Alcohols Flashcards
Making ETHANOL
HYDRATION OF ETHENE:
H2C=CH2(g) + H2O(g) —— CH3CH2OH(g)
Requirements:
- Phosphoric acid catalyst (H3PO4)
- 300 degrees
- 60 atm pressure
- steam
- An ELECTROPHILIC ADDITION reaction
- REVERSIBLE ~ only 5% of ethene entering reactor is converted to ethanol.
- The UNREACTED gases are RECYCLED and the process runs continuously to give an overall conversion close to 100%.
USES of alcohols
- alcoholic drinks
- perfumes and aftershaves
- cleaning fluids
Making METHYLATED SPIRITS
(denatured alcohol)
- ETHANOL is added to 10% METHANOL and a COLOURED DYE such as methyl violet (poisonous).
- The ETHANOL molecules are UNAFFECTED but the solution is TOXIC & UNDRINKABLE.
- Used as a SOLVENT :
- remove paint
- fuel for camping stoves
Fuel
- OCTANE is blended with 10% ETHANOL
- This INCREASES its OCTANE NUMBER
- Allows the fuel to burn more CLEANLY
MP & BP of alcohols & the TREND as chain length increases.
RELATIVELY HIGH :
- Due to hydrogen bonding
- More energy is needed to overcome the strength of the hydrogen bonds.
The TREND:
- BP increase as chain LENGTH INCREASES
- MORE CONTACT POINTS
- Strength of London forces INCREASES
- Takes extra energy to overcome.
VOLATILITY of alcohols compared to ALKANES
Volatility ~ how readily a substance vaporises.
- An alcohol is LESS volatile than an alkane containing the same number of carbon atoms.
- This is because EXTRA ENERGY has to be provided to overcome the strength of the HYDROGEN BONDS.
SOLUBILITY of alcohols
- HYDROGEN BONDS form between WATER and the POLAR -OH group of alcohols.
- This allows alcohols to be SOLUBLE/ MISCIBLE in water.
( methanol and ethanol are COMPLETELY soluble in water)
The TREND in SOLUBILITY of alcohols
- The NON-POLAR HYDROCARBON CHAIN is unable to form hydrogen bonds with water molecules and can only form LONDON FORCES.
- This is the LEAST FAVOURABLE IMF to form with water as it is POLAR and capable of forming hydrogen bonds.
- As the LENGTH of the hydrocarbon chain INCREASES , the RATIO of the London forces to hydrogen bonds INCREASES.
- The alcohols become LESS SOLUBLE as the hydrocarbon chain length INCREASES.
50cm3 of propan-1-ol was added to 50cm3 of water in a measuring cylinder.
- Explain why the concentration of propan-1-ol in the mixture was found to be slightly more than half of the concentration of the original propan-1-ol.
- Explain why the measuring cylinder felt warm.
- When HYDROGEN BONDS form between molecules, the molecules move CLOSER TOGETHER.
- The VOLUME of the mixture DECREASES
- So the concentration of propan-1-ol was SLIGHTLY MORE than half the concentration of the original propan-1-ol.
- HEAT is given out when HYDROGEN BONDS FORM.
- Hydrogen bonds are typically 1/10 the STRENGTH of a covalent bond
- BOND FORMATION is an EXOTHERMIC process.
Primary, secondary and tertiary alcohols
PRIMARY : The carbon carry the -OH is bonded to 2 hydrogens and 1 carbon.
SECONDARY : The carbon carrying the -OH is bonded to 1 hydrogen and 2 carbons.
TERTIARY : The carbon carrying the -OH is bonded to NO hydrogens and 3 carbons.
Partial oxidation of Primary Alcohols
Propan-1-ol + [0] —- Propanal + water
OXIDISING AGENT [0] :
- dil.H2SO4
- K2Cr2O7
- Provides acidified dichromate ions (Cr2O7 2- / H+)
One mole of oxidising agent removes:
- the hydrogen in the -OH group
- One of the two hydrogens bonded to the carbon carrying the -OH group.
- The TWO hydrogens combine with an OXYGEN atom from the oxidising agent to produce one mole of WATER.
