Ethers are organic compounds that have an oxygen atom between two hydrocarbon chains. They are derivatives of alcohols and are represented by the symbol (ROR’). While esters have a carbonyl carbon bonded to an oxygen atom further bonded to an alkyl group. The (-COOR) group represents an ester. They are the derivatives of carboxylic acids.
A functional group is an atom or group of atoms that impart certain physical and chemical properties to a compound. It plays a pivotal role in naming an organic compound.
The first carbon that is attached to the functional group is known as alpha carbon and the carbon next to alpha carbon is known as beta carbon.
Difference between Ethers and Esters
The ether functional groups have an oxygen atom that forms a single bonds with two carbon atoms
The ester functional groups have a carbonyl group bonded to an oxygen atom which is further bonded to an alkyl group
The general formula of ethers is
The general formula of esters is
Ethers may be symmetrical or asymmetrical
Esters are always asymmetrical
Ethers are named as
The name of esters end with a suffix “-ate”
Their melting and boiling points are lower than esters
Their melting and boiling points are higher than ethers
They are derived from alcohols
They are derived from carboxylic acids
Ethers contain sigma bonds only
Esters contain sigma as well as pi bonds
They are less reactive than esters
They are more reactive than ethers
Ethers are hydrolyzed into alcohols
Esters are hydrolyzed into alcohols and carboxylic acid
They have sweet and slightly pungent smell
Esters have fruity smell
They are non-polar in nature
Esters are polar compounds
They can be used as anesthetics
They can be used as synthetic flavors and perfumes
Nomenclature of ethers and esters
The common names of ethers include names of two alkyl groups ending with the word ether. For naming the symmetrical ethers, the prefix “-di” is used with the name of the alkyl group.
For example, ethyl methyl ether, and dimethyl ether, etc.
Esters on the other hand are named with carboxylic acid functionality along with the addition of an alkyl name.
For example, methyl acetate, and ethyl propionate, etc.
In IUPAC system of ethers nomenclature, smaller alkyl groups with oxygen are named alkoxy groups while the larger alkyl groups are taken as parent molecules.
Esters are formed by the combination of alcohols and carboxylic acids. Their names are derived from the same alcohols and acids because of which the names of the esters consist of two separate words:
- The first word is the name of the R group from the alcoholic part, it is named by adding the suffix ‘-yl’.
- The second word is the name of carboxylic acid, the suffix ‘-ic’ is replaced by the ‘-ate’.
Properties of ethers and esters
Solubility of ethers vs Esters
The lower ethers (up till C3) are soluble in water but their solubility decreases as the chain length increases.
Dimethyl ether has more solubility in water because its extent of hydrogen bonding with water molecules is larger as compared to diethyl ether which has lesser solubility.
The low molecular weight esters are also soluble in water due to one-sided hydrogen bonding. The solubility of the esters falls as the chain length of the esters increases. They are, however, soluble in common organic solvents.
The solubilities of methyl ethanoate and ethyl propanoate are as:
Methyl ethanoate = 24.4 g/100ml (water)
Ethyl propanoate = 1.7 g/100ml (water)
Boiling points of ethers vs esters
Ethers with similar molecular weight or sometimes with the same molecular formula, when compared with alcohols, have a lower boiling point. This is because of the presence of strong hydrogen bonding in alcohols. While comparing with esters, ethers have again lower boiling points because of the lesser possibility to make hydrogen bonding with water hydrogens. The boiling points of ethers are close to the hydrocarbons.
For example, the boiling point for dimethyl ether is -24 ºC.
The boiling points of esters are lower than alcohol and carboxylic acid of similar molecular weight. This is because of the presence of strong hydrogen bonding in the alcohols and acids. However, the boiling points of esters are close to those of aldehyde and ketones of similar molecular weights.
The boiling points of esters are higher than ethers.
For example, the boiling point for ethyl acetate is 77 ºC.
Colors and smells of ethers vs esters
Ethers are colorless volatile liquids. They have a pleasant and distinctive odor and are highly flammable.
Esters are colorless volatile liquids and low melting solids and they have fruity smells.
Densities of ethers and esters
Ethers are less dense than water but their densities are higher than hydrocarbons of similar molecular weight and the densities of esters are lesser than water too. This is the reason ester layers float on top of aqueous layers.
Hydrogen bonding in ethers vs esters
The lower ethers like dimethyl ether etc can form hydrogen bonds between the hydrogen atoms of the water molecules and their own oxygen atoms. As chain length increases, this ability of the formation of hydrogen bonds decreases.
Similarly, esters cannot form hydrogen bonds, but they can form a hydrogen bond with the hydrogen of water molecules and their oxygen atoms.
Preparation of Ethers and esters
1. Dehydration of alcohols
Alcohols undergo intermolecular dehydration on heating with conc. H2SO4, resulting in the formation of symmetrical ethers. It involves the SN2 mechanism.
2. Williamson’s Synthesis of ethers
In Williamson’s synthesis, ethers are prepared by treating alkoxide or phenoxide with an alkyl halide. This synthesis involves the SN2 mechanism in which a halide ion from alkyl halide is displaced by the alkoxide or a phenoxide ion. This method is used for the synthesis of symmetrical as well as asymmetrical ethers.
3. Alkoxymercuration-de-Mercuration of alkenes
The alkoxymercuration-demercuration can be used for the synthesis of every kind of ether. It is a reaction in which an alkene is reacted with an alcohol in the presence of mercuric acetate. This reaction produces alkoxymercury intermediate which then reduces to ether in the presence of sodium borohydride.
