(4) Duff, J. C., Steer,E. H., J . Chem. SOC.
1932, 2861. (5) qannery, R. J., Ke B., Grieb, M. W., Tnvlch, D., J . Am. dhem. SOC.77, 2996 (\ -19.55 ). _--
(6)Ha&- J. L.,. James, P. S., Proc. West Va. A d . Sa.33,49 (1961). (7) . . Hein, Fr., Beerstecher, W.,2 . Anorp. AU em.Ch&. 282,93 (1955). (8) olthoff, I. M., Lingane, J. J.,
2
"Polarography," 2nd ed., p. 214, Interscience, New York, 1952. (9) Korshunov, I. M., Malyugina, N. I., Uch. Zap. Gor'kwsk. GOS. Univ., Ser. Khim. 1958. No.32. 21-4. (10) Migd, P. K., 'Pushnyak, A. N., Zh. Neorgan. Khim. 4, 1336 (1959). (11) Pecsok, R. L., Meeker, R. L., Shields, L. D., J . Am. Chem. SOC.83, 2081 (1961).
(12) Subrahmanya, R. S., Proc. Indian Acad. Sn'.46A, 377 (1957).
RECEIVED for review January 29 1962. AcceDted Mav 21. 1962. Di&on of And&al. Ciemistry, 140th Meeting, ACS, Chcago, Ill., September 1961. A NDEA fellowship waa held by one of UB (J.F.F.) during thk time this work waa done.
Differential Thermal Analysis of Some Metal Chelates of 8-Quinolinol and Substituted 8-Quinolinols WESLEY W. WENDLANDT and G. ROBERT HORTON Departmenf o f Chemisfry, Texas Technological College, lubbock, Tex.
b The thermal dissociation of the 8quinolinol and substituted 8-quinolinolmetal chelates of 15 metal ions and the chelating agents was studied by differential thermal analysis (DTA), DTA curves of the chelating agents, in argon, showed the presence of endothermic and exothermic peaks caused by fusion and/or decomposition of the compounds. The metal8-quinolinol chelates decomposed to give DTA curves containing a series of endothermic peaks caused by dehydration or decomposition reactions. A rough order of thermal stability, obtained from peak maxima temTh Sb peratures, was: Sc Pb Co(lll) = Cu Bi Zn Fe AI UOz Ni Co(ll) Mn = Cd. The effect of subs$itution on the 8-quinolinol ring on the thermal stability ' of the copper(ll), aluminum, and thorium(1V) chelates was determined.
<
Ni > Co(II1) >Mn>Cd=Bi>Zn>Pb>Cu. The decomposition of the anhydrous 8quinolinol-metal chelates appears to be a much more complicated process than the dehydration reaction. The exact decomposition mechanism is not known, although some information is available from vacuum TGA experiments on the alkaline earth, lanthanum, and bismuth complexes (2). It was shown that the residues, after pyrolysis, contained considerable amounts of carbon, nitrogen, and hydrogen, as well as the free metal. It is reasonable to assume that the decomposition reaction involves metal-to-oxygen and metal-tonitrogen bond breaking as well as intramolecular decomposition of the chelate molecule. Fusion of the complexes is not involved directly, although the decomposition products may fuse. Most of the energy absorbed is probably involved in the bond-breaking step. In the case of several metal ions-i.e., Co(II1)-a reduction reaction is probably also involved, giving Co(I1) com1100
ANALYTICAL CHEMISTRY
OxCH3 = 2-methyl-;
(4, 6, IO). A rough order of thermal stability for the complexes, obtained from peak maxima temperatures, was: Sc < T h < Sb < P b < Co(II1) = Cu < Bi < Zn < Fe < A < UOz < Ni < Co(I1) < Mn = Cd. TGA studies, based on the temperature st which the complexes began to lose weight in air, indicate that the order for the transition metals was: Co(I1) < Fe (111) < Mn = Cu < Zn < Co(II1). To determine the effect of substitution on the 8-quinolinol ring on the
pounds in the residue. The reduction reaction may also give the free metal. The decomposition peak maxima temperatures for the 8quinolinol chelates ranged from 155' C., in the case of scandium, to 490' C. for manganese. Although the scandium compound contains an extra "solvate" molecule of 8quinolinol (8, IO), it was not evolved to form the "normal" chelate, Sc(0x)a. This is contrary to the behavior observed for the analogous solvated complexes of thorium(1V) and uranium(V1)
l4
80
i!
I
i/ I 1
I
! i
8C
------250
I
PV. I
100
l
I
200
I
I
300
/
l
I
400
'
500
I
I
/
100
I
200
I
TEMPERATURE, 'C.
Figure 4. EA. 88. 8C.
DTA curves of metal chelates
Cu(0xCI.r)~ Cu(OxBrz1~ CU(OX12)2
PA. 98. 9c.
