Results and Discussion
The diazonium salts derived from anilines 1 (sulfanilic acid, 4–nitroaniline, 4–aminosalicylic acid, sulfanilamide, sulfamethoxazole, sulfathiazole, sulfapyridine, sulfamerazine) were coupled with N-(2,4-dimethylphenyl)-3-oxobutanamide (2) in aqueous ethanol containing sodium acetate resulting in the formation of hydrazones 3a–h (Scheme 2).
The UV spectra of products 3 show three ranges of absorption maxima at 203–207, 235–271, and 376–393 nm, except compounds 3e and 3f which had four absorption maxima. Absorption bands attributed to an azo function between 332–360 nm21–22 and above 400 nm23 are missing. Thus, the observation of bands at 376–393 nm is indicative of the hydrazone form of compounds 3a–h.6,9,24–26
ArNH2NaNO2, HCl0–5 °C[ArN=N Cl ] +OH3CNHOCH3CH3OH3CNHOCH3CH3N1231, 3XaHAr = XYYSO3HbHNO2cOHCO2HdHSO2NH2eHSO2NHfHSO2NHSNgHSO2NHNhHSO2NHNNMeArNH– NOMe
Scheme 2. Preparation of [2-[1-(2,4-dimethylphenylamino)-1,3-dioxobutan-2-ylidene]hydrazin- yl]benzenes (3a–h).
The amide proton (-NH-C=O) exhibits a singlet at d 10.98–11.16, the hydrazone proton
(-CH=N-NH-) shows a singlet at d 13.90–14.32; both signal ranges are in agreement with the literature.18,27–29 Furthermore, in the 1H-NMR spectra of compounds 3a-h, signals arising from a >CH-N=N- moiety are expected at 3.00-4.00 ppm,23,25 but were not observed. These findings support the hydrazone structure of the products.
The APCI-MS spectra of 3a–h show molecular ion peaks (M+) confirming their molecular weight; common characteristic fragment ions result from cleavage of the amide bond resulting in
