Name: cleaving ethers with hbr and hi
Uploaded: 2023-04-30T18:28:34.000Z
Duration: 2 min 18 s
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Ethers are generally unreactive towards direct nucleophilic substitutions, as the resulting alkoxide ion is a strong base, and thus, a poor leaving group.
However, when heated with strong acids, such as hydrobromic or hydriodic acids, ethers get converted into alkyl halides.
Acidic cleavage of ethers is a typical nucleophilic substitution reaction. The type of nucleophilic substitution and the conditions required for the reaction depend on the nature of the alkyl groups bonded to oxygen.
Ethers with primary alkyl groups undergo acidic cleavage in the presence of excess hot concentrated acids by an SN2 mechanism.
The reaction mechanism begins with a proton transfer from the acid catalyst to the ether oxygen, forming an oxonium ion, a better leaving group.
Next, the halide ion acts as a nucleophile and attacks the less substituted carbon of the oxonium ion in an SN2 reaction, displacing alcohol and forming the first molecule of alkyl halide.
Excess hydriodic acid subjects the alcohol molecule to another round of SN2 reaction, forming a second molecule of alkyl halide.
Ethers with tertiary, allylic, or benzylic alkyl groups undergo acidic cleavage under mild conditions, such as moderate temperatures and dilute acids, by an SN1 mechanism.
For example, when ethyl tert-butyl ether reacts with dilute hydriodic acid, protonation of ether forms a stable tertiary carbocation with the loss of primary alcohol.
Finally, the tertiary carbocation reacts with the iodide ion by an SN1 mechanism, forming a tert-butyl iodide.
The reactivity of the halogen acids towards ether cleavage increases with the nucleophilicity of the halide ions.
Therefore, both hydriodic and hydrobromic acids readily cleave ethers. Hydrochloric acid is less efficient, and hydrofluoric acid does not cleave ethers.

ethers to alkyl halides: acidic cleavage

Ethers to Alkyl Halides: Acidic Cleavage

Ethers are generally unreactive and unsuitable for direct nucleophilic substitution reactions since the alkoxy groups are strong bases and, therefore, poor leaving groups. However, ethers readily undergo acidic-cleavage reactions. Ethers can be converted to alkyl halides when heated with strong acids such as HBr and HI in a sequence of two substitution reactions.
<img alt="Ester cleavage mechanism with HX, chemical reaction equation, organic chemistry process." src="/files/ftp_upload/11741/11741Figure%201.svg" style="text-align: center; height: 40px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
In the first step, the ether is converted into an alkyl halide and alcohol.
<img alt="Ester hydrolysis reaction; chemical equation showing conversion of ester to alcohol and acid." src="/files/ftp_upload/11741/11741Figure%202.svg" style="text-align: center; height: 30px;" data-altupdatedat="1761830439000" data-alt="Figure2" />
In the second step, the alcohol reacts with the excess HX acid to form another equivalent of an alkyl halide.
<img alt="Alcohol halogenation formula, R-OH + HX &#8594; R-X + H2O, chemical equation diagram." src="/files/ftp_upload/11741/11741Figure%203.svg" style="text-align: center; height: 30px;" data-altupdatedat="1761830439000" data-alt="Figure3" />
Acidic cleavage of ethers can occur either by the SN1 mechanism or SN2 mechanism, depending on the substrate. Ethers with primary and secondary alkyl groups as substrates react with the SN2 mechanism in which the nucleophile attacks the protonated ether at the less hindered site. Ethers with a tertiary, benzylic, or allylic group undergo the SN1 mechanism because the substrates can produce more stable intermediate carbocations. Reactivity of the halogen acids with ethers increases relative to the nucleophilicity of the halide ions. HI and HBr are more reactive, HCl is less efficient, and HF is unsuitable.

Ethers are generally unreactive and unsuitable for direct nucleophilic substitution reactions since the alkoxy groups are strong bases and, therefore, ...

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Organic Chemistry

Unit 1

Ethers, Epoxides, Sulfides

KEY TERMS AND CONCEPTS

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 ether structure. Ethers with primary and secondary alkyl groups usually follow an SN2 mechanism. In this path, the nucleophile attacks the protonated ether at the less hindered site.

Ethers with tertiary, benzylic, or allylic groups usually follow an SN1 mechanism. These substrates can form more stable carbocation intermediates. The choice of acid also matters. HI and HBr are more reactive, HCl is less efficient, and HF is unsuitable.

Cleaving Ethers with HBr and HI

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 from alcohols: alcohol dehydration and williamson ether synthesis

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

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,...

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 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 are cleaved by strong acids like HBr and HI to form alkyl halides. Compare SN1 and SN2 pathways and acid reactivity.

Cleaving Ethers with HBr and HI | JoVE K12

organic chemistry

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Cleaving Ethers with HBr and HI

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