Name: making ethers by dehydration and synthesis
Uploaded: 2023-04-30T18:28:34.000Z
Duration: 2 min 29 s
Channel: JoVE

The two most common methods for preparing ethers from alcohols are alcohol dehydration and Williamson ether synthesis.
Alcohol dehydration is used for the industrial preparation of ethers. The method involves acid-catalyzed dehydration of alcohols via the SN2 mechanism.
Consider the dehydration of ethanol in the presence of sulfuric acid to give diethyl ether.
The reaction begins with a proton transfer from the acid catalyst to the hydroxyl group of ethanol, forming an oxonium ion. The proton transfer converts hydroxyl, a poor leaving group, into an oxonium ion, a better leaving group.
Subsequently, a second ethanol molecule, acting as a nucleophile, attacks the oxonium ion in an SN2 reaction and displaces a water molecule, forming a new oxonium ion.
Finally, proton transfer from the new oxonium ion to water completes the reaction, giving ethoxyethane as the final product.
The alcohol dehydration method is limited to the preparation of symmetrical ethers derived from primary alcohols. Secondary and tertiary alcohols cannot be used because they dehydrate to alkenes.
Additionally, the method is unfit for the preparation of asymmetrical ethers because it yields a mixture of ethers.
A more general method for preparing ethers is the Williamson ether synthesis. It is a two-step process and provides an important route for preparing asymmetrical ethers.
A specific example is the synthesis of ethoxypropane from propanol.
The reaction begins with alcohol deprotonation, where propanol reacts with sodium hydride, a strong base, to form an alkoxide ion.
The second step is an SN2 reaction wherein the alkoxide ion acts as a nucleophile and displaces the iodide ion, forming the ether.
The Williamson ether synthesis prefers methyl or primary alkyl halides as substrates because they are less hindered and have high SN2 reactivity.
In contrast, secondary or tertiary alkyl halides are less preferred, as they are more hindered and undergo elimination instead.

ethers from alcohols: alcohol dehydration and williamson ether synthesis

Ethers from Alcohols: Alcohol Dehydration and Williamson Ether Synthesis

<h4>Overview</h4>
Ethers can be prepared from organic compounds by various methods. Some of them are discussed below,
<h4>Preparation of Ethers by Alcohol Dehydration</h4>
In this method, in the presence of protic acids, alcohol dehydrates to produce alkenes and ethers under different conditions. For example, in the presence of sulphuric acid, dehydration of ethanol at 413 K yields ethoxyethane, whereas it yields ethene at 443 K.
<img alt="Chemical reaction diagram; dehydration of ethanol using H2SO4 at different temperatures, forming ethylene." src="/files/ftp_upload/11731/11731%20PT%20Figure%201v2.svg" style="text-align: center; height: 200px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
This method is a nucleophilic substitution reaction. The two alcohol molecules involved in the reaction play two roles&#8212;one alcohol molecule acts as a substrate while the other acts as a nucleophile. The reaction follows an SN2 mechanism. The dehydration of secondary and tertiary alcohols to get corresponding ethers is unsuccessful as alkenes are formed easily in these reactions.
<h4>Preparation of Ethers by Williamson Ether Synthesis</h4>
It is the most versatile method for the preparation of asymmetrical ethers in laboratories. In this method, initially, the alcohol is deprotonated to form an alkoxide ion. Further, the alkoxide ion functions as a nucleophile and attacks an alkyl halide, leading to the formation of ether. The reaction generally follows the SN2 mechanism for primary alcohol.
<img alt="SN2 reaction mechanism diagram showing nucleophilic substitution of alkoxide ion." src="/files/ftp_upload/11731/11731%20PT%20Figure%202v2.svg" style="text-align: center; height: 75px;" data-altupdatedat="1761830439000" data-alt="Figure2" />
Williamson synthesis exhibits higher productivity when the halide to be displaced is on a methyl or a primary carbon. In the case of secondary alkyl halides, elimination competes with substitution, whereas the formation of elimination products is the only case in tertiary alkyl halides.

Overview
Ethers can be prepared from organic compounds by various methods. Some of them are discussed below,
Preparation of Ethers by Alcohol Dehydration
...

ethers-from-alcohols-alcohol-dehydration-williamson-ether

Education

JoVE Core

Organic Chemistry

Unit 1

Ethers, Epoxides, Sulfides

KEY TERMS AND CONCEPTS

making ethers by dehydration and synthesis

Ethers can be made from alcohols by dehydration and by Williamson ether synthesis. These two routes show how alcohols can act in different roles during ether formation. The first method uses a protic acid, while the second method uses an alkoxide ion and an alkyl halide.

