Methyl/-butyl ether mechanism

Reaction of 2-methylpropene with CH3OH in the presence of H2SO4 catalyst yields methyl tert-butyl ether, CP OQCHT, by a mechanism analogous to that of acid-catalyzed alkene hydration. Write the mechanism, using curved arrows for each step. 

Kang J-W, Hoffmann MR (1998) Kinetics and mechanism of the sonolytic destruction of methyl tert butyl ether by ultrasonic irradiation in the presence of ozone. Environ Sci Tech 32 3194-3199... 

Jr., A Comprehensive Kinetic Mechanism for CO, CH20, and CH3OH Combustion, Int.J. Chem. Kinet. 39, 109-136 (2007) Held, T., The Oxidation of Methanol, Isobutene, and Methyl tertiary-Butyl Ether, No. 1978-T, PJi.D. Dissertation, Princeton University, Princeton, NJ, 1993 Burgess, D. R. F., Jr, Zachariah, M. R., Tsang,... 

A study of the regioselectivity of the 1,3-dipolar cycloaddition of aliphatic nitrile oxides with cinnamic acid esters has been published. AMI MO studies on the gas-phase 1,3-dipolar cycloaddition of 1,2,4-triazepine and formonitrile oxide show that the mechanism leading to the most stable adduct is concerted. An ab initio study of the regiochemistry of 1,3-dipolar cycloadditions of diazomethane and formonitrile oxide with ethene, propene, and methyl vinyl ether has been presented. The 1,3-dipolar cycloaddition of mesitonitrile oxide with 4,7-phenanthroline yields both mono-and bis-adducts. Alkynyl(phenyl)iodonium triflates undergo 2 - - 3-cycloaddition with ethyl diazoacetate, Ai-f-butyl-a-phenyl nitrone and f-butyl nitrile oxide to produce substituted pyrroles, dihydroisoxazoles, and isoxazoles respectively." 2/3-Vinyl-franwoctahydro-l,3-benzoxazine (43) undergoes 1,3-dipolar cycloaddition with nitrile oxides with high diastereoselectivity (90% de) (Scheme IS)." " ... 

Construct a mechanism that shows why methyl tert-butyl ether (MTBE), a common gasoline additive, oxidizes in air to give formaldehyde as well as acetone, fert-butyl formate (HC(0)OC(CH 3),), and methyl acetate (CH3C(0)0CH3). 

This is a second-order reaction because methoxide ion is a strong base as well as a strong nucleophile. It attacks the alkyl halide faster than the halide can ionize to give a first-order reaction. No substitution product (methyl tert-butyl ether) is observed, however. The SN2 mechanism is blocked because the tertiary alkyl halide is too hindered. The observed product is 2-methylpropene, resulting from elimination of HBr and formation of a double bond. 

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. ... 

Catalysts that decrease reaction rates are usually referred to as inhibitors. They often act by interfering with the free-radical processes involved in chain reactions, and the mechanism usually differs from that involved in accelerating a reaction. The most familiar example of the use of inhibitors has historically been the addition of additives such as tetraethyllead or methyl terf-butyl ether to gasoline to improve its antiknock properties. 

The different applications of these zeolites in pervaporation include alcohol dehydration water removal in acid solutions organic dehydration separations such as water/ tetrahydrofuran (THF), water/dioxane, or water/dimethyl-formamide (DMF) removal of organics from water and organic/organic separations such as methanol/methyl-tert-butyl ether (MTBE) or p-xylene/o-xylene. In the following subsections, the mechanism of pervaporation in zeolite membranes will be briefly described and we will provide the details about the different applications. 

In the commercial synthesis of methyl fert-butyl ether (MTBE), once used as an antiknock, octane-improving gasoline additive, 2-methylpropene and methanol are passed over an acid catalyst to give the ether. Propose a mechanism for this reaction. (See Examples 5.5,5.6)... 

---