PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
named after S. M. Kirov

Vol. 198
1974

STUDY OF THE INTERMOLECULAR INTERACTION OF ALKYLATED ACETAMIDES AND GLYCINAMIDES WITH NITROPHENOLS

L. P. PETRENKO, N. D. STRELNIKOVA, V. D. GOLDTSEV,
A. G. PECHENKIN, A. A. ZHELNOV

(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)

Previously we studied the interaction of diamides of dicarboxylic acids and other amides with isomeric nitrophenols in water [1]. It was of interest to determine the influence of alcohols and nonpolar solvents on the intermolecular interaction of amides of carboxylic and amino-carboxylic acids with p-nitrophenol and dihalonitrophenols. In an earlier work we investigated the interaction of amides of carboxylic and dicarboxylic acids with 2,6-dibromo-4-nitrophenol in anhydrous methyl alcohol [2]. The present work gives the results of a study of the intermolecular interaction of N-methyl-, N,N-dimethyl-, N,N-diethylacetamide, N,N′-dimethyl-, N,N,N′,N′-tetramethylglycinamide in butyl and isobutyl alcohols and in chloroform with nitrophenols: 2,6-dibromo-, 2,6-dichloro-4-nitrophenol, and p-nitrophenol.

Since acetamide is very poorly soluble in these solvents, and its complex-forming ability, as previous investigation shows, is much lower in anhydrous methanol than that of its alkyl derivatives, this did not allow us to quantitatively investigate its interaction with various nitrophenols in these solvents.

The study was carried out by ultraviolet and infrared spectroscopy.

Experimental Part

The electronic absorption spectra of the systems studied were recorded on an SF-4A in the range 220–440 mμ. In all the systems studied, changes in the spectra were observed: for p-nitrophenol, under the influence of amides and amino-amides of carboxylic acids, there is a shift and an increase in the intensity of the 310 mμ band; for dihalonitrophenols, there is a decrease in the intensity of the 310 mμ band and the appearance of a new band at 350–420 mμ (solvent—chloroform, butyl alcohol). Figure 1 presents the absorption spectra of reaction and additive mixtures of alkyl derivatives of acetamide and glycinamide with 2,6-dibromo-4-nitrophenol in chloroform.

Measurements of the equilibrium constants of the systems studied were carried out in the region 350–410 mμ at a temperature of 21–22°C. The indicated amides are optically transparent in this region of the spectrum.

The equilibrium constants were calculated by the Ketelaar method [3]. The data were processed by the least-squares method [4]. The rectilinear dependence of the function \(y=\dfrac{C_D}{D-D_0}\) on \(x=\dfrac{1}{C_D}\) shows that complexes of composition 1:1 are formed in the systems (\(C_A\) is the concentration of nitrophenol, \(C_D\) is the concentration of amide, \(l\) is the thickness of the absorbing layer, \(D\) is the optical density of nitrophenol, and \(D\) is the optical density of the system).

Fig. 1. Electronic absorption spectra of 2,6-dibromo-4-nitrophenol (2,6-DBNP) + amides of different structure:
1 — 2,6-DBNP, \(C=1\cdot10^{-3}\) mol/l;
2 — 2,6-DBNP + \(N_1,N'\)-dimethylglycinamide, \(C=1\cdot10^{-2}\) mol/l;
3 — 2,6-DBNP + \(N\)-methylacetamide, \(C=5\cdot10^{-1}\) mol/l;
4 — 2,6-DBNP + \(N_1,N_1,N_1',N'\)-tetramethylglycinamide, \(C=1\cdot10^{-2}\) mol/l;
4 — 2,6-DBNP + \(N_1,N\)-diethylacetamide, \(C=1\cdot10^{-2}\) mol/l.

The equilibrium constants of these systems were also calculated by the Nagakura method [5]. Agreement was obtained between the values of the equilibrium constants determined by these methods. All data, processed statistically [4], are summarized in Table 1.

Discussion of Results

According to the data of a number of researchers, coordination of amides with phenols and nitrophiles occurs through the oxygen atom of the carbonyl group and the protons of phenols. With the aid of IR spectra we

It was established that, in the interaction of amides and amino-amides with both phenol and dihalonitrophenols, the band of the stretching vibrations of the carbonyl group of the amides shifts toward higher frequencies. Thus, for the system \(N,N,N^1,N^1\)-tetramethylglycinamide + 2,6-dibromo-4-nitrophenol, the band of the stretching vibrations of the \(>C=O\) group shifts by \(43\ \text{cm}^{-1}\). The band of the stretching vibrations of the hydroxyl group of the dihalonitrophenols is displaced under the influence of hydrogen bonding with the carbonyl group of these amides toward lower frequencies.

With the introduction of alkyl radicals into the amide group, the electron density on the oxygen atom increases; the interaction of methylated and, still more, ethylated acetamides with nitrophils is characterized by a larger equilibrium constant (Table 1).

Table 1

Values of equilibrium constants and composition of complexes of alkylated amides and amino-amides with nitrophenols in various solvents

It is interesting to note that, with increasing stability constants, the values of \(\Delta \lg \varepsilon\) of the spectral bands of reaction mixtures having identical concentrations of donor and acceptor also increase synchronously.

In studying the influence of solvents on intermolecular interaction, it was found that in chloroform the complex-forming ability of amides decreases significantly.

Conclusions

1. By the spectrophotometric method, the complex-forming ability of 5 amides with nitrophenols of various structures in bu-

ethyl, isobutyl alcohols, and chloroform. Intermolecular interaction was detected in all systems.

1. The composition of the complexes, 1:1, was established, and the equilibrium constants of alkyl derivatives of acetamide and glycinamide with nitrophenols in the indicated solvents were calculated.

2. On the basis of IR-spectroscopic data it was established that coordination in the complexes of alkyl derivatives of acetamide and aminoacetamide occurs through the carbonyl group of the amides and the hydroxyl protons of phenols of different structures.

3. It is shown that alkylated \(NH_2\) groups in acetamides increase the values of their equilibrium constants with nitrophenols in the given solvents.

4. It was established that introduction of a methylated amino group—

\[ -\!N\!\begin{matrix} \diagup R\\[-2pt] \diagdown R \end{matrix} \]

into acetamide increases the magnitude of the equilibrium constants of glycinamides, as compared with amides, in their reactions with dihalonitrophenols.

1. Introduction of substituents into the 2,6 positions of p-nitrophenol leads to an increase in their proton-donor activity.

REFERENCES

1. V. D. Goltsev, N. D. Strelnikova, A. P. Izokenaite. In: Organic Complex Compounds, Tomsk, 1964.

2. L. P. Petrenko, V. D. Goltsev, N. D. Strelnikova, A. G. Pechenkin, A. A. Zhelnov. Izvestiya TPI (in press).

3. Norman J. Rose and Russell S. Drago. J. Amer. Chem. Soc. (1959), 81, 6138.

4. A. Albert, E. Serjeant. Ionization Constants of Acids and Bases. 1964, Moscow–Leningrad.

5. S. Nagakura, J. Amer. Chem. Soc. (1954), 76, 3070.