Tiago Gomes - 16-11-2004 at 15:21
Is this copper complex a good catalyst for the epoxidation of styrene with iodosobenzene(Ph-I=O). Is the oxo-catalyst specie formed?
Any thoughts on this?
Is this species involved in any other studies? (I couldn´t find almost nothing)
Darkfire - 16-11-2004 at 15:53
The use of per(acetic/formic) acid or oxone is the best OTC choice for epoxidation.
Tiago Gomes - 16-11-2004 at 15:58
how did you arrived to that conclusion?
JohnWW - 16-11-2004 at 16:37
Epoxides are most commonly obtained from alkenes by addition of oxygen across the double bond with peroxy-carboxylic acids, often peroxyformic,
peroxyacetic, or peroxybenzoic acids. M-chloroperoxyacetic acid is the favorite reagent because it is more stable and easily handled than most other
peroxy-acids. Alkaline hydrogen peroxide can also be used, and is preferred where one of the alkene substituting groups is polar. CH2Cl2 is a solvent
commonly used, but the polarity of the solvent does not appreciably affect reaction rates.
However, none of the textbooks I have indicate that any catalyst is needed for the reaction, let alone a Cu complex. The peroxy-acid is the
electrophilic agent.
These peroxy-acids are reduced to the ordinary carboxylic acids. Where such distinction occurs, cis and trans alkenes stereospecifically give
different products, which may be enantiomeric mixtures.
They can also be made by reactions involving carbonyl compounds with carbenes produced as reactive intermediates.
svm - 16-11-2004 at 19:11
I believe that the common agent that JohnWW referred to is m-chloroperbenzoic acid.
the hydrogen peroxide/NaOH mixture operates by a different mechanism than the peracids. peracids are good for epoxidizing electron rich alkenes,
while the H2O2/NaOH mix is selective for the epoxidation of enones.
there are tons of metals that catalyze epoxidation reactions. many are enantioselective when used with chiral ligands. others are more selective
than the peracids because they can be directed by things like OH groups in the molecule. using metals also generally allows for more mild oxidants to
be used (peracids can cause other reactions, e.g. Baeyer-Villiger).