In organic chemistry, the pKa is a property used to compare the acidity behavior for many substances, and to locate the position of equilibria in acid-base reactions and to provide information about structure and reactivity. Evidence in the literature shows that the values of pKa for water and hydronium ion, commonly cited in organic chemistry textbooks, are incorrect. The values of 15.74 for H2O and -1.74 for H3O+ are due to a propagated misconception in the equilibrium calculations while the correct values are 14.0 for H2O and 0.0 for H3O+. This subtle difference of 1.74 units on the pKa scale between both values reflects an error greater than 55 times in the level of acidity for these chemical species. An immediate correction of these values is necessary for the adequate teaching of organic chemistry. A literature search was conducted on the most used organic chemistry books in graduate and undergraduate courses in Brazil, revealing that almost all values cited were inadequate. The textbook Chemistry of Organic Compounds, 3rd edition (1965), by Carl Robert Noller is suggested as possible source of this misinformation in organic chemistry textbooks.

OXYGEN IN THE COVID-19 CONTEXT: WHAT WE KNOW ABOUT THE MOLECULE WE BREATHE AND THE CENTRAL ROLE OF CHEMISTRY. In this work, the role of chemistry in the coronavirus disease 2019 (COVID-19) pandemic is highlighted through the medical oxygen supply crises in Brazil, as an example of oxygen utility in health. Starting from oxygen chemical characterization, the oxygen cycle in nature is discussed to show how oxygen is formed through photosynthesis, followed by the description of the industrial oxygen production from atmospheric air, including physical-chemical aspects. The use of medical oxygen concentrator is presented and how this device works from the chemical point of view. Besides, the noninvasive and painless oximetry is described in terms of how oxygen saturation level in blood is measured using LED - light emitting diode.

Medicines are employed in undergraduate courses as motivational strategy. The experiment herein developed compares the extraction of paracetamol from generic and brand name drugs. Tablets were used from two commercial sources purchased from local drugstores. Twenty tablets of each drug type were individually weighed to average weight analysis and mass dispersion was statistically analyzed in simulating of quality control. Average weight had variation in accordance with the limit of ±5% specified by Brazilian Pharmacopeia. Tablets of each drug were pulverized and extracted in triplicate with ethyl acetate, and the active ingredient was obtained and identified by melting point and FTIR analyzes. Comparing different student groups at different times, there was change in the mass of paracetamol extracted by a simple extraction, affording mass recovery in the range of 59±17% to 28±1%. However, mass recovery of paracetamol extraction of generic and brand name drugs was similar in each student group. Under Soxhlet extraction condition mass recovery was 80-85%. The procedure developed was adequate to undergraduate laboratory, involves simple infrastructure and execution, tablets are easily obtained, and allows discussion on pharmaceutical equivalence and interchangeability.

This article is dedicated to element copper in honor to International Year of the Periodic Table celebrated in 2019. Copper is one of the oldest discovered chemical elements and manipulated by human being. In this sense, aspects about the element copper and its importance in different areas are described, from its mineral exploration through its processing and applications. Inorganic aspects such as structure of copper compounds and their main properties are presented as well the importance of this element in biological systems and organic reactions is explored, showing how essential copper is for life and society.

A didactic alternative approach is proposed for deducing the molecular orbital topology of acyclic and cyclic polyenes and then evaluating their bonding, antibonding, and nonbonding character. The relative energies of molecular orbitals of neutral molecules and ions were described, in addition to the orbital degeneracy to cyclic conjugated polyenes, and the method deduce correctly the relative stability of polyenes. This alternative method complements the lack of explanation of a substantial number of organic chemist undergraduate textbooks in relation to orbital degeneracy in benzene and is a pedagogical approach to teach aromaticity and antiaromaticity.

An undergraduate organic chemistry experiment for oil extraction and biodiesel production using alternative biomass was developed, whereby oils of avocado, coconut and spent coffee grounds were obtained and submitted to transesterification reaction with CH3OH under NaOH catalysis. Avocado and coffee oils were obtained by typical extraction and coconut oil was obtained through water evaporation of coconut milk in a domestic microwave oven. The commercial oil of licuri (Syagrus coronate), a Brazilian native biomass, was also converted to biodiesel. All four oils and four biodiesels were characterized by 1H-NMR and FTIR, and a comparative study of these spectra reveled that FTIR analyses alone provides enough information to discriminate between oil and biodiesel and confirm transesterification reaction. Besides, the unsaturation degree of all oils was determined by 1H-NMR. A mechanistic proposal concerning the role of NaOH catalysis is presented, excluding the sodium methoxide formation.

In this work is proposed a didactic alternative vision to teach pericyclic reactions. To this end, they were classified according to the connectivity of reactants systems, as connected atom reactions (CAR) and the other possibility, as not connected atom reactions (NOCAR). Electrocyclic reactions and sigmatropic rearrangements are examples of CAR categorization, and the cycloadditions being NOCAR. With these two categories, a pedagogical alternative description is proposed to the orbital topology in reactants to explain the pericyclic reactions. According to this classification, the HOMO's topology is adequate to all CAR, while the traditional HOMO-LUMO's topology is adequate to NOCAR. All issues typically deduced by the traditional treatment, such as allowed and forbidden reactions, and stereochemical aspects are also explained by the alternative approach.

