Cold microwave chemistry: synthesis using pre-cooled reagents

Bose, Ajay K.; Ganguly, Subhendu N.; Manhas, M. S.; He, William; Speck, J. Matthäus

doi:10.1016/j.tetlet.2006.03.059

Cited by 17 publications

(12 citation statements)

References 1 publication

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“…21 A formação dos produtos e a evolução da reação puderam ser acompanhadas por cromatografia em camada fina (CCF) e posterior visualização em câmara de ultravioleta ou revelação com iodo. Após uma corrida cromatográfica utilizando como eluente uma mistura de hexano:acetato de etila (7:3), os produtos 5-nitro-salicilaldeído e 3-nitro-salicilaldeído foram observados como manchas com Rfs 0,6 e 0,5.…”

Section: Resultsunclassified

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

Teixeira¹,

Santos²,

Bastos³

et al. 2010

Quím. Nova

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Recebido em 13/10/09; aceito em 3/4/10; publicado na web em 9/8/10 THE USE OF DOMESTIC MICROWAVE OVEN IN EXPERIMENTAL CLASSES OF ORGANIC CHEMISTRY: SALICYLALDEHYDE NITRATION. The use of microwave in chemistry has known benefits over conventional heating methods, e.g. reduced reaction times, chemical yield improvement and the possibility if reducing or eliminating the use of organic solvents. We describe herein a procedure for the nitration of salicylaldehyde in water using a domestic microwave oven, which can be used as an experiment in the undergraduate chemistry laboratory. The experiment involves safe and rapid preparation and identification of the position isomers by thin layer chromatography and 1H NMR, or by their melting points.Keywords: microwave; nitration; salicylaldehyde. INTRODUÇÃODesde a 2° Guerra Mundial os aparelhos que emitem radiação de micro-ondas passaram a estar presentes em nosso cotidiano. Inicialmente, funcionavam como radar (Radio Detection and Ranging) para detectar aeronaves inimigas. As micro-ondas, ao serem refletidas pelo objeto procurado, eram detectadas pelo radar que fornecia sua posição, forma, velocidade e direção. 1 Em 1947, Percy L. Spencer fez alterações nestes aparelhos e a companhia Raytheon apresentou o primeiro forno de micro-ondas para aquecer ou descongelar alimentos. Chamado de Radarange, o micro-ondas possuía 1,5 m de altura, pesava cerca de 340 kg e custava entre US$ 2.000 e 3.000. Hoje, os fornos de micro-ondas domésticos são bem mais leves e acessíveis. 1As micro-ondas (MO) são ondas eletromagnéticas geradas por um magnetron situadas na região do espectro eletromagnético, entre a radiação do infravermelho e as ondas de rádio. A frequência das micro-ondas oscila entre 300 MHz (300 x 10 6 Hz) e 300 GHz (300 x 10 9 Hz), com comprimentos de onda de 1 mm a 1 m, respectivamente. A frequência utilizada em fornos comerciais é de 2,450 GHz. 2,3O aquecimento através das micro-ondas ocorre por dois mecanismos, polarização dipolar e condução iônica. As micro-ondas ao penetrarem em materiais que contêm moléculas polares, provocam o alinhamento dos pólos destas moléculas com o campo eletromagnético aplicado. A responsável pelo efeito descrito é a componente do campo elétrico, ao invés do campo magnético. Com a remoção do campo eletromagnético, as moléculas voltam ao estado desordenado, fazendo com que a energia absorvida para a orientação seja dissipada na forma de calor. Este processo ocorre em ciclos devido à oscilação do campo eletromagnético. [1][2][3][4][5][6] A capacidade de um material ou solvente converter energia de micro-ondas em calor depende da frequência de relaxação do material e da constante dielétrica do solvente. Quanto maior o dipolo elétrico, mais intensa será a orientação molecular e quanto maior a constante dielétrica, maior será a quantidade de energia armazenada. A constante dielétrica se relaciona à tangente de perda, que é a razão entre a constante dielétrica e o fator de perda. Este último mede a eficiência da conversão de energia eletromagnética em cal...

