<p class="jove_content">Confirmação é feita para os doadores de American química sociedade petróleo fundo de investigação do suporte parcial desta pesquisa. Estamos gratos à Fundação Nacional de ciência (-0619275 e-0963165) para renovação e instrumentação subsídios que apoiou esta pesquisa.</p>

<p class="jove_title">1. padrão protocolo para a separação de aldeídos aromáticos de uma mistura. Exemplo: Separação de benzila butirato de uma mistura 1:1 com Anisaldeído.</p>
<ol><li>Dissolver 175 μL de Anisaldeído e 250 μL de butirato de benzila em 5 mL de metanol e transferir a solução para um funil de separação.<br>Cuidado: Bissulfito de sódio pode gerar gás dióxido de enxofre, assim, o presente protocolo deve ser efectuado com ventilação adequada, como em uma coifa.</li>
	<li>Adicionar 1 mL de bissulfito de sódio aquosa saturada e agitar vigorosamente por cerca de 30 s.</li>
	<li>Adicionar 25 mL de água desionizada e 25 mL de acetato de etila/hexanos de 10% e agitar vigorosamente.</li>
	<li>Separe as camadas. Seque a camada orgânica com sulfato de magnésio anidro. Filtre a solução para remover o sulfato de magnésio e concentre-se <em>no vácuo</em> usando um evaporador rotativo.</li>
</ol><p class="jove_title">2. separação de aldeídos alifáticos e cetonas de uma mistura. Exemplo: Separação de benzila butirato de uma mistura 1:1 com Benzylacetone.</p>
<ol><li>Dissolver 213 μL de benzylacetone e 250 μL de butirato de benzila em 10 mL de dimetilformamida e transferir a solução para um funil de separação.<br>Cuidado: Bissulfito de sódio pode gerar gás dióxido de enxofre, assim, o presente protocolo deve ser efectuado com ventilação adequada, como em uma coifa.</li>
	<li>Adicionar 25 mL de bissulfito de sódio aquosa saturada e agitar vigorosamente por cerca de 30 s.</li>
	<li>Adicionar 25 mL de água desionizada e 25 mL de acetato de etila/hexanos de 10% e agitar vigorosamente.</li>
	<li>Separe as camadas. Retornar a fase aquosa para o funil de separação, adicionar 25 mL de acetato de etila/hexanos de 10% e agitar vigorosamente. Escorra a camada aquosa, deixando a camada orgânica no funil de separação. Adicione a anterior camada orgânica para o funil de separação.</li>
	<li>Lave as camadas orgânicas combinadas três vezes com água desionizada (10 mL para cada lavagem). Seque a camada orgânica com sulfato de magnésio anidro. Filtre a solução para remover o sulfato de magnésio e concentre-se <em>no vácuo</em> usando um evaporador rotativo.</li>
</ol><p class="jove_title">3. separação de aldeídos de uma mistura contendo um alqueno. Exemplo: Separação de benzila butirato de uma mistura 1:1 com citronelal.</p>
<ol><li>Dissolver 255 μL de citronelal e 250 μL de butirato de benzila em 10 mL de dimetilformamida e transferir a solução para um funil de separação.<br>Cuidado: Bissulfito de sódio pode gerar gás dióxido de enxofre, assim, o presente protocolo deve ser efectuado com ventilação adequada, como em uma coifa.</li>
	<li>Adicionar 25 mL de bissulfito de sódio aquosa saturada e agitar vigorosamente por cerca de 30 s.</li>
	<li>Adicionar 25 mL de água desionizada e 25 mL de hexanos e agitar vigorosamente.</li>
	<li>Separe as camadas. Retornar a fase aquosa para o funil de separação, adicionar hexanos 25 mL e agitar vigorosamente. Escorra a camada aquosa, deixando a camada orgânica no funil de separação. Adicione a anterior camada orgânica para o funil de separação.</li>
	<li>Lave as camadas orgânicas combinadas três vezes com água desionizada (10 mL para cada lavagem). Seque a camada orgânica com sulfato de magnésio anidro. Filtre a solução para remover o sulfato de magnésio e concentre-se <em>no vácuo</em> usando um evaporador rotativo.</li>
</ol><p class="jove_title">4. re-isolamento de aldeídos a partir de uma mistura. Exemplo: Separação de Piperonal de uma mistura 1:1 com butirato de benzila.</p>
<ol><li>Dissolver 217 mg de piperonal e 250 μL de butirato de benzila em 5 mL de metanol e transferir a solução para um funil de separação.<br>Cuidado: Bissulfito de sódio pode gerar gás dióxido de enxofre, assim, o presente protocolo deve ser efectuado com ventilação adequada, como em uma coifa.</li>
	<li>Adicionar 1 mL de bissulfito de sódio aquosa saturada e agitar vigorosamente por cerca de 30 s.</li>
	<li>Adicionar 25 mL de água desionizada e 25 mL de acetato de etila/hexanos de 10% e agitar vigorosamente.</li>
	<li>Separe as camadas. Retorna a camada aquosa para o funil de separação.<ol>
<li>Opcional: Lavar a camada aquosa, uma vez com 25 mL de 10% de acetato de etilo/hexanos, para remover a pequena quantidade de butirato de benzila restantes.</li>
	</ol>
</li>
	<li>Adicionar 25 mL de acetato de etilo e adicione hidróxido de sódio 50% até uma faixa de pH indica que o pH é 12. Agite vigorosamente.<br>Cuidado: Evolução de gás tem sido observada durante esta etapa e pode causar o acúmulo de pressão. Certifique-se de ventilar adequadamente o funil de separação. Ampliação deste procedimento fará com que evolução de gás mais pronunciada. Tenha cuidado.</li>
	<li>Separe as camadas. Retornar a fase aquosa para o funil de separação e adicionar 25 mL de acetato de etila. Agite vigorosamente.</li>
	<li>Separe as camadas. Combine a camada orgânica com a camada orgânica da etapa anterior. Seque a camada orgânica combinada com sulfato de magnésio anidro. Filtre a solução para remover o sulfato de magnésio e concentre-se <em>no vácuo</em> usando um evaporador rotativo.</li>
</ol>

