Thermochemical Titrations in Fused Salts JOSEPH JORDAN, JbRG MEIER, EDWARD J. BILLINGHAM, Jr., and JAMES PENDERGRAST Department o f Chemistry, The Pennsylvania State University, University Park, Pa.
b A comprehensive report is presented on continuous titrations performed in fused salt solvents. In the range of 1 0-4 and concentrations between 8 2 molal, chloride was determined in a molten alkali nitrate eutectic by a thermometric precipitation titration method using standard silver nitrate as titrant. The end point corresponded to the stoichiometry: Ag+ CI- = AgCl (s). The titrations were performed automatically by remote control in an adiabatic titration cell operated a t 150" to 200" C., in which random temperature fluctuations have been minimized to k0.0005" C. The change in temperature during the titration was monitored with the aid of a thermistor bridge, the unbalance potential of which was fed to a high-impedance recorder. The general significance of the results is discussed critically in terms of applicability to convenient, precise, and accurate quantitative analysis in fused salts. The pertinent heats of reaction can b e determined directly from extrapolated ordinate projections of the thermometric titration curves.
x
x
I
C
+
I
preliminary communication from these laboratories (Q), the first known instance was recently reported of a continuous titration performed in fused salts: Chloride was titrated with standard silver nitrate in a molten lithium nitrate-potassium nitrate eutectic solvent. The end point was determined from an enthalpy-dependent "thermometric titration curve" recorded automatically under adiabatic conditions. This article contains a detailed report and a critical discussion of results in terms of precision, accuracy, and general significance. Interest in the development of a thermometric titration method applicable to fused salts was engendered by the scarcity of known techniques adaptable to determinations in situ in fused salts (IO). From experience with thermochemical titrations in aqueous solutions ( I , 3, 7, 8) it was anticipated that enthalpy-dependent automatic titrations in melts may provide means for rapid, convenient, and accurate analytical determinations. Furthermore, heats of reaction can be determined from thermometric titration N A
Figure 1 . mentation
Block diagram of instru-
A.
Automatic titrator Adiabatic titration calorimeter Temperature monitoring system C,. Thermistor CP. Wheatstone bridge C3. Recorder 6. C.
-
curves under virtually isothermal conditions. Enthalpy information on reactions in fused salt media is conspicuous by its absence. The method described in.this paper is applicable to titrimetric determinations involving precipitation, oxidation-reduction, and complexation processes in fused salt solvents. A systematic study is bound to yield significant information regarding the heats of these reactions. Because the corresponding free energy data are available to a somewhat greater extent (and/or can be more readily determined by use of electrochemical methods applicable to fused salts), the corresponding entropies can be calculated. Clues on the nature of associative phenomena in fused salts-e.g., solvation, ion-pair formation, dimerization, etc.-are inherent in the interpretation of entropies as a measure of order-disorder transitions. METHODOLOGY
Principles of Thermometric Titrations. The theory of thermochemical titrations in aqueous solutions has been summarized (6). Fundamentally similar principles are applicable to fused salt solvents as well. Thermometric titrations depend upon the judicious interpretation of titration curves which reflect the variation of temperature (in an adiabatic system) as a function of added titrants. For the effective en-
thalpy changes to approximate AH" the concentration of the species titrated must be in the millimolal or centimolal concentration range, yielding temperature changes on the order of 0.1' to 1" C. during the titration. Consequently, if heats of reaction are to be determined with a precision and accuracy to l%, it is imperative to use an adiabatic titration cell where random temperature fluctuations should not exceed lo-* " C. during the titration. To meet these requirements without resorting to unduly cumbersome calorimetric precautions, the titration must be completed in as short a time as possible. This imposes the following related restrictions which any satisfactory experimental design in fused salts a t elevated temperatures must meet: Rates of stirring and rates of reaction must be rapid compared to the addition of titrant. The response of the temperaturerecording device must be instantaneous. Materials. Reagent grade anhydrous chemicals were used throughout. The solvent consisted of a eutectic lithium nitrate-potassium nitrate melt (43 mole yo lithium nitrate, melting point under 1-atm. pressure 132" C.) (11) which was prepared by direct fusion of the pure nitrates. The eutectic melt was filtered through a heated fritted-glass funnel of medium porosity. The melt was dried and stored in vacuo a t a temperature exceeding its melting point. Apparatus. A schematic block diagram of the titration apparatus is shown in Figure 1. It included three main components: automatic titrator, adiabatic titration calorimeter, and temperature-monitoring system. Titrator. As a titrator, a modified Aminco-Koegel Menisco-matic buret (American Instrument Co., Inc., Silver Spring, Md.) was used (Figure 2). The Menisco-matic buret, as commercially supplied, can be operated from a standard 110-volt alternating current power supply. It is driven by a direct current servomotor which is connected t o the power source via a transformer and rectifier. Servomotor, transformer, and rectifier are fncased in a compact mechanism housing. By interposing between the outside alternating current power line and the buret-drivebssembly a 115-volt constant voltage transformer, a conVOL. 32, NO. 6, MAY 1960
