arsenic trichloride arsenic trichloride arsenic trichloride is an inorganic compound with the formula ascl3, also known as arsenous chloride or butter of arsenic. this poisonous oil is colourless, although impure samples may appear yellow. it is an intermediate in the manufacture of organoarsenic compounds. arsenic trichloride names other names arsenic(iii) chloride, arsenous trichloride, butter of arsenic, de valagin's solution identifiers cas number 7784-34-1 y 3d model (jsmol) interactive image chemspider 22974 y echa infocard 100.029.144 ec number 232-059-5 pubchem cid 24570 rtecs number cg1750000 unii 5xw39m1300 un number 1560 comptox dashboard (epa) dtxsid3042556 inchi inchi=1s/ascl3/c2-1(3)4 ykey: oeyohulqrfxulb-uhfffaoysa-n yinchi=1/ascl3/c2-1(3)4key: oeyohulqrfxulb-uhfffaoyag smiles cl(cl)cl properties chemical formula ascl3 molar mass 181.28 g/mol appearance colourless oily liquid density 2.163 g/cm3, liquid melting point −16.2 °c (2.8 °f; 256.9 k) boiling point 130.2 °c (266.4 °f; 403.3 k) solubility in water hydrolyzes solubility soluble in alcohol, ether, hcl, hbr, chloroform, ccl4 magnetic susceptibility (χ) -79.9·10−6 cm3/mol refractive index (nd) 1.6006 viscosity 9.77 x 10−6 pa s hazards occupational safety and health (ohs/osh): main hazards very toxic, carcinogen, corrosive, decomposes on contact with water releasing hcl ghs labelling: pictograms signal word danger hazard statements h301, h310, h314, h331, h350, h410 precautionary statements p201, p202, p260, p261, p262, p264, p270, p271, p273, p280, p281, p301+p310, p301+p330+p331, p302+p350, p303+p361+p353, p304+p340, p305+p351+p338, p308+p313, p310, p311, p321, p322, p330, p361, p363, p391, p403+p233, p405, p501 nfpa 704 (fire diamond) 4 0 1 lethal dose or concentration (ld, lc): ld50 (median dose) 48 mg/kg lclo (lowest published) 100 mg/m3 (cat, 1 hr)200 mg/m3 (cat, 20 min)338 ppm (rat, 10 min) niosh (us health exposure limits): pel (permissible) twa 0.010 mg/m3 rel (recommended) ca c 0.002 mg/m3 idlh (immediate danger) ca related compounds other anions arsenic trioxide, arsenic trifluoride other cations antimony trichloride except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). y verify (what is yn ?) infobox references structure ascl3 is a pyramidal molecule with c3v symmetry. the as-cl bond is 2.161 å and the angle cl-as-cl is 98° 25'±30. ascl3 has four normal modes of vibration: ν1(a1) 416, ν2(a1) 192, ν3 393, and ν4(e) 152 cm−1. synthesis this colourless liquid is prepared by treatment of arsenic(iii) oxide with hydrogen chloride followed by distillation: as2o3 + 6 hcl → 2 ascl3 + 3 h2o it can also be prepared by chlorination of arsenic at 80–85 °c, but this method requires elemental arsenic. 2 as + 3 cl2 → 2 ascl3 arsenic trichloride can be prepared by the reaction of arsenic oxide and sulfur monochloride. this method requires simple apparatus and proceeds efficiently: 2 as2o3 + 6 s2cl2 → 4 ascl3 + 3 so2 + 9 s a convenient laboratory method is refluxing arsenic(iii) oxide with thionyl chloride: 2 as2o3 + 3 socl2 → 2 ascl3 + 3 so2 arsenic trichloride can also be prepared by the reaction of hydrochloric acid and arsenic(iii) sulfide. as2s3 + 6 hcl → 2 ascl3 + 3 h2s reactions hydrolysis gives arsenous acid and hydrochloric acid: ascl3 + 3 h2o → as(oh)3 + 3 hcl although ascl3 is less moisture sensitive than pcl3, it still fumes in moist air. ascl3 undergoes redistribution upon treatment with as2o3 to give the inorganic polymer asocl. with chloride sources, ascl3, forms salts containing the anion −. reaction with potassium bromide and potassium iodide give arsenic tribromide and arsenic triiodide, respectively. ascl3 is useful in organoarsenic chemistry, for example triphenylarsine is derived from ascl3: ascl3 + 6 na + c6h5cl → as(c6h5)3 + 6 nacl the poison gases called lewisites are prepared by the addition of arsenic trichloride to acetylene: ascl3 + c2h2 → clch=chascl2 safety inorganic arsenic compounds are highly toxic, and ascl3 especially so because of its volatility and solubility (in water). it is classified as an extremely hazardous substance in the united states as defined in section 302 of the u.s. emergency planning and community right-to-know act (42 u.s.c. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.