<ol><li>Boucher, M. M., Furigay, M. H., Quach, P. K., Brindle, C. S. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.oprd.7b00231">Liquid-Liquid Extraction Protocol for the Removal of Aldehydes and Highly Reactive Ketones from Mixtures.</a> <em>Org. Process Res. Dev</em>. <strong>21</strong> (9), 1394-1403 (2017).</li>
<li>Separation of Aldehydes and Ketones. , US2552513 A (1951).</li>
<li>Hsu, W. L. <em><a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aHsu%2C+WL+%22Separation+of+Aldehydes+from+Ketones+via+Acid-Catalyzed+Cyclotrimerization+of+the+Aldehyde%22">Separation of Aldehydes from Ketones via Acid-Catalyzed Cyclotrimerization of the Aldehyde</a></em>. , October 4701561(1987).</li>
<li>Process for Separating Aldehydes and Ketones. , US2295760 A (1942).</li>
<li>Separation of Aldehyde-Ketone Mixtures. , US2355140 A (1944).</li>
<li>Masilamani, D., Manahan, E. H., Vitrone, J., Rogic, M. M. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/jo00173a028">Organic Reactions of Sulfur Dioxide. Reactions with Nucleophilic Double Bonds Leading to the Isomerization, Aromatization, Selective Hydrogen-Deuterium Exchange, and Electron-Transfer Proceses.</a> <em>J. Org. Chem</em>. <strong>48</strong> (25), 4918-4931 (1983).</li>
<li>Masilamani, D., Rogic, M. M. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ja00482a072">Organic Reactions of Sulfur Dioxide. 4. A Facile Regiospecific Hydrogen-Deuterium Exchange in Olefins. Consequence of the Intermediacy of Allylic Sulfinic Acids in the Ene Reaction of Sulfur Dioxide with Double Bonds.</a> <em>J. Am. Chem. Soc</em>. <strong>100</strong> (14), 4634-4635 (1978).</li>
<li>Makitra, R. G., Kal'muk, S. D., Bryk, D. V., Polyuzhin, I. P. <a target="_blank" href="https://link.springer.com/article/10.1134/S0036023610080310">Factors Controlling Sulfur Dioxide Solubilities in Organic Solvents.</a> <em>Russ. J. Inorg. Chem</em>. <strong>55</strong> (8), 1322-1329 (2010).</li>
<li>van Dam, M. H. H., Lamine, A. S., Roizard, D., Lochon, P., Roizard, C. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/ie970111f">Selective Sulfur Dioxide Removal Using Organic Solvents.</a> <em>Ind. Eng. Chem. Res</em>. <strong>36</strong> (11), 4628-4637 (1997).</li>
<li>Li, H., Jiao, X., Chen, W. <a target="_blank" href="http://www.tandfonline.com/doi/abs/10.1080/00319104.2013.830720">Solubility of Sulphur Dioxide in Polar Organic Solvents.</a> <em>Phys. Chem. Liq</em>. <strong>52</strong> (2), 349-353 (2014).</li>
<li>Trost, B. M., Brindle, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Direct+Catalytic+Asymmetric+Aldol+Reaction%5BTitle%5D)+AND+%22Chem.+Soc.+Rev%22%5BJournal%5D)">The Direct Catalytic Asymmetric Aldol Reaction.</a> <em>Chem. Soc. Rev</em>. <strong>39</strong> (5), 1600(2010).</li>
</ol>

<p class="jove_content">Os autores não têm nada para divulgar.</p>

<p class="jove_content">Tentativas iniciais para usar a reação de bissulfito como um método para remover aldeídos usando uma extração em duas fases típica levaram a níveis muito baixos de remoção. Formulamos a hipótese que a reação não foi rápida o suficiente para ocorrer durante o tempo muito limitado que as duas camadas estavam em contato. Para aumentar o contato entre os reagentes, desenvolvemos um protocolo de extração de dois estágios, em que um solvente miscível com água é usado inicialmente para permitir suficiente d...

<p class="jove_content">A separação dos componentes de misturas de um outro é essencial para a preparação de materiais puros. O método descrito neste documento permite a fácil separação dos aldeídos e desimpedido estericamente cíclico e metil cetonas de outras moléculas orgânicas<sup class="xref">1</sup>. A técnica baseia-se a reatividade de bissulfito com o grupo carbonila para criar uma carga aduto que podem ser separados em uma camada aquosa, enquanto outros componentes separam em uma camada orgânica imiscível. A chave para alcançar a reatividade entre bissulfito e a carbonila é a utilização de um solvente miscível, o que permite que a reação ocorra antes a separação em fases separadas. Sem a adição da separação mínima solvente miscível é obtida, presumivelmente devido ao mau contacto entre o bissulfito hidrofílico e os produtos orgânicos hidrofóbicos.</p>
<p class="jove_content">A vantagem deste método de separação para a purificação é a facilidade do protocolo. Extração líquido-líquido é uma operação simples para executar e pode ser realizado em grande escala. Técnicas de purificação alternativos, tais como cromatografia de coluna, são muito mais caro, demorado e desafiador para executar em grande escala e requerem suficiente diferenciação dos componentes em termos de polaridade. Purificação por recristalização ou destilação requer suficiente diferenciação entre a solubilidade ou pontos de ebulição dos componentes da mistura, respectivamente. Como a extração de bissulfito depende da diferença de reatividade do grupo carbonila de aldeídos e cetonas, compostos com pontos de ebulição, solubilidade similar ou polaridades podem ser efetivamente separados. Outros métodos de separação química existem para a separação selectiva de aldeídos e cetonas de misturas, por exemplo, a formação seletiva de oximas<sup class="xref">2</sup>, acetais cíclicos<sup class="xref">3</sup>ou formação de<sup class="xref">4</sup> mercaptal. Esses métodos requerem uma etapa adicional para separar as espécies formadas da mistura, porque o produto não é solúvel em água e, portanto, não pode ser separado por um protocolo de extração simples. Oxidação de aldeído para formar os ácidos carboxílicos removíveis é outro relatou a técnica<sup class="xref">5</sup>, mas a etapa de oxidação necessária é menos chemoselective do que as condições de bissulfito suave aqui descritos e requer o uso de gás oxigênio e um catalisador de cobalto.</p>
<p class="jove_content">Este método é aplicável para a separação de aldeídos (<strong>Figura 1</strong>) e desimpedido estericamente cíclicas e metil cetonas (<strong>Figura 2</strong>) de moléculas que não contêm estes grupos funcionais. Cetonas particularmente reativas, tais como α-ceto ésteres também são removidas usando este processo. Alcanos, alcenos, dienos, alquinos, ésteres, amidas, ácidos carboxílicos, haletos de alquila, álcoois, fenóis, nitrilos, cloretos de benzila, epóxidos, anilinas, acetais, e ligeiramente prejudicada, α, β-insaturados, ou arila cetonas são todos ́ nas condições e pode ser separado do aldeído ou componente reativa cetona da mistura (<strong>figuras 2</strong> e <strong>3</strong>). Etílico cetonas ou cetonas cíclicas α-substituídos, por exemplo, são suficientemente prejudicadas e, portanto, são separáveis de aldeídos e cetonas mais reativas. Ao usar alcenos, hexano é recomendado como o solvente imiscível para evitar a decomposição indesejada devido ao dióxido de enxofre presente na solução de bissulfito. A grupo funcional de compatibilidade do protocolo de extração de bissulfito é extremamente ampla e, portanto, é aplicável a um vastíssimo leque de separações, se o contaminante de carbonila ser separado da mistura é um aldeído ou uma progressista metil ou cetona cíclica. Menos reativas cetonas não reagem com bissulfito nestas condições e, portanto, não são removidas.</p>

