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| Identifiers | |
|---|---|
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.014.075 |
| 35185 | |
| KEGG | |
| |
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| Properties | |
| As4O6 | |
| Molar mass | 395.680 g·mol−1 |
| Appearance | white solid |
| Density | 3.74 g/cm3 |
| Melting point | 312.2 °C (594.0 °F; 585.3 K) |
| Boiling point | 465 °C (869 °F; 738 K) |
| 20 g/L (25 °C (77 °F; 298 K))[citation needed] | |
| Hazards | |
| GHS labelling:[citation needed] | |
    | |
| Danger | |
| H300,H314,H350,H410 | |
| P201,P202,P260,P264,P270,P273,P280,P301+P330+P331,P303+P361+P353,P304+P340+P310,P305+P351+P338+P310,P308+P313,P363,P391,P405,P501 | |
Threshold limit value (TLV) | 0.05 mg/m3[1] (TWA) |
| NIOSH (US health exposure limits):[2] | |
PEL (Permissible) | 0.010 mg/m3 (TWA, as As) |
REL (Recommended) | 0.002 mg/m3 (15 minute, as As) |
IDLH (Immediate danger) | 5 mg/m3 (as As) |
| Safety data sheet (SDS) | Safety Data Sheet |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Arsenic trioxide is theinorganic compound with theformulaAs4O6.[3] As an industrial chemical, its major uses include the manufacture ofwood preservatives,pesticides, andglass. For medical purposes, it is sold under the brand nameTrisenox among others[4][5] when used as a medication to treat a type ofcancer known asacute promyelocytic leukemia.[6] For this use it is given byinjection into a vein.[6]
Arsenic trioxide was approved for medical use in the United States in 2000.[6] It is on theWorld Health Organization's List of Essential Medicines.[7] Approximately 50,000tonnes were produced in 1991.[8] Due to its toxicity, a number of countries have regulations around its manufacture and sale.[9]
Arsenic trioxide is the dominant form of arsenic for commercial applications. Industrial uses include usage as a precursor to forestry products, in colorless glass production, and in electronics. Being the main compound of arsenic, the trioxide is the precursor toelemental arsenic, arsenic alloys, andarsenidesemiconductors. Bulk arsenic-based compoundssodium arsenite andsodium cacodylate are derived from the trioxide.[8]
A variety of applications exploit arsenic's toxicity, including the use of the oxide as awood preservative.Copper arsenates, such aschromated copper arsenate, are derived from arsenic trioxide. These compounds were once used on a large scale as wood preservatives in the U.S. and Malaysia, but are now banned in many parts of the world. This practice remains controversial.[8] When combined withcopper(II) acetate, arsenic trioxide gives the vibrant green pigment known asParis green, which finds some use as aninsecticide.[10]
Despite the well known toxicity of arsenic, arsenic trioxide was used intraditional Chinese medicine, where it is known aspi-shuang (Chinese:砒霜;pinyin:pīshuāng;lit. 'arsenic frost'). Some discreditedpatent medicines, e.g.,Fowler's solution, contained derivatives of arsenic oxide.[11]
Arsenic trioxide is used to treat a type of cancer known asacute promyelocytic leukemia (APL).[6] It may be used both in cases that are unresponsive to other agents, such asall-trans retinoic acid (ATRA) or as part of the initial treatment of newly diagnosed cases.[6] This initial treatment may include combination therapy of arsenic trioxide with all-trans retinoic acid (ATRA).[12][13]
Arsenic trioxide can be generated via routine processing of arsenic compounds including the oxidation (combustion) of arsenic and arsenic-containing minerals in air. Illustrative is the roasting oforpiment, a typical arsenic sulfide ore.
Smelting and related ore processing often generate arsenic trioxide, which poses a risk to theenvironment. For example, theGiant Mine in Canada processed substantial amounts ofarsenopyrite-contaminated gold ores.
