Alcohols and EthersAH Chemistry Unit 3(b)
Alcohols
Physical properties• When comparing the boiling point of
ethanol with an alkane, which alkane would you compare it with?
• Which would have the higher boiling point?
• Why?
• Alcohols exhibit hydrogen bonding.
• As a result, they exhibit higher boiling points than (most) other organic compounds of similar molecular mass.
• Which is more soluble in water: ethanol or hexan-1-ol?
• Why?
• The lower alcohols are miscible with water but as their chain length increases their solubility in water decreases.
Preparation of alcohols• There are 2 principle methods for
producing alcohols in industry. What are they?
1. Acid-catalysed hydration of alkenes (electrophilic addition)
2. Nucleophilic substitution of halogenoalkanes
Reactions of alcohols• With metals
– produces alkoxides• Dehydration
– produces alkenes• With carboxylic acids
– produces esters, slowly• With acid chlorides
– produces esters, more vigorously
Acid chlorides
Carboxylic acids can be converted into acid chlorides by reaction with:
– Thionyl chloride– Phosphorus(III) chloride– Phosphorus(v) chloride
Producing esters• Use full structural formulae to illustrate
how ethyl propanoate can be produced from an alcohol and an acid chloride.
• What type of reaction is this?
Ethers
General formula
Uses• Solvents
• Reasons:– Dissolve many organic compounds– Volatile (so removed easily by distillation)
Preparation of ethers• Q: How can you prepare an ether in the
lab?
• A: Reaction of a halogenoalkane with a metal alkoxide.
• Q: What type of reaction is this?
• A: Nucleophilic substitution
Naming ethers
Methoxymethane
Methoxyethane
Ethoxypropane
Naming Ethers• Name the longest continuous chain e.g.
pentane
• Name the alkoxy group by removing “yl” from the substituent name and adding “oxy” e.g. propyl becomes propoxy
• Add the appropriate number in front of the substituent if the ether is branched e.g. 3
• Name a halogenoalkane and metal alkoxide combination you could use to prepare ethoxybutane.
• Name a halogenoalkane and metal alkoxide combination you could use to prepare 2-ethoxybutane.
• Name the ether produced by reacting 1-chloropropane with sodium ethoxide.
Physical properties – mp / bp• How do the melting and boiling points
of ethers compare to alcohols?
• Why?
Physical properties - solubility• Why are ethers of low molecular mass
soluble in water?
Chemical properties• Flammable
• Form peroxides on exposure to air / light (these are unstable and explosive) e.g. ethoxyethane peroxide