Name: separating mixtures with solvent extraction
Uploaded: 2020-03-26T07:22:28.000Z
Duration: 2 min 55 s
Channel: JoVE

La extracción es una técnica para separar los componentes de una mezcla. Ya está familiarizado con la extracción. Cada vez que remojas el té, estás extrayendo compuestos solubles en agua, como la cafeína y los sabores, de las hojas de té en el agua caliente. Este es un ejemplo de extracción sólido-líquido.
La extracción líquido-líquido es otro tipo de extracción en la que la mezcla se disuelve en dos fases líquidas inmiscibles. Los disolventes deben ser inmiscibles, es decir, no mezclarse y ser fases separadas. Las extracciones líquido-líquido se realizan en un embudo separador para que el solvente más denso se deposite en el fondo y el solvente menos denso se asiente en la parte superior. Luego, cada compuesto de soluto se transferirá a la fase en la que sea más soluble. Por lo tanto, es importante elegir solventes con diferentes polaridades.
En general, los solutos no polares se dividirán en la fase orgánica y los solutos polares se dividirán en la fase acuosa. El coeficiente de partición, K, es la relación entre la concentración de soluto en la fase orgánica y la de la fase acuosa. Una vez que los solutos se han separado, se recogen las dos fases diferentes. Tenga en cuenta que es probable que haya residuos de cada componente en ambas fases.
Una extracción ácido-base es un tipo especial de extracción líquido-líquido que separa los compuestos ácidos y básicos en función de las diferencias de solubilidad. Recordemos que un ácido es un compuesto que dona un protón cuando se disuelve en agua, y una base es un compuesto que acepta un protón.
Para separar los compuestos ácidos, se agrega una base a la mezcla. La base aceptará un protón del compuesto ácido, convirtiéndolo en iónico. Por el contrario, la adición de un ácido transferiría un protón a un compuesto básico. En ambos casos, el compuesto iónico se transferirá a la fase acuosa y los compuestos neutros se dividirán en la fase orgánica. El compuesto iónico se recoge y luego se desprotona o se reprotona para convertirlo de nuevo en su compuesto original.
En este laboratorio, separará una mezcla de celulosa, ácido benzoico y cafeína. En primer lugar, utilizará la extracción y la filtración para aislar la celulosa. Luego, realizará una extracción ácido-base para separar el ácido benzoico y la cafeína.

