Cations benzoyl

The oxygen transfer to the -acetylenic carbon results in the very intense benzoyl cation, whereas the transfer to the a-carbon, via a series of fragments corresponding to the loss of OH , CO and CO2, respectively, leads to annelated heterocycles such as the radical cation of carbazole, as a result of elimination of CO81. The generation of the benzoyl cation was rationalized as shown in Scheme 1281. 

C-protonated cation has also been reported for 2,4,6-triniethyl-benzoic acid in 99-103% sulphuric acid, in which it exists in equilibrium with the carbonyl-protonated cation and the corresponding benzoyl cation (Beistel and Atkinson, 1969). The latter appears in 100% sulphuric acid, increases in concentration with increasing acid concentration at the expense of the other forms and is the only form observed at concentrations >105% sulphuric acid. 

The higher stability of the benzoyl cation agrees with the higher sensitivity to polar effects of the corresponding radical. 

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

The consecutive formation of o-hydroxybenzophenone (Figure 3) occurred by Fries transposition over phenylbenzoate. In the Fries reaction catalyzed by Lewis-type systems, aimed at the synthesis of hydroxyarylketones starting from aryl esters, the mechanism can be either (i) intermolecular, in which the benzoyl cation acylates phenylbenzoate with formation of benzoylphenylbenzoate, while the Ph-O-AfCL complex generates phenol (in this case, hydroxybenzophenone is a consecutive product of phenylbenzoate transformation), or (ii) intramolecular, in which phenylbenzoate directly transforms into hydroxybenzophenone, or (iii) again intermolecular, in which however the benzoyl cation acylates the Ph-O-AfCL complex, with formation of another complex which then decomposes to yield hydroxybenzophenone (mechanism of monomolecular deacylation-acylation). Mechanisms (i) and (iii) lead preferentially to the formation of p-hydroxybenzophenone (especially at low temperature), while mechanism (ii) to the ortho isomer. In the case of the Bronsted-type catalysis with zeolites, shape-selectivity effects may favor the formation of the para isomer with respect to the ortho one (11,12). 

Aromatic Amides Benzamide (Fig. 2.1) is a typical example. Loss of NH2 from the molecular ion yields a resonance-stabilized benzoyl cation that in turn undergoes cleavage to a phenyl cation. 

Mass spectra of hydroxy- and alkoxy-coumarins have been very intensively studied. The decomposition sequence of 3-hydroxycoumarin is initiated by carbon monoxide loss from the molecular ion giving a 2-hydroxybenzofuran ion. Subsequent fragmentation occurs by two major pathways, involving a further loss of CO and expulsion of a formyl radical. The former leads to the base peak, and thence by another loss of CO to give the abundant benzene radical cation at m/e 78. The other main pathway gives a benzoyl cation which leads to the phenonium ion at m/e 77 (77IJC(B)816). 

The first example of a perfluorinated cation - F-cylopropenium - was reported by Sargeant and Krespan in 1969 [60], and it was followed by the discovery of F-benzyl [61] and F-benzoyl cations [21]. Since several unsuccessful attempts to generate F-allyl carbocations were reported [21, 40, 62], another stepwise approach to polyfluorinated delocalized cations has been developed. Stability of a polyfluorinated allylic system could be significantly increased by introduction... 

Gokel, G. W., Cram, D. J., (1973) Molecular complexes of arenediazonium and benzoyl cations by macrocyclic polyethers Chem. Commun. 481-482. 

In general, the state diagram on the left in Figure 2 is a good description for organic ions. As an example, the photodissociation spectrum of benzoyl cation obtained by monitoring process 8 has two maxima at 260 nm and 310 nm... 

Cotter and Knight have reported the ionic and thermal fragmentation of 2,5-diphenyl-l,3,4-oxadiazole 24. The major fragmentation pathways for the molecule ion 8) and neutral 27) are shown in Eq. (13) and (14) respectively. The benzoyl cation mje 105) is certain to be relatively more stable than its neutral analog the reverse is true of the benzonitrile molecule. It seems likely that products which result from loss of H2, including benzoyl radicals will be obtained from 24 on photolysis. 

For the ortho, meta and para isomers, however, two dissociation routes compete (Scheme 28), i.e. that forming the pair comprised of the isomeric aminobenzoyl cations of m/z 120 and aminophenyl cations of m/z 92, and that forming the pair comprised of the benzoyl cation of m/z 105 and phenyl cation of m/z 77. Note that for the ortho... 

In a comparative study on the acylation of mesitylene and anisole with BC, promoted by clayfen, - it is observed that mesitylene reacts faster (by a factor of three) when the reactions are carried out separately. However, when the two substrates are reacted jointly, competition favors anisole (by fhe same factor of three). A tentative explanation for this reversal activity can be based on the assumption that benzoylation of mesitylene and anisole follows fwo different mechanisms characterized by different levels of interaction of fhe catalysf surface with the aromatic substrate and the benzoyl cation. In particular, it must be taken into consideration that anisole interacts more strongly than mesitylene with the acid centers of the catalyst and, consequently, its intrinsic higher reactivity toward the acyl cation can be dramatically lowered, and the acid sites are less available for mesitylene acylation reaction. 

It is known that, in acylation reactions in homogeneous [14,15] or heterogeneous [16] conditions, the rate determining step is the attack of the electrophilic species RCO+, previously formed in a fast step, on the aromatic ring. Electrophilicity of benzoyl cations X-Ar-CO+ increases with the presence of electron-withdrawing substituent, while it decreases with electron-donating substituents on the aromatic ring. 

Such a result is assumed to be directly related to the high reactivity of thiophene towards electrophiles. The rate of the attack of the benzoyl cation X-ArCO on the heterocyclic ring (slow step) is not affected by its electrophilicity, high or weak, once it is formed (fast step). 

The base peak in the mass spectrum appears at mie = 105. This peak is likely due to the formation of a benzoyl cation. 

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