Ethyl phenols

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Ethyl phenols
Surname 2-ethylphenol 3-ethylphenol 4-ethylphenol
other names 2-ethyl hydroxybenzene 3-ethyl hydroxybenzene 4-ethyl hydroxybenzene
Structural formula Structure of o-ethylphenol Structure of m-ethylphenol Structure of p-ethylphenol
CAS number 90-00-6 620-17-7 123-07-9
PubChem 6997 12101 31242
Molecular formula C 8 H 10 O
Molar mass 122.16 g mol −1
Physical state liquid firmly
description yellow-brown liquid light yellow liquid yellow solid
Melting point −18 ° C −4 ° C 40-42 ° C
boiling point 207 ° C 217 ° C 219 ° C
density 1.037 g / ml (25 ° C) 1.001 g / ml (25 ° C) 0.98 g / ml (25 ° C)
Vapor pressure 0.17 hPa (20 ° C)
solubility 4.9 g / l (25 ° C)
pK s value 10.2 9.90 10.01
GHS
labeling
05 - Corrosive 07 - Warning
danger
05 - Corrosive 07 - Warning
danger
05 - Corrosive
danger
H and P phrases 302-315-318-335 302 + 312 + 332-314 314
no EUH phrases no EUH phrases no EUH phrases
261-280-305 + 351 + 338 280-305 + 351 + 338-310 280-305 + 351 + 338-310
LD 50 600 mg / kg (mouse, oral) 138 mg / kg (mouse, ip)

The ethylphenols form a group of substances derived from both phenol and ethylbenzene . The structure consists of a benzene ring with attached hydroxyl group  (-OH) and ethyl group  (-CH 2 -CH 3 ) as substituents . Their different arrangement ( ortho , meta or para ) results in three constitutional isomers with the empirical formula C 8 H 10 O. They can primarily be viewed as ethyl-substituted phenols.

presentation

o - and p -Ethylphenol

Synthesis of o - and p -Ethylphenol passes from ethylbenzene from that by a Friedel-Crafts alkylation of benzene and bromoethane with aluminum chloride as a catalyst can be prepared. Nitric acid and sulfuric acid nitration leads to a mixture of o-ethylnitrobenzene and p-ethylnitrobenzene , which is reduced with iron and hydrochloric acid to the corresponding ethylanilines . The separation of the two isomers is carried out after acetylation of the amino groups with acetic anhydride - the p -isomer is poorly water-soluble, whereas the o -isomer remains in solution. The amides are saponified by boiling with hydrochloric acid and, after diazotization with sodium nitrite and subsequent boiling of the diazonium salt , the desired compounds are obtained.

m -ethylphenol

One synthesis route for m -ethylphenol starts from p -ethylaniline , which is acetylated with acetic anhydride in order to obtain 4-ethyl-2-nitroaniline after subsequent nitration and saponification of the amide with hydrochloric acid . The amino group is diazotized and removed with sulfuric acid, the 3-ethylnitrobenzene formed is reduced to m-ethylaniline with iron and hydrochloric acid . Renewed diazotization and boiling of the diazonium salt gives the desired m -ethylphenol.

properties

The 4-ethylphenol, which has the highest symmetry, has the highest melting point. In contrast to the other two isomers, it is a solid. The ethyl group has little influence on the acidity of the phenolic OH group , the pK s values have only minor differences to the phenol (9.99) on.

Meaning in wine

The yeast Brettanomyces bruxellensis is u. a. responsible for a wine fault , especially in red wines. The taste -forming substances here are 4-ethylphenol, together with 4-ethylguaiacol and 4-ethylcatechol . The perception threshold of 4-ethylphenol is 440 µg per liter. The substance is perceived as having a paint smell, smelling of horse sweat , phenolic or leathery. 4-Ethylphenol was first detected in wine by Albert Dinsmoor Webb and colleagues in the late 1960s .

4- Ethylphenol is biochemically produced from p -umaric acid in a two-stage process. Here, p -umaric acid is decarboxylated to vinylphenol and then oxidized to 4-ethylphenol . The first reaction is catalyzed by a hydroxycinnamic acid decarboxylase in Brettanomyces , the second by a vinylphenol reductase.

Analytical evidence

With iron (III) chloride , o -ethylphenol forms a blue-violet color, m -ethylphenol a violet color and p- ethylphenol a blue color. m -Ethylphenol forms a liquid acetate with acetic anhydride, which smells fruity and has a boiling point of 222–223 ° C. The qualitative-analytical detection can also be carried out using the easily prepared benzoyl derivatives .

Individual evidence

  1. ↑ a b Data sheet 2-Ethylphenol from AlfaAesar, accessed on August 16, 2010 ( PDF )(JavaScript required) .
  2. ↑ a b c d data sheet 3-ethylphenol from Sigma-Aldrich , accessed on November 8, 2016 ( PDF ).
  3. ↑ a b c d e 4-Ethylphenol data sheet from Sigma-Aldrich , accessed on November 8, 2016 ( PDF ).
  4. ↑ a b c d e CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
  5. ↑ a b c data sheet 2-ethylphenol from Sigma-Aldrich , accessed on November 8, 2016 ( PDF ).
  6. ↑ a b c d A. Béhal, E. Choay: "Sur les éthylphénols", in: Compt. Rend. Hebd. , 1894 , 118 , pp. 422-425 ( digitized on Gallica ).
  7. ↑ Data sheet 4-Ethylphenol (PDF) from Merck , accessed on August 16, 2010.
  8. ↑ Data sheet 4-Ethylphenol at Acros, accessed on August 16, 2010.
  9. ^ A b Riccardo Flamini and Pietro Traldi: Mass Spectrometry in Grape and Wine Chemistry . John Wiley & Sons; 2010. ISBN 978-0-470-39247-8 ; P. 145.
  10. ^ AD Webb: Wine flavor: Volatile aroma compounds of wines . In: HW Schultz (Hrsg.), EA Day (Hrsg.), LM Libbey (Hrsg.): The chemistry and physiology of flavors . The AVI Publishing Company Inc., Westport Co (1967).
  11. ↑ Brettanomyces Monitoring by Analysis of 4-ethylphenol and 4-ethylguaiacol at etslabs.com