TABLE 3.11 Functional Groups in Some Explosive Compounds

Structural Feature

Compound

—C=C—

Acetylenic compound

—C=C-M

Metal acetylide or carbide

—C=C—X

Haloacetylide

 

Diazo compounds

 

Nitroso compounds

 

Nitroalkanes, C-nitro and

polynitroaryl compounds,

polynitroalkyl compounds,

trinitroethyl compounds

C-O-N=O

Acyl or alkyl nitrites

C-O-NO2

Acyl or alkyl nitrates

C-O-O-C

Alkyl or acyl peroxides

 

Alkyl hydroperoxides

 

Dialkyl peroxycarbonates

CNO-M

Metal fulminates or aci-nitro salts, oximates

—N3

Organic azides, acyl azides

Metal azides, metal azide complexes

M(CO)n

Transition metal-carbonyl compounds

—C=N

Metal cyanides, organic nitriles, cyanogen halides

 

SOURCE: Adapted from Bretherick (1990), pp. S20-S22.

light, by the presence of a radical source, and by the peroxide itself. Oxygen adds to the R radical, producing the peroxy radical R—O—O. The chain is propagated when the peroxy radical abstracts a hydrogen atom from R—H. Excluding oxygen by storing potential peroxide-formers under an inert atmosphere (N2 or argon) or under vacuum greatly increases their safe storage lifetime. In some cases, stabilizers or inhibitors (free-radical scavengers that terminate the chain reaction) have been added to the liquid to extend its storage lifetime. Because distillation of the stabilized liquid will remove the stabilizer, the distillate must be stored with care and monitored for peroxide formation.

Note that alkali metals and their amides may form peroxides on their surfaces. Do not apply standard peroxide tests to such materials because they are both water and oxygen reactive!

For purposes of managing the storage of chemicals that can form peroxides upon aging, the three classes given in Table 3.13 provide useful distinctions. As part of its Chemical Hygiene Plan (CHP), an institution should provide guidelines for handling these three classes. For example, if on-site incineration is available, disposal of chemicals in Class III after 3 months might be recommended. Various time limits for disposal of the different classes have been given.

3.D.3.3 Other Oxidizers

Oxidizing agents may react violently when they come into contact with reducing materials, and sometimes with ordinary combustibles. Such oxidizing agents include the halogens, oxyhalogens and organic peroxyhalogens, chromates, and persulfates as well as peroxides. Inorganic peroxides are generally stable. However, they may generate organic peroxides and hydroperoxides in contact with organic compounds, react violently with water (alkali metal peroxides), and form superoxides and ozonides (alkali metal peroxides). Perchloric acid is a powerful oxidizing agent with organic compounds and other reducing agents. Perchlorate salts can be explosive and should be treated as potentially hazardous compounds.

For many years, sulfuric acid—dichromate mixtures were used to clean glassware (a sulfuric acid—peroxy-disulfate solution is now recommended because disposal of chromate is a problem). Confusion about cleaning baths has led to explosions on mixing potas-

TABLE 3.12 Types of Compounds Known to Autooxidize to Form Peroxides

• Aldehydes

• Ethers, especially cyclic ethers and those containing primary and secondary alkyl groups (never distill an ether before it has been shown to be free of peroxide)

• Compounds containing benzylic hydrogens

• Compounds containing allylic hydrogens (C = C—CH), including most alkenes; vinyl and vinylidene compounds

• Compounds containing a tertiary C—H group (e.g., decalin and 2,5-dimethylhexane)



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