4.1 How Ethers Fit Into What You Have Learned So Far

In the first three modules you looked closely at alcohols: what their structure looks like, why they dissolve in water or not, and how they react. Ethers share some features with alcohols because both contain oxygen bonded to carbon. The key difference is that an ether has an oxygen atom bonded to two carbon atoms, while an alcohol has oxygen bonded to one carbon and one hydrogen. Learning about ethers now deepens your picture of oxygen-containing organic compounds and lets you compare how a small change in structure leads to a different set of properties and uses.

Thank you for reading this post, don't forget to subscribe!

4.2 The Ether Functional Group

4.2.1 Basic Structure

• General formula: R–O–R´• R and R´ stand for alkyl or aryl groups (carbon chains or rings).• The angle around the oxygen is close to the tetrahedral angle (≈ 109.5°) because oxygen has two lone electron pairs that occupy space.

 

When R and R´ are the same, the ether is symmetrical (for example, CH₃–O–CH₃, called dimethyl ether). When R and R´ are different, the ether is asymmetrical (for example, CH₃–O–C₂H₅, called ethyl methyl ether).

4.2.2 Ether vs. Alcohol at the Atomic Level

Both alcohols and ethers have a C–O sigma bond that is polar. What makes them behave differently is the absence of an –O–H bond in ethers. This missing hydrogen keeps ethers from forming strong hydrogen bonds with each other, which affects their boiling points and solubility.

4.3 Naming Ethers

4.3.1 Common (Trivial) Names

1. Name each alkyl or aryl group attached to oxygen.

2. List them in alphabetical order.

3. Add the word “ether.”

Example: CH₃–O–CH₂CH₃ → methyl ethyl ether

4.3.2 IUPAC System

1. Find the longest carbon chain; this becomes the parent.

2. Treat the –OR part as an “alkoxy” substituent.

3. Number the parent chain so the alkoxy group gets the lowest possible number.

4. Combine the location number with the name of the alkoxy group and the parent name.

Example: CH₃CH₂–O–CH₂CH₂CH₃Longest chain = propane. The –O–CH₂CH₃ group is an ethoxy substituent on carbon 1.IUPAC name: 1-ethoxypropane.

4.3.3 Practice

Name these using both systems:a) CH₃–O–CH₃b) CH₃CH₂–O–CH₂CH₃Answers are in Section 4.11.

4.4 Physical Properties of Ethers

4.4.1 Boiling Points

• Ethers have lower boiling points than alcohols of similar molecular weight because they cannot form strong intermolecular hydrogen bonds.• Example: Ethanol (C₂H₅OH) boils at 78 °C, while dimethyl ether (CH₃–O–CH₃) boils at –24 °C.

4.4.2 Solubility in Water

• Small ethers (up to about four carbons total) dissolve reasonably well in water because the lone pairs on oxygen can hydrogen-bond with water molecules.• As the carbon chain length grows, the non-polar part dominates and solubility drops.

4.4.3 Density and Odor

Most ethers are less dense than water and float on top of it. Many have a pleasant, sweet smell, which is why you sometimes detect an “ether-like” odor around certain solvents or old hospital equipment.

4.4.4 Comparison Table

(Alcohol vs. Ether with the same carbon count)• Hydrogen bonding between molecules: yes/almost none• Typical boiling point: higher/lower• Flammability: both flammable but ethers often form more volatile vapors

4.5 Chemical Behavior of Ethers

4.5.1 Relative Inertness

Ethers do not react readily with many reagents that attack alcohols. The C–O bonds in ethers are stable to bases, many oxidizing agents, and mild acids. This stability is why ethers are popular as solvents in laboratories and industry.

4.5.2 Acidic Cleavage

Strong acids like concentrated HI or HBr can cleave ethers, producing alkyl halides and alcohols or two alkyl halides:R–O–R´ + HX (excess) → RX + R´X + H₂OMechanism varies (SN1 or SN2) depending on the structure of R groups.

