Carbonyl Compounds

INTRODUCTION Organic Compounds having C O group are called carbonyl compounds and C O group is known as carbonyl or oxo group. It's general formula is Cn H2nO (n = 1, 2, 3......) Carbonyl compounds are grouped into two categories. O (a) Aldehydes : Aldehyde group is (b) Ketones : The carbonyl group ( C H (also known as formyl group). It is a monovalent group C O) is a Ketonic group when its both the valencies are satisfied by alkyl group. It is a bivalent group. STRUCTURE AND BONDING IN ALDEHYDES AND KETONES The carbonyl carbon atom is sp2 hybridized. The unhybridized p-orbital overlaps with a p-orbital of oxygen to form a pi bond. The double bond between carbon and oxygen is shorter, stronger, and polarized. Orbital diagram for the formation of carbonyl group is as follows: R 120° R R C O R .. C=O .. major 120° R R + ..C – O: .. minor This polarity confirms that there is nucleophilic addition reaction takes place in carbonyl compound. The double bond of the carbonyl group has a large dipole moment because oxygen is more electronegative than carbon. Carbonyl carbon act as an electrophile (Lewis acid) Carbonyl oxygen act as a nucleophile (Lewis base) 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 C O group is polar.. Hence aldehydes and Ketones posses dipole moment. Ketones are further classified as : (i) Simple or Symmetrical ketones : Having two similar alkyl groups. (ii) Mixed or unsymmetrical ketones : Having two different alkyl groups. R R R R' C O C O CARBONYL COMPOUNDS Ex : (Ketones) : Symmetrical Unsymmetrical CH3 CH3CH2 CH3 C O CH3 (Acetone or Dimethyl ketone) 2–Propanone C O (Ethyl methyl ketone) 2–Butanone S KEEYYPPOOIN INTTS O C O O .. OH, C .. O .. C X, NH2, C .. OR, In all the compounds given above, lone pair of electrons and double bond are conjugate. O O C .. so resonance occurs. These compounds have Z group still they are not carbonyl compounds C because carbonyl group takes parts in resonance with the lone pair of electrons. GENERAL METHODS OF PREPARATION (A) FOR BOTH ALDEHYDES AND KETONES By Oxidation of Alcohols : Primary alcohols [O] [O] Secondary alcohols Aldehydes Ketones By K2Cr2O7 / H2SO4 : Oxidation of primary alcohols gives aldehyde and oxidation of secondary alcohols gives Ketones. Here, (K2Cr2O7 / H2SO4) is a strong oxidising agent. [O] RCH 2OH R CH K2Cr2O7/ H2SO4 R [O] K2Cr2O7/ H2SO4 (Aldehyde) RCHO R C R (Ketone) OH O Aldehydes are quite susceptible to further oxidation to acids RCH2OH [O] R—CHO [O] R—COOH Thus oxidation of primary alcohols is made at the temperature much above the boiling point of aldehyde and thus aldehydes are vapourised out and prevented from being oxidised. KEY POINTS Aldehydes can be prepared from 1° alcohol, secondary alcohols can be oxidized to ketones, by oxidation with pyridinium chlorochromate (PCC) in CH2Cl2 solvent, pyridinium dichromate (PDC) and with Jones reagent (CrO3+H2SO4) in acetone. Oppenauer Oxidation : The oxidation of secondary alcohols to ketones by heating them with specific reagent : [(CH 3)3CO]3Al (Aluminium-t-butoxide) in presence of acetone. Primary alcohols may also be oxidized to aldehydes if ketones is replaced by a better