On the Structure of Diacyl Derivatives of Benzylurea

N. S. DOBYCHINA

(Presented by the Scientific-Methodological Seminar of the CTF)

Earlier, in our work [1], upon acylation of benzylurea with substituted benzoic acids containing a substituent in the para position, diacyl derivatives were obtained. It was of interest to determine to which of the amide groupings—the one substituted by acyl or by alkyl—the second acyl radical becomes attached.

In previous investigations [2], by calculation using the LCAO MO method and by counter synthesis, we established that upon acylation of alkylurea with acids of the fatty series, \(N, N'\)-alkylacyl derivatives of urea are obtained, i.e., acylation occurs at the unsubstituted amide grouping. The analogy in the structure of acyl derivatives of alkylureas is preserved when the latter are acylated with benzoic acid and heterocyclic acids. However, when benzylurea is acylated with para-substituted benzoic acids, a deviation from the indicated analogy arises.

To elucidate the structure of the diacyl derivatives of benzylurea obtained by us, infrared and PMR spectra were recorded. Interpretation of the IR spectra does not provide corresponding information on the structure of the compounds obtained. The PMR spectra of di-(p-chlorobenzoyl) and di-(p-nitrobenzoyl)benzylureas were recorded in dimethyl sulfoxide and chloroform on an instrument with an operating frequency of 60 MHz, using hexamethyldisiloxane as the standard.

The values of the chemical shifts are given in parts per million (ppm) relative to tetramethylsilane (\(\delta\)-scale). The signals of the samples are clearly resolved, and their integral intensity corresponds to the number of protons. Thus, in the region of 9.25 ppm and 9.17 ppm, the proton of the NH group is recorded with an intensity equal to 1. In this case, it appears possible to judge the nature of the substituents only by the character of the chemical shift.

Since there is very little information in the literature on PMR spectra of urea derivatives, and for the compounds under study the spectra are being recorded for the first time, the chemical shift must be judged from the spectra of compounds containing protons in an analogous chemical environment. Thus, for example, in \(N\)-tolylsulfonyl-\(N'\)-butylurea the proton belonging to the NH group bonded to an alkyl radical is recorded in the region of 6.53 ppm [3], or, for example, in \(\beta\)-phenylethylacetamide the amide proton is recorded in the region of 6.50 ppm [4]. At the same time, for acylamides not bonded to alkyl radicals, na-

for example, in phenylacylamides, the proton of the amide group resonates in a weaker field—from 7.5 to 9.5 ppm [4].

On the basis of the literature data cited, it may be assumed that in the compounds under study (the peak of the proton of the NH group appears in the region of 9–9.25 ppm), the proton belongs to an NH group not bonded to an alkyl radical. It is probable that the acyl group replaces the hydrogen atom at the amide group bonded to the benzyl radical, whereas the second amide group, containing the proton, is bonded to the second acyl group. Thus, the following structure of the diacyl derivatives is more probable:

\[ \begin{array}{c} \mathrm{C_6H_5CH_2} \\ \mathrm{RC_6H_4C} \\ \| \\ \mathrm{O} \end{array} >\!>\mathrm{N{-}C{-}NH{-}C{-}C_6H_4R,} \qquad \begin{array}{cc} \| & \| \\ \mathrm{O} & \mathrm{O} \end{array} \]

where \(R=\mathrm{Cl}, \mathrm{Br}, \mathrm{NO_2}\) and is in the para position.

Conclusions

On the basis of interpretation of the PMR spectra, the structure of the diacyl derivatives of benzylurea is proposed.

LITERATURE

1. N. S. Dobychina, A. G. Pechenkin, S. G. Veshnyurtseva. Izv. TPI (in press).
2. N. S. Dobychina. Dissertation, Tomsk, 1966.
3. Varian analytical instrument division high resolution NMR spectra catalog, volume 2.
4. L. A. Kazitsyna, N. B. Kupetskaya. Application of UV, IR, and NMR Spectroscopy in Organic Chemistry, “Khimiya,” 1970.