Hydroylysis of esters vs ethers
Classification of chemical compounds makes it easier to analyze their properties within the group as a whole. Both esters and ethers are types of functional classes of chemical compounds that are extensively produced, used and has industrial values.
The difference between ester and ether lies in their chemical structure. The main difference between Ester and Ether is that an ester group needs two Carbon atoms and two Oxygen atoms to complete its characteristic structure. An ester group needs only one Oxygen atom and two Carbon atoms for its structure. What is Ester As mentioned above, an ester group needs two Oxygen atoms and two carbon atoms for the completion of its structure.
Esters are produced as a derivative of carboxylic acids. This step makes esters less reactive when compared to carboxylic acids. Carbonyl refers to a group that has an Oxygen atom doubly bonded to a Carbon atom. Due to this carbonyl group, the esters are easily polarizable. Esters are more polar when compared to ethers, however, less polar when compared to carboxylic acids.
For example, Butyl Acetate. The concept of ester formation can also be extended to inorganic compounds. Ex: Triphenyl Phosphate, which is a phosphate ester. Furthermore, such substitution reactions of alcohols and ethers are rare, except in the presence of strong mineral acids. Clearly, the mechanism by which acylation reactions occur must be different from the SN1 and SN2 procedures described earlier.
In any substitution reaction two things must happen. The bond from the substrate to the leaving group must be broken, and a bond to the replacement group must be formed. The timing of these events may vary with the reacting system.
In nucleophilic substitution reactions of alkyl compounds examples of bond-breaking preceding bond-making the SN1 mechanism , and of bond-breaking and bond-making occurring simultaneously the SN2 mechanism were observed. On the other hand, for most cases of electrophilic aromatic substitution bond-making preceded bond-breaking. As illustrated in the following diagram, acylation reactions generally take place by an addition-elimination process in which a nucleophilic reactant bonds to the electrophilic carbonyl carbon atom to create a tetrahedral intermediate.
This tetrahedral intermediate then undergoes an elimination to yield the products. In this two-stage mechanism bond formation occurs before bond cleavage, and the carbonyl carbon atom undergoes a hybridization change from sp2 to sp3 and back again. The facility with which nucleophilic reagents add to a carbonyl group was noted earlier for aldehydes and ketones. Acid and base-catalyzed variations of this mechanism will be displayed in turn as the "Mechanism Toggle" button is clicked.
Also, a specific example of acyl chloride formation from the reaction of a carboxylic acid with thionyl chloride will be shown. The number of individual steps in these mechanisms vary, but the essential characteristic of the overall transformation is that of addition followed by elimination. Acid catalysts act to increase the electrophilicity of the acyl reactant; whereas, base catalysts act on the nucleophilic reactant to increase its reactivity.
In principle all steps are reversible, but in practice many reactions of this kind are irreversible unless changes in the reactants and conditions are made. The acid-catalyzed formation of esters from carboxylic acids and alcohols, described earlier , is a good example of a reversible acylation reaction, the products being determined by the addition or removal of water from the system. The reaction of an acyl chloride with an alcohol also gives an ester, but this conversion cannot be reversed by adding HCl to the reaction mixture.
Mechanisms of Ester Cleavage Esters are one of the most common carboxylic derivatives. Cleavage of the alkyl moiety in an ester may be effected in several different ways, the most common being the acyl transfer mechanism described above; however, other mechanisms have been observed. For examples and further discussion Click Here. Thus far we have not explained the marked variation, noted above , in the reactivity of different carboxylic acid derivatives.
The distinguishing carbonyl substituents in these compounds are: chloro acyl chlorides , acyloxy anhydrides , alkoxy esters and amino amides. They are therefore inductively electron withdrawing when bonded to carbon, as shown in the diagram on the right. The consequences of such inductive electron withdrawal on the acidity of carboxylic acids was previously noted. By clicking the "Toggle Effect" button the electron shift in both effects will be displayed sequentially.
This competition between inductive electron withdrawal and conjugative electron donation was discussed earlier in the context of substituent effects on electrophilic aromatic substitution. In the illustration on the right, R and Z represent the remainder of a benzene ring. Inductive electron withdrawal by Y increases the electrophilic character of the carbonyl carbon, and increases its reactivity toward nucleophiles.