In alcohol dehydration, the alcohol loses water in the presence of a protic acid such as sulfuric acid. Ethanol gives ethoxyethane at 413 K, but it gives ethene at 443 K. This reaction is a nucleophilic substitution reaction, and it follows an SN2 mechanism. Two alcohol molecules take part. One acts as the substrate, and the other acts as the nucleophile.

This dehydration route does not work well for secondary and tertiary alcohols. In those cases, alkenes form more easily than the corresponding ethers. The reaction conditions therefore control whether the product is an ether or an alkene.

Williamson ether synthesis is a more versatile lab method for making asymmetrical ethers. It starts by deprotonating an alcohol to form an alkoxide ion. The alkoxide then acts as a nucleophile and attacks an alkyl halide to form the ether. For primary substrates, the reaction usually follows an SN2 mechanism.

Williamson synthesis works best when the halide is attached to a methyl or primary carbon. With secondary alkyl halides, elimination can compete with substitution. With tertiary alkyl halides, elimination is the main outcome. This makes the method especially useful for preparing ethers from primary starting materials.

Making Ethers by Dehydration and Synthesis

making-ethers-by-dehydration-and-synthesis

structure and nomenclature of ethers

Ethers: Bonding, Types, and Naming

Ethers are organic compounds with an oxygen atom bonded to two groups. Those groups may be the same or different, and they can be alkyl, aryl, or vinyl groups. In dimethyl ether, the simplest ether, the C–O–C link has an angle of about 110.3 degrees. The oxygen is sp3-hybridized, and the C–O distance is about 140 pm. Ethers are classified by the groups attached to the oxygen atom. Symmetrical ethers have identical groups on both sides, such as dipropyl ether and diphenyl ether. Unsymmetrical...

physical properties of ethers

Ether Solubility and Boiling Points

Ethers have a net dipole moment because the C-O bonds are polar. This polarity helps explain why their boiling points are lower than alcohols with similar molecular weight and slightly higher than hydrocarbons with similar molecular weight. Ethers can also accept hydrogen bonds, which makes them more water-soluble than hydrocarbons. However, they cannot donate hydrogen bonds, so they are much less soluble in water than alcohols. Their mix of hydrogen bonding with other molecules and London...

Ethers can be made from alcohols by dehydration and by Williamson ether synthesis. These two routes show how alcohols can act in different roles during ether formation. The first method uses a protic acid, while the second method uses an alkoxide ion and an alkyl halide. In alcohol dehydration, the alcohol loses water in the presence of a protic acid such as sulfuric acid. Ethanol gives ethoxyethane at 413 K, but it gives ethene at 443 K. This reaction is a nucleophilic substitution reaction,...

ethers from alkenes: alcohol addition and alkoxymercuration-demercuration

ethers-from-alkenes-alcohol-addition-alkoxymercuration

Making Ethers with Alkene Reactions

Ethers can be made from alkenes by adding alcohols under acidic or organomercury conditions. The two routes shown here are acid-catalyzed addition of alcohol to an alkene and alkoxymercuration-demercuration. Both methods start with an alkene and an alcohol and end with an ether. In acid-catalyzed addition, the alkene reacts with an excess of alcohol in the presence of an acid catalyst. Under the right conditions, the hydrogen adds to the less substituted carbon. This lets the alcohol group...

ethers to alkyl halides: acidic cleavage

Cleaving Ethers with HBr and HI

Ethers can be cleaved into alkyl halides when heated with strong acids such as HBr and HI. This reaction is useful because ethers are usually unreactive in direct nucleophilic substitution. Their alkoxy groups are strong bases, so they are poor leaving groups. The acid cleavage happens in two substitution steps. First, the ether is converted into one alkyl halide and one alcohol. Then the alcohol reacts with excess HX acid to form a second alkyl halide. The reaction pathway depends on the...

autoxidation of ethers to peroxides and hydroperoxides

autoxidation-of-ethers-to-peroxides-and-hydroperoxides

Why Stored Ethers Can Form Explosive Peroxides

Stored ethers can slowly turn dangerous because they react with oxygen in air and form peroxides. This process is called autoxidation, which means a compound oxidizes on its own while standing in air. Over time, ethers can produce hydroperoxides and dialkyl peroxides. These peroxide products can be explosive if they become concentrated or are heated. For that reason, ethers should be bought in small amounts, kept in tightly sealed containers, and used soon after opening. Careful storage helps...

crown ethers

Crown Ether Binding and Ion Solubility

Crown ethers are cyclic polyethers with several oxygen atoms arranged in a ring. Their ring shape gives them a crown-like form. Charles Pederson first synthesized the first crown ether at DuPont in 1967, and he later shared the 1987 Nobel Prize in Chemistry for that work. Crown ethers are named with the format x-crown-y. In this name, x is the total number of atoms in the ring, and y is the number of ether oxygen atoms. A common example is 18-crown-6. These molecules can bind specific alkali...

