Nitrogen pentoxide solvent effects

There are very few cases where one can compare directly the same reaction taking place by the same mechanism in both gas phase and solution. If at all temperatures the reactions have equal velocities in the two phases the values of 5 and of E are the same, and it may be safely assumed that the reaction mechanisms are identical and the solvent has no effect. Undoubtedly the simplest comparison exists in the unimolecular decomposition of nitrogen pentoxide and in this reaction the solvent has little effect. The unimolecular racemization of pinene at 200° proceeds at the same rate in the gas phase, in liquid pinene and in a solution of petrolatum. 

The simplest reaction which has been studied directly in the gas phase and in solution is the decomposition of nitrogen pentoxide.11 It is not a chain reaction and it is free from wall effects. The gas phase reaction seems to be free from complications and it has been checked in many laboratories. It is an excellent unimolec-ular reaction, the decomposition rate being exactly proportional to the concentration. This proportionality constant is nearly the same from 0.05 mm. to 1,000 mm. in the gas phase and up to an osmotic pressure of fifty atmospheres in solution, and the energy of activation is practically the same in the gas phase and in a group of chemically inactive solvents. 

Solvent Effects. In the experimental measurements on solutions the purified nitrogen pentoxide in various solvents is sealed off in... 

Liquid carbon tetrachloride, as would be expected, is considerably more effective in deactivating excited nitrogen dioxide than is an atmosphere of carbon dioxide. At 2,800 and at 2,650 A most of the radiation is absorbed directly by nitrogen pentoxide and here also the solvent appears to deactivate the molecules effectively even though collision with a second molecule does not seem to be necessary for chemical decomposition. 

Nitration can be effected at low temperatures by mixed acids (sulfuric and nitric) by nitric acid of high concentration by nitric acid and acetic anhydride (acetyl nitrate is formed in such mixtures and they must not be concentrated) and by nitrogen pentoxide in halogenated hydrocarbon solvents with or without the addition of sodium fluoride to complex with the nitric acid formed 129) ... 

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