Chapter 1--Title

Aldehydes and Ketones I. OXIDATION, REDUCTION AND SYNTHESIS

OBJECTIVESName by the IUPAC system on aldehyde and ketone structure (or sketch the hydrocarbon given its IUPAC name). Relate molecular structure to physical properties such as boiling point, solubilityPredict the product form by reduction of aldehyde and ketone using catalytic reduction, hydride reducing reagents: NaBH4, LiAlH4 and complete removal of carbonyl group; Clemmensen and Wolf-Kishner ReductionPredict the product of aldehydes and ketones from reduction of acid chlorides and esters using Rosenmund Reduction and DIBAL-HPredict the product of aldehyde and ketone through oxidation of alcohols by using oxidation of 1o and 2o alcohols, Jones, Sarret and PCC Reagents Describe the Tollens Test for aldehyde and ketone

Chapter 22The Carbonyl GroupThe carbonyl group consists of one s bond formed by the overlap of sp2 hybrid orbitals, and one p bond formed by the overlap of parallel 2p orbitals

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Structure of AldehydesThe functional group of an aldehyde is a carbonyl group bonded to a H atom in methanal, it is bonded to two H atomsin all other aldehydes it is bonded to one H and one carbon atom4555Structure of KetonesThe functional group of a ketone is a carbonyl group bonded to two carbon atoms

56661. Name by the IUPAC system on aldehyde and ketone structure (or sketch the hydrocarbon given its IUPAC name).

Chapter 26NOMENCLATURE

ALDEHYDE AND KETONEChapter 27PAGE : 730-731Nomenclature-AldehydesIUPAC names: select as the parent alkane the longest chain of carbon atoms that contains the carbonyl groupbecause the carbonyl group of the aldehyde must be on carbon 1, there is no need to give it a number

For unsaturated aldehydes, show the presence of the C=C by changing the infix -an- to -en- the location of the suffix determines the numbering pattern8777Nomenclature-Aldehydes

ethanal propanal 2-ethyl-5-methylhexanal9888Nomenclature-AldehdyesFor cyclic molecules in which the -CHO group is attached to the ring, the name is derived by adding the suffix -carbaldehyde to the name of the ring

cyclohexanecarbaldehyde

2-cyclopentenecarbaldehyde10999Nomenclature-KetonesIUPAC names: select as the parent alkane the longest chain that contains the carbonyl group, indicate its presence by changing the suffix -e to -one, and number to give C=O the smaller number

11101010Chapter 212ALDEHYDE

Aldehydes are named by replacing the -e of the corresponding parent alkane with -alThe aldehyde functional group is always carbon 1 and need not be numberedSome of the common names of aldehydes are shown in parenthesis

Aldehyde functional groups bonded to a ring are named using the suffix carbaldehydeBenzaldehyde is used more commonly than the name benzenecarbaldehyde

Chapter 213KETONE Ketones are named by replacing the -e of the corresponding parent alkane with -oneThe parent chain is numbered to give the ketone carbonyl the lowest possible numberIn common nomenclature simple ketones are named by preceding the word ketone with the names of both groups attached to the ketone carbonyl

Common names of ketones that are also IUPAC names are shown below

Chapter 214Sometimes, acyl groups must be named as substituents. The three most common acyl groups are shown below

2. Relate molecular structure to physical properties such as boiling point, solubility

Chapter 215Chapter 216Physical Properties (PG : 733)

Molecules of aldehyde (or ketone) cannot hydrogen bond to each other They rely only on intermolecular dipole-dipole interactions and therefore have lower boiling points than the corresponding alcohols

Aldehydes and ketones can form hydrogen bonds with water and therefore low molecular weight aldehydes and ketones have appreciable water solubility

Physical PropertiesOxygen is more electronegative than carbon (3.5 vs 2.5) and, therefore, a C=O group is polar

aldehydes and ketones are polar compounds and interact in the pure state by dipole-dipole interactionthey have higher boiling points and are more soluble in water than nonpolar compounds of comparable molecular weight

17131313Chapter 218

3. Predict the product form by reduction of aldehyde and ketone using catalytic reduction, hydride reducing reagents: NaBH4, LiAlH4 and complete removal of carbonyl group; Clemmensen and Wolf-Kishner Reduction

Chapter 219Mechanism of ReductionThe mechanism involves:

Addition of nucleophilic hydride ion, H-, to the positively polarized electrophilic carbon of C=O to form an alkoxide ion intermediate

Protonation of the alkoxide ion intermediate20Chapter 220ReductionAldehydes can be reduced to 1 alcohols and ketones to 2 alcohols. In addition, the C=O group can be reduced to a -CH2- group

219696Reduction of a carbonyl compound in general gives an alcohol

Note that organic reduction reactions add the equivalent of H2 to a molecule

1. CATALYTIC REDUCTION (PAGE : 552)22Chapter 222Aldehydes are reduced to give primary alcoholsKetones are reduced to give secondary alcohols 23Chapter 223Catalytic reductions are generally carried out from 25 to 100C and from 1 to 5 atm H2

A carbon-carbon double bond may also be reduced under these conditions

- be careful choice of experimental conditions, it is often possible to selectively reduce a carbon-carbon double in the presence of an aldehyde or ketone

