Presentation on theme: "Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions."— Presentation transcript:
Carbonyl chemistry -Production of carbonyl compounds -Oxidation and Reduction reactions -Further oxidation reactions.
Formation of carbonyl compounds Starting with an alcohol, react with an oxidising agent (such as acidified potassium dichromate) Propan-1-ol + [O] Propanal +water
The carbonyl functional group The bond is polar due to the difference in electronegativity. PLANAR WITH BOND ANGLES OF 120° ORBITAL OVERLAP NEW ORBITAL
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
Identification of carbonyls IR spectroscopy shows a strong peak around cm -1
Oxidation of carbonyl Reacting an aldehyde with an oxidising agent (acidified dichromate ions) produces a carboxylic acid. Propanal + [O] Propanoic acid +water
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.
Reduction of carbonyls Propanal is reduced to a primary alcohol by sodium borohydride. Propanal + 2[H] Propan-1-ol
Reduction continued NaBH 4 reacts with ketones also. Propanone + 2[H] propan-2-ol
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
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
Carbonyl chemistry 2 chemical tests on carbonyls -How to detect a carbonyl group -Aldehyde or ketone?
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.
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.
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.
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
Tollen’s reagent. Silver ions are reduced to silver metal Ag + (aq) + e - Ag (s) Aldehyde + [O] Carboxylic acid
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.
Carbonyl chemistry 3 Identifying a carbonyl compound -Determining experimentally an unknown carbonyl compound
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.
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.