Chemistry 4.4 - Aldehydes and Ketones.

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Conditions for the oxidation of alcohols to form aldehydes/ketones?
Acidified potassium dichromate OR acidified potassium manganate, reflux.
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When primary alcohols are oxidised they will form...
An aldehyde, THEN a carboxylic acid.
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When secondary alcohols are oxidised they will form...
A ketone.
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What colour will potassium dichromate become upon oxidation?
Orange --> green.
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What colour will potassium manganate become upon oxidation?
Purple --> colourless.
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How is the oxidising agent represented in these equations?
[O]
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Aldehydes and ketones can be reduced to reform their 1' and 2' alcohols respectively. Conditions?
Sodiumborohydride, aqueous.
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How is the reducing agent represented in these equations?
2[H]
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C.acids require a strong reducing agent to form their 1' alcohols. Name the reducing agent.
Lithium aluminium hydride (and ether).
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How can we test for the presence of aldehydes or ketones?
Tollen's or Fehling's test.
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When will these two chemicals give a positive result?
In the presence of aldehydes only.
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Positive result for Tollen's test?
Colourless --> grey ppt OR silver mirror.
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Positive result for Fehling's test?
Blue --> orange/red ppt.
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Aldehydes/ketones can react with HCN to form hydroxynitriles. Why?
The C of the C=O bond is electron deficient and so is susceptible to attack by a nucleophile, e.g. :CN-
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Conditions for the addition of HCN to aldehydes/ketones?
HCN and sulfuric acid.
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The mechanism for this reaction is...
Nucleophilic addition.
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The hydroxynitriles produced by this reaction can be hydrolysed to form hydroxyacids. Conditions?
Refluxing with a dilute acid.
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HCN is a poisonous gas. What can be used as an alternative?
NaCN or KCN.
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This overall reaction is important because...
It increases the chain length and introduces chirality.
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What does 2,4-DNP identify?
The presence of a carbonyl (C=O) group: the presence of an aldehyde or ketone. It can also be used to determine the presence of a specific aldehyde or ketone using their melting temperatures.
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How can 2,4-DNP be converted into Brady's reagent?
Dissolved in an acid.
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How is Brady's reagent used to identify the presence of a specific aldehyde/ketone.
The orange ppt formed will have a definite boiling temperature, whereas liquid aldehydes/ketones have boiling temperatures that are all similar. The solid can be filtered, purified and its boiling point compared to a table of known values.
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What is this process called?
Derivatisation.
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The iodoform test identifies the presence of...
CH3CO- group.
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A positive result gives a...
Yellow ppt.
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Conditions for this test?
Iodine in aqueous NaOH.
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Give some examples of compounds that will give positive results.
1. Ethanal 2. Ethanol (oxidised to form an aldehyde) 3. Any alcohol with the -OH in the 2' position.
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Other cards in this set

Card 2

Front

When primary alcohols are oxidised they will form...

Back

An aldehyde, THEN a carboxylic acid.

Card 3

Front

When secondary alcohols are oxidised they will form...

Back

Preview of the front of card 3

Card 4

Front

What colour will potassium dichromate become upon oxidation?

Back

Preview of the front of card 4

Card 5

Front

What colour will potassium manganate become upon oxidation?

Back

Preview of the front of card 5
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