Alkanes Friedel-Crafts reaction

Synthesis of Aromatic Alkanes (Friedel-Crafts Reaction)... 

For a monograph, see Roberts, R.M. Khalaf, A.A. Friedel-Crafts Alkylation Chemistry Marcel Dekker NY, 1984. For a treatise on Friedel-Crafts reactions in general, see Olah, G.A. Friedel-Crafts and Related Reactions Wiley NY, 1963-1965. Volume 1 covers general aspects, such as catalyst activity, intermediate complexes, and so on. Volume 2 covers alkylation and related reactions. In this volume the various reagents are treated by the indicated authors as follows alkenes and alkanes, Patinkin, S.H. Friedman, B.S. p. 1 ... 

The other 60% of the alkyl groups for LAS detergents are made through linear a-olefins. n-Alkanes can be dehydrogenated to a-olefins, which then can undergo a Friedel-Crafts reaction with benzene as described above for the nonlinear olefins. Sulfonation and basification gives the LAS detergent. 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

Related classes of gitonic superelectrophiles are the previously mentioned protoacetyl dications and activated acyl cationic electrophiles. The acyl cations themselves have been extensively studied by theoretical and experimental methods,22 as they are intermediates in many Friedel-Crafts reactions. Several types of acyl cations have been directly observed by spectroscopic methods and even were characterized by X-ray crystal structure analysis. Acyl cations are relative weak electrophiles as they are effectively stabilized by resonance. They are capable of reacting with aromatics such as benzene and activated arenes, but do not generally react with weaker nucleophiles such as deactivated arenes or saturated alkanes. 

The acidic salts of heteropolyacids, in which the protons are partially substituted with Cs+, are active for acid-catalyzed reactions such as Friedel Crafts reactions, Ritter-type reactions, and skeletal isomerization of alkanes. The... 

For some time the main emphasis of Friedel-Crafts reactions was chiefly on aromatic compounds. The development of aliphatic Friedel-Crafts chemistry was of minor importance until World War 2, when isomerization of alkanes and cycloalkanes, preparation of high-octane aviation gasoline and synthetic rubber, and polymerization of alkenes achieved considerable importance these contributed to the growth of aliphatic Friedel-Crafts chemistry. 

More stable catalysts are obtained by using fluorinated graphite or fluorinated alumina as backbones and Lewis acid halides, such as SbFs, TaFs and NbFs, which have a relatively low vapor pressure. These Lewis acids are attached to the fluorinated solid supports through fluorine bridging. They show high reactivity in Friedel-Crafts reactions including the isomerization of straight chain alkanes such as n-hex-ane. 

Mixtures of CF3S03H and the triflates of B, A1 or Ga form a new superacid system, i.e. CF3S03H2 + [E(0S02CF3)4]- (E = B, A1 or Ga), which show superior catalytic activity in isomerization of alkanes, in trans-bromination and trans-alkylation of aromatics and in other related Friedel-Crafts reactions as compared with CF3S03H alone30-33. The relative reactivity sequence is B > Ga > Al. The triflates E(0S02CF3)3 were prepared from the reaction of EX3 (X = Br, Cl) with CF3S03H33. 

Alkylation of Aromatics. Aromatic hydrocarbons containing a replaceable hydrogen can be alkylated unless steric effects prevent introduction of the alkyl group (61,78-82). The reaction is called the Friedel-Crafts alkylation, first realized in the presence of aluminum chloride, which is the catalyst still the most frequently used and studied in Friedel-Crafts reactions. In addition, many other acid catalysts are effective (80,82-84). These include other Lewis acids (other aluminum halides, gallium chloride, boron trifluoride, ferric chloride, zinc chloride, stannous and stannic chloride, antimony chloride) and protic acids (hydrogen fluoride, concentrated sulfuric acid, phosphoric acid, polyphosphoric acid, trifluo-romethanesulfonic acid, and alkane- and arenesulfonic acids). 

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