Nomenclature
CAS number: 7440-10-0
Description and references
Pr; at. wt 140.90765; at. no. 59; valences
3, 4. A lanthanide; belongs to the cerium group of rare earth metals.
Naturally occurring isotope (mass number): 141; known artificial
radioactive isotopes: 126, 129-140; 142-152. Prepn of radioactive
isotopes by bombardment: Seaborg, Chem. Rev. 27, 199 (1940); Huber et al., Helv. Phys. Acta 18, 221 (1945).
Abundance in earth's crust 5.5-9.1 ppm; found in rare earth minerals.
Reported in 1843 by Mosander as didymium which was a mixture of Pr and Nd; separated in 1885 by
von Welsbach. Separated from other rare earth elements by fractional
crystn. Also by ion exchange: Spedding et al., J. Am. Chem. Soc. 69, 2786, 2812
(1947). Prepn of metal by electrolysis: Muthmann, Weiss, Ann. 331, 1 (1904); Canneri, Rossi, Gazz. Chim. Ital. 62, 1160 (1932);
Mazza, Atti X Congr. Int. Chim. 3, 604 (1939); Trombe, Mahn, Compt. Rend. 220, 778 (1945). Toxicity study:
Haley et al., Toxicol. Appl. Pharmacol. 6, 614 (1964). Reviews of prepn, properties and compds:
The Rare Earths, F. H. Spedding, A. H. Daane, Eds. (Krieger,
Huntington, N.Y., 1971, reprint of 1961 ed.) 641 pp; Hulet, Bode, “Separation
Chemistry of the Lanthanides and Transplutonium Actinides” in MTP Int. Rev. Sci.: Inorg. Chem., Ser. One Vol. 7, K. W. Bagnall, Ed. (Univ. Park Press, Baltimore,
1972) pp 1-45; Moeller, “The Lanthanides”, Comprehensive Inorganic Chemistry Vol. 4, J.
C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973)
pp 1-101; F. H. Spedding in Kirk-Othmer Encyclopedia
of Chemical Technology vol. 19 (John Wiley
& Sons, New York, 3rd ed., 1982) pp 833-854; Chemistry of
the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press,
New York, 1984) pp 1423-1449. Brief review of properties: G. T.
Seaborg, Radiochim. Acta 61, 115-122 (1993).
Properties
Yellowish metal, forms oxide film on exposure
to moist air. Two crystalline forms: hexagonal α-form, d 6.475, transforms to β-form at 798°;
body-centered cubic β-form, d 6.64, exists at >798°. mp 935°. bp 3020°; also reported as bp 3520° (Spedding). E0 (aq) Pr3+/Pr -2.47 V
(calc). Experimental reduction potentials (referred to a normal calomel
electrode): -1.875, -1.990 V: Noddack, Brukl, Angew. Chem. 50, 362 (1937). Heat of sublimation
(25°): 355.6 kJ/mol. Heat of fusion: 6.912 kJ/mol (Spedding, 1982).
Also reported as heat of fusion: 11.3 ±2.1 kJ/mol (Greenwood, Earnshaw).Derivative
Oxide.
Pr
2O
3; mol wt 329.81.
Pr 85.45%, O 14.55%.
Properties
d 7.07, prepd by reducing with hydrogen the oxides PrO2 or
Pr6O11. Oxidizes to Pr6O11 on heating in air; forms the dioxide, PrO2, on fusing
with potassium chlorate.Derivative
Hydroxide.
Pr(OH)
3; mol wt 191.93.
Pr 73.42%, O 25.01%, H 1.58%.
Properties
A gelatinous pale green precipitate, obtained
by the action of alkali hydroxide on a soln of a praseodymium salt;
a purple powder when obtained by the action of water on praseodymium
carbide.Derivative
Chloride.
PrCl
3; mol wt 247.27.
Pr 56.99%, Cl 43.01%.
Properties
Heptahydrate, green crystals; mp in its water of crystn at 111°; on partial dehydration yields the hexa-, tri-, or monohydrate;
on heating to 180-200° in a stream of hydrogen chloride yields the
anhydr chloride, green needles, mp 769-782°, sol in water, alcohol. LD50 in mice: 600 mg/kg i.p.; 4.5 g/kg orally (Haley).Derivative
Sulfate.
Pr
2(SO
4)
3; mol wt 570.00.
Pr 49.44%, S 16.88%, O 33.68%.
Properties
Light green crystals, prepd by evaporating a soln
of the oxide in H2SO4 and cooling the resulting
product over phosphorus pentoxide. Several hydrates and double sulfates
are known.