Resonance electron donation by Y decreases the electrophilic character of the carbonyl carbon. The strongest resonance effect occurs in amides, which exhibit substantial carbon-nitrogen double bond character and are the least reactive of the derivatives. An interesting exception to the low reactivity of amides is found in beta-lactams such as penicillin G.
The angle strain introduced by the four-membered ring reduces the importance of resonance, the non-bonding electron pair remaining localized on the pyramidally shaped nitrogen. Finally, anhydrides and esters have intermediate reactivities, with anhydrides being more reactive than esters. Carbonyl Reactivity and IR Stretching Frequency An interesting correlation between the reactivity of carboxylic acid derivatives and their carbonyl stretching frequencies exists.
For a discussion of this topic Click Here. From the previous discussions you should be able to predict the favored product from each of the following reactions. The acyl derivative is the reactant on the left, and the nucleophilic reactant is to its right. Click the "Show Products" button to display the answers.
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The flexibility of the angles allows for certain physical properties of the compounds, like lower melting point and increased volatility. The presence of the carbonyl group also increases the polarity of the compound as the charge developed can be distributed to the carbon and oxygen to generate a stable structure. Esters are mostly used in food industries for the incorporation of the aroma of many fruits like apples, bananas, pears, etc.
Esters also occur in fats in the form of trimesters which are essential for the structure and energy of living systems. Ether Definition Ether General Structure Ether is a group of organic compounds consisting of the ether group -O- connecting two alkyl or aryl groups.
Ethers can be broadly classified as symmetrical and mixed or asymmetrical ethers depending on the type of alkyl or aryl groups present on the sides of the oxygen atom. If the same alkyl or aryl groups are present, it is a simple or symmetrical ether, but if the groups are different, the ethers are called mixed or asymmetrical ethers. Ethers are more acidic than simple hydrocarbons as well as esters, as the oxygen atom is more electronegative than carbon.
Ethers usually have a lower boiling point and are less soluble than the respective alcohols. These occur in the form of pleasant-smelling colorless liquid. Different ethers have different applications in various industrial fields as some are essential in medicine and pharmacology for the preparation of anesthetics.
Ethyl ether, in particular, is used as an excellent solvent for the extraction of various chemicals. The ability of ethers to be used as solvents due to the possibility of the formation of hydrogen bonds with other molecules. Ethers can be prepared artificially by the dehydration of alcohols and alkyl halide. The most popular method of synthesis of ethers is via the Williamson ether synthesis.
Ether is a group of organic compounds consisting of the ether group -O- connecting two alkyl or aryl groups. Functional group The functional group in ester is —COO- which is also called the ester group. The functional group in ether is —O- which is also called the alkoxy group. Carbonyl group Esters contain a carbonyl group.
No carbonyl group is present in ethers. Ethers are named alkoxyalkanes. Esters are derived from carboxylic acids. Ethers are derived from alcohol. Soaps are made using this chemical reaction and the process for making soaps is known as saponification. The steps for the mechanism of ester hydrolysis are as follows- In the first step, the electrophile is attacked by the hydroxide nucleophile at the carbonyl carbon atom. The intermediate formed in this step is a tetrahedral intermediate.
When the intermediate is lost, the carbonyl carbon atom loses the alkoxide group. In this reaction, an equilibrium exists between acid and base reaction and the acid workup allows carboxylic acid to obtain from the reaction and the base allows alcohol to be formed. Applications of Ester Hydrolysis The applications of ester hydrolysis are as follows- Soaps are synthesised in laboratories by the chemical reaction of ester hydrolysis.
These soaps are further of two kinds- soft and hard soaps. Hard soaps are composed of sodium hydroxide and soft soaps are made of potassium hydroxide. Fire extinguishers are made using ester hydrolysis and they work in a similar mechanism to that of saponification reaction. Using ester hydrolysis sodium acetic acid salts can be made. We hope this article was helpful for preparing for exams.
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The acid will release hydrogen ions in the solution which act as a catalyst auto-catalysis for the reaction. This is why the reaction is slow in the beginning.
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