Thermometric titrations are evidently a powerful tool for the rapid determination of heats of reaction in fused salts under virtually isothermal conditions. Flengas and Rideal (4) have determined (by laborious electrochemical measurements) the solubility product of silver chloride in an equimolar potassium nitrate-sodium nitrate melt, in a range of temperatures between 250" and 350' C. The corresponding heat of precipitation was -18.30 kcal. per mole, which is in remarkable agreement with the value obtained in this study. Extrapolation of the data by Flengas and Rideal to a temperature of 158' C. yields a molal solubility product on the order of 10-7 for silver chloride, which compares with a value of 3 X 10-8 obtained in this investigation. Thus i t
Argonne Sational Laboratory, unpublished manuscript, 1958. (6) Jordan, J., Record Chem. Progr. (Kresge-Hooker Scz. Lzb.) 19,193 (1958). (7) Jordan, J., Alleman, T. G., AXAL. CHEX29, 9 (1957). (8) Jordan, J., Dumbaugh, W. H., Jr., Zbid., 31,210 (1959). (9) Jordan, J., Meier, J., Billingham, E. J., Jr., Pendergrast, J., Zbid., 31, 1439 (1959). (10) ru'achtrieb, N. H., Zbid., 30, 1892
appears that the thermodynamic properties of silver chloride in our fused lithium nitrate-potassium nitrate eutectic melt a t 158' C. are similar to those found by Flengas and Rideal in a potassium nitrate-sodium nitrate melt a t higher temperatures. Evidently both alkali nitrate melts had similar solvent properties and approximated ideal behavior conditions.
11968). ~~.--,. (11) Randles, J. E. B., White, R., 2. Elektrochem. 59, 666 (1955).
LITERATURE CITED
RECEIVED for review October 29, 1959. Accepted January 22, 1960. Presented in part before the Division of Analytical Chemistry, Reckman Award Symposium on Chemical Instrumentation, 135th hleeting, ACS, Boston, Mass., A ril 1959. Work su ported by the U. Atomic Energy 8omrnission under Contract AT(30-1)2133 with the Pennsylvania State University.
(1) Alleman, T. G., thesis, Pennsylvania State University, 1956. (2) Charles, R. G., J. Am. Chem. SOC. 76, 5854 (1954). (3) Dumbaueh. W. H.. Jr.. thesis. ' Pennsylvagia State University, 1959: (4) Flengas, S. N., Rideal, E., Proc. Roy. Soc. (London)A233,443 (1956). (5) Gruen, D. M., McBeth, R. L.,
Differential Thermal Analysis and Thermogravimetry of Some Salts of Guanidine and Related Compounds MAE I. FAUTH Indian Head, Md.
Research and Development Department, U.
S. Naval Propellant Plant,
b Because picrates and styphnates are frequently used for the analysis and characterization of organic bases, their thermal behavior under rapid heating rates was studied. The picrates and styphnates of hydrazine, guanidine, aminoguanidine, guanylurea, N-methylguanidine, and N-ethylguanidine have been prepared and their thermogravimetric and differential thermal analysis curves determined. The thermal behavior of guanidine sulfate, Nethylguanidine sulfate, guanidine nitrate, and nitroguanidine has also been studied. The impact sensitivity of the six styphnates and some of the picrates has been determined. The temperature range covered was from room temperature to the point of decomposition of the compound under investigation. The average heating rate was 8' C. per minute.
analysis curves determined : hydrazine, guanidine, aminoguanidine, guanylurea, 1V-methylguanidine, and N-ethylguanidine. , The thermal behavior of guanidine sulfate, N-ethylguanidine sulfate, guanidine nitrate, and nitroguanidine was also studied. The impact sensitivity of the six styphnates and some of the picrates was determined. The preparation and properties of salts of hydrazine (S), guanidine ( 2 ) , and guanylurea (1) have been described. Lieber and Smith (6)have summarized the reactions of aminoguanidine. Methods are given for preparing alkyl derivatives of guanidine (7). The picrate of N-ethylguanidine has been characterized (8, 10). The sulfate, nitrate, and picrate of guanylurea were prepared (9) by the following reaction:
T
picrates, styphnates, and similar salts have long been used for the analysis and characterization of organic bases. Because these materials exhibit explosive properties, the determination of their thermal behavior under rapid heating rates was desirable. In the present investigation, the picrates and styphnates of the following bases were prepared and their differential thermal and thermogravimetric HE
+ H10 + HX
HzNC/" \HCN NH
HX 'NHCONH~
The picrate, styphnate, and picrolonate (4) were found unsuitable for the determination of guanylurea unless a correction was applied for solubility.
