April, 1959
HEATSTABILITIES OF METALCHELATES
Site-bound Water and Relationship to Dextran Structure.-The general interpretation of the convex (to the humidity axis) portion of the isotherm a t low humidities is that in this region water is absorbed on some localized “surface)) or hydration sites. Various theoretical treatments give measures of these sorption sites in the sample. The treatment developed by Hailwood and Horrobin16 can be applied in the region of the lower half of the humidity scale, and it was used by Northcotes in characterizing his polysaccharides. In the Hailwood-Horrobin treatment, three parameters are determined by a curve fitting procedure.ls From these can be deduced the weight of dextran associated with 1 mole of theoretical water-binding sites. From our mean “amorphous” isotherms were determined the values of 177 g. from absorption and 123 g. from desorption. These values are only approximate; because of a rather irregular shape of the isotherm, curve fitting was not precise. When these values are compared with the molecular weight of the glucose residue, 162, the calculated figures roughly agree with the concept that every glucose residue is accessible (16) A. J. Hailwood and E. Horrobin, Trans. Furudug Soc., 4¶B, 84 (1946). (16) C. H. Nicholla and J. B. Speakman, J . Teztile Inet., 46, T264 (1955).
603
and can form a hydrate with 1 molecule of water. However, the significance of this agreement is obscure, The fact that the absorption isotherms of all dextran samples were nearly identical a t low humidities is evidence in agreement with Northcotes and contrary to the concept that the primary 6-hydroxyl groups are the principal water-binding sites. From the analyses of Jeanes, et CJZ.,~ presented in Table I, these dextrans range in primary hydroxyl content from as low as 5% to a t least 40’% of the number of glucose residues, if it is assumed that the various types of linked units have the meanings suggested by Rankin and Jeanes.* A directly proportional variation should be found in numbers of sorption sites and, hence, in water absorption a t low humidities if the primary hydroxyls were the principal binding sites for water. This investigation does not rule out a relatively stronger hydrogen bond in primary hydroxyl interactions. First, the most reactive groups should be saturated a t low humidities, and perhaps an investigation of lower humidities would discover differences in sorptive power among the dextrans before saturation is complete. Moreover, it is possible that the most reactive water-binding groups are satisfied to a correspondingly greater extent by bonding to other polymer groups.
HEAT STABILITIES AND VOLATILITIES OF METAL CHELATES DERIVED FROM 8-HYDROXYQUINOLINE BY ROBERT G. CHARLES AND ALOISLANGER Westinghouse Research Laboratories, Pittsburgh 36,Pennsylvania Received September 94,1968
The behavior of eighteen metal 8-hydroxyquinolatesupon heating i n vacuo has been investigated. Many of the comounds were observed to sublime completely, without appreciable decomposition over fairly narrow tem erature ranges. &he temperature ran e of volatilization was found to be a function of metal ion eiectronegativity for the &valent metal 8hydroxyquinolates. I n contrast to this behavior, nearly all of the trivalent metal 8-hydroxyquinolaks volatilized over the same temperature range, 250 to 350’. Sublimation of the Ca(I1) and Bi(II1) 8-hydroxyqumolateswas accompanied (or preceded) by significant decomposition, while the Ba(II), Sr(11) and La(II1) compounds did not sublime appreciably, but decomposed at sufficiently high temperatures.
Recent interest’-* in metal chelate polymers has made desirable a more complete knowledge of the heat stabilities characteristic of the various metal chelate ring systems which might be incorporated into such polymers. A number of workers4J have investigated the heat stabilities, in air, of the metal 8-hydroxyquinolates I, chiefly from the standpoint of establishing suitable drying temperatures for these compounds. Under the conditions used by these authors the chelates may be subjected to oxidative attack as well as to pyrolysis. It was the purpose of the present investigation to determine the behavior of the 8-hydroxyquinolates when heated in the absence of oxygen. (1) W. C. Fernelius, Wright Air Development Center, Report WADC 56-203 (Oct. 1956). (2) J. P. Wilkins and E. 1,. Wittbecker, U. S. Patent 2,659,711 :Nov. 17, 1953). (3) K. V. Martin, J . A m . Chem. Soc., 80, 233 (1958). (4) C. Duval, ”Inorganic Thertnogravimetric Analysis,” Elsevier Pub. Co., New York, N . Y.. 1983. (6) M. Borrel and R. Paris, A n d . Chim. Ada, 4, 267 (1960).
