Monomethyl isomers

Davies and Warren have investigated the nitration of naphthalene, ace-naphthene and eight dimethylnaphthalenes in acetic anhydride at o °C. Rates relative to naphthalene were determined by the competition method, and the nitro-isomers formed were separated by chromatographic and identified by spectrophotometric means. The results, which are summarised in the table, were discussed in terms of various steric effects, and the applicability of the additivity rule was examined. For the latter purpose use was made of the data of Alcorn and Wells (table 10.2) relating to the nitration of monomethyl-naphthalenes at 25 °C. The additivity rule was found to have only limited utility, and it was suggested that the discrepancies might be due in part to the... 

Reaction of (T)-(-)-2-acetoxysuccinyl chloride (78), prepared from (5)-mahc acid, using the magnesiobromide salt of monomethyl malonate afforded the dioxosuberate (79) which was cyclized with magnesium carbonate to a 4 1 mixture of cyclopentenone (80) and the 5-acetoxy isomer. Catalytic hydrogenation of (80) gave (81) having the thermodynamically favored aH-trans stereochemistry. Ketone reduction and hydrolysis produced the bicycHc lactone acid (82) which was converted to the Corey aldehyde equivalent (83). A number of other approaches have been described (108). 

The most accurate data on isomer distributions in alkylation of heterocycles have been obtained from the reaction of 3-n-butylpyridine with methyl radicals in acetic aeid. The ratio of the monomethyl products was determined by infrared spectroscopy and gas chromatography and is showm in (27). A small amount of 2,6-dimethyl-3-n-butylpyridine was also obtained. These ratios again show a high proportion of ortho substitution. 

Experiments at different flow rates and with difierent catalyst grain sizes confirmed that the reaction kinetics is not influenced by external or internal mass transfer. Catechol conversions (X) were always less than 0.05 allowing the reaction to be carried out in the differential kinetic region. The initial yields (Yi,o) for the monomethylated isomers were measured under steady-state conditions (after 8-10 hours of the catalyst activity stabilisation) and were used to compare the catalysts selectivities ... 

Figure 4. Initial selectivity of the monomethylated isomers as function of Mg content.

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

Only large-pore zeolites exhibit sufficient activity and selectivity for the alkylation reaction. Chu and Chester (119) found ZSM-5, a typical medium-pore zeolite, to be inactive under typical alkylation conditions. This observation was explained by diffusion limitations in the pores. Corma et al. (126) tested HZSM-5 and HMCM-22 samples at 323 K, finding that the ZSM-5 exhibited a very low activity with a rapid and complete deactivation and produced mainly dimethyl-hexanes and dimethylhexenes. The authors claimed that alkylation takes place mainly at the external surface of the zeolite, whereas dimerization, which is less sterically demanding, proceeds within the pore system. Weitkamp and Jacobs (170) found ZSM-5 and ZSM-11 to be active at temperatures above 423 K. The product distribution was very different from that of a typical alkylate it contained much more cracked products trimethylpentanes were absent and considerable amounts of monomethyl isomers, n-alkanes, and cyclic hydrocarbons were present. This behavior was explained by steric restrictions that prevented the formation of highly branched carbenium ions. Reactions with the less branched or non-branched carbenium ions require higher activation energies, so that higher temperatures are necessary. 

Halogenation of w-triazole and several monomethyl and dimethyl derivatives has been studied.Bromination of v-triazole gives the 4,5-dibromo derivative with an excess of sodium hypobromite, a 1,4,5-tribromo derivative can also be isolated. Attempted chlorination gave the hydrochloride salt instead, although 1-methyltriazole gives a 4-chloro derivative. A 1-iodo derivative, which rearranges on heating to the 4-isomer, is obtained with iodine. 

Thus, the dominant contributor of cracking selectivity of Super D is expected to be the REY zeolite present in the catalyst. Yields of Cs to C paraffin isomers measured during the cracking of the gas oil at 500 C by the steam treated REY catalyst are shown in Table III. The yield of branched paraffins was generally five to ten times higher than the yield of normal paraffins and the major (>50%) portion of the branched paraffin yield consisted of monomethyl paraffins. 

