Hydrazono structure

Equally popular are azo couplings of diazonium salts that keep the nitrogen atoms in the product. The solid-solid version is very suitable with appropriate phenols such as 296 and 299. The waste-free and quantitatively obtained azo dye salts can be neutralized. The free dyes have the hydrazono structure (297, 298) or the azo structure (300) [99-100] (Scheme 45). The prescription should be carefully followed for safety reasons ... 

Keywords solid diazonium salt, barbituric acid, pyrazolinone, azocoupling, solid-solid reaction, hydrazono structure... 

The barbituric acid derivative 2 (0.50 mmol) was ground in an agate mortar. Solid diazonium salt 1 (0.50 mmol) was added and co-ground in 5 portions for 5 min, each. Most of the diazonium band at 2280 cm-1 had disappeared, but completion of the reaction was achieved by 24 h ultrasound application in a test tube. After neutralization (0.5 n NaOH, 20 mL), washings (H20) and drying, the quantitatively obtained products 3a-e assume the hydrazono structure. 

The pyrazolone 5 (1.00 mmol) and the solid diazonium salt 4 (1.00 mmol) were cautiously co-ground in an agate mortar for 5 min. The mixture was transferred to a 100 mL flask which was then evacuated. Me3N (0.5 bar) was let in. After 12 h at room temperature, excess gas was recovered in a remote trap at -196 °C. The salt was washed away with water (20 mL) and the residual solid dried. The yield was 98-99% of pure 6a-d with the hydrazono structure. 

Solid diazonium salt 1 (0.50 mmol) and jS-naphthol 2 (0.60 mmol) were separately ground in agate mortars and cautiously mixed. In the case of Id MgSC>4 2H20 (0.50 mmol) was added to the mixture. The mixtures rested for 24 h in test tubes and were then exposed to ultrasound for 24 h in a cleaning bath. The quantitatively obtained azo-dye salts 3-HX were neutralized and freed from excess 2 by washings with 0.5 n NaOH (20 mL) and water (20 mL). The yields of the neutral dyes with the hydrazono structure 3a-d were 100, 98, 99 and 99%. 

Triazolopyrimidines containing azo groups in the 6-position are depicted in different forms Unlike the description of 6-arylazo TPs in the usual 411-7-oxo form, some authors derive a 6-hydrazono structure 95 (97JCR(M)2378) or 6H-6-arylazo-7-0X0 structures, such as 96 (92JSC165, 98MI2), from spectroscopic data (Scheme 26). For the same reason, 7-hydrazono form 97 is preferred to a possible 7-hydrazino structure (99JHC1199). 

---