We described herein a solvent-free synthesis of 4-chloroacetanilide both under hand grinding and mechanical grinding of stoichiometric amounts of acetanilide with trichloroisocyanuric acid. The synthetic approach was developed in the context of undergraduate organic chemistry and is the greener preparation of this compound already described.

Cachaça (brazilian sugarcane spirit) was applied for the first time as an alternative solvent in undergraduate experiments of organics synthesis, and natural dye extraction. The classical Claisen-Schmidt condensation of benzaldehyde with acetophenone and with acetone were employed to demonstrate the cachaça viability as solvent. Cachaça was also the recrystallization solvent of obtained benzalacetophenone and dibenzalacetone. The natural pigment of urucum (Bixa orellana L.) was obtained using as extractor solvent a 5% NaOH solution in cachaça. Considering that in Brazil cachaça is easily available and cheaper than the 40% mixture of ethanol/water, it can be found in every marketplace and is exported to 54 countries, the cachaça use as solvent is viable and attractive to green chemistry experiments in undergraduate courses, in Brazil and abroad.

An expeditious and green synthesis of acetamides in a solvent-free simple way is described, without catalyst or additives, and in good yield by an instantaneous reaction of anilines or 2-aminothiazoles and acetic anhydride without external heating, and with simple purification. Sixteen substituted acetanilides and four N-benzothiazole-2-yl-acetamides were formed, but aliphatic amines of low molecular weight were not as effective as aromatic ones, and only cyclohexylamine and the enaminone ethyl 3-amino-2-butenoate afforded the corresponding acetamides in good yield.

The synthesis of 3-coumarin-carboxylic acids and their application to the total synthesis of the natural products ayapin, coumarin, and umbeliferone in undergraduate organic chemistry experiments is described herein. The synthetic approach consists of a one-pot cyclization between salyciladehydes and Meldrum's acid in water to produce the above mentioned acids, followed by decarboxylation under basic or radical conditions.

<p>We described herein a solvent-free synthesis of acetanilide developed in the context of green chemistry. The synthetic approach consisted of the reaction of aniline with acetic anhydride without additives, while using smaller amounts of reagents and water than previously described for this undergraduate experiment. The E Factor was 0.6 by experienced chemists and 0.9 by students.</p>

Este trabalho descreve um método simples de síntese de 4-aril-tetraidroquinoline-2,5-dionas através da reação tricomponente entre enaminonas N-aril-substituídas derivadas da dimedona, aldeídos aromáticos e o ácido de Meldrum. A síntese ocorre sem o uso de catálise e aquecimento, não sendo necessário o emprego de solventes especiais ou condições reacionais sofisticadas.

A simple green synthesis of 4-aryl-tetrahydroquinoline-2,5-diones was developed, improving the three-component reaction of N-aryl substituted dimedone-based enaminones, aromatic aldehydes and Meldrum's acid. The method does not employ catalyst, heating or any special solvent or reaction condition, and has facile work-up and purification. Variations of enaminones and aldehydes substituents were somewhat tolerated.

This article describes an undergraduate experiment for the synthesis of p-nitrophenyldiazonium chloride and its coupling with acetylacetone and two enaminones, 4-phenylamino-pent-3-en-2-one and 4-amino-pent-3-en-2-one, in an adaptation of a previously reported synthetic protocol. The azo dyes 4-(E)-phenylamino-3-[(E)-2-(4-nitrophenylazo)]-3-penten-2-one and 4-(E)-amino-3-[(E)-2-(4-nitrophenylazo)]-3-penten-2-one were obtained, and the solid state structure of this latter azo compound was characterized by single crystal X-ray diffraction studies. This two-week integrated laboratory approach involves simple synthetic experiments and microwave chemistry in the organic laboratory plus crystallography analysis, suitable for novice students on undergraduate experimental chemistry courses.

This work describes a green chemistry experiment for the synthesis of Erlenmeyer-Plöchl azalactones mediated by microwave irradiation, employing both dedicated and domestic equipment. Hippuric acid was reacted with equimolar amounts of benzaldehyde, p-chloro-benzaldehyde or p-N,N-dimethyl-benzaldehyde in acetic anhydride as the solvent. Acid hydrolysis of obtained 4-benzylidene-2-phenyloxazol-5(4H)-one under microwave and convectional heating afforded Z-α-(benzoylamino)cinnamic acid at a 51-61.5% yield. The UV-Vis molecular spectra of 4-benzylidene-2-phenyloxazol-5(4H)-one and 4-(4'-N,N-dimethylbenzylidene)-2-phenyloxazol-5(4H)-one were obtained in ethanol, CH2Cl2 and DMSO and bathochromic shift was observed for the latter azalactone.