structure and nomenclature of epoxides

Epoxide Ring Strain and Naming Rules

Epoxides are three-membered cyclic ethers that contain two carbon atoms and one oxygen atom in the ring. Cyclic ethers are heterocyclic compounds, which means the ring includes atoms other than carbon. Their names depend on the number of carbon atoms in the ring. A three-membered cyclic ether is called an oxirane. Four-membered rings are called oxetane, five-membered rings are called oxolane, and six-membered rings are called oxane. Smaller rings have more angle strain, and the three-membered...

preparation of epoxides

How Alkenes Form Epoxides

Alkenes can form epoxides through oxidation. This reaction can happen with air, peroxy acids, hypochlorous acids, or halohydrin cyclization. Epoxides are three-membered oxygen rings, and they are common products in alkene chemistry. A common lab method uses a peroxy acid such as meta-chloroperoxybenzoic acid, or MCPBA. In this reaction, the carbon-carbon double bond is converted into an epoxide by adding electrophilic oxygen. Because the O-O bond in a peroxy acid is very weak, the oxygen adds...

sharpless epoxidation

Chiral Control in Sharpless Epoxidation

Sharpless epoxidation is a chiral reaction that converts allylic alcohols into epoxides. It was discovered by K. Barry Sharpless. The reaction is useful because it can favor one enantiomer, or mirror-image product, over the other. The key to this selectivity is a chiral catalyst. It is mainly a complex of titanium tetraisopropoxide and a tartrate ester with a specific stereoisomer, or 3D arrangement. The stereoisomer in the catalyst controls which enantiomer forms in excess. Using...

acid-catalyzed ring-opening of epoxides

Epoxide Ring Strain and Acidic Opening

Epoxide ring strain makes these three-membered ethers highly reactive. Because the ring is so strained, epoxides can open in reactions with halogen acids or with weak nucleophiles when a mild acid is present. The acid catalyst changes the epoxide oxygen into an oxonium ion, which is a better leaving group. This makes the ring-opening reaction possible. The reaction follows an S N 2 mechanism, and the protonated oxygen does not leave the molecule on its own. The product pattern depends on the...

base-catalyzed ring-opening of epoxides

Epoxide Ring Opening by Strong Nucleophiles

Epoxide ring opening by strong nucleophiles happens because epoxides have a highly strained three-membered ring. This strain makes them ready for nucleophilic substitution in either acid or base. In the base-catalyzed pathway, a strong nucleophile or base attacks the ring and opens it. Common nucleophiles for this reaction include sodium hydroxide, sodium alkoxide, sodium hydrosulfide, sodium cyanide, lithium aluminum hydride, and Grignard reagents. The attack follows an SN2 mechanism and...

structure and nomenclature of thiols and sulfides

structure-and-nomenclature-of-thiols-and-sulfides

Sulfur in Thiols and Sulfides

Thiols and sulfides are sulfur-based organic compounds. Thiols are sulfur analogs of alcohols, and sulfides are sulfur analogs of ethers. In thiols, the sulfur atom is written as RSH, where R is an alkyl group and SH is the functional group. Sulfides have a central sulfur atom bonded to two hydrocarbon groups, one on each side. These compounds can be symmetrical or asymmetrical, depending on the groups attached. Both thiols and sulfides have a bent shape, much like alcohols and ethers. The...

preparation and reactions of thiols

Thiols: Making and Oxidizing Sulfur Compounds

Thiols are sulfur compounds that can be made by nucleophilic substitution with alkyl halides. In one route, the hydrosulfide anion acts as the nucleophile. For example, bromobutane reacts with sodium hydrosulfide to form butanethiol. That direct method has a limitation. If excess alkyl halide is present, the thiol product can react again and form a sulfide as a by-product. A better route uses thiourea as the nucleophile. This reaction first gives an alkyl isothiourea salt as an intermediate.

preparation and reactions of sulfides

Sulfide Synthesis and Oxidation

Sulfides are sulfur compounds that contain two hydrocarbon groups attached to one sulfur atom. They are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohols. Depending on the groups attached, sulfides may be symmetrical or asymmetrical. Symmetrical sulfides can be made by an S N 2 reaction. In this method, two equivalents of an alkyl halide react with one equivalent of sodium sulfide. Asymmetrical sulfides are prepared from thiols, an alkyl halide, and a base. This...

key terms and concepts

Learn how ethers form from alcohols through acid-catalyzed dehydration and Williamson ether synthesis, including SN2 steps and why primary halides work best.

Making Ethers by Dehydration and Synthesis | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Making Ethers by Dehydration and Synthesis

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