# Oxidative Thermolysis of Sulfobutyl-Ether-Beta-Cyclodextrin Sodium Salt: A Kinetic Study
## 3 Results and Discussion  
The UATR-FTIR (Universal Attenuated Total Reflection Fourier Transform Infrared Spectroscopy) instrumental technique is widely used in the field of pharmaceutical research since it is able to provide reliable results in a very short amount of time, allowing the identification and purity evaluation of each compound. In the case of SBECD, the obtained FTIR spectrum was drawn up and is presented in Figure 2. Considering the structure of the compound (Figure 1), the identity of the compound was evaluated by comparing the obtained results with the available literature data [32; 33; 34; 35]. As such, the presence of the main structural characteristics of SBECD were revealed on the FTIR spectrum. The presence of the O-H bonds can be correlated with the broad band seen in the 3700-3050 cm\({}^{-1}\) spectral range determined by the stretching vibrations of these bonds. The characteristic stretching vibrations of the methylene groups are revealed at 2932 cm\({}^{-1}\) (the asymmetric stretching vibration of the C-H bond) and 2885 cm\({}^{-1}\) (the symmetric stretching vibration of the same bond type). A well-defined signal can be seen at 1643 cm\({}^{-1}\), its presence being due, according to the literature data, to the bending vibration of the H-O-H bonds belonging to the water molecules intercalated in the structure of SBECD [16; 36]. The two low-intensity bands observed at 1411 and 1365 cm\({}^{-1}\) may be correlated with the association of the in-plane bending vibration of the O-H bonds with the wagging deformation vibration of the C-H bonds present in the structure of SBECD. The vibrations of the C-O bonds, that are usually visible in the 1260-1000 cm\({}^{-1}\) spectral range [34], cannot be observed since their low intensity is masked by the presence of other bands. The presence of the sulfonate anion in the structure of SBECD determines the most intense spectral signals, with two wide bands being revealed with peaks at 1149 and 1026 cm\({}^{-1}\), representing the asymmetric and symmetric stretching vibrations, respectively, of the S=O bond. The results are in good agreement with reported data [16]. Figure 2: The UATR-FTIR spectrum of SBECD. Figure 3 presents the PXRD pattern of SBECD, which reveals only one broad peak centered in the 18.20-19.55\({}^{\circ}\) interval (with maximum intensity at 18.20\({}^{\circ}\)), indicating the amorphous nature of the sample, even if this cyclodextrin contains in the structure a saline sulfone-sodium ionic moiety. The thermoanalytical profile of SBECD recorded in dynamic air flow at a heating rate of \(\beta\) = 10 \({}^{\circ}\)C-min\({}^{-1}\) (Figure 4) reveals a dehydration step between 40 and 137 \({}^{\circ}\)C, with a corresponding \(\Delta\)m = 8.16%, leading to a water content of 10.67 mol water per mol anhydrous SBECD. The water content from the SBECD sample was also determined using a two-component Karl Fischer titration based on the methodology published by [PERSON], [PERSON], and [PERSON] [37], revealing a total water content of 8.02 \(\pm\) 0.27%. The good agreement between the KFT method and thermal analysis suggests that this mass loss process is solely due to the presence of water in the structure of SBECD, and no other volatile compounds. Anhydrous SBECD seems stable for a large temperature range, namely between 137 and 239 \({}^{\circ}\)C, when a continuous mass loss process takes place up to 434 \({}^{\circ}\)C (\(\Delta\)m = 45.79%). In the 434-500 \({}^{\circ}\)C temperature range, the residual mass remains constant at 46.05%. The DTG curve reveals the dehydration process that took place in the 40-137 \({}^{\circ}\)C temperature range, followed by another two consecutive processes associated with the decomposition of anhydrous SBECD, namely in the 239-313 \({}^{\circ}\)C range (DTGpeak at 273 \({}^{\circ}\)C) and in the 313-379 \({}^{\circ}\)C range (DTGpeak at 352 \({}^{\circ}\)C), followed by another process in the 379-500 \({}^{\circ}\)C range (DTGpeak at 394 \({}^{\circ}\)C).