<table><tbody><tr><td>sodium bisulfite</td><td>Fisher</td><td>AC419440010&amp;nbsp;</td><td>1 kg</td></tr><tr><td>benzyl butyrate</td><td>Fisher</td><td>AAB2424130&amp;nbsp;</td><td>250 g</td></tr><tr><td>anisaldehyde</td><td>Fisher</td><td>AC104801000&amp;nbsp;</td><td>100 mL</td></tr><tr><td>magnesium sulfate</td><td>Fisher</td><td>M65-500&amp;nbsp;</td><td>500 g</td></tr><tr><td>ethyl acetate</td><td>Fisher</td><td>E195-4&amp;nbsp;</td><td>4 L</td></tr><tr><td>hexanes</td><td>Fisher</td><td>H292-4&amp;nbsp;</td><td>4 L</td></tr><tr><td>methanol&amp;nbsp;</td><td>Fisher</td><td>A456-1&amp;nbsp;</td><td>1 L</td></tr><tr><td>dimethylformamide</td><td>Fisher</td><td>D119-1&amp;nbsp;</td><td>1 L</td></tr><tr><td>citronellal</td><td>Fisher</td><td>AAL15753AE&amp;nbsp;</td><td>100 mL</td></tr><tr><td>benzylacetone&amp;nbsp;</td><td>Fisher</td><td>AC105832500&amp;nbsp;</td><td>250 mL</td></tr><tr><td>deionized water</td><td>Fisher</td><td>BP28194&amp;nbsp;</td><td>4 L</td></tr><tr><td>piperonal&amp;nbsp;</td><td>Sigma-Aldrich</td><td>P49104-25G</td><td>25 G</td></tr><tr><td>sodium hydroxide</td><td>Fisher</td><td>S318-1&amp;nbsp;</td><td>1 kg</td></tr><tr><td>separatory funnel with cap</td><td>Fisher</td><td>10-437-5B&amp;nbsp;</td><td>125 mL</td></tr><tr><td>ring stand</td><td>Fisher</td><td>03-422-215</td><td>3 aluminum rods</td></tr><tr><td>ring clamp</td><td>Fisher</td><td>12-000-104&amp;nbsp;</td><td>5 cm</td></tr><tr><td>cork ring</td><td>Fisher</td><td>07-835AA&amp;nbsp;</td><td>8 cm outer dimension</td></tr><tr><td>round bottom flask</td><td>Fisher</td><td>31-501-107&amp;nbsp;</td><td>100 mL</td></tr><tr><td>rotary evaporator with accessories</td><td>Fisher</td><td>05-000-461&amp;nbsp;</td><td>cold trap bondenser</td></tr><tr><td>bump trap 14/20 joint</td><td>Fisher</td><td>CG132201</td><td>14/20 joint</td></tr><tr><td>funnel</td><td>Fisher</td><td>05-555-6&amp;nbsp;</td><td>organic solvent compatible</td></tr><tr><td>cotton</td><td>Fisher</td><td>22-456-881</td><td>non-sterile</td></tr><tr><td>glass pipets</td><td>Fisher</td><td>13-678-20A&amp;nbsp;</td><td>borosilicate 5.75&quot;</td></tr><tr><td>two 250 microliter syringes</td><td>Fisher</td><td>14-813-69&amp;nbsp;</td><td></td></tr><tr><td>4 erlenmeyer flasks</td><td>Fisher</td><td>10-040D&amp;nbsp;</td><td>125 mL</td></tr><tr><td>fume hood&amp;nbsp;</td><td>Fisher</td><td>13-118-370&amp;nbsp;</td><td></td></tr><tr><td>nitrile gloves</td><td>Fisher</td><td>19-149-863B&amp;nbsp;</td><td>medium</td></tr><tr><td>safety goggles</td><td>Fisher</td><td>17-377-403&amp;nbsp;</td><td></td></tr><tr><td>spatula</td><td>Fisher</td><td>14-357Q</td><td></td></tr><tr><td>balance</td><td>Fisher</td><td>01-912-403&amp;nbsp;</td><td>120 g capacity</td></tr></tbody></table>

separation of aldehydes and reactive ketones from mixtures using a bisulfite extraction protocol

<p class="jove_content">A purificação de compostos orgânicos é um componente essencial das operações de rotina sintéticos. A capacidade de remover contaminantes em uma fase aquosa, gerando uma estrutura carregada fornece uma oportunidade para usar extração como uma técnica de purificação simples. Combinando o uso de um solvente orgânico miscível com bissulfito de sódio saturada, aldeídos e cetonas reativas pode ser transformado com sucesso em cobrado bissulfito adutos que pode então ser separada de outros componentes orgânicos de uma mistura pelo introdução de uma camada orgânica imiscível. Aqui, descrevemos um protocolo simples para a remoção dos aldeídos, incluindo aldeídos Neopentil impedida estericamente e algumas cetonas, de misturas químicas. Cetonas podem ser separadas, se eles são desimpedidos estericamente cíclica ou metil cetonas. Para aldeídos alifáticos e cetonas, dimetilformamida é usada como solvente miscível para melhorar as taxas de remoção. A reação de adição de bissulfito pode ser revertida por Basificação da camada aquosa, permitindo o re-isolamento do componente reactive do carbonyl de uma mistura.</p>

<p class="jove_content" fo:keep-together.within-page="1">Procedimento <strong>1</strong> para remoção de aldeído é usado para aldeídos aromáticos. Procedimento <strong>2</strong>, no qual dimetilformamida é usada como solvente miscível, deve ser usado para cetonas e aldeídos alifáticos. Procedimento <strong>2</strong> também deve ser usado em misturas que não são totalmente solúvel em metanol. O material obtido a partir de cada um dos protocolos é analisada para pureza usando <sup>1</sup>análise de integração H NMR e taxa de r...

Watch this Scientific Journal Video about Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol at JoVE.com

Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

Separação de aldeídos e cetonas reativas de misturas usando um protocolo de extração de bissulfito

<p class="jove_content">Aqui, apresentamos um protocolo para remover aldeídos e cetonas reativas de misturas por um protocolo de extração líquido-líquido diretamente com bissulfito de sódio saturada em um solvente miscível. Este protocolo combinado é rápida e fácil de executar. O aldeído ou cetona pode ser re-isolada, a Basificação da camada aquosa.</p>

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer ...

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34.0K visualizações.  Trinity College. Aqui, apresentamos um protocolo para remover aldeídos e cetonas reativas de misturas por um protocolo de extração líquido-líquido diretamente com bissulfito de sódio saturada em um solvente miscível. Este protocolo combinado é rápida e fácil de executar. O aldeído ou cetona pode ser re-isolada, a Basificação da camada aquosa.