651
stant delivery speed within 0.5% was maintained. The servomotor operated a worm gear yielding vertical motion. This gear was rigidly coupled (via a stainless steel push rod) to the plunger of a 1-ml. borosilicate glass hypodermic syrin e. When the motor was operated, t e syringe plunger could be raised or lowered, while the body of the syringe was held immobile by a brass collar nut rigidly attached to the mechanism housing which was clamped above the top of the oven. The syringe-buret delivered 2 to 4 pl. of titrant per second with a precision of the order of 0.02 pl. per second. The hypodermic syringe was equipped with a ca illary glass tip which was immersed in t i e melt titrated. The syringe was lubricated with DowCorning silicone stopcock grease. During the titration the entire syringe was enclosed within the adiabatic titration calorimeter, in a supernatant argon atmosphere above the titrated melt. Titration Calorimeter. As s n adiabatic titration calorimeter a Dewar flask inserted in an electric oven was used. The oven was of the UltraTemp type (Blue M Electric Co., Model C H H 12, Ace Glass, Inc., Vineland, N. J.). It has a cubical working cavity 25 liters in volume, and is protected by a ceramic and glass wool insulation 17 cm. in thickness. For circulating air and/or an inert atmosphere (argon), the oven was equipped with a motor-driven propellertype fan positioned at the bottom of the cavity and pointed vertically upward. Long range temperature constancy on the order of 0.05" C. was maintained in the oven cavity in a range of temperatures between 100" and 300" C. over test periods of 24 hours. To achieve satisfactory temperature control the helical coiled wire heating elements supplied with the oven were modified (connected in series, yielding an effective resistance of 16 ohms) and operated continuously with the aid of a constant voltage alternating current source and variable transformers. The applied e.m.f. was 45 to 75 volts, depending on the specific temperature desired. To provide fine temperature control, an '80-watt intermittent heater was superimposed on the continuous heater. Operation of the fine control heater was regulated by a thermistor thermoregulator (Thermistemp temperature controller, Model 71, Yellow Springs Instrument Co., Inc , Yellow Springs, Ohio), coupled with a Veco bead thermistor, Model 45A1 (Victory Engineering Corp., Union, N. J.). The titrations were carried out in 250-ml. Dewar flasks positioned in the oven on a custom-machined metal turntable. A cross section of the experimental setup is shown in Figure 3. The turntable was equipped with four cylindrical holders for Dewar flasks located a t 90" radial intervals, and was operated by remote control from above the oven top with the aid of an axial stainless steel handle, a crossbar which could be alternatively fitted into two transversal holes, a horizontal crossed-slit guide plate, and a
a
652
ANALYTICAL CHEMISTRY
Figure 2. Automatic titrator A. B. C. D. E.
F.
G.
H. 1. J. K.
Motor Mechanism housing Worm gear Brass collar nuts Stainless steel tubing Stainless steel push rod Syringe plunger 1 -mi. syringe Capillary tip Constant voltage transformer Power line, 1 1 0-volt ax.
vertical guide slit. The turntable could be maintained within the oven in two predetermined horizontal planes. In each plane it could be rotated around the axis in four 90" "steps." By rotating the turntable (while in the lower horizontal plane) it was possible to position the Dewars in succession opposite an asbestos stopper held by a clamp attached to the oven ceiling. The turntable could be raised to have the stopper fit into the desired Dewar. The stop er was equi ped with appropriate through wLch the following devices were immersed: A temperature-detecting thermistor. An efficient propeller-type glass stirrer, operated via a shaft from above the oven by a synchronized motor at 600 r.p.m. A microcalorimetric calibration heater used to determine the effective heat capacity of the titrated systems. An inert gas inlet. The syringe end of the titrator. Temperature-Monitoring System. The temperature-monitoring system consisted of a thermistor, C1, and thermistor bridge, Cz,coupled to a recording potentiometer, Cs. The temperature detector vvas a Model 51 A 1 Veco bead-type thermistor (enclosed in a glass envelope), which had the following parameters:
bois
U
Figure 3. Cross section of experimental setup for enthalpy titrations in fused salt melts A. M. R. TR. V.
