meta-Chloroperoxybenzoic acid

From Wikipedia, the free encyclopedia
Jump to: navigation, search
meta-Chloroperoxybenzoic acid
Meta-Chloroperoxybenzoic acid.svg Meta-chloroperbenzoic-acid-Spartan-HF-6-31Gstar-3D-balls.png
Identifiers
CAS number 937-14-4 YesY
ChemSpider 63480 N
RTECS number SD9470000
Jmol-3D images Image 1
Properties
Molecular formula C7H5ClO3
Molar mass 172.57 g mol−1
Appearance White powder
Melting point 92 to 94 °C (198 to 201 °F; 365 to 367 K) decomposes
Acidity (pKa) 7.57
Hazards
R-phrases R7 R22 R34
S-phrases S17 S26 S36/37/39 S45
Main hazards Oxidizing, corrosive
Related compounds
Related compounds peroxyacetic acid; peroxybenzoic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

meta-Chloroperoxybenzoic acid (mCPBA) is a peroxycarboxylic acid used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling. The main areas of use are the conversion of ketones to esters (Baeyer-Villiger oxidation), epoxidation of alkenes (Prilezhaev reaction), conversion of silyl enol ethers to silyl α-hydroxy ketones (Rubottom oxidation), oxidation of sulfides to sulfoxides and sulfones, and oxidation of amines to produce amine oxides.[1] mCPBA is a strong oxidizing agent that may cause fire upon contact with flammable material.

Preparation[edit]

mCPBA can be prepared by reacting m-chlorobenzoyl chloride with hydrogen peroxide in the presence of magnesium sulfate, aqueous sodium hydroxide, and dioxane, followed by acidification.[2]

Availability and purity[edit]

As a pure substance, mCPBA can be detonated by shock or by sparks. It is therefore sold commercially as a much more stable mixture that is less than 72% mCPBA, with the balance made up of m-chlorobenzoic acid (10%) and water.[1] The peracid can be purified by washing the commercial material with a slightly basic buffer solution and then drying.[3] Peracids are generally slightly less acidic than their carboxylic acid counterparts, so one can extract the acid impurity by careful control of pH. The purified material is reasonably stable against decomposition if stored at low temperatures in a plastic container.

In reactions where the exact amount of mCPBA must be controlled, a sample can be titrated to determine the exact amount of active oxidant.

Epoxidation example[edit]

The following scheme shows the reaction of cyclohexene with mCPBA to give an epoxide.

Reaction of cyclohexene with mCPBA.png

The epoxidation mechanism is concerted: the cis or trans geometry of the alkene starting material is retained in the epoxide ring of the product.

References[edit]

  1. ^ a b "3-Chloroperoxybenzoic acid". Organic Chemistry Portal. 
  2. ^ Richard N. McDonald, Richard N. Steppel, and James E. Dorsey (1988), "m-Chloroperbenzoic Acid", Org. Synth. ; Coll. Vol. 6: 276 
  3. ^ Armarego, W. L. F.; Perrin, D. D. (1996). Purification of Laboratory Chemicals (4th ed.). Oxford: Butterworth-Heinemann. p. 145. ISBN 0-7506-3761-7.