Neohexane reactions

A study on neohexane reactions revealed (167, 168) that the inactive additives suppress hydrogenolysis of neohexane in a way similar to that which suppresses hydrogenolysis of hexane. It can be further seen (see Fig. 16) that these additives do not substantially alter the regularly observed preference of Pt for the reactions induced by 3Cay complexes, as opposed to those which are induced by 2Ca/J complexes. Alloying with Au or Ag only strengthens this preference. Rather surprisingly, the addition of Cu has quite different consequences (see below). 

The study of archetype molecules. This method has been proposed and widely used by Rooney, Burwell, Anderson, and others (see, for review, 155,156,160). In this method a molecule is used which can form an archetype of chemisorbed complex ( caged molecules as derivatives of ada-mantane or ethane in its hydrogenolysis, neopentane in exchange with D2 or in reforming reactions, etc.) or which can form several complexes, but the contribution of these complexes to the overall mechanism is easily derived from the product spectrum [as is the case, for example, with neohexane (167, 168). ... 

Results on reactions of neohexane and neopentane confirmed that Pt and, to a less extent, Pd are able to form 3Cay-type complexes rather than the... 

Fig. 14. Product patterns as a function of temperature in neohexane/H2 reactions (a) Pure Ni measured at low temperatures (b) pure Ni diluted by Si02 and self-poisoned by the running reactions (notice that methane > neopentane, i.e., multiple reactions are also running at the lowest conversions) (c) alloy of Ni/Cu in the ratio 65 35 (increase in methane < decrease in neopentane this indicates that molecules other than methane are formed, i.e., the role of ay is larger here). From V. Ponec el at., Faraday Discuss. No. 72, p. 33.

Fig. 15. Selectivity for nondestructive reactions in hexane (HEX) and neohexane (NEOHex) reactions (in H2) in the temperature range 173-603 K. From V. Ponec et ai, Faraday Discuss. No. 72, p. 33.

Fig. 16. Selectivity in the formation of various adsorbed 3C and 2C complexes upon reactions of neohexane with hydrogen for Pt/Si02, Pt-Ag/Si02, and Pt-Au/Si02 with compositions and temperatures of reactions as indicated (H-hydrogenolysis).

Palladium alloys and their behavior in hexane reactions were already mentioned above. Figure 17 shows that the behavior of neohexane is similar to that of hexane. 

Although in some cases radicals were observed as the primary products of radiolysis, they might also be produced in secondary reactions. Thus the production of the (-butyl radical in the radiolysis of neopentane, neohexane and 2,2,4-trimethylpentane was attributed to the addition of hydrogen atoms to isobutylene... 

Fig. 5.9. Total activity (conversion per mg/cat) as a function of catalyst composition, in reactions of neohexane on Pt-Re/ AI2O3 catalysts.

For example, the reaction of propane with ethylene at 510° and 4500 p.B.i. pressure resulted in a liquid product containing 55.5% by weight isopentane and 16.4% ii-pentane, 7.3% hexanes and 10.1% heptanes 7.4% alkenes were also present. The formation of alkenes and other by-products indicates that thermal cracking occurred. The alkylation of isobutane with ethylene under the same conditions yielded a liquid product containing 44.3% by weight neohexane, 11.6% isohexane, 1.1% n-hexane, 4.5% heptanes, 9.6% octanes as well as minor amounts of other alkanes and alkenes. This reaction has served as a means for producing neohexane commercially. 

Other alkanes have not however been neglected. n-Pentane has been less studied, perhaps because the more limited scope of its reactions, and, although the Cs ring is strain-free, n-pentane is less easily cyclised than n-hexane, and indeed n-heptane cyclises even more effectively (see Table 14.1). neoHexane (2,2-dimethylbutane) has three types of C—C bond, the reactivities of which differ, while 2,2,3,3-tetramethylbutane has only two types of C—C bond, the breaking of which gives either two molecules of wobutane or methane - -trimethylbutane. These have been usefully employed to characterise catalysts, and the different reactivities of C—C bond in other branched alkanes have also been examined (Section 14.2.4). 

The possible reaction paths available to neohexane (2,2-dimethylbutane) were shown in Scheme 14.3. On various supported platinum catalysts, values of Si (to all isomers) were between 36 and 74%, depending no doubt on factors such as dispersion and surface composition, but only 9% on platinum black. ° Detailed product analysis revealed that most of the products (50-70%) were formed through the ay route and most of the remainder through the ay route. 2.2-Dimethylbutane reacted similarly on Pt/Si02 at 568 This is striking evidence of the ease with which such species can be found on platinum surfaces, to... 

Nariginase, MA copolymer coupled, 445, 451 Neocarzinostatin, SMA resin reaction, 445 Neohexane, MA CTC, 210... 

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