Oxidation of Alkylaromatics to Corresponding Hydroperoxides

Aerobic selective oxidation of alkylaromatics, including cumene (CU), ethylbenzene (EtB), and cyclohexylbenzene (CyB), to the corresponding hydroperoxides (CHPs) represents a key step for several large-scale productions, including the Hock process for the synthesis of phenol (see Chapter 2) [15] and the Shell styrene monomer/propylene oxide (SM/PO) process for the production of propylene oxide (PO) and styrene monomer (SM) [16]. 

The last decade has been characterized by a huge amount of patent applications in this field. Sheldon and Degussa (now Evonik) first reported in 2001 the NHPI-catalyzed oxidation of a wide range of alkyl aromatics at 100 °C in the absence of 

In 2009, Fierro and Repsol Quimica S.A. reported the beneficial effect of combining NHPI with parts per million amounts of NaOH for the synthesis of hydroperoxides [22], with the dual effect of promoting the formation of PINO in the absence of transition metal salts and of neutralizing the acidic by-products of the reaction. This approach was particularly effective for increasing conversion and selectivity in the oxidation of secondary alkylaromatics [23]. 

In all earlier mentioned approaches, the reactions are conducted in heated solution of hydrocarbons, at temperatures higher than 100 °C in order to guarantee complete solubilization of NHPI. However, as previously disclosed, these harsh operating conditions favor the self-decomposition of the catalyst, partially limiting the applicability at industrial scale. 

The results of our investigation in this field, in collaboration with Polimeri Europa (now Versalis S.p.A., Eni Group), have convinced us that the presence of variable amounts of polar cosolvents was crucial to operate under homogenous and mild conditions ( 80 °C). We also proposed the possible use of tiny amounts of acetaldehyde to initiate the radical chain even at ambient temperature [24], 

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