the oxalates of lanthanum, praseodymium, and neodymium; the second consists of samarium, europium, and gadolinium; the third contains yttrium. holmium, and erbium. I n the first group, there i ~ a sno evidence for the formation of intermediate hydrates. The 10-hydrates decomposed directly to the anhydrous oxalates. Ho\\ ever, the anhydrous oxalates n ere verj unstahle and immediately drconiposed to give the oxides. I n only one case, lanthanum. was a basic cwboiiate observed. The minimum oxidr level temperatures in this group w r e higher than in the other two b'I oups. I n the second group, the formation of intermediate hydrates was first obs e n ~ 1 .S o levels were obtained, per1i:ips because of the heating rate eniploy~tl.but iireaks in the curve viere
found for the 6- and the 2-hydrates. Again, the composition for the anhydrous oxalates n-as approached, but no horizontal weight levels were obtained. The oxide levels were obtained a t slightly loner temperatures than in the first group. The oxide leiel temperature for europium was anomalously lower than for the other two elcmeiits in this group. I n the third group, the first stable intermediate hydrate levels n ere observed. The 2-hydrates appeared to be stable, giving stable levels over a temperature interval of 40 " to 90 ". Breaks in the curve ncre noted for the anhydrous oxalates. n-liich immediately decomposed to give the oxides. ACKNOWLEDGMENT
The author would like to thank James
R. Slagle for preparing the methyl oxalate used in this investigation. LITERATURE CITED
(1) Backer, H. J., Klaassens, K. H., 2. anal. Chem. 81, 104 (1930). (2) Blatt, A . H., "Organic Syntheses," Coll. Vol. 2 , p. 414, Wiley, New York, 1043.
(3) Duval, C., "Inorganic Thermogravimetric Analysis," Chap. 20, pp. 50-6, Elsevier, Houston, Tex., 1953. ( 4 ) Marsh, J. K., J . C'hem. SOC.1943, 40. (5) Riley; R F., Ph.D. thesis, Michigan State University, 1954. (6) Vickery, R. C., "Chemistry of the Lanthanons," p. 222, Academic Press. iYew York. 1953. ( 7 ) Kendlandt, W. W.,- ~ N A L . CHEM. 30,56 (1958).
RECEIVEDfor review May 4, 1957. Accepted September 16, 1957.
Thermolysis of Oxine Molybdophosphate WESLEY W. WENDLANDT Department o f Chemistry and Chemical Engineering, Texas Technological College, lubbock, Tex.
J. A. BRABSON Division of Chemical Development, Tennessee Valley Authority, Wilson Dam, Ala.
,The thermal decomposition of precipitated oxine molybdophosphate was reinvestigated on the thermobalance. The air-dried precipitate was converted to the anhydrous compound in the range 60" to 85" C. The anhydrous compound was found over the range 85" to 285" C. The results confirm a previous conclusion that 140" C. i s a good drying temperature.
T
ilrtailed investigation of the precipitation of phosphorus as the oxiiie salt of molybdophosphoric acid has presented nexv information as to the composition of the precipitated compound. Brabson and Edwards ( 2 ) found that if the precipitate was carefully prepared, properly n-ashed, and dried a t 140" C., the composition corres p o n d d to t h r formula 3 C s H 7 0 S H3(P?\Io12040). On the basis of phosphorus content. the precipitate gave accurate and reproducible results. Tlicir rcsults w r e in disagreement w t h previous work. Berg ( 1 ) concluckd that the dried precipitate corresponded to the 2-hydrate, 3C9HiOS. Hi [P(RIO,O~)~] 2H,O. Duval ( 3 ) ,from his study of the thermolysis of this compound, reported that the 2-hydrate n a s stable from 1T6" to 225" C. The oiganic part of the molecule was elimiHE
nated starting a t 300", without evidence for the formation of the anhydrous compound. D u d prepared the precipitate according to the instructions of Hecht arid Donau (4). taken from the original work of Scharrer ( 5 ) ,n-liich specify that the precipitate be washed with a n animoiiium nitrate solution prior to drying. Ignition of the organic compound with ammonium nitrate might be expected to cause accelerated decomposition. d s it appeared that the compound prepared by Brabson and Edwards ( 2 ) would exhibit different properties upon ignition, it was of interest to investigate the thermolysis of the aiiimonium nitrate-free compound on the therniobalance.
47 0
'\ 10 MG.
B 455
TEMPERATURE 'C.
Figure 1. Thermal decomposition curves .of oxine molybdophosphate
A . .\ir-dried B. Oven-dried at 140' C. EXPERIMENTAL
Thermobalance. An automatic recording thermobalance m s used (6). The sample sizes weighed betiveen 80 and 100 mg. The heating rate was 5.4" C. per minute. Preparation of Precipitate. T h e oxine molybdophosphate was prepared as previously described ( 2 ) . Samples of the air-dried and oven-dried (140" C. for 2 hours) compounds were studied on the thermobalance.
