We developed a project during an undergraduate course (advanced experimental chemistry) on the microwave-assisted synthesis of biodiesel (BD), via base-catalyzed transesterification of coconut fat (CF) and soybean oil (SO) by ethanol, followed by product analysis by gas chromatography/mass spectrometry. Our goals were to introduce a problem with relevant socio-economic impact (production of BD); to discuss and compare methods for biofuel analysis, and to gain insight into transesterification mechanism as an important example of acyl-transfer reactions. Comparison of both BFs showed clear difference in fatty acid composition; that from CF contains shorter, saturated chains (mainly ethyl dodecanoate- and tetradecanoate), whereas biodiesel from SO is essentially composed of longer unsaturated chains (e.g., ethyl oleate and linoleate). The project takes eight hours to complete, is conceptually simple, being suitable for inclusion in the undergraduate science curriculum.

In the early seventies, Giuseppe Cilento (São Paulo University), Emil White (Johns Hopkins University) and Angelo Lamola (AT&T Bell Laboratories) postulated that typical photochemical reactions could occur in dark parts of living organisms if coupled to enzymatic sources of electronically excited products. Their paradoxical hypothesis of "photochemistry without light" was chemically anchored on the synthesis and weak chemiluminescence of several 1,2-dioxetanes, unstable cyclic peroxides whose thermal cleavage produces long-lived and reactive triplet carbonyls. Collisional reactions or energy transfer of triplet species to cellular targets could eventually result in "photo" products that potentially trigger normal or pathological responses. These ideas flourished in the labs of various researchers who attempted to explain the presence and biological roles of "dark" secondary metabolites, including plant hormones, pyrimidine dimers, alkaloid lumi-isomers, protein adducts, and mitochondrial permeators, thereby broadening the field of photobiology.

Peróxidos cíclicos de quatro membros são intermediários de alta energia importantes em diversas transformações quimi e bioluminescentes. Especificamente, α-peroxilactonas (1,2-dioxetanonas) têm sido consideradas sistemas modelo para a eficiente bioluminescência do vaga-lume. Contudo, a preparação deste tipo de compostos altamente instáveis é extremamente difícil e, por isso, apenas alguns poucos grupos de pesquisa puderam estudar as propriedades dessas substâncias. Neste trabalho, a síntese, purificação e caracterização de três 1,2-dioxetanonas são relatadas e é apresentado um procedimento detalhado para a preparação do peróxido de difenoíla, outro importante composto-modelo para a geração química de estados eletronicamente excitados. Para a maioria destes peróxidos, a caracterização espectroscópica completa é relatada pela primeira vez.

Cyclic four-membered ring peroxides are important high-energy intermediates in a variety of chemi and bioluminescence transformations. Specifically, α-peroxylactones (1,2-dioxetanones) have been considered as model systems for efficient firefly bioluminescence. However, the preparation of such highly unstable compounds is extremely difficult and, therefore, only few research groups have been able to study the properties of these substances. In this study, the synthesis, purification and characterization of three 1,2-dioxetanones are reported and a detailed procedure for the known synthesis of diphenoyl peroxide, another important model compound for the chemical generation of electronically excited states, is provided. For most of these peroxides, the complete spectroscopic characterization is reported here for the first time.

In this review article, we give a general introduction on the mechanisms involved in organic chemiluminescence, where three basic models for excited state formation are presented. The chemiluminescence properties of 1,2-dioxetanes - four membered ring peroxides - are briefly outlined in the second part. In the main part, the mechanisms involved in the decomposition of 1,2-dioxetanes and analogous peroxides are discussed: (i) the unimolecular decomposition of 1,2-dioxetanes; (ii) the electron transfer catalyzed decomposition of peroxides by an intermolecular CIEEL (Chemically Initiated Electron Exchange Luminescence) mechanism; (iii) 1,2-dioxetane decomposition catalyzed by an intramolecular electron transfer mechanism (intramolecular CIEEL). Special emphasis is given to the latter subject, where recent examples with potential analytical applications are presented.

The generation of "cold light", visible to the human eye, by chemical reactions has attracted the attention of the scientific community since the beginning of this century. Besides the academic interest in the elucidation of the mechanisms of excited state formations, many chemiluminescence reactions have found widespread analytical applications. Moreover, the phenomenon of chemiluminescence can also be used as a tool in undergraduate and college teaching. In this article, we describe several known chemiluminescence demonstrations, which are suitable for school teaching. The main objective of this work is to produce didactic material in Portuguese to stimulate Brazilian secondary and high school teachers to use these experiments in the classroom. The demonstrations include singlet oxygen emission, the luminol reaction, oscillating chemiluminescence and the peroxyoxalate reaction.