O-nitration with

The Henry condensation of nitroform and terminal dinitromethyl compounds with formaldehyde and other aldehydes, followed by nitration of the resulting alcohol functionality, has been used to synthesize numerous explosives. The nitrate esters (104), (105), (106) " and (107)155 ij yg ijggjj synthesized from the action of absolute nitric acid on the parent alcohols. In a similar manner, NMHP (109) is synthesized from the condensation of TNHP (108) with formaldehyde, followed by O-nitration with absolute nitric acid. ... 

The desilylative nitration involves initial O-nitration. with phenyl ni trate readily rearranging (catalyzed by the add formed in the intact ring nitration) to nitrophenols. In case of pentafluorophenyl ( -trimethylsil>l ether, no rearrangement can occur but there is indication of bimolecular condensation. 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

Phenol may be nitrated with dilute nitric acid to 3deld a mixture of o- and nitrophenols the 3deld of p-nitrophenol is increased if a mixture of sodium nitiute and dilute sulphuric acid is employed. Upon steam distilling the mixture, the ortho isomer passes over in a substantially pure form the para isomer remains in the distillation flask, and can be readily isolated by extraction with hot 2 per cent, hydrochloric acid. The preparation of m-nitrophenol from wt-nitroaniline by means of the diazo reaction is described in Section IV,70. 

Fig. 5.1. Zeroth-order rates of nitration with acetyl nitrate compared with those for other systems, (a) HNOa/ sulpholan, (i) HNO3/CCI4, (c) AcONOj/AcjO/O % AcOH, (d) AcONOj/AcaO/O % AcOH/[mesitylene] = o-8 mol l-i,n (e) AcONOj/AcaO/ [AcOH] = 2-2moll-i,ii >(/)AcONOa/AcaO/[AcOH] = 1-96 mol l-i and (g) AcONOa/ AcaO/[AcOH] 3 9i mol l-i/[mesitylene] = o-8 mol 1-i H.

Nitrations of the zeroth order are maintained with much greater difficulty in solutions of acetyl nitrate in acetic anhydride than in solutions of nitric acid in inert organic solvents, as has already been mentioned. Thus, in the former solutions, the rates of nitration of mesi-tylene deviated towards a dependence on the first power of its concentration when this was < c. o-05-o-i mol 1 , whereas in nitration with nitric acid in sulpholan, zeroth-order kinetics could be observed in solutions containing as little as 10 mol 1 of mesitylene ( 3.2.1). 

In solutions of acetyl nitrate in acetic anhydride, prepared from purified nitric acid, the 0 -ratio increases slightly with increasing concentrations of acetyl nitrate (table 5.7, expts. 11,13,16). The use of fuming nitric acid in the preparation of the acetyl nitrate considerably accelerates the rates of reaction and also increases the proportion of o-substitution (table 5.7, expts. 12, 15, 18). These effects resemble, but are much stronger than the corresponding effects in nitrations with solutions of nitric acid in acetic acid contaimng dinitrogen tetroxide. 

The isomer proportions for the nitration of the chlorotoluenes, to be expected from the additivity principle, have been calculated from the partial rate factors for the nitration of toluene and chlorobenzene and compared with experimental results for nitration with nitric acid at o °C. The calculated values are indicated in brackets beside the experimental values on the following structural formulae. In general, it can be... 

The nitration of some substituted nitrobenzenes has been studied in connection with the high o -ratios produced by [ —/ — A/] substituents. Thus nitration in sulphuric acid of 2,5-dialkyl-nitrobenzenes produces the isomer distributions shown below. As has been seen ( 9.1.3), one explanation for the occurrence of high o -ratios with [-/—A/] substituents is that the latter specifically deactivate para positions. In the... 

Despite the considerable amount of work which has been reported, our knowledge of the nitration of biphenyl is not in a satisfactory state. The 0 p-T3.tw varies considerably with the conditions of nitration, and the cause of the variation is not fully understood. Nitrations with solutions prepared from nitric acid and acetic anhydride have generally given o -ratios greater than unity, the most consistent value being 2-2, obtained at o °C. The corresponding partial rate factors are reported later. 