2497972. Metal Hydride ReductionThe most common laboratory reagents for the reduction of aldehydes and ketones are NaBH4 and LiAlH4both reagents are sources of hydride ion, H:-, a very powerful nucleophile

2599992A. HYDRIDE REDUCING AGENT : i) Sodium Borohydride (NaBH4) (PAGE : 553) NaBH4 is not sensitive to moisture and it does not reduce other common functional groupsIt adds the equivalent of H-26Chapter 226NaBH4 ReductionThe key step in metal hydride reduction is transfer of a hydride ion to the C=O group to form a tetrahedral carbonyl addition compound

27101101COMPARISON BETWEEN CATALYTIC REDUCTION AND METAL HYDRIDE REDUCTIONMetal hydride reducing agents do not normally reduce carbon-carbon double bonds, and selective reduction of C=O or C=C is often possible

28103103LiAlH4 is more powerful, less specific, and very reactive with water

Like NaBH4, it adds the equivalent of H-2. HYDRIDE REDUCING AGENT : ii) Lithium Aluminum Hydride (LiAlH4) (PAGE : 553) 29Chapter 229Unlike NaBH4, LiAlH4 reacts violently with water, methanol, and other protic solvents. Reductions using it are carried out in diethyl ether or tetrahydrofuran (THF)

301021023. REMOVAL OF CARBONYL GROUP : DeoxygenationReduction of C=O to CH2

Two methods:Clemmensen reduction if molecule is stable in hot acid.Wolff-Kishner reduction if molecule is stable in very strong base.

31Chapter 2i. Clemmensen Reduction (PAGE : 690-691)

32Chapter 2Refluxing an aldehyde or ketone with amalgamated zinc in concentrated HCl converts the carbonyl group to a methylene groupii. Wolff-Kishner ReductionIn the original procedure, the aldehyde or ketone and hydrazine are refluxed with KOH in a high-boiling solvent. The same reaction can be brought about using hydrazine and potassium tert-butoxide in DMSO33Chapter 2

Wolff-Kishner Reduction

4. Predict the product of aldehydes and ketones from reduction of acid chlorides and esters using Rosenmund Reduction and DIBAL-H

5. Predict the product of aldehyde and ketone through oxidation of alcohols by using oxidation of 1o and 2o alcohols, Jones, Sarret and PCC Reagents

Chapter 235PREPARATION OF ALDEHYDE

Chapter 236Oxidation of primary alcohol (1)-Can be using two reagents;

PCC in CH2Cl2(PAGE 733)

Collins/Sarrret reagents (CrO3 in pyridine)- Primary Alcohols are oxidized to aldehydes.

PCC Reagents- Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones.- A reagent which stops the oxidation at the aldehyde stage is pyridinium chlorochromate (PCC)-PCC is made from chromium trioxide under acidic conditions-It is used in organic solvents such as methylene chloride (CH2Cl2- Pyridinium chlorochromate, or PCC, will not fully oxidize a primary alcohol to the carboxylic acid as does the Jones reagent.- A disadvantage to using PCC is its toxicityChapter 238

2) Reduction of acid chlorides and esters

Using Diisobutylaluminium hydride (DIBAL-H) (PAGE : 735)Reduction to an aldehyde can be accomplished by using a more reactive carboxylic acid derivatives such as an acyl chloride, ester or nitrile and a less reactive hydride source

The use of a sterically hindered and therefore less reactive aluminum hydride reagent is important

Acid chlorides react with Diisobutylaluminium hydride (DIBAL-H) at low temperature to give aldehydes

ii) Reduction of an acid chloridei) Reduction of an ester

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acid chlorideesterOnly 1 equivalent of very cold DIBAL-H is used to avoid further reduction of the aldehyde to an alcohol.Dry ice (solid CO2) sublimes at 78C.Chapter 2Chapter 242Reduction of an ester to an aldehyde can be accomplished at low temperature using DIBAL-HAs the carbonyl re-forms, an alkoxide leaving group departs

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3) ROSENMUND REDUCTIONChemical reactionthatreducesanacid halideto analdehydeusinghydrogen gasoverpalladium-on-carbon poisoned withbarium sulfate.PREPARATION OF KETONE

Chapter 244Oxidation of secondary alcohols (2) (PAGE 738,557)Can be using;PCC in CH2CI2

Jones reagent (CrO3 with diluted H2SO4 in acetone)Secondary alcohols are oxidized to give ketones. (PAGE : 558)

iii) Collins/Sarrret reagents (CrO3 in pyridine)- Secondary Alcohols are oxidized to ketones.

Chemistry 243 - Lecture 25 and 2646

2) Acid Chlorides + Lithium Dialkyl Copper (Gilman Reagent):

2-heptanone6. Describe the Tollens Test for aldehyde and ketoneChapter 2485. Tollens Test (PAGE : 761)For identifying aldehydes and ketones.It is a mixture of aqueous silver nitrate and ammonia.In this reaction aldehyde is oxidised to carboxylate ion and argentum is deposited onthe wall of the test tube as silver mirror.Tollens (works for aliphatic aldehydes, aromatic aldehyde reacts slowly, ketones NO reactions)

49Chapter 2Chapter 250