I. INTRODUCTION
Amines have the ability to bond with carbon dioxide gas, which leads to the formation of compounds called carbonates or carbamates (Zhou et al., Reference Zhou, Shi, Tian, Zhang and Deng2007; Leszczyński et al., Reference Leszczyński, Kornacki, Terlecki, Justyniak, Miletic, Halasz, Bernatowicz, Szejko and Lewiński2022). Aqueous solutions of selected aliphatic diamines were exposed to the slow action of carbon dioxide from air under normal conditions. As a result of the syntheses, several products were obtained and were investigated by performing chemical analyses and recording diffraction patterns.
Studies devoted to these compounds seem to be significant in the analysis of products formed on various types of surfaces near the plugs and valves of tanks containing amines or their solutions. In the case of the synthesis of chemical compounds with the participation of amines in aqueous solutions, there is a high probability of contamination of these compounds by products similar to those presented in this work. These impurities may be formed in parallel with the main product, or the obtained main product may slowly decompose under the influence of the aggressive action of carbon dioxide. Furthermore, understanding the reactivity and nature of the formation of the studied compounds may be useful from the point of view of green chemistry and in the broad sense of research in the field of “carbon dioxide capture”, which will undoubtedly contribute to environmental protection.
Products formed in the reaction of aliphatic diamines with metal halides [for instance, coordination polymers MX2 ← NH2 − (CH2)n − NH2 → MX2, hybrid compounds ZnS-1,3-diaminopropane (Luberda-Durnaś et al., Reference Luberda-Durnaś, Gaweł, Łoś and Łasocha2011; Gonzalez et al., Reference Gonzalez, Oszajca, Luberda-Durnaś and Lasocha2019)], stored under normal conditions and dried in the air, exhibit higher carbon contents than expected from the structural data. Our research may contribute to explaining the causes of this frequently observed phenomenon.
In fact, powder diffraction data for compounds denoted as 12-propCO2 and 13-dytekCO2 corrects diffraction data submitted by us previously to the PDF-4+ database (Gates-Rector et al., Reference Gates-Rector and Blanton2019). Trying to obtain new molybdates of 1,2-diaminopropane and 1,3-diaminopentane, MoO3 was dissolved in excess of the relevant amine and water. By slow evaporation in air white precipitates (usually wet and greasy) were obtained. Diffraction patterns for the obtained solids were indexed, and deposited as entries 00-61-1246 for 12-prop and 00-62-0980 in the case of 13-dytek. MoO3 used in the reaction probably remained as an amorphous salt dissolved in excess of amine (the sticky fraction surrounding the crystalline carbamates). Preparative studies without the use of MoO3 and tests using IR spectroscopy indicate the correctness of our hypothesis and confirm the formation of 12-propCO2 and 13-dytekCO2 monocarbamates in our present studies.
II. EXPERIMENTAL
All chemicals were purchased from commercial sources and used without further purification. The following amines purchased from Sigma-Aldrich were used for the experiment: 1,2-diaminopropane (12-dap), purity 99%; 1,3-diaminopropane (13-dap), purity 98%; and 1,3-diaminopentane (13-dytek), purity 98%.
A. Sample preparation
1. Synthesis
Five milliliters of diamine 12-dap, 13-dap, and 13-dytek were added to 20 ml of water and the prepared solutions were left to air dry in a beaker covered with filter paper at room conditions. After 2 months, the obtained white powder products, marked as 12-propCO2, 13-propCO2, and 13-dytekCO2, were thoroughly powdered and investigated by X-ray powder diffraction (XRPD) techniques and elemental analysis.
The elemental analysis showed the following percentage composition for
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12-propCO2 C: 40.59%, H: 8.092%, N: 23.57%; calculated values C: 40.67%, H: 8.53%, N: 23.71%;
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13-propCO2 C: 39.00%, H: 8.992%, N: 21.69%; calculated values C: 40.67%, H: 8.53%, N: 23.71%;
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13-dytekCO2 C: 49.30%, H: 9.627%, N: 18.76%; calculated values C: 49.30%, H: 9.65%, N: 19.16%.
Similar studies were carried out for 1,2-diaminoethane. A mixture of products with known structures deposited in the CSD (Cambridge Structural Database, 2022) were obtained as a result of the reaction, also listed in ICDD PDF-4+ as PDF 00-034-1993 and 00-034-1992.
