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Chemistry > Alcohols > Flashcards

Alcohols Flashcards

1
Q

Making ETHANOL

A

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%.
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2
Q

USES of alcohols

A
  • alcoholic drinks
  • perfumes and aftershaves
  • cleaning fluids
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3
Q

Making METHYLATED SPIRITS
(denatured alcohol)

A
  • 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
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4
Q

Fuel

A
  • OCTANE is blended with 10% ETHANOL
  • This INCREASES its OCTANE NUMBER
  • Allows the fuel to burn more CLEANLY
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5
Q

MP & BP of alcohols & the TREND as chain length increases.

A

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.

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6
Q

VOLATILITY of alcohols compared to ALKANES

A

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.
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7
Q

SOLUBILITY of alcohols

A
  • 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)

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8
Q

The TREND in SOLUBILITY of alcohols

A
  • 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.
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9
Q

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.
A
  • 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.
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10
Q

Primary, secondary and tertiary alcohols

A

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.

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11
Q

Partial oxidation of Primary Alcohols

A

Propan-1-ol + [0] —- Propanal + water

OXIDISING AGENT [0] :
- Potassium dichromate & dilute sulfuric acid.
- 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

REACTION CONDITIONS:
- heat gently
- distil aldehyde product immediately when formed to prevent further oxidation.

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12
Q

Complete oxidation of Primary alcohols

A

Propan-1-ol + 2[0] —- Propanoic acid + H2O

OXIDISING AGENT:
- 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 with excess acidified K2Cr2O7.

  • Leads to complete oxidation of the primary alcohol to a carboxylic acid due to reagents being UNABLE TO ESCAPE reaction flask.
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13
Q

Reflux

A

The CONTINUAL boiling and condensing of a reaction mixture to convert ALL REACTANTS to PRODUCTS.

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14
Q

Oxidation of secondary alcohols

A

Butan-2-ol + [0] ——- Butanone + H2O

  • 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
- With excess acidified dichromate ions

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15
Q

Oxidation of TERTIARY alcohols

A

NO REACTION.

  • Dichromate ions remain ORANGE ( Cr oxidation number is +6)
  • Oxidation NOT POSSIBLE due o absence of hydrogen atoms attached to the carbon carry the -OH group
  • WATER cannot be formed

REACTION CONDITIONS:
- Heat under reflux

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16
Q

Potassium Dichromate

A

Changes colour from ORANGE to GREEN

When an ALCOHOL or ALDEHYDE is oxidised.

17
Q

Esterification

A

Carboxylic acid + alcohol ——- ester + water

Example:
Ethanoic acid + methanol – methyl ethanoate + water

  • ending of carboxylic acid changes from -oic acid to -oate.
  • Alcohol name becomes a prefic from -ol to -yl

TYPE OF REACTION:
Condensation ~ the ester is formed by the removal of a small molecule, water, across the reactant molecules

18
Q

Dehydration of alcohols

A

These groups are REMOVED from the alcohol:
- OH group
- One of the Ha toms on the adjacent C.

PRODUCTS:
- Alkene
- water

CONDITIONS:
- Concentrated acid ~ H2SO4 or H3PO4
- 180 degrees

TYPE OF REACTION:
- Elimination ~ one mole of reactant gives two moles of product, with one product having a low Mr (H2O)

19
Q

Substitution of alcohols

A
  • Alcohols react with HYDROGEN HALIDES to form HALOALKANES.
  • The alcohol is heated under REFLUX with concentrated H2SO4, which acts as a CATALYST, and a SODIUM HALIDE.
  • The hydrogen halide is formed in place and reacts with the alcohol:

NaX(s) + H2SO4(aq) —– NaSO4(aq) + HX(aq)

20
Q

Reagent Vs Reactant

A

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 .

21
Q

The reagents & conditions for the halogenation of an alcohol

A
  • Alcohol
  • Concentrated sulfuric acid
  • Sodium halide , NaX(s)
  • Heat under reflux
22
Q

In the process of IODINATION of an alcohol, what do we use instead of sulfuric acid and why?

A

PHOSPHORIC ACID

  • Iodide ions are oxidised to form iodine , I2
  • The YIELD of the iodoalkane is very LOW.

Chemistry (21 decks)

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