DISCUSSION
The thermal decomposition curves are given in Figure 1 with the coinposition data in Table I. The air-dried precipitate began to lose weight a t 60" C. 85" C., a horizontal n-eight level appeared which extended to 285" C. Calculations from the resulting weight data indicated that air-dried compound corresponded to the VOL. 30, NO. 1 , JANUARY 1958
61
%hydrate, 3CeH,ON.Ha(PMoxzO& . 2H20. However, this finding may be fortuitous, as the air-dried precipitate loses virtually the same amount of water in an evacuated desiccator. The horizontal weight level which began at 85" C. corresponded to the anhydrous compound and confirmed the earlier conclusion (2) that 140" C. is a good drying temperature. The anhydrous compound began t o decompose a t 285" C., resulting in a horizontal weight level from 335" to 375" C. The composition of this level corresponded to a compound with a n apparent molecular weight of 1970. This roughly corresponds to a compound containing only one oxine molecule, or CgH70N.Ha(PMOI~O~O), with a molecular weight of 1967.8. Apparently, one of the oxine molecules is held more strongly than the other two. This compound began to decompose at 375" C., resulting in the oxide level, 24MoOa .P*O6, beginning at 470" C. I n general, the thermal decomposition curve for the oven-dried sample was similar to that for the air-dried sample. The water of hydration had been removed by heating, so does not appear in the curve. The first weight loss was observed at 280" C. After the loss of two oxine molecules, a horizontal weight
Table 1.
Composition Data for Oxine Molybdophosphate
Assumed Composition 3CgH70N. Ha(PMoiiOu).2 H20
78.1 78.6 78.4 79.5", 79.38 79.6, 79.6 92.1 92.8 92.8 91.0
I
3CoH7ON.Ha(PM0izOu) CgH7ON. Ha(PM0iiOw)
a
b
78.40
79.65 91.38
Air-dried precipitate. Oven-dried precipitate.
level appeared from 325" t o 345" C. The oxide level began at 455" C. As the curves are in disagreement with those reported by Duval, it is assumed that his use of a n ammonium nitrate wash liquid could cause accelerated decomposition of the organic matter. The method of Brabson and Edwards gave consistent and reproducible results, and as the precipitated compound exhibited a broad temperature stability range, it could be readily dried to a stable weighing form. LITERATURE CITED
(1) Berg, R., "Das o-Oxychinolin (Oxin),"
(2) (3) (4)
(5)
(6)
Vol. XXXIV in series, "Die Chemische Analyse," F. Enke, Stuttgart, 1936. Brabson, J. A,, Edwards, 0. W., ANAL.CHEM.28, 1485 (1956). Duval, C., "Inorganic Thermogravimetric Analysis," pp. 130, 132, Elsevier, Houston, Tex., 1953. Hecht, F., Donau, J., "Inorganic Gravimetric Microanalysis," p. 256, Julius Springer, Vienna, 1940. Scharrer, K., Biochem. 2. 261, 444 (1933). Rendlandt, W. W., ANAL. CHEM. 30,56 (1958).
RECEIVED for review February 23, 1957. Accepted September 16, 1957.
Photometric Determination of Iproniazid and Related Compounds REM0 J. COLARUSSO, MORTON SCHMALL, ERNEST G. WOLLISH, and E. G. E. SHAFER Analytical Research laboratory, Hoffmann-la Roche Inc., Nutley, ,A rather specific and rapid method for the determination of iproniazid (Marsilid) in pharmaceuticals has been developed. This drug has attracted considerable attention as a psychic energizer. The reaction of molybdic acid with iproniazid in a medium of acetone results in a reddish complex formation, which is stable in solution. The color absorbance follows Beer's law and can be determined photometrically at either 430 or 535 mp with good precision. The procedure is sensitive down to 10 y. As breakdown products will not react, it can be applied to stability studies. The specificity of this reaction and its application to analogs are discussed. Related compounds of the following general structure will produce the color 0 with varied intensity:
//
R '-C-N
62
ANALYTICAL CHEMISTRY
HNHC-R
N. J.
where R = alkyl or aryl and R' = pyridine.
(I - isonicotinyl - 2 - isopropylhydrazine, Marsilid) has recently attracted considerable attention as a psychic energizer. A sufficiently sensitive and specific method for the determination of this compound in pharmaceutical preparations wasdesired. For the colorimetry of isonicotinic acid hydrazide (isoniazid) , Wollenberg (6) has described a reaction with vanadic acid in acid medium, resulting in a reddish color. Deltombe (d), using molybdic acid, has obtained a rosebrown precipitate m-ith this compound, which turned white on heating. A survey of a great number of heteropoly acid reactions has been published by Vignoli, Cristau, and Pfister ( 5 ) .
I
PROKIAZID
DEVELOPMENT OF M E T H O D
It was assumed that iproniazid, because of its hydrazine moiety with reducing properties, would also produce a color when subjected to a heteropoly acid reaction with molybdate. When iproniazid reacted with molybdate in acid medium, no color change occurred, but when this solution was made alkaline, a blue color resulted. However, this color was unstable and was also formed by many other similar compounds. Bernhart and Kreath (1) had demonstrated the advantage of using acetone in order to intensify and help solubilize the phosphomolybdate color obtained in phosphoric acid determinations of organic phosphates. When in a similar experiment a small quantity of aqueous iproniazid solution was diluted with acetone and then reacted