- An ALDEHYDE is formed
- colour change from orange to green(Cr is reduced)
REACTION CONDITIONS:
- HEAT gently
- DISTIL aldehyde product immediately when formed to prevent further oxidation.
Complete oxidation of Primary alcohols
Propan-1-ol + 2[0] —- Propanoic acid + H2O
OXIDISING AGENT:
- K2Cr2O7
- dil. H2SO4
- One mole removes 2 hydrogen atoms from the alcohol to produce an ALDEHYDE functional group.
- The second mole inserts an OXYGEN ATOM between C & H in the aldehyde to make an CARBOXYLIC ACID.
COLOUR CHANGE:
- from ORANGE to GREEN
- Cr is reduced from +6 in the dichromate ion,Cr2O7 2- , to +3 in Cr3+.
REACTION CONDITIONS:
- Heat under REFLUX
- Leads to complete oxidation of the primary alcohol to a carboxylic acid due to reagents being UNABLE TO ESCAPE reaction flask.
Reflux
The CONTINUAL boiling and condensing of a reaction mixture to convert ALL REACTANTS to PRODUCTS.
Oxidation of secondary alcohols
Butan-2-ol + [0] ——- Butanone + H2O
OXIDISING AGENT:
- K2Cr2O7
- dil.H2SO4
- One mole of oxidising agent removes the hydrogen in the -OH group and the hydrogen bonded to the carbon carrying the -OH.
- The two hydrogens combine with an oxygen atom from the oxidising agent to produce one mole of WATER.
- A KETONE functional group is formed
- The colour changes from ORANGE to GREEN as Cr is REDUCED from +6 to +3.
- NO further OXIDATION possible due t the absence of hydrogen bonded to C=O.
- An oxygen atom CANNOT be inserted between the C&H atoms.
REACTION CONDITIONS:
- Heat under reflux
Oxidation of TERTIARY alcohols
NO REACTION.
- Dichromate ions remain ORANGE ( Cr oxidation number is +6)
- Oxidation NOT POSSIBLE due to absence of hydrogen atoms attached to the carbon carry the -OH group
- WATER cannot be formed
REACTION CONDITIONS:
- Heat under reflux
Potassium Dichromate
Changes colour from ORANGE to GREEN
When an ALCOHOL or ALDEHYDE is oxidised.
Esterification
Carboxylic acid + alcohol ——- ester + water
Example:
Ethanoic acid + methanol – methyl ethanoate + water
CH3COOH + CH3OH —- CH3COOCH3 + H2O
CONDENSATION ~ the ester is formed by the removal of a small molecule, water, across the reactant molecules
CONDITIONS:
- heat under reflux
- c.H2SO4
Dehydration of alcohols
These groups are REMOVED from the alcohol:
- OH group
- One of the H atoms on the adjacent C.
PRODUCTS:
- Alkene
- water
CONDITIONS:
- Concentrated acid ~ H2SO4 or H3PO4
- 180 degrees
ELIMINATION ~ one mole of reactant gives two moles of product, with one product having a low Mr (H2O)
NUCLEOPHILIC SUBSTITUTION of alcohols
- Alcohols react with HYDROGEN HALIDES to form HALOALKANES.
REAGENTS & CONDITIONS:
- heat under reflux
- c.H2SO4
- NaX
- The hydrogen halide is formed in place and reacts with the alcohol:
CHOH + NaX + H2SO4 —— CHX + NaHSO4 + H2O
Reagent Vs Reactant
REAGENT ~ the substance ‘taken off the shelf’ and added to the reaction flask to bring about a chemical reaction.
REACTANT ~ the actual species which participates in the reaction.
SOLVENTS & CATALYSTS are NOT classified as reactants as they are involved in the reaction but not consumed .
The reagents & conditions for the halogenation of an alcohol
- Alcohol
- Concentrated sulfuric acid
- Sodium halide , NaX(s)
- Heat under reflux
In the process of IODINATION of an alcohol, what do we use instead of sulfuric acid and why?
PHOSPHORIC ACID
- Iodide ions are oxidised to form iodine , I2
- The YIELD of the iodoalkane is very LOW.
