Methyl tert-butyl ether synthesis conditions

By tailoring the reaction conditions, alkenes may be cleaved oxidatively to yield aldehydes and carboxylic acids [10f]. The presence of a Brpnsted acid, e. g., HBF4 or HCIO4, required to accelerate the oxidation of the olefin with respect to the deactivation of the catalyst, results in the synthesis of the aldehyde without overoxidation to the acid. Significant quantities of the diol are also present, however. A three-fold excess of H2O2 is required to oxidize the alkene to the acid. However, this also results in the simultaneous oxidation of the methyl tert-butyl ether solvent to the peroxide. 

Another form of nonuniform deactivation can occur if catalyst sites differ in their activity and their adsorption affinity or chemical sensitivity. Usually, the most active sites are also the most susceptible to deactivation. If so, the activity of a fresh catalyst declines steeply at first and then at a steady, slower pace. This is believed to happen in some petroleum refining operations. Another example is loss of sulfonic acid groups in synthesis of methyl tert. -butyl ether catalyzed by ion exchangers. In this application, the acid shed by the catalyst causes corrosion problems, and catalysts are therefore "aged" under reaction conditions to eliminate the most labile acid groups before being charged to the reactors. 

Olah et al. reported the triflic acid-catalyzed isobutene-iso-butylene alkylation, modified with trifluoroacetic acid (TFA) or water. They found that the best alkylation conditions were at an acid strength of about//q = —10.7, giving a calculated research octane number (RON) of 89.1 (TfOH/TFA) and91.3 (TfOH/HaO). Triflic acid-modified zeohtes can be used for the gas phase synthesis of methyl tert-butyl ether (MTBE), and the mechanism of activity enhancement by triflic acid modification appears to be related to the formation of extra-lattice Al rather than the direct presence of triflic acid. A thermally stable solid catalyst prepared from amorphous silica gel and triflic acid has also been reported. The obtained material was found to be an active catalyst in the alkylation of isobutylene with n-butenes to yield high-octane gasoline components. A similar study has been carried out with triflic acid-functionalized mesoporous Zr-TMS catalysts. Triflic acid-catalyzed carbonylation, direct coupling reactions, and formylation of toluene have also been reported. Tritlic acid also promotes transalkylation and adaman-tylation of arenes in ionic liquids. Triflic acid-mediated reactions of methylenecyclopropanes with nitriles have also been investigated to provide [3 + 2] cycloaddition products as well as Ritter products. Tritlic acid also catalyzes cyclization of unsaturated alcohols to cyclic ethers. ... 

Hydroalkoxylation reactions refer to the addition of an alcohol over an insaturation. This highly atom economical process is potentially a straightforward and clean access to ethers, and the reaction is successfully applied at the industrial level for the production of MTBE (methyl terf-butyl ether) and ETBE (ethyl tert-butyl ether) from isobutylene and methanol or ethanol. If this transformation is well known with activated olefins (reaction referred to a Michael addition), a real challenge is the synthesis of ethers from unactivated olefins. Veiy few reactions involving carbohydrates or polyols have been reported to date and most of them involve isobutylene as this substituted olefin is prompt to generate stabilized carbenium ion under acidic conditions. Dimerization reactions of the alcohol or isobutylene are the main side reactions that have to be avoided in order to reach high selectivities into the desired ethers. ... 

An alternative method for dialkyl peroxide synthesis is the nucleophilic addition of an alkyl hydroperoxide to an alkene under acid catalysis reported by Davies and coworkers (Scheme 31, path B)113. A similar reaction is the nucleophilic addition of alkylhy-droperoxides to vinyl ethers under acid catalysis, producing perketals. Perketals can be deprotected under mild conditions (THF/water/acetic acid) and this hydroperoxide protection-deprotection sequence has been used by Dussault and Porter as a means for the resolution of racemic hydroperoxides (see also Section II.A.2)67. In this respect more detailed studies were carried out with the perketals 75, which were prepared via reaction of alkyl hydroperoxides with vinyl ethers (Scheme 33). Weissermel and Lederer reported that in the presence of tert-butyl hypochlorite, a-chlorodialkyl peroxides can be formed in yields between 12% and 45% (Scheme 31, path C)114. a-Alkoxydialkyl peroxides and diperoxyacetals were prepared by Rieche and coworkers via acid catalyzed reaction of one or two equivalents of alkyl hydroperoxides with acetals, ketals or aldehydes (Scheme 31, path D)115 or by methylation of the corresponding a-alkoxy hydroperoxides with diazomethane (yields 11%, 27%)"6. The diperoxyacetals 76 were isolated in yields ranging from 39 to 77%. 

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