyde a t the wave lengths of maximum and minimum absorption are given in Table I. PAM, in concentration of 2.5 y per ml., can be determined without interference from the acid hydrolytic products, PCAM and hydroxylamine, by reading in acid solution a t 292 mp or in alkaline solution a t 333 mp. The precision of the method can be seen from the values shown in Table 11, Ultraviolet absorption spectra of the syn configuration of PAM, in concentrations equivalent t o those shown in Figure 1, were obtained. It has the same absorption spectrum as pyridine2-carboxaldehyde methiodide. Thus, in acid or aqueous solution, the syn form has the same spectrum as its parent aldehyde, while the anti configuration displays not only greater absorbance, but also a significant wave length shift from 263 to 292 mp.
Table 11.
Analysis of Mixtures of Pyridine-2-aldoxime Methiodide (PAM) and Pyridine-2-carboxaldehyde Methiodide (PCAM)
PAM Taken,
PCAAI Taken,
Y/ML
Y/W.
5 10 10 5 .5
2.5 2.5 1 5 0
0 5 2.5 2.5 5 10 5 8 10 5
A
Absorbance
0.233 0.458 0.458 0.234 0.233 0.115 0.115 0.047 0.234 0.000
B
0.000 0.120 0.058 0.056 0.121 0.238 0.119 0.190 0.233 0.114
PAM Found, y/ML
PCAM Found, -//Ml.
5,1 10.0 10.0 5.1 ? .I1 2.5 2.5 1.0 5.1 0.0 ~~
0.0 5.1 2.5 2.4 5.1 10.0 5.0 8.0 10.0 4.8
A. Total absorbance at 292 mp in acid solution. B. Difference between total absorbance at 263 m p and that due to PAM at 263 nip.
LITERATURE CITED
(1) Czaky, T. Z., Acta Chem. Scand. 2,450 (1948). (2) Ginsburg, S., Kilson, I. B., J. Am. Chem. SOC.79,481 (1957). (3) Kewitz, H., Wilson, I. B., Sachmansohn, D., Arch. Biochem. Biophys. 64, 456 (1956). (4) Kondritzer, -4.A., Zvirblis, P. J., Am. Pharm. Assoc. 46, 531 (1957).
( 5 ) Lenart, G., Ber. deuf. chem. Ges. 47, 808 (1914). ( 6 ) Wills, J. IT., Kunkel, A. A 1 Bron-n, R. V., Groblewski, G. E., Sc&ce 125, 743 (1957). (7) Zvirblis, P., Socholitsky, I., Kondritzer, A. A, J . Am. Pharin. .4ssoc., Sci. Ed. 45, 450 (1956).
RECEIVEDfor review April 25, 1058. Accepted August 12, 1958.
Photometric Determination of Aluminum and Titanium in Polyethylene WlLLlAM T. BOLLETER Monsanto Chemical Co., Texas City, Tex.
b Wet- and dry-ashing procedures are used for the decomposition of polyethylene with the attendant dissolution of the metals in the polymer. Aluminum is determined photometrically after extraction of the aluminum 8-quinolinolate into trichloroethylene from an ammoniacal solution. The absorbance of the complex is measured a t 390 mp. Titanium is determined photometrically using chromotropic acid
(4,5 -dihydroxy-2,7-naphthalenedisulfonic acid) for the development of titanium-chromotropic acid complex. The maximum absorbance of the color produced occurs a t 420 mp when the p H is adjusted to about 5. Moderate to large amounts of foreign ions do not interfere. Amounts as low as 5 p.p.m. of both metals in a single 2gram polyethylene sample can b e readily determined.
w
and dry-ashing-fusion procedures have been employed for the decomposition of polyethylene and dissolution of the metals in the polymer. The wet-ashing method is rapid and is ET-
not subject to the losses experienced in normal dry-ashing procedures for organic samples, nor to the tedious recovery and subsequent dissolution of metal oxides following combustion in an oxygen bomb. A 2- to 3-gram sample of polyethylene can be prepared for the determination of both titanium and aluminum in about 30 minutes, exclusive of the time required to cool the solution. With normal care the wetashing of polyethylene is not hazardous. Several hundred samples have been metashed in this laboratory without incident. The dry-ashing-fusion method of sample decomposition employs a niixture of potassium sulfate and nitrate to facilitate combustion of the polymer and recovery of the metals. A 5-gram sample of polyethylene can be ashed in about 15 minutes and the total time required to prepare a sample for analysis is the same as for the acid digestion procedure. The method for the spectrophotometric determination of aluminum by measurement of the intensity of the
yellow chloroform extract of the aluminum 8-quinolinolate has been reported (1, 8). A number of metal ions may interfere but procedures have been developed Tyhich eliminate (7, 1%’)or mask (5) this interference. The pH of the aqueous solution from TT hich the aluminum 8-quinolinolate is extracted is an important factor in the determination (6). In this investigation, a method for the determination of aluminum in polyethylene makes unnecessary the elimination of foreign ions and careful adjustment of the pH. Trichloroethylene has been substituted for chloroform as the extraction solvent because of its lower volatility. The determination of titanium in polyethylene reported by Anduze ( 2 ) requires the separation of titanium from interfering ions before development of the color with hydrogen peroxide. A method for the determination of titanium with 4,5-dihydroxy-2,7-naphthalenedisulfonic acid (chromotropic acid) which is more sensitive than the hydrogen peroxide method has been VOL 31, NO. 2, FEBRUARY 1959
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