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CHAPTER IV

NITRATION WITH NITRATING MIXTURES

NITRATING MIXTURES

COMPOSITION OF NITRATING MIXTURES

THE composition of a nitrating mixture should be chosen very carefully with

regard to the compound being nitrated and the number of nitro groups to be intro-

duced. It is clear that the more nitro groups to be introduced, the higher the acid

concentration should be.

The nitration of aromatic compounds is carried out with only a slight excess

of nitric acid. This is smaller when lower nitrated compounds are prepared (0.2-5%

of HNO 3 in excess of the calculated weight) and larger when higher nitrated com-

pounds are to be obtained (3-100% or more in excess of the calculated weight

of HNO 3 ).

The ratio of the quantities of components of the nitrating acid, HNO 3 , H 2 SO 4

and H 2 O, is also important. The fact that water is formed during the nitration pro-

cess, thus diluting the nitrating mixture, must be taken into consideration. Since

among the components of the mixture, sulphuric acid is the principal one which

binds water, the amount of H 2 SO 4 must be chosen in such a proportion that it

can take up all the water formed during the nitration. Otherwise nitration might

be incomplete.

The concentration ratio, or the so-called spent acid strength or dehydrating

value of sulphuric acid (D. V. S.) is of importance:

[H 2 SO 4 ]

D.V.S. =

[H 2 O]i + [H 2 O]f

where: [H 2 O]i is the initial concentration of water in the nitrating mixture before

nitrating and [H 2 O]f is the concentration of water formed during nitration.

For example, if benzene is being nitrated according to the equation:

C 6 H 6 + HNO 3 -> C 6 H 5 NO 2 + H 2 O

mol. weight 78^6312318

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