Ionic Liquids: Synthesis and Applications in Catalysis
The use of ionic liquids (ILs) as a solvent and an electrolyte for electro organic synthesis has been reviewed
Table of Contents: Ionic liquids in organic synthesis
After separation of the organic and the aqueous layer, the amine can be recovered by addition of a strong base like NaOH or KOH to the acidic extract i.e., lidocaine synthesis. Note that amides are usually not basic enough to undergo the same protonation (pKa of conjugate acid: ~ -0.5).
Most neutral compounds cannot be converted into salts without changing their chemical nature. Many of these neutral compounds tend to react in undesired ways i.e., esters undergo hydrolysis upon contact with strong bases or strong acids. One has to keep this in mind as well when other compounds are removed. For instance, epoxides hydrolyze to form diols catalyzed by acids and bases. Ketones and aldehydes undergo condensation reactions catalyzed by both, acids and bases. Esters also hydrolyze to form carboxylic acids (or their salts) and the corresponding alcohol. In order to separate these compounds from each other, chromatographic techniques are often used, where the compounds are separated based on their different polarities (see Chromatography chapter).
Based on the discussion above the following overall separation scheme can be outlined. Which sequence is the most efficient highly depends on the target molecule. There is obviously no reason to go through the entire procedure if the compound sought after can be isolated in the first step already. Note that many of these steps are interchangeable in simple separation problems.
Functionalized ionic liquids (FILs) synthesized with specific desired chemical properties have shown promising results in various areas of organic synthesis. In supported organic synthesis, FILs have become known as a new alternative to commonly used PEG and fluorous soluble supports. This review summarizes the progress of recent development in the synthesis of functionalized ionic liquids with emphasis on their applications as reagents and scavengers in organic synthesis.
Ionic liquid as a support of organic and inorganic catalysts /
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 . Strictly speaking, the two operations are targeting different parts in the mixture: while the extraction removes the target compound from an impure matrix, the washing removes impurities from the target compound i.e., water by extraction with saturated sodium chloride solution. 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.e., 5 % NaOH, 5 % HCl), the miscibility of the solvent with water is a crucial point as well as the compatibility of the reagent with the compounds and the solvent of the solution to be extracted. Solvents like dichloromethane (=methylene chloride in older literature), chloroform, diethyl ether, or ethyl ester will form two layers in contact with aqueous solutions if they are used in sufficient quantities. Ethanol, methanol, tetrahydrofuran (THF) and acetone are usually not suitable for extraction because they are completely miscible with most aqueous solutions. However, in some cases it is possible to accomplish a phase separation by the addition of large amounts of a salt (“salting out”). Commonly used solvents like ethyl acetate (8.1 %), diethyl ether (6.9 %), dichloromethane (1.3 %) and chloroform (0.8 %) dissolved up to 10 % in water. Water also dissolves in organic solvents: ethyl acetate (3 %), diethyl ether (1.4 %), dichloromethane (0.25 %) and chloroform (0.056 %). 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.e., wet Jacobsen ligand in ethyl acetate. 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.e., benzoic acid) was deprotonated using a base or an amine (i.e., lidocaine) was protonated using an acid, it would become more water-soluble because the resulting specie carries a charge. Chlorinated solvents (i.e., dichloromethane, chloroform) exhibit a higher density than water, while ethers, hydrocarbons and many esters possess a lower density than water (see solvent table), thus form the top layer . One rule that should always be followed when performing a work-up process:
Never dispose of any layer away until you are absolutely sure (=100 %) that you will never need it again. 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.e., convert a carboxylic acid into a carboxylate by adding a base. Standard solutions that are used for extraction are: 5 % hydrochloric acid, 5 % sodium hydroxide solution, saturated sodium bicarbonate solution (~6 %) and water. 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.
N2 - Functionalized ionic liquids (FILs) synthesized with specific desired chemical properties have shown promising results in various areas of organic synthesis. In supported organic synthesis, FILs have become known as a new alternative to commonly used PEG and fluorous soluble supports. This review summarizes the progress of recent development in the synthesis of functionalized ionic liquids with emphasis on their applications as reagents and scavengers in organic synthesis.
Staff View: Ionic liquids in organic synthesis
For instance, if the target compound was the base in the system, the extraction with HCl should be performed first. Whatever remains in the organic layer is not of interest anymore afterwards, unless one of the other compounds has to be isolated from this layer as well. If the target compound was an acid, the extraction with NaOH should be performed first. This strategy saves steps, resources and time, and most of all, greatly reduces waste.
Practical Aspects of an Extraction
An extraction can be carried out in macro-scale or in micro-scale. In macro-scale, usually a separatory funnel (on details how to use it see end of this chapter) is used. Micro-scale extractions can be performed in a conical vial or a centrifuge tube depending on the quantities. Below are several problems that have been frequently encountered by students in the lab:
Salunkhe -- |g 16. |t Toward green processes for fine chemicals synthesis : biocatalysis in ionic liquid-supercritical carbon dioxide biphasic systems / |r Pedro Lozano, Teresa De Diego, Said Gmouh, Michel Vaultier and Jose L.
Ionic Liquids in Organic Synthesis - Sanjay V
APPLICATIONS OF IONIC LIQUIDS IN ORGANIC SYNTHESIS …
Ionic Liquids in Synthesis, ..
Ionic Liquids in Synthesis - Wiley Online Library
Recent Progress in Ionic Liquids and their Applications in Organic Synthesis ..
Molecules | Special Issue : Ionic Liquids in Organic Synthesis
Ionic Liquids in Synthesis
Ionic Liquids in the Chemical Synthesis of Pharmaceuticals
RING CLOSING METATHESIS
Powerful method for creating
Complex natural products
ILs v/s VOSs
Ionic liquid in synthesis
GREEN ASPECTS OF ILs
The preparation yield of Ionic liquid is as high as 99%.
Ionic Liquid and Microwave-Assisted Organic Synthesis: …
The use of this novel IL-phase in liquid-phase organic synthesis (LPOS) offers considerable advantages because the side product is removed by simple extraction and washings from the cleaved IL-phase, so no chromatography is necessary.
Ionic Liquids in Synthesis - Organic Chemistry Portal
FISCHER INDOLE SYNTHESIS
41–92% product yield was achieved by using chloroaluminate ionic liquid both as a solvent and catalyst.
The procedure proved safer with respect to the amount of catalyst, its hazard, and cost.
"Ionic Liquids in Synthesis" is a book ..
They are liquid below 100°C.
If they are liquid at room temperature, we call them room temperature ionic liquids (RTILs).
DIFFERENCE BETWEEN IONIC LIQUID AND IONIC SOLID
Traditional salts like sodium chloride are able to efficiently pack to form a crystal lattice
With ionic liquids, the cations are asymmetrically substituted with different length groups to prevent the packing of the cations/anions into a crystal lattice
STRUCTURE OF IONIC LIQUIDS
NO3-, ClO4-,HSO4- , Br- ,Cl- , I- , BF4- , CH3COO-
PROPERTIES OF IONIC LIQUIDS
Low vapour pressure
Excellent thermal stability
Recyclable and Reusable
Miscible with organic solvents /water
Good solubility in organic and inorganic materials.
18 crores ILs are accessible.
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