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Carbonyl chemistry -Production of carbonyl compounds

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Presentation on theme: "Carbonyl chemistry -Production of carbonyl compounds"— 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
PLANAR WITH BOND ANGLES OF 120° ORBITAL OVERLAP NEW ORBITAL The bond is polar due to the difference in electronegativity.

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 C = O H CH3 C = O CH3 C = O C2H5 CH3

5 Naming aldehydes/ketones
Aldehydes C2H5CHO propanal Ketones CH3COCH3 propanone CH3CH2COCH3 butanone CH3COCH2CH2CH3 pentan-2-one CH3CH2COCH2CH3 pentan-3-one C6H5COCH3 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 NaBH4 reacts with ketones also.
Propanone + 2[H]  propan-2-ol

11 Reduction explained The BH4 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 NaBH4

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 CH3COCH3 and CH3CH2CHO 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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