Most arsenic oxide is, however, obtained as a volatile by-product of the processing of other ores. For example,arsenopyrite, a common impurity in gold- and copper-containing ores, liberates arsenic trioxide upon heating in air. The processing of such minerals has led to numerous cases of poisonings,[14] and after the mine is closed, the leftover trioxide waste will present environmental hazard (as was the case with theGiant Mine, for example). Only in China are arsenic ores intentionally mined.[8]
In the laboratory, it is prepared by hydrolysis ofarsenic trichloride:[15]
As2O3 occurs naturally as two minerals,arsenolite (cubic) andclaudetite (monoclinic). Both are relatively rare secondary minerals found inoxidation zones of As-rich ore deposits.
Arsenic trioxide is anamphoteric oxide, and its aqueous solutions are weakly acidic. Thus, it dissolves readily in alkaline solutions to givearsenites:[16]
Arsenic trioxide is less soluble in acids, although it will dissolve inhydrochloric acid.[17][page needed]
When treated with anhydrous HF and HCl, arsenic trioxide converts to the corresponding trihalide.[18] The tribromide and triiodide are made using concentratedhydrobromic acid andhydroiodic acid, respectively:[19]
Only with strong oxidizing agents such as ozone, hydrogen peroxide, and nitric acid does it yieldarsenic pentoxide,As2O5 or its corresponding acid:[18]: 601
In terms of its resistance to oxidation, arsenic trioxide differs fromphosphorus trioxide, which readily combusts tophosphorus pentoxide.[clarification needed]
Reduction gives elemental arsenic orarsine (AsH3) depending on conditions:[18]: 593–594
This reaction is used in theMarsh test.[20]
Arsenic trioxide has played a special role as entry toorganoarsenic chemistry. In the 18th century it was found that combining arsenic trioxide and four equivalents ofpotassium acetate (CH3CO2K) gives a product called "Cadet's fuming liquid", which is often considered the firstorganometallic compound. Cadet's fuming liquid is a derivative ofcacodylic acid,((CH3)2As)2O andcacodyl,((CH3)2As)2.[21]
Arsenic trioxide reacts withphenyl magnesium bromide as described by the following idealized equation:[17]
Like many other oxides, arsenic trioxide condenses with transition metal oxyanions to givepolyoxometallates. Many such clusters have been characterized byX-ray crystallography.[22] It reacts with aqueous copper(II) acetate to giveCu(C2H3O2)2·3Cu(AsO2)2, known asParis green.[23][24]
In the gas phase below 800 °C (1,470 °F), arsenic trioxide has the formulaAs4O6 and is isostructural withP4O6. Above 800 °C (1,470 °F)As4O6 dissociation into molecularAs2O3, with the same structure asN2O3, becomes significant. Three crystalline forms (polymorphs) are known: a high temperature (over 110 °C (230 °F)) cubic form, containing molecularAs4O6, and two related polymeric forms.[25][page needed] The polymers, which both crystallize as monoclinic crystals, feature sheets of pyramidalAsO3 units that share O atoms.[26][page needed] One of the polymeric forms (presumably I, as II was not known at the time) is apparently[27] the most stable form.
 |  |  |
arsenolite (cubic) | claudetite I (monoclinic) | claudetite II (monoclinic) |
The liquid state is agreed to be polymeric,[by whom?] and can form a glass; the liquid and glass have bonding of the same general type as the polymeric crystalline forms.[28]
As with other inorganic arsenic compounds, arsenic trioxide is toxic to living organisms. Arsenic trioxide is readily absorbed by the digestive system. Ingestion of as little as100 mg can be fatal.[8]
Chronic arsenic poisoning is known as arsenicosis. This disorder affects workers insmelters, in populations whosedrinking water contains high levels of arsenic (0.3–0.4 ppm), and in patients treated for long periods with arsenic-based pharmaceuticals. Long-term ingestion of arsenic trioxide either in drinking water or as a medical treatment can lead to skin cancer. Reproductive problems (high incidences of miscarriage, low birth weight, congenital deformations) have also been indicated in one study of women exposed to arsenic trioxide dust as employees or neighbours of a copper foundry.
In Austria, there lived the so-called "arsenic eaters ofStyria", who ingested doses far beyond the lethal dose of arsenic trioxide without any apparent harm. Arsenic is thought to enable strenuous work at high altitudes, e.g. in the Alps.[29][30][31]
