Oxiranes ethylene oxide

In selective etherification, it is important to distinguish between reversible and irreversible reactions. The former class comprises etherifications with dimethyl sulfate, halogen compounds, oxirane (ethylene oxide), and diazoalkanes, whereas the latter class involves addition reactions of the Michael type of hydroxyl groups to activated alkenes. In this Section, irreversible and reversible reactions are described separately, and a further distinction is made in the former group by placing the rather specialized, diazoalkane-based alkylations in a separate subsection. 

Polymer production proceeds as described in structure 5.25. An initiator, such as sulfuric acid, produces an oxonium ion and a gegenion. The oxonium ion then adds to the oxirane, ethylene oxide, producing a macrooxonium ion with growth eventually terminated by chain transfer with water. 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

Figure 15-5 Important commercial reactions of oxacyclopropane (oxirane, ethylene oxide)...

Some details of the preparation of allyloxy polyethers are now described. This involves the base-catalyzed ring opening of one or more of the oxiranes ethylene oxide, propylene oxide and butylene oxide in a three-step process as described by Whitmarsh [1]. 

The first set of reactions is the mainstay of the petrochemical industry 1 outstanding examples are the oxidation of propene to propenal (acrolein) catalysed by bismuth molybdate, and of ethene to oxirane (ethylene oxide) catalysed by silver. In general these processes work at high but not perfect selectivity, the catalysts having been fine-tuned by inclusion of promoters to secure optimum performance. An especially important reaction is the oxidation of ethene in the presence of acetic (ethanoic) acid to form vinyl acetate (ethenyl ethanoate) catalysed by supported palladium-gold catalysts this is treated in Section 8.4. Oxidation reactions are very exothermic, and special precautions have to be taken to avoid the catalyst over-heating. 

For example, ethylmagnesium bromide reacts with oxirane (ethylene oxide) to form the magnesium salt of butan-l-ol. Protonation gives the neutral alcohol. 

Cationic polymerization of the unsubstituted oxirane (ethylene oxide) leads to the mixture of relatively low molecular weight (M < 103) linear polymer and up to >90% of cyclic oligomers, predominantly cyclic dimer (1,4-dioxane) 191,102]. The same behavior was observed for polymerization of substituted oxiranes, propylene oxide [103], epichlorohydrin [104], and other oxiranes having one or more substituents in the ring, although the distribution of cyclic fraction varied, depending on the structure of monomer. 

There is no unique isodesmic reaction for a particular problem. For example, to compare the ring strain in oxacyclopropane (oxirane, ethylene oxide) with that in cyclopropane, one might calculate the reaction energy ofthe oxygen exchange reaction (remember that isodesmic reactions do not have to be experimentally achievable) ... 

Oxidative decarboxylations. See Decarboxylation Oxidative -elimination. See ( Elimination Oxidative sulfitolysis, 239-240. V-, P- and 5-Oxides deoxygenation, 115 Oximes Beckmann rearr., 136-137 heterocycles from, 307-308 reduction of, 98, 112 Oxirane (ethylene oxide) ... 

Oxirane (ethylene oxide), a colourless, water-soluble, extremely poisonous gas of bp 10.5°C, is made on an industrial scale by direct air oxidation of ethene in the presence of a silver catalyst. Oxirane is important as an intermediate in the petrochemical industry. The annual production worldwide is estimated to be seven million tons. 

Cyclic ethers with three- and four-membered rings represent a special group of ethers the epoxides (oxiranes) and oxetanes, respectively. These compounds are very reactive and have important uses in industry. The most basic cyclic ether, oxirane, ethylene-oxide is used for artificial maturation of vegetables. 

Oxiranes. Both anionic and cationic polymerization can be used to synthesize telechelics from oxiranes. Anionic polymerization of oxirane (ethylene oxide) yields a , )-dihydroxy poly(ethylene oxide) (274,275). 

A cyclic compound whose ring contains more than one kind of atom. Oxirane (ethylene oxide), for example, is a heterocycle whose ring contains two carbon atoms and one oxygen atom. 

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