PERCHLORIC ACID
(AND INORGANIC PERCHLORATES)

Perchloric acid (and inorganic perchlorates)
CAS 7601-90-3

HClO₄(maximum concentration commercially available is an aqueous solution containing about 72% HClO₄by weight)

Colorless liquid
72% HClO₄: bp 203 °C, mp -18 °C
Miscible with water

Odorless

6.8 mmHg at 25 °C

LD₅₀ oral (rat) 1100 mg/kg

LD₅₀ oral (dog) 400 mg/kg

Highly corrosive to all tissues; reacts violently with many oxidizable substances; anhydrous form and certain salts are highly explosive.

Perchloric acid is a highly corrosive substance that causes severe burns on contact with the eyes, skin, and mucous membranes. The acute toxicity of perchloric acid is moderate. This substance is a severe irritant to the eyes, mucous membranes, and upper respiratory tract. Perchlorates are irritants to the body wherever they contact it.

Perchloric acid has not been shown to be carcinogenic or to show reproductive or developmental toxicity in humans.

Perchloric acid is noncombustible. The anhydrous (dehydrated) acid presents a serious explosion hazard. It is unstable and can decompose explosively at ordinary temperatures or in contact with many organic compounds.

Many heavy metal perchlorates and organic perchlorate salts are extremely sensitive explosives; the ammonium, alkali metal, and alkali earth perchlorates are somewhat less hazardous. Mixtures of perchlorates with many oxidizable substances are explosive.

Cold 70% perchloric acid is a strong acid but is not considered to be a strong oxidizing agent; however, more concentrated solutions are good oxidizers. Temperature increases the oxidizing power of perchloric acid, and hot concentrated solutions are very dangerous. Evaporation of a spill of the 70% solution may lead to the formation of more dangerous concentrations. Reaction of 70% perchloric acid with cellulose materials such as wood, paper, and cotton can produce fires and explosions. Oxidizable organic compounds including alcohols, ketones, aldehydes, ethers, and dialkyl sulfoxides can react violently with concentrated perchloric acid.

All perchlorates are potentially hazardous when in contact with reducing agents.

Because of their extreme reactivity, perchloric acid and all organic and inorganic perchlorates should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with reactive and explosive compounds (Chapter 5.G). In particular, splash goggles and rubber gloves should be worn when handling perchloric acid, and containers of the acid should be stored in a well-ventilated location separated from organic substances and other combustible materials. Work with >85% perchloric acid requires special precautions and should be carried out only by specially trained personnel.

In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If perchloric acid is ingested, obtain medical attention immediately. If large amounts of this compound are inhaled, move the person to fresh air and seek medical attention at once.

In the event of a spill, dilute the perchloric acid with water to a concentration of <5%, absorbed with sand or vermiculite, place in an appropriate container, and dispose of properly. Organic absorbants must not be used. Respiratory protection may be necessary in the event of a large spill or release in a confined area.

Excess perchloric acid and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.