Alcohols part 2
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- Created by: Hindleyc
- Created on: 30-06-18 13:40
What is potassium dichromate?
K2Cr2O7(VI) An oxidising agent that causes alcohols to oxidise
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What does the exact reaction depend on?
Type of alcohol eg 1.,2.,3./ conditions
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What is the reaction for the partial oxidation of primary alcohols?
Primary alcohol- aldehyde
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Reagent?
Potassium dichromate solution and dilute sulphuric acid
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Conditions?
Use limited amount of dichromate and warm gently and distil out the aldehyde as it forms
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Aldehyde FG, bond
-al and C=O bond on first C atom of chain
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What is being removed?
2 H
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What is formed
Aldehyde and water
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What are the observations?
Orange dichromate ion Cr2O7^2- reduces to the green Cr^3+ ion
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So what is the suitable oxidising agent?
Acidified potassium dichromate (VI)
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EQN? (word)
Propan-1-ol + [O]= Propanal + Water
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What do you use [O] for?
To represent O from oxidising agent
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What do you write aldehydes as?
CHO
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What is distillation?
Separation technique to separate an organic product from its reacting mixture
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What do you need to collect
Distillate of the approx b.p range of desired liquid
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Where should the bulb of the thermometer be?
At T junction connecting to condenser to measure correct BP
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Where doe water go in?
At bottom of condenser to go against gravity and allow more efficient cooling and prevents back flow of water
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Why are electric heaters often used to heat organic chemicals?
Because organic chemicals are normally highly flammable and could set on fire with a naked flame
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What flask?
Round bottomed
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What is the full oxidation of primary alcohols?
Primary alcohol- carboxylic acid
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Overall oxidation fg
Primary alcohol- aldehyde- carboxylic acid
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Reagent
Potassium dichromate solution and dilute sulphuric acid
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Conditions
Use excess of dichromate and heat under reflux (distill off product after the reaction has finished)
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Reaction
Propan-1-ol +[O]=Propanone +[O]= Propanoic acid
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Overall eqn
Propan-1-ol+2[O]=Propanoic acid+ H2O
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Eqn for first reaction using R
RCH2OH+[O]=RCHO+H2O
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Eqn for second reaction using R
RCHO+[O]=RCOOH
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Observation
Orange dichromate ion C2O7^2- reduces to green Cr^3+ ion
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When is reflux used?
When heating organic reaction mixtures for long periods.
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What does the condenser do?
Prevent organic vapours from escaping by condensing back to liquids
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Why should you never seal end of condenser
Build up of gas pressure could cause apparatus to explode (also includes any apparatus where volatile liquids heated including distillation set up
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Why are anti numbing granules added to flask in distillation and reflux?
To prevent vigorous uneven boiling by making small bubbles form instead of large bubbles
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Ketone FG and if 5+ C?
-one, No. for position of C=O
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Reaction for oxidation secondary alcohols?
Secondary alcohol- ketone
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Reagent
Potassium dichromate solution and dilute sulphuric acid
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Conditions
Heat under reflux
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Observation
Orange dichromate ion Cr2O7^2- reduces to green Cr^3+ ion
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EQN words
Propan-2-ol + [O]= Propanone +H2O
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What is there ?
No further oxidation of ketones under these conditions
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What about Tertiary alcohols?
Cannot be oxidised at all by potassium dichromate because no hydrogen atom bonded to carbon with OH group
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What is the chemical basis for the two tests to distinguish between aldehydes and ketones?
Aldehydes can be further oxidised
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How is Tollens reagent formed?
,mixing aqueous ammonia and silver nitrate -
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What is the active substance
[Ag(NH3)2]^+
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Conditions ?
Heat gently
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Reaction?
Aldehydes only are oxidised by Tollen's into carboxylic acid and silver (I) ions reduced to silver atoms
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Observation
With aldehydes a silver mirror forms coating inside of test tube- ketone=no visible change
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eqn
CH3CHO+2Ag^+ +H2O= CH3COOH+2Ag+2H+
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Reagent for Fehling solution
Fehling solution containing blue Cu2+ ions
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Conditions
Heat gently
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Reaction
Aldehydes only are oxidised by Feelings solution into a carboxylic acid and copper ions reduced to copper oxide
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Observations
Aldehydes - blue Cu^2+ ions in solution change to red precipitate of Cu2O, Ketones don't react
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EQN
CH3CHO+2Cu^2+ +2H2O= CH3COOH+Cu2O+4H+
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Carboxylic acid test
Add sodium carbonate and will fizz and produce CO2
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EQN
2CH3CO2H+Na2CO3=2CH3CO2-Na+ +H2O + CO2
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Other cards in this set
Card 2
Front
What does the exact reaction depend on?
Back
Type of alcohol eg 1.,2.,3./ conditions
Card 3
Front
What is the reaction for the partial oxidation of primary alcohols?
Back
Card 4
Front
Reagent?
Back
Card 5
Front
Conditions?
Back
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