Aldehydes, Ketones and Carboxylic Acids

Chapter 11 Aldehydes, Ketones and Carboxylic Acids Introduction and Structure of Carbonyl Compound ➤ Carbonyl Compound ➤ Nomenclature and Structure of Carbonyl Group Preparation of Aldehydes and Ketones ➤ General Method of Preparation ➤ General Method of Only Aldehyde and Ketone (for Aldehyde only) Rosenmund's reduction and Stephun's reduction ➤ (for Ketones only) From Grignard's reagent From dialkyl Cadmium) ➤ compounds Physical Properties ➤ Physical Properties of Aldehyde and Ketones Chemical Reactions Nucleophilic Addition ➤ Oxidation Reactions ➤Other Reactions of Aldehyde and Ketones Nomenclature and Structure of Carboxyl Group ➤ Carboxylic Acid Methods of Preparation of Carboxylic Acids ➤ General Introduction and Method of Preparation of Carboxylic Acid Physical Properties of Carboxylic Acid INTRODUCTION AND STRUCTURE OF CARBONYL COMPOUND Carbonyl compound Organic Compounds having > C = 0 group are called carbonyl compounds and > C = 0 group is known as carbonyl or oxo group. It's general formula is C_{n}*H_{2n}*O ( n = 1, 2, 3 ,.....) Carbonyl compounds are grouped into two categories. (a) Aldehydes: Aldehyde group is group). -H (also known as formyl It is a monovalent group. (b) Ketones: The carbonyl group (> c = 0 ) is a Ketonic group when it's both the valencies are satisfied by alkyl group. It is a bivalent group. Nomenclature And Structure of Carbonyl Group Structure And Bonding in Aldehydes and Ketones The carbonyl carbon atom displays sp² hybridization. The unhybridized p-orbital of carbon forms a pi bond through overlap with a p-orbital of oxygen. This results in a double bond between carbon and oxygen, which is characterized by being shorter, stronger, and polar in nature. Orbital diagram for the formation of carbonyl group is as follows + → R 120 deg 120 deg C = 0 C-0 The presence of polarity indicates that nucleophilic addition reactions occur in carbonyl compounds. The carbonyl group's double bond possesses a significant dipole moment due to the higher electronegativity of oxygen compared to carbon. Carbonyl carbon act as an electrophile (Lewis's acid) Carbonyl oxygen act as a nucleophile (Lewis's Base) Chemical Properties of carboxylic acid [÷<] The C-C-O and H-C-O bond angles are of 120°. Due to electro-negativity difference in C & O atoms, the >C=O group is polar. 8- Hence aldehydes and Ketones possess dipole moment. Ketones are further classified as (i) Simple or Symmetrical ketones: Having two similar alkyl groups. R (ii) Mixed or unsymmetrical ketones: Having two different alkyl groups. >C=0 Ex: (Ketones) Symmetrical CH =0 CH (Acetone or Dimethyl ketone) 2-Propanone Unsymmetrical CH CH CH (Ethyl methyl ketone) 2-Butanone 2 By hydrogen cyanide: When hydrogen cyanide reacts with a Grignard reagent and then undergoes double decomposition with water, it leads to the formation of an aldehyde through an aldimine intermediate. H-CRY RMgBr H-CNMgBr H:O/H H-CN H₂O/H H-CO+NH3 R Aldimine R Aldehyde Oxo reaction or hydro formylation In this reaction symmetrical alkene gives 10 aldehydes