Copper (Cu) Reagent: Dehydrogenation & Coupling

chemca.in

Home Articles Quizzes About

Reagents & Reactions

Copper ($Cu$)

Master Dehydrogenation at 573K and Aromatic Coupling.

By chemca Team • Updated Oct 2026

Copper ($Cu$) plays several specialized roles in organic chemistry. Most notably, passing alcohol vapors over heated Copper at 573 K ($300^\circ C$) causes catalytic dehydrogenation (or dehydration). Additionally, Copper dust/powder acts as a crucial catalyst/reagent in aromatic substitution and coupling reactions like the Ullmann and Gattermann reactions.

1. Action of Heated Copper on Alcohols

Dehydrogenation vs. Dehydration at 573 K

Conditions: Alcohol vapors passed over heated $Cu$ tube at 573 K ($300^\circ C$).

1. Primary ($1^\circ$) Alcohols $\rightarrow$ Aldehydes

Undergoes dehydrogenation (removal of $H_2$).

$$ \underset{\text{Ethanol (1}^\circ\text{)}}{CH_3-CH_2OH} \xrightarrow{Cu, \ 573 \ K} \underset{\text{Ethanal (Acetaldehyde)}}{CH_3-CHO} + H_2 \uparrow $$

2. Secondary ($2^\circ$) Alcohols $\rightarrow$ Ketones

Undergoes dehydrogenation (removal of $H_2$).

$$ \underset{\text{Propan-2-ol (2}^\circ\text{)}}{CH_3-CH(OH)-CH_3} \xrightarrow{Cu, \ 573 \ K} \underset{\text{Propanone (Acetone)}}{CH_3-CO-CH_3} + H_2 \uparrow $$

3. Tertiary ($3^\circ$) Alcohols $\rightarrow$ Alkenes

Exception! Undergoes DEHYDRATION (removal of $H_2O$) instead of dehydrogenation.

$$ \underset{\text{2-Methylpropan-2-ol (3}^\circ\text{)}}{(CH_3)_3C-OH} \xrightarrow{Cu, \ 573 \ K} \underset{\text{2-Methylpropene}}{CH_2=C(CH_3)_2} + H_2O $$

Why do $3^\circ$ alcohols undergo dehydration? Dehydrogenation requires removing a hydrogen from the oxygen and a hydrogen from the alpha-carbon (the carbon attached to the -OH). Tertiary alcohols do not have an alpha-hydrogen, so they undergo elimination (dehydration) to form alkenes instead.

2. Aromatic Reactions using Copper Dust

Ullmann Reaction & Gattermann Reaction

A. The Ullmann Coupling Reaction

Action: Aryl halides (especially iodides) react with Copper powder at high temperatures to couple together, forming biaryls. It is analogous to the Wurtz-Fittig reaction but uses Cu instead of Na.

$$ \underset{\text{Iodobenzene}}{2 \ C_6H_5-I} + Cu \xrightarrow{\Delta} \underset{\text{Biphenyl}}{C_6H_5-C_6H_5} + CuI_2 $$

B. The Gattermann Reaction

Action: Used to synthesize aryl halides from Diazonium salts. It is a modification of the Sandmeyer reaction, using finely divided Copper powder in the presence of $HX$ (HCl or HBr) instead of Cuprous halides ($Cu_2X_2$).

$$ \underset{\text{Benzenediazonium Chloride}}{C_6H_5N_2^+Cl^-} \xrightarrow{Cu \text{ powder}, \ HCl} \underset{\text{Chlorobenzene}}{C_6H_5-Cl} + N_2 \uparrow $$

3. Summary Table

Substrate	Reagent / Condition	Reaction Name / Type	Product
Primary ($1^\circ$) Alcohol	$Cu / 573 \ K$	Dehydrogenation	Aldehyde + $H_2$
Secondary ($2^\circ$) Alcohol	$Cu / 573 \ K$	Dehydrogenation	Ketone + $H_2$
Tertiary ($3^\circ$) Alcohol	$Cu / 573 \ K$	Dehydration	Alkene + $H_2O$
Aryl Iodide ($Ar-I$)	$Cu$ powder, $\Delta$	Ullmann Reaction	Biaryl ($Ar-Ar$)
Diazonium Salt ($Ar-N_2^+Cl^-$)	$Cu$ powder / $HCl$	Gattermann Reaction	Aryl Chloride ($Ar-Cl$)

Knowledge Check

Test your understanding of Copper Reagents

© 2026 chemca.in. All rights reserved.

Optimized for learning Organic Chemistry.

Quiz Revision Notes Downloads Class Notes Video Lectures

🧪 Organic Chemistry Master Hub

⚗️ Complete Guide to Organic Chemistry Reagents

Master more than 100 important organic chemistry reagents including oxidizing agents, reducing agents, Grignard reagent, PCC, KMnO₄, LiAlH₄, NaBH₄, NBS, DIBAL-H and many more with reactions, applications, mechanisms and exam-focused notes for JEE Main, JEE Advanced, NEET and CBSE.

🚀 Explore the Complete Organic Reagents Hub

🏠 Home 📝 Quiz 📘 Revision Notes ⬇ Downloads 📚 Class Notes ▶ Video Lectures

Get new posts by email

Powered by

📚 Also Read

Lecture Notes