O C. Aldehyde: O C H 3 CH 2 C H propanal propionaldehyde. O C H 3 CH 2 C CH 2 CH 3 3-pentanone diethylketone

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1 Aldehydes and Ketones Both contain the functional group Aldehyde: R Ketone R R' Aldehydes omenclature. IUPA: drop the 'e' from the name of the alkane and add 'al'. There are also common names which are often derived from the name of the corresponding carboxylic acid. methanal formaldehyde 3 ethanal acetaldehyde 3 2 propanal propionaldehyde butanal butyraldehyde The aldehyde group has to be at the end of the chain, so it is not necessary to designate its position. The group to which the aldehyde group is attached is named according to the appropriate rules, l chloropropanal 3-chloropropionaldehyde Ketones omenclature. IUPA: drop the 'e' from the name of the corresponding alkane and add 'one'. Indicate the position of the carbonyl group if necessary. ommon names are similar to those of ethers using the names of the groups attached to the carbonyl. 3 3 propanone dimethyl ketone acetone butanone methylethylketone pentanone diethylketone ,4-dimethyl-3-pentanone diisopropylketone The chain is numbered so that the carbonyl group has the lowest possible number. 1,4-cyclohexanedione phenylcylcopentanone diphenylketone phenylethanone methylphenylketone acetophenone phenyl-1-butanone phenylpropylketone

2 Preparation of Aldehydes and Ketones 1. zonolysis of alkenes 2. ydration of alkynes xidation of alcohols 1) 3 2) Zn, S 4 gs 4 + K 2 r 2 7 r 3 /pyridine or pyridinium chlorochromate P ketones from secondary alcohols aldehydes from primary alcohols 2 4. Rosenmunde reduction of acyl halides to aldehydes 2, Pd-S R R l or LiAl(( 3 ) 3 ) 3 The sulfur partially deactivates the palladium catalyst. Lithium tert-butylaluminum hydride is a less powerful reducing agent than LiAl 4. Acyl chlorides can be prepared from acids R Sl 2 R thionyl chloride l l Sl 2 2 /Pd-S or LiAl(( 3 ) 3 ) orey reaction to form ketones -80 o R l + (R') 2 uli R R' Sl 2 l ( 2 5 ) 2 uli -80 o 2 5

3 6. Aromatic Ketones by Friedel rafts acylation All 3 Ar + l R Ar R + All 3 l excellent yield (4-methylphenyl)-1-propanone Instead of an acyl chloride, the acid anhydride can be used All o succinic anhydride 3 All phenyl-4-oxo-butanoic acid Reactions of Aldehydes and Ketones Many reactions involve addition to the carbon-oxygen double bond. Since the oxygen is electron withdrawing, the carbon carries a partial positive charge and we get nucleophilic addition to the carbon. + u u 3 + u is a nucleophile which can be either an anion or a neutral compound with unshared electrons. This reaction is written as if it were reversible which is often true. Grignard reaction (which we have already discussed) MgX δ δ R-MgX R R u

4 Reduction to Alcohols (an important reaction) 1) LiAl 4 -ether 2) 2 or 1) ab 4, 3 2) 3 + The mechanism involves the transfer of a hydride ion ' - ' from the metal hydride to the ketone. B 3 a + + B - a f the two reducing agents, sodium borohydride is the milder reagent and is the one of preference for aldehydes and ketones since it is specific for these two functional groups. Lithium aluminum hydride will reduce many types of compounds very quickly. Reduction to hydrocarbons (we saw this used to reduce ketones to alkyl groups in the Freidel rafts reaction) a) lemmensen reduction. zinc amalgam This reaction requires strong acid Zn/g l - l b) Wolff Kishner reduction This reaction requires strong base 2 2 K ~190 o Therefore, use the lemmensen reduction when it is undesirable to have strong base in the reaction and the Wolff Kishner when it is undesirable to have strong acid in the reaction. Example of the use of these reactions to make a fused ring system: ethylbenzene l All 3 Sl Zn/g, l All 3 2 2, K o Pt ethylnaphthalene Pt, ethyldecalin

5 yanhydrin formation + a S 4 cyanhydrin which is formed in situ from sodium cyanide and sulfuric acid is added across the - double bond The cyanhydrin group is readily oxidized to a carboxylic acid and so this reaction can be used to make a hydroxy acid. a S heat 3 3 very mild conditions for oxidation 2-hydroxy-2-methylpropanoic acid 6 5 benzaldehyde a S heat mandelonitrile, found in almonds, peach buds, peach seeds millipede defence substance found in laetrile 6 5 mandelic acid, bacteriacide used in treating urinary infections Bisulfite Addition This is a reversible reaction in which a solid product is formed which can be used to purify aldehydes and ketones. + a + S or - S 3 - a + soluble in water, insoluble in organic solvents The bisulfite addition compound cna be used to separate a mixture of an aldehyde and an alcohol as 3 / 2 extract with ether S - 3 a + in aqueous layer in ether layer

6 Addition of ammonia, amines and their derivatives p imine Mechanism Substituted ammonias, 2 -Z, can be added where Z is a large variety of groups Z Z + 2 Examples 2 -Z Product ammonia 2 imine 2 -R primary amine -R + 2 alkyl or aryl amine (Schiff's base) 2 - hydroxylamine oxime 2-2 hydrazine hydrazone phenylhydrazine phenylhydrazone ,4-dintrophenylhydrazine semicarbazide Specific examples: ,4-dinitrophenylhydrazone semicarbazone E-butanone oxime Z-butanone oxime The geometric isomerism of oximes is due to the restricted rotation about the = bond and the geometry of the groups around the nitrogen.