urbaf2

NITRATION AND NITRATING AGENTS 23

deal of light on the changes which nitric acid undergoes on dilution with water,

sulphuric acid, oleum, etc.

Chedin [6,60,61] gave the following results of the examination of the nitric

acid Raman spectrum at concentration of the acid from 6.3 to 99.8% (Table 1).

TABLE 1

THE RAMAN LINES OF NITRIC ACID AT DIFFERENT CONCENTRATIONS

99.8% 95% 89.% 64% 52.1% 30.2% 24.5% 6.3%

611 cm-1

674

922

1048

1103

1295

1

1537

1679

According to Chédin, the Raman line at 1050 cm-1 can be assigned to the

NO 3

• ion.
  Chédin and Fénéant [62] found the following bands and lines in their further
  investigations of high frequency Raman spectra:
  2550 cm-1
  weak lines at 2700
  3150
  and a strong line at 3400

On adding water the intensity of the band 3400 cm

-1

decreases while that of

the other bands increases. It seems very likely that the bands at ~3400 cm-l belong

to nitric acid molecules linked by hydrogen bond (pp. 7-8), while the lines at 2550,

2700 and 3150 cm-1 probably belong to nitric acid hydrate molecules.

Médard [48] and in 1935 Chédin [60] stated, that solutions of nitric acid in

sulphuric acid produced a Raman spectrum with two characteristic lines: at 1050

and 1400 cm-1. As we have seen the 1050 cm-1 line is present in nitric acid of

various concentrations, while the line 1400 cm

-1

has not been observed.

Further investigations of Chédin [60a-62] and of Susz, Briner and Favarger [63]

have shown that a solution of nitric anhydride (N 2 O 5 ) in nitric acid produces both

1050 and 1400 cm

-1

lines. From this the assumption has been advanced that the

two lines indicate the presence of N 2 O 5 in mixtures of nitric and sulphuric acids.

Thus it seemed that Sapozhnikov’s theory (p, 10) had been confirmed. However,

further investigations have shown that this interpretation of the results is not

quite right. For Chédin stated that solutions of N 2 O 5 in carbon tetrachloride,

chloroform, nitromethane and phosphorus oxychloride produced the 707, 860,
1033, 1240 and 1335 cm-1 lines (in addition to the solvent line), while there were