Reactions of Aldehydes and Ketones - Organic Chemistry II - Lecture Slides, Slides of Organic Chemistry

Download Reactions of Aldehydes and Ketones - Organic Chemistry II - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Reactions of aldehydes and ketones: oxidation reduction nucleophilic addition 1) Aldehydes are easily oxidized, ketones are not. 2) Aldehydes are more reactive in nucleophilic additions than ketones. docsity.com alkane alcohol aldehyde ketone carboxylic acid oxidation reduction reduction addition product nucleophilic addition docsity.com Mechanism: nucleophilic addition to carbonyl, acid catalyzed C O + H C OH C OH + HZ RDS C OH ZH C OH ZH C OH Z + H 1) 2) 3) docsity.com Aldehydes & ketones, reactions: 1) Oxidation 2) Reduction 3) Addition of cyanide 4) Addition of derivatives of ammonia 5) Addition of alcohols 6) Cannizzaro reaction 7) Addition of Grignard reagents 8) (Alpha-halogenation of ketones) 9) (Addition of carbanions) docsity.com 1) Oxidation a) Aldehydes (very easily oxidized!) CH3CH2CH2CH=O + KMnO4, etc.  CH3CH2CH2COOH carboxylic acid CH3CH2CH2CH=O + Ag +  CH3CH2CH2COO - + Ag Tollen’s test for easily oxidized compounds like aldehydes. (AgNO3, NH4OH(aq)) Silver mirror docsity.com 2) Reduction: a) To alcohols H2, Ni NaBH4 or LiAlH4 then H+ C O C OH H docsity.com H2, Pt 1. NaBH4 2. H+ O cyclopentanone OH cyclopentanol C CH3 O CHCH3 OH acetophenone 1-phenylethanol H docsity.com C O H H2, Pt CH2OH CH3CHCH=O CH3 LiAlH4 H+ CH3CHCH2OH CH3 benzaldehyde benzyl alcohol isobutyraldehyde isobutyl alcohol docsity.com + AlCl3 Zn(Hg), HCl n-pentylbenzene cannot be made by Friedel-Crafts alkylation due to rearrangement of carbocation Cl O O docsity.com 3) Addition of cyanide C O 1. CN - 2. H+ C CN OH cyanohydrin O + NaCN; then H+ OH CN docsity.com C O mechanism for addition of cyanide nucleophilic addition RDS C O C N C O C N + Na+ C ONa C N + C N then + H+ 1) 2) docsity.com C O + H+ C OH C OH + H2N G acid catalyzed nucleophilic addition mechanism followed by dehydration C NH2 OH G C NH2 OH G C N G + H2O + H + RDS 1) 2) 3) docsity.com CH2 CHO phenylacetaldehyde + H2NOH CH2 CH NOH an oxime O + H2NHNCNH2 O H+ NHNCNH2 O a semicarbazonecyclohexanone CH3CH2CH2CH2CHO + NHNH2 phenylhydrazine hydroxylamine semicarbazide pentanal CH3CH2CH2CH2CH N NH a phenylhydrazone docsity.com melting points of derivatives ketones bp semi- 2,4-dinitro- oxime carbazone phenylhydrazone 2-nonanone 195 119 56 acetophenone 202 199 240 60 menthone 209 189 146 59 2-methylacetophenone 214 205 159 61 1-phenyl-2-propanone 216 200 156 70 propiophenone 220 174 191 54 3-methylacetophenone 220 198 207 55 isobutyrophenone 222 181 163 94 docsity.com CH2CHO (xs) EtOH, H+ CH2 CH OEt OEt O (xs) CH3OH, dry HCl OCH3 OCH3 acetal ketal docsity.com CHO OHH HHO OHH OHH CH2OH O H HO H HO H OH OHH H OH O H HO H HO H H OHH OH OH nucleophilic addition of -OH on carbon 5 to the