lyst that has been used in the reaction with special care because it can be a source of spontaneous ignition upon contact with air.

(Also see section 5.C.)

5.G.6 Reactive or Explosive Materials Requiring Special Attention

The following list is not intended to be all-inclusive. Further guidance on reactive and explosive materials should be sought from pertinent sections of this book (see Chapter 3, sections 3.D.2 and 3.D.3) and other sources of information (note sources included in Chapter 3, section 3.B).

Acetylenic compounds can be explosive in mixtures of 2.5 to 80% with air. At pressures of 2 or more atmospheres, acetylene (C2H2) subjected to an electrical discharge or high temperature decomposes with explosive violence. Dry acetylides detonate on receiving the slightest shock. Acetylene must be handled in acetone solution and never stored alone in a cylinder.

Aluminum chloride (AlCl3) should be considered a potentially dangerous material. If moisture is present, there may be sufficient decomposition to form hydrogen chloride (HC1) and build up considerable pressure. If a bottle is to be opened after long storage, it should first be completely enclosed in a heavy towel.

Ammonia (NH3) reacts with iodine to give nitrogen triiodide, which detonates on touch. Ammonia reacts with hypochlorites to give chlorine. Mixtures of NH3 and organic halides sometimes react violently when heated under pressure. Ammonia is combustible. Inhalation of concentrated fumes can be fatal.

Azides, both organic and inorganic, and some azo compounds can be heat- and shock-sensitive. Azides such as sodium azide can displace halide from chlorinated hydrocarbons such as dichloromethane to form highly explosive organic polyazides; this substitution reaction is facilitated in solvents such as dimethyl sulfoxide (DMSO).

Carbon disulfide (CS2) 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 light bulb.

Chlorine (C12) is toxic and may react violently with hydrogen (H2) 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 diazo compounds should be treated with extreme caution. They are very toxic, and the pure gases and liquids explode readily even from contact with sharp edges of glass. Solutions in ether are safer from this standpoint. An ether solution of diazomethane is rendered harmless by drop wise addition of acetic acid.

Diethyl, diisopropyl, and other ethers, including tetrahydrofuran and 1,4-dioxane and particularly the branched-chain type of ethers, sometimes explode during heating or refluxing because the presence of peroxides has developed from air oxidation. Ferrous salts or sodium bisulfite can be used to decompose these peroxides, and passage over basic active alumina can remove most of the peroxidic material. In general, however, old samples of ethers should be disposed of after testing, following procedures for disposal of peroxides (see Chapter 7, section 7.D.2.5).

Dimethyl sulfoxide (DMSO), (CH3)2SO, decomposes violently on contact with a wide variety of active halogen compounds, such as acyl chlorides. Explosions from contact with active metal hydrides have been reported. Dimethyl sulfoxide does penetrate and carry dissolved substances through the skin membrane.

Dry benzoyl peroxide (C6H5CO2)2 is easily ignited and sensitive to shock. It decomposes spontaneously at temperatures above 50 °C. It is reported to be desensitized by addition of 20% water.

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 of 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, as is also true for all types of dry-ice-cooled cooling baths.

Drying agents, such as Ascarite® (sodium hydroxide-coated silica), 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 drying gases.

Dusts that are suspensions of oxidizable particles (e.g., magnesium powder, zinc dust, carbon powder, and flowers of sulfur) in the air can constitute powerful explosive mixtures. These materials should be used with adequate ventilation and should not be exposed to ignition sources. When finely divided, some solids, including zirconium, titanium, Raney nickel, lead

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