Nitrating mixture Raman spectrum

When acetic anhydride was in excess over nitric acid, acetyl nitrate and acetic acid were the only products. When the concentration of nitric acid was greater than 90 moles %, dinitrogen pentoxide, present as (N02+)(N0a ), was the major product and there were only small traces of acetyl nitrate. With lower concentrations of nitric acid the products were acetic acid, acetyl nitrate and dinitrogen pentoxide, the latter species being present as covalent molecules in this organic medium. A mixture of z moles of nitric acid and i mole of acetic anhydride has the same Raman spectrum as a solution of i mole of dinitrogen pentoxide in 2 moles of acetic acid. 

There was no doubt at that stage of the investigation that nitric acid reacts with sulphuric acid. Yet the research work described had put forward a problem without giving a clear answer. It was only in recent investigations that, due to more accurate physico-chemical methods, especially to the application of Raman spectrum analysis, inferences about the interaction of the nitrating mixture components have been confirmed. 

Fig. 1 Raman spectrum of an aqueous mixture of nitrate, sulphate and phosphate salts. 

Figure 4 Raman spectrum of (top) a standard mixture of 5000 ppm each of nitrate, sulfate, phosphate, and perchlorate in water at pH 13 (note the phosphate and perchlorate peaks overlap), (middle) same at pH 5, which is below pK 2 of phosphoric acid, and (bottom) a perchlorate-contaminated fertilizer dissolved 1 to 10 in water. The pH of the fertilizer solution, which was unadjusted, was 5.

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