W.
Argon Inlet Motors far stirrer, fan, and automatic titrator Recorder Thermistor thermoregulator Heater circult for simulated titration Thermistor bridge
resistance a t 25" C., 100,000 ohms; dissipation constant, 1.0 mw./" C ; time constant in molten salt media, less than 1second; effective resistance a t 170" C., 1600 ohms. The thermistor was wired as one arm of a direct current Wheatstone bridge. The unbalance potential of the bridge yielded a linear response with change in temperature, over spans up to 2" C. The bridge output was fed to a pen-recordin Bristol direct current millivoltmeter wifich had the following s ecifications: full scale (28-cm.) deZction, l mv.; en speed, 0.4 second for full scale dezction; input impedance, 10,000 ohms; sensitivity and accuracy, 0.1%. The e.m.f. to the Wheatstone bridge was supplied by a 1.bvolt dry cell source, via a precision 10-turn B e c h a n Helipot potentiometer (with a linearity of 0.1%) which served as a sensitivity adjustor. At maximum sensitivity setting, the thermistor bridge yielded a temperature response of 0.15" C. per mv., which is equivalent to the sensitivity of a 1000junction Pt/Pt-lO'% Rh thermocouple. Temperature fluctuations on the order of O.OO0lo C. could thus be detected on the recorder chart ordinate. The recorder chart was driven by a synchronous motor yielding chart speeds between 5 cm. per minute and 2 em per
Table I.
Thermometric Titrations in Fused Salts at 158' C."
Melt Titrated Weight of solvent,b g.
109.0 101 .o 100.5 94.0 100.0 a
b e
Amount of KC1 Mg. Mmoles '7.0
15.9 39.0 82.0 148.0
0.0939 0.2133 0.5231 1.100 1.985
Chloride molality 8.61 X lo-' 2.11 X 5.20 X lo-* 1.17 X 1.99 X
Titrant Melt
VOl. titrant,
7 molaljty g./cc. ml. 1.841 1.841 1.145 1.841 1.841
2.25 2.25 2.15 2.25 2.25
0.031 0.065 0,255 0.332 0.627
End Point Stoichiometry Mg. AgNOt./ mg. C1-
Moles A +/ mole
4.99 4.61 4.81 4.56 4.78 4.75 f 0.08
1.04 0.96 1.00 0.95 1.00 0.99 & 0 . 0 2
CY-
Mean valuesd All titrations carried out at 158' f 2' C. Temperature change in any given titration was between 0.03' and 1' C. Lithium nitrate-potassium nitrate eutectic. Extrapolated from titration curve ordinates, as exemplified in Figures 5 and 6. Precision indicated in terms of standard deviation of mean.
0. h i .
I
output of 14 cal. per minute. Subsequently the titrant was delivered a t a constant rate, and since the recorder chart was driven by a synchronous motor, an automatic thermometric titration curve was obtained on the recorder chart, because the buret drive and the chart speed were quasi-synchronously coupled. The chart abscissa was calibrated in milliliters of titrant per millimeter of chart. The chart ordinate actually corresponded to temperature change. However, under the prevailing adiabatic conditions i t was more convenient to calibrate directly in terms of calories per millimeter. RESULTS
Figure 4. Simulated titration in lithium nitrate-potassium nitrate melt A. 8. M-N.
