Nomenclature of Aldehydes and Ketones

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1 Aldehydes and Ketones

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5 Nomenclature of Aldehydes and Ketones Common aldehydes H H Methanl (formaldehyde) H3C H CH3CH2 ethanl (acetaldehyde) H propanal (propionaldehyde) CH3CH2CH2 butanal (n-butyraldehyde) H H H H H Me benzaldehyde salicylaldehyde (2-hydroxybenzenecarbaldehyde) H cyclopentanecarbaldehyde H Vanillin

6 Common Ketones CH3 H3C propanone (acetone) cyclohexanone H3C CH3 CH3 H3C 2-butanone 3-pentanone (ethyl methyl ketone) (diethyl ketone) H3C acetophenone (methyl phenyl ketone) benzophenone (diphenyl ketone)

7 Nomenclature of aldehydes and ketones (al) aldehyde, (one) ketone alkanes < alkenes < H < ketone < aldehyde < acid < ester Examples CH3 CH CH3 H 2 H3C Cl 2,4-dimethyl-3-hexanone 2-cholro-3-methylbutanal H H hydroxy-2-pentanone 6 3 CH oxobutanl CH3 3-hexen-2-one

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10 Acyl groups

11 Common aldehydes and ketones Formaldehyde CH3H Ag CH2 = oc + H2 Formaldehyde is a gas (b. p. -21 oc) Formalin (37% aqueous solution of formaldehyde) Acetaldehyde (Wacker synthesis) Pd - Cu 2 CH2 = CH2 + 2 CH3CH = oc (bp 20 oc) Acetone (Wacker synthesis) Pd - Cu 2 CH3 C CH3 2 CH3CH2 = CH oc (bp 56 oc) From isopropylbenzene H 1) 2 ١١ 2) dil H2S4 + H3C CH3

12 Synthesis of aldehydes and Ketones 1) xidation of Alcohols primary gives aldehydes using pyridinium chlorochromate (PCC). secondary gives ketones

13 2) H3C Friedel-Crafts CH3CCl AlCl3 3) From Alkynes : xymercuration Hydration Markovnikov H CH3CH2C CH HgS4, H2S4 H 2 CH3CH2C=CH2 an enol CH3CH2CCH3 a ketone

14 4- Aldehydes from Acid Chlorides - Lithium tri-t-butoxyaluminum hydride reduction - Rosenmund reduction LiAlH(-t-bu) 3 R C Cl ether R C Cl H 2 / Pd / S BaS 4 Rosenmund catalyst R C H R C H

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16 5- Ketones from Acid Chlorides Gilman Reagent with Acid Chlorides

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18 6- zonolysis Alkene Cleavage

19 7-Reduction of Acids and their derivatives by Lithium Aluminum hydride (LAH)

20 R C R' or R C NH 2 or R C NHR' or R C NR 2 ' 1. Diisobutylaluminum hydride (DIBAH) 2. H3 + R C H

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23 Naturally occuring aldehydes and Ketones

24 The carbonyl group

25 Reactions of the carbonyl group

26 A. Hydration and Hemiacetal Formation Water adds rapidly to the carbonyl function of aldehydes and ketones. In most cases the resulting hydrate (a geminal-diol) is unstable relative to the reactants and cannot be isolated. Exceptions to this rule exist, one being formaldehyde (a gas in its pure monomeric state). Thus, a solution of formaldehyde in water (formalin) is almost exclusively the hydrate, or polymers of the hydrate. Another is chloral hydrate H CCl3 H H Chloral hydrate

27 Addition of Alcohols

28 Examples

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31 Addition of hydrogen cyanide to aldehydes and ketones

32 Addition of sodium hydrogensulphite to aldehydes and ketones ٣٢ Uses of the reaction The reaction is usually used during the purification of aldehydes (and any ketones that it works for). The addition compound can be split easily to regenerate the aldehyde or ketone by treating it with either dilute acid or dilute alkali.

33 Reducing Agents The reduction of an aldehyde You get exactly the same organic product whether you use lithium tetrahydridoaluminate or sodium tetrahydridoborate. For example, with ethanal you get ethanol:

34 The reduction of a ketone Again the product is the same whichever of the two reducing agents you use. For example, with propanone you get propan-2-ol: Reduction of a ketone leads to a secondary alcohol.

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36 REACTIN F ALDEHYDES AND KETNES WITH GRIGNARD REAGENTS

37 The reaction between Grignard reagents and methanal 1) EtMgBr 2) H2, H+ The reaction between Grignard reagents and other aldehydes 1) EtMgBr 2) H2, H+ The reaction between Grignard reagents and ketones 1) EtMgBr 2) H 2, H +

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39 Reaction with Acetylides

40 XIDATIN F ALDEHYDES AND KETNES

41 ADDITIN-ELIMINATIN REACTINS F ALDEHYDES AND KETNES

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43 with hydroxylamine The product is an "oxime" - for example, ethanal oxime.

44 Formation of Imines and Related Compounds The reaction of aldehydes and ketones with ammonia or 1ºamines forms imine derivatives, also known as Schiff bases, (compounds having a C=N function).

45 Keto-Enol Tautomerism Keto-enol tautomerism refers to a chemical equilibrium between a keto form )a ketone or an aldehyde) and an enol. The enol and keto forms are said to be tautomers of each other. The interconversion of the two forms involves the movement of a proton and the shifting of bonding electrons; hence, the isomerism qualifies as tautomerism. A compound containing a carbonyl group (C=) is normally in rapid equilibrium with an enol tautomer, which contains a pair of doubly bonded carbon atoms adjacent to a hydroxyl ( H) group, C=C-H. The keto form predominates at equilibrium for most ketones. Nonetheless, the enol form is important for some reactions. Furthermore, the deprotonated intermediate in the interconversion of the two forms, referred to as an enolate anion, is important in carbonyl chemistry, in large part because it is a strong nucleophile.

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47 Acidity of α-hydrogen

48 Examples of -Hydrogen exchange

49 The Aldol Condensation The name aldol is derived from "aldehyde" and "alcohol". An aldol is a β-hydroxycarbonyl compound.

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