Aldehydes and Ketones O C Both contain the functional group Aldehyde: R O C Ketone H R O C R' Aldehydes Nomenclature. IUPAC: 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. H O C O C H3C H ethanal acetaldehyde H methanal formaldehyde O C O C H3 CH2CH2C H butanal butyraldehyde H3CH2C H propanal propionaldehyde 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, e.g. ClH2CH2C O C H 3-chloropropanal 3-chloropropionaldehyde Ketones Nomenclature. IUPAC: drop the 'e' from the name of the corresponding alkane and add 'one'. Indicate the position of the carbonyl group if necessary. Common names are similar to those of ethers using the names of the groups attached to the carbonyl. H3C O C CH3 H3CH2C propanone dimethyl ketone acetone O C CH3 butanone methylethylketone H3CH2C O C CH2CH3 3-pentanone diethylketone H3C CH O C CH CH3 CH3 CH3 2,4-dimethyl-3-pentanone diisopropylketone The chain is numbered so that the carbonyl group has the lowest possible number. C6H5 O 1 O 3 2 O C C O 3-phenylcylcopentanone O diphenylketone 1,4-cyclohexanedione C6H5 CH3 phenylethanone methylphenylketone acetophenone O C C6H5 CH2CH2CH3 1-phenyl-1-butanone phenylpropylketone Preparation of Aldehydes and Ketones 1. Ozonolysis of alkenes 1) O 3 C C 2. Hydration of alkynes C C + O C OH H 2SO4 H 2O + C O 2) Zn, H2O CH 3COOH CH HgSO4 CH 2 C O C 3. Oxidation of alcohols OH C K 2Cr2O 7 ketones from secondary alcohols aldehydes from primary alcohols CrO 3/pyridine or pyridinium chlorochromate PCC 4. Rosenmunde reduction of acyl halides to aldehydes O R C O H2, Pd-S Cl or LiAlH(OC(CH 3)3)3 R C H The sulfur partially deactivates the palladium catalyst. Lithium tert-butylaluminum hydride is a less powerful reducing agent than LiAlH4 . Acyl chlorides can be prepared from acids O O SOCl 2 R C OH COOH e.g. thionyl chloride R C O Cl O C Cl SOCl 2 C H H 2/Pd-S or LiAlH(OC(CH 3)3)3 C2H 5 C2H 5 C2H 5 5. Corey reaction to form ketones O R C Cl C + O OH (R')2 CuLi SOCl 2 -80oC R C O C R' O (C2H5)2 CuLi Cl -80oC C O C2H5 6. Aromatic Ketones by Friedel Crafts acylation O O AlCl3 Ar C ArH + Cl C R R O e.g. + O Cl C CH2CH3 C CH 2CH3 AlCl3 excellent yield CH 3 CH3 1-(4-methylphenyl)-1-propanone Instead of an acyl chloride, the acid anhydride can be used. e.g. + H3CH2C O O H3C C O C CH3 O O 4 C AlCl3 O + AlCl3 O C CH3 H3CH2C 3 2 O C C C OH H2 H2 150oC O succinic anhydride 4-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. O C O O C C O + Nu C H3O+ Nu OH C Nu Nu 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. e.g. Grignard reaction O C + (which we have already discussed) OMgX δ− δ+ C R-MgX R H3O+ OH C R Reduction to Alcohols (an important reaction) O C 1) LiAlH4 -ether 2) H 2O OH C or 1) NaBH 4, CH 3OH H + 2) H 3O The mechanism involves the transfer of a hydride ion 'H -' from the metal hydride to the ketone. O C OBH3 Na+ C H + H B- H Na+ H OH C H H3O+ H Of 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 Crafts reaction) a) Clemmensen reduction. This reaction requires strong acid zinc amalgam H O Zn/Hg + H2 O + Cl C C HCl H b) Wolff Kishner reduction This reaction requires strong base O C H C NH2 NH2 KOH ~190o C HOCH2CH2OH + N2 + H2 O H Therefore, use the Clemmensen 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: O O O AlCl3 + C CH2 CH2 C OH H3CH2C H3CH2C O ethylbenzene O CH2 CH2 CH2 C Cl H3CH2C Zn/Hg, HCl O SOCl2 AlCl3 NH2 NH2, KOH H3CH2C O CH 2 CH2 CH2 C OH H3CH2C Pt CH2 O C HOCH2CH 2OH H3CH2C CH 2 o 190 C C H2 H3CH2C 2-ethylnaphthalene Pt, H2 H3CH2C 2-ethyldecalin Cyanhydrin formation O + Na+CN - C OH H2SO4 HCN which is formed in situ from sodium cyanide and sulfuric acid is added across the C-O double bond C CN cyanhydrin The cyanhydrin group is readily oxidized to a carboxylic acid and so this reaction can be used to make a hydroxy acid. OH O OH NaCN H3O+ C C C H2SO4 CH3 H C CH 3 CH C heat H 3 H3C 3 3 COOH very mild conditions CN for oxidation 2-hydroxy-2-methylpropanoic acid O C6H5 C H NaCN H2SO4 benzaldehyde C6H5 OH C H CN H3O+ heat mandelonitrile, found in almonds, peach buds, peach seeds millipede defence substance found in laetrile OH C6H5 C H COOH 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. OH soluble in water, insoluble in organic O C solvents + + Na HSO3 C - Na+ + SO H3O or OH 3 The bisulfite addition compound cna be used to separate a mixture of an aldehyde and an alcohol CH3CH2CH 2CH 2CHO + CH 3CH2CH2CH2CH 2OH NaHSO3/H2 O extract with ether OH CH3CH2CH 2CH 2CH SO3 -Na + in aqueous layer CH 3CH2CH2CH2CH 2OH in ether layer Addition of ammonia, amines and their derivatives O pH 3-4 + C NH3 + C NH H2 O imine Mechanism O C H N H H OH C OH C N N H H H3O OH2 + C + C N N H H H H -H2O H H Substituted ammonias, NH2-Z, can be added where Z is a large variety of groups. O + C C NH2 -Z + H2O H2O imine NZ Examples NH2 -Z Product C N-H + C N-R H2N-OH hydroxylamine C N-OH H2N-NH2 hydrazine C N-NH2 + H 2O H2N-NH-C6H5 phenylhydrazine C N-NH-C6H 5 + H2O C N-NH H2N-H ammonia H2N-R primary amine NO2 H2N-NH O2N H3C C O CH2CH3 NH2 OH + H2 O O2N 2,4-dintrophenylhydrazine O H2N-NH-C-NH2 semicarbazide Specific examples: + H2O C H3C C HO N O N-NH-C-NH2 CH2CH3 alkyl or aryl amine (Schiff's base) oxime hydrazone phenylhydrazone NO2 2,4-dinitrophenylhydrazone + H2O semicarbazone H 3C CH2CH3 C N OH Z-butanone oxime E-butanone oxime The geometric isomerism of oximes is due to the restricted rotation about the C=N bond and the geometry of the groups around the nitrogen.