Heater switched on Heater switched off Corrected temperature increment
hour. The chart speeds were adjusted with the aid of interohan eable gears. Procedure. One fundred-gram samples of fused salt melts were brought to temperature equilibrium within the Dewars in the closed oven. Random fluctuationa in the melta were minimized to 10.0005°. The titrant melt waa moved t o a suitable position and aspirated into the syringe. The turntable was lowered and the buret tip was carefully wiped with Kimwipe tissue (Type 900-5, Kimberly Clark). The fused salt solution to be titrated was now moved under the buret, the turntable was raised, and sufficient time was allowed for temperature equilibration. T o determine the effective heat capacity of the system (titrated melt plus the titration cell), a simulated titration was performed by turning the electric calibration heater on for 15 t o 60 seconds. The heater was made of Manganin wire protected by a borosilicate glass envelope. It had a resistance of 4 ohms, was powered by a 2-volt storage battery, and had an
Attainment of Thermal Equilibrium. Temperature-time curves recorded in melts in the adiabatic titration cell indicated that random temperature fluctuations did not exceed f O . O 0 l o C. over time periods on the order of 1 hour. During 5-minute intervals (required to complete titrations) the fluctuations were 0.0005° C. or less. Determination of Effective Heat Capacities. A simulated thermometric titration curve is illustrated in Figure 4. It reflects the time-temperature response of a melt sample in the titration calorimeter t o which a controlled amount of caloric energy has been supplied electrically. The ordinate projection, M - N , corresponding t o the concomitant corrected net rise in temperature, was used to calibrate the recorder chart ordinate calorimetrically. Calibrations were carried out before and after each titration, and averaged. (This procedure warranted the choice of the ordinate projection M-N a t the initial point of the heating curve, rather than a t the mid-point as in conventional calorimetric work.) The calibration factor, q, expressed in calories per millimeter of chart ordinate, represents a measure of the effective heat capacity of the system titrated. From plots of the type shown in Figure 4,q was calculated from the equation
Pptn. Enthal y of Ag&o
~cal./dole -18.2 -18.9 -19.5 -18.2 -19.8 -18.9 f 0 . 3
where E represents the total energy supplied (expressed in calories) and M-N the corresponding ordinate (expressed in millimeters) in the simulated titration curve, The value of Q is a function of the nature and amount of melt and of the prevailing instrumental characteristics (thermistor bridge sensitivity setting, etc.).
Precipitation Titrations of Chloride with Sfiver Nitrate. The precipitation titration of chloride ion with silver ion in an alkali nitrate melt was selected for a pilot study, because the reaction Ag+ + C1AgCl(s) (2) was anticipated to exhibit in fused nitrates a behavior generally similar to the one it possesses in aqueous solution (4). A lithium nitrate-potassium nitrate eutectic was used as a convenient solvent in this study, primarily on account of its low melting point and the ease with which it can be prepared (6). It was ascertained by preliminary qualitative experiments that both potassium chloride and silver nitrate were appreciably soluble in the eutectic melt, At 150' C. the solubility of potassium chloride was of the order of 0.15 molal; silver nitrate solutions as concentrated as 1.5 molal could readily be prepared. Upon addition of a drop of silver nitrate (in the eutectic solvent) to a 0.01 molal fused salt solution of potassium chloride, a precipitate was formed instantaneously. The precipitate was considerably more crystalline in appearance than the typical silver chloride curds normally obtained from aqueous solutions. At 158' C. a series of five titrations of potassium chloride (in a range of concentrations between 8 X 10-4 and 2 X IO-* molal) was carried out with silver nitrate titrant. The titrant concentration was on the order of 1 molal-i.e., 50 to 1500 times more concentrated than the chloride titrated. As a result, the VOL. 32, NO. 6, MAY 1960
653
volume of the titrant used in any one titration varied between 0.03 and 1 ml., as compared to a n initial volume of about 50 ml. of melt titrated. The weight (and molal) concentrations of chloride or silver in the melts were computed directly from the known weights of the components from which they lvere made up. However, the abscissa on the recorded titration curves was calibrated to yield volume of titrant. To compute the corresponding weight ratios (and mole ratios), the specific gravities of the titrant melts were determined and used as conversion factors. Typical thermometric titration curves of chloride ion in the fused alkali nitrate eutectic solvent with silver nitrate (in the same melt) are illustrated in Figures 5 and 6. The distance B"-C' was taken as the measure of the volume of titrant corresponding to the end point. The distance B-B'on the ordinate was used to estimate the temperature change engendered by the chemical process occurring during the titration. Extrapolation to B' along the excess reagent lines (C-D) is believed to correct adequately for extraneous effects, such as temperature differences between titrant and titrated melts, heats of dilution, etc. The "effective heat capacity calibration factor]" q, was used to calculate the pertinent enthalpy change with the aid of the equation: -AHn
H
-AH
= B-B' X q X
1
-N m
(3)
where B-B' is the extrapolated ordinate projection expressed in millimeters, and N, denotes the number of moles of product which would be formed at the stoichiometric end points (C in Figures 5 and 6) if the reaction were 100% complete. Quantitative results of a series of five titrations are summarized in Table I. DISCUSSION
The data in column 9 of Table I indicate that the composition of the crystalline white precipitate in the fused alkali nitrate solvent (formed when chloride was titrated with silver nitrate) corresponded to silver chloride. The shape of the titration curve obtained in 8.6 X molal solution (Figure 5 ) shows that precipitation a t the equivalence point was about 20% incomplete, attaining a 99% completeness in the presence of 100% excess silver nitrate. In contradistinction, it is evident from Figure 6 that precipitation in 2 X 10+ molal solution mas 98.5y0 complete a t the equivalence point. From the curvature of the titration curves in the vicinity of the equivalence points the solubility product of silver chloride (under the prcvailing experimental conditions) can rcadily bc calculated. 654
ANALYTICAL CHEMiSTRY
I(
1
0 IOml.3
/
I
0.02'C.
