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Arsenic Trioxide

Arsenic Trioxide is a substance that is often used for medical treatments.  But it is not a completely harmless chemical. Read on to know more about this chemical compound.

What is Arsenic Trioxide?

Arsenic Trioxide is an inorganic compound. It is the main originator for organoarsenic compounds (compounds containing arsenic-carbon chemical bond) and numerous other arsenic compounds. Many applications of As2O3 are controversial because of the toxic nature of arsenic. The trade name for this compound is Trisenox.

Arsenic Trioxide Formula

The chemical formula of this compound is As2O3.

Arsenic Trioxide Molecular Weight

The molecular weight of this compound is 197.841 g/mol.

Arsenic Trioxide Preparation

There are many ways to prepare As2O3 from arsenic compounds. One way to produce this chemical compound is from Orpiment, an arsenic sulfide ore. It is done by the roasting of the orpiment. The chemical reaction happens in the following way:

2 As2S3 + 9 O2 → 2 As2O3 + 6 SO2

Most arsenic oxides can be obtained as the by-product of the processing of other arsenic ores. Arsenopyrite is a common impurity in gold and copper and it releases Arsenic Trioxide if heated in the presence of air. This can cause serious arsenic poisoning.

Arsenic ores are not intentionally mined, except in China.

Pictures of Arsenic Trioxide
Picture 1 – Arsenic Trioxide
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Arsenic Trioxide structure

Arsenic Trioxide has the formula As4O6 in its liquid and gas phase (below 800 °C). In these phases it is isostructural with Phosphorus Trioxide (P4O6). But above 800°C, As4O6 breaks down into molecular As2O3. In this phase, As2O3 is isostructural with Dinitrogen Trioxide (N2O3). In its solid state, this compound shows polymorphic capability (the ability to exist in two or more forms of crystal structure).

Arsenic Trioxide Properties

Some of the main properties of Arsenic Trioxide are as follows:

  • The solutions of Arsenic Trioxide form weak acids with water. This is due to the fact that the compound is an amphoteric oxide.
  • It is soluble in alkaline solutions and gives Arsenites.
  • Arsenic Trioxide has high solubility in Hydrochloric Acid (HCl) and finally gives Arsenic Trichloride and concentrated acid.
  • It gives Arsenic Pentoxide (As2O5) in the presence of strong oxidizing agents like Hydrogen Peroxide, Ozone and Nitric Acid.
  • It is almost insoluble in organic solvents.
  • It appears as a white solid in its normal physical state.
  • It has a melting point of 312.2°C and a boiling point of 465°C.
  • The density of this substance is 4.15 g/cm3.

Arsenic Trioxide Classification

This chemical substance belongs to the class of antineoplastic agents.

It has the EU classification of Very toxic (T+).

Arsenic Trioxide in Cancer Treatment

The toxicity of arsenic is well known. But Arsenic Trioxide is a chemotherapy drug and has been used for the treatment of specific types of cancer for many years. The solution used for this treatment is called the Fowler’s Solution. In the year 1878, the Boston City Hospital reported that this solution can be effective in reducing white blood cell counts in human. As a result, As2O3 was principally used in the treatment of Leukemia until the radiation therapy replaced it. But after 1930s, it gradually regained its popularity in Leukemia treatment. Until modern chemotherapy came into existence, As2O3 was considered to be the best treatment for Chronic Myelogenous Leukemia (CML).

Even today, this substance is used for the treatment of a particular type of Acute Promyelocytic Leukemia (APL) when the retinoid or anthracycline chemotherapy fails. It is also used for the treatment of

  • Chronic Myelogenous Leukemia
  • Multiple Myeloma
  • Acute Myelogenous Leukemia

Arsenic Trioxide is also used for the treatment of Lymphoma, cancer of the lymphatic system.

Arsenic Trioxide Uses

Know about some of the main uses of this compound.

  • As2O3 was used as a precursor to forestry goods.
  • It is widely used in the production of colorless glass.
  • As2O3 also has diverse usefulness in the field of electronics.
  • It is the main arsenic compound and is used as the originator of arsenic semiconductors, elemental arsenic and arsenic alloys.
  • Copper arsenates, which are used as wood preservative in US and Malaysia, are derived from As2O3.
  • Paris Green, which is used as a rodenticide, is produced with the help of As2O3. It is also used in paints.
  • Arsenic Trioxide may prove to be an effective treatment for Brain Tumor in recent future.
  • This substance has been used in dentistry in the past. But as it is a highly toxic compound, its use has been reasonably abandoned by modern dentists.

Arsenic Trioxide Dosage

In case of induction treatment, 0.15 mg/kg of As2O3 should be taken once daily. 25 doses can be taken over a period of 4-5 weeks. After completing the induction therapy, one should wait for 3-4 weeks before using Arsenic Trioxide dosage. The number of induction doses should never exceed over 60.

Arsenic Trioxide MSDS

This compound has a high level of toxicity. So, it is always important to take the necessary precautions before handling it. It can be highly hazardous in the following cases:


If As2O3 is ingested by accident, you should seek medical attention immediately. It is not advisable to try and induce vomiting before getting medical advice. You should loosen any tight clothing like a tie, collar, belt etc.

Skin contact

In case of skin contact, you should immediately wash the affected area with a lot of water. The infected clothes and shoes should be removed immediately and they should be washed before re-using. In case of serious skin contact, you should immediately go for medical attention. Washing the infected area with a disinfectant soap and applying anti-bacterial cream can be helpful.

Eye contact

If As2O3 comes in contact with the eyes, the first thing to do would be to remove any contact lenses and wash the eyes with a lot of water for 15 minutes in the least. Using cold water is advisable. In this case too, take medical attention immediately.


People who have inhaled this gas must relocate to a fresh, airy place and seek medical attention immediately. If it is hard to breath, oxygen should promptly be administered. If the victim is not found to be breathing, artificial respiration must be given.

This compound can have poisonous effects on human. In case of over exposure, Arsenic Trioxide may even cause death.  Safety glasses and gloves should always be used at the time of working with As2O3. The work should always be done in a well ventilated place.

Arsenic Trioxide side effects

The common side effects of this substance are:

  • Poor appetite
  • Vomiting
  • Nausea
  • Abdomen pain
  • Constipation
  • Headache
  • Tiredness
  • Dizziness
  • Fever
  • Trouble in breathing
  • High white blood cell count
  • High level of blood sugar
  • Skin rash

The less common side effects include:

  • Dry mouth
  • Low blood cell count
  • Shortness of breath
  • Chest pain
  • Low white blood cell count
  • Muscle and bone aching
  • Swelling of the face and eyes
  • Diarrhea
  • Tremor
  • Low level of blood sugar
  • Low levels of oxygen in the blood

The rare side effects of As2O3 are:

  • Irregular heartbeat (it may even cause death)
  • Weight gain
  • Fainting
  • Confusion
  • Coma
  • Seizures
  • Swollen abdomen
  • Darkening of skin

APL Differentiation Syndrome

The life threatening symptoms of Arsenic Trioxide are collectively called the APL Differentiation Syndrome (APLDS). These symptoms include:

  • Weight gain
  • Fever
  • Difficulty in breathing
  • Shortness of breathing
  • Chest pain
  • Cough

Arsenic Trioxide is a highly toxic substance which may even cause the death of a human. Yet, it has its usefulness in the medical field. Safety precautions should always be taken while working with As2O3. You should always strictly adhere to the advice of your doctor while using Arsenic Trioxide medications.



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