CU(OXCH~ Cu(0~lCIh Cu(0xl)n
I
300
8
1
400
1
1
500
/
thermal stability of the metal chelate, metal chelates of a divalent [Cu(III) I, a trivalent [Al(III)], and a quadrivalent [Th(IV)] ion with the various substituted 8-quinolinols were studied. The peak maxima temperature variations for the three series of complexes are given in Table 11. The order of stability was very different for the three metal ions. For the thorium chelates, substitution on the 8-quinolinol ring decreased the thermal stability, while for the other two metal ions, the general trend was an increase in stability. For the copper and aluminum chelates the order of decreasing thermal stability was: 5,7-dichloro- > 8-quinolinol > 5-iodo-7-chloro- = 5,7dibromo> 5,7-diiodo- > 5-iodo- > 2-methyl-. For a given chelating agent, 8-quinolinol, the thermal stability with various central metal ions was in the order: A1 > T h > Cu. For the 5,7-dichloroand 5,7-dibromwmetal chelates, the order was: A1 > Cu > Th. All of the aluminum chelates with the substituted 8-quinolinols gave DTA curves which contained only endothermic peaks, while for the other metal ions, the 5,7-dihalochelates all gave exothermic peaks. These exothermic peaks must be related to the oxidation of the halogen, although it is not known why this effect does not take place with aluminum. Perhaps it is related t o the thermal stability of the metal halide
Table II.
Peak Maxima Temperatures for Metal Chelates Containing Substituted 8-Quinolinols
Chelating Agent 8-Quinolinol %Methyl5,7-Dichloro5,7-Dibromo5.7-Diiodo-
CoPPe: Aluminuom Chelates, C. Chelates, C. 335 415 230 Unknown* 340 (exo.)~ 335 315 (exo.) 405 290 (exo.)d 330 (em.j 5-Iodo-7-chloro315 (exo.) 350 5-Iod0260 ’ 330 a All were normal chelates, Th( 0 ~ ) ~ . b Cannot be prepared. exo = exothermic peak; all others are endothermic. d Small peak.
Thoriuy Chelates, C. 2700 440 245 (exo.) 200 200
240 (exo.) 240
0
which might be formed as an intermediate compound. LITERATURE CITED
(1) Berg, R., “Die Anal ische Verwendung von o-Oxychinoin (Oxin) und seiner Derivate,” 2nd ed., F. Enke, Stuttgart, 1938. (2) Charles, R. G., Langer, A., J . Phys. Chem. 63,603 (1959). (3) Duval, C., “Inorganic Thermogravimetric Analysis,” Elsevier, Houston, Tex.. -1953. --(4) Frere, J. F., J . Am. Chem. SOC.55, 4362 (1933). (5) Hecht, F., Reich-Rohrwig, W., Momtsh. 53, 596 (1929). (6) Hollingshead, R. G. W., “Oxine and Its Derivatives,” Vols. I to IV, Butterworths, London, 1954. (7) Newkirk, A. E., ANAL. CHEW 32, 1558 (1960).
T
~
I
(8) Pokras, L., Bernays, P. M., J . Am. Chem. SOC.73, 7 (1951); ANAL.CHEM. 23, 757 (1951). (9) Smothers, W. J., Chiang, Y., “Differential Thermal Analysis: Theory and Practice,” Chemical Publishing Co., New York. 1958. (10) Wendlandt, -W. W.,ANAL. CHEM. 28, 499 (1956). (11) Wendlandt, W. W . , dnal. Chim. Acta 17,428 (1957). (12) Wendlandt, W. W., George, T. D., Horton. G. R.. J . Znoro. Nucl. Chem. 17, 273 (1961).‘ (13) Wendlandt, W. W., Van Tassel J. H., Horton, G. R., Anal. Chim. Acta 23, 332 (1960). RECEIVED for review February 15, 1962. Accepted June 7, 1962. Work sponsored in part by the U. S. Atomic Energy Commission through Contract AT-(40-1)2482.
Differential Thermal Analysis of Organic Samples Effects of Geometry and Operating Variables EDWARD M. BARRALL Ill and L. B. ROGERS2 Departmenf of Chemistry and laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Mass.
Quantitative analyses of 1 to 10 mg. of organic materials have been demonstrated with salicylic acid. Under carefully controlled conditions, measurements of the endothermal depth had approximately half the error of an area measurement. The standard deviation for a depth measurement was 0.07 mg. of acid or 5% relative, whichever was larger; that for area was 0.15 mg. or 7%. A study of variables has shown that equations developed for pure samples can be extended to diluted samples. In addition, the specific heat of melting of salicylic acid, 28.2 f 0.5 cal. per gram, has been determined using silver nitrate to calibrate the apparatus.
b
D
IFFERENTIAL
THERMAL
ANALYSIS
(DTA) has been most widely used by geologists and mineralogists for studying clays (15), coals ( 5 ) , and organic material of geological origin (6). Its use by chemists to characterize pure substances has been relatively slight but is increasing rapidly (19). Despite the almost universal reporting of melting points in the organic literature, phase changes of organic compounds have received the least attention (7-10, 16-18, 2 2 ) . The technique should be more widely used now that the effects of reaction kinetics on the curve shape ( I , 3, 4, 11, 12) and the direct calculation of heats of transformation (2, 3, 8, 23) from the curve have provided a
sound basis for interpretation of data. The writers and Vassallo (21) independently concluded that the usefulness of DTA would be considerably greater if the accuracy, precision, and sensitivity were improved, if the mass of the apparatus were reduced so that cooling could be effected rapidly to permit more analyses to be made, if factors affecting flatness of the baseline were controlled, and if the required amount of sample
1 Present address, California Research Corp., 576 Standard Ave., Richmond, Calif. * Present address, Chemistry Department, Purdue University, Lsfayette, Ind .
VOL 34, NO. 9, AUGUST 1962
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