Good first-order kinetics of solvolysis of the above-named diene in water and in 6.5–43.6% H2SO4 at 25°C, and in water and in 15.2–58.8% H2SO4 at 5°C have been observed. The yields of 4-chlorotoluene, 5-chloro-2-methylphenyl acetate, 5-chloro-2-methylphenol, 4-chloro-2-nitrotoluene, 4-chloro-3-nitrotoluene, and 4-methyl-2-nitrophenol produced in water and in 21.5–92.4% H2SO4 at 25°C in the presence of sulphanilic acid or hydrazinium sulphate, and additionally of 2- and 4-nitroanisole when anisole was also added, have been measured. The solvolysis proceeds by an acid-catalysed elimination of nitrous acid (confirming a tentative conclusion in another case 1), which competes with AAC2 and AAL1 ester solvolyses. With increasing acidity the solvolyses become dominant, the AAL1 reaction increasingly so. The small yield of 4-chloro-3-nitrotoluene comes from a thermal reaction of the diene unrelated to the elimination and solvolyses. The AAL1 reaction generates the ipso-Wheland intermediate (WiMe) that is also formed in the nitration of 4-chlorotoluene. The intermediate reacts by return to 4-chlorotoluene and nitronium ion (which can be captured by anisole), by 1,2- and 1,4-nucleophilic capture by water (giving 5-chloro-2-methylphenol and 4-methyl-2-nitrophenol, respectively), and by 1,2-rearrangement to 4-chloro-2-nitrotoluene. The first of these reactions never accounts for more than about 12% of the WiMe and competition between capture and rearrangement moves strongly in favour of the latter with increasing acidity. Re-examination of the nitration of 4-chlorotoluene has revealed products arising from 1,2- and 1,4-capture of WiMe, previously overlooked. An improved assessment of positional reactivities shows 59% of primary attack by nitronium ion to occur at C–Me in 63% H2SO4.

The kinetics of nitration in sulphuric acid of 2-chloro-4-methyl-, 4-chloro-, 2,4-dichloro-, and 4-fluoroanisole and of the corresponding phenols have been determined. The reaction products from the anisoles and from 2-chloro-4-methyl- and 4-fluoro-phenol have been determined. Results for 4-methylanisole supplementary to earlier ones are also reported. Generally the anisoles give the 2-nitro-derivatives and the 2-nitrophenols, and from 2-chloro-4-methylanisole, 2-chloro-4-methyl-4-nitrocyclohexa-2,5-dienone was formed as an intermediate. The decomposition of this dienone in sulphuric acid, like those of others, changes from a non-acid-catalysed to an acid-catalysed form with increasing acidity. The first form is regarded as a decomposition into an aryloxyl radical and nitrogen dioxide which can recombine to give the 2-nitrophenol. The formation of a small amount of 2-(4-fluorophenoxy)-4-fluorophenol in the nitration of 4-fluorophenol is seen as support for this view. The acid-catalysed form is regarded as the decomposition of the protonated dienone into a phenol–nitronium ion encounter-pair which can give the nitrophenol. A consequence of the mechanism is that if the phenol were nitrated at less than the encounter rate, the phenol itself would in appropriate conditions be a product of the ipso-nitration of the original anisole. 4-Methyl-, 2-chloro-4-methyl-, and 4-chloro-phenol have been so identified. Quantitative analysis of the results allows evaluation of the partitioning of dienone decomposition between the two modes. The mechanism accounts for the formation from 2,4-dichloro-anisole of both 2,4-dichloro-6- and 2,4-dichloro-5-nitroanisole, but only 2,4-dichloro-6-nitrophenol.

The kinetics in 61.8–79.5% H2SO4 and the products formed in 61.8–84.3% H2SO4 for the solvolyses of the above-named diene have been determined. The reactions are interpreted as involving concurrent elimination of nitrous acid and AAL1 generation of the same ipso-intermediate as arises in the nitration of 2,3-dimethylbenzonitrile. This intermediate reacts by intermolecular rearrangement (as is proved by the isolation from the solvolyses of 2,3-dimethylbenzonitrile and the trapping of nitronium ion by reaction with 4-fluorophenol), by nucleophilic capture by water, and by 1,2-intramolecular rearrangement to 2,3-dimethyl-4-nitrobenzonitrile. The results permit the partitioning of the overall solvolytic rate coefficient and the demonstration that the derived coefficient for the reaction competing with the elimination depends on acidity as would be expected for an AAL1 reaction. The elimination of nitrous acid is also acid-catalysed and may not be a simple E1 reaction. The solvolytic reactions of the diene do not lead to a 1,3-intramolecular rearrangement of the nitro-group and the observed 1,3-rearrangement of the diene to give 2,3-dimethyl-5-nitrobenzonitrile under non-solvolytic conditions appears to be a thermal reaction of the diene molecule. By combining the solvolysis results with those for the nitration of 2,3-dimethylbenzonitrile in 70.4–82.5% H2SO4 it is shown that the major primary consequence of the nitration is ipso-attack and that it is possible to determine the positional reactivities in the nitrile.

The reaction in sulphuric acid of 1,2,3-trimthoxy-5-nitrobenzene with mixtures of nitrous and nitric acids occurs under conditions in which reactions with either acid alone are negligibly slow, and it has the limiting kinetic form zeroth-order in nitric acid which is consistent with the electron-transfer mechanism for NO+-catalysis proposed by Giffney and Ridd.

