Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses include in the manufacture of wood preservatives, pesticides, and glass. As a medication, it is used to treat a type of cancer known as acute promyelocytic leukemia. For this use it is given by injection into a vein.Common side effects include vomiting, diarrhea, swelling, shortness of breath, and headaches. Severe side effects may include APL differentiation syndrome and heart problems. Use during pregnancy or breastfeeding may harm the baby. Arsenic trioxide has the formula As2O3. Its mechanism in treating cancer is not entirely clear.Arsenic trioxide was approved for medical use in the United States in 2000. It is on the World Health Organizations List of Essential Medicines. Approximately 50,000 tonnes are produced a year. Due to its toxicity, a number of countries have regulations around its manufacture and sale. Uses
Medical
Arsenic trioxide is used to treat a type of cancer known as acute promyelocytic leukemia (APL). It may be used both in cases that are unresponsive to other agents, such as all-trans retinoic acid (ATRA) or as part of the initial treatment of newly diagnosed cases. This initial treatment may include combination therapy of arsenic trioxide with all-trans retinoic acid (ATRA).Effectiveness appears similar to Realgar/Indigo naturalis, which can be taken by mouth and is less expensive but is less available.In the 1970s, Chinese researcher Zhang Tingdong and colleagues discovered this use. It was approved for leukemia treatment in the United States in 2000.
Properties and reactions
Arsenic trioxide is an amphoteric oxide, and its aqueous solutions are weakly acidic. Thus, it dissolves readily in alkaline solutions to give arsenites. It is less soluble in acids, although it will dissolve in hydrochloric acid.With anhydrous HF and HCl, it gives AsF3 and the trichloride:
As2O3 + 6 HX → 2 AsX3 + 3 H2O (X = F, Cl)Only with strong oxidizing agents such as ozone, hydrogen peroxide, and nitric acid does it yield arsenic pentoxide, As2O5 or its corresponding acid:
2 HNO3 + As2O3 + 2 H2O → 2 H3AsO4 + N2O3In terms of its resistance to oxidation, arsenic trioxide differs from phosphorus trioxide, which readily combusts to phosphorus pentoxide. Reduction gives elemental arsenic or arsine (AsH3) depending on conditions:
As2O3 + 6 Zn + 12 HNO3 → 2 AsH3 + 6 Zn(NO3)2 + 3 H2OThis reaction is used in the Marsh test. Structure
In the liquid and gas phase below 800 °C, arsenic trioxide has the formula As4O6 and is isostructural with P4O6. Above 800 °C As4O6 significantly dissociates into molecular As2O3, which adopts the same structure as N2O3. Three forms (polymorphs) are known in the solid state:  a high temperature ( > 110 °C) cubic As4O6, containing molecular As4O6, and two related polymeric forms. The polymers, which both crystallize as monoclinic crystals, feature sheets of pyramidal AsO3 units that share O atoms. Society and culture
Environmental effects
Smelting and related ore processing often generate arsenic trioxide, which poses a risk to the environment.