Propylene hydroperoxide intermediate

Considerable evidence exists that indicates the selective oxidation of propylene proceeds via the formation of a symmetrical allyl species. Subsequent steps may vary as a function of the catalyst. Some catalyst systems may abstract a second hydrogen atom before the insertion of oxygen. Others may add molecular oxygen, forming a hydroperoxide intermediate, which may then subsequently decompose into acrolein and water. 

Keulks et al. (7) discussed evidence for a model in which the selective oxidation of propylene proceeded via the formation of a symmetric allylic species with subsequent steps depending on the nature of the catalyst. In some catalytic systems the abstraction of a second hydrogen atom seemed to precede the insertion of oxygen, while others appeared to add molecular oxygen to form a hydroperoxide intermediate which subsequently decomposed into acrolein and water. 

The most widely used process for the production of phenol is the cumene process developed and Hcensed in the United States by AHiedSignal (formerly AHied Chemical Corp.). Benzene is alkylated with propylene to produce cumene (isopropylbenzene), which is oxidized by air over a catalyst to produce cumene hydroperoxide (CHP). With acid catalysis, CHP undergoes controUed decomposition to produce phenol and acetone a-methylstyrene and acetophenone are the by-products (12) (see Cumene Phenol). Other commercial processes for making phenol include the Raschig process, using chlorobenzene as the starting material, and the toluene process, via a benzoic acid intermediate. In the United States, 35-40% of the phenol produced is used for phenoHc resins. 

Propylene oxide [75-56-9] (methyloxirane, 1,2-epoxypropane) is a significant organic chemical used primarily as a reaction intermediate for production of polyether polyols, propylene glycol, alkanolamines (qv), glycol ethers, and many other useful products (see Glycols). Propylene oxide was first prepared in 1861 by Oser and first polymerized by Levene and Walti in 1927 (1). Propylene oxide is manufactured by two basic processes the traditional chlorohydrin process (see Chlorohydrins) and the hydroperoxide process, where either / fZ-butanol (see Butyl alcohols) or styrene (qv) is a co-product. Research continues in an effort to develop a direct oxidation process to be used commercially. 

Olefin epoxidation is an important industrial domain. The general approach of SOMC in this large area was to understand better the elementary steps of this reaction catalyzed by silica-supported titanium complexes, to identify precisely reaction intermediates and to explain catalyst deachvahon and titanium lixiviation that take place in the industrial Shell SMPO (styrene monomer propylene oxide) process [73]. (=SiO) Ti(OCap)4 (OCap=OR, OSiRs, OR R = hydrocarbyl) supported on MCM-41 have been evaluated as catalysts for 1-octene epoxidation by tert-butyl hydroperoxide (TBHP). Initial activity, selechvity and chemical evolution have been followed. In all cases the major product is 1,2-epoxyoctane, the diol corresponding to hydrolysis never being detected. 

The second manufacturing method for propylene oxide is via peroxidation of propylene, called the Halcon process after the company that invented it. Oxygen is first used to oxidize isobutane to r-butyl hydroperoxide (BHP) over a molybdenum naphthenate catalyst at 90°C and 450 psi. This oxidation occurs at the preferred tertiary carbon because a tertiary alkyl radical intermediate can be formed easily. 

The search for a new epoxidation method that would be appropriate for organic synthesis should also, preferably, opt for a catalytic process. Industry has shown the way. It resorts to catalysis for epoxidations of olefins into key intermediates, such as ethylene oxide and propylene oxide. The former is prepared from ethylene and dioxygen with silver oxide supported on alumina as the catalyst, at 270°C (15-16). The latter is prepared from propylene and an alkyl hydroperoxide, with homogeneous catalysis by molybdenum comp e ts( 17) or better (with respect both to conversion and to selectivity) with an heterogeneous Ti(IV) catalyst (18), Mixtures of ethylene and propylene can be epoxidized too (19) by ten-butylhydroperoxide (20) (hereafter referred to as TBHP). 

Propylene oxide (PO) is a major bulk chemical that is useful as an intermediate for the production of glycols, polyethers and polyols. World PO production is about 7 million tons per year, with the market growing by approximately 5% annually. PO comes from two current industrial processes the chlorohydrin process and the organic hydroperoxide process (Scheme 3.1). These processes require multiple steps and suffer from the additional drawback of not producing the desired PO alone. 

Olefins with hindered double bonds may be transformed stereospecifically to oxiranes by treatment with ozone. The epoxidation of propylene has been achieved with alkoxyalkyl-hydroperoxides obtained by the ozonization of olefins in the presence of alcohol.The yield depends on whether the alcohol is a primary, secondary, or tertiary one. The low-temperature (—70°) epoxidation of olefins with a yield of about 30% has been performed with electrophilic intermediates produced in the course of the ozonization of alkynes these intermediates are probably five-membered cyclic trioxides. This epoxidation is almost totally stereospecific. 

Whereas so far oxidation reactions with O2 have been discussed, an important heterogeneous catalytic oxidation reaction is the epoxidation of propylene to propylene epoxide. Using hydroperoxide the reaction can be done over Ti dispersed on silica [133]. Ti becomes 4 coordinated as Si in Si02. With hydrogen-peroxide the reaction has been found to occur for Ti incorporated in the lattice of MFI zeolite [134]. The unique property of these systems is that the electrophilic nature of oxygen intermediates does not cause reaction with the allylic CH bond. It is proposed that the adsorbed intermediate is ... 