Vídeo: Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine

<p class="jove_content">Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. Their synthesis by conventional organic chemistry often requires tedious multi-step synthesis processes, with difficult control of the stereochemical outcome. We present a protocol to enzymatically synthetize amino alcohols starting from the readily available L-lysine in 48 h. This protocol combines two chemical reactions that are very difficult to conduct by conventional organic synthesis. In the first step, the regio- and diastereoselective oxidation of an unactivated C-H bond of the lysine side-chain is catalyzed by a dioxygenase; a second regio- and diastereoselective oxidation catalyzed by a regiodivergent dioxygenase can lead to the formation of the 1,2-diols. In the last step, the carboxylic group of the alpha amino acid is cleaved by a pyridoxal-phosphate (PLP) decarboxylase (DC). This decarboxylative step only affects the alpha carbon of the amino acid, retaining the hydroxy-substituted stereogenic center in a beta/gamma position. The resulting amino alcohols are therefore optically enriched. The protocol was successfully applied to the semipreparative-scale synthesis of four amino alcohols. Monitoring of the reactions was conducted by high performance liquid chromatography (HPLC) after derivatization by 1-fluoro-2,4-dinitrobenzene. Straightforward purification by solid-phase extraction (SPE) afforded the amino alcohols with excellent yields (93% to &#62;95%).</p>

<p class="jove_content">Chiral amino alcohols are versatile molecules for use as scaffolds in organic synthesis. Starting from L-lysine, we synthesize amino alcohols by an enzymatic cascade reaction combining diastereoselective C-H oxidation catalyzed by dioxygenase followed by cleavage of the carboxylic acid moiety of the corresponding hydroxyl amino acid by a decarboxylase.</p>

Reações Enzimáticas em Cascata para a Síntese de Aminoálcoois Quirais a partir de L-lisina

Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. ...

Química

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

<p class="jove_content">&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond&#8211;forming arylation and allylation reactions. At the heart of these methods is the preparation of the intermediate and highly reactive enolonium species prior to addition of a reactive nucleophile. This strategy is thus reminiscent of the preparation and use of metal enolates in classical synthetic chemistry. This strategy allows the use of nucleophiles that would otherwise be incompatible with the strongly oxidizing hypervalent iodine reagents. In this paper we present a detailed protocol for chlorination, azidation, N-heteroarylation, arylation, and allylation. The products include motifs prevalent in medicinally active products. This article will greatly assist others in using these methods.</p>

<p class="jove_content">A two step one-pot protocol for the umpolung of ketone enolates to enolonium species and addition of a nucleophile to the &#945;-position is described. Nucleophiles include chloride, azide, azoles, allyl-silanes, and aromatic compounds.</p>

Um Protocolo em Duas Etapas para Funcionalização de Umpolung de Cetonas via Espécies de Enolonium

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. ...

Synthesis of Esters Via a Greener Steglich Esterification in Acetonitrile

<p class="jove_content">The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the reaction is commonly performed using chlorinated or amide solvent systems, which are hazardous to human health and the environment. Our methodology utilizes acetonitrile as a greener and less hazardous solvent system. This protocol exhibits rates and yields that are comparable to traditional solvent systems and employs an extraction and wash sequence that eliminates the need for the purification of the ester product via column chromatography. This general method can be used to couple a variety of carboxylic acids with 1&#176; and 2&#176; aliphatic alcohols, benzylic and allylic alcohols, and phenols to obtain pure esters in high yields. The goal of the protocol detailed here is to provide a greener alternative to a common esterification reaction, which could serve useful for ester synthesis in both academic and industrial applications.</p>

<p class="jove_content">A modified Steglich esterification reaction was used to synthesize a small library of ester derivatives with primary and secondary alcohols. The methodology uses a non-halogenated and greener solvent, acetonitrile, and enables product isolation in high yields without the need for chromatographic purification.</p>

Síntese de ésteres através de uma esterificação Steglich mais verde em acetonitrila

The Steglich esterification is a widely-used reaction for the synthesis of esters from carboxylic acids and alcohols. While efficient and mild, the ...

Reducing Agents

<p class="jove_content">Source: Vy M. Dong and Daniel Kim, Department of Chemistry, University of California, Irvine, CA</p>
<p class="jove_content">Controlling the reactivity and selectivity during the synthesis of a molecule is very important criteria for chemists. This has led to the development of many reagents that allow chemists to pick and choose reagents suitable for a given task. Quite often, a balance between reactivity and selectivity needs to be achieved. This experiment will use IR spectroscopy to monitor the reaction and to understand the reactivity of carbonyl compounds as well as the reactivity of hydride-reducing reagents.</p>

Reduction of Carbonyl Compounds

Agentes redutores

Source: Vy M. Dong and Daniel Kim, Department of Chemistry, University of California, Irvine, CA
Controlling the reactivity and selectivity during the ...