extracción

extracción
La extracción es una técnica común utilizada en química orgánica para aislar un compuesto objetivo. En el proceso de extracción, un soluto se transfiere de una fase a otra para separarlo de los materiales de partida no reaccionados o de las impurezas. La extracción también se utiliza para facilitar el aislamiento de un soluto de un solvente de reacción que es difícil de eliminar por evaporación, como un solvente con un punto de ebullición alto.<span style="color: rgb(0, 0, 0); familia de fuentes: Roboto, RobotoDraft, Helvetica, Arial, sans-serif; tamaño de fuente: 13px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; peso de la fuente: 400; espaciado entre letras: normal; huérfanos: 2; text-align: inicio; sangría de texto: 0px; text-transform: ninguno; espacio en blanco: pre-envoltura; viudas: 2; espaciado entre palabras: 0px; -webkit-text-stroke-width: 0px; color de fondo: RGB (255, 255, 255); text-decoration-style: inicial; text-decoration-color: inicial; Pantalla: en línea !importante; flotación: ninguno;" > Generalmente, hay tres tipos de extracciones. En primer lugar, en la extracción sólido-líquido, el soluto se transfiere de una fase sólida a una fase líquida. En la extracción líquido-líquido, un soluto se transfiere de un líquido a otro. En la extracción ácido-base, un soluto se transforma en un compuesto iónico y se transfiere de una fase orgánica a una fase acuosa. Un ejemplo común de extracción es la preparación de café o té. La fase sólida, que contiene la cafeína, los sabores y los olores de las plantas, se extrae mediante el agua caliente en la fase líquida.
Extracción líquido-líquido
Una extracción líquido-líquido transfiere un compuesto orgánico que se disuelve en una fase acuosa a un solvente orgánico, o se utiliza para transferir reactivos, sales y otras impurezas solubles en agua sin reaccionar a la fase acuosa mientras deja el compuesto orgánico de interés en la fase orgánica. Los líquidos inmiscibles son líquidos que nunca forman una solución homogénea, incluso cuando se mezclan completamente. En cambio, los líquidos inmiscibles se separan en diferentes fases, como el aceite y el agua.
Una extracción líquido-líquido transfiere un compuesto orgánico que se disuelve en una fase acuosa a un disolvente orgánico. Para realizar una extracción líquido-líquido, primero se agrega la solución acuosa que contiene el soluto a un embudo separador. A continuación, se añade un disolvente orgánico no soluble en agua al embudo de separación. Cuando el contenido del embudo se mezcla bien, el compuesto orgánico se divide en la fase orgánica en función de su mayor solubilidad en la fase orgánica que en la fase acuosa.
Dado que los dos disolventes son inmiscibles, los dos líquidos forman capas discretas, con el líquido denso en la parte inferior y el líquido menos denso en la parte superior. Una vez que las dos fases se vuelven a asentar en dos capas, se separan abriendo la llave de paso en la parte inferior del embudo de separación y permitiendo que una capa fluya. El líquido al que se le eliminó el soluto se llama refinado, mientras que el líquido que obtuvo el soluto se llama extracto.
El compuesto orgánico se reparte entre las dos capas en función de su solubilidad en cada fase. El equilibrio se alcanza cuando el potencial químico del soluto es el mismo en las dos fases. El coeficiente de partición de un soluto, K, es la relación entre la concentración de la muestra en la capa orgánica y la concentración en la fase acuosa. El coeficiente de partición es una constante que depende tanto del soluto como del par de disolventes utilizados en la extracción. El coeficiente de partición es una expresión de preferencia del soluto para cada uno de los dos disolventes. Los solutos con un coeficiente de partición grande tienen una mayor tendencia a ser extraídos en la capa de solvente orgánico. Los solutos con coeficientes de partición pequeños prefieren pasar a la fase acuosa.
Determinar qué par de disolventes utilizar para una extracción líquido-líquido es un paso vital. Tenga en cuenta lo siguiente a la hora de elegir qué disolventes utilizar: En primer lugar, el soluto debe ser más soluble en el disolvente que en el agua. Por lo tanto, es necesario conocer el coeficiente de partición del soluto en un par de solventes potenciales. En segundo lugar, el par de disolventes debe ser inmiscible en agua y no formar una solución homogénea cuando se mezcla. En tercer lugar, los disolventes deben ser inertes y no reaccionar con el soluto. El solvente también debe ser volátil para que pueda eliminarse fácilmente del soluto. El solvente orgánico inmiscible en agua generalmente posee una polaridad no polar o baja.
También es fundamental conocer las densidades de los disolventes para determinar las identidades de las capas superior e inferior. La mayoría de los líquidos orgánicos tienen una densidad más baja que el agua, con la excepción de los solventes orgánicos clorados, y se depositarán en el fondo del embudo de separación.
Extracción ácido-base
La extracción ácido-base es un tipo de extracción líquido-líquido que separa los compuestos orgánicos en función de sus propiedades ácido-base. Si un soluto es un ácido o una base, su carga cambia a medida que cambia el pH. En general, la mayoría de los compuestos orgánicos son neutros y, por lo tanto, más solubles en disolventes orgánicos que en agua. Sin embargo, si el compuesto orgánico se vuelve iónico, entonces se vuelve más soluble en agua. Esto es útil para extraer un ácido orgánico o compuesto base de una fase orgánica a una fase acuosa.
La extracción ácido-base aprovecha esta propiedad transformando el soluto en su forma de sal soluble en agua, cambiando así su solubilidad. La solubilidad del compuesto orgánico y su sal debe ser drásticamente diferente para que la técnica sea efectiva.
Por ejemplo, considere una mezcla que contiene un ácido carboxílico orgánico, una amina y un compuesto neutro. Los ácidos carboxílicos que constan de seis carbonos o más son insolubles en agua y totalmente solubles en disolventes orgánicos. Sin embargo, sus bases conjugadas (un compuesto iónico) son solubles en agua e insolubles en disolventes orgánicos. Una amina que consta de al menos siete carbonos es insoluble en agua, pero soluble en solventes orgánicos. El ácido conjugado de esa amina (un compuesto iónico) es soluble en agua e insoluble en disolventes orgánicos.
Cuando reacciona con una base, el ácido carboxílico se neutraliza a su forma de sal. Los demás compuestos de la mezcla permanecen neutros. Una vez que el ácido carboxílico se transforma en una sal, se dividirá a la fase acuosa, mientras que los compuestos neutros permanecen en la fase orgánica.
La extracción ácido-base también se utiliza para separar dos ácidos débiles o dos bases débiles con una diferencia significativa en su pKa. En el caso de los ácidos, el ácido relativamente más fuerte, que tiene un valor de pKa pequeño, se neutraliza a una sal utilizando una base débil. La base débil no reacciona eficientemente con el ácido más débil, y solo el ácido más fuerte se transforma en una sal. A continuación, la sal se extrae en la fase acuosa durante la extracción. El proceso sigue de manera similar para las bases débiles, donde la base relativamente más fuerte se neutraliza a una sal usando un ácido débil.
Referencias
<ol>
	<li style="font-size:17px">Harris, D.C. (2015). Análisis químico cuantitativo. Nueva York, NY: W.H. Freeman and Company.</li>
</ol>