hydrogen acceptor, e.g. p-benzoquinone. The equilibrium can be controlled by the amount of acetone, an excess of which favours the oxidation of the alcohol. R R CHOH CH3 C CH3 + 2O Alcohol O R [(CH 3)3CO] 3Al R C O+ Acetone RCH2OH + O 10 Alcohol CH3 Ketone [(CH 3)3CO] 3Al O CH3 R—CHO + HO— Quinone CH OH Isopropyl alcohol —OH Aldehyde Quinol Note : The reaction is the reverse of Meerwein-Ponndorf -verley reduction. Mild Oxidising Agent : o o 1 alcohols will get oxidised with CrO3 / Pyridine, collin's reagent Ag / O2 at 250 C RCH2OH + [O] RCHO + H2O  By this reaction, good yield of aldehyde is possible. Dehydrogenation of alcohols : CH3CH2OH Cu 300°C CH3 Cu 300°C CH3CHO (Acetaldehyde) O CHCH3 CH3 C CH3 (Acetone) OH CH3 CH3 C CH2 OH Cu 300°C C + H2O (Isobutylene) CH3 CH3 CH3 By Hydrolysis of gem dihalides : Terminal gem-dihalides on hydrolysis give aldehydes while the non-terminal dihalides give ketone. CH3CH Cl KOH (aq.) Cl Terminal gem-dihalide CH3CH OH [unstable] C Cl H2O CH3CHO Acetaldehyde OH Cl CH3 OH CH3 KOH (aq.) CH3 C O CH3 OH unstable H2O CH3 C CH3 Acetone CARBONYL COMPOUNDS Wacker process : Alkenes can directly be oxidised to corresponding aldehydes or ketones by treating them with a solution of PdCl 2 containing a catalytic amount of CuCl2 in presence of air or O2 . Except ethene any higher alkene will give ketone. CuCl2 air or O2 CH2 = CH2 + H2O + PdCl2 CH3 – CH = O + Pd + 2HCl O R – CH = CH2 + H2O + PdCl2 Note CuCl2 air or O2 R – C – CH3 + Pd + 2HCl During the reaction PdCl2 is reduced to Pd and CuCl2 is reduced to Cu(I) By Oxidation of diols : With periodic acid (HIO4) & lead tetra acetate (CH3COO)4 Pb vicinal diols gets oxidised to form carbonyl compounds R CH CH OH OH R R R C C R' + HIO 4  RCHO + R'CHO + HIO3 + H2O O R' + HIO4  R C O R + R' C R + HIO3 + H2O OH OH By Ozonolysis of alkenes : This reaction is used to determine the position of double bond in alkene. O RCH CH2 + O3 O RCH Ozone –H2O CH2 RCHO + HCHO Zn O Ozonide R C R CH2 + O3 R O O C CH2 R O Unbranched alkene Branched alkene –H2O Zn R C R Aldehyde Ketone O + HCHO By dry distillation of Ca-salts of carboxylic acid : O R COO R COO O Ca + Ca O C C H  H 2RCHO + 2CaCO3 O Calcium formate H COO HCO O R COO RCO O C R and HCHO formed) O (Also R Ca  Ca  HCHO + CaCO3 R R C O + CaCO 3 Calcium-alkanoate Ketone Calcium salts of acids other then formic acid on heating together gives ketone O R COO R COO Ca + Ca O C R' O C R' O  2R C R' + 2CaCO3 Ketone O To prepare ethyl methyl ketone Calcium acetate and Calcium propionate are used : O CH3 CH3 OCO Ca + Ca OCO O O C C CH2CH3 CH2CH3 O Calcium Acetate Calcium propionate 2  CH + H2O  [CH2 C2H5 C O + 2CaCO3 Ethyl methyl ketone From Alkyne : Hydration of alkyne : With dil H2SO4 & 1% HgSO4 at 60-800C. CH CH3 CHOH] O CH3 C H (Tautomerisation) Other alkynes give ketone : Hydroboration of alkynes : Reaction with B2H6, 2BH3 or R2BH give dialkyl borane. 