Propene ethylbenzene hydroperoxide

The epoxidation of propene with tert-butylhydroperoxide (TBHP) or ethylbenzene hydroperoxide (EBHP), for example, accounts for more than one million tons of propene oxide production on an annual basis (Fig. 4.19). 

Synthesis is carried out in three separate steps (Scheme 6.3). The oxidant for propene is ethylbenzene hydroperoxide (EEHP). 

We have developed an effective method for the selective autoxidation of alky-laromatic hydrocarbons to the corresponding benzylic hydroperoxides using 0.5 mol% NHPI as a catalyst and the hydroperoxide product as an initiator. Using this method we obtained high selectivities to the corresponding hydroperoxides, at commercially viable conversions, in the autoxidation of cyclohexylbenzene, cumene and ethylbenzene. The highly selective autoxidation of cyclohexylbenzene to the 1-hydroperoxide product provides the basis for a coproduct-free route to phenol and the observed inq)rovements in ethylbenzene hydroperoxide production provide a basis for in roving the selectivity of the SMPO process for styrene and propene oxide manufacture. 

The competitive process, the Oxirane process, starts either from isobutane or from ethylbenzene. This starting materials are converted to hydroperoxides by catalytic oxidation with air or oxygen to give tert-butyl hydroperoxide or ethylbenzene hydroperoxide. The hydroperoxides oxidize the propene in the presence of catalysts to give propylene oxide, and as byproducts either tert-butyl alcohol (2.8 t/t PO), which is converted to methyl-tert-butyl ether, or 1-phenyl-ethanol (2.5 t/t PO), which is converted to vinylbenzene (styrene). 

The first variant works with isobutane as the hydroperoxide precursor, which is oxidized to TBHP by molecular oxygen. During the epoxidation of propene, TBHP is transformed to ferf-butanol, which is converted to methyl ferf-butyl ether. The second procedure employs ethylbenzene, which is oxidized by molecular oxygen to phenyl ethyl hydroperoxide, which transfers an oxygen to propene and so is reduced to phenylethanol. This by-product of the process is converted to styrene, a versatile bulk chemical. 

Two variants of the Oxirane process are used (Figure 1) for the commercial production of propene oxide (PO) [29]. They differ in the hydrocarbon (isobutane or ethylbenzene (EB)) that is the precursor of the hydroperoxide, and, hence, in the alcohol co-product. ARCO operates both processes using a homogeneous molybdenum catalyst. Shell, in contrast, operates only the EB variant and uses a heterogeneous Ti /Si02 catalyst. 

We turned our attention next to the autoxidation of ethylbenzene (EB) to the corresponding hydroperoxide (EBHP) which constitutes the first step in the SMPO (styrene monomer propene oxide) process for the co-production of styrene and propene oxide from ethylbenzene and propene (Scheme 7). The overall selectivity to propene oxide obviously depends on the selectivity to EBHP in the first step, which is believed to be 80-85% in the commercial process. This is lower than for cumene as a result of secondary (in the case of EB) versus tertiary (in the case of cumene) C-H bond oxidation. The main byproduct in the autoxidation of ethylbenzene is acetophenone (16). From an economic viewpoint die production of acetophenone should be kept as low as possible. 

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