Structure, aromatic properties and preparation of the quinazolin-4-one molecule

. The government has emphasized the significance of making significant investments in scientific research to develop herbicides, fungicides, bactericides, anthelmintic agents, weed and pest control agents, and alternative pesticides that are eco-friendly and can be exported. In this research, the aromaticity of quinazolin-4-one a and p was studied. A one-stage method for obtaining quinazolin-4-one a was developed by condensation of anthranilic acid and formamide when heated to Wood's alloy. Quinazolin-4-one exhibits conformity with Hückel's rules upon undergoing a reaction with alkali metals, hydrides, and alkalis. An investigation was performed to assess the aromaticity of both para and ortho quinazolin-4-one. Quinazolin-4-one a was obtained through a one-step process, which involved condensing anthranilic acid and formamide using Wood's alloy at a temperature of 130-135 º С for two hours, which was found to be optimal.


Introduction
The government is giving significant importance to the development of agriculture, medicine, and veterinary medicine, with particular emphasis on animal husbandry and chemical processing of lands. They have also implemented measures to enhance the quality of education and effectiveness of scientific research in the areas of chemistry and biology. This focus on these fields is a recent development [1][2][3][4].
The government has highlighted the importance of extensively investing in scientific research for the production of herbicides, fungicides, bactericides, anthelmintic agents, weed and pest control agents, and replacement pesticides that are environment-friendly and suitable for export. They are also giving attention to improving their chemical and biological properties. This emphasis on research in these fields is supported by references to several sources [2][3][4][5][6][7].
Quinazolin-4-ones and thiones are heterocyclic compounds that find extensive use in agriculture, medicine, and veterinary medicine. They include compounds like 5-methylfluorouracilquinazolines used for cancer treatment, and 2-Methoxycarbonylaminoquinazolinone for combating cotton wilt, nymiesal gammos, and root rot [8][9][10][11]. Apart from the aforementioned compounds, various drugs with herbicidal, fungicidal, bactericidal, insecticidal, and anthelmintic properties have been discovered among quinazoline derivatives. As a result, there has been research conducted on the methylation reactions of 2-substituted quinazolin-4-ones and -thiones, examining the factors that affect their outcome, such as the type of methylating agent, the solvent used, and temperature. The study also explores the changes in the ratio of N3/O4 isomers, investigates their patterns, determines their physical, chemical, and biological properties, and develops new pesticides and drugs based on these active substances. The references to several sources support this statement [8][9][10][11][12].

