Methyl substituted aromatics

The disruption of chain regularity by the introduction of lateral substituents or kinks on repeating units is a supplementary means to decrease the melting temperature of aromatic polyesters.72 This is illustrated in Table 2.9, where the melting temperatures of unsubstituted and methyl-substituted aromatic-aliphatic and aliphatic acids are reported. Regularity disruptions often cause significant... 

The scope and mechanism of the isomerization of arylamines to methyl-substituted aromatic heterocycles have been studied. Aniline, toluidines, naphthylamines and m-phenylenediamine all gave the corresponding ortho-methyl-substituted aza-aromatics when exposed to high NHj pressure and elevated temperature in the presence of acid catalysts, e.g., zeolites. The yiel of pyridines formed by this process range from low to moderate <95JC(155)268>. 

Jahnke M, E Lehmann, A Schoebel, G Auling (1993) Transposition of the TOL catabolic genes Tn46521 into the degradative plasmid pSAH of Alcaligenes sp. 0-1 ensures simultaneous mineralization of sulpho-and methyl-substituted aromatics. J Gen Microbiol 139 1959-1966. 

Taeger K, H-J Knackmuss, E Schmidt (1988) Biodegradability of mixtures of chloro- and methyl- substituted aromatics simultaneous degradation of 3-chlorobenzoate and 3-methylbenzoate. Appl Microbiol Bio-technol 28 603-608. 

Selifonov SA, M Grifoll, RW Eaton, PJ Chapman PJ (1996) Oxidation of naphthenoaromatic and methyl-substituted aromatic compounds by naphthalene 1,2- dioxygenase. Appl Environ Microbiol 62 507-514. 

Oxidation of Methyl-Substituted Aromatics. Autoxidation of alkyl-substituted... 

Methyl-substituted aromatics may also be converted to the corresponding carboxylic acids. As was mentioned above, a shift in the selectivity of the autoxidation of methyl-substituted arenes is brought about by metal ions eventually producing carboxylic acids. Carboxylic acids may also be formed by the base-catalyzed autoxidation of methyl-substituted arenes.848 Oxidation with tert-BuOK in HMPA affords carboxylic acids in moderate yields with very high selectivities. 

The radical mechanism has also been proposed as a general mechanism for oxidation of alkenes and aromatics, but several objections have been raised because of the absence of products typically associated with radical reactions. In classical radical reactions, alkenes should react also at the allylic position and give rise to allyl-substituted products, not exclusively epoxides methyl-substituted aromatics should react at the benzylic position. The products expected from such reactions are absent. Another argument was made against the radical mechanism based on the stereoselectivity of epoxidation. Radical intermediates are free to rotate around the C C bond, with the consequence that both cis- and /rani-epoxides are formed from a single alkene isomer, contrary to the evidence obtained with titanium silicates (Clerici et al., 1993). 

According to this hypothesis, the results are modified from what would be expected from classical radical reactions. The interest in this hypothesis is that, with the sole exception of saturated hydrocarbons, it could apply to all the compounds that can be coordinated at the Tiiv center, such as alkenes, aromatics, alcohols, and sulfides. According to this hypothesis, the weak Lewis acidity of Tilv would help to bring the reactant into its coordination sphere. The initial coordination of the reactant would explain the oxidation of methyl-substituted aromatics in the aromatic ring and not in the side chain, even with a radical-type mechanism. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

Methyl-substituted aromatic hydrocarbons are readily oxidized by permanganate into benzoic acid derivatives.311 Toluene, p-xylene and mesitylene are respectively converted to benzoic, terephthalic and trimesic acids in ca. 90% yield by potassium permanganate in the presence of cetyltrimethylammonium chloride.321... 

Streitwieser Jr, A. Schwager, I. 1962 A molecular orbital study of the polarographic reduction in dimethylformamide of unsubstituted and methyl-substituted aromatic hydrocarbons. J. Am. chem. Soc. 66, 2136-2320. 

Similarly, cobaltic and argentic ion have been generated by anodic oxidation of cobaltous and argentous ion, respectively, and used for the oxidation of methyl-substituted aromatic hydrocarbons to aldehydes 18a Electrogenerated mercuric ion can be used for the conversion of propene to acrolein 18al ... 

Computational studies of the OH interactions with other methyl substituted aromatic compounds have been performed by only a few research groups... 