while unsymmetrical alkene gives isomeric aldehyde (Chain isomers). CH₂CH₂CO+H Water gas CO 150°C CH₂CH₂CHO CH3-CHCH2 + CO + H2 CO 150°C CH3CH2CH2CHO+ CH3-CH-CH CHO For Ketones only From Grignard's reagent 2H₂O RMgX+R-CN H-CNMgX R-CO+NH3 + Mg X OH R R OMgX OH H₂O RMgX+R-C-CI R-C-CI R-C-CI R-C+HCI R RMgX+R-C-NH2 RH+ (RCONH) Mg (X) Ketone does not form. RMAX+R-C-CI RMgX + R-C-CI OMgX R-C-CI H₂O R OH 0 R-C-CI R-C+ HCI R 11 By acylation or benzoylation of aromatic hydrocarbon (Friedel-Crafts Reaction) C_{6}*H_{6} +CH 3 COCl Dry AiCl 3 C 6 H 5 COCH 3 + HCL C_{6}*H_{6} +C 6 H 5 COCl Dry AtCl 3 Acetophenone C_{6}*H_{5}*CO*C_{6}*H_{5} + HCL Benzophenone C6H6 + COCI2 Dry AlCl 3 C_{6}*H_{5}*CO*C_{6}*H_{5} + HCL excess Benzophenone From diallyl Cadmium RCdR' (diallyl Cadmium) is an organometallic compound. RCOCI + RCdR' → RCOR' + RCdCl This process is more advantageous compared to the Grignard Reaction because the ketones produced can subsequently react with Grignard reagents to yield tertiary alcohols. C2H5 CH Ex.: CH3COCI+ >Cd C2H5 C = 0+ C2H5 C2H5 >Cd From R₂CuLi: R₂CuLi + R'COCI →R'COR + RCu + LiCl By hydrolysis of Aceto Acetic Ester (AAE): CH3-C-CH2-COC2H5 A CH-C-CH2-C-OH CH3-C-CH -C2H5OH β 0 0 (Acetone) (B-keto acid) Ex: CHC-CH-C-OC2H5 O CH3 0 12 A -CO2 CH3-C-CH2-CH3 !! HO -C2H5OH βα CH3-C-CH-C-OH-O CHO PREPARATION OF ALDEHYDES AND KETONES General Methods of Preparation General Method of Only Aldehyde and Ketone (A) For Both Aldehydes and Ketones By Oxidation of Alcohols [0] Primary alcohols Aldehydes [0] Secondary alcohols Ketones By K2Cr207/H2SO4 The oxidation of primary alcohols results in the formation of aldehydes, while secondary alcohols, when oxidized, produce ketones. Here, (K2Cr207/H2SO4) is a strong oxidising agent. RCH OH [0] K2Cr2O7/H2SO4 RCHO (Aldehyde) R-CH R [0] K2Cr2O7/H₂SO₄ R-CH OH OH R (Ketone) Aldehydes are quite susceptible to further oxidation to acids - RCH2OH 0, R-CHOF, R-COOH Therefore, the oxidation of primary alcohols is carried out at temperatures significantly higher than the boiling point of aldehydes. This high temperature causes the aldehydes to vaporize and prevents them from undergoing further oxidation. Aldehydes can be synthesized from primary alcohols, while secondary alcohols can be oxidized to ketones using various reagents such as pyridinium chlorochromate (PCC) in CH2Cl2 solvent, pyridinium dichromate (PDC), or Jones reagent (CrO3+H2SO4) in acetone. Oppenauer Oxidation The transformation of secondary alcohols into ketones is achieved through the application of a specialized reagent, [(CH3)3CO]3Al (Aluminum-t-butoxide), while being heated in the presence of acetone. In the case of primary alcohols, they can be oxidized to aldehydes when ketones are substituted with a more effective hydrogen acceptor, such as p-benzoquinone. The balance of this reaction can be managed by adjusting the quantity of acetone, with an excess of acetone promoting the oxidation of the alcohol. CHa CHOH + CO CH3 CH-OH R R [(CH3)CO] Al R Ketone CH3 C0+ CH Isopropyl alcohol 3 2ª Alcohol Acetone [(CH),CO] AI RCH2OH + O 0 Quinone