Other methods of nitration that Laali investigated were with isoamyl nitrate in combination with a Bronsted or Lewis acid in several ionic liquids, with [EMIM][OTf] giving the best yields (69 %, 1.0 1.0 o p ratio). In the ionic liquid [HNEt( Pr)2] [CE3CO2] (m.p. = 92-93 °C), toluene was nitrated with a mixture of [NH4][N03] and trifluoroacetic acid (TEAH) (Scheme 5.1-37). This gave ammonium trifluoroacetate [NH4][TEA] as a by-product, which could be removed from the reaction vessel by distillation (sublimation). 

Nicotinic anhydridf, 47, 89 Nitration of o aminobiphenyl to o-amino p -nitrobipheny 1, 46, 86 of o Lolumlrilc with minimum lelra-fluoroboiate, 47, 56... 

O- and N-containing heterocyclics Aliphatic nitrates with an a-methyl group (CH3CHONOz)... 

Dinitro-1-Naphthol (2,4-Dinitro-l-oxy-naphthalene). Yellow crysts, mp 139.5°. Sol in ale chlf. Prepn from naphthalene as a byproduct during nitration with dil nitric acid Hg(II) nitrate. The Lead Salt of the above can be shown as Pb[O.C loHs(N02)2]2, mw 729.57, N 7.68%, OB to C02 -76.75%. The explosive sensitivity of this salt compared to PA is 49%... 

Nitric acid also undergoes reactions with organic compounds wherein the acid serves neither as an oxidizing agent nor as a source of hydrogen ions. The formation of organic nitrates by esterification (O-nitration) involves reaction with the hydroxyl group ... 

Which of these options is the best Lewis structure Actually, no single Lewis structure by itself is an accurate representation of NO3. Any single structure of the anion shows nitrate with one NDO double bond and two N— O single bonds. In Section 9 1, we show that single and double bonds between the same types of atoms have different lengths and different energies. In contrast, experiments show that the three nitrate N—O bonds are identical. To show that the nitrate N—O bonds are all alike, we use a composite of the three equivalent Lewis structures. These are traditionally called resonance structures. Resonance stmctures are connected by double-headed arrows to emphasize that a complete depiction requires all of them. 

There are some cases where o-substitution occurs to the almost total exclusion of any p-attack. These commonly arise from complexing of the substituent already present with the attacking electrophile so that the latter is steered into the adjacent o-position. Thus when the ether l-methoxy-2-pheny ethane (58) is nitrated with nitrating mixture, 32 % o- and 59 % p-isomers are obtained (quite a normal distribution) but nitration with N205 in MeCN results in the formation of 69 % o-and 28% p-isomers. This preferential o-attack in the second case is believed to proceed ... 

Isomeric product distributions. Isomeric product distributions obtained from toluene and anisole have been the subject of considerable mechanistic discussion in electrophilic aromatic nitration (Schofield, 1980 Olah et al., 1989). As applied to nitrations with iV-nitropyridinium ion, the yellow colour of the EDA complex immediately attendant upon the mixing of toluene and PyN02 in acetonitrile persists for about a day (in the dark), whereas the charge-transfer colour of toluene and Me2PyNOj is discharged within 10 min at 25°C. Both bleached solutions afford an identical product mixture (81), consisting of o- (62%), m- (4%) and p-nitrotoluenes (34%)... 

By further nitration with more concentrated acid o- and p-nitro-phenols are converted into the same 2 4-dinitrophenol, and finally into picric acid. Polynitro-derivatives of benzene, such as picric acid and trinitrotoluene, can be caused to explode by detonation with mercury fulminate or lead azide. (The formulae of these two compounds should be written.) They are endothermic, i.e. the oxygen of the nitro-group can oxidise carbon and hydrogen within the molecule and heat is liberated. This intramolecular combustion is rather considerable in the case of picric acid, which is decomposed in accordance with the equation ... 

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