It has been shown for both the selective oxidation of butane (43) and the ammoxidation of methyl-substituted aromatics (55) that the strength of spin-spin exchange in -containing bulk catalysts is related to the catalytic performance. Moreover, results discussed in this section illustrate that the spin-spin exchange properties are already determined by the conditions of catalyst formation and can be assessed in a unique way by EPR spectroscopy. Thus, this technique provides local structural information even for amorphous constituents or disordered phases—information that is hardly accessible by other methods such as XRD. This point is significant because active sites in real catalysts are frequently not located in well-crystallized phases but instead in disordered or even amorphous phases. 

As with preparing allyl of benzyl halides and alkali useful route to benzylalkali R-R coupling. Benzylalkali prepared by (1) addition of arylalkenes, (2) cleavage of benzyl ethers (equation 28), (3) transmetallation (equations 29-31), and (4) metallation of methyl substituted aromatics. a, a -Bis(trimethylsilyl)benzyl potassium can be prepared by metallation with a mixture of butyllithium and potassium 3-methyl-3-pentanolate in THF. ... 

A methyl substituted aromatic compound such as p-cresol can be best converted to the corresponding aldehyde such as p-hydroxy benzaldehyde by reacting a methanolic alkaline p-cresol in presence of a mixed co-acetate-Mn-acetate catalyst at a pressure of 8-lOkg/cm and temperature of 75-100°C in presence of air and a solvent such as piperidine or an amine (ammonia, triethylamine, etc.) that would yield approximately 80-90% of the aldehyde in about 16-18 hr. 

Due to the shape-selective pore structure of the ZSM-5 class catalysts, the hydrocarbons fall predominantly in the gasoline boiling range. The product distributions are influenced by the temperature, pressure, space velocity, reactor type, and Si/Al ratio of the catalyst [73,74]. Paraffins are dominated by isoparaffins, while aromatics are dominated by highly methyl-substituted aromatics. The C9+ aromatics are dominated by symmetrically methylated isomers reflecting the shape selective nature of the catalysis. The Cj0 aromatics are mostly durene (1,2,4,5-tetramethylbenzene), which has an excellent octane... 

Benzylic oxidation of aromatic side-chains is also a well established technology in the bulk chemicals arena, e. g. toluene to benzoic acid and p-xylene to ter-ephthalic acid [1,2]. These processes involve homogeneous catalysis by, e. g., cobalt compounds, however, and also fall outside the scope of this book. Ammoxi-dation of methyl-substituted aromatic and heteroaromatic compounds is performed over heterogeneous catalysts in the gas phase but this reaction is treated elsewhere (Section 9.5). Transition metal-substituted molecular sieves have been widely studied as heterogeneous catalysts for oxidation of aromatic side-chains in the liquid phase, but there are serious doubts about their heterogeneity [5,6]. Here again, a cursory examination of the literature reveals that supported palladium seems to be the only heterogeneous catalyst with synthetic utility [4]. 

Another refinement of the isodesmic approach to defining aromatic stabilization is to compare methyl-substituted aromatics with the corresponding... 

Lissi et al. (1985) measured the reactivity of r-C4H90 radicals with a number of methyl-substituted aromatic compounds in benzene solution at 120°C. Their results are given in Table 24. They found that the reactivity depended almost exclusively on the aromatic moiety and was almost independent of the methyl-group position. 

Besides the internal and external vibrations of the molecules, there are, as already mentioned, also stochastic or at higher temperatures nearly free rotations of entire molecules in some molecular crystals (e.g. the benzene molecules in a benzene crystal or the -CH3 groups in methyl-substituted aromatics). And finally, molecules in molecular crystals, like atoms in atomic crystals, can diffuse. 

This family of foidamers consists of two, three, or five alternating aromatic heterocydes (pyridazine, pyrimidine, or pyrazine) and methyl-substituted aromatic carbocycles (tolyl, o-xylyl, or m-xylyl) cormected via urea groups (8 Figure 9.3) [14]. In a typical synthesis, heterocyclic diamine compounds were treated with aryl diisocyanate compounds to install a urea linkage between aromatic heterocyde and aromatic carbocyde (Umax = 5). 

T. D. Greenwood, R. A. Kahley, and J. E Wolfe, 7/-methyl-substituted aromatic polyamides, Journal of Polymer Science Polymer Chemistry Edition, 18, 1047(1980). 

Hydroxylation of monophenols to predominantely />-diphenols or oxidation of methyl-substituted aromatics by persulfates ... 

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