233Nitrite in Biochemistry
Sodium nitrite is used for the curing of meat because it prevents bacterial growth and, in a reaction
with the meat's myoglobin, gives the product a desirable dark red color. Because of the relatively
high toxicity of nitrite (the lethal dose in humans is about 22 milligrams per kilogram of body weight),
the maximum allowed nitrite concentration in meat products is 200 ppm.
Under certain conditions - especially during cooking - nitrites in meat can react with degradation
products of amino acids, forming nitrosamines, which are known carcinogens.
Nitrite is detected and analyzed by the Griess Reaction, involving the formation of a deep red-
colored azo dye upon treatment of a NO 2 −-containing sample with sulfanilic acid and naphthyl-1-
amine in the presence of acid. Nitrite can be reduced to nitric oxide or ammonia by many species
of bacteria.
Under hypoxic conditions, nitrite may release nitric oxide, which causes potent vasodilation.
Several mechanisms for nitrite conversion to NO have been described, including enzymatic
reduction by xanthine oxidoreductase, nitrite reductase, and NO synthase (NOS), as well as
nonenzymatic acidic disproportionation reactions.
Organic Nitrites and Nitro Compounds
A Nitrite EsterAromatic Nitration
In organic chemistry, nitrites are esters of nitrous acid and contain the nitrosoxy functional group.
Nitro compounds contain the C-NO 2 group. Nitrites have the general formula RONO, where R is
an aryl or alkyl group.
Nitrobenzene is a simple example of a nitro compound. In aromatic nitration reactions a C-H bond
is broken, leaving the two electrons on the carbon atom. These two electrons are added to the
nitronium ion, reducing it to nitrite.