Ethyl group

From Wikipedia, the free encyclopedia
Ethyl group (highlighted blue) as part of a molecule, as the ethyl radical, and in the compounds ethanol, bromoethane, ethyl acetate, and ethyl methyl ether.

In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula −CH2CH3, derived from ethane (C2H6). Ethyl is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated two-carbon moiety in a molecule, while the prefix "eth-" is used to indicate the presence of two carbon atoms in the molecule.

Ethylation[edit]

Ethylation is the formation of a compound by introduction of the ethyl group. The most widely practiced example of this reaction is the ethylation of benzene with ethylene to yield ethylbenzene, a precursor to styrene, which is a precursor to polystyrene. Approximately 24.7 million tons of ethylbenzene were produced in 1999.[1]

Many ethyl-containing compounds are generated by electrophilic ethylation, i.e. treatment of nucleophiles with sources of Et+. Triethyloxonium tetrafluoroborate [Et3O]BF4 is such a reagent. For good nucleophiles, less electrophilic reagents are employed, such as ethyl halides.

Stereochemistry[edit]

In unsymmetrical ethylated compounds, the methylene protons in the ethyl substituent are diastereotopic. Chiral reagents are known to stereoselectively modify such substituents.

Etymology[edit]

The name of the group is derived from the Aether, the first-born Greek elemental god of air (and at that time a general term for any highly volatile compound) and "hyle", referring to "stuff". The name "ethyl" was coined in 1835 by the Swedish chemist Jöns Jacob Berzelius.[2]

See also[edit]

References[edit]

  1. ^ Welch, Vincent A.; Fallon, Kevin J.; Gelbke, Heinz-Peter (2005). "Ethylbenzene". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a10_035.pub2. ISBN 3527306730.
  2. ^ In 1834, the German chemist Justus Liebig had argued that the group C2H5 constituted a "radical" (a cluster of atoms that did not undergo changes during chemical reactions). (See: Justus Liebig (1834) "Ueber die Constitution des Aethers und seiner Verbindungen" (On the composition of ethers and their compounds), Annalen der Pharmacie, 9 : 1–39.) In reporting on Liebig's findings (and related work by others), Berzelius coined the names "methyl" and "ethyl" for the "radicals" CH3 and C2H5, respectively. From Jacob Berzelius, Årsberättelsen om framsteg i fysik och kemi [Annual report on progress in physics and chemistry] (Stockholm, Sweden: P.A. Norstedt & Söner, 1835), p. 376: "Man får då ge namn åt etherradikalerna; man kan kalla den äldre C4H10, ethyl, den nyare C2H6, methyl, … " (One may then give names to ether radicals; one can call the older [one] C4H10, ethyl, the newer [one] C2H6, methyl, … [Note: At that time, chemists used the wrong atomic masses (e.g., 6 for carbon instead of 12); hence the coefficients shown here must be divided by two.]) In his translation into German of Berzelius' report, the German chemist Friedrich Wöhler transliterated "ethyl" as "Aethyl". (See: Jöns Jacob Berzelius with Friedrich Wöhler, trans., Jahresbericht über die Fortschritte der physischen Wissenschaften (Annual report on the progress of the physical sciences), 15 : 381.)