Carbonyl Compounds

Aldehydes and Ketones

Contents• Aldehydes vs. Ketones• Testing for Carbonyl Compounds• Distinguishing Between Aldehydes and Ketones M l i d Mx t onida i

• Oxidation of Aldehydes (Primary Alcohols)• Oxidation of Ketones (Secondary Alcohols)• Neucleophilic Addition Reaction• Definitions• Summary

Aldehydes vs. Ketones• The functional group is:

>C=O• Polar bond• The aldehyde has the

functional group attached to one carbon

• Suffix = -al• Oxidation of primary

alcohols• Has a low boiling point• Soluble in water

• The functional group is: >C=O

• Polar bond• The ketone has the

functional group attached to two carbon

• Suffix = -one• Oxidation of secondary

alcohols• Has a low boiling point• Soluble in water

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Testing for Carbonyl Compounds

• Brady’s reagent or a 2,4-DNPH solution• When added to a carbonyl compound it

produces a yellow-orange precipitate• Works with ketones and aldehydes• Does not work with carboxylic acids, esters,

esters, acid clorides and amides which contains the >C=O group

• Find the boiling point of the precipitate and the identity of the carbonyl compound can be found

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Distinguishing Between Aldehydes and Ketones Mild Oxidation

• Tollen's Reagent• Involves a ammoniacal silver

nitrate solution• A aldehyde or ketone is shaken

with the ammoniacal silver nitrate solution

• If there is an aldehyde then the test tube will form a “silver mirror” silver precipitate

• This is due to the silver ion being reduced

• The silver may be formed as a black precipitate

• This works with all aldehydes

• Fehling's Reagent• Involving copper (II) ions• When added to a aldehyde and

placed into a water bath, it will form a red precipitate

• The red precipitate is Cu₂O• But it only works with aliphatic

aldehydes

In both tests the aldehyde is oxidised to a carboxylate salt

Tollen’s Reagent is better because it works with all aldehydes.

Both don’t work with ketones but vigorous oxidation will work

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Oxidation of Aldehydes (Primary Alcohols)

• Mild oxidation• CH₃CH₂OH (l) [O] CH₃CHO (l) + H₂O(l)• This is done by distillation• CH₃CHO (l) + [O] CH₃COOH (l)• This is done by refluxing• Easily oxidised to acids unlike ketones

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Oxidation of Ketones (Secondary Alcohols)

• CH₃CHOHCH₃ (l) + [O] CH₃OCOCH₃ (l) + H₂O• C₂HCOCH₂CH₃ (l) + 3[O] C₂HCOOH (l) +

CH₃COOH (l)• Only oxidised under vigorous conditions to

acids

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Neucleophilic Addition Reaction• Occurs with both aldehydes and ketones• Reagent: NaBH₄• Conditions: Aqueous/ alcoholic solution• Nucleophile: H⁻• CH₃CHO + 2[H] CH₃CH₂OH • CH₃COCH₃ + 2[H] CH₃CHOHCH• Mechanism:

Primary alcohol

Secondary alcohol

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Definitions • Redox reaction – both reduction and oxidation take place• Reflux – continual boiling and condensing of a reaction

mixture to ensure that the reaction takes place without the contents of the flask boiling dry

• Neucleophile – an atom or group of atoms attracted to an electron-deficient centre, where it donates a pair of electrons to form a new covalent bond

• Functional group – the part of an organic molecule responsible for its chemical reactions

• Electronegativity – a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

• Stem – the longest carbon chain present in an organic molecule

• Suffix – the part of the name added after the stem

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Summary

Aldehyde

Reacts with2,4-DNP(H)

Yellow/orangeprecipitate

Reduced toPrimary alcohol

Oxidised toCarboxylic acid

Ketones

Reacts with2,4-DNP(H)

Yellow/orangeprecipitate

Reduced toSecondary alcohol Not oxidised

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