Trimethylpentane, aromatization

Aromatics were measured in a 20% blend with a 60/40 mixture of 2,2,4-trimethylpentane and / -heptane. 

Kazansky et al. (5) estimated the role of C5 cyclic intermediates in aromatization to be about 5% over platinum on carbon. Dautzenberg and Platteeuw found about 11% C5 cyclic pathway with nonacidic platinum on alumina (23). 2,2,4-Trimethylpentane is forced to produce aromatics via C5 cyclization because of its structure here the quaternary carbon atom facilitates ring enlargement (5, 23). 

Ipatieff and coworkers observed first that A1C13 catalyzes the destructive alkylation of aromatics with branched alkanes.179 For example, rm-butylbenzene (35%), p-di-rm-butylbenzene (25%), and considerable isobutane are the main products when benzene is reacted at 20-50°C with 2,2,4-trimethylpentane. Toluene and biphenyl are alkylated at 100°C in a similar way.180 Straight-chain alkanes required more severe reaction conditions. n-Pentane reacted at 175°C to yield 8% propylbenzene, 25% ethylbenzene, and 20% toluene.181 Phosphoric acid afforded similar products at higher temperature (450°C).182 Pentasil zeolites and dealumi-nated pentasils have been found to promote alkylation of benzene with C2—C4 alkanes to form toluene and xylenes.183,184... 

More information is available about orientation, when a second alkyl group is introduced into the aromatic ring, and about relative rates. As might be expected, propene reacts more easily than ethylene [342,346] and isobutene more easily than propene [342]. Normal butenes are sometimes isomerised in the process practically the same product composition, consisting mainly of 2,2,4-trimethylpentane, is obtained in the alkylation of isobutane whether the olefin component is isobutene or 2-butene [339]. In the alkylation of aromatic hydrocarbons, this side reaction is negligible. 

Triems [12,13] classified oils by fractionating the top residue of the oil, freed from compounds boiling at more than 200°C, on silica gel with 2,2,4-trimethylpentane, benzene and acetone as eluants. Three classes of oil were differentiated, viz. paraffinic-naphthenic, naphthenic-aromatic and aromatic-naphthenic. Each class is subdivided into three groups according to their sulphur content. 

Shuikin (370) passed methyl and dimethyl cyclohexanes over nickel at 330-350°. In addition to the usual demethylation and dehydrogenation reactions, he found evidence of methyl transfer methylcyclohexane gave some p-xylene, while dimethylcyclohexane gave some trimethylbenzene. Platinum at these temperatures did not cause this methyl transfer. Plate and O. A. Golovina (306) reported that appreciable demethylation of 2,2,4-trimethylpentane took place over molybdena-alumina at 150-250°C. and was accompanied by the formation of small amounts of aromatics. 

Other saturated hydrocarbons commonly used are cyclohexane (bp 81°), methylcyclohexane (bp 101°), and 2,2,4-trimethylpentane (isooctane, bp 99°). The latter compound has the advantage of being free of aromatic hydrocarbons, since it is prepared by the hydrogenation of diisobutylene. 

On the other hand, the 1-5 ring closure-ring enlargement process is supported by the initial formation of aromatics from a number of alkanes with only five carbon atoms in a linear chain (22, 25, 26, 33, 70, J32), by the easy aromatization of substituted cyclopentanes (63, 69, 132-134), and by the identical aromatic product distributions from 2,2,4-trimethylpentane and... 

The metallocyclobutane mechanism, already invoked to account for some aspects of the bond shift and cyclic mechanisms, allows one to rationalize the mechanism of 1-5 ring closure-ring enlargement. This mechanism is best represented by Schemes 61 and 62 for the aromatization of 1,1,3-trimethylcyclopentane and 2,2,4-trimethylpentane, respectively. It is emphasized that in the former case carbene-olefin recombination must be favored over carbene isomerization to di-Tt-adsorbed olefin, since xylenes are the major reaction products while 2,4-dimethylhexane is not detected (69). 

The octane number is increased by increasing the ratio of branched or aromatic hydrocarbons to straight-chain hydrocarbons. The 0-100 octane number scale assigns 0 to n-heptane and 100 to 2,2,4-trimethylpentane. 

Petroleum (Otto fuels) and aromatic hydrocarbons 40 % by volume 2,2,4-trimethylpentane (isooctane) 30 % by volume methylbenzene (toluene) 20 % by volume dimethyl- benzene (xylene) 10 %by volume methylnaphthalene... 

Octane number is measured by research. The octane number of hexane is 24.9, branched alkane wobutane is 101.3 and 2,3,4-trimethylpentane is 102.5, in aromatic compounds benzene is 106, toluene is 110 [28,29]. These compounds having high octane numbers are used for blending agents to gasoline. 

Figures 2.8 through 2.12 illustrate the general C-H absorption spectra-structure correlation by using three model compounds trimethylpentane, -decane, and toluene. Note that there are 12 methyl C-H bonds and 6 methylene C-H bonds in trimethyl-pentane and there are 6 methyl C-H bonds and 16 methylene C-H bonds in n-decane. In the toluene molecule, there are 3 methyl C-H bonds 0 methylene C-H bonds and 5 aromatic C-H bonds.

Phenyl radicals have an important role to play in the combustion of fossil fuels and in the formation of polycyclic aromatic hydrocarbons. The absolute rate constant for the reaction of CeHs with 2-methylpropane, 2,3-dimethylbutane and 2,3,4-trimethylpentane has been measured using cavity ring-down spectromehy between 290 and 500 K. The reactions were found to be dominated by the extraction of H atoms from the tertiary C—H bonds. ... 

The smoke point of a test fuel is compared to reference blends. A standard 40%/60% (volume/volume) mixture of toluene with 2,2,4-trimethylpentane has a smoke point of 14.7, while pure 2,2,4-trimethylpentane has a smoke point of 42.8. Clearly, isoparaffins have better smoke points than aromatics. 

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