PREPARATION AND ANALYSIS OF COMPOUNDS
Hydrazine. Hydrazine monohydrochloride (Olin Mathieson Co.) and picric and styphnic acids (Eastman White Label) were used. One hundredth mole was dissolved in the minimum amount of water and added t o an equivalent amount of the organic acid dissolved in the minimum amount of methanol. The reactions were run a t room temperature. Precipitation of the bright yellow picrate and styphnate began almost mmediately. Elemental analyses were obtained for all compounds used. Guanidine Salts. Eastman White Label guanidine sulfate wa8 used without further purification. By reaction of 0.01 mole of an aqueous solution of guanidine sulfate with a warm methanol solution of 0.01 mole of organic acid, the picrate and sty hnate were prepared. Juanidine nitrate was obtained from crude plant material by recrystallizing three times from water. The melting point of the final product was 213' C. Guanidine Derivatives. Eastman White Label aminoguanidine sulfate was used for preparing the picrate and styphnate. Methods of preparation were the same as for the guanidine salts. Nitroguanidine, Eastman White Label, was used without further purification. The guanylurea salts were made from nitrate supplied by the American Cyanamid Co. VOL. 32, C'O. 6, MAY 1960
655
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*t LOSB, C. 110
270 220
130
205 105 120
100 130 100
150 195 220 160
150 100
Behavior at Highest Temp. Reached Lost 12% up to 260' C. Lost 2% up to 295' C. Decompd. at 240' C. Detonated at 182' C. Detonated at 210' C. Detonated at 105' C. Detonated at 125' C. Detonated at 105' C. Detonated at 180' C. Decompd. at 125' C. Decompd. at 190' C. Decompd. at 210' C. Decompd. at 222' C. Decompd. at 175' C. Lost 72% up to 280" C. Lost 95% up to 250' C.
RESULTS
Differential thermal analysis curves are given in Figure 1 for 16 compounds. Because this investigation was undertaken primarily to evaluate the safety factors involved in handling these compounds, the data are intended to be qualitative in character. For compounds of an explosive nature such as the picrates and styphnates, it is known that stability against thermal decomposition is affected by rate of heating, mass of material, and state of aggregation of the sample. Data taken from the thermogravimetric curves are collected in Table 11. The weight losses are given as per cent of the original sample. Because the compounds were air-dried a t room temperature, some compounds lost moisture a t relatively low temperatures. The experimental setup a t the time this work was done required that different ovens be used for thermogravimetric and differential thermal analysis. Be-
cause of this, an exact comparison of the two sets of data is not possible. A comparison of the literature values for the melting points of the picrates with the maximum decomposition rate of these compounds as taken from the curves, gave the following values.
Temp.
of iMax. Melting
Compound Hydrazine picrate A;-Methylguanidine picrate N-Ethylguanidine picrate Guanidine picrate Guanylurea icrate Aminoguanixine picrate
Decompn. Point Fte, (I$.), C. C. 115 20 1 180
20 1
195
180 333 265
222
190 160
available
Sot
The decomposition temperatures obtained in this laboratory are, except for the N-ethylguanidine salt, considerably below the reported literature values. This is to be expected, because a t rapid heating rates thermodynamic equilibrium is probably not attained and the existence of large thermal gradients in the sample is probably conducive to the formation of “hot spots” which
lead to rapid decomposition, or in the case of the styphnates, to detonation. For the six picrates examined, the order of increasing thermal stability under rapid heating rates is: hydrazine, aminoguanidine, N-ethylguanidine, guanylurea, A’-ethylguanidine, and guanidine. For the styphnates the rate and violence of the decomposition were such that these compounds could be considered to undergo detonation. The relative stability in terms of increasing temperature of detonation is: hydrazine, N-methylguanidine, N-ethylguanidine, guanidine, guanylurea, and aminoguanidine. It was considered desirable from the standpoint of safe handling of the styphnates to determine the sensitivity to impact as indicated by the 5-kg. drop test. The results obtained are given in Table I. When listed with the most sensitive (least stable to impact) first and the least sensitive a t the end, the order is: hydrazine, guanylurea, N methylguanidine, N-ethylguanidine, guanidine, and aminoguanidine.
