Nitronium tetrafluoroborate nitration with

Without further studies little weight can be given to these ideas. In particular there is the possibility that with acetanilide, as with anisole, nitrosation is of some importance, and further with nitrations in sulphuric acid the effect of protonation of the substrate needs quantitative evaluation. The possibility that the latter factor may be important has been recognised, and it may account for the difference between nitration in sulphuric acid and nitration with nitronium tetrafluoroborate. 

For nitration with nitronium tetrafluoroborate in sulpholan. " See table 4.1. 

The nitrogen atoms of heterocycles like imidazoles and triazoles have been converted into IV-nitroimide groups. The A -nitroimide (164) is synthesized from 1-amino-1,3,4-triazole (162) by IV-amination of the tertiary nitrogen with 0-picrylhydroxylamine, addition of nitric acid to give the nitrate salt (163), followed by IV-nitration with nitronium tetrafluoroborate in acetonitrile. The 1,2,3-triazole (165) and the imidazole (166) ° are synthesized in a similar way. The synthesis of IV-nitroimides has been the subject of an excellent review. ... 

During nitration with nitronium tetrafluoroborate or ethyl nitrate 4-amino-1,2,4-triazole is converted into the corresponding nitroimide [351] (Scheme 39). 

The amines and amine derivatives which were nitrated with nitronium tetrafluoroborate are summarized in Table II. 

Low Substrate and High Positional Selectivity. Nitrations with nitronium tetrafluoroborate in nitromethane and nitronium hexa-fluorophosphate in nitromethane solution, respectively, show low substrate selectivities (generally expressed by the k /kg rate ratios) but at the same time the nitrations maintained high positional selectivity. Typical isomer distributions in the nitration of toluene are 6 J% ortho, k% meta, and 29% para nitrotoluene. The data summarized in Table XIV show the relative reactivities of a number of alkylbenzenes over those of benzene, together with the isomer distributions of the mononitro products. 

The nitration of olehns, particularly those containing electron donating substituents, by nitronium salts is complicated by side reactions and does not always lead to the expected result. In many instances nitration with nitronium tetrafluoroborate takes place with higher yields in the presence of a-picoline [91,132]. In this case the nitrating agent is apparently not the nitronium salt but 2-methyl-W-nitropyridinium tetrafluoroborate, which is formed rapidly when NO2 BFJ is mixed with a-picoline [73b],... 

This allows one to assume that even by nitrating with nitronium tetrafluoroborate 2-nitro-4-isopropyltoluene is to a great extent formed by the initial addition of the nitronium cation at the 1-position and the subsequent shift of the nitro group to the 2-position. In this case discussing the relative reactivity of the 2- and 3-positions from the ratio of the formed 2- and 3-nitro derivatives is meaningless. 

Olah, G. A. Lin, H. C. Synthetic methods and reactions. XL Convenient direct preparation of 1,3,5-trinitrobenzene from m-dmitrobenzene by nitration with nitronium tetrafluoroborate in lluorosulfuric acid solution. Synthesis 1974, 444-445. 

The triphenylmethyl cation is nitrated with nitronium tetrafluoroborate in the presence of TfOH (eq 28). ... 

The data of table 4.1, column [a), do not suggest that nitration of the alkylbenzenes with nitronium tetrafluoroborate in sulpholan occurs upon encoimter mesitylene might be so reacting ( 3.3) but comparison with a more inherently reactive substance would be necessary before this possibility could be considered. 

It has been necessary to comment upon these various studies because Olah and his co-workers have suggested that whilst nitrations, like those with nitronium salts, which give a relative rate of reaction of toluene with respect to benzene not much greater than unity involve the nitronium ion as the electrophile, this is not so in other cases. It is important to consider these opinions closely. In the earlier of the two relevant papers it is agreed that since nitrations of toluene with nitronium tetrafluoroborate in sulpholan show no abnormal o -ratio there... 

Nitration of acetylenes with nitryl iodide followed by elimination of HI gives nitroacetylenes, but nitroacetylenes are too thermally unstable to be useful for organic synthesis.77 Recently, nitro-trimethylsilyl-acetylenes are prepared as stable nitroacetylenes by the reaction of bis(trimethylsily)acetylene with nitronium tetrafluoroborate (Eq. 2.39).78... 

The nitration of the 2,7-diamino-77/-[l,2,4]triazolo[3,4-c][l,2,4]triazolium ion 44 with nitronium tetrafluoroborate affords after workup with base the corresponding potassium bis(iV-nitro imides) 45 <1991IZV1239>. 

Olsen and co-workers reported the nitration of secondary nitroalkanes to m-dinitro compounds with nitronium tetrafluoroborate in acetonitrile at 0 °C. Yields are lower compared to the Kaplan-Shechter reaction and significant amounts of pseudonitroles are formed, but this is possibly due to impure reagent. 

