Chemical Reactions of Alcohols: Cleavage of C-O bond
Reactions involving the breaking of the carbon-oxygen bond, such as reaction with hydrogen halides, phosphorus trihalides, and dehydration reactions.
What is Chemical Reactions of Alcohols: Cleavage of C-O bond?
A chemical reaction where the bond between the carbon atom and the oxygen atom in an alcohol molecule is broken.
Key formula / rule: Reaction with Hydrogen Halides (General)
Key points
- Understand the mechanism of C-O bond cleavage in alcohols.
- Predict the products of reactions of alcohols with hydrogen halides.
- Explain the dehydration of alcohols to form alkenes.
- Differentiate between primary, secondary, and tertiary alcohols using chemical tests.
Common exam trap
Confusing SN1 and SN2 mechanisms for different alcohol types.
Definitions
- Term
C-O Bond Cleavage
- Meaning
A chemical reaction where the bond between the carbon atom and the oxygen atom in an alcohol molecule is broken.
- Term
Lucas Reagent
- Meaning
A solution of anhydrous zinc chloride (ZnCl2) in concentrated hydrochloric acid (HCl), used to distinguish between primary, secondary, and tertiary alcohols.
- Term
Dehydration
- Meaning
A reaction in which a molecule of water is removed from a substrate.
Learning objectives
Understand the mechanism of C-O bond cleavage in alcohols.
Predict the products of reactions of alcohols with hydrogen halides.
Explain the dehydration of alcohols to form alkenes.
Differentiate between primary, secondary, and tertiary alcohols using chemical tests.
Formulae
- Name
Reaction with Hydrogen Halides (General)
- Note
X = Cl, Br, I. Mechanism depends on R group (SN1 for 3°, SN2 for 1°).
- Expression
R-OH + HX → R-X + H2O
- Name
Dehydration of Alcohols
- Note
Forms alkenes. Mechanism E1 or E2 depending on alcohol structure.
- Expression
R-CH2-CH2-OH --(H+, Heat)-→ R-CH=CH2 + H2O
- Name
Reaction with Thionyl Chloride
- Note
Often preferred for preparing alkyl chlorides as gaseous byproducts are easily removed.
- Expression
R-OH + SOCl2 → R-Cl + SO2 + HCl
- Name
Reaction with Phosphorus Trihalides
- Note
X = Cl, Br. PCl3 and PBr3 are commonly used.
- Expression
3 R-OH + PX3 → 3 R-X + H3PO3
Prerequisites
Structure and nomenclature of alcohols
Polarity of covalent bonds
Nucleophilic substitution reactions (SN1 and SN2)
Elimination reactions (E1 and E2)
Acids and bases
Common mistakes
Confusing SN1 and SN2 mechanisms for different alcohol types.
Incorrectly predicting the product of dehydration (e.g., carbocation rearrangements).
Forgetting the role of catalysts and temperature in dehydration.
Assuming all alcohols react with Lucas reagent at the same rate.
Keywords
Alcohols
C-O bond cleavage
Hydrogen halides
Alkyl halides
Dehydration
Alkenes
Lucas reagent
SN1
SN2
E1
E2
Thionyl chloride
Phosphorus trihalides
Practice preview
Dehydration of ethanol at 443 K in the presence of concentrated sulfuric acid yields:…
easy
Which of the following statements about the reaction of alcohols with hydrogen halides is INCORRECT?…
medium
The reaction of an alcohol with hydrogen halide to form an alkyl halide is an example of:…
easy