About carbonyl compounds

1. CARBONYL COMPOUNDS
PRESENTED BY GROUP 3 AND 4
GROUP 3 HEAC 2023/24 1

2. GROUP 3
GROUP 3 HEAC 2023/24 2
NAME REG.NUMBER
KWAGALA LINDA ANNEBRITE 2023/HEAC/082/PS
KYOBUTUNGYI PATIENCE 2020/HEAC/088/PS
LEMI CEASER CELEMENT 2020/HEAC/088/PS
MWESIGWA PETER 2020/HEAC/123/PS
NALUBEGA CAROLYN 2020/HEAC/141/PS
NAMWANJE LEONIA 2020/HEAC/149/PS
NANDHEGO STELLA 2020/HEAC/153/PS
KASOZI DERRICK 2020/HEAC/063/PS
AINEMBABAZI OLLEN 2020/HEAC/009/PS
MUKUNGU DONALD EMMANUEL 2020/HEAC/111/PS

3. Definition: carbonyl compounds are organic compounds
with a carbonyl function group.
There are two classes of carbonyl compounds: aldehydes and
ketones.
•Aldehydes (alkanals)
These compounds have the functional group in the terminal
position. They have a general formula RCHO where R is an
alkyl group or hydrogen. They posses a single hydrogen atom
attached to the carbonyl carbon with exception of methanal
HCHO, that possesses two hydrogen atoms attached to the
carbonyl carbon.
GROUP 3 HEAC 2023/24 3

4. • Ketones (alkanones)
These compounds have the functional group in the non- terminal
position with the general formula RCOR’
The general formula of saturated aliphatic aldehydes and ketones
is CnH2nO The cyclic ketones have a general formula CnH2n-2O
The difference in the structure of aldehydes and ketones affects
their properties in two ways:
a) Aldehydes are quite easily oxidized whereas ketones are
oxidized only with difficulty.
b) Aldehydes are usually more reactive than ketones towards
nucleophilic addition. GROUP 3 HEAC 2023/24 4

5. Nomenclature
• The IUPAC nomenclature of aldehydes considers dropping the ending
“-e” of the corresponding alkane and replacing it with the suffix “-al”.
The main carbon chain is name, the carbonyl carbon is considered as
carbon number 1.
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6. • For ketones the IUPAC names are derived by taking the stem of the name
of the corresponding alkane and replacing the ending “-e” with a suffix
“-one”.
• The position of the carbonyl group is indicated by a number, the carbonyl
carbon being given the lowest possible number.
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7. Isomerism
• Carbonyl compounds exhibit structural isomerism. They canshow chain
isomerism and position isomerism among themselves.
• They can also show functional group isomerism among themselves and with
alcohols, alkenes, enols and ethers. E.g. For C4H8O
GROUP 3 HEAC 2023/24 7

8. PHYSICAL PROPERTIES.
1. Physical state
Methanal is a gas, other aliphatic aldehydes and ketones of relatively
low molecular weight are colorless liquids at 200C. Those with high
molecular masses are solids.
2. Solubility
The liquid aldehydes and ketones of low molecular weight are very
soluble in water, for example methanal, ethanal and propanone are all
miscible with water, this is because the form intermolecular hydrogen
bonds with water molecules.
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9. Higher carbonyl compounds with more than five carbon atoms and the
aromatic carbonyl compounds are insoluble in water.
Carbonyl compounds are soluble in the usual organic solvents.
Solubility in water decreases with increase in size of the molecule
because increased molecular size distorts the formation of hydrogen
bonds with water.
3. Boiling points
The polar carbonyl group makes aldehydes and ketones polar
compounds hence they have higher boiling points than non-polar
compounds of comparable molecular weight. For example, propanone
has a higher boiling point (560C) than butane (-0.50C) yet both
compounds have the same molecular weight. The oxygen atom in
propanone is more electronegative than the carbon atom to which it is
bonded thus it pulls the bonding electrons more towards itself gaining a
partial negative charge and the carbon atom gains a partial positive
charge. GROUP 3 HEAC 2023/24 9

