Liquid-phase oxidation of isopropylbenzene in the presence of N-hydroxyphthalimide

Abstract

96Alkylarene oxidations are the key reactions in the promising methods of obtaining various oxygen con taining organic compounds, namely, alkylphenols and aliphatic ketones, which are widely used in the synthe sis of valuable polymers.Among these reactions, the cumene method of producing phenol and acetone [1] and the simulta neous synthesis of styrene and propylene oxide (Hal con process) [2] have been investigated in detail and widely commercialized. The basic step of these pro cesses is the initiated liquid phase oxidation of isopro pylbenzene or ethylbenzene into the corresponding hydroperoxide. The economic characteristics of the overall process depend directly on the efficiency of this step. It is, therefore, necessary to optimize the oxida tion conditions so as to increase the conversion of the initial hydrocarbon into the hydroperoxide (including through employment of an efficient catalyst) without affecting a high hydroperoxide selectivity and chang ing the existing technology.Kinetic studies of the liquid phase oxidation of iso propylbenzene demonstrated that N hydroxyphthal imide (N HPI) at a concentration of 2-3 wt % increases the hydrocarbon oxidation rate by a factor of 2 relative to the oxidation rate under the standard pro cess conditions. At 120-130°C, the isopropylbenzene conversion is 40-50% in 2-3 h with a hydroperoxide selectivity of 90-95% [3]. Thus, N HPI intensifies the process by increasing the reaction rate and hydrocar bon conversion without reducing the high hydroper oxide selectivity. Considering that phenol is produced in great amounts, this intensification provides means to markedly improve the efficiency of the process.In order to confirm the appropriateness of employ ing N HPI and its structural analogues as agents accelerating the oxidation of isopropylbenzene, we calculated, using the PM3 (unrestricted open shell Hartree-Fock) method, the reactivity index, specifi cally, the difference between the energy of the singly occupied molecular orbital (|E SOMO |) of the substrate (isopropylbenzene) radical and the same energy of the nitrogen containing compound (NC) (|ΔE SOMO |).Japanese researchers [4] recommend to select the catalytic systems, in which the difference between the E SOMO values from 0 to 10 eV, preferably, 0-4 eV. This approach will allow the suitability of a catalyst and the process rate to be estimated a priori, providing a basis for further technological investigation. The |ΔE SOMO | values for the systems examined here fall in the 1-1.5 eV range; therefore, N HPI and its structural analogues are usable in the liquid phase oxidation of isopropyl benzene.N HPI is known to accelerate the oxidation of alkanes, alkylbenzenes, alcohols, ethers, and acetals into oxygen containing compounds (such as ketones and carboxylic and dicarboxylic acids) [5]. It is believed that, in these oxidation processes, the inter action of N HPI with the initiator radical or with the peroxy radical of an oxidizer yields the N oxyphthal imide radical (N OPIR) that is capable of selectively sub...

Aerobic oxidation of isopropylaromatic hydrocarbons to hydroperoxides catalyzed by N-hydroxyphthalimide

“…This study complements the papers published thus far on the oxidation of isopropylarenes in the presence of NHPI [6][7][8][9][10][11][12] with respect to the range of the influence of temperature and the electron-donating substituents (methoxy, phenyl) on the course of the reaction as well as catalyst recovery and air application. The oxidation of hydrocarbons 2, 4 and 7 in the presence of NHPI to hydroperoxides are reported for the first time.…”

“…The slight differences in hydroperoxides yields obtained using oxygen (Table 5) and air (Table 8) were probably the results of different process conditions (time of reaction, type of apparatus). Previously, the application of air in the NHPI-catalyzed isopropylarenes oxidation has been reported only in the papers [8,11]. However Ishii [8] oxidized hydrocarbon 6 using air under pressure of 20 atm., while Koshel' et al [11] oxidized cumene under the conditions similar to the industrial process (120°C, without polar solvent, 2.7 % NHPI) and obtained lower hydroperoxide yield in process with air than with oxygen (17 and 28 wt%, resp.…”

“…Koshel' et al [11] described the NHPI-catalyzed cumene oxidation reactions carried out without polar solvent at conditions similar to industrial process. At 120°C, in the presence of NHPI (2.7 wt%) and AIBN, after 1 h of reaction, products containing 16.8 and 27.7 % of cumene hydroperoxide were obtained using air and oxygen, respectively.…”

“…The oxidation processes of isopropylaromatic hydrocarbons to hydroperoxides, as recently shown, can be catalyzed by N-hydroxyphthalimide (NHPI) [4][5][6][7][8][9][10][11] as well as its derivatives [12]. Literature data concerning the NHPI-catalyzed oxidation of isopropylarenes are collected in Table 1.…”

Aerobic Oxidation of Alkylaromatics using a Lipophilic N‐Hydroxyphthalimide: Overcoming the Industrial Limit of Catalyst Solubility

“…Reports in the literature show how liquid-phase oxidation of HC catalyzed by 1 can be conducted in the absence of cosolvent, only if the operating temperature is higher than 100 8C. [14,25] Under these conditions, despite the low solubility of 1, the process proceeds, at least in the initial stages, mainly through the classical uncatalyzed autoxidation mechanism. The formation of products (peroxides, alcohols, ketones) contributes to an increase of the polarity of the reaction mixture with time.…”