Nitronium salts conductivity

The nitration of aliphatic hydrocarbons with dinitrogen pentoxide and nitronium salts has been described. Topchiev gives an extensive discussion of works related to hydrocarbon nitration conducted prior to 1956. 

Olah has extensively reviewed the synthesis and use of nitronium salts in aromatic nitration and so only a brief discussion is given here. A review by Gidaspov brought to light much important research conducted by Russian chemists in this area. 

In 1,2-dichloroethane, UV/VIS spectroscopic data indicate that in the mixtures of 33 and bromine there are 2 1, 1 1, 1 2 and 1 3 (33 Br2) complexes. Conductivity measurements of the same mixtures indicate that the complex 1 1 is a CT complex whilst the other complexes are ionic in character. The complexes with stoichiometry 1 2 and 1 3 (33 Br2) are bromonium tribromide and pentabromide, respectively, as indicated in Scheme 13. CT complexes with moderate stability were also reported90 between 33 and different charged electrophiles (nitrosonium and nitronium salts)... 

Specific conductivity of nitronium tetrafluoroborate varies linearly with concentration. Cryoscopic measurements in sulfolane solution indiate that the nitronium salt is present as ion pairs and the conductance must be due to ion triplets and not separated ions [54]. 

Cryoscopic investigations suggest that in sulpholan nitronium tetrafluoroborate exists predominantly as ion pairs. - The specific conductivity of these solutions increases linearly with the concentration of the salt (up to 0-4 mol 1 ), and is attributed to the existence of ion-triplets rather than free ions. ... 

Olah and co-workers ° conducted a comprehensive study into the use of N-nitropyridinium salts for nitration. Such salts are easily prepared from the slow addition of the appropriate heterocyclic base to an equimolar suspension of nitronium tetrafluoroborate in acetonitrile. Olah studied the effect on nitration of changing both the structure of the heterocyclic base and the counter ion. Three of these salts (20, 21, 22) illustrated above have been synthesized and used for the 0-nitration of alcohols with success. Transfer nitrations with Al-nitropyridinium salts are particularly useful for the preparation of nitrate esters from acid-sensitive alcohols and polyols because conditions are essentially neutral. 

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