R-CHO+НО- -OH 1°Alcohol Aldehyde Quinol Note: The reaction is the reverse of Meerwein - Ponndorf-verley reduction. Mild Oxidising Agent 1º alcohols will get oxidised with CrO3/Pyridine, Collin's reagent Ag/02 at 250°C RCH2OH + [0] RCHO + H2O By this reaction, good yield of aldehyde is possible. Dehydrogenation of alcohols CH 300°C CH3CHO (Acetaldehyde) CH3CH2OH CH3-CHCH3 OH CH 300°C CH3-C-CH3 (Acetone) (Isobutylene) CH CH-C-OH 1 CH3 CH 300°C CH2 CH3-C+H₂O CH By Hydrolysis of gem dihalides Terminal gem-dihalides on hydrolysis give aldehydes while the non-terminal dihalides give ketone. C1 CH.CH KOH(aq.) CHICH Terminal gem-dihalide [unstable] -H₂O CHICHO Acetaldehyde CI KOH (aq) CH-C-CH CI CH-C-CH₃ CI Unstable -H₂O CI CH-C-CH Acetone Wacker process Alkenes can be oxidized to their respective aldehydes or ketones by subjecting them to a solution of PdCl2, which includes a catalytic quantity of CuCl2 in the presence of air or O2. Except ethene any higher alkene will give ketone. CH2=CH2 + H2O + PdCl2 CuCl2 Air or O2 CH-CHO+Pd+ 2HCl R-C-CH3+ Pd + 2HCl CH2=CH2 + H2O + PdCl2 CuClz Air or O2 Note During the reaction PdCl2 is reduced to Pd and CuCl2 is reduced to Cu(1) By Oxidation of diols When subjected to periodic acid (HIO4) and lead tetra acetate (CH3COO), Pb, vicinal diols undergo oxidation to produce carbonyl compounds. R-CH-CH-R' + HIO он он RCHO + R'CHO + HIO + H₂O R-C-C-R' + H1O4 RR OH OH R-C-R+R-C-R+HIO3 + H2O By Ozonolysis of alkenes This reaction is used to determine the position of double bond in alkene. 0 RCH=CH2 + 03 RCH CH₂ -HO Zn RCHO + HCHO Ozone Ozonide R-C=CH2+O 0 R-C CH2 -H2O Zn R-CO+HCHO R R R Unbranched alkene Branched alkene Aldehyde Ketone By Dry Distillation of Ca-Salts of Carboxylic Acid R COO Ca + Ca H H R COO 2RCHO+ 2CaCO₃ R-C-R Calcium format (Also and HCHO formed) H COO HCHO + CaCO3 Ca A H COO R COO R Ca R CC=0+ CaCO R COO Calcium-alkenoate Ketone 5 Calcium salts of acids other then formic acid on heating together gives ketone R COO Ca + Ca R COO R i 2R-C-R+2CaCO3 Ketone To prepare ethyl methyl ketone Calcium acetate and Calcium propionate are used 0 CHOCO O-C-CH2CH3 CH Ca + Ca 2 C=0+2CaCO₃ CHOCO OC-CH2CH3 CH Calcium Acetate Calcium propionate Ethyl methyl ketone From Alkyne Hydration of Alkyne: With dill H2504 & 1% HgSO4 at 60-80°C. CHCH + H2O [CH2CHOH] CH-C-H (Tautomerization) Other Alkynes give ketone A CH₂C=CH + H₂O ← CH-C-CH2 OH (enol) CH-CH 0 Hydroboration of Alkynes: Reaction with B2H6, 2BH3 or R2BH give dialkyl borane. 1-alkyne gives other alkyne Aldehyde Ketone A R-CCH + R2BH R-CH=CHBR2 H₂O OH Tautomerism RCH=CHOH R-CH2 C-R2BOH CH CC CH3 + R2BOH → CH3CH=C-CH HO OH BR → CH3CH2 C CH₃+ R2BOH OH RBOH + CH3-CH=C-CH 6 By Thermal Decomposition of Carboxylic Acids Vapour of carboxylic acids when passed over MnO/300°C give carbonyl compounds 2 HCOOH MnO 300°C HCHO + H2O + CO2 2 CH3COOH Mno 300°C CH3 CO+CO2 + H2O CH RCOOH + HCOOH Mno 300°C RCHO + CO2 + H2O RCOOH + R'COOH MnO 300°C RCOR' + CO2 + H2O By Nef's Reaction Nitro alkanes are used in this reaction. The a-H of nitro alkane shows acidic nature. R-CHO+N2O + H2O+NaOH 