Extraction is one of the most common and often used techniques in organic chemistry. It is a common way of separating a desired compound from a mixture. The separation itself is usually based on polarity differences between the molecule you are interested in isolating and the other components of the mixture. Often times a chemical reaction is needed to alter the polarity of one of the components of the mixture.
Monday, December 30, Extraction Part 1 After a reaction is completed, the solution often times does not only contain the desired product, but also undesired byproducts of the reaction, unreacted starting material s and the catalyst if it was used.
These compounds have to be removed in the process of isolating the pure product. A standard method used for this task is an extraction or often also referred to as washing.
Strictly speaking, the two operations are targeting different parts in the mixture: Washing is also used as a step in the recrystallization procedure to remove the impurity containing mother liquor adhering to the crystal surface.
Many liquid-liquid extractions are based on acid-base chemistry. The liquids involved have to be immiscible in order to form two layers upon contact. Since most of the extractions are performed using aqueous solutions i.
Ethanol, methanol, tetrahydrofuran THF and acetone are usually not suitable for extraction because they are completely miscible with most aqueous solutions. Commonly used solvents like ethyl acetate 8. Water also dissolves in organic solvents: Oxygen containing solvents are usually more soluble in water and vice versa because of their ability to act as hydrogen bond donor and hydrogen bond acceptor.
The higher water solubility lowers the solubility of weakly polar or non-polar compounds in these solvents i.
Other solvents such as alcohols increase the solubility of water in organic layers significantly because they are miscible with both phases and act as a mediator. This often leads to the formation of emulsions. The most important point to keep in mind throughout the entire extraction process is which layer contains the product.
For an organic compound, it is relatively safe to assume that it will dissolve better in the organic layer than in most aqueous solutions unless it has been converted to an ionic specie, which makes it more water-soluble. If a carboxylic acid i. One rule that should always be followed when performing a work-up process: The only time that you can really be sure about it is if you isolated the final product in a reasonable yield, and it has been identified as the correct compound by melting point, infrared spectrum, etc.
Keep in mind that it is always easier to recover the product from a different layer in a beaker than from the waste container or the sink.
In this context it would be wise to label all layers properly in order to be able to identify them correctly later if necessary. In order to separate compounds from each other, they are often chemically modified to make them more ionic i. Standard solutions that are used for extraction are: All of these solutions help to modify the organic compound and make it more water-soluble and therefore remove it from the organic layer.
More concentrated solutions are rarely used for extraction because of the increased evolution of heat during the extraction, and potential side reactions with the solvent.
What do I use when to extract? The carboxylic or mineral acid and the base react to form a sodium salt, which is usually exhibits a higher solubility in aqueous solutions due to its negative charge and higher polarity as indicated by a more negative log Kow value i.
Which of the two reagents should be used depends on the other compounds present in the mixture. Sodium hydroxide is usually easier to handle because it does not evolve carbon dioxide as a byproduct.
In addition, the concentration can be increased significantly if is needed. However, if compounds were present that are sensitive towards strong bases or nucleophiles i.
It does not react with these compounds because it is a weaker base and a weak nucleophile due to its resonance stabilization.
Note that the formation of carbon dioxide as a byproduct causes a pressure build-up in the separatory funnel, the centrifuge tube or the conical vial. Thus, additional precautions i.
The target compound can subsequently be recovered by adding a mineral acid to the basic extract i.Largest & Most Skilled Sales Force in the Country.
Continuous training to ensure up to date knowledge. Extraction is one of the most common and often used techniques in organic chemistry. It is a common way of separating a desired compound from a mixture. The separation itself is usually based on polarity differences between the molecule you are interested in isolating and the other components of the mixture.
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