Robert G. Coombes

Preparation of 2,5-Diamino-3,6-Dinitropyrazine (ANPZ-i): A Novel Candidate High Energy Insensitive Explosive

2,5‐Diamino‐3,6‐dinitropyrazine (ANPZ‐i) has been prepared via the electrophilic nitration of 2,5‐diethoxypyrazine using nitronium tetrafluoroborate in sulpholane and subsequent amination under autoclave conditions. Molecular modelling studies have been carried out which indicate that ANPZ‐i should have a similar performance to RDX but with an expected higher insensitivity. ANPZ‐i (1) is therefore a novel candidate high energy insensitive explosive.

Aromatic sulphonation. Part 91. The sulphonation of anisole, phenol, phenyl methanesulphonate, potassium phenyl sulphate, and a series of methyl-, bromo-, and chloro-substituted anisoles and phenols in concentrated aqueous sulphuric acid

The (homogeneous) sulphonation of a number of aromatic ethers and alcohols, viz. anisole (1), 3- methyl-(2), 4-methyl-(3). 2-bromo-(4), 4-bromo-(5), 2-chloro-(6), and 4-chloro-anisole (7), phenol (8), 2-methyl-(9), 3-methyl-(10), 4-methyl-(11), 4-bromo-(12), 2-chloro-(13), and 4- chloro-phenol (14), phenyl methanesulphonate (15), and potassium phenyl sulphate (16) in concentrated aqueous sulphuric acid at 25.0 °C has been studied, and rates and isomer distributions have been determined. The sulphonation is first-order in the aromatic substrate, and from the rate measurements it is concluded that the species undergoing sulphonation in the phenyl ring is an unprotonated substrate species. In the lower acid concentrations the sulphonating entity is H3SO4+. With increasing sulphuric acid concentration there is a gradual change-over in the sulphonating entity from H3SO4+ to H2S2O7. The acid concentrations of equal rate contribution by the two entities for anisole and phenol are 87 and 90 ± 1%, respectively. Sulphonation on the oxygen atom (i.e., sulphation) does not occur. The o/p-ratios for (1) and (8) do not vary over the studied sulphuric acid range of 75–90% H2SO4. Partial rate factors for the 2- and 4-position of (1) and (8) are reported. The very low partial rate factors for the 4-substitution of (1) and (8) and the observed extreme suppression and compression of the reactivities of the substrates (1)–(14) are ascribed to hydrogen bonding of the substrates with the acidic solvent species present. It is tentatively suggested that the relatively high contents of sulphonation ortho to –OR with anisole (36%) and phenol (48%) are due to specific complexation of the substrates with the sulphonating electrophile.

Electrophilic aromatic substitution. Part 16. The nitration of anisole, o-methylanisole, and p-methylanisole in aqueous sulphuric acid

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.

ELECTROPHILIC AROMATIC SUBSTITUTION. PART 24. THE NITRATION OF ISOPROPYLBENZENE, 2‐ AND 4‐ISOPROPYLTOLUENE, 1‐CHLORO‐4‐ISOPROPYLBENZENE, 4‐ISOPROPYLANISOLE, AND 2‐BROMOTOLUENE: NITRODEISOPROPYLATION

Die Nitrierung z.B. des Toluols (Ia) in 65-79proz. H2SO4 fuhrt zu den Produkten (II)-(IV), wobei die Nitrodeisopropylierung sich mit zunehmender Saurekonzentration nur wenig andert und der Anteil des Nitroderivats (III) auf Kosten des Oxidationsproduktes (IV) zunimmt.

Nitration of aromatic compounds by tetranitratotitanium(IV) in carbon tetrachloride solution

Tetranitratotitanium(IV) reacts with some simple aromatic compounds of a wide range of expected reactivity in carbon tetrachloride solution at room temperature to give good yields of nitro-compounds. Results of direct rate measurements, competition studies, and determinations of isomeric product proportions are reported. The anomaly of the low intermolecular and high intramolecular selectivity of the substitution is discussed, and the existence of at least three stages of reaction is established. A special mechanism of nitration by this reagent is proposed to account for these observations.

Products of nitration of aromatic and heteroaromatic compounds by some transition-metal nitrato-compounds

Compounds of a wide range of aromatic reactivity are nitrated by the nitrato-complexes of zirconium(IV) and iron(III) at room temperature. Product isomer ratios are reported. Studies of the nitration of pyridine with these reagents and with tetranitratotitanium(IV) have established conditions under which either 3- or mainly 4-nitropyridine may be formed. Either 7- or mainly 3-nitroquinoline may be obtained from the nitration of quinoline.

Electrophilic aromatic substitution. Part 23. The nitration of phenol and the cresols in aqueous sulphuric acid

The quantitative mononitration of phenol and o-, m-, and p-cresol by nitric acid in 58–80% sulphuric acid involves reaction with the nitronium ion at or very close to the encounter-controlled rate. For phenol the o : p ratio changes smoothly from 2.4 to 0.9 over the range 56–83% sulphuric acid. For o-cresol the ratio of 2-methyl-6-nitrophenol to the 4-nitro isomer changes from 1.5 to 0.8 over 50–83% sulphuric acid, and for m-cresol the ratios of both 3-methyl-2- and 3-methyl-6-nitrophenol to the 4-nitro isomer fall over 58–81% sulphuric acid (0.6 to 0.2 and 1.5 to 0.7 respectively). These changes, and those for some related methyl ethers reported previously, are discussed. The nitration of p-cresol in 68–72% sulphuric acid involves ca. 40%ipso substitution at C–Me and the 4-methyl-4-nitrocyclohexadienone formed undergoes an acid-catalysed rearrangement to 4-methyl-2-nitrophenol. 2-Methyl-6-nitrophenol is established as an important product of nitration of o-methylanisole and a mechanism involving demethoxylation of a Wheland intermediate, formed by ipso-substitution at C–Me, and a subsequent specific 1,3-rearrangement is proposed.

The ipso-nitration of p-cresol

Abstract The nitration of p -cresol by nitric acid in aqueous sulphuric acid involves ~40% ipso -substitution at C Me . The 4-methyl-4-nitrocyclohexa-2,5-dien-1-one (I) formed undergoes an acid-catalysed rearrangement to 4-methyl-2-nitrophenol.

Mechanism of reaction of nitrogen dioxide with alkenes in solution

In spite of the observation of 15N nuclear polarisation expected from the separate addition of two NO2˙ radicals in the reaction of nitrogen dioxide with allylbenzene and some other alkenes, kinetic studies indicate that both NO2˙ and N2O4 are reactive species, each leading only to addition products.

Dual reactivity of 2,3,5,6-tetrabromo-4-methyl-4-nitrocyclohexa-2,5-dienone

2,3,5,6-Tetrabromo-4-methyl-4-nitrocyclohexa-2,5-dienone in acetone solution nitrates 4-methoxyphenol by a radical mechanism, but acts mainly as a brominating agent towards phenol, after rearrangement.