Question

What is the five steps mechanism of dehydration reaction

Answer 1

• When heated with strong acids catalysts (most commonly H₂SO₄, H₃PO₄), alcohols typically undergo a 1,2-elimination reactions to generate an alkene and water.
• Also known as dehydration since it involves the removal of a molecule of water.
• Alcohol relative reactivity order : 3^o > 2^o > 1^o
• Regioselectivity : major product is usually the more highly substituted alkene (alkene stability) zaitsev's rule
• Stereoselectivity : trans- > cis- again controlled by stability
• Reaction usually proceeds via an E1mechanism which proceeds via a carbocation intermediate, that can often undergo rearrangement.
• Primary alcohols will proceed via an E2 mechanism since the primary carbocation is highly unfavourable.
• Other common strong acids such as HCl, HBr or HI are less suitable catalysts as nucleophilic substitution reaction will probably interfere.