Title: Thallium
CAS Registry Number: 7440-28-0
Literature References: Tl; at. wt 204.3833; at. no. 81; valence 1, 3. Group IIIA(13). Naturally occurring isotopes: 203 (29.50%), 205 (70.50%); artificial, radioactive isotopes: 191-202; 204; 206-210. Occurs in crookesite, (Cu,Tl,Ag)2Se, found in Sweden; in lorandite, TlAsS2, found in Greece; in hutchinsonite, (Tl,Cu,Ag)2S.PbS.2As2S3, found in Switzerland. Occurrence in the earth's crust: 0.7 ppm. Discovered by Crookes in 1861. Prepn: Sanderson, Can. Mining J. 65, 624 (1944). Use in organic syntheses: McKillop et al., Tetrahedron Lett. 1970, 5281; Taylor et al., ibid. 5285. Review: Wade, Banister in Comprehensive Inorganic Chemistry vol. 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 997-1000, 1119-1172. Review of toxicity: E. Browning, Toxicity of Industrial Metals (Appleton-Century-Crofts, New York, 2nd ed., 1969) pp 317-322; of toxicology and human exposure: Toxicological Profile for Thallium (PB93-110856, 1992) 114 pp.
Properties: Bluish-white, very soft, inelastic, easily fusible, heavy metal; leaves a streak on paper. Oxidizes superficially in air forming a coating of Tl2O. Forms alloys with other metals and readily amalgamates with mercury. d 11.85. Begins to volatilize at 174°. mp 303.5°. bp 1457°. Specific heat at 20° 0.031 cal/g/°C. Latent heat of fusion 5.04 cal/g. Brinell hardness: 2. May be distilled in a stream of hydrogen. Insol in water; reacts with nitric or sulfuric acid; difficultly with hydrochloric acid.
Melting point: mp 303.5°
Boiling point: bp 1457°
Density: d 11.85
CAUTION: Potential symptoms of overexposure are nausea, diarrhea, abdominal pain and vomiting; ptosis, strabismus; peripheral neuritis, tremor; retrosternal tightness, chest pain and pulmonary edema; seizure, chorea and psychosis; liver and kidney damage; alopecia; paresthesia of legs. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 304. See also Patty's Industrial Hygiene and Toxicology vol. 2A, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York, 3rd ed., 1981) 1914-1931.
Use: In semi-conductor industry; alloyed with mercury for switches and closures which operate at subzero temps. In manuf of highly refractive optical glass. Has been used in admixture with 97-98% of inert substances as poison for rats and other rodents.

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