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Aldehydes & Ketones

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Aldehydes & Ketones. In General. Fragrant odors Basic building block of housing materials Hormones Digestion Vision. In General. Carbonyl group C=O Aldehydes RCH=O Formyl Ketones RC=OR’. Nomenclature. Aldehydes IUPAC end in “al” Common end in “ aldeyde ” - PowerPoint PPT Presentation
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Aldehydes & Ketones

Aldehydes & Ketones

In GeneralFragrant odorsBasic building block of housing materialsHormonesDigestionVision

2In GeneralCarbonyl groupC=OAldehydesRCH=OFormyl

KetonesRC=OR3NomenclatureAldehydesIUPAC end in alCommon end in aldeydeCarbonyl C is always #1Cyclic cpdsCarbaldehyde is ending for most4NomenclatureAldehydes

methanal(formaldehyde)ethanal(acetaldehyde)propanal(propionaldehyde)butanal(n-butyraldehyde)5NomenclatureAldehydes3-methylbutanal3-butenal2,3-dihydropropanal(glyceraldehyde)

6NomenclatureAldehydescyclopentanecarbaldehyde(formylcyclopentane)benzenecarbaldehyde(benzaldehyde)2-hydroxybenzenecarbaldehyde(salicylaldehyde)

7NomenclatureKetonesIUPAC end in oneCommon end in ketoneCarbonyl C is never #1, but always gets low number preferenceCyclic cpdsCarbaldehyde is ending for most8NomenclatureKetonespropanone(acetone)2-butanone(ethyl methyl ketone)3-pentanone(diethyl ketone)

9NomenclatureKetonescyclohexanone2-methylcyclopentanone3- buten-2-one(methyl vinyl ketone)

10NomenclatureKetonesacetaphenone(methyl phenyl ketone)benzophenone(diphenyl ketone)dicyclopropyl ketone

11Common Aldehydes & KetonesFormaldehydeSimplest aldehydeManufactured on large scale (8 billion lbs per annum) from catalyzed oxidation of methanol CH3OH CH2=O + H2Gas at RT (bp = -21C) but cannot be stored in free state due to polymerizationNormally 37% soln called formalin (preservative)Most used in making of plastics, insulation, particle board, and plywood

12Common Aldehydes & KetonesAcetaldehydeBoils close to RT (bp = 20C)Made by catalyzed oxidation of ethylene2 CH2=CH2 + O2 2 CH3CH=O~1/2 is oxidized to acetic acidRemainder used for production of 1- butanol and others.

13Common Aldehydes & KetonesAcetoneSimplest ketoneLarge scale production like formaldehydeProduced from oxidation of propene, isopropyl alcohol, or isopropylbenzene

~30% used directly, great solvent, H2O miscibleRest used to make stuff like epoxy resins

14

Common Aldehydes & KetonesQuinonesCyclic conjugate diketonesSimplest is 1,4-benzoquinoneAll are colored and are thus used often as dyesAlizarinused to dye the red coats of the British Army during American RevolutionVitamin K is required for normal clotting of blood

15Common Aldehydes & Ketones16

1,4-benzoquinonealizarin

vitamin KVitamin KSynthesis of Aldehydes & KetonesOxidation1 ROH gives aldehyde2 ROH gives ketoneCr reagents (PCC) are common

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Synthesis of Aldehydes & KetonesFriedel-Crafts AcylationRecall the rxn?Makes aromatic ketones

18

benzophenonebenzyl chlorideSynthesis of Aldehydes & KetonesHydration of terminal alkynesGives methyl ketonesCatalyzed by acid and mercuric ion

19

Aldehydes & Ketones in NatureMany have pleasant odorsUsed in the perfume industryExtremely expensive to gather from natural producersChanel No. 5 (my moms fave perfume) was first perfume to use synthetic organic chemicals in 1921

20Aldehydes & Ketones in Nature

21

benzaldehydecinnamaldehydevanillinThe Carbonyl GroupC atom is sp2 hybridizedBond angles?C=O bond length is 1.24 (compared to 1.43 for C-O in ROH and RORO is more EN than CMakes a polar bond

22The Carbonyl GroupMost carbonyl reactions are nucleophilic attacks on the carbonyl CC=C usually is attacked by an electrophileDue to polarization, physical properties differ from HCs and ROHsbps are higher than HCs, lower than ROHs

23The Carbonyl GroupC=O is permanently polarizedPositive part of one molecule is attracted to negative part of another moleculeDipole-dipole forces, weaker than H-bonds, stronger than LDF

24

The Carbonyl GroupC=Os with low MW are soluble in waterCan form H-bonds with water or ammonia

25An Overview of Nucleophilic Addition to Carbonyl GroupsWhy does the attack occur?If rxn occurs in hyroxylic solvent (water or ROH), a proton is usually added to the O

26An Overview of Nucleophilic Addition to Carbonyl GroupsCarbonyl cpds are weak Lewis bases due to lone pairs on OAcids can catalyze the addition of weak nucleophiles to carbonyl cpds through protonation

27An Overview of Nucleophilic Addition to Carbonyl GroupsNucleophiles add reversiblyGood leaving groups, CB of SANucleophiles add irreversiblyPoor LG, CB of WAIn general, ketones are less reactive than aldehydesStericsp2 v. sp3, R v. HElectronicalkyl groups are electron-donatingketones have two

28Addition of Alcohols: Formation of Hemiacetals and AcetalsAlcohols are oxygen nucleophilesOR goes to C, and H goes to OBecause ROHs are weak nucleophiles, acid catalyst must be usedProduct is a hemiacetalContains both alcohol and ether on same CAddition is reversible29Addition of Alcohols: Formation of Hemiacetals and AcetalsMechanism of hemiacetal formation has 3 stepsCarbonyl O is protonated by acid catalystROHs O then attacks carbonyl CProton is then lost from resulting +OEach step is reversible

30Do You Get It?Write an equation for the formation of a hemiacetal from acetaldehyde, ethanol, and an acid catalyst. Show each step in the rxn mechanism.

31Addition of Alchols: Formation of Hemiacetals and AcetalsExcess ROH means hemiacetals react further to produce acetalsHydroxyl group of hemiacetal is replaced by an alkoxyl group.Acetals have two ether groups on same C

32Addition of Alchols: Formation of Hemiacetals and AcetalsMechanism of acetal formation

33Addition of Alchols: Formation of Hemiacetals and AcetalsMechanism of acetal formation

34Addition of Alchols: Formation of Hemiacetals and AcetalsAldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal5-hydroxypetanal

35Addition of Alchols: Formation of Hemiacetals and AcetalsAldehydes that have appropriately located hydroxyl group can exist in equilibrium with a cyclic hemiacetal5-hydroxypetanal

36Addition of Alchols: Formation of Hemiacetals and AcetalsCpds with hydroxyl group 4 or 5 Cs from the aldehyde group tend to form cyclic hemiacetals and acetals due to lack of strainCarbohydrates

37Addition of Alchols: Formation of Hemiacetals and AcetalsKetones also form acetalsIf a glycol is used, product is cyclic

38Addition of Alchols: Formation of Hemiacetals and AcetalsSummaryAldehyde or ketone reacts with ROHHemiacetal is formedFurther ROH makes acetal

39Addition of Water: Hydration of Aldehydes and KetonesWater is an oxygen nucleophile, like ROHsCan add reversibly

40Addition of Water: Hydration of Aldehydes and KetonesAside from formaldehyde hydrate most other hydrates cannot by isolated because they lost waterKeq

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