Styrene oxide, basicity

Side-Chain Alkylation. There is continued interest in the alkylation of toluene with methanol because of the potential of the process in practical application to produce styrene.430 Basic catalysts, specifically, alkali cation-exchanged zeolites, were tested in the transformation. The alkali cation acts as weak Lewis acid site, and the basic sites are the framework oxygen atoms. The base strength and catalytic activity of these materials can be significantly increased by incorporating alkali metal or alkali metal oxide clusters in the zeolite supercages. Results up to 1995 are summarized in a review.430... 

Epoxides react with cyanide under basic reaction conditions to yield 3-hydroxypro-pionitriles by nucleophilic attack at the sterically less demanding carbon atom (Scheme4.86). Me3SiCN can also be used as reagent, but trimethylsilyl ethers will be the main products. With some types of epoxide (e.g. styrene oxide [372]) the products readily dehydrate to yield ,/i-unsaturated nitriles [373] (Scheme4.86). 

Catalysts prepared by usual DP had slightly poorer performance (in terms of conversion and selectivity) when compared with the ones prepared by homogeneous DP [421,422]. The Au loading, Au particle size and performance in the epoxidation of the supported Au catalysts are found to be strongly influenced by the transition metal oxide support used in the catalyst (prepared by HDP method). Generally, the catalysts containing more basic support showed better performance in the epoxidation. Au/In203 showed not only the best performance and also excellent reusability in the epoxidation (in the third reuse of the catalyst, the conversion and styrene oxide selectivity were found to be 51% and 48%, respectively) [421]. 

Scheme 4.26 Basic enzymatic polymerization of oxiranes (Glycidyl phenyl ether GPE benzyl glycidate BG glycidyl methyl ether GME styrene oxide SO) and dicarboxylic anhydrides (succinic anhydride SA maleic anhydride MA phthalic anhydride PA).

Syntheses of Alkylidene cyclopropanes Via the Selenonium route The selenonium route proved to be more valuable. It has been specifically designed by us to replace the deficient selenoxide route (Scheme 38). It was expected to produce alkylidene cyclopropanes by a mechanism which mimics the selenoxide elimination step but which involves a selenonium ylide in which a carbanion has replaced the oxide. Cyclopropyl selenides are readily transformed to the corresponding selenonium salts on reaction with methyl fluorosulfonate or methyl iodide in the presence of silver tetrafluoroborate in dichloromethane at 20 °C and, as expected, methylseleno derivatives are more reactive than phenyl-seleno analogs. Alkylidene cyclopropanes are, in turn, smoothly prepared on reaction of the selenium salts at 20 °C with potassium tert-butoxide in THF (Scheme 38). Mainly alkyl cyclopropenes form at the beginning of the reaction. They then slowly rearranges, in the basic medium, to the more stable alkylidene cyclopropanes( 6 kcal/mol). In some cases the complete isomerisation requires treatment of the mixture formed in the above reaction with potassium fcrt-butoxide in THF. The reaction seems to occur via a selenonium ylide rather than via a P-elimina-tion reaction promoted by the direct attack of the /crt-butoxide anion on the P-hydrogen of the selenonium salt, since it has been shown in a separate experiment that the reaction does not occur when a diphenylselenonium salt (imable to produce the expected intermediate) is used instead of the phenyl-methyl or dimethyl selenonium analogs. It has also been found that the elimination reaction is the slow step in the process, since styrene oxide is formed if the reaction is performed in the presence of benzaldehyde which traps the ylide intermediately formed... 

The reaction of trimethylsulfonium iodide with benzaldehyde under basic phase transfer conditions catalyzed by chiral quaternary ammonium salts such as (-)-N,N-dimethyl-ephedrinium bromide has been reported to yield styrene oxide in high optical purity [19], which may be somewhat overestimated [20]. 

Based on a reasoned discussion of the following experimental data, propose a mechanism for the hydrolysis of substituted styrene oxides in acidic and basic media. 

