Phenyltrimethylammonium ion

There is increasing evidence that the ionisation of the organic indicators of the same type, and previously thought to behave similarly, depends to some degree on their specific structures, thereby diminishing the generality of the derived scales of acidity. In the present case, the assumption that nitric acid behaves like organic indicators must be open to doubt. However, the and /fp scales are so different, and the correspondence of the acidity-dependence of nitration with so much better than with Hg, that the effectiveness of the nitronium ion is firmly established. The relationship between rates of nitration and was subsequently shown to hold up to about 82 % sulphuric acid for nitrobenzene, />-chloronitrobenzene, phenyltrimethylammonium ion, and p-tolyltrimethylammonium ion, and for various other compounds. ... 

Wheland intermediate (see below) as its model for the transition state. In this form it is illustrated by the case mentioned above, that of nitration of the phenyltrimethylammonium ion. For this case the transition state for -nitration is represented by (v) and that for p-substitution by (vi). It is argued that electrostatic repulsions in the former are smaller than in the latter, so that m-nitration is favoured, though it is associated rvith deactivation. Similar descriptions can be given for the gross effects of other substituents upon orientation. 

The log rate versus acid strength curve for the latter compound is of the exact form expected for reactions of the free base, whilst that of the former compound is intermediate between this form and that obtained for the nitration of aniline and phenyltrimethylammonium ion, i.e. compounds which react as positive species. That these compounds react mainly or entirely via the free base is also indicated by the comparison of the rate coefficients in Table 8 with those in Table 5, from which it can be seen that the nitro substituent here only deactivates weakly, whilst the chloro substitutent appears to activate. In addition, both compounds show a solvent isotope effect (Table 9), the rate coefficients being lower for the deuterium-containing media, as expected since the free base concentration will be lower in these. 

In this work, Brand and Horning158 showed that the rate of sulphonation of phenyltrimethylammonium ion was linearly related to the calculated concentration of protonated sulphur trioxide HSO3, indicating it to be the electrophile. Added sulphate anions reduced the rate for 4-nitrotoluene in direct proportion to their concentration, and this followed from the equilibrium... 

Phenyltrimethylammonium Ion, N+(CH3)S-CaHe.—In this ion, as in toluene, we ignore the electrons involved in bonds from nitrogen to the attached groups, and consider only the inductive effect. The positive charge on the nitrogen atom increases its electron affinity to a value still greater than that for neutral nitrogen, so that we... 

By introducing reasonable values (about 2 for nitrogen, 4 for oxygen) for the electron affinity parameter relative to carbon, 8, and for the induced electron affinity for adjacent atoms (32/8i = Vio), we have shown that the calculated permanent charge distributions for pyridine, toluene, phenyltrimethylammonium ion, nitrobenzene, benzoic acid, benzaldehyde, acetophenone, benzo-nitrile, furan, thiophene, pyrrole, aniline, and phenol can be satisfactorily correlated qualitatively with the observed positions and rates of substitution. For naphthalene and the halogen benzenes this calculation does not lead to results... 

Exercise 22-26 Construct an energy diagram, similar to Figure 22-8, for nitration of phenyltrimethylammonium ion in the meta and para positions. 

One test of this approach is to calculate the rate coefficient under the limiting conditions in terms of the concentrations of the aromatic substrate and the nitronium ion as in (26). The concentration of nitronium ions in the reaction medium cannot be measured directly, but an indirect estimation is possible from the fact that nitric acid is entirely converted to nitronium bisulphate in 90% sulphuric acid and the assumption that the change in reaction rate with the concentration of sulphuric acid comes essentially from the change in the position of the nitric acid-nitronium ion equilibrium. Then, from the rate coefficient for the nitration of mesitylene in 68.3% sulphuric acid (2.1 mol-1 s 1 dm3) (Coombes et al., 1968), the rate coefficient for the nitration of the phenyltrimethylammonium ion in 90.1% sulphuric acid (3.5 x 10 2 mol-1 s dm3) (Gillespie and Norton, 1953), and the relative reactivity of mesitylene and the phenyltrimethylammonium ion (a factor of 1.0 x 109) (Table 6 see also Gastaminza et al., 1969) it is possible to calculate that the concentration of nitronium ions in 68.3% sulphuric acid is less than the stoichiometric concentration of nitric acid by a factor of ca. 6 x 10 8. The value of the rate coefficient for mesitylene in (26) then becomes 3.5 X 107 mol-1 s dm3. This is... 

In the nitration of the phenyltrimethylammonium ion, 90% of the product is mefa-substituted (with 10% para) and kinetic studies show that the nitration proceeds approximately 107 times more slowly than the nitration of benzene. 

The phenyltrimethylammonium ion on sulfonation under conditions believed to give kinetic control, produces 8% ortho, 78% meta and 14% para substitution The rather surprising relatively high yield of ortho and para isomers apparently refutes the above mechanistic view according to which para sulfonation in strong acid media requires dissociation to free amines and reaction in the latter form This work seems to confirm the conclusion , that substitution occurs overwhelmingly through the ammonium ion. 

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