CARBONYL COMPOUNDS.pptx classifications and properties

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 C n H 2n O The cyclic ketones have a general formula C n H 2n-2 O The difference in the structure of aldehydes and ketones affects their properties in two ways: Aldehydes are quite easily oxidized whereas ketones are oxidized only with difficulty. 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. GROUP 3 HEAC 2023/24 5

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. GROUP 3 HEAC 2023/24 6

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 C 4 H 8 O GROUP 3 HEAC 2023/24 7

8. PHYSICAL PROPERTIES. Physical state Methanal is a gas, other aliphatic aldehydes and ketones of relatively low molecular weight are colorless liquids at 20 C. Those with high molecular masses are solids. 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. GROUP 3 HEAC 2023/24 8

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. 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 (56 C) than butane (-0.5 C) 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. GROUP 3 HEAC 2023/24 10

11. Methods of preparation of carbonyl compounds From controlled oxidation of alcohols . 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. GROUP 3 HEAC 2023/24 11

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. 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. GROUP 3 HEAC 2023/24 13

14. Oxidation can also be achieved by dehydrogenation of the alcohols when passed over copper catalyst heated to about 300 C. Industrially, methanal is formed by oxidation of methanol vapour over heated silver. Ethanal can be formed in a similar way. GROUP 3 HEAC 2023/24 14

15. 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. From Grignard reagents Ketones can be prepared when a Grignard reagent is added to an aryl nitrile and the product hydrolyzed with dilute acid. GROUP 3 HEAC 2023/24 15

16. 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. GROUP 3 HEAC 2023/24 16

17. Decarboxylation of calcium salts of carboxylic acids. By Friedel crafts acylation. Aromatic ketones can be formed by reacting benzene with acyl chlorides in presence of anhydrous aluminum chloride catalyst. GROUP 3 HEAC 2023/24 17

18. Ozonolysis Carbonyl compounds can be formed by bubbling ozone through a solution of an alkene in tetrachloromethane at temperature below 20 c to form an ozonide. The ozonide is then hydrolyzed using zinc and ethanoic acid. GROUP 3 HEAC 2023/24 18

19. Hydration of alkynes. Carbonyl compounds can be formed by reacting alkynes with dilute sulphuric acid in presence of mercury(II) sulphate catalyst at 60 C. Ethyne forms ethanal while other alkynes form ketones. GROUP 3 HEAC 2023/24 19

20. GROUP 4

21. CHEMICAL REACTIONS NUCLEOPHILIC ADDITION REACTIONS. 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 CH₃CHCN OH  

22. Ketones CH₃COCH₃ + HCN 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 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 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 CH₃CHCH₂CHO OH Mechanism  

30. With concentrated sodium hydroxide solution 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. 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) Acidified potassium permanganate solution Aldehydes; purple solution turns colorless Ketones; no observable change With acidified potassium dichromate(VI) solution Aldehydes; orange solution turns green Ketones; no observable change

33. 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