1º nitro alkane aligned R CHz\ N zeta 0 ^ 0 0 sqrt - R\ CH equiv N * zeta_{0} ^ (OH) * (Na * 0H)/(Na * 0H) + R - cH =N zeta 0 ^ 0^ Theta Na H 30 Theta (Allehvde) ^ Theta H 30 H 30 ,\\ (Alehvde) aligned Na RICH-NC-NOH NAOH RC-NON HOR ← (Nitro form) (Aci form) CON2O+H2O+NaOH (Ketone) 2 deg nitro alkane R-RC-NO NaOH No Reaction 3 deg nitro alkane) By Hydrolysis of Carbonyl Derivatives R-CHN-OH (Aldoxime) R>C=N-OH (Ketoxime) R>CC=0+2ROH (Aldehyde) (Alcohol) 7 RC (Ketal) OR OR H2O/H R >C=0+2ROH (Ketone) (Alcohol) By Oxidation of Alkyl Halides Oxidation takes place by (CH3)2SO dimethyl sulphoxide (DMSO). R-CH2-X+(CH3)2SO RCHO + (CH3)2S + HX Alkyl halide (Aldehyde) (Dimethyl thio ether) X R-CHOH (CH3)S=O R-C-R 2º halide Ketone From Grignard Reagents By Cyanides using RMgX H2O/H RMgX+R-C EN →R-CN-MgX R C-R+NH3+Mg 0 (Ketone) OH By Esters using RMgX: HCHO can't be prepared by this method. 0 RMgX+ R-C OR OMgX OH H₂O R OR R-C-OR R-CO R (Alkyl Alkenoate) R (Hemiacetal) R (Ketone) 0 OMgX OH H₂O -ROH RMgX+H-C-OR H OR H-C-OR H-C-0 (Alkyl format) R R (Hemiacetal) (Aldehyde) By acid chlorides using RMgX R-C-CI+ RMgX 0 R>C=0+Mg < 8 From ẞ-keto acids The decarboxylation reaction takes place via formation of six membered ring transition state. (a) H-C-CH2-C-OH 110°C CH3CHO+CO2 βα (b) CH3-C-CH2-C-OH Δ -CO: 0 (B) For Aldehydes Only CH-C-CH3 Reduction of acyl halides, esters and nitriles Alkenes can be oxidized to their respective aldehydes or ketones by subjecting them to a solution of PdCl2, which includes a catalytic quantity of CuCl2 in the presence of air or O2. LIAIH [OC(CH3)3]. at-78°C. 0 CI (1) LAH(t-BuO)-78℃ (ii) H₂O R H DIBAL-H can be used to reduce both esters and nitriles to yield aldehydes. This reduction process should be conducted under low-temperature conditions. Subsequent hydrolysis of the intermediates produces the aldehyde. 0 0 (1) DIBAL-H, hexane-78°C (ii) H2O CI H R-CN (1) DIBAL-H, hexane - 78°C (ii) H₂O R H Rosenmund's reduction Quinoline or sulfur serves as a catalyst inhibitor, regulating the subsequent conversion of aldehydes into alcohols. RCOCI + H₂ Pd/BaSO4 Quinoline or sulphur RCHO + HCI Pd RCOCI + H₂ RCHO RCH2OH Formaldehyde cannot be prepared by this method. Ex. C2H5COCI + H₂ Propionyl Chloride Pd/BaSO Quinoline or sulphur C₂H₂CHO + HCI Propenal 9 Reimer-Tiemann Reaction By this method phenolic aldehyde is prepared Phenol OH CHO CHCI/KOH Salicylic aldehyde Stephen's reduction OH Alkyl cyanides are reduced by SnCl2 and HCl. R-CN SnCl2/HCl R-CHNH H₂O+ RCHO + NH R-CN SnCl₂/HCI R-CHNH HO RCHO + NH From hydrocarbons By oxidation of methyl benzene and its derivative using chromyl chloride (CrO2Cl2) CH CH(OCrOHCl2)2 CS2 CHO + CrO2Cl2 HO Toluene Chromium complex Benzaldehyde This reaction is called Etard reaction. By oxidation of methyl benzene and its derivative using chromic oxide (CrO3) in acetic anhydride CH CH(OCOH3)2 CHO +CrO3+ (CH3CO)20 273-283 K HO Benzaldehyde By Gattermann-Koch reaction: Benzene or its derivative CO₂HCI Anhy.AlCl3/CuC Benzaldehyde or substituted benzaldehyde CHO COHCI Benzene Anhy. AlCl3/CuCl Benzaldehyde 10