10. This makes the carbon-oxygen double bond polar and the whole
molecule polar. Propanone molecules are held by stronger
intermolecular forces of attraction that require a higher amount of
energy to break. However, butane molecules are non-polar hence have
weaker forces of attraction that require a lower amount of energy to
break.
However, carbonyl compounds have lower boiling points as compared
to alcohols or carboxylic acids of comparable molecular mass. This is
because of their inability to form hydrogen bonds between their
molecules.
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11. Methods of preparation of carbonyl
compounds
a) From controlled oxidation of alcohols.
I. Aldehydes: can be prepared by controlled oxidation of primary
alcohols using an acidified potassium dichromate(VI) solution or
acidified potassium permanganate solution. The reactions require
heating.
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12. NB: Primary alcohols may undergo secondary oxidation to carboxylic
acids. The aldehyde must be distilled from the reaction mixture as it is
formed.
Also in order to avoid the secondary oxidation, it is preferable to use a
dichromate(VI) solution rather than manganate (VII) solution since
dichromate ions are milder in the oxidizing action. The orange
solution turns green in case a dichromate is used.
• Acidified chromium(VI) oxide may be used or acidified manganese(II)
oxide on heating in both cases.
GROUP 3 HEAC 2023/24 12

13. II. Ketones: can be formed by oxidation of secondary alcohols
using acidified potassium dichromate(VI) solution, acidified
manganate(VII) solution, acidified chromium( VI) oxide or
acidified manganese(IV) oxide. Heat is required in all cases.
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14. • Oxidation can also be achieved by dehydrogenation of the alcohols when
passed over copper catalyst heated to about 3000C.
Industrially, methanal is formed by oxidation of methanol vapour over heated
silver. Ethanal can be formed in a similar way.
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15. b) Hydrolysis of gem dihalides
Gem dihalides are hydrolyzed with aqueous sodium hydroxide to form ketones or
aldehydes depending on the position of the halogen atoms.
c) From Grignard reagents
Ketones can be prepared when a Grignard reagent is added to an aryl nitrile and
the product hydrolyzed with dilute acid.
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16. d) From acyl chlorides.(the rosenmund reaction)
This is only suitable for preparation of aldehydes. Acyl chlorides are
reduced to aldehydes by hydrogen on a poisoned palladium catalyst
supported on barium sulphate. The catalyst is poisoned using
Sulphur and quinoline. This prevents reduction of the aldehyde to a
primary alcohol.
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17. e) Decarboxylation of calcium salts of carboxylic acids.
f) By Friedel crafts acylation.
Aromatic ketones can be formed by reacting benzene with acyl
chlorides in presence of anhydrous aluminum chloride catalyst.
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18. g) Ozonolysis
Carbonyl compounds can be formed by bubbling ozone through a solution
of an alkene in tetrachloromethane at temperature below 200c to form an
ozonide. The ozonide is then hydrolyzed using zinc and ethanoic acid.
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19. h) Hydration of alkynes.
Carbonyl compounds can be formed by reacting alkynes with dilute
sulphuric acid in presence of mercury(II) sulphate catalyst at 600C. Ethyne
forms ethanal while other alkynes form ketones.
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20. GROUP 4

21. CHEMICAL REACTIONS
NUCLEOPHILIC ADDITION REACTIONS.
1. REACTION WITH HYDROCYANIC ACID
Both aldehydes and ketones react with hydrocyanic acid to form
hydroxynitriles
Hydrocyanic acid is unstable and hence prepared insitu from KCN and
Concentrated H₂SO₄
KCN + H₂SO₄ HCN + KHSO₄
CH₃CHO + HCN
10−20℃
𝑁𝑎𝑂𝐻
CH₃CHCN
OH

22.  Ketones
CH₃COCH₃ + HCN
10−20℃
𝑁𝑎𝑂𝐻
CH₃CCH₃CN
OH
Mechanism
Note: The nitrile is hydrolyzed or alkaline hydrolyzed

23. 2. Reaction with sodium hydrogen sulphite
(sodium bisulphite)
Both ketones and aldehydes react with a saturated solution of sodium
hydrogen sulphite to produce a white crystalline precipitate of
aldehyde or ketone sodium bisulphite. The reaction is used to confirm a
carbonyl compound
Aldehyde
CH₃CHO + NaHSO₃ CH₃CHSO₃⁻Na⁺
Ketone
CH₃COCH₃ + NaHSO₃ CH₃CHCH₂SO₃⁻Na⁺
OH
Mechanism

24. 3. Addition of Phosphorus Pentachloride
The carbonyl group reacts with phosphorus pentachloride or bromide
to form gem dihalides
Aldehyde
CH₃CHO + PCl₅ CH₃CHCl₂ + POCl₃
Ketone
Br
CH₃COCH₃ + PBr₅ CH₃CCH₃ + POBr₃
Br

