Methyl radical

Source: Wikipedia, the free encyclopedia.
Methyl radical
Names
IUPAC name
Methyl[1]
Identifiers
3D model (
JSmol
)
1696831
ChEBI
ChemSpider
57
MeSH Methyl+radical
UNII
  • InChI=1S/CH3/h1H3 checkY
    Key: WCYWZMWISLQXQU-UHFFFAOYSA-N checkY
  • [CH3]
Properties
CH3
Molar mass 15.035 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Methyl radical is an

reductant
, and is quite corrosive to metals.

Chemical properties

Its first ionization potential (yielding the methenium ion, CH+
3) is 9.837±0.005 eV.[2]

Redox behaviour

The carbon centre in methyl can bond with electron-donating molecules by reacting:

CH•
3 + R• → RCH
3

Because of the capture of the nucleophile (R•), methyl has oxidising character. Methyl is a strong oxidant with organic chemicals. However, it is equally a strong reductant with chemicals such as water. It does not form aqueous solutions, as it reduces water to produce methanol and elemental hydrogen:

2 CH•
3 + 2 H
2O → 2 CH
3OH + H
2

Structure

The

trifluoromethyl radical, CF•
3, with a much more substantial inversion barrier of around 25 kcal/mol (100 kJ/mol).[3]

Chemical reactions

Methyl undergoes the typical chemical reactions of a radical. Below approximately 1,100 °C (1,400 K), it rapidly dimerises to form

methylene
and atomic hydrogen:

CH•
3 → CH• + H
2
CH•
3 → CH•
2 + H•

Methyl is very corrosive to metals, forming methylated metal compounds:

M + n CH•
3 → M(CH3)n

Production

Biosynthesis

Some radical SAM enzymes generate methyl radicals by reduction of S-adenosylmethionine.[4]

Acetone photolysis

It can be produced by the ultraviolet photodissociation of acetone vapour at 193 nm:[5]

C
3H
6O → CO + 2 CH•
3

Halomethane photolysis

It is also produced by the ultraviolet dissociation of halomethanes:

CH
3X → X• + CH•
3

Methane oxidation

Further information: Atmospheric methane § Removal processes

It can also be produced by the reaction of methane with the hydroxyl radical:

OH• + CH4 → CH•
3 + H2O

This process begins the major removal mechanism of methane from the atmosphere. The reaction occurs in the troposphere or stratosphere. In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere.

This reaction in the troposphere gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with •OH, •Cl and •O1D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.[6]

Azomethane pyrolysis

Methyl radicals can also be obtained by pyrolysis of azomethane, CH3N=NCH3, in a low-pressure system.

In the interstellar medium

Methyl was discovered in interstellar medium in 2000 by a team led by Helmut Feuchtgruber who detected it using the Infrared Space Observatory. It was first detected in molecular clouds toward the centre of the Milky Way.[7]

References

  1. ISBN 978-0-85404-182-4
    .
  2. doi:10.1016/0368-2048(72)80022-7
    .
  3. ^ Anslyn E.V. and Dougherty D.A., Modern Physical Organic Chemistry (University Science Books, 2006), p.57
  4. PMID 24328215
    .
  5. doi:10.1063/1.460741
    .
  6. ^ "Trace Gases: Current Observations, Trends, and Budgets". Climate Change 2001, IPCC Third Assessment Report. IPCC/United Nations Environment Programme.
  7. ^ "ISO detects a new molecule in interstellar space". Science & Technology. European Space Agency. Retrieved 17 June 2013.
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