USE OF QUANTUM-CHEMICAL PARAMETERS FOR FORECASTING ANTIRADICAL (HO·) ACTIVITY OF RELATED STRUCTURES CONTAINING A CINNAMIC MOLD FRAGMENT. III. CHALCONES, FLAVANONES AND FLAVONES WITH PHLOROGLUCINIC TYPE OF RING “A”

42 derivatives of chalcone, flavanone and flavone having a phloroglucinic type of ring “A” and containing the same electron-donating substituents on ring “B”, have been studied. Flavonoids with the phloroglucinic type of ring “A” are the most common in nature, which is due to the peculiarities of biogenetic formation with the participation of malonyl and acetyl fragments.The aim of the article is to determine the effect of the hydroxy group in position 6' of chalcones and in position 5 of flavanones and flavones on bond numbers (Nµ), free valence indices (Fµ), Mulliken charges (a.e), electron density, unsaturation indices (IUA) of the carbon atoms C-1 → C-6 → C-7 → C-8.Materials and methods. The calculations of the listed above parameters with the use of the semi-empirical method PM7 (WinMopac 2016 program) have been carried out on a workstation with an Intel Xeon E5-1620 3.5 GHz processor, 20 GB of RAM.Results. The quantum-chemical characteristics of the considered derivatives having a phloroglucinic type of the “A” ring, indicate that the OH group in position 6' of chalcones (in the corresponding flavanones and flavones in position 5) has different effects: a slight increase occurs in chalcones negative charge (a.e.) and electron density, the bond numbers take different values, which depends on the position and number of substituents on the ring "B". In flavanones, Nµ practically remains at the same level of 3.822-3.829. For flavones, the binding numbers Nµ for C-8 are in the range of 3.700-3.706, and the Mulliken charges are in the range from -0.4120 to -0.4356. For position-substituted C-3 (6anone and 7anone), the charges are -0.4436 and -0.4479, respectively. The charge on C-7 of chalcones is negative for compounds 4x, 5x, 10x and 13x from -0.0204 to -0.0470. The remaining derivatives of the chalcone, as well as the corresponding flavanones and flavones, are characterized by a positive value of a.e. on C-7. Based on the bond numbers (Nµ), free valency indices (Fµ) have been found for the carbon atoms of the cinnamoyl fragment C-1 → C-6 → C-7 → C-8. When comparing the obtained data, it was found out that for chalcones on C-1 → C-8 atoms, the values of the free valence indices are in the range of 0.900-0.980 for compounds 12x, 13x, where Fµ> 1. For flavanones on C-1, C-3, and C-5 atoms (compounds 12anone and 13anone), the free valence indices are in the range of 0.984-1.024, and for the remaining atoms the value of Fµ is approximately the same as that of chalcones. On the C-8 atoms of all the derivatives, as well as on C-1, C-3 and C-5 (compounds 12one, 13one), Fµ ≥ 1.0. It can be assumed that at values of Fµ = 0.850-0.955 for all the analyzed compounds, coupling reactions on the double bond are possible, and if Fµ ≥1, the coupling will take place according to the free radical mechanism. The data obtained indicate that the OH group in position 6’ for the chalcone and 5 for the flavanones, does not significantly effect the Mulliken charge (a.e) and the electron density on C-8 atoms.Conclusion. It has been established that the OH group in position 6' of the "A" ring of chalcones (in position 5 of the "A" ring in flavones and flavanones) has a conflicting effect on the bond numbers: when passing from chalcone to flavanone, Nµ increases, and then, in flavone, sharply decreases. For C-8 of all flavone derivatives, Fµ ≥1. The following conclusion has been confirmed: at the initial stage of the reaction the electrophilic hydroxyl radical is attached at the C-8 position of the cinnamoyl fragment

Dirhodium(II)-Catalyzed Diamination Reaction via a Free Radical Pathway

Unlike C-N bond formation with classical dirhodium(II)-nitrenoids as the key intermediate, dirhodium(II)-catalyzed 1,2-and 1,3-diamination reactions are realized by a free radical mechanism. A mechanistic study revealed that the reactions undergo...

Autocatalytic deoximation reactions driven by visible light

Photocatalytic deoximation reaction was found to be an autocatalytic process that occurs via free-radical mechanism. Understanding the mechanism may help chemical engineers to develop related techniques to avoid the decomposition of oximes.

Catalytic Pyrolysis as a Technology to Dispose of Herbal Medicine Waste

The use of herbal medicine has increased tremendously over the last decades, generating a considerable amount of herbal medicine waste. Pyrolysis is a promising option to dispose of biomass and organic waste such as herbal medicine waste. Herein, an activated carbon-supported Pt catalyst (Pt/AC) and carbon dioxide (CO2) were applied to the pyrolysis of real herbal medicine waste to develop a thermal disposal method to prevent the formation of benzene derivatives that are harmful to the environment and human health. When using the Pt/AC catalyst in the pyrolysis of the herbal medicine waste at 500 °C, the generation of benzyl species was suppressed. This was likely because the Pt catalytic sites accelerate a free radical mechanism that is dominant in the thermal cracking of carbonaceous substances. However, the employment of CO2 (instead of typically used N2) as a pyrolysis medium for the herbal medicine waste pyrolysis did not decrease the concentrations of benzyl compounds contained in the pyrolytic products of the herbal medicine waste. This study might help develop a method to thermally dispose of agricultural biowaste, preventing the formation of harmful chemicals to the environment and human beings.

