PHYSICOCHEMICAL ANALYSIS OF THE SYSTEMS: NITROBENZENE—NITRIC ACID AND NITROBENZENE—OLEIC ACID

Kh. A. Lel’chuk

(Presented by Professor B. V. Tronov, Doctor of Chemical Sciences)

Nitration reactions of organic compounds, especially of the benzene series, are of enormous technical importance. In connection with this, a large number of works by both Russian and foreign authors have been devoted to the study of the mechanism of the nitration reaction.

B. V. Tronov and his co-workers also devoted much attention to this question [1—3]. B. V. Tronov and A. P. Grigor’eva [4] carried out a study of the nitration of nitrobenzene with nitric acid under various conditions. Fuming nitric acid of specific gravity 1.52 was used. On the basis of kinetic studies, the assumption was made that complex compounds of molecular composition 1:1 and 1:2 are formed.

We studied the viscosity and density of the systems nitrobenzene—nitric acid and nitrobenzene—oleic acid.

The present investigation was undertaken with the aim of confirming, by methods of physicochemical analysis, the possibility of complex formation in the above-mentioned systems and of determining the composition of the complexes formed.

Experimental part and discussion of results

For the investigation, chemically pure, absolutely anhydrous nitric acid of specific gravity 1.5467 was used; it was obtained by the method of K. P. Mishchenko [5] by repeated (up to 4 times) distillation of nitric acid of specific gravity 1.40 with chemically pure sulfuric acid of specific gravity 1.84 in a water bath at a temperature of 25—40°C and at pressures of 25—40 mm Hg.

Nitrobenzene was synthesized by the method indicated in the handbook of P. D. Pryanishnikov [6].

From nitrophenols and nitrosophenols, which are by-products in the synthesis of nitrobenzene, the latter was purified by repeated shaking with a strong solution of sodium hydroxide hydrate. Then the nitrobenzene was washed again from alkali with distilled water, dried with anhydrous calcium chloride, and distilled twice.

The nitrobenzene obtained had a specific gravity of 1.2034 at 20° and a boiling point of 210.9° at a pressure of 765 mm.

The viscosity and density of the nitric acid—nitrobenzene system were determined at two temperatures, 0° and 10°C, and for the oleic acid—nitrobenzene system at one temperature, 20°C.

To maintain a constant temperature, the work was carried out in thermostats equipped with thermoregulators and mechanical stirrers.

Viscosity was determined in a closed-type Ostwald viscometer for volatile liquids.

Nitrobenzene—nitric acid system

The reaction of nitration of nitrobenzene with nitric acid at 0°C, in particular, and also at 10°, proceeds slowly, but in order to exclude as completely as possible the formation of dinitrobenzene, we proceeded as follows: the required amount of nitrobenzene was poured into a flask with a ground-glass stopper and frozen at 0°C; after this, the required calculated amount of nitric acid at a temperature of 0°C was added and quickly mixed—

lowered the contents of the flask. Upon addition of nitric acid, nitrobenzene melted rapidly and formed a homogeneous mixture; in this case no warming was observed.

This eliminated the possibility that the nitration process might accelerate upon heating of the mixture, owing to complex formation.

The results of the study are presented in Table 1 and graphically in Fig. 1.

Table 1

Viscosity isotherms (curves 1, 2) and density isotherms (curves 3, 4) of the system nitric acid—nitrobenzene: 1, 3—10°C; 2, 4—0°C.

On the viscosity isotherm (curve 2) at 0°C, as well as on the viscosity isotherm at 10° (curve 1), we have a break at approximately 61 mole percent nitric acid and a small maximum within the range of 80—85 mole percent. This course of the curves indicates that, when the components are mixed in the given system, complex formation takes place; the presumed molecular composition of the compounds formed is 1:2 and 1:4. The density isotherms (curves 3, 4) also give deviations from additivity, which points to chemical interaction.

System nitrobenzene — butyric acid

When the components were mixed, no heating was observed. The results of the investigation are presented in Table 2.

Table 2

The viscosity and density isotherms give no indication of the presence of chemical interaction between the components. They are straight lines. In most cases, in the absence of chemical interaction we have negative curves, i.e., curves with a slight convexity toward the composition axis, but rectilinear isotherms are also possible in the case where the components under investigation have close viscosity values [7]. In our case the viscosities of the components are close, as is seen from the data: the viscosity of nitrobenzene is equal to 1.986 centipoises, and the viscosity of butyric acid is equal to 1.606 centipoises at 20°C.

It should be noted that this system was also studied by Ferrands [8] by methods of physicochemical analysis. He studied the viscosity, density, and surface tension for this system. The results obtained by Ferrands also indicate the absence of chemical interaction between the components.

Conclusions

1. The viscosity and density of the systems nitrobenzene—nitric acid at 0 and 10°C and of the system nitrobenzene—butyric acid at 20°C have been studied.

2. On the basis of the data obtained, it has been established that in the nitrobenzene—nitric acid system, complex formation takes place between the components; the presumed molecular composition of the compounds formed is 1:2 and 1:4.

3. It has been established that in the nitrobenzene—butyric acid system no chemical interaction occurs between the components at 20°C.

References

1. Tronov B. V., Izv. SKhTI, 2, 1, 1931.
2. Tronov B. V., Sibgatullin N. Kh., ZhRKhO, 62, 2267, 1930.
3. Tronov B. V., Ladygina L. V., Ukrainian Chemical Journal, 7, 55, 1932.
4. Tronov B. V., Grigorieva A. P., Proceedings of the Siberian Physico-Technical Institute, 1, 7, 1932.
5. Mishchenko K. P., Journal of Applied Chemistry, 2, 521, 1929.
6. Pryanishnikov N. D., Laboratory Manual in Organic Chemistry, Goskhimizdat, 115, 1950.
7. Andosov V. Ya., Pogodin S. A., Fundamental Principles of Physicochemical Analysis, Goskhimizdat, 157, 1947.
8. Vetrauds V. A., Chem. Abstr., 6066, 1949.