PERCHLORIC ACID

Description

Perchloric acid is a corrosive inorganic liquid that is colorless, odorless, and oily in nature. It is miscible with water and has a boiling point of 203 °C, a melting point of 19 °C, and a low vapor pressure of 6.8mmHg at 25 °C. A cold 70% aqueous perchloric acid solution is considered to be a strong acid or superacid (stronger than sulfuric and nitric acids) but is not necessarily a strong oxidizing agent. However, as the concentration and temperature of the perchloric acid are increased, so does its oxidizing power. Hot concentrated solutions of perchloric acid can be extremely dangerous (explosion hazard, fire hazard). Perchloric acid can react violently at room temperature with cellulose materials (e.g., wood, paper), oxidizable organic materials (e.g., alcohols, ketones, and aldehydes), and strong basic materials, resulting in an increased risk of fire and/or explosion. When heated, perchloric acid can decompose and generate toxic and corrosive fumes. Many types of metals can react with perchloric acid to produce flammable/explosive gases. Because perchloric acid becomes increasingly unstable (volatile) with increasing concentration, it is not marketed at concentrations greater than 72% v/v in water. It may explode by shock or concussion as an anhydrous material (e.g., if a spill of 70% perchloric acid is allowed to dehydrate). Mixtures of perchlorates with oxidizable substances are often explosive. Perchloric acid is attracted to water and disassociates readily to yield the perchlorate anion. The toxicity of perchloric acid comes from the toxicity of the perchlorate anion.
The potential danger of working with perchloric acid is sadly illustrated in a workplace tragedy. A mixture of perchloric acid and acetic anhydride exploded in a Los Angeles factory in 1947, killing 15, injuring 400, and causing $2 million in damages.

Chemical properties

Perchloric acid, HCIO4, also known as Fraude's reagent,is a colorless, fuming,hygroscopic liquid that boils at 16°C(61OF). It is a strong oxidizer and is soluble in water. Cold dilute perchloric acid reacts with metals such as zinc and iron to yield hydrogen gas and the metallic perchlorate. Perchloric acid is used in electrolytic baths, electropolishing, explosives, analytical chemistry, and medicine.

Chemical properties

Perchloric Acid is a colorless, fuming, oily liquid, miscible with H2O, volatile under diminished pressure. A maximum constant-boiling solution (203 °C, 760 millimeters Hg) results when the concentration of HClO4 reaches 73% in H2O. Cold dilute perchloric acid reacts with such metals as zinc and iron, yielding hydrogen gas and the corresponding perchlorate in solution. It is stable from the point of view of oxidation and reduction (except that iodine is oxidized to periodic acid, with liberation of chlorine, ferrous salt solutions to ferric, titanous salt solutions to titanic). Concentrated hot perchloric acid, on the other hand, is a powerful oxidizing agent, exploding violently in contact with charcoal, paper, or alcohol; causes serious wounds in contact with the skin. Prepared by distilling ammonium perchlorate with HNO3 and HCl.

Physical properties

Perchloric acid, HClO4, is a colorless liquid soluble in water. It is a strong acid comparable in strength to sulfuric and nitric acids. It is useful for preparing perchlorate salts, but it is also dangerously corrosive and readily forms explosive mixtures. Perchloric acid is produced by the treatment of sodium perchlorate with sulfuric acid and by the electrochemical oxidation of aqueous chlorine.

The Uses of PERCHLORIC ACID

Perchloric acid salts are used as explosivesand in metal plating. They are also used as anoxidizer and as a reagent in chemical analysis. These salts are produced by distillingpotassium chlorate with concentrated H2SO4under reduced pressure..

The Uses of PERCHLORIC ACID

The acid in analytical chemistry as an oxidizer and for separation of potassium from sodium. Its salts for explosives and for plating of metals.

The Uses of PERCHLORIC ACID

Perchloric acid is used in the preparation of perchlorate salts (e.g., ammonium perchlorate, a solid oxidizer in rocket propellants). It is also used industrially for electropolishing and etching of various metals (e.g., aluminum, molybdenum). Perchloric acid is used in a process to separate potassium from sodium, as well as in many other laboratory tests and industrial processes (e.g., as an eluant in ion-exchange chromatography). Uses for the salts of perchloric acid include the manufacture of explosives and plating of metals. Perchlorate is also present in bleach and fertilizers.

Definition

ChEBI: Perchloric acid is a chlorine oxoacid. It is a conjugate acid of a perchlorate.

General Description

A clear colorless odorless aqueous solution. Corrosive to metals and tissue. Closed containers may rupture violently under prolonged exposure to heat.

Air & Water Reactions

Water soluble with heat generation.

Reactivity Profile

PERCHLORIC ACID is a solution of a strong oxidizing acid. May react vigorously or deflagrate when mixed with oxidizable material [Merck]. This includes (but is not limited to) alcohols, amines, boranes, dicyanogen, hydrazines, hydrocarbons, hydrogen, nitroalkanes, powdered metals, silanes, or thiols [Bretherick 1979. p.174]. Perchloric acid ignites on contact with sulfinyl chloride. (Bailar, 1973, Vol. 2, 1442).

Health Hazard

Inhalation, ingestion or contact (skin, eyes) with vapors or substance may cause severe injury, burns or death. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause pollution.

