Please enable JavaScript.
Coggle requires JavaScript to display documents.
Module 4 Chapter 14 (14.1 Properties of alcohols (Physical Properties…
Module 4
Chapter 14
14.1 Properties of alcohols
-OH
-functional group
Methanol- CH3OH
- Used as a fuel because of its very efficient combustion, very important in feedstock and can be converted into polymers, paints solvents etc.
Ethanol- C2H5OH
- mainly used in alcoholic drinks and as fuel
Naming
Add the suffix -ol to the stem name of the longest carbon chain
Position of the alcohol functional group in the chain indicated with number
e.g. Butan-1-ol
Physical Properties
Alcohols are less volatile, have higher melting points and greater water solubility than alkanes
As Carbon chain length increases the differences become smaller
Blue=Alcohol Orange= Alkane
Differences because
Alkanes= non-polar bonds
(electronegativity of carbon and hydrogen very similar
So alkane is non-polar
Intermolecular forces between non-polar and
very weak London forces
Alcohols= polar O-H bond
(difference in electronegativity)-
Alcohols are polar
Intermolecular forces=
weak London forces AND strong hydrogen bonds between polar O-H groups
e.g.
Volatility and boiling points
Liquids
- Intermolecular hydrogen bonds hold alcohol molecules together- strong bonds must be broken to turn into a gas
Requires more energy than that to overcome weak London forces in alkanes- so alcohols have a
lower volatility and higher boiling points
than alkanes with the same number of carbons
Volatility
-Tendency of a substance to vaporise
Solubility in water
Completely soluble in water
as a hydrogen bond forms between the polar -OH group and the water molecule
Solubility decreases as carbon chain length increases
More -OH groups= more hydrogen bonds= more soluble
e.g.
Classifying alcohols
Primary
-OH group is attached to a carbon atom that is attached to 2 hydrogen atoms and 1 alkyl group
Secondary
-OH group is attached to a carbon atom that is attached to 1 hydrogen atom and 2 alkyl groups
Tertiary
-OH group is attached to a carbon atom that is attached to 0 hydrogen atoms and 3 alkyl groups
14.2 Reactions of alcohols
Oxidation
Primary and secondary alcohols can be oxidised
Oxidising agent is usually potassium dichromate (VI)
K2Cr2O7
acidified with dilute sulfuric acid
H2SO4
If oxidised, the
orange
solution containing
dichromate (VI)
ions is reduced to a
green
solution containing
chromium (III)
ions
Primary
Aldehydes
Aldehyde is distilled out of the reaction mixture as it forms- prevents further oxidation
Dichromate (VI) ions= orange->green
Gentle heating with distillation
Primary alcohol + [O] + distillation -> Aldehyde + Water
Carboxylic acids
Heated strongly under reflux with excess K2Cr2O7
Complete oxidisation
Primary Alcohol + 2[O] + reflux -> Carboxylic acid + water
Secondary
Secondary alcohol + [O] -> Ketone + Water
Alcohol heated under reflux with oxidising mixture
Dichromate (VI) ions= orange-> green
Tertiary
- Don't undergo oxidation
Combustion
Burn in a plentiful supply of oxygen to form carbon dioxide and water
e.g. Ethanol
C2H5OH(l) +3O2(g)-> 2CO2(g) + 3H2O(l)
Reaction is exothermic- releases lots of heat energy
Longer carbon chain= more heat energy per mole
Dehydration
-Elimination reaction
Dehydration
- any reaction where a water molecule is removed from the starting material
Alcohol heated under
reflux
in presence of
acid catalyst
i.e Concentrated sulfuric acid
Alcohol + Acid Catalyst -> Alkene + Water
Substitution
Condition-
Reflux
with sulfuric acid and a sodium halide and a hydrogen bromide is formed in situ
NaBr (s) + H2SO4 (aq)-> NaHSO4(aq) +HBr(aq)
e.g Propan-2-ol +HBr
Reaction=
Propan-2-ol + Hydrogen Bromide -> 2-bromopropane + H2O
Overall equation (including the reaction of NaBr with H2SO4)
CH3CHOHCH3 + NaBr + H2SO4-> CH3CHBrCH3 + NaHSO4 +H2O
Alcohol + Hydrogen Halide-> Haloalkane + Water