Durene (1,2,4,5-tetramethylbenzene) is nitrated in sulphuric acid at the encounter rate. Nitrations of nitrodurene and nitroprehnitene (nitro-1,2,3,4-tetramethylbenzene) are complicated by the formation of nitrous acid, presumably as a consequence of ipso-attack, and subsequent unidentified reactions of this. When an efficient nitrous acid trap is present the complications are removed and the kinetics become straightforward. Although nitrobenzene is 108 times less reactive than benzene in nitration, nitroprehnitene and nitrodurene are only 41 and 20 times less reactive than their respective parent hydrocarbons. These reduced relative reactivities are a consequence of the fact that prehnitene and durene react at the encounter rate. The low relative reactivity of durene and 3-nitrodurene leads to the formation of some 3,6-dinitrodurene in the nitration of durene, even under the most favourable circumstances, and if mixing is inefficient the dinitro-compound may be the main product. By measuring the yield of 3-nitrodurene, as it varies with acidity, it is possible to determine the amount formed by direct attack at C-3 as distinct from that formed by ipso-attack followed by rearrangement. As a consequence the ratio of positional selectivity between C-3 and C-1 is shown to be 1 : 3.6. Thus, positional selectivity does not disappear. The intrinsic rate constants for nitronium ion nitrations in sulphuric acid of a number of methylnitrobenzenes show an excellent linear correlation with those for nitrations with nitronium hexafluorophosphate in nitromethane deduced by application of a theoretical mixing–reaction model. Differences between the two systems are not large, but appear to be in the direction showing the electrophile in sulphuric acid to be rather more reactive and more selective than that in the organic solvent.

AbstractDurch Nitrierung in wäßriger H2SO4 geht das Cinnamat (Ia) quantitativ in ringnitrierte Mononitroderivate wie z.B. (IIa) über mit einer Isomerenverteilung von 2‐:3‐:4‐NO2‐Derivat wie 31:1:25.

AbstractDie Nitrierung z.B. des Toluols (Ia) in 65‐79proz. H2SO4 führt zu den Produkten (II)‐(IV), wobei die Nitrodeisopropylierung sich mit zunehmender Säurekonzentration nur wenig ändert und der Anteil des Nitroderivats (III) auf Kosten des Oxidationsproduktes (IV) zunimmt.

Studies of the kinetics of nitration of anisole in 66–80% H2SO4, 64–70% HClO4, and 88–97% CH3SO3H, and of toluene in 74–79% H2SO4 are reported. Concentrations of the aromatic compound were high enough for the reaction to be less than first-order in them. Rate constants for formation of the nitronium ion are reported, and rate constants for the reverse reaction estimated. It is suggested that the reaction is a one-step process.

The title reactions involve capture by water of the ipso-Wheland intermediates, followed by loss of methanol, then of nitronium ion to give solvent-caged ion pairs of para-substituted phenol and nitronium ion which can combine before or after diffusion apart.

AbstractDie pH‐Geschwindigkeitsprofile für die Nitrierung z.B. der Aromaten (I) und (II) in wäßriger HClO4 sind unter Berücksichtigung eventueller Protonierungen alle sehr ähnlich.

AbstractBenzol, Chlorbenzol, Toluol, Di‐ und Trimethylbenzole werden mit HNO, quantitativ mononitriert.

In the quantitative mononitration of anisole in 54–82% sulphuric acid at 25° the o : p ratio varies from 1.8 to 0.7. It is suggested that the rate-limiting step is the formation of an encounter pair between the nitronium ion and an anisole molecule which is hydrogen-bonded to a hydronium ion. The change in the o : p ratio may be due to competition between direct formation of Wheland intermediates from the hydrogen-bonded encounter pair, and loss of the hydronium ion to give a nitroniurn ion–anisole encounter pair, with subsequent formation of Wheland intermediates. With o- and p-methylanisole the products, and changes in product ratios with acidity are interpreted by considering the fates of the ipso-Wheland intermediates formed at C–Me. 4-Methyl-2-nitrophenol is an important product of the nitration of p-methylanisole, and results from ipso-attack by nitronium at C–Me, followed by attack of water and loss of methoxy.

AbstractDie Mononitrierung wird mit 54‐82%iger Schwefelsäure/HNO, in Essigsäure durchgeführt.

The kinetics of nitration in sulphuric acid of o- and p-dibromobenzene, p-bromo- and p-chloro-toluene, 2-bromo-m-xylene, and p-bromochlorobenzene are reported. For these compounds and for bromobenzene and p-bromofluorobenzene the yields of products formed over a range of acidities have been determined. Nitrodebromination was not detected with o-dibromobenzene and 2-bromo-m-xylene, but was a major outcome of nitrating p-dibromobenzene, p-bromotoluene, and p-bromochlorobenzene. The degree of nitrodebromination increased with increasing dilution of the sulphuric acid and evidence is provided to show that Wheland intermediates formed at brominated carbon atoms (WiBr) are either debrominated or rearranged by nitro-group migration. There is no intramolecular migration of bromine and little or no nucleophilic capture of the Wheland intermediates.When methyl groups are present ipso-nitration at C(Me) occurs and is followed by nucleophilic capture by water and by nitro-group migration in proportions which varied with the acidity. Nitrodechlorination was not observed, but even if attack at C(Cl) is assumed to occur a choice between subsequent decomposition of the Wheland intermediate to its components and nitro-group migration cannot be made. In p-dibromobenzene the C(Br) positions are at least as reactive as the C(H) positions.

AbstractEs wird die Nitrierung z.B. von w‐Phenyl‐Co‐ C4‐alkansulfonsäuren untersucht.