1 -alkyl-2,3,6-trimethylbenzenes

The shape selective catalysis was examined by choosing five kinds of the reactions, Eqs. (1) - (5), that is, dehydration of 2-hexanol, decompositions of three kinds of esters and alkylation of 1,3,5-trimethylbenzene with cyclohexene. 

Figure 3. Catalytic activities of CsxH3-xPWi2O40 for decomposition of cyclohexylacetate and the alkylation of 1,3,5-trimethylbenzene as a function of the surface acidity.

Figure 5 shows the cataljdic activities of small-pore Cs2.1 and Cs2.2 relative to Cs2.5. Cs2.5 catalyzed all reactions with considerably high activities (the reaction rates are shown in the parentheses in Figure 5). On the other hand, although Cs2.2 was as active as Cs2.5 for the dehydration of 2-hexanol and decomposition of isopropylacetate, it was much less active for the decomposition of cyclohexylacetate and the alkylation of 1,3,5-trimethylbenzene. In the case of...

At a later stage alkylation with propylene to form l-isopropyl-2,4-trimethylbenzene is an important reaction to produce a bulky molecule. 

The course of the reaction of methyl-substituted benzene derivatives with cesium fluoroxysulfate in acetonitrile at 35-40 C strongly depends on the structure of the molecule. Toluene (16, R1 = R2 = H) and other alkyl-substituted benzenes 16 and 17 are mainly functionalized on the side chain, while 1,3.5-trimethylbenzene (18) gives mainly ring-substituted products 24 however. 1.2.4,5-tetramethylbenzene (19) and hexamethylbenzene again give mainly or exclusively side-chain products.25... 

The HO-toluene adduct corresponds to the methyl-substituted o-, m- and p-hydroxycyclohexadienyl radical isomers. The kinetics of formation and of unimolecular dissociation of HO-aromatic adducts have been studied extensively [30], The benzyl radical -CH2 is converted to the aldehydic product 0-CHO in the presence of NO via a series of reactions analogous to those involving simple alkyl radicals. Bandow et al. [144-146] have determined the yields of aromatic aldehydes to be < 12% of the overall reactions of toluene, xylenes, and trimethylbenzenes, and thus, the H-atom abstraction channel is relatively small but significant. In the case of 0-CHO, the... 

The influence of the heteroatom on the acid strength is shown, for example, in Fig. 28. Here the rates of alkylation of 1,3,5-trimethylbenzene and the decomposition of cyclohexyl acetate catalyzed by the acid forms of several 12-tungstates are plotted against the negative charge of polyanion for solid heteropolyacids (63, 183). The catalytic activities correlate well with the acid strength in solution (Fig. 14). This correlation indicates that the acid strength of... 

As described in Section II, the pore size of the acidic Cs salts can be controlled by the Cs content. CS2.2H0.8PW12O40 (Cs2.2) has pores having an effective size of 6.2-7.5 A, and the pore size of Cs2.5 is larger than 8.5 A. Figure 30 shows the catalytic activities of Cs2.1 (the pore size is less than 5.9 A) and Cs2.2 for each reaction relative to the activity of Cs2.5 (48). Cs2.5 catalyzed all the reactions with considerable activities (the reaction rates are shown in parentheses in Fig. 30). On the other hand, although Cs2.2 was found to be as active as Cs2.5 for dehydration of 2-hexanol (molecular size, 5.0 A) and decomposition of isopropyl acetate (molecular size, 5.0 A), it was much less active for the decomposition of cyclohexyl acetate (molecular size, 6.0 A) and alkylation of 1,3,5-trimethylbenzene (molecular size, 7.5 A). Therefore, Cs2.2 is... 

Fig. 31. Catalytic activities of acidic Na or Cs salts of HjPW 204o as a function of Na or Cs content, (a) M = Na (O) dehydration of 2-propanol, (A) decomposition of formic acid, ( ) conversion of methanol, ( ) conversion of dimethyl ether, (b) M = Cs (O) dehydration of 2-propanol, ( ) conversion of dimethyl ether, (A) alkylation of 1,3,5-trimethylbenzene with cyclohexene. (From Refs. 46 and 128.)...

Fig. 33. Catalytic activities of various acid catalysts for liquid-phase reactions. TMB Alkylation of 1,3,5-trimethylbenzene with cyclohexene CA Decomposition of cyclohexyl acetate. (From Ref. 47.)...

A range of diols and cyclic ethers were used to carry out alkylation of aromatics (benzene, toluene, xylenes, trimethylbenzenes, naphthalene) in the presence of triflic acid.204 310 In a recent study,311 various methyl-substituted benzene derivatives were alkylated with 1,4-diols [Eq. (5.117)] to form substituted tetralin derivatives in high yields. The transformations involve an intermolecular alkylation step followed by intramolecular alkylation (cyclialkylation). 2,2,5,5-Tetramethyltetrahydrofuran is similarly effective. For example, it alkylates benzene to give octamethyloctahydroan-thracene (98% yield) and reacts with naphthalene to yield octamethyloctahydrote-tracene [Eq. (5.118)]. 

An attempt to generate an amino-aryl carbene 154 from the alkylated phenanthridinium salt 153 (Equation 78) <2006TL531> was unsuccessful due to steric interactions. The actual reaction with a variety of strong, sterically hindered bases/nucleophiles is shown (Equations 79-81). The mesityllithium products proved that a carbene intermediate is not possible. Unlike /-butyl alcohol and hexamethyldisilazane, trimethylbenzene, the conjugate acid of mesityllithium, is not prone to carbene insertion reactions. Electronically this is explained by the planar nature of 153 which serves to lower the lowest unoccupied molecular orbital (LUMO) energy of the iminium moiety. 

As with HZSM5-la, we attribute the initial deactivation to blocking of catalytically active sites by adsorbed xylene molecules preventing toluene methylation to occur at these sites. The longer residence time of the bulkier xylene isomers in the larger crystals of HZSM5-2 (see Table 1) seems to favour further alkylation of m- and o-xylene to trimethylbenzenes over isomerization to p-xylene Once trimethylbenzene is formed, dealkylation is rather difficult at 573 K and its rate of transport is too low to be able to diffuse out of the zeolite pores. It forms, thus, a dead end product that decreases the availability of active sites and reaction intermediates (leading to slow deactivation). 

Figure 4. Changes in catalytic activity for the alkylation of 1,3,5-trimethylbenzene (TMB) with cyclohexene and surface acidity (number of protons on the surface) as a function of Cs content in CsxHj xPWi204o-...

The group B salts of H3PW12O40 are also strong acids unless they are stoichiometrically neutralized. These salts catalyze various kinds of reactions in the liquid phase as solid catalysts. For the alkylation of 1,3,5-trimethylbenzene with cyclohexene, the activity of CS2.5H0.5PW12O40 (abbreviated as CS2.5W) is much higher than those of SC>4 /Zr02 and Nafion. Here, CS2 5W is not soluble and the reactions take place on the surface of the solid. 

Figure 7 Shape selective trans alkylation of m-xylene to 1,2,4-trimethylbenzene.

Analyses of l-alkyl-2,3,6-trimethylbenzenes from Silurian and Devonian oils in western Canada indicate the existence of green sulfur bacteria in restricted seas about 400 million years ago [44]. 

Alkylation of toluene with methanol Al-M Xylenes and trimethylbenzenes were the main products. Selectivity to xylenes increased with time on stream due to deactivation. 39... 

---