Friedel-Crafts acylation acyl cations

The electrophile in a Friedel-Crafts acylation reaction is an acyl cation (also referred to as an acylium ion) Acyl cations are stabilized by resonance The acyl cation derived from propanoyl chloride is represented by the two resonance forms... 

An acyl cation is an intermediate m Friedel-Crafts acylation reactions... 

PoIysuIfonyIa.tlon, The polysulfonylation route to aromatic sulfone polymers was developed independendy by Minnesota Mining and Manufacturing (3M) and by Imperial Chemical Industries (ICI) at about the same time (81). In the polymerisation step, sulfone links are formed by reaction of an aromatic sulfonyl chloride with a second aromatic ring. The reaction is similar to the Friedel-Crafts acylation reaction. The key to development of sulfonylation as a polymerisation process was the discovery that, unlike the acylation reaction which requires equimolar amounts of aluminum chloride or other strong Lewis acids, sulfonylation can be accompHshed with only catalytic amounts of certain haUdes, eg, FeCl, SbCl, and InCl. The reaction is a typical electrophilic substitution by an arylsulfonium cation (eq. 13). 

Friedel-Crafts acylation, 2, 322 Quinoline, methyl-basicity, 2, 172 NMR, 2, 120 radical cations... 

Among the most common and synthetically-usef electrophiles are nitronium and acyl cations, NO2+ at CH3CO+, respectively. The former is the active agent electrophilic nitration while the latter is the active reage in Friedel-Crafts acylation. 

Friedel-Crafts acylation involves electrophilic attack by acyl cation (CHsCO ) on the ring, and the ring s electronic character should indicate its susceptibility to attack. Compare electrostatic potential maps of ferrocene and acetylferrocene. Which molecule contains the most electron-rich ring Which acylation reaction should be faster Does an acetyl substituent enhance or diminish ring reactivity What should be the major product when ferrocene is combined with one equivalent of acetic anhydride ... 

Figure 16.9 Mechanism of the Friedel-Crafts acylation reaction. The electrophile is a resonance-stabilized acyl cation, whose electrostatic potential map indicates that carbon is the most positive atom (blue).

The mechanism of Friedel-Crafts acylation is not completely understood, but at least two mechanisms probably operate, depending on conditions. In most cases the attacking species is the acyl cation, either free or as an ion pair, formed by ° ... 

Furthermore, if the 2,4,6-triphenyl ester (187a) is dissolved in cone. H2S04 the brilliant colour of 1,3-diphenylfluorenone is at once observed—obtained via ring-closure (intramolecular Friedel-Crafts acylation) of the acyl cation (188a) ... 

The first example of SILP-catalysis was the fixation of an acidic chloroaluminate ionic liquid on an inorganic support. The acidic anions of the ionic liquid, [AI2CI7] and [AI3CI10], react with free OH-groups of the surface to create an anionic solid surface with the ionic liquid cations attached [72]. The catalyst obtained was applied in the Friedel-Crafts acylation of aromatic compounds. Later, the immobilisation of acidic ionic liquids by covalent bonding of the ionic liquid cation to the surface was developed and applied again in Friedel-Crafts chemistry [73]. 

Acyl-transfer reactions are some of the most important conversions in organic chemistry and biochemistry. Recent work has shown that adjacent cationic groups can also activate amides in acyl-transfer reactions. Friedel-Crafts acylations are known to proceed well with carboxylic acids, acid chlorides (and other halides), and acid anhydrides, but there are virtually no examples of acylations with simple amides.19 During studies related to unsaturated amides, we observed a cyclization reaction that is essentially an intramolecular acyl-transfer reaction involving an amide (eq 15). The indanone product is formed by a cyclization involving the dicationic species (40). To examine this further, the related amides 41 and 42 were studied in superacid promoted conversions (eqs 16-17). It was found that amide 42 leads to the indanone product while 41... 

A Friedel-Crafts acylation is a synthetic method that avoids the problem of rearrangement of the cation. Figure 7-10 illustrates the generation of the electrophile (the acylium ion) from an acid chloride. The presence of resonance stabilizes the acylium ion, and that reduces the possibility of rearrangement. 

Friedel Crafts acetylation of butadiene complex 56 proceeds smoothly to give a mixture of 1-acetyldienes 58 and 59 via the cationic 7r-allyl complex 57 [16]. Intramolecular Friedel-Crafts acylation with the acid chloride of the diene complex 60, promoted by deactivated AICI3 at 0 °C, gave the cyclopentanones. The (Z)-dienone complex 61 was the major product and the ( )-dienone 62 the minor one [17]. Acetylation of the 1,3-cyclohexadiene phosphine complex 63 proceeded easily at —78°C to give the rearranged complex 65 in 85% yield. Without phosphine coordination, poor results were obtained [18,19], In this reaction, the acetyl group at first coordinates to Fe, and attacks at the terminal carbon of the diene from the same... 

The Friedel-Crafts acylation of acetanilide with chloroacetyl chloride yields l-acetamido-4-chloroacetylbenzene. The trimethylammonium group is introduced by reaction with trimethylamine, followed by hydrolysis of the acetamide group. This diazo component is a constituent of numerous yellow, orange, and red cationic azo dyes. Using diethyl- m-toluidine as the coupling component, the lightfast red dye 35 [67905-12-8] is obtained [99],... 

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