Specific Chemicals

Organic peroxides are a class of compounds that have unusual stability problems that make them among the most hazardous substances handled in laboratories. As a class, organic peroxides are considered to be powerful explosives. They are sensitive to heat, friction, impact, and light as well as to strong oxidizing and reducing agents. All organic peroxides are flammable. Types of compounds known to form peroxides are listed in Table

Table 2: Common compounds that form peroxides during storage.

Ethyl ether Isopropyl ether
Tetrahydrofuran Divinyl acetylene
Dioxane Vinylidene chloride
Acetal Potassium metal
Methy i-butyl ketone Sodium amide
Ethelyene glycol dimethl ether (glyme) Butadine
Vinyl ethers Tetrafluoroethylene
Dicyclopentadiene Vinyl acetylene
Methyl acetylene Vinyl acetate
Cumene Vinyl chloride
Tetrahydronaphthalene Vinyl pyridine
Cyclohexene Chlorobutadiene
Methylcyclopentane Butandiene

All peroxidizable materials should be stored in a cool place, away from light. Metal cans are preferable; do not store ethers in ground stoppered bottles. Ethers and peroxidizable materials should be ordered only in small quantities, and should be dated upon receipt and when opened. They should be discarded within a year after receipt if unopened, or within months of opening. Ethers should always be handled in a hood to assure proper ventilation. This will protect individuals from inhaling the vapors and prevent accumulation of explosive concentrations of the vapor. For methods of peroxide detection and removal, consult the DESHS.
Certain combinations of chemicals are particularly dangerous and should be avoided. Table  indicates the compatibility of various chemicals.

Table 3: Examples of incompatible chemicals

Chemical Is Incompatible With
Hydrofluoric acid (anhydrous) Ammonia (aqueous or anhydrous)
Hydrogen peroxide Copper, chromium, iron, most metals or their salts, alkochols, acetone, organic materials, aniline, nitromethane, combustible materials
Hydrogen sulfide Fuming nitric acid, oxidizing gases
Hypochlorites Acids, activated carbon
Iodine Acetylene, ammonia (aqueous or anhydrous), hydrogen
Mercury Acetylene, fulminic acid, ammonia
Nitrates Acids
Nitroparaffins Inorganic bases, amines
Oxalic acid Silver, mercury
Oxygen Oils, grease, hydrogen, flammable liquids, solids, or gases
Perchloric acid Acetic anhydride, bismuth and its alloys, alcohol, paper, wood, grease, oils
Peroxides, organic Acids (organic or mineral), avoid friction, store cold
Phosphorus (white) Air, oxygen, alkalis, reducing agents
Potassium Carbon tetrachloride
Potassium chlorate Sulfuric and other acids
Potassium perchlorate (see also chlorates) Sulfuric and other acids
Potassium permanganate Glycerol, ethylene glycol, benzaldehyde, sulfuric acid
Selenides Reducing agents
Silver Acetylene, oxalic acid, tartartic acid, ammonium compounds, fulminic acid
Sodium Carbon tetrachloride, carbon dioxide, water
Sodium nitrate Ammonium nitrate and other ammonium salts
Sodium peroxide Ethyl or methyl alcohol, glacial acetic acid, acetic anhydride, benzaldehyde, carbon disulfide, glycerin, ethylene glycol, ethyl acetate, methyl acetate, furfural
Sulfides Acids
Sulfuric acid Potassium chlorate, potassium perchlorate, potassium permaganate (similar compounds of light metals, such as sodium, lithium)
Tellurides Reducing agents

Other chemical hazards that may result explosions or fires include: 

Acetylenic compounds
are explosive in mixture 2.5-80% with air. At pressures of 2 or more atmospheres, acetylene (C2H2) subjected to electrical discharge or high temperature decomposes with explosive violence. Dry acetylides detonate on receiving the slightest shock. 

Aluminum chloride
(AlCl3) should be considered a potentially dangerous material. If moisture is present, there may be sufficient decomposition to build up a considerable pressure of HCl.

Ammonia
reacts with iodine to form nitrogen triiodide, which is explosive, and hypochlorites to form chlorine.

Benzoyl peroxide
when dry, is easily ignited and sensitive to shock. It decomposes spontaneously at temperatures above 50°C

Carbon disulfide
is both very toxic and very flammable; mixed with air, its vapors can be ignited by a steam bath or pipe, a hot plate, or a glowing light bulb.

Chlorine
may react violently with hydrogen or with hydrocarbons when exposed to sunlight.

Chromium trioxide-pyridine
complex (CrO3-C5H5N) may explode if the CrO3 concentration is too high. The complex should be prepared by addition of CrO3 to excess C5H5N.

Diazomethane
(CH2N2) and related compounds should be treated with extreme caution. They are very toxic, and the pure gases and liquids explode readily. Solutions in ether are safer from this standpoint.

Dimethyl sulfoxide
(CH3)2SO] decomposes violently on contact with a wide variety of active halogen compounds. Explosions from contact with active metal hydrides have been reported. Its toxicity is still unknown, but it does penetrate and carry dissolved substances through the skin membrane.

Dry ice
should not be kept in a container that is not designed to withstand pressure. Containers of other substances stored over dry ice for extended periods generally absorb carbon dioxide (CO2) unless they have been sealed with care. When such containers are removed from storage, and allowed to come rapidly to room temperature, the CO2 may develop sufficient pressure to burst the container with explosive violence. On removal such containers from storage, the stopper should be loosened, or the container itself should be wrapped in towels and kept behind a shield. Dry ice can produce serious burns.

Drying agents
“Ascarite'' should not be mixed with phosphorus pentoxide (P2O5) because the mixture may explode if it is warmed with a trace of water. Because the cobalt salts used as moisture indicators in some drying agents may be extracted by some organic solvents, the use of these drying agents should be restricted to gases.