1. Fischer esterification
When alcohols are treated with a carboxylic acid in the presence of mineral acids such as H2SO4 and dry HCl, esters are formed and the reaction is known as “Fischer esterification”. It is an important ester preparing reaction.
It is a reversible reaction, and the ester yield can be increased by removing water from the reaction mixture as it gets formed.
2. Esters by the use of diazomethane
When a carboxylic acid is reacted with diazomethane in ethereal solutions, methyl esters are prepared. This reaction is limited due to the high price and hazardous nature of diazomethane.
3. Esters from acyl chloride
Acyl chlorides are reacted with alcohols which result in the formation of esters. This reaction occurs rapidly due to the high reactivity of acid chlorides. It is an irreversible reaction because of the greater stability of esters than acid chloride.
Reactions of ethers and Esters
Hydrolysis of ether vs esters
When ethers are heated with water in the presence of sulphuric acid they undergo hydrolysis and form alcohols. This reaction is the reverse of etherification and follows the SN2 mechanism.
When the esters are heated with water in the presence of mineral acids or alkali, they hydrolyze, resulting in alcohol and carboxylic acid formation.
It is a reaction in which ester is refluxed with an alcohol in the presence of strong H2SO4 and dry HCl or a base. It results in the displacement of -OR group of an ester with another -OR group. This reaction is also called alcoholysis.
Ethers do not show alcoholysis.
Uses of Ethers and Esters
- Ethers are used as solvents for fats, oils, resins, gums, dyes, and hydrocarbons because of their inertness to many reagents. They can dissolve both polar and nonpolar substances. They can also solvate cations by donating electron pairs from their oxygen atoms.
- Dimethyl ether is used as an anesthetic for surgical procedures.
- Dimethyl ether can also be used as a propane substitute in LPG. Liquified petroleum gasses are used in industrial and domestic level fuels.
- Methoxy benzene is used in the production of polyesters.
- Tetrahydrofuran, dioxane, dimethoxyethane are used in the pharmaceutical industries.
- Esters are used in making perfumes because of their sweet smell. They are also used in foods for flavorings.
- Insecticides, miticides, and fumigants for soil are also the products of ethers.
- Diphenyl ether is widely used in the soap industry as a fragrance and as a processing aid in the production of polyesters.
- Naturally, esters are used to make pheromones.
- Natural fats are fatty acid esters of glycerol.
- Esters are used as flavors and perfumes because of their pleasant or fruity smell.
- Esters are used as food flavors and cosmetics too because of the intense fragrance of some esters.
- Isoamyl phenylacetate is used for chocolate flavoring.
- They are used in the preparation of soaps due to the process of hydrolysis in the presence of an alkali.
- The volatile esters are used as organic solvents.
- Some esters are used in the medical industry as well.
- Phenyl salicylate is used in the treatment of rheumatic arthritis.
- Polyesters are used to make plastics.
- Nitrate esters are used for making explosives.
- DNA is composed of phosphate esters.
Are esters more reactive or ethers?
Esters are more reactive than ethers because of the presence of polarity i.e. charge separation. Esters contain a carbonyl group which is highly electrophilic while ethers lack the carbonyl group functionality.
How are esters formed?
Esters are the derivatives of carboxylic acids. When the carboxylic acid reacts with alcohols in the presence of mineral acids, esters are formed. This reaction is known as the esterification reaction.
Esters are also formed by the use of diazomethane and other derivatives of carboxylic acid like acid chlorides and acid anhydrides.
Are ethers acid or basic?
Ethers are basic due to their ability to lose electron pairs present on the oxygen atom. When ethers are reacted with strong acids such as H2SO4, they produce highly reactive salts.
Why do esters have a higher boiling point than ethers?
Esters contain the carbonyl group which is polar in nature while ethers lack the carbonyl group. The dipole-dipole interaction in the esters is stronger than the ethers which is the reason, they have high boiling points.
Why are ethers not used for anesthesia anymore?
Diethyl ether is highly flammable and can cause severe damage if not handled properly. This is the reason, it is no longer used in surgical and anesthetic techniques.
Why do we add sodium carbonate at the end of esterification reactions?
Sodium carbonate solution (5%) is added at the end of esterification reactions because it neutralizes unreacted carboxylic acid, if present in the reaction mixture.
When Na2CO3 reacts with carboxylic acids, carbon dioxide gas evolves which can be seen. When no further acid will be present in the reaction mixture, bubbles will stop coming out.
Are ethers soluble in water?
Ethers are less soluble in water because they can form hydrogen bonds only with an oxygen atom to the hydrogen atom of the water molecule. Their miscibility decreases as the chain length increases.
Can LiAlH4 reduce ethers?
LiAlH4 reduces those functional groups which contain carbonyl groups like esters, carboxylic acid, amide, etc. It does not reduce non-polar bonds. Ethers contain non-polar bonds with no carbonyl group. So, it cannot be reduced by LiAlH4.
What is an ester linkage?
In esters, the bond formed between the carbonyl carbon and the oxygen atom having an alkyl or aryl group is known as the ester bond. In biochemistry, the ester bond is referred to as ester linkage.
What is an ether linkage?
Ethers are organic compounds that have an oxygen atom that forms a single bond with two carbon atoms. Such linkage is known as ether linkage.
Why are ethers kept in brown bottles?
Ethers are very sensitive to light because they react with oxygen to form peroxides that are explosive in the presence of light. The brown-colored bottles called amber bottles stop the entrance of UV light, so the ethers are kept in brown bottles for safety purposes.
- Organic Chemistry: Principles and Mechanisms Third Edition by Joel Karty