H-NMR studies on 2,6-dimethylmorpholine314 and N-substituted 2,6-dimethylmorpholines315 are consistent with the single diequatorial conformation 391 for the cis isomers and with the equilibrium 392 393 for the trans isomers. The 13C-NMR spectrum of the monomethyl-, 2,3-, 2,5-, 2-6-, 3-5-dimethyl-, 2,3,4-, 2,3,6-trimethyl-, and 2,3,5,6-tetramethylmorpholines are largely consonant with expectations based on conformational principles derived from cyclohexane conformational analysis.316 The all-cis 2,3,5,6-isomer, which did not prove amenable to analysis by H-NMR spectro-... 

Possible inter relationships of natural substances are important. Similarities of the low molecular weight alkane isomers from crude oil and Fischer-Tropsch synthesis product have been reported. A similar composition for high temperature coal carbonization has been found. The C4 to C7 alkane isomers from these sources can be calculated quantitatively with equations developed for Fischer-Tropsch products. A reversal of the concentrations of the monomethyl isomers from CG (2 Me > 3 Me) to C7 (3 Me > 2 Me) occurs in all three products comparisons at higher carbon numbers indicate some dissimilarities. Naphthene isomers for crude oil and high temperature coal carbonization also have similar compositions. Aliphatic hydrocarbons from low temperature coal processes are considerably different. The C1 isotopic composition of pure compounds from the various sources are being compared in order to provide information on their origin. 

Other data on analyses of coal products have been given by Girling (9). A list of alkanes found, but not quantitatively determined, from C through C7, indicates that the normals and monomethyl isomers predominate. This again is similar to crude oil and Fischer-Tropsch product. 

Branched chain fatty acids are present in milk (Kurtz 1974 Patton and Jensen 1976), and the following have been identified monomethyl 11-24 13-19, three or more positional isomers and multimethyl 16-28. Iverson (1983) and Iverson et al. (1965) identified the branched and other acids with the aid of urea fractionation. Saturated n-fatty acids of longer chain length form inclusion complexes with urea more readily than acyls with functional groups. The branched chain fatty acids do not form adducts. 

It is proposed that the high selectivity to isomers even at high conversion is obtained because the formation of n-hydrocarbon from the monomethyl isomers, i.e. the reverse reaction, occurs at a higher rate over the molybdenum oxycarbide catalysts than the bifunctional Pt/jS-zeolite catalyst. Over the Pt/jS-zeolite catalyst this reverse reaction would involve... 

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,... 

Oxidation with Potassium Permanganate.—Oxidation with potassium permanganate of 2- and 3-desoxyhexose monomethyl ethers, obtained from the cardiac glycosides or by synthesis, has been employed extensively by Reichstein and his colleagues, since valuable information on the structures of the sugars is thereby provided. This reaction results in the formation from either a 2-desoxyhexose 3-methyl ether or a 3-desoxyhexose 2-methyl ether, of one of the isomers of methoxysuccinic acid, which is usually isolated as the diamide. 

Despite the fact that both normal and monomethyl-substituted paraffins readily enter the pores of ZSM-5 and ZSM-11, preferential sorption of the normal isomer is observed under thermodynamic equilibrium, non-kinetically controlled conditions. Whereas small-pore zeolites, such as 5A and erionite, totally exclude branched hydrocarbons, and large-pore zeolites exhibit little preference, the intermediate pore-size zeolites ZSM-5 and ZSM-11 show a marked preference for sorption of the linear paraffin, even under equilibrium conditions. Competitive liquid phase sorption studies at room temperature indicated selectivity factors greater than ten in favor of n-hexane relative to... 

Fig. 10) has been carried out (52) and the result was compared with those of the monomethyl acetals 50 and 1, and the gem-dimethyl acetals 52 and 53. Each pair of isomers gave essentially an identical result, i,e. 33% of the equatorial and 77% of the axial isomer ( 2%) after equilibration in benzene at 70°C. This corresponds to a aG of =0.8 kcal/mol, a value close to that predicted for the relative stability of rotamer A over E (0.6 kcal/mol). 

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