Meta-Chloroperoxybenzoic acid

Chembox new
ImageFile = Mcpba-2D-skeletal.png ImageSize = 100px
ImageFile1 = Mcpba-3D-vdW.png ImageSize1 = 100px
IUPACName = 3-chloroperoxybenzoic acid
OtherNames = meta-chloroperoxybenzoic acid;m-chloroperoxybenzoic acid;meta-chloroperbenzoic acid;3-chloroperbenzoic acid;mCPBA
Section1 = Chembox Identifiers
CASNo = 937-14-4
PubChem =
SMILES = O=C(OO)C1=CC(Cl)=CC=C1
RTECS = SD9470000
Section2 = Chembox Properties
Formula = C₇H₅ClO₃
MolarMass = 172.57 g/mol
Appearance = White powder
Density =
MeltingPt = 92 - 94 °C, decomposes
BoilingPt =
Solubility =
pKa = 7.57
Section3 = Chembox Hazards
MainHazards = Oxidizing, corrosive
FlashPt =
Autoignition =
RPhrases = R7 R22 R34
SPhrases = S17 S26 S36/37/39 S45
Section8 = Chembox Related
OtherAnions =
OtherCations =
OtherFunctn =
Function =
OtherCpds = peroxyacetic acid; peroxybenzoic acid

"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, oxidation of sulfides to sulfoxides and sulfones, and oxidation of amines to produce amine oxides. mCPBA is a strong oxidizing agent that may cause fire upon contact with flammable material.

Preparation

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. [OrgSynth | author = Richard N. McDonald, Richard N. Steppel, and James E. Dorsey | title = "m"-Chloroperbenzoic Acid | collvol = 6 | collvolpages = 276 | year = 1988 | prep = cv6p0276]

Availability and purity

As a pure substance, "m"-CPBA can be detonated by shock or by sparks. It is therefore sold commercially as a much more stable mixture that is less than 72% "m"-CPBA, with the balance made up of "m"-chlorobenzoic acid (10%) and water.cite web | title = 3-Chloroperoxybenzoic acid | publisher = Organic Chemistry Portal | url = http://www.organic-chemistry.org/chemicals/oxidations/meta-chloroperbenzoicacid.shtm] The peracid can be purified by washing the commercial material with a slightly basic buffer solution and then drying. [cite book |coauthors= Armarego, W. L. F.; Perrin, D. D. |title= Purification of Laboratory Chemicals |edition= 4^th ed. |year= 1996 |publisher= Butterworth-Heinemann |location= Oxford |isbn= 0750637617 |pages= 145 ] 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 "m"-CPBA must be controlled, a sample can be titrated to determine the exact amount of active oxidant.

Epoxidation example

The following reaction shows the reaction of cyclohexene with mCPBA to give an epoxide; the reaction mechanism is not shown. 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