Health Hazard

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

Health Hazard

Concentrated perchloric acid is a highly corrosive substance that can produce burns on skin contact. It is also a severe irritant tothe eyes and mucous membranes. The toxicity of this compound is moderate. The toxicsymptoms from ingestion include excitement, decrease in body temperature, and distress in breathing. An oral LD50 value in dogsis reported as 400 mg/kg (NIOSH 1986)..

Fire Hazard

These substances will accelerate burning when involved in a fire. Some may decompose explosively when heated or involved in a fire. May explode from heat or contamination. Some will react explosively with hydrocarbons (fuels). May ignite combustibles (wood, paper, oil, clothing, etc.). Containers may explode when heated. Runoff may create fire or explosion hazard.

Fire Hazard

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.

Flammability and Explosibility

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.

Safety Profile

Poison by ingestion and subcutaneous routes. A severe irritant to the eyes, skin, and mucous membranes. A powerful oxidlzer. A severe explosion hazard; the anhydrous form can explode spontaneously. Potentially explosive reaction with acetic anhydride + acetic acid + organic materials, acetic anhydride + organic materials + transition metals (e.g., chromium, iron, nickel), acetonitrile, alcohols, azo dyes + orthoperiodic acid, bis (2-hydroxyethyl) terephthalate + ethanol + ethylene glycol, bismuth (above 1 10°C), antimony (above llO°C), carbon, charcoal + chromium trioxide + heat, cellulose and derivatives + heat, combustible materials, dehydrating agents, dichloromethane + dimethylsulfoxide, dethyl ether, dimethyl ether, dloxane + nitric acid + heat, fecal material + nitric acid, graphitic carbon + nitric acid, hydrofluoric acid + structural materials, ironQI) sulfate, nitric acid + organic matter + heat, nitric acid + pyridme + sulfuric acid, nitrogenous epoxides, organic materials + sodmm hydrogen carbonate (above 2OO0C), phenyl acetylene (at -78OC), sodmm phosphinate + heat, sulfuric acid + organic materials, sulfur trioxide. Reacts to form explosive products with anline + formaldehyde, ethylbenzene + thallium triacetate (at 65℃), fluorine (forms fluorine perchlorate), glycerol + lead oxide, hydrogen + heat, hydrogen halides, phosphine, pyridme, sulfoxides. Violent reaction or igmtion with acetic acid, acetic acid + acetic anhydride, acetic anhydride, acetic anhydride + carbon tetrachloride + 2-methyl cyclohexanone, antimony compounds, azo pigments, bis1,2-diaminopropane-cis-dichlorochromium(ⅡI) perchlorate, carbon, 1,3-bis(di-ncyclopentadtenyl iron) -2-propen1 -one, CH3OH, CC4, copper dichromium tetraoxide (at 120℃), DNA, dibutyl sulfoxide, dunethyl sulfoxide, ethylbenzene, glycol ethers, glycols, HNO3, HCl, H2SO4, hypophosphttes, iron sulfate, iodides, ketones, PbO + glycerin, methanol + triglycerides, 2-methylpropene + metal oxides, 2-methyl cyclohexanone, NI3, nitrogenous epoxides, nitrosophenol, operiodlc acid, oleic acid, organophosphorus compounds, paper, PzOj + CHCl3, PzOj, PzZns, sodium iodde + hydroiodic acid, solum phosphtnate, steel, sulfinyl chloride, so3, trichloroethylene, vegetable matter, wood, zinc phosphide. When heated to decomposition it emits toxic fumes of Cl-. See also PERCHLORATES.

Environmental Fate

Perchloric acid, in the presence of moisture, forms the negatively charged perchlorate anion. The largest natural deposit of perchlorate is located in Chile; the origin of the deposit is not known.
Atmospheric perchlorate may be found near the sites where it is manufactured and the locations where it is used. Accidental spills of perchloric acid are another source of airborne perchlorate. Perchlorate has a low vapor pressure and is not found in the atmosphere as such; however, airborne particles are known to be a source of perchlorate. The particles may fall to the soil or be washed to the soil via rain. Soil particles containing perchlorate can migrate in air currents or with surface water or groundwater.
Perchlorate anions are highly mobile in groundwater because of their charged state and because they adsorb to soil particles poorly. Perchlorates in groundwater or surface water are extremely persistent. They are extremely stable under ambient conditions and tend not to react or degrade. Some types of anaerobic bacteria are known to biodegrade perchlorate; however, they are effective only under specific environmental conditions (high levels of organic carbon and low levels of oxygen and nitrate). Groundwater extraction is considered inefficient for the removal of perchlorate.
Plants exposed to perchlorate in the soil moisture can also take up perchlorate; some types of plants are known to concentrate perchlorate.

storage

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.

Purification Methods

The 72% acid is been purified by double distillation from silver oxide under vacuum: this frees the acid from metal contamination. Distillation at atmospheric pressure is dangerous and explosive. The anhydrous acid is obtained by adding gradually 400-500mL of oleum (20% fuming H2SO4) to 100-120mL of 72% HClO4 in a reaction flask cooled in an ice-bath. The pressure is reduced to 1mm (or less), with the reaction mixture at 20-25o. The temperature is gradually raised during 2hours to 85o; the distillate is collected in a receiver cooled in Dry-ice. For further details of the distillation apparatus see Smith [J Am Chem Soc 75 184 1953]. It is HIGHLY EXPLOSIVE; a strong protective screen should be used at all times. [Schmeisser in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 318-320 1963.]

Incompatibilities

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.

Waste Disposal

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.