4.5.3 Peroxide Formation

In the presence of oxygen from air and light, many ethers slowly form dangerous peroxides (RO–O–R). These can explode when heated or distilled to dryness. For safe use, ethers are stored with antioxidants and checked before concentration.

4.6 Methods of Preparing Ethers

Creating ethers relies on building the R–O–R´ bond under conditions that do not overheat or dehydrate sensitive groups. Three common laboratory methods are outlined below.

4.6.1 Williamson Ether Synthesis

Reaction: R–X + R´–O⁻ → R–O–R´ + X⁻• R–X = primary alkyl halide (Cl, Br, I)• R´–O⁻ = alkoxide ion, usually made by deprotonating an alcohol with NaH, Na, or K.

 

Step-by-step:

1. Convert the alcohol to an alkoxide:CH₃CH₂OH + NaH → CH₃CH₂O⁻ Na⁺ + H₂↑

2. Add a suitable alkyl halide:CH₃CH₂O⁻ Na⁺ + CH₃CH₂Br → CH₃CH₂–O–CH₂CH₃ + NaBr

Key points for success:• Best if the halide is primary; secondary gives lower yield, tertiary rarely works (elimination competes).• Polar aprotic solvents such as acetone or DMSO speed up SN2 substitution.

4.6.2 Acid-Catalyzed Dehydration of Alcohols

2 R–CH₂–OH –(H⁺, Δ)→ R–CH₂–O–CH₂–R + H₂O

 

• Works well with primary alcohols at moderate temperatures (110–130 °C).• For secondary and tertiary alcohols, elimination to alkene competes.• Example: Two molecules of ethanol react under sulfuric acid to give diethyl ether.

 

Mechanism in brief:

1. Protonate the –OH to make a better leaving group (water).

2. One alcohol molecule attacks the carbocation-like center of another, forming the ether linkage.

3. Deprotonation restores the acid catalyst.

4.6.3 Alkoxymercuration–Demercuration of Alkenes

Alkene + ROH + Hg(OAc)₂ → (RO)(HgOAc)CH–CH₂–RThen NaBH₄ reduces to give R–CH(OR)–CH₃.

 

• Provides Markovnikov addition of an alcohol across a double bond.• Mild conditions avoid rearrangements.• Widely used when the target ether would be hard to access by Williamson due to steric factors.

4.6.4 Other Specialized Methods (Overview)

• Reactions using silver oxide (Ag₂O) as base for aryl halides.• Mitsunobu reaction: converts an alcohol plus a phenol into an ether with inversion of configuration at a chiral center.• Symmetrical ethers by dialkyl carbonate transesterification (green chemistry route).

 

These advanced techniques are not required for basic mastery, but knowing they exist shows there is more than one way to construct an R–O–R link.

4.7 Comparing Ethers and Alcohols: Why the Differences Matter

Property	Alcohol	Ether
Boiling point (same carbon count)	higher	lower
Hydrogen bonding between molecules	yes	negligible
Acidity (pKa)	15–17	~35 (much weaker acid)
Common lab role	reagent, solvent, starting material	mostly solvent
Typical reactions	oxidation, substitution, elimination	limited, cleavage only with strong acids

These contrasts trace back to the replacement of the acidic hydrogen in –OH with an alkyl group. Recognizing this link between structure and behavior is a central theme you have met since Module 1.

4.8 Real-World Uses of Ethers

1. Solvents in laboratories and manufacturing• Diethyl ether, tetrahydrofuran (THF), and methyl tert-butyl ether (MTBE) dissolve many organic substances and evaporate quickly, making them ideal for extraction or reaction media.

2. Fuel additives• MTBE and ethyl tert-butyl ether (ETBE) raise gasoline octane numbers and reduce knocking in engines.

3. Medical settings• Diethyl ether was the first widely used inhalation anesthetic. Although replaced by safer agents today, its historical importance is huge.

4. Consumer products• Glycol ethers (e.g., 2-butoxyethanol) appear in cleaners and paints because they mix well with both water and oils.

