Study of the Intermolecular Interaction of Urea and Its Derivatives with 2,6-Dibromo-4-Nitrophenol
Abstract Generated abstract
This study examines intermolecular complex formation between urea, selected N-alkyl and N-acyl urea derivatives, and 2,6-dibromo-4-nitrophenol in anhydrous methanol using ultraviolet spectrophotometry. Changes in the electronic spectra, especially decreased absorption near 300 nm and increased absorption near 400 nm, were used to identify interaction and to determine complex composition and stability constants by the Ketelaar method with statistical processing. The investigated systems formed 1:1 complexes, with urea showing a higher stability constant than its N-alkyl and N,N-dialkyl derivatives, while acylation markedly reduced complex-forming ability and prevented reliable calculation of constants for the acyl derivatives.
Full Text
STUDY OF THE INTERMOLECULAR INTERACTION OF UREA AND ITS DERIVATIVES WITH 2,6-DIBROMO-4-NITROPHENOL
L. P. PETRENKO, V. D. GOL’TSEV, N. D. STREL’NIKOVA,
A. G. PECHENKIN, N. S. DOBYCHINA
(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)
Reactions of complex formation of urea and its alkyl and acyl derivatives with nitrophenols in various solvents are of considerable interest both theoretically and from the standpoint of the needs of medical practice. However, the intermolecular interaction of these groups of compounds has so far been little touched upon by research. In studying the complex formation of urea and some of its alkyl and acyl derivatives possessing anticonvulsant action, we selected the following series of compounds for the present study: urea, $N$-methyl-, $N$-dimethyl-, $N$-benzyl-, $N_1$-acetyl-, $N$-benzoyl-, $N$-bromodiethylacetyl-, $N_1N^1$-methylbenzoyl-, $N_1N^1$-methylvaleryl-, $N_1N^1$-methylisovaleryl-, $N_1N^1$-methylbenzoyl-, $N_1N^1$-benzylacetyl-, $N_1N^1$-benzylvaleryl-, $N_1N^1$-benzylisovaleryl-, $N_1N^1$-benzylbenzoylureas.
As the second component in the reactions of intermolecular interaction we chose 2,6-dibromo-4-nitrophenol, for which the most significant, constant, and well-reproducible changes in the electronic spectra caused by intermolecular interaction are observed. Anhydrous methyl alcohol served as the solvent. The studies were carried out by ultraviolet spectroscopy.
The electronic absorption spectra of the systems under study were recorded on an SF-4A in the wavelength region 220–440 mμ, and in all the systems studied changes were found in the spectra: a decrease in the optical density of the short-wavelength band of 2,6-dibromo-4-nitrophenol (300 mμ) and an increase in the optical density of the long-wavelength band (400 mμ), which is more sensitive to intermolecular interactions (Fig. 1).
Measurements of the stability constants of the systems studied were carried out in the spectral region 370–430 mμ at a temperature of 21–22°C. Urea and its derivatives are optically transparent in the indicated spectral region. As an example, Table 1 gives data for the system urea + 2,6-dibromo-4-nitrophenol at $\lambda = 380$ mμ.
The stability constants of urea, $N$-methyl-, $N$-dimethyl-, $N$-benzyl-, and $N$-bromodiethylacetylurea were determined by the Ketelaar method [1] graphically and by processing by the least-squares method [2, 3]. Graphically, the rectilinear dependence of the function $y = \dfrac{C \cdot L}{D - D_0}$ on
of the reciprocal concentration of the donor
\[ x=\frac{1}{C_D} \]
for several wavelengths (370, 380, 390 mµ) of the urea + 2,6-DBNP system, shown in Fig. 2, indicates that a complex of composition 1 : 1 is formed.