[e?]. x=2or3 I
The experimental method used in this work involved following sample weight loss in vacuo as a function of temperature, as the temperature was increased linearly with time. Because of the apparent non-volatility of most of the 8-hydroxyquinolates in air, it was hoped that, under the present conditions, decomposition would occur a t temperatures below those required to volatilize the unchanged chelates. In practice this has been found to be true for only a small number of the compounds examined. Experimental Preparation of Compounds.--The metal 8-hydroxyquinolates were prepared in high purity by precipitation from aqueous solution, using conventional analytical procedures.6 (6) R. G. W. Hollingmhead, “Oxine and Its Derivatives,” Vols. I and 11, Butterwortha Publications, London, 1964.
ROBERTG. CHARLES AND ALOISLANGER
604
,1
Divalent Metals
I
Trivalent Metals I
Bi I Hour
Pb
"I
Go
H
I l l l l l r l l l l l l l l l l l l 1 ~1 0 200 400 600 0 200
I I
1
1
400
I
I
E-+ I I l l 1 600 000
Temperature ("C), Fig. 1.-Weight loss curves for metal 8-hydroxyquinolates in vacuo. Fifty-mg. samples were used. For clarity curves are displaced along the ordinate. The chelates were collected in sintered glass crucibles and washed thoroughly with hot water to remove excess 8-hydroxyquinoline. To facilitate handling, the chelates were dried by allowin to stand at room temperature in the open air for a periof of one week (protected from dust and strong light) and then stored in sto pered vials. Most of the compounds contained water of hydration after this period, although the amount of water may not have been the same as initially present in the air-dried precipitates. The water contents for a number of the compounds were established by drying weighed portions of the hydrated compounds in air in an oven maintained at the approximate midpoint of the temperature ranges recommended by Duval4 to obtain the anhydrous com ounds. Per cent. weight losses obtained were: Cu, 5.8; k i , 9.9; Co, 9.7; Zn, 9.4; Cd, 9.7; Mn, 5.0; Mg, 11.5; Ca, 12.6; Al, 3.1; In, 1.9; Fe, 0.5; Cr, 1.9; La, 1.0. Apparatus.-An automatic recording vacuum thermobalance constructed in these laboratories waa used for the present studies. The sample to be heated was contained in a shallow platinum crucible which was suspended by a h e nichrome wire from one end of a light quartz beam. This load was balanced a t the other end of the beam by a small c lindrical permanent magnet suspended within a solenoid! The beam was supported by jewel bearings. Weight changes were recorded automatically aa a function of time in terms of the current supplied to the solenoid to maintain balance. Weight changes of 0.1 mg. could be detected readily. The entire balance, and the sample, were surrounded by a glass and uartz envelope which could be evacuated to 10-6 mm. '&e tube surrounding the sample was of quartz and was contained in a cylindrical tube furnace mounted vertically. Temperature was plotted sutomatically as a function of time, using a thermocouple in close roximity to the sampIe. The temperature of the tube krnace was varied with time by means of a Variac variable transformer driven by a synchronous motor and reducing gear system. By starting a run a t a volta e setting of 30, a nearly linear temperature-time plot waa ottaiined. Procedure.-The a paratus waa assembled using a 50.0mg. sample of the 8-gydroxy uinolate (finely powdered as obtained by precipitation). %he system was evacuated and heating begun. After the run was completed any appreciable residue remaining in the sam le container was stored in a desiccator for analysis. d e r e possible, any sublimate on the walls of the tube surrounding the sample was scraped into a vial with a wire. The sublimate was then dried in a vacuum oven a t 100' for an hour to remove any water adsorbed from the air during the scraping procedure and finally the infrared spectrum (3-15 p ) of the sublimate was determined in KBr . The resulting s ectra were compared with those of the authentic anhygous S h y droxyquinolates. The latter were obtained by drying the chelates in air at the temperatures recommended by DuVal. 4.1 (7) DuvaP does not give suitable drying temperatures for the Pb and Gs compounds. In the present work these were dried in a vaou u m oven at 100°.
