Xanthoproteic acid is a noncrystallizable yellow substance derived from proteins upon treatment with nitric acid.

Nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

reacts with proteins to form xanthoproteic acid. This reaction is known as the

xanthoproteic reaction The xanthoproteic reaction is a method that can be used to detect a presence of protein soluble in a solution, using concentrated nitric acid. The test gives a positive result in amino acids carrying aromatic groups, especially in the presence of ...

. This test is carried out by adding concentrated nitric acid to the substance being tested, and then heating the mixture. If proteins are present that contains amino acids with aromatic rings, the mixture turns yellow . Upon adding a strong base such as liquid ammonia, the color turns orange . These color changes are caused by nitrated aromatic rings in the protein . The xanthoproteic test is specific for aromatic compounds such as

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

and phenylalanine . Xanthoproteinic acids are also formed when the acid contacts the skin and are a certain giveaway of inadequate care when handling nitric acid . Minor stains are harmless and resolve in a few days . It is a mixture of

nitro compound In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitr ...

s of tyrosine, tryptophan, and phenylalanine such as 2-amino-3-(4-hydroxy-3-nitrophenyl)propionic acid, 2-amino-3-(4-nitroindolyl-3)propionic acid, and others .

References

{{reflist Organic acids

See also

References