B. XRPD measurements and crystallographic studies
13-propCO2 and 13-dytekCO2 were thoroughly powdered in a mortar and placed into a flat sample holder. In the case of 12-propCO2, the obtained product was placed into the thin-walled glass capillary (0.1 mm) filled with the amine 12-dap.
The XRPD measurements were performed at the Faculty of Chemistry, Jagiellonian University, using an X'Pert PRO MPD diffractometer, equipped with a diffracted beam graphite monochromator, a PIXcel 1-D detector and Cu long fine focus ceramic tube (generator setting: 40 kV and 30 mA) at 298 K. The diffraction data were collected over the 2θ angular range from 3 to 80° (for capillary measurements from 6 to 100°) with a step size of 0.02°. The divergence of the X-ray beam was 0.25°.
III. RESULTS AND DISCUSSION
The initial analysis of the recorded powder diffraction data was conducted using the PANalytical X'pert HighScore program (Degen et al., Reference Degen, Sadki, Bron, König and Nénert2014) and the PDF-4+ database (Gates-Rector and Blanton, Reference Gates-Rector and Blanton2019) to verify the purity of the products. For 12-propCO2, no additional phases were found. In the powder data set for 13-propCO2 and 13-dytekCO2, some low-intensity reflections were observed. These are most likely related to the formation of competing phases that differ in hydration or the progressing carbonization process. In order to obtain the unit cell parameters and the space group, the XRPD patterns of 12-propCO2, 13-propCO2, and 13-dytekCO2 were indexed using the N-TREOR program built in the program EXPO2014 (Altomare et al., Reference Altomare, Cuocci, Giacovazzo, Moliterni, Rizzi, Corriero and Falcicchio2013). For each compound, the space group was determined by the reflection conditions derived from the indexed reflections. The observed integrated intensities were extracted by the Le Bail method using the program EXPO2004. The monoclinic cell a = 9.3005, b = 9.2471, c = 7.4743 Å, and β = 111.1854°, V = 599.53 Å3, with figures of merit M 20 = 44 and F 20 = 56 (0.005329, 68) (De Wolf, Reference De Wolf1968; Smith and Snyder, Reference Smith and Snyder1979) were found for 12-propCO2. All lines were indexed. The analysis indicated the most probable space group as Ia (FoM = 0.536). For 13-propCO2, the solution with highest figures of merit M 20 = 64 and F 20 = 98 (0.007339, 28) indexed all reflections in the monoclinic system with unit cell parameters a = 5.0003, b = 12.1937, c = 4.8968 Å, β = 96.47°, and V = 296.67 Å 3. P2 1 was indicated as the most probable space group (FoM = 0.889). For 13-dytekCO2, the hexagonal unit cell with the highest figures of merit M 20 = 53 and F 20 = 90 (0.008288, 27), unit cell parameters a = 28.3506, b = 28.3506, c = 5.1702 Å, and V = 3598.87 Å3 were obtained. The analysis indicated the most probable space group as R 
$\bar{3}$ (FoM = 0.282). The structural formulas of the investigated compounds are illustrated in Figure 1.
Figure 1. Structural formulas of the obtained compound.
Experimental powder diffraction patterns are presented in Figure 2. XRPD data of the studied compounds are shown in Tables I–III. The structural data for all three compounds are given in Table IV. The diffraction patterns for all compounds are available in SI in cif and xy format.
Figure 2. Experimental powder diffraction pattern of the investigated carbamates: 12-propCO2 (black line), 13-propCO2 (red line), and 13-dytekCO2 (blue line).
TABLE I. X-ray powder diffraction data of 12-propCO2.
TABLE II. X-ray powder diffraction data of 13-propCO2.
TABLE III. X-ray powder diffraction data of 13-dytekCO2.
TABLE IV. Crystal data for the investigated compounds.
IV. CONCLUSION
On the basis of the conducted research, it was established that all the obtained compounds: 12-propCO2, 13-propCO2, and 13-dytekCO2 are monocarbamates. Unit cell parameters and probable space groups were determined. Structural studies are the subject of ongoing research.
Monocarbamates can be formed as unexpected, unwanted products of synthetic reactions carried out in the presence of moisture and air, in which amines are used as substrates.
V. DEPOSITED DATA
CIF and xy data files for the three reported compounds were deposited with ICDD. You can request these data by contacting ICDD at [email protected].
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0885715623000404.
