Chromotropic acid

Chemical reagent used in colorimetric chemical analysis From Wikipedia, the free encyclopedia

Chromotropic acid is a chemical compound with the formula (HO)2C10H4(SO3H)2. Its name is derived from the two ancient Greek words χρωμός (chromos, color) and τροπέιν or τρέπω (verb: tropein, trepo, changing, turning), meaning it changes of color when reacting with some other compounds. This property is put to use in analytical chemistry for the colorimetric assay of various compounds such as formaldehyde, nitrate anions and even some herbicides.

Quick facts Names, Identifiers ...
Chromotropic acid
Skeletal formula
Skeletal formula
Ball-and-stick model
Ball-and-stick model
Names
Preferred IUPAC name
4,5-Dihydroxynaphthalene-2,7-disulfonic acid[1]
Identifiers
3D model (JSmol)
1827764
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.005.194 Edit this at Wikidata
KEGG
UNII
  • InChI=1S/C10H8O8S2/c11-8-3-6(19(13,14)15)1-5-2-7(20(16,17)18)4-9(12)10(5)8/h1-4,11-12H,(H,13,14,15)(H,16,17,18) checkY
    Key: HLVXFWDLRHCZEI-UHFFFAOYSA-N checkY
  • InChI=1/C10H8O8S2/c11-8-3-6(19(13,14)15)1-5-2-7(20(16,17)18)4-9(12)10(5)8/h1-4,11-12H,(H,13,14,15)(H,16,17,18)
    Key: HLVXFWDLRHCZEI-UHFFFAOYAH
  • O=S(=O)(O)c1cc(O)c2c(c1)cc(cc2O)S(=O)(=O)O
Properties
C10H8O8S2
Molar mass 320.29 g·mol−1
Acidity (pKa) 5.36, 15.6[2]
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chromotropic acid is used for testing for the presence of formaldehyde.[3][4] The usefulness of this reagent in quantitative determination is the formation of a red coloration (peaking at 580 nm wavelength) when chromotropic acid in 50% sulfuric acid reacts with formaldehyde. The coloration is specific to this aldehyde and is not produced from other organic species such as other aldehydes, ketones and carboxylic acids. The NIOSH Formaldehyde method #3500 is the reference analytical standard that uses chromotropic acid.

Chromotropic acid is also used for the direct spectrophotometric determination of nitrate anions according to a method developed by West and Lyles in 1960.[5]

It can also be used as a reagent for the quantitative determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D).[6]

References

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