Theoretical DFT study of Cannizzaro reaction mechanism: A mini perspective

In regards to the Cannizzaro reaction and its peculiar mechanism, some researchers have presented a free radical mechanism for the Cannizzaro reaction, while others have found that it is feasible through an ionic mechanism, but the actual mechanism has not been finalized yet. The researchers have given the proof of both the mechanisms through their papers published. Actually, Cannizzaro reaction may occur through both mechanisms depending on both molecular structure and different conditions which are yet to be explained. Recently published papers describe that free radical mechanism occurs only in a heterogeneous medium, while an ionic mechanism occurs in a homogeneous medium. We revealed no explanation of the molecular structure-based reason, responsible for a radical or an ionic mechanism. The present paper reviews not only homogeneous/heterogeneous medium conditions but also molecular structure-based facts, which may be responsible for the Cannizzaro reaction to occur through the radical or ionic mechanism, and that may be acceptable to the scientific society. Besides, Density Functional Theory study using Gaussian software was also involved in the explanation of the molecular structure, responsible for one of the two mechanisms. Also, the present paper specifies all points related to future perspectives on which additional studies are required to understand the actual mechanism with a definite molecular structure in the different reaction media.

Copper Catalyzed Autoxidation of Sulphur Dioxide and Inhibition by Methanoic Acid

Background:: Today, acid rain problem is one of the serious global problems to the environment in which pH of the rain water decreases, causing harmful effect to nature, buildings, monuments, vegetation and human being as well. Therefore, the objective of the paper to find out some organic inhibitors present in the atmosphere that inhibited the acid rain. Objective:: In this paper, we studied the chemistry of Cu (II)-methanoic acid-S(IV)-O2 in acetate buffered medium by earlier reported methods in literature. Gravimetric analysis was carried out to find the end product and confirmed that it was sulphate with 98 % recovery. Methods:: Experiments were carried out at 303 ≤ T/K ≤ 313, 4.0 ≤ pH ≤ 5.35, 1.0×10−3 mol/dm3 ≤ S(IV) ≤ 10.0×10−3 mol/dm3, 5×10−6 mol/dm3 ≤ [Cu(II)] ≤ 2.5×10−5 mol/dm3, 6×10−6 mol/dm3≤[methanoic acid]≤7×10-4 mol/dm3. The value of apparent activation energy and inhibition parameter B was calculated in the presence of methanoic acid found as 29.07 kJ mol-1and 3.18 x 103 mol dm-3, respectively. The thermodynamic parameters were found as frequency factor (1.59 x 10-6s-1), entropy (-358.92 J K-1 mol-1), enthalpy (20.97 k J mol-1), and Gibbs free energy (172.83k J mol-1), respectively. Results:: We observed that methanoic acid acts as an inhibitor in copper catalyzed autoxidation of SO2 in acidic medium. Therefore, on the basis of the observed results a free radical mechanism has been identified. The results are useful for modeling rain water acidity and therefore a great use of meteorology and atmospheric chemistry. This study is important in understanding the mechanism of the oxidation of S(IV) by O2. Conclusion:: This study suggests that since organic inhibitors are found in the atmosphere, their concentrations and their influence on the oxidation of aqueous SO2 should be taken into account. The intervention of methanoic acid in the autoxidation of aqueous SO2 plays a role in deciding the fate of both methanoic acid and SO2. The influence of inhibitors may be used to calculate the lifetime of SO2, Methanoic acid has high values of kinh and, therefore, it would be degraded by sulfate radical anions in atmospheric waters.

Analysis of Carbon Tetrachloride-Extractable Species from Daxing Bituminous Coal

Soxhlet extraction (SE), ultrasonic-assisted extraction (UAE), and microwave-assisted extraction (MAE) were carried out on Daxing coal with carbon tetrachloride. The extracted components were analyzed by GC-MS while the residues of the coal after extractions were analyzed by FT-IR spectroscopy. The obtained IR spectra indicated that the functional groups were barely changed in strength for the coal before and after extractions concluding that the macromolecular structures of coal were not destroyed in the extraction processes. XRD diagrams showed the peak around θ = 47 was totally disappeared by all the three extractions, indicating that the graphite-like structural substances in the coal were totally destroyed in the extraction processes. GC/MS analysis showed that: (1) The SE method extracted the least number of substances from the coal; on the other hand, the extracted compounds are largely chlorinated which can be explained by the free radical mechanism. (2) MAE extracted 75 organic compounds of which 53 are oxygen-containing substances. A small portion of non-alkanes (1.19%) was found, which is in contrast to the other two extraction methods. Moreover, a few biomarker compounds were also identified including hexaoxane, 2-methylcholest-3-ene, 6,9,12-tripropylheptadecane, and 17α-21β-28,30-bisnorhopane. (3) The three extraction methods gave totally different extraction patterns for the same coal, highlighting that the extraction method can dominate the outcome of the extracted products. The mechanisms behind these extraction processes are discussed. This study provides a base for the future choice of the extraction methods in terms of outcomes of the extraction products.