Monomethyl isomer, isomerization

Figure 3. Isomerization of solvent to monomethyl isomers (9) (------), model pre-...

It has been demonstrated that highly selective and active catalysts can be formed by activating either oxidized molybdenum carbide Mo2C or molybdenum oxide Mo03 itself with a hydrocarbon/hydrogen mixture. The active catalysts obtained from the two sources are similar in their catalytic behaviour and are probably both molybdenum oxycarbide (MoO Cy). They are selective for the isomerization of a number of n-hydrocarbons with the main products always consisting of monomethyl isomers but with an important contribution from the dibranched products,... 

Furthermore, it was found for this isomerization that SAPO-11 gave the higher content of the mono-substituted methyl-C15 isomers over a range of pour points (Figure 10.25) and the number of branches was minimized with this catalyst (Figure 10.26). Miller s concept of the isomerization process is that the 2- isomer is produced first, which leads to the other single methyl isomers by methyl migration down the chain. The monomethyl isomers can then subsequently react further catalytically to form 2-, 3-, and 3+ branched isomers. 

Let us start with the three isomeric C-monomethylated species (the toluidines or methyl-benzenamines) and accept the recent experimental measurements and analysis17. This source points out the contradictory and incomplete measurements for these species and uses the expression in disarray to describe the literature. From thermoneutral equation 2, we would predict enthalpies of formation of —12, —5 and 55 kJ mol-1 for all three solid, liquid and gaseous toluidines, in reasonable agreement with the experimental values. We note that the o-isomer is slightly more stable than its m- and p-isomers. In comparison, the spread of enthalpy of formation values for the isoelectronic and isosteric xylenes is but 1 kJ mol 1 and for the so-related methylphenols3 (cresols) is but 7 kJ mol 1. As an additional check for thermochemical accuracy, consider the formal methylation reaction 4. For Ar = Ph, the enthalpies of reaction are —36.6 (lq) and —32.2 (g) kJ mol 1. For Ar = C6H4NH2, the ortho, meta and para gas-phase enthalpies of reaction are the... 

The application of the standard Torgov procedure for the preparation of 7 7 dimethyl-6-oxasteroids led surprisingly to the formation of the 8a,146-isomer. The authors postulate that a steric interaction between the gem-dimethyl group and the 15"proton caused isomerization of the intermediate to a l46-A -isomer. Subsequent reduction of the A -doubie bond was reportedly influenced by the 146-center to produce an 8a,9a-ring junction. However, when employing a similar synthesis to prepare a 7a-monomethyl-6-oxa system, the normal 86,9a,l4a-steroid was produced, although again some difficulty was encountered in the reduction of the A -bond to the l4a-isomer. ... 

The acidic component with a melting point of 169.5°C, which forms a monobenzoate and a monomethyl ether, is the isomeric 2,2,8,8-tetramethyl-10-(2-methylpropanoyl)benzo(1,2-b 5.4-b ]-3,4,6,7-tetrahydrodipyran-5-ol (189, Figs. 107 and 113). The similarity between the two compounds appears from the respective UV absorption spectra. Furthermore, the angular dipyran 190 is converted to the linear isomer 189 in warm dihydrogen sulfate. 

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