Diethyl, diisopropyl, and other ethers
sometimes explode during heating or refluxing because of the presence of peroxides. Ferrous salts or sodium bisulfite can be used to decompose the peroxides, and passage over basic active alumina will remove most of the peroxidic material. In general, however, old samples of ethers should be discarded.

Ethylene oxide
(C2H4O) has been known to explode when heated in a closed vessel. Experiments using ethylene oxide under pressure should be carried out behind suitable barricades.

Halogenated Compounds
Chloroform (CHCl3), carbon tetrachloride (CCl4), and other halogenated solvents should not be dried with sodium, potassium, or other active metal; violent explosions are usually the result of such attempts. Many halogenated compounds are toxic.

Hydrogen peroxide
(H202) Stronger than three percent can be dangerous; in contact with the skin, it may cause severe burns. Thirty percent H2O2 may decompose violently if contaminated with iron, copper, chromium, or other metals or their salts.

Liquid-nitrogen-cooled traps
open to the atmosphere rapidly condense liquid from the air. Then, when the coolant is removed, an explosive pressure buildup occurs, usually with enough force to shatter glass equipment. Hence, only sealed or evacuated equipment should be so cooled.

Lithium aluminum hydride
(LiAlH4) should not be used to dry inethyl ethers or tetrahydrofuran; fires from this are very common. The products of its reaction with CO2 have been reported to be explosive. Carbon dioxide or bicarbonate extinguishers should not be used against LiAlH4 fires, which should be smothered with sand or some other inert substance.

Ozone
(O3) is a highly reactive and toxic gas. It is formed by the action of ultraviolet light on oxygen (air) and, therefore, certain ultraviolet sources may require venting to an exhaust hood.
Palladium or platinum on carbon, platinum oxide, Raney nickel, and other catalysts should be filtered from catalytic hydrogenation reaction mixtures carefully. The recovered catalyst is usually saturated with hydrogen and highly reactive and, thus, will inflame spontaneously to exposure to air. Particularly in large-scale reactions, the filter cake should not be allowed to become dry. The funnel containing the still moist catalyst filter cake should be put into water bath immediately after completion of the filtration. Another hazard in working with such catalysts is the danger of explosion if an additional catalyst is added to a flask in which hydrogen is present.

Parr bombs
used for hydrogenations have been known to explode. They should be handled with care behind shields, and the operator should wear goggles.

Perchlorates
The use of perchlorates should be avoided wherever possible. Perchlorates should not be used as drying agents if there is possibility of contact with organic compounds in proximity to a dehydrating acid strong enough to concentrate the perchloric acid (HClO4) more than 70% strength (e.g., in a drying train that has a bubble counter containing sulfuric acid). Safer drying agents should be used. Seventy percent HClO4 can be boiled safely approximately 200°C, but contact of the boiling undiluted acid or the hot vapor with organic matter, or even easily oxidized inorganic matter (such as compounds of trivalent antimony), will lead to serious explosions. Oxidizable substances must never be allowed to contact HClO4. Beaker tongs, rather than rubber gloves should be used when handling fuming HClO4. Perchloric acid evaporations should be carried out only in fume hoods designed specifically for this purpose.

Permanganates
are explosive when treated with sulfuric acid. When both compounds are used in an absorption train, an empty trap should be placed between them.

Peroxides
(inorganic)-when mixed combustible materials, barium, sodium, potassium peroxides form explosives that ignite easily.

Phosphorus
(P) (red and white) forms explosive mixtures with oxidizing agents. White P should be stored under water because it is spontaneously flammable in air. The reaction of P with aqueous hydroxides gives phosphine, which may ignite spontaneously in air or explode.

Phosphorus trichloride
(PCl3) reacts with water to form phosphoric acid, which decomposes on heating to form phosphine, which may ignite spontaneously or explode. Care should be taken in opening containers of PCl3, and samples that have been exposed to moisture should not be heated without adequate shielding to protect the operator.

Potassium
(K) is in general more reactive than sodium. It ignites quickly on exposure to humid air and, therefore, should be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene (see Sodium).

Residues from vacuum distillations
(for example, ethyl palmitate) have been known to explode when the still was vented to the air before the residue was cool. Such explosions can be avoided by venting the still pot with nitrogen, by cooling it before venting, or by restoring the pressure slowly.

Sodium
(Na) should be stored in a closed container under kerosene, toluene, or mineral oil. Scraps of Na or K should be destroyed by reaction with n-butyl alcohol. Contact with water should be avoided because Na reacts violently with water to form H2 with evolution of sufficient heat to cause ignition. Neither carbon dioxide nor bicarbonate fire extinguishers should be used on alkali metal fires.

Sodium azide
may react violently with benzoyl chloride plus potassium hydroxide, bromine, carbon disulfide, chromium oxychloride, copper, lead, nitric acid, dimethylsulfate and ibromomalonitrile. It is especially important that sodium azide not be allowed to come in contact with heavy metals (for example, by being poured into a lead or copper drain) or their salts; heavy metal azides detonate with notorious ease.

Sulfuric acid
(H2SO4) should be avoided, if possible, as a drying agent in desiccators. If it must be used, glass beads should be placed in it to help prevent splashing when the desiccator is moved. The use of H2SO4 in melting point baths should be avoided (silicone oil should be used). To dilute H2SO4, add the acid slowly to cold water.

Trichloroethylene
(Cl2CCHCl) reacts under a variety of conditions with potassium or sodium hydroxide to form dichloroacetylene, which ignites spontaneously in air and detonates readily even at dry-ice temperatures. The compound itself is highly carcinogenic, and precautions should be taken decreasing solvent.