JoVE Science Education

Química Orgânica II

Identification of Unknown Aldehydes and Ketones

<p>Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA</p>
<ol class="note-items">
	<li data-note-item="1" data-parent-collapse="">DNPH Test for Aromatic Aldehydes and Ketones<button class="expand">Expand</button>
	<p>In this lab, you&#39;ll use the DNPH test, the Tollens&#39; test, and the iodoform test to identify two unknown aldehydes or ketones. You&#39;ll use butanone and benzaldehyde as known compounds to confirm that the tests are working as expected.</p>
	<p>You&#39;ll start the lab with the DNPH test, which relies on the reaction between 2,4-dinitrophenylhydrazine, or DNPH, and aldehydes and ketones. When you combine DNPH and an aldehyde or ketone in an acidic environment, they undergo a condensation reaction to form the corresponding hydrazone. The hydrazone then precipitates from solution. If the precipitate is red to orange, the aldehyde or ketone was aromatic. If it&#39;s orange to yellow, the aldehyde or ketone was non-aromatic or aliphatic.</p>
	<ul class="lab-items">
		<li data-sub-note-item="1-3">
		<div class="lab-step">Put on a lab coat, safety glasses, and nitrile gloves.<strong> Note: </strong>Many chemicals in this lab are toxic, corrosive, or flammable, so you will perform this lab in a fume hood. Change your gloves if you get any chemicals on them.</div>
		</li>
		<li data-sub-note-item="1-4">
		<div class="lab-step">Get a vial of each known compound and choose two unknown compounds to analyze. Write the codes for your unknowns in your lab notebook.</div>
		</li>
		<li data-sub-note-item="1-5">
		<div class="lab-step">Label a 250-mL beaker for aqueous waste and a 600-mL beaker for used pipettes. Put several clean Pasteur pipettes in another beaker and get more whenever you need them.</div>
		</li>
		<li data-sub-note-item="1-6">
		<div class="lab-step">Obtain four small test tubes in a rack and label them with the four compound names, or codes, and the name of the first test.</div>
		</li>
		<li data-sub-note-item="1-7">
		<div class="lab-step">Bring a 50-mL beaker and a graduated cylinder to the reagent hood and obtain 8 mL of the DNPH solution.</div>
		</li>
		<li data-sub-note-item="1-8">
		<div class="lab-step">Use four Pasteur pipettes to place 3 &#8211; 4 drops of each compound into its test tube. <strong>Note:</strong> Don&#39;t reuse pipettes during this lab because cross-contamination will invalidate the test results.</div>
		</li>
		<li data-sub-note-item="1-9">
		<div class="lab-step">Add 2 mL of the DNPH solution to one of the test tubes and mix it well with a glass rod. Thoroughly rinse the glass rod with deionized water over your aqueous waste beaker to remove all traces of the ketone or aldehyde.</div>
		</li>
		<li data-sub-note-item="1-10">
		<div class="lab-step">Add 2 mL of the DNPH solution to each of the other three test tubes in the same way. Make sure to thoroughly clean the glass rod after each one. When you&#39;re finished, let the solution sit for 15 min.</div>
		</li>
		<li data-sub-note-item="1-11">
		<div class="lab-step">While you wait, set up for vacuum filtration and fill a 250-mL beaker with deionized water.</div>
		</li>
		<li data-sub-note-item="1-12">
		<div class="lab-step">After 15 minutes, inspect the precipitates in the test tubes. <strong>Note:</strong> Benzaldehyde has an aromatic group, so you should see a red to orange solid in its test tube. Butanone is aliphatic, so you should see an orange to yellow solid in its test tube. Record the results in your lab notebook.
		<h4><strong>Table 1: DNPH, Tollens&#39;, and Iodoform Results</strong></h4>
		<table align="center" height="224" style="border-collapse: collapse; font-size: 17px; line-height: 24px;">
			<tbody>
				<tr>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>Compound</strong></td>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>DNPH </strong></td>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>Tollens&#39; </strong></td>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>Iodoform </strong></td>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>Solubility in water </strong></td>
					<td style="border: 1px solid; padding: 0px; text-align: center;"><strong>Hydrazone m.p. </strong></td>
				</tr>
				<tr>
					<td style="border: 1px solid; padding: 0px;">Butanone</td>
					<td style="border: 1px solid; padding: 0px;"></td>
					<td style="border: 1px solid; padding: 0px;"></td>
					<td style="border: 1px solid; padding: 0px;"></td>
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				</tr>
				<tr>
					<td style="border: 1px solid; padding: 0px;">Benzaldehyde</td>
					<td style="border: 1px solid; padding: 0px;"></td>
					<td style="border: 1px solid; padding: 0px;"></td>
					<td style="border: 1px solid; padding: 0px;"></td>
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				</tr>
				<tr>
					<td style="border: 1px solid; padding: 0px;">&#160; &#160;</td>
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				</tr>
				<tr>
					<td style="border: 1px solid; padding: 0px;">&#160; &#160;</td>
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				</tr>
			</tbody>
		</table>
		<a href="https://www.jove.com/CDNSource/lm/labs/69/Table_1._DNPH,_Tollens_,_and_Iodoform_results.xlsx" target="_blank">Click Here to download Table 1</a></div>
		</li>
		<li data-sub-note-item="1-13">
		<div class="lab-step">Compare the solids from the unknown compounds to the known compounds. For each unknown, record whether this solid was more red-orange, like benzaldehyde, or more orange-yellow, like butanone.</div>
		</li>
		<li data-sub-note-item="1-14">
		<div class="lab-step">Use a clean Pasteur pipette to wet the filter paper of the vacuum filtration setup with deionized water and collect the solid from one of your unknowns by vacuum filtration. Rinse out any solid left in the tube with deionized water.</div>
		</li>
		<li data-sub-note-item="1-15">
		<div class="lab-step">Wash the solid on the filter paper with 10 mL of deionized water.</div>
		</li>
		<li data-sub-note-item="1-16">
		<div class="lab-step">Pick up a tiny amount of the solid with a clean glass rod and smear it on pH paper. If the pH is below 6.5, rinse the solid with another 10 mL of deionized water. Keep rinsing the solid and checking its pH until it is between 6.5 and 7.</div>
		</li>
		<li data-sub-note-item="1-17">
		<div class="lab-step">Label a small watch glass for the unknown and carefully transfer the filter paper and solid to the watch glass to dry.</div>
		</li>
		<li data-sub-note-item="1-18">
		<div class="lab-step">Thoroughly rinse the B&#252;chner funnel with deionized water, dispose of the filtrate in the DNPH solution waste, and reassemble the vacuum filtration setup with a new piece of filter paper.</div>
		</li>
		<li data-sub-note-item="1-19">
		<div class="lab-step">Collect and wash the solids from the second unknown compound and from the two known compounds in the same way.</div>
		</li>
		<li data-sub-note-item="1-20">
		<div class="lab-step">Leave the four solids in your fume hood to dry (1 h).</div>
		</li>
	</ul>
	</li>
	<li data-note-item="2" data-parent-collapse="">The Tollens&#8217; Test<button class="expand">Expand</button>
	<p>When you combine an aldehyde with diammine silver(I), or Tollens&#39; reagent, the reagent is reduced to metallic silver and ammonia. The silver either coats the inside of the reaction vessel or precipitates as a black solid, so it&#39;s easy to see that the reaction happened.</p>
	<p>Most ketones are harder to oxidize than aldehydes and therefore don&#39;t react with the Tollens&#39; reagent. For this lab, you can assume that if silver appears, the compound is an aldehyde. If silver does not appear, the compound is a ketone.</p>
	<p>The Tollens&#39; reagent solution contains a strong base and must be disposed of specially to avoid forming an explosive decomposition product. Handle it carefully and remember to put the Tollens&#39; test waste in the designated container.</p>
	<ul class="lab-items">
		<li data-sub-note-item="2-4">
		<div class="lab-step">Place your used test tubes in a beaker and label four new tubes with the compound names or codes and Tollens&#39; test.</div>
		</li>
		<li data-sub-note-item="2-5">
		<div class="lab-step">Bring a clean 50-mL beaker and a 5-mL graduated cylinder to the reagent hood and obtain 4 mL of Tollens&#39; reagent.</div>
		</li>
		<li data-sub-note-item="2-6">
		<div class="lab-step">Use clean pipettes to place 3 &#8211; 4 drops of each compound in its test tube.</div>
		</li>
		<li data-sub-note-item="2-7">
		<div class="lab-step">Add 1 mL of Tollens&#39; reagent to each test tube and mix the solutions well with a clean glass rod, thoroughly rinsing the rod with deionized water between tubes. Set the rack of tubes to the side and let it sit for 10 min.</div>
