The key difference between dehydration by H2SO4 and H3PO4 is that dehydration by H2SO4 is less safe and facilitates a complex reaction, whereas dehydration by H3PO4 is safer and facilitates a less complex reaction.
Dehydration is basically the removal of H2O. Dehydration of ethanol and other alcohols can be done using two different acid catalysts: sulfuric acid (H2SO4) and phosphoric (V) acid (H3PO4). In this process, ethanol is dehydrated to get an alkene product.
CONTENTS
1. Overview and Key Difference
2. What is Dehydration by H2SO4
3. What is Dehydration by H3PO4
4. Side by Side Comparison – Dehydration by H2SO4 vs H3PO4 in Tabular Form
5. Summary
What is Dehydration by H2SO4?
Dehydration by H2SO4 is a chemical process that is useful in forming alkenes from alcohols using sulfuric acid as an acid catalyst. Therefore, this reaction includes the formation of an unsaturated compound from a saturated compound. In other words, the reactants of this reaction have only single bonds, whereas the products of this reaction have both single and double bonds.
Sulfuric acid is an acid catalyst for the dehydration of alcohols. In this process, we should use concentrated sulfuric acid. However, using this acid catalyst gives somewhat messy results. It is because sulfuric acid is a very strong oxidizing agent, and it can reduce some of the alcohols to give carbon dioxide gas and reduce itself to produce sulfur dioxide gas. Therefore, both these gases occur as contaminants in the final product and should be removed. In addition, there are some other reactions as well; for example, sulfuric acid reacts with alcohol to give a carbon mass.
In the process of dehydration, the alcohol is heated with sulfuric acid in a concentrated state. Here, an excess amount of sulfuric acid should be used in order to make sure all the alcohols react with the acid. A sodium hydroxide solution can be used to remove the unwanted gases produced in this reaction.
What is Dehydration by H3PO4?
Dehydration by H3PO4 is a chemical process that is useful in forming alkenes from alcohols using phosphoric (V) acid as an acid catalyst. Therefore, this reaction includes the formation of an unsaturated compound from a saturated compound. In other words, the reactants of this reaction have only single bonds, whereas the products of this reaction have both single and double bonds.
Figure 02: Dehydration Reaction
Similar to the above-discussed method, this method also requires the acid catalyst in its concentrated state. We also need to use an excessive amount of phosphoric (V) acid in order to make sure all the alcohol molecules are reacted with the acid catalyst to give the desired alkene. Moreover, dehydration using phosphoric acid is used mainly in the production of liquid state alkenes. The major advantage of this reaction over dehydration by sulfuric acid is that this reaction does not give messy results and it is comparatively safe (no harmful products are produced, e.g. sulfur dioxide produced when using sulfuric acid as the acid catalyst is a harmful product).
What is the Difference Between Dehydration by H2SO4 and H3PO4?
Dehydration by H2SO4 is a chemical process that is useful in forming alkenes from alcohols using sulfuric acid as an acid catalyst. Dehydration by H3PO4 is a chemical process that is useful in forming alkenes from alcohols using phosphoric (V) acid as an acid catalyst. The key difference between dehydration by H2SO4 and H3PO4 is that dehydration by H2SO4 is less safe and facilitates a complex reaction, whereas dehydration by H3PO4 is safer and facilitates a less complex reaction.
Below infographic tabulates more comparisons to discern the difference between dehydration by H2SO4 and H3PO4.
Summary – Dehydration by H2SO4 vs H3PO4
Dehydration of ethanol and other alcohols can be done using two different acid catalysts; sulfuric acid and phosphoric (V) acid. The key difference between dehydration by H2SO4 and H3PO4 is that dehydration by H2SO4 is less safe and facilitates a complex reaction, whereas dehydration by H3PO4 is safer and facilitates a less complex reaction.
Image Courtesy:
1. “Bogert-Cook Synthesis” By Mephisto spa – Own work (Public Domain) via Commons Wikimedia
2. “Ethylenetetracarboxylic dianhydride via acid dehydration” By DMacks (talk) – Own work (Public Domain) via Commons Wikimedia