Mechanism + Description
Nuclophilic addition of the perborate anion to the alkene followed by loss of borate to form the epoxide.
α,β-Unsaturated ketones are rapidly converted to epoxyketones at room temperature in aqueous sodium perborate in the presence of a phase transfer catalyst. Organic solvents can be used to modify the rate of epoxidation. The epoxidation of spiro[3.5]non-7-en-6-one was mediated by sodium perborate. This proved beneficial over the standard protocols employing hydrogen peroxide since a much safer process was accomplished. Carried out on 26 kg scale. This method may not be suitable where other functional groups are sensitive to oxidation.
Relevant scale up example
26 kg scale
Org. Process Res. Dev. 2003, 7, 913-916
Atom efficiency (by-products Mwt)
Reasonable atom efficacy with sodium borate produced as a by-product.
- Safety Concerns
Sodium perborate is much safer to transport and store compared to peracid reagents like mCPBA. Usually used in aqueous solution, care needs to be taken if certain co-solvents are employed. The safety of oxidation processes run in potentially peroxidisable solvents (e.g. THF, acetone) is dependent on many factors; in these cases, Process Safety should be consulted as soon as possible. Some combinations may generate detonable mixtures or by-products. The work up must ensure that oxidants are removed or destroyed prior to product isolation and waste is treated or appropriately disposed of. To avoid secondary decomposition which may have fatal consequences, it is important to ensure that active oxidants are not present in waste streams. Use of an alternate solvent may avoid such safety concerns.
- Toxicity and environmental/aquatic impact
Main issues are around the generation of boric acid on exposure to water. Boric acid is a suspect mutagen and harmful to the unborn child with aligned restrictions and authorization within REACH legislation.
- Cost, availability & sustainable feedstocks
Sodium perborate is made on industrial scale is cheap and readily available.
- Sustainable implications
Materials are abundant and readily available. Key issue is the generation of boric acid.