		</li>
		<li data-sub-note-item="2-8">
		<div class="lab-step">While you wait, get about 100 mL of water in a 150-mL beaker and set it on a hotplate. Position a small 3-prong clamp above the beaker.</div>
		</li>
		<li data-sub-note-item="2-9">
		<div class="lab-step">Check the benzaldehyde tube after 10 min.<strong> Note:</strong> Benzaldehyde should have a positive result, as indicated by a silver film or precipitate. If you don&#39;t see a positive result in the benzaldehyde tube, secure a thermometer to the test tube and heat in the water bath at 35 &#176;C for 5 min. The silver film, or precipitate, should then appear. Record this result in your lab notebook.</div>
		</li>
		<li data-sub-note-item="2-10">
		<div class="lab-step">Butanone won&#39;t react with Tollens&#39; reagent. <strong>Note: </strong>The butanone tube is an example of a negative Tollens&#39; test result. Record this in your lab notebook.</div>
		</li>
		<li data-sub-note-item="2-11">
		<div class="lab-step">Check the tubes of your unknowns. If you see a silver mirror or precipitate, record a positive Tollens&#39; test result for that unknown. If you don&#39;t, heat the tube in the water bath for 5 min and check again. If the test is still negative, record that result in your lab notebook.</div>
		</li>
		<li data-sub-note-item="2-12">
		<div class="lab-step">When you&#39;re done, turn off the hotplate and dispose of the Tollens&#39; test solutions in the appropriate waste container. Put silver-coated tubes in the collection box for acid cleaning and put the rest in your beaker.</div>
		</li>
	</ul>
	</li>
	<li data-note-item="3" data-parent-collapse="">Iodoform Test for Methyl Ketones<button class="expand">Expand</button>
	<p>When you combine iodine and a methyl ketone in aqueous base, iodine replaces the alpha methyl&#39;s hydrogens. An addition-elimination reaction followed by proton transfer yields iodoform and a carboxylate anion. Iodoform is insoluble in water, so you&#39;ll see a yellow precipitate if the compound that you&#39;re testing is a methyl ketone. If it is not a methyl ketone, the test solution will eventually turn brown because of the unreacted iodine.</p>
	<ul class="lab-items">
		<li data-sub-note-item="3-2">
		<div class="lab-step">Before the iodoform test, check the solubility of all four compounds in water. Label four clean test tubes with the compound names or codes and H<sub>2</sub>O. Label another four test tubes with the compound names and CHI<sub>3</sub>.</div>
		</li>
		<li data-sub-note-item="3-3">
		<div class="lab-step">Use clean Pasteur pipettes to place 3 &#8211; 4 drops of each compound in its test tube.</div>
		</li>
		<li data-sub-note-item="3-4">
		<div class="lab-step">Add 2 mL of deionized water to each labeled tube. Mix well with a clean glass rod. Thoroughly clean the rod with deionized water between tubes.</div>
		</li>
		<li data-sub-note-item="3-5">
		<div class="lab-step">Wait a few minutes for the liquids to settle before evaluating them. <strong>Note:</strong> Butanone is moderately soluble in water, so you should see little to no separation. Benzaldehyde is sparingly soluble in water, and its density is a little higher than water&#39;s. You should see a small layer at the bottom of the tube.</div>
		</li>
		<li data-sub-note-item="3-6">
		<div class="lab-step">Inspect your unknowns for liquid layers and record the results for all four compounds in your lab notebook.</div>
		</li>
		<li data-sub-note-item="3-7">
		<div class="lab-step">Add 2 mL of deionized water to the butanone tube and any water-soluble ketones and mix them well with a clean glass rod. <strong>Note: </strong>If you have an unknown ketone that is insoluble in water, instead add 2 mL of 1,2-dimethoxyethane and mix it well with a clean glass rod.</div>
		</li>
		<li data-sub-note-item="3-8">
		<div class="lab-step">Now, perform the iodoform test, which is for ketones only. Use a clean 50-mL beaker and a small graduated cylinder to obtain 4 or 6 mL of 3 M NaOH, depending on whether you have two or three ketones to test.</div>
		</li>
		<li data-sub-note-item="3-9">
		<div class="lab-step">Pour ~10 mL of iodoform reagent into another 50-mL beaker.</div>
		</li>
		<li data-sub-note-item="3-10">
		<div class="lab-step">Add 2 mL of 3 M NaOH to each ketone tube and mix well, thoroughly cleaning the glass rod with deionized water between each tube.</div>
		</li>
		<li data-sub-note-item="3-11">
		<div class="lab-step">Obtain a clean Pasteur pipette and add the iodoform reagent dropwise to the butanone tube, frequently stirring until you see a yellow precipitate. <strong>Note:</strong> Butanone is a methyl ketone, so it will produce a positive result.</div>
		</li>
		<li data-sub-note-item="3-12">
		<div class="lab-step">Rinse the glass rod with deionized water and start adding the iodoform reagent dropwise to your first, or only, unknown ketone, while stirring frequently. Continue adding the reagent until either yellow iodoform precipitates, like you saw with butanone, or the solution stays brown, even after you stir it well. <strong>Note: </strong>The latter is a negative result.</div>
		</li>
		<li data-sub-note-item="3-13">
		<div class="lab-step">If you have another unknown ketone, clean the glass rod well and repeat the test with your second ketone.</div>
		</li>
		<li data-sub-note-item="3-14">
		<div class="lab-step">When you&#39;re finished, dispose of your iodine-containing solutions in the appropriate waste container.</div>
		</li>
		<li data-sub-note-item="3-15">
		<div class="lab-step">Once the solids from the DNPH test are dry, measure the melting point of each solid and record them in your lab notebook. Put the remaining solutes in the waste container for solid DNPH derivatives.</div>
		</li>
		<li data-sub-note-item="3-16">
		<div class="lab-step">Dispose of the leftover organic liquids and the aqueous aldehyde mixtures in the usual waste containers.</div>
		</li>
		<li data-sub-note-item="3-17">
		<div class="lab-step">Rinse the Pasteur pipettes used for the aldehydes and ketones with acetone before putting them in the glass waste. Pour your aqueous waste down the drain with running tap water. Clean your glassware, put away your lab equipment, and collect and throw out any trash in your fume hood before you leave.</div>
		</li>
	</ul>
	</li>
	<li data-note-item="4" data-parent-collapse="">Results<button class="expand">Expand</button>
	<ul class="lab-items">
		<li data-sub-note-item="4-1">
		<div class="lab-step">Identify your unknown compounds. There are six options: acetophenone, butanal, 3-methyl-2-butanone, pentanal, 2-pentanone, and 3-pentanone.</div>
		</li>
		<li data-sub-note-item="4-2">
		<div class="lab-step">Look at the DNPH results. If the precipitate was red to orange, the unknown aldehyde or ketone is aromatic. If it was yellow, the unknown is aliphatic. <strong>Note:</strong> Since only one possible compound is aromatic, red precipitate means that the unknown was acetophenone. As confirmation, you should also have seen a negative Tollens&#39; test and a positive iodoform test.</div>
		</li>
		<li data-sub-note-item="4-3">
		<div class="lab-step">A yellow precipitate in the DNPH test means that the unknown could be any of the other five compounds.</div>
		</li>
		<li data-sub-note-item="4-4">
		<div class="lab-step">Look at the results of the Tollens&#39; test. If you saw a silver mirror or silver-gray precipitate in the test tube, the unknown compound is an aldehyde. If you didn&#39;t see any change, then the unknown compound is a ketone. If your unknown is an aldehyde, it could be pentanal or butanal.</div>
		</li>
		<li data-sub-note-item="4-5">
		<div class="lab-step">Compare the melting point of the unknown&#39;s hydrazone derivative to literature values for each aldehyde to figure out which one it was.</div>
		</li>
		<li data-sub-note-item="4-6">
		<div class="lab-step">If Tollens&#39; test was negative and the DNPH test showed an aliphatic compound, the unknown could be 3-methyl-2-butanone, 2-pentanone, or 3-pentanone.</div>
		</li>
		<li data-sub-note-item="4-7">
		<div class="lab-step">Check the results of the iodoform test to narrow it down. If you saw solid yellow iodoform, the compound was a methyl ketone. If you saw a brown solution, it was not a methyl ketone.</div>
		</li>
		<li data-sub-note-item="4-8">
		<div class="lab-step">Only one of the aliphatic ketones is not a methyl ketone, so if you saw a brown solution, the unknown was 3-pentanone. If you saw yellow iodoform precipitate from solution and the DNPH test also had yellow precipitate, then the unknown is 3-methyl-2-butanone or 2-pentanone.</div>
		</li>
		<li data-sub-note-item="4-9">
		<div class="lab-step">Use the melting point of the unknown&#39;s hydrazone derivative to figure out which methyl ketone you had.</div>
		</li>
	</ul>
	</li>
</ol>

