Hydrogen peroxide for chemical process applications
Among the most critical reactions in organic chemistry in which hydrogen peroxide is used are the synthesis of peroxides (peracids, hydroperoxides, diacyl peroxides), epoxidation of olefins, hydroxylation of phenol, oxidation of amines and hydrazine hydrate.
Synthesis of peroxides
The peracids (peracetic acid, perpropionic acid) are produced by oxidation of the corresponding acids by hydrogen peroxide in presence of an acidic catalyst. These reactions are governed by a chemical equilibrium; peracid content at the equilibrium is much higher when the hydrogen peroxide used is more concentrated. Another means to shift this equilibrium in order to obtain anhydrous solutions of peracid consists of eliminating water by azeotropic distillation (heteroazeotrope solvent/water) as it is formed.
The hydroperoxides may be prepared by oxidation of the corresponding alcohols by means of H2O2 in presence of an acidic catalyst (H2SO4 for example). Diacyl peroxides can be synthesized from the corresponding acid chloride, hydrogen peroxide and caustic soda.
Epoxidation of double C=C
Different routes are available to carry out epoxidation of double bond; C=C:
- epoxidation by hydroperoxides
- epoxidation by peracids
- epoxidation by hydrogen peroxide
Epoxidation by peracids may be performed either by a peracid prepared in a preliminary step (see above concerning "synthesis of peracids"), or by a peracid prepared in situ. A process of the latter type consists of using hydrogen peroxide and formic acid simultaneously, an acidic catalyst and the material to epoxidize.
Another route of epoxidation, developed in the late 80’s, uses hydrogen peroxide directly in presence of titanium based zeolites (titanosilicalite). Due to the specific size of the pores of the zeolites, reaction selectivity are shape-oriented. This process can be applied only to molecules of small size, which are able to enter the channels of these catalysts. Therefore, propylene oxide can be easily produced by reaction of propylene and H2O2 by this process.
Hydroxylation of phenols
Hydrogen peroxide is an efficient chemical for the hydroxylation of aromatic rings. On this principle, several commercial processes have been developed for the production of hydroquinone and catechol from phenol. Hydrogen peroxide is activated with an acidic catalyst, which allows reaching a high selectivity in monohydroxylation products (hydroquinone/catechol).
Amines react with hydrogen peroxide differently regarding the type of amine (primary, secondary, tertiary) and according to the operating conditions. Primary amines lead to the formation of either hydroxylamines or oximes or nitroalcanes. Secondary amines are oxidized mainly in N-substituted hydroxylamines. For tertiary amines, the chemistry is simpler because only the corresponding amine oxides are formed.
Arkema has a large range of commercial hydrogen peroxides Albone® and Peroxal®, which meet perfectly the requirements of the reactions described above. Our customers may choose the hydrogen peroxide concentration, which allows them to guarantee the safety of the process and, in some cases, a distilled grade (low content of carbon and of stabilizer).