Reactions (7) and (8) represent the formation of a chloride-doped, oxygen-deficient, subsurface oxide film, which we believe portrays the true nature of the catalyst. Oxygen is then adsorbed on this surface as in reaction (9). The presence of surface and subsurface chloride will tend to inhibit the dissociative adsorption, leaving the associative form as the major reactive species. Ethylene can be reversibly adsorbed on Ag" or irreversibly adsorbed on the two oxygen species [reactions (10), (11), and (13)]. Reactions (11) and (12) lead to ethylene oxide via the intermediates observed by Kilty et al. and also Foice and Bell. With propylene, the hydroperoxide can be formed, which subsequently combusts... 

Ethylbenzene can also be oxidized to form ethylbenzene hydroperoxide, an intermediate in a process to produce propylene oxide. 

A subsequent step in the sequence is the formation of Ti-hydroperoxo species from the reaction of H2O2 and tetrahedral Ti sites, more likely Ti tripodal sites. This Ti-hydroperoxo species has been proposed as an intermediate in the gas-phase epoxidation of propylene by analogy with the well-known chemistry for oxidations in the liquid phase with H2O2 and TS-1 [105,106,401,446]. In gas-phase reactions, hydroperoxide species have been inferred by D2 isotopic experiments [431] and detected by ex situ INS [432] and in situ UV-vis measurements [433]. Other species in this simplified sequence include adsorbed propylene on a Ti-hydroperoxo site and adsorbed PO on a Ti tripodal site. Desorption of PO and water results in the original Ti species, which closes the catalytic cycle. 

J. J. Bravo-Suarez, K. K. Bando, J. Lu, M. Haruta, T. Eujitani, S. T. Oyama, Transient technique for identification of true reaction intermediates Hydroperoxide species in propylene epoxidation on gold/titanosilicate catalysts by X-ray absorption fine structure spectroscopy, /. Phys. Chem. C. 112 (2008) 1115. 

Propylene oxide (PO) is an important chemical intermediate, which is mainly used in the manufacture of polyols, propylene glycols, and propylene glycol ethers [1]. The world annual production capacity of PO is about 7 million metric tons [2]. PO is mainly produced commercially by either the chlorohydrin (about 43%) or organic hydroperoxide processes. The chlorohydrin route produces large amounts of salt by-product, and new plants have used the hydroperoxide processes [3]. 

Styrene is manufactured nearly entirely by the direct dehydrogenation of ethylbenzene. Smaller amounts are obtained indirectly, as a co-product, from the production of propylene oxide by the Oxirane and Shell technologies, industrialized in the United States, the Netherlands and Spain, and whose essential intermediate step is the formation of ethylbenzene hydroperoxide, or from the production of aniline, by a technique developed in the USSR, which combines the highly exothermic hydrogenation of nitrobenzene with the highly endothermic dehydrogenation of ethylbenzene. 

It may be noted that the above mechanism for propylene oxidation over cuprous oxide differs substantially from that proposed by Margolis (I) he postulates an allyl hydroperoxide, C3H5OOH, as an intermediate. His mechanism does not allow for a symmetrical intermediate, nor for the required abstraction of two hydrogens before the symmetry is destroyed. 

Methylphenylcarbinol is also an intermediate in the Halcon process, in which ethylbenzene is oxidized to a hydroperoxide at around 130 °C with air, then converted with propylene into propylene oxide and carbinol. The carbinol is subsequently dehydrated on a titanium catalyst at 180 to 280 °C to styrene. This process, first commercialized by Atlantic Richfield, has found large-scale application in a few isolated cases (e.g. Shell (Netherlands), Alcudia (Spain) and Nihon Oxirane (Japan)) it is only viable if there is sufficient demand for propylene oxide. 

In the epoxidation of propylene by the hydroperoxide route, the oxidant is generated by the oxidation of ethylbenzene or isobutane, as are major amounts of corresponding alcohols (1-phenylethanol and r-butanol, respectively). The latter, which are also produced in the epoxidation step, are valuable intermedi-... 

Phenol is an important raw material for the synthesis of petrochemicals, agrochemicals, and plastics. Examples of the uses of phenol as an intermediate include the production of bisphenol A, phenolic resins, caprolactam, alkyl phenols, aniline, and other useful chemicals. Today, almost 95% of worldwide phenol production is based on the so-called cumene process which is a three-step process (the conversion of benzene and propylene to cumene using supported phosphoric acid catalysts, the conversion of cumene to cumene hydroperoxide with air, and the decomposition of hydroperoxide to phenol and acetone with sulfuric acid). The great interest in the oxidation reaction of benzene to phenol is Unked to some disadvantages of the cumene process (environmental impact, production of an explosive hydroperoxide. 

The problem of selective oxidation of alkylarens to hydroperoxides is economically sound. Hydroperoxides are used as intermediates in the large-scale production of important monomers. For instance, propylene oxide and styrene are synthesized from a-phenyl ethyl hydroperoxide (PEH), and cumyl hydroperoxide is the precursor in the synthesis of phenol and acetone. The method of modifying the Ni" and Fe° complexes used in the selective oxidation... 

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