Water as Solvent for Organic and Material Synthesis - …

Most phenols are weak acids (pKa= ~10) and do not react with sodium bicarbonate, which is a weak base itself (pKa(H2CO3)=6.37, 10.3). However, they do react with a strong base like NaOH. This difference in acidity can be exploited to separate carboxylic acids and phenols from each other in an organic layer. While many phenols dissolve poorly in water (8.3 g/100 mL at 20 oC, log Kow=1.46), phenolates dissolve very well in aqueous solutions. After the extraction, the phenol can be recovered by adding a mineral acid to the basic extract.

Water as solvent in organic synthesis - ResearchGate

as photosensitive agents and as synthetic agents in organic and pharmaceutical chemistry.

Water as Solvent in Organic Synthesis | SpringerLink

Abstract: The increasing environmental consciousness of the chemical community has led to the search for alternative, non-polluting media and processes for chemical and organic synthesis (). Due to the natural abundance of water as well as the inherent advantages ...

Chemistry | Science of Synthesis: Water in Organic Synthesis

A broad and common class of non-aqueous solvents is called solvents; see the entry on for more about organic materials.If your solvents are , be aware that they can be ignited by the static electricity generated by pouring solvent from one container to another.

T1 - Near-critical water, a cleaner solvent for the synthesis of a metal-organic framework
Reusability of catalyst and elimination of organic solvents and oxidizing agents are advantages of this method.

What is an Aliphatic Ester? - Definition, Synthesis & Solvent

It has simple set-up and work-up and is environmentally friendly and the condition of the reactions are comparable to other methods but we avoided the use of organic bases, Lewis acids and solvents.3 3.

In this work a number of green chemistry-related improvements to the synthesis of tetrasubstituted imidazoles are reported.

Use of Water in Chemistry Synthesis | ACS Network

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.





Water as a potentially benign solvent for reactions and syntheses is discussed

Transitioning organic synthesis from organic solvents …

Many reactions produce heat; care must be taken when dealing with such situations. Frequently, stirring can be utilized as a means of dispersing the heat. Also, if the heating problem is anticipated, the reagents can be combined slowly to avoid excessive heating. Also keep in mind that although a reaction may be exothermic, it may be necessary to heat it to increase the rate at which the reaction occurs. For example, the synthesis of SnI4 from tin and I2 requires heat to begin the reaction. Once begun, the reaction produces heat and the external source of heat must be removed.