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A2 Chemistry > 4.3 - Alcohols > Flashcards

4.3 - Alcohols Flashcards

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1
Q

How are alcohols produced from a haloalkane?

A

Heating under reflux is heating method where a condenser is used to stop gas vapour from the reagents escaping.
The mechanism is nucleophilic substitution.

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2
Q

What are the 2 methods of producing alcohols from nucleophilic substitution?

A

Hydroylsis - haloalkane + water
With dilute alkali - haloalkane + NaOH-
Both under reflux, essentially the same but hydrolysis is slower

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3
Q

What is the reactivity series for the haloalkanes?

A

Most reactive
c-f
c-cl
c-br
c-I
Least reactive

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4
Q

Why are primary alcohols the main yield?

A

The production of alkenes.

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5
Q

What does the reduction of aldehydes and ketones result in?

A
  • aldehydes and ketones can be converted back into primary and secondary alcohols
  • reduction is the loss of oxygen or the gain of hydrogen
    eg ethanal + hydrogen - ethanol
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6
Q

What does reduction of an aldehyde result in?

A

A primary alcohol

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7
Q

What does the reduction of a ketone result in?

A

A secondary alcohol

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8
Q

What 2 chemicals are used for the reduction of carbonyls?

A
  • lithium aluminium hydride (LiAlH4)
  • sodium borohydride (NaBH4)
    They are used as reducing agents.
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9
Q

What are the conditions for reducing carbonyls?

A

LiAlH4 is a very strong reducing agent whch reacts dangerously with water producing huge quantities of hydrogen gas. It needs to be dissolved in dry ethoxyethane, or dry ether
NaBH4 is not as powerful a reducing agent but will still react with water unless its alkaline.

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10
Q

Compare the boiling point of alkanes and alcohols.

A

Alcohols have a higher boiling point than alkanes of a similar size due to the hydrogen bonding which occurs between molecules.

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11
Q

When can combustion of alcohols occur?

A

Complete combustion occurs in an adequate supply of oxygen
c2h5OH + 3O2 - 2CO2 + 3H2O
ethanol + oxygen - carbon dioxide + water

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12
Q

How can alcohols be converted back into halogenalkanes?

A

Addition of hydrogen halides
c2h5OH + HX - c2h5x +h2o

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13
Q

What are the 3 substitution reactions for ethanol and chlorine, and what does it produce?

A
  • add PCl3 (=H3PO3)
  • add PCl5 (=POCl3 + HCl)
  • add SOCL2 (SO2 +HCl)
    Produces white steamy fumes
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14
Q

What are the 2 subsitution reactions for bromine and ethanol?

A

c2h5OH + HBr = C2H5Br + H2o
Either hydromic acid is used or generated with 50%/50% mix of NaBr and conc H2SO4 which generates the HBr
2NaBr + H2SO4 = 2HBr + Na2SO4

3C2H5OH + PBr3 = 3C2H5I + P(OH)3
Phosphorus trihalide is generated from its elements
2P + 3Br2 = 2PBr3

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15
Q

What is the substitution reaction for iodine and ethanol?

A

3C2H5OH + PI3 = 3C2H5I + P(OH)3
Phosphorus trihalide is generated from its elements
2P + 3I2 = 2PI3

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16
Q

What happens is an elimination reaction for alcohol? What are the conditions?

A

Dehydration with concentrated sulphuric acid
c2h5OH = Ch2=Ch2 +h2O
ethanol = ethene + water

17
Q

What does the full/partial oxidation of a primary alcohol result in?

A

Aldehydes or carboxylic acids

18
Q

What does the oxidation of secondary alcohols result in?

A

The production of ketones?

19
Q

What does the oxidation of tertiary alcohols result in?

A

Cannot occur with acidified dichromate.

20
Q

What are alcohols usually oxidised with. and what is its formula?

A

Acidified dichromate
H+/Cr2O7 2-

21
Q

What happens in the first stage of oxidising an alcohol?

A

Once you add acidified alcohol is oxidised and the dichromate is reduced
cr2o7 2- + 14+ + 6e- = 2Cr3+ + 7H2O
An aldehyde forms

22
Q

How can an aldehyde be isolated?

A

If you heat the mixture and distil at the correct temperature you can isolate the aldehyde
CH3Ch2OH + (O) = CH3CHO + H2O

23
Q

What happens if an aldehyde is heated under reflux?

A

Oxidation into a carboxylic acid.
CH3CHO + (O) = CH3COOH
ethanol > ethanal > ethanoic acid

24
Q

How can alcohols be identified?

A

By the production of hydrogen gas from the addition of sodium
alcohol + sodium - alkoxide + hydrogen

example
2C2H5OH + 2Na = 2C2H5O-Na+ + H2
ethanol + sodium - sodium ethoxide + hydrogen

Steamy white fumes can be seen if PCl5 is added to an alcohol.

25
Q

How can acidified dichromate identify a primary, secondary or tertiary alcohol?

A

Colour change
Primary green
Secondary green
Tertiary orange
(Tertiary won’t react)

26
Q
A

A2 Chemistry (7 decks)

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