Jiří Šibor

Acid-Base Initiated Cyclization and Retrocyclization Reactions of Ethyl 2-(3-Acylselenoureido)benzoates, -thiophene-3-carboxylates and the Corresponding 2-(3-Acylisoselenoureido) Derivatives

Acid and base initiated cyclization and retrocyclization reactions of the selenoureas 1-6 and isoselenoureas 7-12 to fused 4H-1,3-selenazine and 1,2,3,4-tetrahydropyrimidine-4-one skeletons are reported. Fused 2-acylamino-4H-1,3-selenazine-4-ones 13-18 were formed by the action of concentrated sulfuric acid on acylselenoureas 1-6 or on 2,2-dimethylpropanoylisoselenoureas 10-12 at room temperature. On the other hand, benzoylisoselenoureas 7-9 were not obtained in this cyclocondensation under the same conditions. The reaction of potassium ethoxide on selenazines 13-18 in the ethanol solution evoked retrocyclization to the starting acylselenoureas 1-6. Both types of the title compounds, i.e. selenoureas 1-6 and isoselenoureas 7-12, were deprotonated in a methanol solution of potassium hydroxide used in an equimolar amount, giving rise to potassium salts 19-24, which were isolated only for the thiophene series. By heating the separated potassium salts 20, 21, 23 and 24 in the methanol solution provided, deacylation and isoselenoureas 26, 27 were formed. The in situ prepared salts 19, 22 cyclized under the same conditions with deacylation to 4-selanyl-3,4-dihydroquinazoline-4-one 28. The title compounds 1-6, 7-12 and products of their deacylation 26, 27 on boiling in methanolic potassium hydroxide cyclized to the corresponding fused 2-selenoxo-1,2,3,4-tetrahydropyrimidine-4-one potassium salts. These compounds provided pyrimidine-4-ones 28-30 on acidification. Acid initiated retrocyclization 28-30 to the corresponding 2-amino-4H-1,3-selenazine-4-ones was unsuccessful. C, H, N, Se elemental analyses, FTIR, 1H-NMR, and 13C-NMR spectroscopies supported the structure of synthesized compounds.A short review on cardiotonic steroids and their analogues is presented. The natural, semisynthetic and synthetic derivatives, as well as their mechanism of action and structure-activity relationships are shown, with a special reference to aminoguanidine derivatives.

NEW WAYS OF HETEROCYCLIC CHEMISTRY TEACHING

Interest of students in natural sciences shows a declining tendency all over the world. Chemistry along with physics belongs to the least popular subjects. Research shows that one of the main causes of this state is the way chemistry is taught at schools. The students´ style of learning is currently changing due to the influence of information and communication technologies. It is thus necessary to seek innovative approaches to teaching chemistry. Using a digital classroom and laboratories is one of such approaches. The present paper describes an interactive relationship of heterocyclic chemistry for lower secondary schools. Heterocyclic compounds are basic components of both living matter and chemistry of other materials around us. Teaching of heterocyclic compounds is difficult for students on primary and secondary schools. The general educational program of Ministry of Education appeals interdisciplinary approach to chemistry studies. The topic of this paper is heterocyclic chemistry composition in educational process for primary and secondary schools. The goal of the process is barrier elimination among computer, classroom, laboratories and reality. We would like to describe these compounds not only as chemical species, but characterize heterocyclic compounds as biologic components of the live around, laying emphasis on their physiology activity. Next connection indicated the scheme (cooperation of chemistry, physics, mathematics, biology, etc.). Photosynthesis (for example) is a chain of chemical reactions occurring in chloroplasts (chlorophylls are typical heterocyclic compounds composed from pyrrole), the microscopic organelles inside the green plant tissue. In the course of the photosynthesis, a plant uses the energy of sunlight and, from the molecules of carbon dioxide and water; it synthesizes glucose (heterocycle), with oxygen being produced as a by-product. Photosynthesis is paramount importance for the life on the Earth because it releases oxygen and produces sugar which, either directly or indirectly, serve as food for the majority of animals. All described processes in computational field (including laboratory) are founding.

HIDDEN RISKS OF (SCHOOL) CHEMICAL LABORATORY

The article deals with a quite usual laboratory activity – pipetting. This method of measuring the volume of liquids appears to be relatively safe in comparison with other chemical operations. But, on the other hand, the use of classical glass pipettes is connected with many security and health risks. The usual chemical hazards associated with inhalation of the pipetted substance or its intrusion into the mouth are repeatedly mentioned to the pupils and students and they are trained to prevent these situations. However, the health risks associated with the use of glass pipettes are being nearly never mentioned at schools, and that is why Czech pupils and students are aware of them only exceptionally. In the introduction to our article we explain the safety risks and health risks, advantages and disadvantages associated with different pipetting methods. Afterwards, we do analyze the results of a questionnaire survey between the students of chemistry teaching, focused on their favorite pipetting method and reasons to their decision. The last part of our research is the analysis of the results of different methods of pipetting carried out by the 3rd grade students of chemistry teaching at Faculty of Education, Masaryk University, Czech Republic. The analysis is focused on the correctness of pipetting (mean value of the pipetted volume) and accuracy of pipetting (relative standard deviation in repeated pipetting of the same volume).

Modelování chemických pojmů

Na zakladě teoretických poznatků (systemoveho přistupu k chemii a jeji výuce) byly zpracovany komentovane grafove modely chemických pojmů. Výběr pojmů byl volen tak, aby odražely pojmy běžně použivane při výuce chemie na zakladni skole, někdy ale poněkud rozsiřene. Jsou zde zahrnuta temata: uloha a rozděleni chemie, hmota, stavba atomu, radioaktivita, chemicka vazba, chemicke reakce, periodicka soustava prvků, směsi, slouceniny jednak anorganicke a organicke, ty jsou nasledně cleněny na uhlovodiky, jejich derivaty a organicke přirodni latky