Test for Aldehydes and Ketones: DNPH, Tollen's Test, and Iodoform Test - Procedure

Identificação de aldeídos e cetonas desconhecidos

Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA

	DNPH Test for Aromatic Aldehydes and KetonesExpand
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Alcohols from Carbonyl Compounds: Reduction

<p>Reduction is a simple strategy to convert a carbonyl group to a hydroxyl group. The three major pathways to reduce carbonyls to alcohols are catalytic hydrogenation, hydride reduction, and borane reduction.</p>
<p><strong>Catalytic hydrogenation</strong> is similar to the reduction of an alkene or alkyne by adding H<sub>2</sub> across the pi bond in the presence of transition metal catalysts like Raney Ni, Pd–C, Pt, or Ru. Aldehydes and ketones can be reduced by this method, often under mild to moderate heat (25–100°C) and pressure (1–5 atm H<sub>2</sub>), to yield 1° and 2° alcohols, respectively.</p>
<p style="text-align: center"><img alt="Hydrogenation reaction diagram; cyclohexanone to cyclohexanol using H₂/Pt, Pd, Ni catalyst, 90–95% yield." src="/files/ftp_upload/11925/11925_PT_Figure_1.svg" style="text-align: center; height: 90px;" data-altupdatedat="1747908711000" data-alt="Figure1"></p>
<p align="center"><strong>Figure 1.</strong> Catalytic hydrogenation can be suitable for industrial applications when harsh conditions are not required, but unsaturated carbon–carbon bonds are also reduced.</p>
<p><strong>Hydride reduction</strong> can be achieved by hydride transfer reagents, like sodium borohydride (NaBH<sub>4</sub>) and lithium aluminum hydride (LiAlH<sub>4</sub>, or LAH), as nucleophilic attack by a free hydride ion, <strong><img alt="Lewis structure of hydride ion, H⁻, showing a hydrogen atom with a lone pair and a negative charge." src="/files/ftp_upload/11925/11925_PT_Figure_2.svg" style="height: 18px;" data-altupdatedat="1747908711000" data-alt="Figure2"></strong>, is almost unknown for NaH salts due to its high charge density, making it a strong base. The hydrogen atoms of LAH and NaBH<sub>4</sub>, being covalently bonded to boron and aluminum atoms, have partial negative charges, thereby enhancing their nucleophilicity at the cost of basicity. The first step of nucleophilic addition leads to the formation of alkoxide ions. The byproduct alkoxyborohydride or alkoxyaluminate reduces three more carbonyl molecules, successively transferring all their hydrogen atoms. Since hydride is a poor leaving group, the hydride transfer steps are irreversible, and therefore the reaction proceeds to completion. Lastly, the reaction mixture is worked up with solvent (i.e., water or alcohol in the case of NaBH<sub>4</sub> and dilute acid in the case of LAH).</p>
<p style="text-align: center"><img alt="Chemical reaction diagram: ester reduction by LiAlH4 to form alcohols, showcasing reduction process." src="/files/ftp_upload/11925/11925_PT_Figure_3.svg" style="text-align: center; height:55px;" data-altupdatedat="1747908711000" data-alt="Figure3"></p>
<p align="center"><strong>Figure 2.</strong> Aldehydes and symmetrical esters produce one 1° alcohol product. Unsymmetrical esters produce a mixture of 1° alcohols.</p>
<p>LAH, NaBH<sub>4</sub>, and their derivatives are highly useful in the reduction of aldehydes and ketones. LAH, a powerful reducing agent, can also reduce carbonyl compounds like acids, esters, acyl chlorides, and amides. LAH reacts violently with water and other protic solvents, liberating hydrogen gas and forming metal hydroxides/alkoxides. Hence, LAH reductions are typically carried out in aprotic solvents like anhydrous diethyl ether and THF.</p>
<p style="text-align: center"><img alt="Organic reduction reaction equation, LiBH4/EtOH, carboxylic acid to alcohol conversion, chemical synthesis." src="/files/ftp_upload/11925/11925_PT_Figure_4.svg" style="text-align: center; height: 45px;" data-altupdatedat="1747908711000" data-alt="Figure4"></p>
<p align="center"><strong>Figure 3.</strong> An alcoholic solution of lithium borohydride is a non-hazardous alternative to LAH in selectively reducing esters over acids.</p>
<p>On the other hand, NaBH<sub>4</sub> is of a milder nature and generally reduces only in protic solvents like ethanol or methanol. Therefore, NaBH<sub>4</sub> can be used to reduce aldehydes and ketones in the presence of functional groups like alkyl halides, esters, alkyl tosylates, and nitro groups. Diisobutylaluminum hydride (DIBAL-H) can also convert carbonyls to alcohols at room temperature by two successive additions of hydride ions. However, when reacted with esters at low temperatures, this reaction can be stopped at the aldehyde stage by adding only one equivalent of hydride ion.</p>
<p><strong>Borane reduction</strong> uses a borane (BH<sub>3</sub>) solution in diethyl ether, THF, or Me<sub>2</sub>S to selectively reduce electron-rich carbonyl groups like carboxylic acids in the presence of other reducible functional groups such as esters and even ketones.</p>
<p style="text-align: center"><img alt="Hydroboration-oxidation reaction equation; organic chemistry; synthesis of alcohols; reaction diagram." src="/files/ftp_upload/11925/11925_PT_Figure_5.svg" style="text-align: center; height: 65px;" data-altupdatedat="1747908711000" data-alt="Figure5"></p>
<p align="center"><strong>Figure 4.</strong> The formation of a reactive triacylborate intermediate with a more electrophilic carbonyl group than the starting ester molecule drives the reduction reaction forward.</p>
<p>For living organisms, reduced coenzyme NADH or its phosphoester NADPH is equivalent to laboratory hydride reagents in enzyme catalysis of similar biological reductions.</p>

Álcoois de Compostos Carbonílicos: Redução

Reduction is a simple strategy to convert a carbonyl group to a hydroxyl group. The three major pathways to reduce carbonyls to alcohols are catalytic ...

