Perchlorates and Chlorates
Inorganic chlorates are strong oxidizer which means they aid in the combustion of other material. Because of the increased explosion potential, extreme caution must be used when working with perchloric acid and inorganic perchlorates.
The following information is taken from Appendix F of the University of California San Francisco Chemical Safety Manual. Appendix F is titled Safe Handling Guide for Corrosive Chemicals and the section below is Safe Handling Guide for Perchloric Acid and Perchlorates. Specific information such as phone numbers has been changed to reflect UAF numbers. Also, where UAF has additional protocols, information is given in italics. A link to the entire appendix is listed under the Helpful Links section of this module.
Perchloric acid is a colorless, fuming, oily liquid. When cold, its properties are that of a strong acid; but when hot, the concentrated acid acts as a strong oxidizing agent. Aqueous perchloric acid can cause violent explosions if misused, or when used in concentrations greater than the normal commercial strength of 72%. Anhydrous perchloric acid is unstable at room temperatures and ultimately decomposes spontaneously with violent explosion. Contact with oxidizable material can cause immediate explosion.
Each perchlorate or perchlorate system must be separately evaluated as many are extremely sensitive. Organic solutions containing perchlorate salts are capable of violent explosions during evaporation or distillation operations. Small amounts of unstable organic perchlorates are formed which are less volatile than the solute being removed. Near the end of the operation, the temperature rises because of these less volatile components. The higher temperature is enough to detonate the concentrated perchlorate residue. Whenever possible, an excess of water should be present to prevent the accumulation and to slow the temperature rise. Distillation or evaporation of organic-perchlorate mixtures should be halted with enough heel (residue) to keep residues diluted. Shielding should be used between the apparatus and laboratory personnel in addition to wearing personal protective equipment.
Perchlorate fumes and dusts are irritating, and the acid can cause severe burns to the eyes, nose, and throat. The literature for more than a century reveals descriptions of explosions in laboratories using perchloric acid. The accidents are usually very severe, with the primary cause being contact of the acid with organic material, or the accidental formation of the anhydrous acid. There is an extreme hazard encountered when strong reducing agents come into contact with concentrated (72%) perchloric acid.
A water spray can be used to extinguish small fires and cool fire-exposed containers. Water is also the best preventative measure against the occurrence of such fires. However if more than a small, contained fire is involved, vacate the area and notify the police. (UAF policy is that students and employees evacuate the area and call 911. The fire department can also be reached by activating a pull down station located near the exits of nearly every building. Faculty, staff, and students are not encouraged to fight a fire).
Perchloric acid should not be purchased, stored, or handled until the potential user is familiar with the hazards and has read the manufacturer's SDS and this module.
Do not store perchloric acid near or in contact with combustible materials such as cotton, wood, excelsior, paper, burlap, rags, grease, oil, or organic compounds. Perchloric acid must be stored separately in a deep glass tray with sufficient capacity to hold the entire contents in case of breakage. Storage should be within a fume hood designated solely for perchloric acid use. The bottle and tray should be rinsed daily and after each use. All glass apparatus used should also be rinsed thoroughly. If any discoloration of the liquid is noted, the acid should be discarded. Submit an online Hazardous Waste Pickup Request. Go learn how or call 474-5617 or 474-5197.
The use of perchloric acid should be limited as much as practicable and the quantity on hand should not exceed one 450g (1 lb) bottle. Order only 60% solutions; remember that the vaporization of perchloric acid in a chemical fume hood is prohibited unless it has water wash-down capability. Such hoods are designed to preclude the formation of explosive compounds.
Glass hoods (fume eradicator with or without a reflux head or with a dropping funnel) can sometimes be used to effectively control fumes which are generated by perchloric acid digestion methods. These glass hoods, which are intended as temporary control measures for short term procedures only, are commercially available from laboratory supply companies. You must obtain permission from EHSRM prior to the purchase of such hoods.
The glass surface tends to discourage the buildup of perchlorates. However, the equipment should be thoroughly rinsed and cleaned routinely after use. Change the scrubbing solution (sodium hydroxide) after each use, since saturation of the solvent may occur and cause a carryover of toxic materials into the sewage system (this is to be avoided).
If a fume hood is suspected of having perchloric acid contamination, call EHSRM at 474-5413 and request a survey of the suspected hood. The hood should also be surveyed for the presence of perchlorates prior to maintenance work. EHSRM may check suspected surfaces with a solution of diphenylamine sulfate (1 gram diphenylamine in 100 ml of 1 to 1 H 2 SO 4). The liquid turns black upon contact with a perchlorate. The solution also reacts with nitrates by turning blue. An alternative test for perchlorates uses a solution of methylene blue in methanol. In the event of a spill, contact EHSRM if assistance is needed for cleanup. Otherwise, spills should also be reported to EHSRM for verification that a clean-up has been properly completed and that no perchlorate hazard exists.
- Order 60% perchloric acid solutions or less.
- Wear personal protective clothing and eye wear.
- Transfer acid over a sink or deep glass tray to catch spills and afford a ready means of disposal.
- When conducting perchloric acid procedures involving wet combustion, first treat the sample with nitric acid to destroy easily oxidizable matter.
- Procedures involving heating of the perchloric acid must be conducted in an EHSRM approved perchloric acid hood.
- Do not store any organic materials in the perchloric acid hood.
- Do not allow perchloric acid to come in contact with strong dehydrating agents (e.g. fuming sulfuric acid, anhydrous phosphorus pentoxide).
- Standard analytical procedures from authoritative analytical texts should be followed when working with perchloric acid.
- Perchloric Acid (Greater than 60%): The following additional practices are required.
- Only experienced lab workers who are familiar with the literature should handle concentrated perchloric acid.
- A second person should be informed of the intended use of the acid and be in the same room with the research worker (buddy system).
The hazards of breakage due to thermal or mechanical shock are sufficient to warrant quartz apparatus; especially, if it is necessary to chill from boiling. Glass, Teflon TM, and Duriron TM can be used with perchloric acid. "O" rings and seals made of one of the fluorocarbons such as "Viton TM" are acceptable. For heat transfer or lubrication "Fluorolube TM" has been used. Fume hoods should be constructed of stone, PVC, or transite.
Pneumatically driven stirrers, as opposed to the electric motor type, should be used to minimize the fire hazard.
Hot plates (electric), electrically or steam heated sand baths, or a steam bath are recommended for heating perchloric acid. Direct flame heating or an oil bath should never be used.
Perchloric acid spilled on the lab bench or floor presents a definite hazard. Do not mop or soak up the acid spill with dry combustibles. First, neutralize the spill with soda ash and flood with large amount of water. Then, soak up with rags or paper towels. Limit the flooded area by using inert sand around the spill. Keep contaminated rags and paper towels wet to prevent combustion upon drying. Discard into a plastic bag, seal, and place in a flammable-waste disposal can, not in the ordinary trash.
Clean the spill only if it is small and the user has the appropriate cleaning materials and personal protective equipment (PPE) to handle the spill. If it is large spill, or if the correct type of materials are not available, or if the user is not trained with the cleanup procedures, please call EHSRM at 474-5617 or 474-6771.