Nitronium tetrafluoroborate is a very efficient reagent for the D-nitration of alcohols and glycols containing both primary and secondary hydroxy functionality (Equation 3.7). Yields of nitrate ester are high and frequently quantitative. 0-Nitration with nitronium salts produces a strong acid and so an acid-binding agent should be present for acid sensitive substrates. 

Allylic and homoallylic alcohols are particularly susceptible to oxidation and dehydration. Hiskey and Oxley successfully nitrated both allyl alcohol and l-buten-4-ol with nitronium tetrafluoroborate in diethyl ether at -71 °C. 

Olah and Lin reported obtaining pure TNB (2) in 50 % yield from the nitration of m-dinitrobenzene (32) with nitronium tetrafluoroborate in fluorosulfuric acid at 150 °C higher yields of TNB can be obtained by reducing reaction time but the product then contains some unreacted m-dinitrobenzene. A solution of dinitrogen pentoxide in sulfuric acid at 160 °C is also reported to effect the conversion of m-dinitrobenzene to TNB. TNB is rarely prepared via these routes and is best obtained from TNT via an indirect route (Section 4.9). 

Nitronium salts are efficient and powerful nitrating agents. Nitronium tetrafluoroborate is the most commonly used nitronium salt for nitration and is commercially available as a solid or as a solution in sulfolane in which the ions are highly solvated and exist as an ion pair. Nitronium tetrafluoroborate shows poor solubility in most organic solvents and so the more soluble nitronium hexafluorophosphate is sometimes preferred for nitrations. Olah and co-workers - have studied the nitration of a vast array of aromatics with nitronium salts. Solutions of nitronium salts in aprotic organic solvents are useful for the nitration of acid sensitive or readily oxidized substrates. Nitronium tetrafluoroborate has been used for the... 

Trinitrochlorobenzene (picryl chloride) (87) can be prepared from the nitration of 2,4-dinitrochlorobenzene with nitronium tetrafluoroborate or mixed acid composed of fuming nitric acid and oleum. Picryl chloride is also synthesized from the reaction of phosphorous oxychloride with the pyridinium salt of picric acid. ... 

Graindorge and co-workers" reported the synthesis of 2,5,7,9-tetranitro-2,5,7,9-tetraaza-bicyclo[4.3.0]nonane-8-one (113) (K-56, TNABN) from the nitration of 2,5,7,9-tetraazabi-cyclo[4.3.0]nonane-8-one dihydrochloride (112) with dinitrogen pentoxide in absolute nitric acid, the latter obtained from the condensation of urea with l,4-diformyl-2,3-dihydroxy-piperazine (111) in hydrochloric acid. Treatment of (112) with nitronium tetrafluoroborate in nitromethane results in the nitration of the piperazine ring nitrogens only and the isolation of (114) in 86 % yield (Table 5.2). 

Ammonium dinitramide (152) is synthesized by treating a solution of ammonium ni-trourethane (150) with nitronium tetrafluoroborate or dinitrogen pentoxide in methylene chloride at -30 °C, followed by ammonolysis of the resulting ethyl A,lV-dinitrourethane (151)7 Ammonium dinitramide can be prepared from the nitration of ethyl carbamate and ammonium carbamate with the same reagents. This is currently the most efficient route to ammonium dinitramide and is used for its manufacture (Section 9.11). 

The nitration of nitramine (153) with nitronium tetrafluoroborate, followed by neutralization of the resulting dinitraminic acid with ammonia, also generates ammonium dinitramide (152). Neutralization of this reaction with alkylamines, instead of ammonia, yields the corresponding alkylammonium salts of dinitramide. The nitration of ammonia with dinitrogen pentoxide (15 %) or nitronium salts like the tetrafluoroborate (25 %) yield ammonium dinitramide (152) through the initial formation of nitramine. 

Alkyl lV,lV-dinitramines (154) have been prepared from the reaction of the tetraalkylam-monium salts (155) of primary nitramines with nitryl fluoride in acetonitrile at subambient temperature. The same reaction with the primary nitramine or its alkali metal salts yields the corresponding nitrate ester. Treatment of the ammonium, potassium, or lithium salts of primary nitramines (156) with a solution of nitronium tetrafluoroborate in acetonitrile at subambient temperature yield alkyl iV,iV-dinitramines. ° The same reactions in ether or ester solvents enables the free nitramine to be used. The nitrolysis of A-alkylnitramides (157) and N,N-diacylamines with nitronium tetrafluoroborate in acetonitrile, and the nitration of aliphatic isocyanates with nitronium tetrafluoroborate and nitric acid in acetonitrile, also yield alkyl A,A-dinitramines (154). 

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