Organic peroxide
Hydroperoxides are a class of organic chemical compounds with the general structure R -O- OH wherein R is a carbon-containing radical.
Production and representation
Hydroperoxides in autoxidation processes usually develop ( self- oxidizing ) by reaction of organic compounds with oxygen in the air or by the reaction of organometallic compounds (e.g., Grignard reagents ) with oxygen. The equation shows the light-induced mechanism of hydroperoxide formation using the example of diethyl ether hydroperoxide ( " Etherperoxid " formation ):
The radical initially formed by light irradiation of the diethyl ether reacts with oxygen to Etherperoxidradikal, which reacts with another molecule of diethyl ether to Diethyletherhydroperoxid and turn a Etherperoxidradikal. Since in each conversion cycle a Etherperoxidradikal arises, there is a chain reaction as long as oxygen is present. Photooxygenations of alkenes with at least one hydrogen atom in the allyl lead to hydroperoxides.
For n -alkanes, the reaction with atmospheric oxygen to form hydroperoxides is hardly measurable, branched hydrocarbons - especially those with a tertiary carbon atom - but the auto-oxidation are more accessible. Cumene hydroperoxide produced by air oxidation of cumene in the benzyl position. This process plays an important role in the industrial production of phenol and acetone from benzene and propylene.
Properties
Hydroperoxides are unstable compounds that can usually be made only in solution and only in exceptional cases isolated in substance. They are usually unstable and often explosive. For this reason, ethers, which can react with oxygen according to the above mechanism, are kept under light and air exclusion. Furthermore, potassium hydroxide pellets are added to the Etherbehältnis to convert hydroperoxides formed by deprotonation of the corresponding potassium salts. These are insoluble in the ether phase and fall to the ground, which in Etherentnahme the simultaneous conversion of hydroperoxide in reaction vessels and the like is prevented. The decomposition of hydroperoxides usually happens also radically.
Hydroperoxides are weakly acidic and form the hydroperoxide ion R -O -O-. The salts can not be isolated in general.
A qualitative indication of hydroperoxides based on their oxidative effect. Dissolve by heating a little potassium iodide in glacial acetic acid, adding a few drops of the substance to be tested. Are hydroperoxides (or peroxides ) are present, the previously colorless solution turns deep brown immediately because of the forming iodine. The commercially available potassium iodide - starch paper ( colored in the presence of oxidants deep blue- violet ) can also be used for rapid test. Ethervorräte that have been stored for a long time, should be checked in this manner for their peroxide before they are used or even distilled. Since the Etherhydroperoxide have a higher boiling point than the underlying ether, would increase to dangerous levels in a distillation of peroxide content in the residue, which can cause an explosion.
Use
An industrially important hydroperoxide is cumene hydroperoxide, which occurs as a non-isolated intermediate in the synthesis of acetone by the Hock process. In the laboratory, the synthesis largely stable, and therefore commercially available tert- butyl hydroperoxide is used for the epoxidation. A particularly well known application of this type is the Sharpless epoxidation.