In
chemistry,
pyrophosphate is a
phosphorus oxyanion. Compounds such as
salts and
esters are also called pyrophosphates. The group is also called
diphosphate or
dipolyphosphate, although this should not be confused with two
phosphates. As a
food additive, diphosphates are known as
E450. A number of hydrogen pyrophosphates also exist, such as Na
2H
2P
2O
7, as well as the normal pyrophosphates.