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Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes

<p>Aldehydes and ketones are prepared from alcohols, alkenes, and alkynes via different reaction pathways. Alcohols are the most commonly used substrates for synthesizing aldehydes and ketones. The conversion of alcohol to aldehyde, which involves the oxidation process, depends on the class of the alcohol used and the strength of the oxidizing agent. For instance, primary alcohol will form an aldehyde when treated with a weak oxidizing agent; however, it gets over-oxidized to a carboxylic acid in the presence of a strong oxidizing agent. Hence, a mild oxidant like pyridinium chlorochromate is used to convert primary alcohols to aldehydes.</p>
<p>Similarly, Swern and Dess&#8211;Martin oxidations, which employ weaker oxidizing agents, convert primary alcohols to aldehydes. The strength of the oxidizing agent is irrelevant when converting secondary alcohol to a ketone. Both mild and strong oxidants give ketones from secondary alcohols.</p>
<p>Unsaturated hydrocarbons like alkenes undergo an ozonolysis reaction to give aldehydes and ketones. The product formed depends on the substitution present across the double bond in an alkene. A monosubstituted alkene forms formaldehyde and another aldehyde molecule. However, disubstitution gives rise to two cases. A 1,1-disubstituted alkene upon ozonolysis forms a mixture of formaldehyde and ketone, while a 1,2-disubstituted alkene yields a mixture of aldehydes. Both aldehydes and ketones are formed when trisubstituted alkenes undergo ozonolysis, while tetrasubstituted alkenes form ketones exclusively.</p>
<p>Alkynes&#160;also form aldehydes and ketones under hydroboration-oxidation and acid-catalyzed hydration reaction conditions. The hydroboration-oxidation reaction favors anti-Markovnikov&#8217;s addition. Hence terminal alkynes form aldehydes, and internal alkynes&#160;yield ketones. On the other hand, the acid-catalyzed hydration reaction follows Markonikov&#8217;s addition, and thus both terminal and internal alkynes generate&#160;ketones.</p>

Preparação de Aldeídos e Cetonas a partir de Álcoois, Alcenos e Alcinos

Aldehydes and ketones are prepared from alcohols, alkenes, and alkynes via different reaction pathways. Alcohols are the most commonly used substrates for ...

Aldeídos e Cetonas

Preparation of Aldehydes and Ketones from Nitriles and Carboxylic Acids

<p>Although it is possible to reduce a carboxylic acid to an aldehyde, strong reducing agents, like lithium aluminum hydride (LAH), prohibit a controlled reduction, instead causing the generated aldehyde to instantly over-reduce to a primary alcohol.</p>
<p>Reducing carboxylic acid derivatives like acyl chlorides (RCOCl), esters (RCO<sub>2</sub>R&prime;), and nitriles (RCN) using milder aluminum hydride agents like lithium tri-<span style="font-style:italic">tert</span>-butoxyaluminum hydride [LiAlH(O-<span style="font-style:italic">t</span>-Bu)<sub>3</sub>] and diisobutylaluminum hydride [DIBAL-H] allows the easy conversion of the derivative to the corresponding aldehyde. This is because alkylaluminum hydrides are less reactive than LAH, as the former is more sterically hindered.</p>
<p>According to recent studies, a reductant like diphenylsilane in combination with an air-stable Ni precatalyst and dimethyl dicarbonate as an activator converts most of the carboxylic acid to the aldehyde without causing any over-reduction.</p>
<p>In other studies, a hydrosilane through visible light photoredox catalysis efficiently reduces carboxylic acids to aldehydes.</p>
<p>Ketones, unlike aldehydes, can be directly prepared from carboxylic acids using organolithium reagents. The acid rapidly reacts with two equivalents of an organolithium reagent to form a dianion. This dianion gets protonated to form the corresponding hydrate, which loses a water molecule to give a ketone.</p>
<p>Both aldehydes and ketones can be prepared from nitriles using suitable reducing agents. Aldehydes are formed by the partial reduction of nitriles in the presence of DIBAL-H. The nitrile first forms an aluminum complex, which later, on hydrolysis, yields the corresponding aldehyde. Nitriles can be reduced to ketones via imine intermediates using Grignard or organolithium reagents.</p>

Preparação de Aldeídos e Cetonas a partir de Nitrilas e Ácidos Carboxílicos

Although it is possible to reduce a carboxylic acid to an aldehyde, strong reducing agents, like lithium aluminum hydride (LAH), prohibit a controlled ...

Preparation of Aldehydes and Ketones from Carboxylic Acid Derivatives

<p>Aldehydes are more reactive than carboxylic acids and hence, can get over-reduced to alcohol in the presence of strong reducing agents. Therefore, carboxylic acids are&#160;inefficient in preparing aldehydes using LAH.</p>
<p>Carboxylic acid derivatives like acid chlorides and esters are more easily reducible than the corresponding acids. The derivatives reduce in the presence of mild reducing agents to give aldehydes. Aldehydes can also be prepared by Rosenmund reduction, that is, the reduction of acid chloride via hydrogenation over a poisoned catalyst. Catalytic poisoning inhibits the over-reduction of aldehydes. A Grignard reagent reduces an acid chloride to tertiary alcohol via a ketone intermediate. The reaction can be stopped at the ketone stage using a milder reducing agent like the Gilman reagent (R<sub>2</sub>CuLi). Aryl ketones can be prepared by Friedel&#8211;Crafts acylation&#160;in which acid chloride is treated with benzene and AlCl<sub>3</sub>.</p>
<p>Another carboxylic acid derivative, an ester, can be reduced to an aldehyde using DIBAL-H at dry ice temperature to give an aldehyde. Ketones cannot be prepared directly from esters because ketones are more reactive than esters and tend to over-reduce to tertiary alcohol.</p>

Preparação de Aldeídos e Cetonas a partir de Derivados de Ácidos Carboxílicos

Aldehydes are more reactive than carboxylic acids and hence, can get over-reduced to alcohol in the presence of strong reducing agents. Therefore, ...

Reactions of Aldehydes and Ketones: Baeyer&ndash;Villiger Oxidation

<p>Baeyer&#8211;Villiger oxidation converts aldehydes to carboxylic acids and ketones to esters. The reaction uses peroxy acids or peracids and is often catalyzed by acid. The reaction is named after its pioneers, Adolf von Baeyer and Victor Villiger. The reaction is achieved by a wide range of peracids such as <em>m</em>-chloroperoxybenzoic acid (<em>m</em>CPBA), perbenzoic acid (C<sub>6</sub>H<sub>5</sub>COOOH), peracetic acid (CH<sub>3</sub>COOOH), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), and <em>tert</em>-butyl hydroperoxide (<em>t</em>-BuOOH).</p>
<p>The carbonyl center is activated by protonating the carbonyl oxygen. The peracid then adds across the C=O bond to give a tetrahedral intermediate called the Criegee intermediate. During the concerted intramolecular rearrangement that follows, the carbonyl group is restored, a group migrates from carbon to oxygen, and the weak peroxide bond cleaves to give an acid (if the substrate is an aldehyde) or an ester (if the substrate is a ketone).</p>
<p style="text-align: center"><img alt="Figure1" src="/files/ftp_upload/12341/12341_PT_Figure_1.svg" style="text-align: center; height: 275px;" /></p>
<p>The migratory aptitude of different groups follows the order of &#8211;H &#62; &#8211;CR<sub>3</sub> &#62; &#8211;CHR<sub>2</sub> &approx; &#8211;Ph &#62; &#8211;CRH<sub>2</sub> &#62; &#8211;&NoBreak;CH<sub>3</sub>. This makes Baeyer&#8211;Villiger oxidation regioselective. Also, the reaction retains the stereochemistry at the migrating center for asymmetrical substrates. Reactions involving cyclic ketones produce lactones.</p>

Reactions of Aldehydes and Ketones: Baeyer&amp;#8211;Villiger Oxidation

Reações de Aldeídos e Cetonas: Oxidação de Baeyer-Villiger

Baeyer&#8211;Villiger oxidation converts aldehydes to carboxylic acids and ketones to esters. The reaction uses peroxy acids or peracids and is often ...