Sodium phenoxide

Sodium phenoxide (sodium phenolate) is an organic compound with the formula NaOC6H5. It is a white crystalline solid. Its anion, phenoxide, also known as phenolate, is the conjugate base of phenol. It is used as a precursor to many other organic compounds, such as aryl ethers.

Sodium phenoxide
Names
Preferred IUPAC name
Sodium phenoxide[1]
Other names
Sodium phenolate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.004.862
UNII
  • InChI=1S/C6H6O.Na/c7-6-4-2-1-3-5-6;/h1-5,7H;/q;+1/p-1
    Key: NESLWCLHZZISNB-UHFFFAOYSA-M
  • InChI=1/C6H6O.Na/c7-6-4-2-1-3-5-6;/h1-5,7H;/q;+1/p-1
    Key: NESLWCLHZZISNB-REWHXWOFAP
  • [Na+].[O-]c1ccccc1
Properties
C6H5NaO
Molar mass 116.09 g/mol
Appearance White solid
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Harmful, Corrosive
Flash point Non-flammable
Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis and structure

Most commonly, solutions of sodium phenoxide are produced by treating phenol with sodium hydroxide.[2] Anhydrous derivatives can be prepared by combining phenol and sodium. A related, updated procedure uses sodium methoxide instead of sodium hydroxide:[3]

NaOCH3 + HOC6H5 → NaOC6H5 + HOCH3

Sodium phenoxide can also be produced by the "alkaline fusion" of benzenesulfonic acid, whereby the sulfonate groups are displaced by hydroxide:

C6H5SO3Na + 2 NaOH → C6H5OH + Na2SO3

This route once was the principal industrial route to phenol.

Structure

Like other sodium alkoxides, solid sodium phenoxide adopts a complex structure involving multiple Na-O bonds. Solvent-free material is polymeric, each Na center being bound to three oxygen ligands as well as the phenyl ring. Adducts of sodium phenoxide are molecular, such as the cubane-type cluster [NaOPh]4(HMPA)4.[4]

Part of the crystal structure of pure sodium phenoxide
Subunit of the crystal structure of pure sodium phenoxide, illustrating the binding of phenoxide ions to sodium through both the oxygen and the arene.

Reactions

Sodium phenoxide is a moderately strong base. Acidification gives phenol:[5]

PhOH ⇌ PhO− + H+          (K = 10−10)

The acid-base behavior is complicated by homoassociation, reflecting the association of phenol and phenoxide.[6]

Sodium phenoxide reacts with alkylating agents to afford alkyl phenyl ethers:[2]

NaOC6H5 + RBr → ROC6H5 + NaBr

The conversion is an extension of the Williamson ether synthesis. With acylating agents, one obtains phenyl esters:

NaOC6H5 + RC(O)Cl → RCO2C6H5 + NaCl

Sodium phenoxide is susceptible to certain types of electrophilic aromatic substitutions. For example, it reacts with carbon dioxide to form 2-hydroxybenzoate, the conjugate base of salicylic acid. In general however, electrophiles irreversibly attack the oxygen center in phenoxide.

The Kolbe–Schmitt reaction.
The Kolbe–Schmitt reaction.

References
  1. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. pp. 1071, 1129. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
  2. C. S. Marvel; A. L. Tanenbaum (1929). "γ-Phenoxypropyl Bromide". Org. Synth. 9: 72. doi:10.15227/orgsyn.009.0072.
  3. Kornblum, Nathan; Lurie, Arnold P. (1959). "Heterogeneity as a Factor in the Alkylation of Ambident Anions: Phenoxide Ions1,2". Journal of the American Chemical Society. 81 (11): 2705–2715. doi:10.1021/ja01520a030.
  4. Michael Kunert, Eckhard Dinjus, Maria Nauck, Joachim Sieler "Structure and Reactivity of Sodium Phenoxide - Following the Course of the Kolbe-Schmitt Reaction" Chemische Berichte 1997 Volume 130, Issue 10, pages 1461–1465. doi:10.1002/cber.19971301017
  5. Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 978-0-471-72091-1
  6. K. Izutsu (1990). Acid-Base Dissociation Constants in Dipolar Aprotic Solvents. Vol. 35. Blackwell Scientific Publications.

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