Chemical Incompatibilities

The risks associated with chemical incompatibility must be managed in any experiment or reaction system. In general, chemicals react to form compounds with the generation or consumption of energy. The dangers inherent with the mixing of incompatible chemicals occur when the products or by-products of the reaction are toxic or hazardous, or when the energy generated is great enough to be destructive. Some of the possible hazardous outcomes that may accompany a chemical reaction are:

Hazard	Example
generation of heat	acid and water
fire hydrogen	sulfide and calcium hypochlorite
explosion	picric acid and sodium hydroxide
toxic gas production	sulfuric acid and plastic
formation of product more toxic than reactants	chlorine and ammonia
flammable gas production	acid and metal
forms of shock sensitive product	ammonia and iodine
pressurization of closed vessel	fire extinguisher
solubilization of toxic substances	hydrochloric acid and chromium
dispersal of toxic dusts and mists	phosphorus trichloride and water
violent polymerization	ammonia and acrylonitrile

Mixing of incompatible chemicals can occur one of two ways - accidentally or intentionally. In the first case, great care must be taken when chemicals are stored (see Safe Chemical Storage) to avoid the potential of accidental mixing. In the second scenario, careful analysis of the properties of the starting products and the presumed characteristics of the products must be conducted to reduce the potential of an explosive or dangerous chemical reaction. Specific examples of explosive combinations are given in the list below.

Explosive Combinations of Common Chemicals

acetone + chloroform in the presence of a base
acetylene + copper, silver, mercury and their salts
ammonia (gas or aqueous) + Cl₂, I₂ or Br₂
carbon disulfide + sodium azide
chlorine + alcohol
carbon tetrachloride or chloroform + powdered Al or Mg
diethyl ether + chlorine
dimethyl sulfoxide + an acyl halide, SOCl₂ or POCl₃
dimethyl sulfoxide + CrO₃
ethanol + calcium hypochlorite
ethanol + silver nitrate
nitric acid + acetic anhydride or acetic acid
picric acid + heavy metal salt, such as Pb, Hg or Ag
silver oxide + ammonia + ethanol
sodium + chlorinated hydrocarbon
sodium hypochlorite + amine

"Hypergolics" are chemicals that ignite upon mixing with an incompatible material. These mixtures create heat when mixed which is sufficient to cause ignition. No ignition source is necessary. Storage and use of these materials must be thought out carefully. Examples of these groups are provided.

perchloric acid + magnesium powder = fire
acetone + 85%nitric acid = fire
nitric acid + phenol = fire
concentrated nitric acid + triethylamine = fire
red fuming nitric acid + aromatic amines = fire
divinyl ether + 96% nitric acid + 5% sulfuric acid = fire
90% solution of potassium permanganate in red fuming nitric acid + alcohols = fire
solid potassium permanganate + ketones, esters, alcohols = fire

Created and maintained by Nancy Magnussen
last revised 1 Dec 1997
nancy@isc.tamu.edu