f
1.00 c a II
1
I
Figure 5. Precipitation titration of 109 grams of 0.86 X 1 0-3 molal potassium chloride with 1.40 molal silver nitrate in fused lithium nitrate-potassium nitrate at 158' C. A-E. E. E-E'. B'.C'. C. C-D.
Temperature-time blank Start of titrotion Corrected temperature change corresponding to reaction enthalpy. Stoichiometric meosure of titrant required End point Excess reagent line
By appropriate comparison of extrapolated and measured ordinates a value of K:;*" = mA,+ X mcl- = 3 X 10-8 (moles/ 1000 g. solvent)* (4)
was obtained. I n Equation 4, K;i8' denotes the molal solubility product of silver chloride at 158' C. in the lithium nitrate-potassium nitrate eutectic melt, and mAst and mcl- are the molal concentrations of silver and chloride] respectively. The solubility product defined by Equation 4 may not have an exact thermodynamic significance] because it implies unit activity coefficients (which may be a n unwarranted approximation). Analytical Significance of Study. The mean silver-chloride mole ratio a t the experimental end points was 0.99, which compares with a theoretical ratio of 1.00. Consequently, the precipitation titration of chloride with silver (or vice versa) is expected t o yield a n accuracy on the order of 1%. The corresponding precision was to 2y0,in terms of standard deviation of the mean. General applicability is anticipated to the rapid and convenient determination of chloride in fused nitrate melts. Thermodynamic Significance. I n the range of concentrations studied
I
Figure 6. Precipitation titration of 94 grams of 1.17 lo-* molal potassium chloride with 1.40 molal silver nitrate in fused lithium nitrate-potassium nitrate a t 1 5 8 " C.
x
A-E. 6. E-8'. EX'. C. C-D.
Temperature-time blank Start of titration Corrected temperature change corresponding to reaction enthalpy Stoichiometric measure of titrant required End point Excess reagent line
the heat of precipitation of silver chloride was constant (Table I, column lo), corresponding to a n average of AH~gc1.1880= -(18.9 A 0.3) kcal. per mole ( 5 ) The value in Equation 5 represents the heat of precipitation of silver chloride from hypothetical to 10+ molal solutions in the fused lithium nitratepotassium nitrate eutectic solvent. Dilution heats of the concentrated silver nitrate titrants are corrected for by backextrapolation along the excess reagent lines (D-C-B' in Figure 5 and 6). The slightly descending slopes of the excess reagent lines are taken to indicate that: The heat of dilution of silver nitrate was relatively small, yielding no appreciable exothermic contribution ( 4 ) ; and the titrant may have been slightly colder than the melt titrated [this extraneous effect is adequately corrected for by the extrapolation used (6, 8 ) ] . Compared to the value in Equation 5, corrections for infinite dilution are negligible (2, 4 ) and the heat of precipitation listed in Table I can be set equal to the ideal heat of precipitation of silver nitrate a t 158' C.-.i.e., ~H:;;m4Jib = A H ~ , C ~ ,=~ S-18.9 ~O
kcal. per mole ( 5 )
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 Plant, Indian Head, Md.
Research and Development Department, U.
S. Naval Propellant
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
