2-Aminophenol

2-Aminophenol is an organic compound with the formula C6H7NO. Along with its isomer 4-aminophenol, it is an amphoteric molecule and a reducing agent. It is a useful reagent for the synthesis of dyes and heterocyclic compounds.[3] Reflecting its slight hydrophilic character, white powder is moderately soluble in alcohols and can be recrystallized from hot water.

2-Aminophenol
Space filling model of 2-aminophenol
Ball-and-stick model of 2-aminophenol
Names
Preferred IUPAC name
2-Aminophenol [1]
Other names
o-Aminophenol
ortho-Aminophenol
2-Hydroxyaniline
2-Amino-1-hydroxybenzene
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.002.211
EC Number
  • 202-431-1
KEGG
RTECS number
  • SJ4950000
UNII
UN number 2512
Properties
C6H7NO
Molar mass 109.13 g/mol
Appearance White orthorhombic pyramidal needles
Density 1.328 g/cm3
Melting point 174 °C (345 °F; 447 K)
slightly soluble in cold water, soluble in hot water
Acidity (pKa)
  • 4.78 (amino; 20 °C, H2O)
  • 9.97 (phenol; 20 °C, H2O)[2]
Hazards
GHS pictograms
GHS Signal word Warning
GHS hazard statements
 H302, H332, H341
P201, P202, P261, P264, P270, P271, P281, P301+312, P304+312, P304+340, P308+313, P312, P330, 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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Infobox references

Synthesis and structure

2-Aminophenol (and its isomer, 4-aminophenol) is industrially synthesized by reducing the corresponding nitrophenol by hydrogen in the presence of various catalysts. The nitrophenols can also be reduced with iron.[3]

The compound exhibits intra- and intermolecular hydrogen bonding involving the neighbouring amine and hydroxyl groups. As a result, 2-aminophenol has a relatively high melting point (174 °C) compared to other compounds with a similar molecular mass; for example, 2-methylphenol melts at 31 °C.[4]

Applications

2-Aminophenol has a variety of uses. As a reducing agent, it is marketed under the names of Atomal and Ortol to develop black-and-white photographs.[3] 2-Aminophenol is an intermediate in the synthesis of dyes. It is particularly useful in yielding metal-complex dyes when diazotized and coupled to a phenol, naphthol, or other aromatic or resonant dye species. Metal complex dyes using copper or chromium are commonly used for producing dull colors. Tridentate ligand dyes are useful because they are more stable than their bi- or mono-dentate counterparts.[5][6]

Due to the adjacency of the amino and hydroxyl groups, 2-aminophenol readily forms heterocycles. These heterocycles, such as benzoxazoles, can be biologically active and useful in the pharmaceutical industry:[3]

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References
  1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 690. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 5–89. ISBN 978-1498754286.
  3. Mitchell, S.C. & Waring, R.H. "Aminophenols." In Ullmann’s Encyclopedia of Industrial Chemistry; 2002 Wiley-VCH, doi:10.1002/14356007.a02_099.
  4. Reference Handbook of Fine Chemicals, Acros Organics Publishers, Fisher Scientific UK, (2007), www.acros.com
  5. Grychtol, K.; Mennicke, W. "Metal-Complex Dyes." In Ullmann’s Encyclopedia of Industrial Chemistry; 2002, Wiley-VCH, doi:10.1002/14356007.a16_299
  6. Hunger, K.; Mischke, P.; Rieper, W.; Raue, R.; Kunde, K.; Engel, A. "Azo Dyes." In Ullmann’s Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, doi:10.1002/14356007.a03_245
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