by melting points and other properties obtained by slow heating. The styphnates of these organic bases are easily prepared, beautifully crystalline compounds, which can be obtained in pure form and used for the identification of these bases, but these conipounds should be considered rather sensitive to detonation both by impact and by rapid heating. LITERATURE CITED
(1) American Cyanamid Co., “Guanyl-
CONCLUSIONS
urea,” New Product Bull. 35 (1952). (2) American Cyanamid Co., Nitrogen Chemicals Digest 4 (1950). (3) Audrieth, L. F., ,?gg, B. A., “Chemistry of Hydrazine, pp. 167-80, Wiley, New York, 1951. (4) Deshusses, L., Mitt. Lebensm. u. H y g . &f04235 (1929). allant, W. K. A “Ap aratus for Differential Thermd a n 8 Thermogravimetric Analysis,’’ Diviaion of Anal tical Chemistry, 133rd Meeting, ZCS, San Franciso, Calif., April 1958. (6) Lieber, E., Smith, G. B. L., Chem. Revs. 25, 213 (1939). (7) Migrdichian, V., “Or anic Synthesis,” Vol. I, pp. 408-9, Rein%old,New York, 1957. (8) Schenk, M., Kirchhof, H., 2. physiol. Chem. 154, 292 (1926). (9) So11, G., Stutzer, A., Ber. 42, 4532 (1909). (10) Traube, W., Gorniak, K., 2. angew. Chem. 42, 379 (1929).
At rapid heating rates considerably lower decomposition temperatures may be expected than would be indicated
RECEIVED for review December 9, 1958. Accepted December 24, 1959. Division of Analytical Chemistry, 134th Meeting, ACS, Chicago, Ill., September 1958.
Differential Thermal Analysis of Hydroxides in Reducing Atmosphere WILLIAM LODDING and LAURENCE HAMMELL Bureau o f Mineral Research, Rutgers, The State University, New Brunswick, N. J.
,The reactions and phase changes occurring during thermal analysis of iron hydroxides and oxides in reducing and oxidizing atmospheres were identified. Exotherms due to transformations can be used to obtain rapid information on the heats involved and the rates at which these changes proceed under controlled conditions of atmosphere and pressure to 400 p.s.i.g. The amount of gibbsite can be determined from the dehydration peak regardless of the iron hydroxides present, by heating to 450” C. in a hydrogen atmosphere and then in air to 1000” C. The exotherm due to conversion of 7- to cr-FenOa is proportional to the iron hydroxides present.
D
thermal analysis (DTA) is a very sensitive tool for the detection and measurement of gibbsite, Al(0H)a. The analysis is often hampered by the presence of hydrated iron oxides. Goethite, aFeO.OH, and lepidocrocite, y-FeO.OH, dehydrate a t approximately the same temperature as gibbsite (1, 2, 4, 6, 7). The closeness of the resulting endothermic peaks does not allow separate measurement of the areas under the peaks. The reaction cannot be used, therefore, to measure the amount of gibbsite present, unless the percentage of iron hydroxides is known. A new method for the determination of iron hydroxides was based on differential IFFERENTIAL
thermal analysis in a strongly reducing atmosphere. EXPERIMENTAL
Apparatus. A new high temperature-pressure vacuum furnace has been described (6). The pressure vessel (Figure 1) consists of a recrystallized alumina tube 11/4 inches in inside diameter and 12 inches long. (The apparatus will be manufactured by Testing Equipment Sales Corp.) Pressures to 500 p.s.i.g. a t 1200” C. have been used. The tube is gas-tight and relatively easy to evacuate because of its small volume and the absence of voluminous insulating material inside the vessel. The heating element is outside of the tube and, therefore, not in contact with the furnace atmosphere. VOL. 32, NO. 6, MAY 1960
0
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