aldehyde functional group CHO OHH HHO OHH OHH CH2OH CH OHH HHO OHH HHOH2C OH O H HO H HO H OH OHH H OH O O H HO H HO H H OHH OH OH   rotate C-5 OH to rear docsity.com 6) Cannizzaro reaction. (self oxidation/reduction) a reaction of aldehydes without α-hydrogens CHO Br conc. NaOH CH2OH COO - Br Br + CH3OH + HCOO -H2C=O conc. NaOH docsity.com C O RMgBr+ RDS C O R + MgBr C O R + MgBr C OMgBr R mechanism = nucleophilic addition 1) 2) docsity.com #3 synthesis of alcohols. Used to build larger molecules from smaller organic compounds. RMgX + H C H O RCH2OMgX H+ RCH2OH formaldehyde 1o alcohol + 1 C RMgX + R' C H O R'CHOMgX R H+ R'CHOH R other aldehydes 2o alcohol + X C's docsity.com R-MgX + R' C R" O R-COMgX R' R" H+ R-COH ketone 3o alcohol + X C's RMgX + H2C CH2 O RCH2CH2OMgX H+ RCH2CH2OH ethylene oxide 1 o alcohol + 2 C's R' R" docsity.com “The Grignard Song” (sung to the tune of “America the Beautiful”) Harry Wasserman The carbonyl is polarized, the carbon end is plus. A nucleophile will thus attack the carbon nucleus. The Grignard yields an alcohol of types there are but three. It makes a bond that corresponds from “C” to shining “C.” docsity.com CH3CH2CH2CH2 C CH3 CH3 OH 2-Methyl-2-hexanol CH3CH2CH2CH2MgBr + CH3CCH3 O H2O CH3CH2CH2CH2 C CH3 CH3 OH 2-Methyl-2-hexanol CH3CH2CH2CH2CCH3 + CH3MgBr H2O O or docsity.com ROH RX -C=O RMgX R´OH HX Mg ox. H2O larger alcohol docsity.com CH3 HBr CH3 Mg CH3 CH3CHCH2OH CH3CHCH2Br CH3CHCH2MgBr H+ K2Cr2O7 CH3 CH3CH2OH CH3CH=O CH3CHCH2CHCH3 special cond. OH 4-methyl-2-pentanol docsity.com Br2,Fe Br Mg MgBr CH3CHCH3 OH CrO3 CH3CCH3 O H2O C CH3 CH3 OH 2-phenyl-2-propanol 2-phenyl-2-propanol docsity.com H3C OH 1-Methylcyclohexanol OHH Cyclohexanol NaOCl O Cyclohexanone CH3OH HBr CH3Br Mg CH3MgBr H2O 1-methylcyclohexanol docsity.com ROH RX -C=O RMgX R´OH HX Mg ox. H2O larger alcohol docsity.com Using the Grignard synthesis of alcohols we can make any alcohol that we need from a few simple alcohols. From those alcohols we can synthesize alkanes, alkenes, alkynes, alkyl halides, ethers, aldehydes, ketones, carboxylic acids… eg. Outline all steps in a possible laboratory synthesis of 3-methyl-1-butene from alcohols of four carbons or less. CH3 CH3CHCH=CH2 docsity.com Retrosynthesis: alkenes, syntheses: 1. Dehydrohalogenation of an alkyl halide 2. Dehydration of an alcohol 3. Dehalogenation of a vicinal dihalide 4. Reduction of an alkyne Methods 3 & 4 start with compounds that are in turn made from alkenes. docsity.com CH3 HBr CH3 CH3CHCH2CH2-OH CH3CHCH2CH2-Br 1o alcohol, SN2 mechanism, no rearrangement! CH3 KOH(alc) CH3 CH3CHCH2CH2-Br CH3CHCH=CH2 Use the Grignard synthesis to synthesize the intermediate alcohol from the starting materials. docsity.com CH3 PBr3 CH3 Mg CH3 CH3CHCH2-OH CH3CHCH2Br CH3CHCH2MgBr K2Cr2O7 CH3OH H2C=O special cond. H2O CH3 CH3CHCH2CH2-OH HBr CH3 KOH(alco) CH3 CH3CHCH=CH2 CH3CHCH2CH2-Br docsity.com