Results and discussion
Of all compounds that possess a closed conjugated system of electrons, aromatic compounds are particularly fascinating due to their unique properties, including their resistance to oxidizing agents and their tendency to undergo substitution reactions instead of addition reactions. Benzene and other substances with similar structure and chemical behavior are considered as the main aromatic compounds. However, it's possible for compounds to be aromatic even if the closed chain contains heteroatoms like S, N, O, and so on, in addition to carbon atoms. The notion of aromaticity was established by the physicist E. Hückel and is known as Hückel's rule. This rule states that flat cyclic structures with all sp2 hybridized atoms and a total of (4n + 2) π electrons, where n equals 0, 1, 2, 3, and so on, are considered to be aromatic molecules.    In molecular orbital theory, it is postulated that electrons in a molecule do not solely belong to individual atoms or chemical bonds, but rather to the entire molecule. The energy levels at which electrons are situated are referred to as molecular orbitals (MOs). Each molecule possesses a specific number of MOs, which can be either unoccupied or occupied. The electrons fill the orbitals beginning from the lowest energy MO. An orbital can have a maximum of two electrons, which spin antiparallel to each other. Molecular orbitals are classified into bonding, non-bonding, and antibonding (destabilizing) orbitals. The number and nature of atoms that constitute a molecule determine its MOs.
Molecular orbitals (MOs) in a molecule can be categorized as bonding, non-bonding, or antibonding based on whether their electron occupancy lowers, does not affect, or raises the energy of the molecule. If filling an MO is energetically favorable, it is a bonding MO, whereas if it is energetically unfavorable, it is an antibonding MO. A nonbonding MO is one where the energy of the molecule is neither lowered nor raised when the orbital is filled. The stability of a molecule can be determined by assessing the nature of its filled Mos (Fig. 5). According to the molecular orbital (MO) theory, the six atomic p orbitals of carbon atoms combine to form six π molecular orbitals in benzene. Among these orbitals, three are bonding and three are antibonding. The lowest energy bonding MO, π1, spans all six carbon atoms and has no nodes. π2 and π3 are degenerate in energy, with each having one node. The node on the π2 orbital is perpendicular to that on the π3 orbital. In benzene, there are six α π-electrons that fill the bonding MOs π1, π2, and π3 in pairs with opposite spins. The remaining three antibonding MOs, π4*, π5*, and π6*, are unoccupied in the ground state. The π4* and π5* orbitals are degenerate and each has two nodes, while the π6* orbital has three nodes (Fig. 6) The stability of cyclic fully conjugated polyenes can be determined using the Frost circle, which is a mnemonic technique. To use this technique, a regular polygon with the same number of sides as the carbon atoms in the cycle is inscribed in a circle, with one vertex at the bottom. The points where the polygon's vertices touch the circle represent the energy levels of the molecular orbitals. By solving a simple geometric problem, the energy levels of π-orbitals can be estimated. The horizontal diameter represents the non-bonding level, while orbitals below the diameter are bonding and those above are antibonding. The energy level diagrams for the corresponding π-orbitals are shown in Fig. 7. All four carbon atoms in the aromatic ring are sp 2 hybridized, giving the aromatic ring four p -orbitals. The first nitrogen atom has two sigma bonds and one unpaired electron.
The steric number of a nitrogen atom determines the number of chemical bonds it can form. If there are three sigma bonds, the nitrogen atom is typically sp2 hybridized. In the case of the heterocyclic system being discussed, the nitrogen atom has three sigma bonds and one paired electron. If there are four sigma bonds, the nitrogen atom is typically sp3 hybridized. This heterocyclic system does not have a free p-electron and is therefore not considered part of the aromatic system. However, under certain conditions, such as the presence of alkali metals or their hydrides and alkalis, the electron at the third nitrogen atom can be transferred to oxygen, forming a double bond to the ring. In this way, both nitrogen atoms become involved in a six-p-electron ring, satisfying the criteria for aromaticity. A reaction was carried out by heating a mixture of 0.1 moles of anthranilic acid and 0.4 moles of formamide in an oil bath at a temperature range of 130-150°C for 20-30 minutes, while refluxing the reaction mixture through a condenser. The resulting mixture was first cooled to room temperature and then in cold water, leading to the formation of crystals that were filtered and dried. The yield of the reaction was determined to be 96%, resulting in the production of 42.5 g of quinazolin-4-one. The melting point of the obtained product was measured using a BOETIUS (Germany) heating table, and its purity was monitored by thin-layer chromatography (TLC) on Silufol UV-254 using a benzene:acetone (5:3) system. Additionally, the mass spectrum of the product was obtained using a Chromatek Crystal with a Chromatek-Crystal 5000 mass spectrometric detector, which confirmed the structure of quinazolin-4-one (Fig. 8).

Conclusion
Aromaticity is a crucial concept in chemistry, but there is no concise definition. It is a combination of special characteristics found in certain cyclic conjugated molecules, some of which can be observed experimentally while others can only be explained through quantum theory. Aromaticity cannot be explained solely by classical structural theory.
Aromatic compounds have a closed electronic system which affects their nuclear magnetic resonance spectra. When subjected to an external magnetic field, a ring current is generated within the molecules, creating a local magnetic field that opposes the external one. This leads to a decrease in shielding of hydrogen and carbon atoms in the aromatic system, resulting in their signals being recorded in the weak field region, known as the "aromatic hydrogen signal region" for 1H NMR spectroscopy and the "aromatic carbon signal region" for 13C NMR spectroscopy.
Quinazolin-4-one shows complete compliance with Hückel's rules after undergoing a reaction with alkali metals, hydrides, and alkalis. A study was conducted to determine the aromaticity of quinazolin-4-one a and p. A one-step method was developed to obtain quinazolin-4-one a through the condensation of anthranilic acid and formamide using Wood's alloy at an optimal reaction temperature of 130-135 ºС for 2 hours.