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Section: Resultsunclassified

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

Teixeira¹,

Santos²,

Bastos³

et al. 2010

Quím. Nova

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“…Probably, the ipsonitrated product and 4-hydroxycinnamic acid go through hydrolysis and oxidation to yield benzoic acid, which is then susceptible to ipso-nitration with decarboxylation. 28,29 LaLonde and colleagues discovered that the use of CAN in acetic acid/water (9:1) results in the conversion of (3aR,4S,9aR) and (3aR,4S,9aS) tetrahydrofurans into ipso-products via simultaneous ipso-nitration and oxidation through the opening of the B-ring of the tetrahydrofurans (Scheme 9). Scheme 9. ipso-Nitration of (3aR,4S,9aR) and (3aR,4S,9aS) tetrahydrofurans with CAN When the (3aR,4S,9aS) derivative was treated with CAN in neat acetic acid, the yield of the final product rose to 41%, whereas the treatment of (3aR,4S,9aR) derivative under the same conditions resulted in a similar yield of mononitroburseran (39%) favoring one of two diastereomeric acetates.…”

Section: Scheme 8 Ipso-nitration Of 4-hydroxycinnamic Acid With Can/mentioning

confidence: 99%

Recent advances in ipso-nitration reactions

Bozorov¹,

Zhao²,

Aisa³

et al. 2016

Arkivoc

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In the present review the various types of ipso-nitration reactions, in particular those advances in ipsonitration reactions that have been reported since the beginning of this century (i.e., from [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015] are discussed. The review highlights the recent developments of the ipso-nitration reactions, a variety of the differences between traditional and modern methods for performing ipso-nitration reactions, as well as the most novel approaches to performing these reactions. In addition, the proposed mechanisms of ipso-nitration reactions are discussed.

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“…[2] Recently, MW processing has been taken into consideration as a special method for materials fabrication, for example, sintering, [3] synthesis of solid materials, [4] and some chemical reaction processes. [5] There are many studies on the chemical reaction kinetics by MW heating in the chemistry field such as organic/inorganic synthesis, [6,7] and some catalytic reactions. [8,9] On the other hand, some studies have been carried out for the high-temperature reduction reaction such as reduction of oxides used in chemical metallurgy.…”

Section: Microwave (Mw) Heating Was Discovered Inmentioning

confidence: 99%

Carbon Reduction Kinetics of NiO by Microwave Heating of the Separated Electric and Magnetic Fields

Yoshikawa

Ishizuka

Mashiko

et al. 2007

Metall Mater Trans B

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A powder mixture consisting of NiO and graphite was heated by microwave (MW) irradiation, and the reduction reaction kinetics was studied. The heating was performed in a single-mode MW applicator operated at 2.45 GHz. The specimen was placed in the waveguide at the maximum positions of either the electric (E-) field or the magnetic (H-) field. The reaction kinetics was investigated mostly at the E-field with variation of the reaction time, temperature, and grain sizes of NiO and graphite. It was shown that the kinetics was enhanced at the higher temperature and using smaller sized powder particles. The difference of the kinetics in the E-field and the H-field was investigated. A tendency was observed that the reduction rate was larger in the H-field than in the E-field at 600°C. Considering the fact that NiO was heated well in the Efield, while graphite was heated in both fields, graphite particles in the powder mixture might be selectively heated in the H-field. The obtained results were discussed considering the thermodynamics and the gas-solid reaction mechanisms.

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Cold microwave chemistry: synthesis using pre-cooled reagents

Cited by 17 publications

References 1 publication

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

O uso de aparelhos de micro-ondas domésticos em aulas experimentais de química orgânica: nitração de salicilaldeído

Recent advances in ipso-nitration reactions

Carbon Reduction Kinetics of NiO by Microwave Heating of the Separated Electric and Magnetic Fields

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