Organic
nitro compounds require special attention to their reaction conditions as they
exothermically decompose at high temperatures. Various process conditions and
impurities can contribute to the dangerous decomposition of nitro compounds.
The most common method of producing organic nitro compounds is
to inject nitric acid into a vessel containing the organic reactant mixed with sulfuric
acid. In this manner, the nitric acid is used as the controlling reactant. The
reaction mixture will contain an organic and an acid liquid phase. The sulfuric acid
has the following effects:
1. Dilution of reaction mixture to help control temperature
2. Removal of water produced by the reaction
3. Provides the necessary solubility for the reaction to proceed
Some additional solvents may be added to improve rates of separations
later in the processing. These solvents may include acetic acid, benzene, and
toluene.
The following process deviations should be avoided in the processing of
organic nitro compounds:
1. Increased reactor temperature may lead to formation of unstable polynitro
compounds or initiate decomposition reactions
2. Variations in sulfuric or nitric acid concentrations may lead to unwanted,
unstable nitro compounds
3. Back-flow of organic phase into the acid feed pipes or back-flow of acid into the
organic feed pipes
A Specific Accident p-chloronitrobenzene was being hydrolyzed with 50% NaOH to produce
p-nitrophenol in a batch reactor. The operator noticed a low conversion rate and
decided to introduce a second charge of NaOH into the vessel. Under alkaline
conditions, the decomposition of sodium p-nitrophenate proceeds autocatalytically.
During reactor cool down, the reactor exploded due to the crystallization of sodium
p-nitrophenate on the reactor walls.