Extracción

Extracción
La extracción es una técnica común utilizada en química orgánica para aislar un compuesto objetivo. En el proceso de extracción, se transfiere un soluto ...

Education

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JoVE Lab Manual

Chemistry

Química

Extraction

separating mixtures with solvent extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point.

There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase into a liquid phase. In liquid-liquid extraction, the solute moves from one liquid into another. In acid-base extraction, the solute is changed into an ionic compound and moved from an organic phase into an aqueous phase. A familiar example is brewing coffee or tea, where hot water extracts caffeine, plant flavors, and odors from the solid material.

Liquid-liquid extraction is used when an organic compound is dissolved in water or when water-soluble impurities need to be removed from an organic product. It works with immiscible liquids, which are liquids that do not form one uniform solution, even after mixing. Oil and water are a common example. To carry out this extraction, the aqueous solution is placed in a separatory funnel, and a non-water-soluble organic solvent is added. After mixing, the compound partitions into the phase where it is more soluble.

Because the two liquids are immiscible, they separate into layers after settling. The denser liquid forms the bottom layer, and the less dense liquid stays on top. The layers are then separated by opening the stopcock at the bottom of the separatory funnel and letting one layer drain out. The layer that loses the solute is called the raffinate, and the layer that gains the solute is called the extract. At equilibrium, the solute has the same chemical potential in both phases.

The partition coefficient, K, describes how a solute divides between the two layers. It is the concentration in the organic layer divided by the concentration in the aqueous layer. This value depends on the solute and the solvent pair used. A large partition coefficient means the solute prefers the organic layer. A small partition coefficient means the solute prefers the aqueous layer. Choosing the right solvent pair is important, so the solute should be more soluble in that solvent than in water, the two solvents should be immiscible, and the solvents should be inert and volatile. The water-immiscible organic solvent is usually non-polar or low in polarity.

Knowing density is also important because it tells which layer is on top and which is on the bottom. Most organic liquids are less dense than water and rise to the top, although chlorinated organic solvents are an exception and can settle to the bottom. Acid-base extraction is a special type of liquid-liquid extraction that separates organic compounds based on acid-base behavior. When pH changes, the charge on an acid or base can change too. Neutral organic compounds are usually more soluble in organic solvents, but ionic forms are more soluble in water.

This property lets chemists turn an organic acid or base into a water-soluble salt. The salt and the neutral compound must have very different solubilities for the method to work well. For example, a mixture may contain an organic carboxylic acid, an amine, and a neutral compound. Carboxylic acids with six carbons or more are insoluble in water and soluble in organic solvents, but their conjugate bases are water-soluble and insoluble in organic solvents. Amines with at least seven carbons are insoluble in water and soluble in organic solvents, while their conjugate acids are water-soluble and insoluble in organic solvents.

When a base is added, the carboxylic acid is neutralized to its salt form, while the other compounds remain neutral. The salt then moves into the aqueous phase, and the neutral compounds stay in the organic phase. Acid-base extraction can also separate two weak acids or two weak bases when their pKa values are far enough apart. For weak acids, the stronger acid with the smaller pKa is converted to a salt using a weak base, while the weaker acid is not reacted much. The same idea applies to weak bases, but a weak acid is used to neutralize the stronger base.

Separating Mixtures with Solvent Extraction

separating-mixtures-with-solvent-extraction

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Learn how solvent extraction separates mixtures in organic chemistry, including liquid-liquid extraction, separatory funnels, partition coefficients, and acid-base extraction.

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Separating Mixtures with Solvent Extraction

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