25. Hydrogenation
Aldehydes
• CH₃CHO + H₂ CH₃CH₂OH
 Ketones
• CH₃COCH₃ + H₂ CH₃CHOHCH₃
•Mechanism

26. NOTE
• The reduction of carbonyl compounds can also be effected by using
other reducing agents such as LiAlH₄/ dry ether, NaBH₄/H₂O,
Na/CH₃CH₂OH
CH₃CHO
𝐿𝑖𝐴𝑙𝐻4
𝑑𝑟𝑦 𝑒𝑡ℎ𝑒𝑟
CH₃CH₂OH

27. CONDENSATION REACTIONS
• Both aldehydes and ketones react with compounds containing an
amino group with loss of water molecule
• The products of these b reactions are brightly colored, crystalline
solids or precipitates with high melting points
• Some of the products are used to identify carbonyl compounds .
• The reagents used include NH₂OH (Hydroxylamine), NH₂NH₂
(Hydrazine), phenyl hydrazine , dinitrophenyl hydrazine, semi
carbazine

28. Examples
Reaction with 2,4-dinitrophenylhydrazine (Brady's reagent)
This reaction is used to confirm the presence of a carbonyl compound. (both
aldehyde and ketone)
Observation; A yellow precipitate forms
Reaction with sodium hydroxide solution
I. With dilute sodium hydroxide solution
Both aldehydes and ketones with α-hydrogen atoms react with dilute
sodium hydroxide solution to form carbonyl compounds with hydroxyl group
Note; α-hydrogen atoms are hydrogen atoms on the carbon atom adjacent
to the carbonyl group

29. With dilute sodium hydroxide solution
2CH₃CHO
𝑑𝑖𝑙 𝑁𝑎𝑂𝐻
CH₃CHCH₂CHO
OH
Mechanism

30. With concentrated sodium hydroxide solution
a. Only aldehydes with α-hydrogen atom(s) react with concentrated
NaOH solution to form a brown resinous mass of unsaturated
aldehydes e.g.
3CH₃CHO conc.NaOH CH₃CH=CHCH=CHCHO
Mechanism

31. b. Aldehydes without α-hydrogen atoms disproportionate on
treatment with concentrated sodium hydroxide solution. Half of the
aldehyde is oxidized to carboxylic acid and the other half reduced to
a primary alcohol
2HCHO HCOOH + CH₃OH
Mechanism

32. Oxidation reactions
I)
a. Acidified potassium permanganate solution
Aldehydes; purple solution turns colorless
Ketones; no observable change
b. With acidified potassium dichromate(VI) solution
Aldehydes; orange solution turns green
Ketones; no observable change

33. II. With Tollen's reagent (Ammoniacal silver nitrate solution)
Aldehyde; silver mirror observed
Ketones; no observable change
RCHO + H₂O RCOOH + 2H⁺ + e
e + Ag⁺ Ag

34. Fehling solution
Aldehydes, except benzaldehyde; reddish brown precipitate
Ketones ; no observable change
RCHO + 2Cu²⁺ +4OH RCOOH + Cu₂O + 2H₂O

35. Iodoform test
• This is used to identify methyl carbonyl compounds which form a
yellow precipitate with triiodo methane
• Ethanal is the only aldehyde with a methyl group directly attached to
the carbonyl carbon and hence it is the only aldehyde that gives a
positive iodoform test. Meanwhile, there are many ketones with a
methyl group attached directly to the carbonyl carbon.
CH₃CHO + 3I₂ + 4NaOH HCOONa + CH₃I+ 3NaI + 3H₂O
CH₃COCH₂CH₃ + 3I₂ + 4NaOH CH ₃ CHCOONa + CH₃I + 3NaI
+3H₂O
Condition; warm

36. Uses of carbonylcompounds
Methanal when dissolved in water forms formalin which is used as a
disinfectant and a preservative
Methanal is used in the manufacture of thermosetting plastics such
as
Ethanal is used in the manufacture of ethanoic acid
Propanone used in the manufacture of a plastic called Perspex
Benzaldehyde used in scenting soap

37. Question 2; Explain why carbonyl group in
aldehydes is more reactive than in ketones
• This is because aldehydes have a hydrogen atom directly bonded to
the carbonyl group and this hydrogen is easily oxidized which is not
the case for ketones because mostly the groups bonded to the
carbonyl group offers positive inductive effect and this tends to
neutralize the positive change in the carbonyl carbon and this
reduces the tendencies of nucleophile attack on it

38. Question 3
• Refer to oxidation reactions