Alkylation with alkanes

Alkylation with Alkanes. Alkylation of aromatic hydrocarbons with alkanes, although possible, is more difficult than with other alkylating agents (alkyl halides, alkenes, alcohols, etc.).178 This is due to the unfavorable thermodynamics of the reaction in which hydrogen must be oxidatively removed. 

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 

Alkylation without cracking was shown by Schmerling et al. to take place when saturated hydrocarbons react with benzene in the presence of A1C13 and a 

Oxidative removal of hydrogen by cupric chloride was suggested by Schmerling to explain the observations 189 

Superacids were shown to have the ability to effect the protolytic ionization of a bonds to form carbocations even in the presence of benzene.190 The formed car-bocations then alkylate benzene to form alkylbenzenes. The alkylation reaction of benzene with Ci—C5 alkanes (methane, ethane, propane, butane, isobutane, isopentane) are accompanied by the usual acid-catalyzed side reactions (isomerization, disproportionation). Oxidative removal of hydrogen by SbF5 is the driving force of the reaction  

---

Benzene alkylation with alkanes over modiBed MFI catalysts... 

Benzene alkylation with alkanes over modified MFI catalysts A.V. Smirnov, E.V. Mazin, O.A. Ponomoreva, E.E. Knyazeva, S.N. Nesterenko and 1.1. Ivanova... 

Aromatics Alkylation With Alkanes, Alkenes, and Alcohols (Cumene, Dimethyinaphthalene, Ethylbenzene, and Diethylbenzene)... 

Table 4 2 lists the boiling points of some representative alkyl halides and alcohols When comparing the boiling points of related compounds as a function of the alkyl group we find that the boiling point increases with the number of carbon atoms as it does with alkanes... 

Chlorination of alkanes is less exothermic than fluonnation and bromination less exothermic than chlorination Iodine is unique among the halogens m that its reaction with alkanes is endothermic and alkyl iodides are never prepared by lodmation of alkanes... 

Bromine reacts direcdy with alkanes but this reaction has Httle value because mixtures are obtained. However, photochemical bromination of alkyl bromides can be quite selective (23). 

Chlorine gas reacts directly and highly exothermically with alkanes, giving rise to alkyl chlorides and hydrogen chloride, e.g., for addition to methane. 

It is very interesting, however, that in alkane potassium diazoate alkylations with Meerwein s reagent (triethyloxonium tetrafluoroborate, Et30+BF4) in CH2C12 suspensions or with alkyl halides in hexamethylphosphoric triamide solutions, azoxy compounds (6.4) are formed, i.e., alkylation takes place at the (3-nitrogen (Moss et al., 1972). 

Structure—Performance Characteristics of Surfactants in Contact with Alkanes, Alkyl Benzenes, and Stock Tank Oils... 

The results of the calculation of the activation energies and the rate constants of peroxyl, alkoxyl, and alkyl radicals with alkanes and cycloalkanes are presented in Table 6.3-Table 6.5. 

Control of H-C(sp3) Bond Cleavage Stoichiometry Clean Reversible Alkyl Ligand Exchange with Alkane in [LPt(Alk)(H)2]+ (L=[2.1.1]-(2,6)-Pyridinophane) (226) this complex activates hydrocarbons RH to yield LPtRHjT. This is similar to the C-H bond activation shown in Scheme 17 but occurs without added acid. 

With propene, n-butene, and n-pentene, the alkanes formed are propane, n-butane, and n-pentane (plus isopentane), respectively. The production of considerable amounts of light -alkanes is a disadvantage of this reaction route. Furthermore, the yield of the desired alkylate is reduced relative to isobutane and alkene consumption (8). For example, propene alkylation with HF can give more than 15 vol% yield of propane (21). Aluminum chloride-ether complexes also catalyze self-alkylation. However, when acidity is moderated with metal chlorides, the self-alkylation activity is drastically reduced. Intuitively, the formation of isobutylene via proton transfer from an isobutyl cation should be more pronounced at a weaker acidity, but the opposite has been found (92). Other properties besides acidity may contribute to the self-alkylation activity. Earlier publications concerned with zeolites claimed this mechanism to be a source of hydrogen for saturating cracking products or dimerization products (69,93). However, as shown in reaction (10), only the feed alkene will be saturated, and dehydrogenation does not take place. 

The polarity of the Al-C bond allows easy derivatization of the five-coordinate aluminum alkyls by alkane elimination (Figure 9). For example, Salen aluminum alkyls LAlMe could be converted to dimeric or polymeric Salen aluminum phosphinates [LAl 02P(H)Ph ] 98 (n = 2 or oo, depending on the Salen ligand backbone)98,99 by reaction with phenyl phosphinic acid, Salen aluminum siloxides LA10SiPh3 by reaction with triphenyl silanol,96 or Salen aluminum alkoxides LAIOR by reaction with an alcohol.100... 

This difference in behavior suggests different mechanisms. As already observed with cyclic alkanes, the initiahon is a C-H bond achvahon (likely via sigma bond metathesis), leading to the corresponding metal-alkyls. With group 4 metals, a... 

With alkanes, substitution occurs producing alkyl chlorides ... 

As already seen, the reactions of OH, N03, and Cl with alkanes generate alkyl radicals. We shall see in the subsequent sections of this chapter that the production of alkyl radicals of various types is a general characteristic of organic oxidations. Here we will trace the atmospheric fates of typical alkyl radicals formed in OH, NO-, and Cl atom oxidations of alkanes. However, the principles are general and can be applied to those formed by the reactions of other organics such as alkenes as well. 

Chlorine or bromine reacts with alkanes in the presence of light (hv) or high temperatures to give alkyl halides. Usually, this method gives mixtures of halogenated compounds containing mono-, di-, tri- and tetra-halides. However, this reaction is an important reaction of alkanes as it is the only way to convert inert alkanes to reactive alkyl halides. The simplest example is the reaction of methane with CI2 to yield a mixture of chlorinated methane derivatives. 

Silicon vapor reacts with alkanes, alkenes, alkynes, arenes, ketones, alkyl halides, and ethers to give mainly polymers (104). 

---