I. INTRODUCTION
Sodium azobarbituric acid dihydrate [C8H5N6O6Na.2H2O] (Figure 1) is an orange-red powder. It is used as the crucial starting material for the synthesis of the industrially important and is now worldwide discussed organic pigment – Pigment Yellow 150, which is the complex of nickel and azobarbituric acid. The pigment is used in paints and in decoration printing inks for laminates.
Figure 1. Structural formula of C8H5N6O6Na.2H2O.
We have inspected the CSD database (Allen, Reference Allen2002) and the PDF4+ database (ICDD, Reference Kabekkodu2012) and have not found any entry for this compound in the mentioned databases. This fact is the reason why we have decided to characterize this compound by X-ray powder diffraction (XRD) technique.
II. SAMPLE PREPARATION
There is more than one way to synthesize monosodium salt azobarbituric acid, but it cannot be prepared by a common diazotization of aminobarbituric acid and the following coupling. The synthetic route using azidoformamidine as the diazo group transfer agent was chosen for the synthesis of azobarbituric acid according to the standard industrial procedure. This synthesis is one-pot reaction, in which azidoformamidine is formed from aminoguanidine and sodium nitrite in acid water media as the first step. In the second step, the diazobarbituric acid is formed and subsequently reacts with an excess of barbituric acid generating azobarbituric acid in the form of dihydrate of monosodium salt in the third step. The final product was dried under vacuum at 70 °C for the elimination of the possible decomposition. This monosodium salt is poorly soluble in water, and its solubility is in the range of tenth of a gram per liter. The thermogravimetric analysis was used to confirm crystal water in the structure of C8H5N6O6Na.2H2O.
III. POWDER DIFFRACTION DATA
The diffraction pattern for the title compound was collected at room temperature with an Empyrean powder diffractometer with transmission Debye–Scherrer geometry using CuKα radiation (focusing mirror, generator setting: 45 kV, 40 mA). An ultrafast PIXCel3D detector was employed to collect XRD data over the angular range from 4 to 80 °2θ with a step size of 0.013 °2θ, and a counting time of 2978,4 s step−1. The sample was placed in the 0.3 mm borosilicate glass capillary. The experimental powder diffraction pattern is depicted in Figure 2. The software package HighScore Plus V3.0e(PANalytical, Almelo, Netherlands) was used to smoothen the data, to fit the background, and to eliminate the Kα 2 component; and the top of the smoothed peaks were used to determine the peak positions and intensities of the diffraction peaks (Table 1). The d-values were calculated using CuKα 1 radiation (λ = 1.5406 Å).
Figure 2. (Color online) X-ray powder diffraction pattern of C8H5N6O6Na.2H2O using CuKα radiation (λ=1.5418 Å).
Table I. Indexed X-ray powder diffraction data for C8H5N6O6Na.2H2O. Only the peaks with I rel of 1 or greater are presented [a = 3.546 (1) Å, b = 9.210 (2) Å, c = 9.738 (4) Å, α = 104.07 (4)°, β = 98.09 (6)°, γ = 98.80 (2)°, unit-cell volume V = 299.6 Å3<>, Z = 1, and space group P − 1]. All lines were indexed. The d-values were calculated using CuK α 1 radiation (λ = 1.5406 Å).
The collected data are consistent with a triclinic unit-cell parameters [a = 3.546 (1) Å, b = 9.210 (2) Å, c = 9.738 (4) Å, α = 104.07 (4)°, β = 98.09 (6)°, γ = 98.80 (2)°, unit-cell volume V = 299.6 Å3, Z = 1, and space group P − 1]. These parameters were derived using DICVOL04 (Boultif and Louër, Reference Boultif and Louër2004 ) with the results all being within the errors indicated. The following figures of merit were achieved: F20 = 45.6 (0.0107,41) (Smith and Snyder, Reference Smith and Snyder1979) and M20 = 26.2 (de Wolff, Reference de Wolff1968).
ACKNOWLEDGEMENTS
This work was supported by the grant no. P106/12/1276 from the Grant Agency of the Czech Republic and by the grant TAČR TA02010781 of the Technological Agency of the Czech Republic.
