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Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions.

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Presentation on theme: "Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions."— Presentation transcript:

1 Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions.

2 Formation of carbonyl compounds Starting with an alcohol, react with an oxidising agent (such as acidified potassium dichromate) Propan-1-ol + [O]  Propanal +water

3 The carbonyl functional group The bond is polar due to the difference in electronegativity. PLANAR WITH BOND ANGLES OF 120° ORBITAL OVERLAP NEW ORBITAL

4 Aldehydes vs. Ketones Aldehydes have the carbonyl group at the end of a carbon chain (joined to only one carbon) Ketones have the carbonyl group bonded to two carbons. C = O H CH 3 C = O H H CH 3 C = O C2H5C2H5 CH 3

5 Naming aldehydes/ketones Aldehydes C 2 H 5 CHOpropanal Ketones CH 3 COCH 3 propanone CH 3 CH 2 COCH 3 butanone CH 3 COCH 2 CH 2 CH 3 pentan-2-one CH 3 CH 2 COCH 2 CH 3 pentan-3-one C 6 H 5 COCH 3 phenylethanone

6 Identification of carbonyls IR spectroscopy shows a strong peak around cm -1

7 Oxidation of carbonyl Reacting an aldehyde with an oxidising agent (acidified dichromate ions) produces a carboxylic acid. Propanal + [O]  Propanoic acid +water

8 Reduction of carbonyls Carbonyl groups can also be reduced. Reduction agent used is Sodium tetrahydroborate(III) (also called Sodium Borohydride) This is classed as a weak reducing agent.

9 Reduction of carbonyls Propanal is reduced to a primary alcohol by sodium borohydride. Propanal + 2[H]  Propan-1-ol

10 Reduction continued NaBH 4 reacts with ketones also. Propanone + 2[H]  propan-2-ol

11 Reduction explained The BH 4 ion is acting as a source of hydride ions (:H - ) » Hydride ions being a negatively charged hydrogen ion containing a lone pair of electrons The mechanism is an example of nucleophilic addition. – H - ion is attracted to the δ+C of the carbonyl, forming a new C-H bond – The resulting O - ion forms a dative covalent bond using the H + from a water molecule

12 Reduction reaction mechanism Propanal + 2[H]  propan-1-ol

13 Carbonyl questions Write equations + mechanisms for the reduction of: – Butanal – 2-methylhexan-3-one Define the term nucleophile Show the mechanism for the reaction between butanone and NaBH 4

14 Carbonyl chemistry 2 chemical tests on carbonyls -How to detect a carbonyl group -Aldehyde or ketone?

15 ILPAC experiment 8.4 Using the instruction sheets, follow the method for experiment 8.4 A and 8.4 B DO NOT DO EXPERIMENT C Make full and detailed notes on what you observe during the reactions.

16 Condensation reactions We can detect the presence of a carbonyl group using 2,4-dinitrophenylhydrazine (abbreviated to 2,4-DNP or 2,4-DNPH). 2,4-DNPH is also called Brady’s reagent when prepared with methanol and sulfuric acid.

17 Using 2,4-DNPH When Brady’s reagent is added to an aldehyde or ketone, a yellow or orange precipitate is formed. The precipitate, called a 2,4- dinitrophenylhydrazone derivative confirms the presence of a carbonyl functional group.

18 Aldehyde or ketone Aldehydes and ketones can be distinguished from each other by using Tollen’s reagent Tollen’s reagent is a weak oxidising agent, the carbonyl group is oxidised to form a carboxylic acid. Ammoniacal silver nitrate

19 Tollen’s reagent. Silver ions are reduced to silver metal Ag + (aq) + e -  Ag (s) Aldehyde + [O]  Carboxylic acid

20 Carbonyl questions 2 The carbonyl compounds CH 3 COCH 3 and CH 3 CH 2 CHO are structural isomers. – Name these compounds – State the reagents used and observations made to prove the presence of a carbonyl group in these compounds – State the reagents and observations made to distinguish between the two chemicals.

21 Carbonyl chemistry 3 Identifying a carbonyl compound -Determining experimentally an unknown carbonyl compound

22 ILPAC 8.5 Using the instruction sheets given last lesson, carry out experiment 8.5, parts A and B Complete a detailed method for identifying a carbonyl compound – Purifying by recrystallisation -> melting point determination -> compare melting point to known values.

23 Carbonyl questions 3 Explain how you would use the solid obtained from the reaction of an aldehyde with 2,4- DNPH to prove the original aldehyde was butanal. The reaction of 2,4-DNPH with ethanal gives water as a product. Suggest the type of reaction taking place.


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