Difference Wiki

Dehydration by H2SO4 vs. Dehydration by H3PO4: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on March 2, 2024
Dehydration by H2SO4 involves removing water using sulfuric acid, while dehydration by H3PO4 uses phosphoric acid.

Key Differences

Dehydration by H2SO4 (sulfuric acid) and dehydration by H3PO4 (phosphoric acid) are both chemical processes used to remove water from organic compounds, but they differ in their mechanism, conditions, and applications. On the other hand, dehydration by H3PO4 is generally milder and often preferred for substrates that might be sensitive to the harsh conditions of H2SO4. Phosphoric acid's weaker acidity compared to sulfuric acid makes it a gentler dehydrating agent, suitable for reactions where control over the reaction conditions is crucial to avoid overreaction or degradation of the product.
In the context of dehydration of alcohols to alkenes, H2SO4 is commonly used because it can facilitate the reaction at lower temperatures and with more efficiency. Conversely, H3PO4 is preferred in the dehydration of more delicate organic compounds, or in processes where the presence of strong acids like H2SO4 could interfere with the desired reaction pathway.
Although both H2SO4 and H3PO4 can act as dehydrating agents, the choice between them depends on the specific requirements of the reaction, including the nature of the substrate, desired yield, and purity of the product. Understanding the properties and reactivity of these acids allows chemists to select the most appropriate dehydrating agent for their specific synthetic needs.

Comparison Chart

Acid Strength

Stronger acid, more vigorous dehydration.
Weaker acid, milder dehydration.

Reaction Conditions

Often requires lower temperatures and shorter times.
May require higher temperatures or longer times.

Substrate Compatibility

Suitable for a broad range of compounds.
Better for sensitive or complex molecules.

Risk of Side Reactions

Higher risk due to strong acidic nature.
Lower risk, gentler on substrates.

Typical Applications

Used in robust dehydration reactions, like converting alcohols to alkenes.
Preferred in delicate synthesis, such as in pharmaceuticals.

Dehydration by H2SO4 and Dehydration by H3PO4 Definitions

Dehydration by H2SO4

H2SO4 is highly hygroscopic, aiding in the removal of water.
H2SO4's hygroscopic properties make it an excellent dehydrating agent.

Dehydration by H3PO4

Dehydration by H3PO4 involves removing water using phosphoric acid.
Dehydration of cyclohexanol by H3PO4 yields cyclohexene.

Dehydration by H2SO4

Dehydration by H2SO4 involves removing water from organic compounds using sulfuric acid.
Dehydration of ethanol by H2SO4 produces ethylene.

Dehydration by H3PO4

H3PO4 provides milder dehydration conditions than H2SO4.
Using H3PO4 allows for dehydration under gentler conditions.

Dehydration by H2SO4

Dehydration by H2SO4 is efficient, often requiring lower temperatures.
Using H2SO4, dehydration can proceed efficiently at moderate temperatures.

Dehydration by H3PO4

H3PO4 is suitable for dehydration of sensitive molecules.
For delicate substrates, H3PO4 is the preferred dehydrating agent.

Dehydration by H2SO4

H2SO4 can dehydrate a wide range of organic compounds.
H2SO4 is versatile, capable of dehydrating various alcohols to alkenes.

Dehydration by H3PO4

H3PO4 is often used in the synthesis of fine chemicals.
In pharmaceutical synthesis, H3PO4 dehydration is commonly employed.

Dehydration by H2SO4

H2SO4 is a strong acid, making it highly effective for dehydration reactions.
The strong acidity of H2SO4 facilitates rapid dehydration.

Dehydration by H3PO4

Dehydration by H3PO4 minimizes the risk of side reactions.
H3PO4's use in dehydration reduces unwanted side reactions.


What is dehydration by H2SO4?

It's a process of removing water from compounds using sulfuric acid.

Why choose H2SO4 for dehydration?

H2SO4 is chosen for its strong acidity and efficiency in driving dehydration reactions.

How does H3PO4 dehydration work?

It involves water removal using phosphoric acid, typically under milder conditions than H2SO4.

Are there substrates unsuitable for H2SO4 dehydration?

Yes, sensitive or complex molecules may degrade under H2SO4's harsh conditions.

What types of compounds can H2SO4 dehydrate?

H2SO4 can dehydrate a broad range of compounds, including alcohols to alkenes.

Is dehydration by H3PO4 slower than H2SO4?

It can be, due to H3PO4's weaker acid strength and milder reaction conditions.

When is H3PO4 preferred for dehydration?

H3PO4 is preferred for sensitive substrates where gentle conditions are required.

What is a common use of H2SO4 in dehydration?

A common use is converting alcohols to alkenes in organic synthesis.

How does acid strength affect dehydration?

Stronger acids like H2SO4 can drive dehydration more vigorously than weaker acids like H3PO4.

Can H2SO4 dehydration cause side reactions?

Yes, due to its strong acidity, H2SO4 can lead to side reactions like carbonization.

What makes H3PO4 suitable for pharmaceutical synthesis?

Its milder action reduces the risk of damaging delicate molecules.

Can H3PO4 replace H2SO4 in all dehydration reactions?

No, due to differences in acidity and reactivity, H3PO4 cannot replace H2SO4 in all cases.

Can H2SO4 be used in dehydration without water formation?

H2SO4 can facilitate dehydration even in reactions where water is not a direct product, through its hygroscopic nature.

Can H3PO4 dehydration be used for all alcohols?

While H3PO4 can dehydrate alcohols, it's more suited to those that might degrade under harsher conditions.

What safety precautions are needed for H2SO4 dehydration?

Proper safety gear and awareness of potential side reactions are crucial due to H2SO4's corrosivity.

How do you control the rate of dehydration with H3PO4?

Adjusting temperature and concentration can help control the reaction rate.

What is the role of temperature in H3PO4 dehydration?

Higher temperatures may be required for H3PO4 to effectively dehydrate some substrates.

What are the environmental considerations for using H2SO4 in dehydration?

Handling and disposal of H2SO4 must consider its potential for environmental harm.

How does the choice between H2SO4 and H3PO4 affect yield?

The choice affects yield by influencing reaction speed, side reactions, and substrate stability.

How does dehydration by H3PO4 impact product purity?

H3PO4's gentler action can lead to higher product purity by minimizing side reactions.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

Trending Comparisons

Popular Comparisons

New Comparisons