Vol. 63
The weightrtime and temperature-time curves obtained from the runs were used to construct the curves given in Fig. 1. The latter curves are for typical runs. Most of the runs were made in duplicate. Duplicate curves were reproducible to about f4' throughout their more vertical portions, when plotted as in Fig. 1.
Results and Discussion Figure 1 shows the weight loss-temperature curves obtained for the metal 8-hydroxyquinolates in vacuo. These curves are very different from those reported for the same chelates in Weight losses up to a temperature of about 200" in Fig. 1 are due in all cases to loss of water of hydration. That this is true is shown by close correspondence of the weight losses up to 200" in Fig. 1 with the weight loss data obtained by heating the compounds to constant weight in air (Experimental section). Similar initial weight losses due to water of hydration are observed in the curves obtained in air by other w0rkers.4.~ The nature of the curves above 200' in Fig. 1 permits dividing the 8-hydroxyquinolates into two classes. The first group of compounds, derived from Cu, Ni, Co, Zn, Cd, Mg, Pb, Al, Ga, In, Fe and Cr volatilize almost completely over fairly narrow temperature ranges. The remaining 8-hydroxyquinolates volatilize only partially over the temperature range studied. The volatilization of the first class of chelates involves simple sublimation of the unchanged 8hydroxyquinolates. For all of these runs apparently homogeneous but non-crystalline sublimates formed on the quartz tube above the furnace throughout the temperature ranges corresponding to weight loss in Fig. 1. The sublimates had the colors expected for the anhydrous 8-hydroxyquinolates. Only traces (0.5 mg. or less) of black residue remained in the sample containers a t the end of the runs. The design of the apparatus, and the small size of the samples, made recovery of the sublimed compounds difEcult. For the Cu, Co, Mn, Zn, Cd, Mg, Pb, Al, Ga, In, Fe and Cr compounds, however, sufficient sublimed material was recovered to permit obtaining infrared spectra. These spectra were found to be essentially identical with the spectra of authentic samples of the anhydrous 8hydroxyquinolates which had been dried in air.' With the exception of the copper compound no additional peaks were noted in the spectra of the sublimed compounds which could be ascribed to decomposition products. A small absorption peak a t 726 cm.-l was present in the spectrum of the sublimed copper chelate which was not found in the spectrum of the air-dried material. Since the remainder of the two spectra were identical, this peak may be due to a difference in crystal structure between the two samples rather than to the presence of impurities in the sublimed material. The Ca and Bi 8-hydroxyquinolates also sublimed to some extent, but for these compounds significant amounts of black residue were left in the sample container a t the conclusion of the runs. Large amounts of black residue were left by the Sr, Ba and La chelates. The latter three compounds were not observed to sublime appreciably and the weight losses observed were due to decomposition.
April, 1959
HEATSOF FORMATION OF FERROUS, FERRIC AND MANGANOUS CHLORIDES
Elemental analyses were obtained for the residues from the Ca, Sr, Ba, La and Bi compounds.s Unlike the results found in air,4v6where the ultimate residues are usually the metal oxides, the residues obtained here contained considerable amounts of carbon and nitrogen, and some hydrogen, as well as metal. An attempt was made to determine the infrared spectra of the Ba and Ca residues in KBr pellets. No recognizable absorption peaks were observed in the wave length region 3 to 15 fi, indicating that complete destruction of the starting chelates had occurred. It is striking that decomposition of the Ba and Sr chelates proceeds with only a small loss of weight. Most of the decomposition products must therefore be non-volatile. Because of the observed volatilities of the unchanged chelates it is difficult to compare the heat stabilities of the 8-hydroxyquinolates among themselves under the conditions used here. It is also difficult to compare the stabilities in vacuo with those observed in air.4J It is interesting, however, that some of the 8-hydroxyquinolates (notably the Mg and Mn compounds) show no decomposition at temperatures in excess of 400". Insofar as a comparison is possible, the 8-hydroxyquinolate chelates appear less stable in air than in v m o . This is reasonable in view of the possibilities of reaction with molecular oxygen in air. From Fig. 1 it will be noted that, for the divalent metal chelates which sublime, the temperature range over which sublimation takes place is a function of the metal present. In contrast to this behavior the trivalent metal 8-hydroxyquinolates all sublime in the same temperature range, 250 to
350". According to the Langmuir equationg 1 the rate of evaporation of a subliming substance in vacuo (8) Elemental analyses of the residue8 left by the 8-hydroxyquinolates of the indicated metals (% C, H and N, respectively): Ca, 03.1. 3.1, 7.0; Sr, 53.5, 1.6. 5.5: Ba. 43.1, 2.1, 6.1; La, 50.7, 1.7, 2.0; and Bi, -, -, 3.1. Only N waa determined for the Bi residue. (9) A. Weiasberger, ed., "Technique of Organic Chemistry." Vol. IV. Interscience Pub., Inc., New York, N. Y., 1951, p. 501.