Fig. 1. Electronic absorption spectra of 2,6-dibromo-4-nitrophenol (2,6-DBNP) + carbamides:
1 — DBNP, \(C=1\cdot10^{-3}\) mol/l;
2 — DBNP + urea, \(C=1\cdot10^{-1}\) mol/l;
3 — DBNP + N-methylurea, \(C=1\cdot10^{-1}\) mol/l;
4 — DBNP + \(N,N\)-dimethylurea, \(C=1\cdot10^{-1}\) mol/l;
5 — adalin + DBNP, \(C=5\cdot10^{-2}\). Solvent — methanol.
Table 1
System urea + 2,6-dibromo-4-nitrophenol in methanol. \(\lambda=380\) mµ, \(C_A=1\cdot10^{-3}\), \(l=1\) cm
| \(C_D\cdot10^{-2}\), mol/l | \(D_0\) | \(D-D_0\) | \(y=\dfrac{C_A\cdot l}{D-D_0}\) | \(K\) (l/mol) |
|---|---|---|---|---|
| 10 | 0,600 | 0,958 | 1,04 | 10,0 |
| 9 | 0,600 | 0,850 | 1,18 | 10,0 |
| 8 | 0,600 | 0,790 | 1,27 | 10,0 |
| 7 | 0,600 | 0,740 | 1,35 | 10,0 |
| 6 | 0,600 | 0,710 | 1,41 | 10,0 |
| 5 | 0,600 | 0,600 | 1,67 | 10,0 |
| 4 | 0,600 | 0,520 | 1,92 | 10,0 |
| 3 | 0,600 | 0,460 | 2,18 | 10,0 |
All the data were statistically processed [2] and are presented in Table 2. Analysis of the results given in Table 2 shows that urea has a greater complex-forming ability than its alkyl derivatives.
The results of a study of the electronic spectra of acyl derivatives of urea and of other amides and diamides with 2,6-dibromo-4-nitrophenol show that acylation greatly reduces the complex-forming ability of amides of different structures; therefore, it does not appear possible to calculate the stability constants of acyl derivatives of urea.
Fig. 2. Dependence of the function
\[
y=\frac{C_A\cdot l}{D-D_0}
\]
on the donor concentration
\[
x=1/C_D
\]
for the system urea + 2,6 DBNP in \(\mathrm{CH_3OH}\). \(C_D\) is the urea concentration; \(l\) is the thickness of the absorbing layer; \(D\) is the optical density of the system; \(D_0\) is the optical density of 2,6 DBNP.
Table 2
Values of the constants (L/mol) and confidence intervals
| Urea | N-methylurea | N₁,N-dimethylurea | Adalin | Benzylurea |
|---|---|---|---|---|
| \(10.5 \pm 0.7\) Composition 1:1 |
\(4.7 \pm 0.2\) 1:1 |
\(3.5 \pm 0.4\) 1:1 |
\(4.8 \pm 0.2\) 1:1 |
\(3.0\) 1:1 |
Conclusions
-
By the spectrophotometric method, the interaction of urea and its \(N\)-alkyl and \(N\)-acyl derivatives with 2,6-dibromo-4-nitrophenol was studied. In all systems, intermolecular interaction was detected; the composition of the complexes formed was 1:1.
-
The stability constants of the complex-formation reactions of urea and its \(N\)-alkyl derivatives, and of adalin, with 2,6-dibromo-4-nitrophenol in methyl alcohol were calculated by the Ketelaar method.
-
It was shown that the stability constants of urea with 2,6-dibromo-4-nitrophenol (10 L/mol) are greater than those of its \(N\)-alkyl and \(N\)-dialkyl derivatives (4.7 and 3.5 L/mol, respectively).
-
It was established that acylation of urea significantly reduces the complex-forming ability of these compounds with respect to nitrophenols.
References
- Norman. J. Rose and Russel S. Drago J. Amer. Chem. Soc. (1959), 81, 6138.
- A. Albert, E. Serjeant. Ionization Constants of Acids and Bases. 1964, Moscow—Leningrad.
- V. M. Vdovenko. Spectrophotometric Methods in the Chemistry of Complex Compounds, 1964, Moscow—Leningrad.