Abstract: Further discussion on the use of the Green Star holistic metric for evaluation of the chemical greenness is presented, based on a preliminary evaluation of chemistry teaching books used in Brazil. The relative nature of the chemistry greenness is discussed, stressing that it depends on the context of the laboratory experiment, for instance, the source of a reagent may alter its level. It is concluded that in the academic training of chemistry teachers explicit attention should be paid to the evaluation of the environmental dimension of the laboratory activities.

Resumen: Nuevas consideraciones acerca del uso de la métrica holística de análisis del verdor químico designada como «estrella verde» son presentadas sobre la base de un análisis preliminar de libros de texto de química brasileños. Entre otros aspectos, se llama la atención sobre el carácter relativo del verdor químico evaluado por las métricas de verdor, toda vez que dependiendo del contexto de realización de la actividad experimental puede ser alterada, por ejemplo, por la fuente de la cual provienen los reactivos. Se destaca asimismo la necesidad de que la evaluación de la dimensión ambiental de las actividades experimentales se convierta en un contenido explícito de la formación de profesores de química.

A reação de 1,2-dicloro-4,5-dinitrobenzeno (DCDNB) com OH- aquoso produz (após acidificação) 2-nitro-4,5-diclorofenol com perda de NO2. No entanto, com OH- > 2 mol L-1, DCDNB foi recuperado devido à formação do complexo estável 3,6-di-hidroxi Meisenheimer (M2-), e que em ácido, reverteu ao reagente inicial. A formação rápida do complexo mono-hidroxi Meisenheimer (M1-) pode ser acompanhada em DMSO:H2O 7:3 v/v e as constantes para sua interconversão com DCDNB e formação e retorno com M2- foram estimadas, com evidência destas reações em DMSO:H2O 1:1 v/v e H2O. A troca rápida de hidrogênio em OD- /D2O limita o uso da técnica de ressonância magnética nuclear (NMR) de¹ H na identificação de intermediários. Sinais de RMN de¹ H e13 C para o di-hidroxi Meisenheimer foram observados em DMSO-H2O-KOH. Existe evidência da formação de radicais livres em DMSO:H2O 4:1 v/v, e a cinética global em meio mais aquoso foi tratada considerando a existência transitória de pares de radicais aniônicos.

The reaction of 1,2-dichloro-4,5-dinitrobenzene (DCDNB) with aqueous OH- produces (after acidification) 2-nitro-4,5-dichlorophenol with loss of NO2. Nevertheless, with > 2 mol L-1 OH-, only DCDNB was recovered due to the formation of the long-lived 3,6-dihydroxy Meisenheimer complex (M2-), and that in acid, reverted to the starting material. Fast formation of monohydroxy Meisenheimer complex (M1-) can be followed in DMSO:H2O 7:3 v/v and rate constants for its interconversion with DCDNB and for formation and return with M2- complex were estimated, with evidence for these reactions in DMSO:H2O 1:1 v/v and H2O. The rapid hydrogen exchange in OD- /D2O limits the use of¹ H nuclear magnetic resonance (NMR) spectroscopy in identifying intermediates. ¹ H and13 C NMR signals of M2- complex were observed in DMSO-H2O-KOH. There is evidence for the formation of free radicals in DMSO:H2O 4:1 v/v, and overall kinetics in more aqueous medium were treated in terms of the transient existence of anionic radical pairs.

A study evaluating Brazilian chemical researchers understanding of the scope of the terms Environmental Sustainability and Sustainable Development, and their assessment of how to deal with environmental fragility and limits, is reported. Results showed a certain degree of acknowledgement of the need for a more sustainable development, but little agreement on the magnitude of the environmental limits. The researchers recognized the limitations of the classical paradigms "of dilution" and "of risk", but showed no agreement on the requirements of the new "ecological paradigm" based on Environmental Sustainability and the 12 principles of Green Chemistry, important to assess the role of Green Chemistry for Sustainability.

A estrutura cristalina e cálculos quânticos semi-empíricos de N,N’-(2’-furfurilideno)bis(morfolina), C13H20N2O3, mostram que: i) o valor de 115,1(2)° do ângulo entre o carbono centro da reação e o nitrogênio de uma morfolina; ii) o carbono centro da reação está fora do plano de mínimos quadrados do anel furano, e estes dois fatos explicam a alta instabilidade observada na síntese e conservação do composto. A estrutura cristalina do composto foi determinada por difração de raios-X, no sistema cristalino monoclínico, grupo espacial C2/c (No. 15) e dimensões de cela a = 18,824(4), b = 7,039(1) c = 20,644(4) Å, beta = 97,32(3)°, V = 2713(2) ų, Z = 8, Dcalc = 1,235 Mg m-3, lambda(MoKalfa) = 0,71073 Å, mi = 0,088 mm-1, F(000) = 1088, T = 295 K, R = 4,35% (wR = 13,3%), com 2454 reflexões medidas, 2376 reflexões independentes, 1731 com I > 2sigma(I) e 206 parâmetros refinados. A molécula exibe contatos intramolecular dos tipos C-H...O e C-H...N. O empacotamento molecular envolve contatos intermoleculares do tipo C-H...O.

The crystal structure and semi-empirical quantum chemical calculations of N,N’-(2’-furfurylidene)bis(morpholine), C13H20N2O3, show that: i) the value of 115.1(2)° for the angle between the carbon atom center of the reaction and the nitrogen atom of one morpholine and ii) the carbon atom center of the reaction is outside the least-squares plane of the furan ring, and these two facts explain the high instability observed in the synthesis and conservation of this compound. The crystal structure of the compound was determined via X-ray diffraction in the monoclinic crystal system, space group C2/c (Nr. 15) and cell dimensions a = 18.824(4), b = 7.039(1) c = 20.644(4) Å, beta = 97.32(3)°, V = 2713(2) ų, Z = 8, Dcalc = 1.235 Mg m-3, lambda(MoKalpha) = 0.71073 Å, mu = 0.088 mm-1, F(000) = 1088, T = 295 K, R = 4.35% (wR = 13.3%), with 2454 measured reflections, 2376 independent reflections, 1731 with I > 2sigma(I) and 206 refined parameters. The molecule has C-H...O and C-H...N intramolecular contacts. The molecular packing involves C-H...O intermolecular contacts.

This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst.