- Email: [email protected]
Solid phases of phosphoric acid and phosphoric acid hemihydrate
Notes
1429
extractant molecules, cl-3) Since HgBr2 is known to form complexes of the type MHgBra and M~HgBr~ with alkali metal bromides, a similar extraction mechanism could be expected for the system of alkali metal bromide-HgBr2-LiNO3. Alkali metal bromides dissolved in fused LiNOs can be assumed to be completely dissociated. no complex formation in this system appears likely. On the other hand, it has been shown by cryoscopic measurements in conjunction with conductivity and viscosity measurements, t~,~ that the predominant species in dilute solutions of alkali metal bromides in fused I-IgBr~ are most likely ions of the type M ÷ and [MHgBrd-; alkali metal ions are part of the anionic complex. The distribution of the alkali metal bromides between the immiscible fused phases of HgBr2 and LiNOs seems therefore to be predominantly governed by the tendency of alkali metal bromides to form anionic complexes of the type mentioned with HgBrz. Unfortunately there are no systemic studies reported in the literature on the stability of these anionic complexes. However, in order to account for the observed increase of the distribution coefficients from Na to Cs (Table 1) it is reasonable to assume that under our experimental conditions, the stability of these complex ions increases with increasing atomic weight of the alkali metal. Mainly because of the complex formation of the alkali metal bromides with HgBr2, a variation of the distribution coefficient, KD, with the alkali metal bromide concentration was expected. Investigation of the dependence of K~ on the KBr concentration showed that this was the case (Fig. 1). Because of the similarity of the properties of solutions of the alkali metal bromides in fused HgBr~, ~4.5~ solutions of other alkali metal bromides can be expected to exhibit the same tendencies. The relatively high mercury concentration of approximately 0'6 % in the LiNO8 phase in contrast to the low lithium concentration of <50 p.p.m, in the HgBr~ phase does not indicate true solubility but arises from the experimental technique. During the quenching of the reaction tube, HgBrz from the still liquid center of the HgBr~ phase vaporizes into the already solidified LiNO3 phase, which solidified instantaneously on quenching in the shape of a hollow cylinder. K. F. GUENTHER
l i T Research Institute Chicago, Illinois ~3~D. F. C. MORRIS, E. L. SHORTand D. N. SLATER,J. Inorg. Nucl. Chem. 26, 627 (1964). c4~G. J. JANZ and J. GOOOKIN,J. Phys. Chem. 64, 808 (1960). ~5~G. JANDERand K. BRODERSEN,Z. anorg. Chem. 264, 57 (1951).
J. Inorg. Nucl. Chem., 1965, Vol. 27, pp. 1429 to 1430. Pergamon Press Ltd. Printed in Northern Ireland
Solid phases of phosphoric acid and phosphoric acid hemihydrate (Recewed 15 January 1965) SINCEit was reported recently ~1~that "rather ill-defined spectra were obtained from mulls of crystalline anhydrous phosphoric acid and its hemihydrate with Nujor'; and since an example of such a spectrum is to be found in literature already, t2~we want to state that well-resolved informative spectra may be recorded (compare Fig. 1.). But for this purpose crystallization of the liquids in a low temperature cell is necessary. Even if every precaution against atmospheric humidity is taken melting is caused by mulling crystals of phosphoric acid with Nujol. tl~ A. C. CHAPMANand L. E. T H I R L W E L L , Spectrochim. Acta 20, 937 (1964). t2) A. MUTSCHrNand K. MAENNCHEN,Z. analyt. Chem. 156, 241 (1957).
1430
Notes
We made use of the cell described (3~ and of KBr windows protected by polyethylene.(~ (At absorptions of this material the traces in the figure are interrupted.) Besides securing temperatures in the cell by a thermocouple and recorder we worked on samples of several ml volume in the manner of thermal analysis as well.
H3PO4 '~" H20 I
H3P04,/H20
glass
HsPO4 IT H3P04 I H3P04 TIT
H3P04 glass
1400 I
t200 tO00 NaCI prism
800 700 [ cr11-1
600 ,500 KBr prism
Fro. 1.--Infra-red spectra of six solid phases of HsPO4 and HaPO4"½H~O in the range of 400 to 1400 cm -1. When we investigated the infra-red spectra of HaPO4 and HsPO4'½HzO in this way as solids we noticed four and three different modifications, respectively. Glasses are obtained, if quenching by liquid nitrogen or solid carbon dioxide is applied to the liquid. Warming H3PO4-glass induces crystallization at --54°C to a phase which we call HaPO4-III. This is converted irreversibly at - - 8 . . . --6°C to H3PO4-I which is stable at room temperature. Another phase HaPO4-II is obtained by crystallization from the melt between + 8 ° and +15°C, if the latter was not heated much above the melting point. This HaPO,-II does not change when cooled to --190°C, but when warmed up then, converts to H3PO4-I at - - 4 . . . 0°C. If H3PO4"½H~O-glass is prepared at first, it crystallizes at - - 5 4 . . . --49°C to H3PO4"½H20-II. An irreversible transformation to HsPO4"½H20-I is marked only by a positive thermal effect at - - 3 2 . . . --30°C without noticeable changes in the spectrum. The discussion of the spectra will be given elsewhere, but we feel obliged to call attention to the different modifications especially for crystallized phosphoric acid at room temperature.
Institut fur Spezielle analytisehe Chemic Technische Universitiit Dresden, Germany ~s~G. I'-IErNTZand K. STOPPERKA,Z. Chem. 2, 282 (1962). c~ E. STEGERand K. HERZOO,Z. Chem. 3, 142 (1963).
