Arsenic oxide: production and properties

In the periodic table, such a chemical element as arsenic occupies a position on the metal-nonmetal boundary. By its activity it is located between hydrogen and copper. Nonmetallic character is manifested in the fact that it is able to exhibit oxidation state -3 (AsH ₃ - arsine). Compounds with a positive oxidation state of +3 have amphoteric properties, and with a degree of +5, its acidic properties are manifested. What is arsenic oxide?

Oxides and hydroxides

There are the following oxides of arsenic: As ₂ O ₃ and As ₂ O ₅ . There are also corresponding hydroxides:

• Metasjanichnaya acid HAsO ₂ .
• Orthophosphorous acid H ₃ AsO ₃ .
• Arsenic dioxide HAsO ₃ .
• Orthosulphonic acid H ₃ AsO ₄ .
• Pyroglysic acid H ₄ As ₂ O ₇ .

What is arsenic trioxide?

Arsenic forms two oxides, of which As ₂ O ₃ is called trioxide. It is a substance that is often used for treatment, but it is not a completely harmless chemical. This is an inorganic compound, which is the main source of organoarsenic compounds (compounds containing a chemical bond with carbon) and many others. Many applications of As ₂ O ₃ are controversial because of the toxic nature of the element. The trade name of this compound is Trisenox.

General information about trioxide

The chemical formula of arsenic trioxide is as follows: As ₂ O ₃ . The molecular weight of this compound is 197.841 g / mol. There are many ways to get this oxide. One of them is the roasting of sulphide ore. The chemical reaction is as follows:

2As ₂ O ₃ + 9 O ₂ → 2As ₂ O ₃ + 6SO ₂

Most oxides can be obtained as a by-product of processing other ores. Arsenopyrite is a general admixture in gold and copper, and it releases arsenic trioxide when heated in the presence of air. This can lead to serious poisoning.

Structure of arsenic trioxide

Arsenic trioxide has the formula As ₄ O ₆ in the liquid and gas phases (below 800 ° C). In these phases it is isostructural with phosphorous trioxide (P ₄ O ₆ ). But at temperatures above 800 ° C As ₄ O _{6 is} destroyed to molecular As ₂ O ₃ . In this phase it is isostructural with diisotron trioxide (N ₂ O ₃ ). In its solid state, this compound shows a polymorphic ability (the ability to exist in two or more forms of crystal structure).

Properties of arsenic trioxide

Some of the main properties of arsenic trioxide are as follows:

• Solutions of trioxide form weak acids with water. This is due to the fact that the compound is an amphoteric arsenic oxide.
• It is soluble in alkaline solutions and gives arsenates.
• Arsenic trioxide has a high solubility in hydrochloric acid (HCl), and finally gives arsenic trichloride and concentrated acid.
• It gives pentoxide (As ₂ O ₅ ) in the presence of strong oxidizing agents, such as hydrogen peroxide, ozone and nitric acid.
• It is almost insoluble in organic solvents.
• It looks like a white solid in normal physical condition.
• 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 / cm ³ .

Application of arsenic trioxide in medicine

This chemical belongs to the class of antitumor agents and is used in the treatment of cancer. The toxicity of arsenic is well known. But arsenic trioxide is a chemotherapeutic drug and has been used to treat certain types of cancer for many years. The solution used for this treatment is called the Fowler solution. In 1878, the Boston City Hospital reported that this solution could be effective in reducing the number of leukocytes in a person.

As a result, As ₂ O ₃ was mainly used to treat leukemia until it was replaced by radiotherapy. But after the 1930s, he gradually regained his popularity in the treatment of leukemia, until modern chemotherapy appeared. This arsenic oxide was considered the best method for treating chronic myelogenous leukemia. Even today, this substance is used to treat a particular type of acute promyelocytic leukemia in unsuccessful retinoic or anthracycline chemotherapy. It is also used to treat chronic myeloid leukemia, multiple myeloma, acute myeloid leukemia, lymphoma, cancer of the lymphatic system.

Use of trioxide

Arsenic trioxide is widely used in the production of colorless glass. This connection is also useful in the field of electronics for the creation of semiconductors and certain alloys. It is also used in paints. Arsenic trioxide can be an effective treatment for brain tumors.

