Salicylaldehyde

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Salicylaldehyde
Skeletal formula Ball-and-stick model
Identifiers
CAS number 90-02-8 YesY
ChemSpider 13863618 YesY
UNII 17K64GZH20 YesY
ChEBI CHEBI:16008 YesY
ChEMBL CHEMBL108925 YesY
Jmol-3D images Image 1
Properties
Molecular formula C7H6O2
Molar mass 122.12 g/mol
Density 1.146 g/cm3
Melting point −7 °C (19 °F; 266 K)
Boiling point 196–197 °C
Related compounds
Related compounds Salicylic acid
Benzaldehyde
Salicylaldoxime
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Salicylaldehyde (2-hydroxybenzaldehyde) is the organic compound with the formula C6H4CHO-2-OH.[1] Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almond odor at higher concentration. Salicylaldehyde is a key precursor to a variety chelating agents, some of which are commercially important.

Production[edit]

Salicylaldehyde is prepared from phenol and chloroform by heating with sodium hydroxide or potassium hydroxide in a Reimer–Tiemann reaction:[2]

Preparation of salicylaldehyde via the Reimer–Tiemann reaction

Alternative, it is produced by condensation of phenol or its derivatives with formaldehyde to give hydroxybenzyl alcohol, which is oxidized to the aldehyde.

Salicylaldehydes in general may be prepared from the corresponding phenol by the Duff reaction, or by treatment with paraformaldehyde in the presence of magnesium chloride and a base.[3]

Natural occurrences[edit]

Salicylaldehyde was identified as a characteristic aroma component of buckwheat.[4]

It is also one of the components of castoreum, the exudate from the castor sacs of the mature North American beaver (Castor canadensis) and the European beaver (Castor fiber), used in perfumery.

Reactions and applications[edit]

Salicylaldehyde is a common highly functionalized arene that has often been exploited as a precursor to still other chemicals, which are shown in the figure, from the left: catechol, benzofuran, a salicylaldehydimine (R = alkyl or aryl), 3-carbethoxycoumarin.

Figure. Illustrative compounds derived from salicylaldehyde.

Salicylaldehyde is converted to chelating ligands by condensation with amines. With ethylenediamine, it condenses to give the ligand salen. Hydroxylamine gives salicylaldoxime. Oxidation with hydrogen peroxide gives catechol (1,2-dihydroxybenzene) (Dakin reaction).[5] Condensation with diethyl malonate gives a derivative of the heterocycle coumarin[6] via an aldol condensation. Etherification with chloroacetic acid followed by cyclisation gives the heterocycle benzofuran.[7] The first step in this reaction to the substituted benzofuran is called the Rap–Stoermer condensation after E. Rap (1895) and R. Stoermer (1900).[8][9]

References[edit]

  1. ^ Merck Index, 11th Edition, 8295
  2. ^ Brühne, F.; Wright, E. (2005), "Benzaldehyde", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a03_463 
  3. ^ Trond Vidar Hansen; Lars Skattebøl (2005), "Ortho-Formylation of Phenols; Preparation of 3-Bromosalicylaldehyde", Org. Synth. 82: 64 
  4. ^ Janeš, D.; Kreft, S. (2008). "Salicylaldehyde is a characteristic aroma component of buckwheat groats". Food Chemistry 109 (2): 293–298. doi:10.1016/j.foodchem.2007.12.032. 
  5. ^ Dakin, H. D. (1923), "Catechol", Org. Synth. 3: 28 ; Coll. Vol. 1: 149 
  6. ^ Horning, E. C.; Horning, M. G.; Dimmig, D. A. (1948), "3-Carbethoxycoumarin", Org. Synth. 28: 24 ; Coll. Vol. 3: 165 
  7. ^ Burgstahler, A. W.; Worden, L. R. (1966), "Coumarone", Org. Synth. 46: 28 ; Coll. Vol. 5: 251 
  8. ^ Rap, E. (November 1895). "Sull' α-Benzoilcumarone" [On the α-Benzoylcoumaron]. Gazzetta Chimica Italiana 2 (4): 285–290. 
  9. ^ Stoermer, R. (1900). "Synthesen und Abbaureactionen in der Cumaronreihe". Liebig's Annalen der Chemie 312 (3): 237–336. doi:10.1002/jlac.19003120302.