5. Polymer chemistry• Polyethers such as polyethylene glycol (PEG) and polypropylene glycol (PPG) form the backbone of many cosmetics, laxatives, and soft contact lens materials.

4.9 Safety and Environmental Notes

• Flammability – Many ethers form flammable vapor–air mixtures even at room temperature; adequate ventilation is essential.• Peroxide Risk – Bottles stored for long periods must be tested with KI/starch papers or handled by professionals before distillation.• Health Hazards – Inhalation of high concentrations causes dizziness and narcosis. Chronic exposure to some glycol ethers can affect blood and reproductive systems.• Disposal – Small lab volumes are collected as halogen-free organic waste. Industrial streams require thermal treatment or regulated solvent recovery.

4.10 Key Points Checklist

✓ Ethers have the structure R–O–R´ with no O–H bond.✓ Their naming follows the common “alkyl alkyl ether” system or the IUPAC “alkoxyalkane” system.✓ Lower boiling points and limited hydrogen bonding reflect the absence of –OH hydrogen.✓ Most ethers are chemically stable but can be cleaved by strong hydrohalic acids and can form peroxides upon standing in air.✓ Main laboratory preparation is the Williamson ether synthesis (SN2 of an alkoxide with a primary alkyl halide).✓ Diethyl ether, THF, MTBE, and glycol ethers illustrate the wide range of practical applications.✓ Safe handling includes controlling ignition sources, testing for peroxides, and using proper waste channels.

4.11 Practice Exercises

1. Naminga) Provide both a common name and an IUPAC name for (CH₃)₂CH–O–CH₃.b) Give an IUPAC name for p-methoxy-toluene (use the benzene ring as the parent).

2. Drawing StructuresDraw the structural formula of “2-methoxy-2-methylpropane.” Identify whether it is symmetrical or asymmetrical.

3. Reaction Predictiona) Outline the major product when ethoxide ion reacts with 1-bromopropane.b) Predict what happens when di-n-butyl ether is heated with excess concentrated HI.

4. Property Reasoninga) Which has the higher boiling point: propan-2-ol or ethoxyethane? Explain briefly.b) Rank the following in order of increasing water solubility: diethyl ether, methanol, butan-1-ol, dimethoxyethane.

5. Mechanism SketchProvide a step-by-step mechanism (with curved arrows) for the formation of diethyl ether by the acid-catalyzed dehydration of ethanol.

Answers

(Keep these hidden until you have tried the questions.)1a) Common: isopropyl methyl ether; IUPAC: 2-methoxypropane1b) 1-methoxy-4-methylbenzene2) The molecule is tert-butyl methyl ether (asymmetrical).3a) Product: ethoxypropane (1-ethoxypropane)3b) 2 equivalents of 1-iodobutane plus water4a) Propan-2-ol (has O–H hydrogen bonding)4b) Methanol > dimethoxyethane > butan-1-ol > diethyl ether

4.12 Discussion Questions and Activities

1. In Module 2 you saw that hydrogen bonding raises boiling points. Based on that, predict how replacing an –OH group with an –OR group in a medicine might change its absorption in the body. Share your reasoning with classmates.

2. Work in pairs to design a laboratory plan that converts cyclohexanol to cyclohexyl propyl ether. Discuss which synthetic route (Williamson vs. dehydration) would be most reliable and why.

3. Some regions phase out MTBE in gasoline due to groundwater concerns. Research alternatives and present a two-minute summary on whether ethers remain a sustainable choice for fuel additives.

4. Collect old bottles of ether solvents in your school lab (under supervision) and test for peroxide formation using a safe qualitative test strip. Record color changes and discuss disposal steps with your instructor.

4.13 Summary Reflection

Think back to the earlier modules on alcohols and note how a simple replacement of one hydrogen atom dramatically alters physical properties, reaction patterns, and industrial roles. Being able to trace such changes all the way from electronic structure to real-world use is a skill you will keep building as you move to the final module on applications.