In the past this substance was used in dentistry, but since this is a highly toxic compound, its use by modern dentists has been discontinued. Arsenic oxide (As ₂ O ₃ formula) is also used as a wood preservative, but such materials are banned in many parts of the world. In combination with copper acetate, arsenic trioxide gives a bright green pigment.

Highly toxic substance

By itself, trioxide has a high level of toxicity. Therefore, it is always necessary to take the necessary precautions before using it. It can be very dangerous in the following cases:

• Eating. If As ₂ O ₃ accidentally enters the digestive tract, you should immediately consult a doctor. It is not recommended to attempt to induce vomiting before seeking medical help. You need to remove any dense clothes, take off your tie, unbutton your collar, belt, etc.
• Contact with skin. In case of contact with any surface of the body, immediately wash the affected area with plenty of water. Infected clothing and shoes should be immediately removed and they should be washed before re-use. In case of serious contact with the skin, you should immediately seek medical help. It may be useful to wash the infected area with disinfectant soap and apply antibacterial cream.
• Contact with eyes. If As ₂ O ₃ comes in contact with the eyes, the first thing to do is remove any contact lenses and wash the eyes with plenty of water for 15 minutes. It is recommended to use cold water. In parallel, someone must call an ambulance.
• Inhalation. People who inhaled this gas should be placed in another place with fresh air. And also you need to immediately seek medical help. If breathing is difficult, oxygen should be injected immediately. If the victim is unable to breathe by himself, artificial respiration should be given.
• This compound can have a toxic effect on a person. In case of ingestion of an excessive amount of arsenic trioxide, it can even lead to death. Protective goggles and gloves should always be used while working with As ₂ O ₃ . Work should always be carried out in a well-ventilated area.

Side effects

Common side effects of this substance include such symptoms as:

• Poor appetite;
• Vomiting;
• nausea;
• abdominal pain;
• constipation;
• headache;
• fatigue;
• dizziness;
• fever;
• Problems with breathing;
• High level of leukocytes;
• High blood sugar;
• skin rash.

Less common side effects include:

• Dry mouth;
• Inconsistent breath;
• chest pain;
• Low level of leukocytes;
• Muscular and bone pain;
• Swelling of the face and eyes;
• diarrhea;
• tremor;
• Low blood sugar;
• Low level of oxygen in the blood.

Rare side effects of As ₂ O ₃ :

• Irregular heartbeats (this can even lead to death);
• Weight gain;
• fainting;
• Distraction;
• coma;
• Swollen abdomen;
• Darkening of the skin.

Dangerous for life symptoms of exposure to arsenic trioxide are weight gain, fever, difficulty breathing, shortness of breath, chest pain, cough.

Arsenic trioxide is a highly toxic substance that can even lead to human death. Nevertheless, it has its usefulness in the medical field. Always take precautions.

Chemical reactions

Arsenic trioxide is an amphoteric higher oxide of arsenic, and its aqueous solutions are slightly acidic. Thus, it dissolves readily in alkaline solutions to produce arsenates. It is less soluble in acids, except for hydrochloric acid.

Only with strong oxidants such as ozone, hydrogen peroxide and nitric acid, it forms penta-arsenic oxide with +5 degree of acidity As ₂ O ₅ . With regard to oxidation resistance, arsenic trioxide differs from phosphorus trioxide, which is readily combusted to phosphorus pentoxide. Reduction gives elemental arsenic or arsine (AsH ₃ ).

Arsenic Pentaoxide

The chemical formula of the pentoxide is As ₂ O ₅ . Its molar mass is 229.8402 g / mol. It is a white hygroscopic powder with a density of 4.32 g / cm ³ . The melting point reaches 315 ° C, at which point it begins to decompose. The substance has good solubility in water and alcohol. The properties of arsenic oxide make it very toxic and dangerous for the environment. It is an inorganic compound that is less common, highly toxic, and therefore finds only limited commercial application, unlike higher arsenic oxide (As ₂ O ₃ formula).

Arsenic is known primarily as a poison and a carcinogen. Its trioxide is a water-soluble powder that produces a colorless, tasteless and odorless solution. It was a popular way of killing in the Middle Ages. Its use continues today, but for peaceful purposes and in small quantities.