A study of the hydrolysis of styrene oxide and its / -MeO, / -Me, p-C and /7-NO2 derivatives under aeidie (HsO and basic (OH ) conditions has been carried out. The experimental results obtained in flie study are as follows ... 

The second and third terms in rate expression Eq. 11.1 ( rLHsO" ] and Aoh[OH"], respectively) clearly indicate that the hydrolysis of styrene oxides is subject to both and OH" catalysis. Acid-base catalyzed reactions have characteristic profiles when plotting log Aobs versus pH (a typical profile is represented in Fig. 11.1). The plots would reflect the contribution of the acid catalysis (a), the spontaneous (uncatalyzed) mode (b) and the basic catalyzed reaction (c). ... 

Clearly, the OH (MeO in the methanolysis reaction) is acting as a nucleophile (not as a base) in the process. In consequence, the hydrolysis (methanolysis) of styrene oxides in basic medium is a nucleophile-catalyzed reaction, not a base-catalyzed process. This is an important point to be considered when proposing a reaction mechanism, because the nucleophile has to be involved in the rate-determining step. 

As expected, the hydrolysis (solvolysis) of / -substituted styrene oxides follows a different mechanism in acidic or basic conditions. At low pH values the reaction is a specific acid-catalyzed process and a carbocation is involved as intermediate. Under basic conditions, the hydrolysis is nucleophile-catalyzed and the attack of the nucleophile takes place at both carbons of the oxirane ring. The a-attack (more hindered position) is preferred when strong /7-electron-donating substituents are placed in the styrene ring. /7-Electron-withdrawing substituents favor the P-attack (less-hindered position). 

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. 

Hydroperoxide Process. The hydroperoxide process to propylene oxide involves the basic steps of oxidation of an organic to its hydroperoxide, epoxidation of propylene with the hydroperoxide, purification of the propylene oxide, and conversion of the coproduct alcohol to a useful product for sale. Incorporated into the process are various purification, concentration, and recycle methods to maximize product yields and minimize operating expenses. Commercially, two processes are used. The coproducts are / fZ-butanol, which is converted to methyl tert-huty ether [1634-04-4] (MTBE), and 1-phenyl ethanol, converted to styrene [100-42-5]. The coproducts are produced in a weight ratio of 3—4 1 / fZ-butanol/propylene oxide and 2.4 1 styrene/propylene oxide, respectively. These processes use isobutane (see Hydrocarbons) and ethylbenzene (qv), respectively, to produce the hydroperoxide. Other processes have been proposed based on cyclohexane where aniline is the final coproduct, or on cumene (qv) where a-methyl styrene is the final coproduct. 

Isoxazolines are partially unsaturated isoxazoles. In most cases these compounds are precursors to the isoxazoles, and as a result, the synthesis can also be found in Sect. 3.2.1b. Kaffy et al., used a 1,3-dipolar cycloaddition of a nitrile oxide (186) with the respective styrene (201a or b) to generate isoxazolines (202a or b, respectively). Depending on the substitution of the vinyl portion of the styrene molecule, either 3- or 4-substituted isoxazolines could be formed (Scheme 55) [94], Simoni et al. employed similar chemistry to produce isoxazolines [60]. Kidwai and Misra emplyed microwave technology to treat chalcones with hydroxylamine and basic alumina [99]. The isoxazoles synthesized by Simoni et al. possess anti-proliferative and apoptotic activity in the micromolar range [60]. 

Methane and Toluene to Styrene Basic catalysts in the presence of oxygen and/or air are reported to be attractive catalysts for this reaction. Most research was performed in the late 1980s and early 1990s. The fundamentals resemble the oxidative coupling reaction of methane to ethylene. 

Double bonds characterize the basic building blocks of the petrochemical business. Ethylene, for example, is the chemical compound used to make vinyl chloride, ethylene oxide, acetaldehyde, ethyl alcohol, styrene, alpha olefins, and polyethylene, to name only a few. Propylene and benzene, the other big-volume building blocks, also have the characteristic double bonds. 

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