K. HERZOG E. SITEGER
1429
extractant molecules, cl-3) Since HgBr2 is known to form complexes of the type MHgBra and M~HgBr~ with alkali metal bromides, a similar extraction mechanism could be expected for the system of alkali metal bromide-HgBr2-LiNO3. Alkali metal bromides dissolved in fused LiNOs can be assumed to be completely dissociated. no complex formation in this system appears likely. On the other hand, it has been shown by cryoscopic measurements in conjunction with conductivity and viscosity measurements, t~,~ that the predominant species in dilute solutions of alkali metal bromides in fused I-IgBr~ are most likely ions of the type M ÷ and [MHgBrd-; alkali metal ions are part of the anionic complex. The distribution of the alkali metal bromides between the immiscible fused phases of HgBr2 and LiNOs seems therefore to be predominantly governed by the tendency of alkali metal bromides to form anionic complexes of the type mentioned with HgBrz. Unfortunately there are no systemic studies reported in the literature on the stability of these anionic complexes. However, in order to account for the observed increase of the distribution coefficients from Na to Cs (Table 1) it is reasonable to assume that under our experimental conditions, the stability of these complex ions increases with increasing atomic weight of the alkali metal. Mainly because of the complex formation of the alkali metal bromides with HgBr2, a variation of the distribution coefficient, KD, with the alkali metal bromide concentration was expected. Investigation of the dependence of K~ on the KBr concentration showed that this was the case (Fig. 1). Because of the similarity of the properties of solutions of the alkali metal bromides in fused HgBr~, ~4.5~ solutions of other alkali metal bromides can be expected to exhibit the same tendencies. The relatively high mercury concentration of approximately 0'6 % in the LiNO8 phase in contrast to the low lithium concentration of <50 p.p.m, in the HgBr~ phase does not indicate true solubility but arises from the experimental technique. During the quenching of the reaction tube, HgBrz from the still liquid center of the HgBr~ phase vaporizes into the already solidified LiNO3 phase, which solidified instantaneously on quenching in the shape of a hollow cylinder. K. F. GUENTHER
l i T Research Institute Chicago, Illinois ~3~D. F. C. MORRIS, E. L. SHORTand D. N. SLATER,J. Inorg. Nucl. Chem. 26, 627 (1964). c4~G. J. JANZ and J. GOOOKIN,J. Phys. Chem. 64, 808 (1960). ~5~G. JANDERand K. BRODERSEN,Z. anorg. Chem. 264, 57 (1951).
J. Inorg. Nucl. Chem., 1965, Vol. 27, pp. 1429 to 1430. Pergamon Press Ltd. Printed in Northern Ireland
Solid phases of phosphoric acid and phosphoric acid hemihydrate (Recewed 15 January 1965) SINCEit was reported recently ~1~that "rather ill-defined spectra were obtained from mulls of crystalline anhydrous phosphoric acid and its hemihydrate with Nujor'; and since an example of such a spectrum is to be found in literature already, t2~we want to state that well-resolved informative spectra may be recorded (compare Fig. 1.). But for this purpose crystallization of the liquids in a low temperature cell is necessary. Even if every precaution against atmospheric humidity is taken melting is caused by mulling crystals of phosphoric acid with Nujol. tl~ A. C. CHAPMANand L. E. T H I R L W E L L , Spectrochim. Acta 20, 937 (1964). t2) A. MUTSCHrNand K. MAENNCHEN,Z. analyt. Chem. 156, 241 (1957).
1430
Notes
We made use of the cell described (3~ and of KBr windows protected by polyethylene.(~ (At absorptions of this material the traces in the figure are interrupted.) Besides securing temperatures in the cell by a thermocouple and recorder we worked on samples of several ml volume in the manner of thermal analysis as well.
H3PO4 '~" H20 I
H3P04,/H20
glass
HsPO4 IT H3P04 I H3P04 TIT
H3P04 glass
1400 I
t200 tO00 NaCI prism
800 700 [ cr11-1
600 ,500 KBr prism
Fro. 1.--Infra-red spectra of six solid phases of HsPO4 and HaPO4"½H~O in the range of 400 to 1400 cm -1. When we investigated the infra-red spectra of HaPO4 and HsPO4'½HzO in this way as solids we noticed four and three different modifications, respectively. Glasses are obtained, if quenching by liquid nitrogen or solid carbon dioxide is applied to the liquid. Warming H3PO4-glass induces crystallization at --54°C to a phase which we call HaPO4-III. This is converted irreversibly at - - 8 . . . --6°C to H3PO4-I which is stable at room temperature. Another phase HaPO4-II is obtained by crystallization from the melt between + 8 ° and +15°C, if the latter was not heated much above the melting point. This HaPO,-II does not change when cooled to --190°C, but when warmed up then, converts to H3PO4-I at - - 4 . . . 0°C. If H3PO4"½H~O-glass is prepared at first, it crystallizes at - - 5 4 . . . --49°C to H3PO4"½H20-II. An irreversible transformation to HsPO4"½H20-I is marked only by a positive thermal effect at - - 3 2 . . . --30°C without noticeable changes in the spectrum. The discussion of the spectra will be given elsewhere, but we feel obliged to call attention to the different modifications especially for crystallized phosphoric acid at room temperature.
Institut fur Spezielle analytisehe Chemic Technische Universitiit Dresden, Germany ~s~G. I'-IErNTZand K. STOPPERKA,Z. Chem. 2, 282 (1962). c~ E. STEGERand K. HERZOO,Z. Chem. 3, 142 (1963).
K. HERZOG E. SITEGER