605
at a given temperature should be a function of the vapor pressure, molecular weight and surface area of the substance. Since the molecular weights of many of the divalent metal 8-hydroxyquinolates are similar, the observed differences in temperature range for these compounds in Fig. 1 must be due primarily to differences in vapor pressure and/or surface area. Q =P/.\/2m
(1)
where Q is the evaporation rate per unit area, P is the vapor pressure of the compound, M is the molecular weight, R is the gas constant and Tis the absolute temperature. It is interesting that a relationship appears to exist between the temperature range of sublimation for the divalent metal 8-hydroxyquinolates and the electronegativitiesIO (XM)of the bonded metal ions. The order of decreasing XMfor these metals is Cu > Ni > Co >Pb > Zn, Cd > Mn> Mg > Ca. With the exceptions of Pb and Zn this is also the order of increasing temperature of sublimation. Since no relation between XM and surface area would be expected, the observed relation between XM and sublimation temperature probably is the consequence of a relationship between X M and vapor pressure for these compounds. Since the vapor pressure is determined, at least in part, by intermolecular forces in the solid compounds, these forces must decrease with increasing values of XM. The lack of dependence upon X M of the sublimation temperature range for the trivalent metal 8-hydroxyquinolates may be due to the additional shielding of the metal atom by the third 8-hydroxyquinolate residue present in these molecules. Acknowledgments.-The writers are grateful to Mrs. M. A. Pawlikowski for the preparation of some of the 8-hydroxyquinolates1 to Dr. H. Lady for the infrared determinations, and to Miss M. A. Knuth for help with some of the sublimation studies. (101 W . Cordy and W. J. 0. Thonim, J . Chem. Phua., 34, 439 (195D).
HEATS OF FORMATION OF FERROUS CHLORIDE, FERRIC CHLORIDE AND MANGANOUS CHLORIDE BY MARYF. KOEHLER AND J. P. COUGHLIN~ Contribution f r o m the Minerals Thermodynamics Experiment Station, Region I I , Bureau of Mines, United States Department of the Interior, Berkeley, Gal. Receivad September 87, 1068
Heats of formation from the elements of anhydrous ferrous chloride, ferric chloride and manganous chloride were determined by measuring appropriate heats of solution and reaction in hydrochloric acid. The results obtained are as follows: ferrous chloride, -81.86 f 0.12; ferric chloride, -95.7 ==! 0.2; and manganous chloride, -115.10 f 0.12 (kcal./mole at 298.15'K.).
Previously existing2-svalues of the heats of for- ba&d upon rather old and somewhat uncertain mation of the chlorides of iron and manganese are Ohermochemical measurements. It is difficult to ( 1 ) Formerly physical ohemiat, Minerals Thermodynamics Experiappraise the accuracy of these values. (Selected ment Station, Bureau of Mines. Region 11, Berkeley, Calif. data in the two references cited differ by as much as (2) F. D. Rossini, D. D. Wagman, W. H. Evans, S. Levine and I. 3.3 kcal./mole.) As a consequence, new deterJaffe. Natl. Bur. Standards Circ. 500, 1952. minatiQns appeared desirable. The present paper (3) 0. Kubaachewski and F. L. Evans, "Metallurgioal Thermoohemistry," John Wiley and Sone, Ino., New York, N. Y., 1956. reports new values for anhydrous ferrous chloride,
