Propylene industrial epoxides

Despite the above drawbacks, metal-peroxo chemistry will have an increasing contribution to clean industrial epoxidations. One of the current technologies used for propylene oxide and epichlorhydrin is the chlorhydrin route, where olefin is reacted with hypochlorous acid (from chlorine) followed by ring-closure of the chlorhydrin with lime ... 

Ethylene oxide and propylene oxide are by far the most important industrial epoxides. The production of these two compounds has been selected as a process example in this textbook and is described in detail in Section 6.12. Table 5.3.5 summarizes the most relevant applications of these important intermediates and gives the actual production capacities. 

Valuable products are produced from the oxidation of both ethylene and propylene (Figs. 1 and 2). Ethylene is epoxidized with oxygen in the vapor phase over a silver catalyst, and propylene is epoxidized with an alkyl hydroperoxide in the liquid phase using a molybdeniim catalyst system. Vinylic oxidation products or their stable isomers, including acetaldehyde, acetone, and vinyl acetate, have been manufactured by a series of related catalytic reactions. These reactions occur either in solutions of palladium complexes or on the surfaces of supported palladium catalysts. Bismuth molybdate is an effective catalyst for allylic oxidations of propylene, which are of paramount importance to the chemical industry. Propylene is oxidized in the vapor phase to give acrolein for acrylic acid manufacture or, in the presence of ammonia, to give acrylonitrile. Second- and third-generation catalysts,... 

Three membered rings that contain oxygen are called epoxides At one time epox ides were named as oxides of alkenes Ethylene oxide and propylene oxide for exam pie are the common names of two industrially important epoxides... 

Propylene oxide and other epoxides undergo homopolymerization to form polyethers. In industry the polymerization is started with multihinctional compounds to give a polyether stmcture having hydroxyl end groups. The hydroxyl end groups are utilized in a polyurethane forming reaction. This article is mainly concerned with propylene oxide (PO) and its various homopolymers that are used in the urethane industry. 

Dichlorides and e2thers are the main by-products in this reaction. Treatment with base produces propylene oxide. Specialty epoxides, eg, butylene oxide, are also produced on an industrial scale by means of HOCl generated from calcium hypochlorite and acetic acid followed by dehydrohalogenation with base. 

Dehydrochlorination to Epoxides. The most useful chemical reaction of chlorohydrins is dehydrochlotination to form epoxides (oxkanes). This reaction was first described by Wurtz in 1859 (12) in which ethylene chlorohydria and propylene chlorohydria were treated with aqueous potassium hydroxide [1310-58-3] to form ethylene oxide and propylene oxide, respectively. For many years both of these epoxides were produced industrially by the dehydrochlotination reaction. In the past 40 years, the ethylene oxide process based on chlorohydria has been replaced by the dkect oxidation of ethylene over silver catalysts. However, such epoxides as propylene oxide (qv) and epichl orohydrin are stiU manufactured by processes that involve chlorohydria intermediates. 

Recently (79MI50500) Sharpless and coworkers have shown that r-butyl hydroperoxide (TBHP) epoxidations, catalyzed by molybdenum or vanadium compounds, offer advantages over peroxy acids with regard to safety, cost and, sometimes, selectivity, e.g. Scheme 73, although this is not always the case (Scheme 74). The oxidation of propene by 1-phenylethyl hydroperoxide is an important industrial route to methyloxirane (propylene oxide) (79MI5501). 

The manufacture and uses of oxiranes are reviewed in (B-80MI50500, B-80MI50501). The industrially most important oxiranes are oxirane itself (ethylene oxide), which is made by catalyzed air-oxidation of ethylene (cf. Section 5.05.4.2.2(f)), and methyloxirane (propylene oxide), which is made by /3-elimination of hydrogen chloride from propene-derived 1-chloro-2-propanol (cf. Section 5.05.4.2.1) and by epoxidation of propene with 1-phenylethyl hydroperoxide cf. Section 5.05.4.2.2(f)) (79MI50501). 

Ethylene glycol and propylene glycol are prepared industrially from the corresponding alkenes by way of their epoxides. Some applications were given in the box in Section 6.21. 

In the organic chemicals industry, H2O2 is used in the production of epoxides, propylene oxide, and caprolactones for PVC stabilizers and polyurethanes, in the manufacture of organic peroxy compounds for use as polymerization initiators and curing agents, and in the synthesis of fine chemicals such as hydroquinone, pharmaceuticals (e.g. cephalosporin) and food products (e.g. tartaric acid). 

The latest industrial strides in PO synthesis are liquid phase epoxidation of propylene with H2O2 over TS... 

Let us recall that by the sol-gel method one can obtain very efficiently very well-defined systems such as Ti silicalite, which can be considered as a single site system where titanium is tetracoordinated in a zeolitic matrix and undergoes epoxidation of propylene or hydroxylahon of benzene to phenol. Bear in mind that it took industry more than 20 years to realize such an industrial processes (Dow-BASF process) [1]). 

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 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). 

One molybdenum-catalyzed epoxidation, which is of industrial importance, needs special mention the Halcon process268, which is the molybdenum-catalyzed epoxidation of propylene with TBHP or 1-phenylethyl hydroperoxide on a large scale (Scheme 74), and has been developed and patented by researchers from Halcon and Atlantic Richfield269. 

The gas-phase oxidation of ethylene to ethylene oxide over a supported silver catalyst was discovered in 1933 and is a commercially important industrial process. Using either air or oxygen, the ethylene oxide is produced with 75% selectivity at elevated temperatures (ca. 250 °C). Low yields of epoxides are obtained with propylene and higher alkenes so that other metal-based catalysts are used. A silver-dioxygen complex of ethylene has been implicated as the active reagent.222... 

Ethylene oxide (qv), propylene oxide (qv), butylene oxide, and other epoxides react with ethanol to give a variety of liquid, viscous, semiwax, and solid products. These products are used in the coatings industry as solvents, and as paints, antioxidants, corrosion inhibitors, and special-purpose polymers. Recent concerns about the health effects of ethanol containing glycol ethers have led to the decline in the production of these compounds. 

Because the petrochemical industry is based on hydrocarbons, especially alkenes, the selective oxidation of hydrocarbons to produce organic oxygenates occupies about 20% of total sales of current chemical industries. This is the second largest market after polymerization, which occupies about a 45% share. Selectively oxidized products, such as epoxides, ketones, aldehydes, alcohols and acids, are widely used to produce plastics, detergents, paints, cosmetics, and so on. Since it was found that supported Au catalysts can effectively catalyze gas-phase propylene epoxidation [121], the catalytic performance of Au catalysts in various selective oxidation reactions has been investigated extensively. In this section we focus mainly on the gas-phase selective oxidation of organic compounds. 

Scheme 3.1 The two main industrial processes for propylene epoxidation production.

Propylene oxide represents a very attractive epoxide monomer for copolymerization with C02, as polypropylene carbonate) is industrially valuable. The low glass transition temperature (Tg) of 313 K, the sharp and clean decomposition above 473 K, and biodegradability of this copolymer are the reasons for its attracting interest in several applications. On a similar basis, H NMR spectroscopy is useful for assessing the coupling products resulting from the reaction of PO and C02 (Figure 8.21). 

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