1  alkyne gives other alkyne Aldehyde Ketone CARBONYL COMPOUNDS CH3—C C—CH3 + R2BH  CH3 CH CH3 C H2O2  OH BR2 R2BOH+CH3 CH C CH3 ‡ˆ ˆˆ ˆ† ˆˆ CH3 CH2 C CH3 + R2BOH O OH By Thermal decomposition of carboxylic acids : Vapour of carboxylic acids when passed over MnO/3000C give carbonyl compounds MnO 2 HCOOH HCHO + H2O + CO2 300°C CH3 MnO 2 CH3COOH CH3 300°C MnO RCOOH + HCOOH O + CO2 + H2O RCHO + CO2 + H2O 300°C MnO RCOOH + R'COOH C RCOR' + CO2 + H2O 300°C By Nef's reaction : Nitro alkanes are used in this reaction. The  of nitro alkane shows acidic nature. (Nitro form) 1° nitro alkane (Nitro form) 2° nitro alkane R R C N (Aci form) (Aci form) O R O (3° nitro alkane) (Aldehyde) NaOH (Ketone) No Reaction By hydrolysis of carbonyl derivatives : R—CH N—OH (Aldoxime) R C N R (Ketoxime) OH H2O / H  H2O / H  R—CHO + NH2—OH (Aldehyde) (Hydroxyl amine) R C O + NH 2 R (Ketone) OH R C OR H OR (Acetal) R C OR R OR (Ketal) H2O / H  H2O / H  R C O + 2ROH H (Aldehyde) (Alcohol) R C O + 2ROH R (Ketone) (Alcohol) By oxidation of alkyl halides: Oxidation takes place by (CH3)2S O dimethyl sulphoxide (DMSO). R—CH2—X + (CH3)2S O  RCHO + (CH3)2S + HX Alkyl halide (Aldehyde) (Dimethyl thio ether) X O (CH3)2S=O R CH R 2° halide R C R Ketone From Grignard reagents : By Cyanides using RMgX : By Esters using RMgX : HCHO can't be prepared by this method. By acid chlorides using RMgX : R' C  Cl + RMgX  O From -keto acids : R' R C O + Mg X Cl The decarboxylation reaction takes place via formation of six membered ring transition state. O (b) O (a) H  C  CH 2  C  OH  110°C CH3CHO+CO2 (B) CARBONYL COMPOUNDS (B) FOR ALDEHYDES ONLY Reduction of acyl halides, esters and nitriles : Acyl chlorides can be reduced to aldehydes by treating them with lithium-tri-tert-butoxyaluminium hydride, LiAIH[OC(CH3)3], at – 78°C. O O (i) LAH(t-BuO)3, 78°C R (ii) H2O R Cl H Both esters and nitriles can be reduced to aldehydes by DIBAL-H. Reduction must be carried out at low temperatures. Hydrolysis of the intermediates gives the aldehyde. O O (i) DIBAL  H, hexane 78°C R (ii) H2O OR' R—CN (i) DIBAL  H, hexane 78°C (ii) H2O R H O R H Rosenmund's reduction : Quinoline or sulphur act as a poisoned catalyst, controls the further reduction of aldehyde to alcohols. Pd/ BaSO 4 RCOCl + H2 RCHO + HCl Quinoline or sulphur RCOCl + H2 RCHO  RCH2OH Pd Formaldehyde can not be prepared by this method. Ex. Pd/ BaSO 4 C2H5COCl + H2 Quinoline or sulphur C2H5CHO + HCl Propionyl Chloride Propanal Reimer-Tiemann Reaction : By this method phenolic aldehyde is prepared OH OH CHO CHCl3/KOH Salicylic aldehyde Phenol Stephen's reduction : Alkyl cyanides are reduced by SnCl2 and HCl. R—C N C2H5—C N SnCl 2/HCl R—CH SnCl 2/HCl C2H5CH NH NH H 3O + H 3O + RCHO+NH3 C2H5CHO + NH3 From hydrocarbons : By oxidation of methyl benzene and its derivative using chromyl chloride (CrO2Cl2) CH3 CHO CH(OCrOHCl2)2 + CrO2Cl2 CS2 Toluene H 3O + + Chromium complex Benzaldehyde This reaction is called Etard reaction. By oxidation of methyl benzene and its derivative using chromic oxide (CrO 3) in acetic anhydride: CHO + CrO3+(CH3CO)2O 273-283 K H 3O + Benzaldehyde By Gattermann-Koch reaction : CO HCl 3 Benzene or its derivative Anhy. AlCl Benzaldehyde or substituted benzaldehyde 3/CuCl CHO CO3HCl Anhy. AlCl3/CuCl Benzene Benzaldehyde By hydrogen cyanide : Hydrogen cyanide on treating with Grignard reagent followed by double decomposition with water gives aldehyde via aldimine.  H – C = O + NH3 H – C = NH R Aldehyde R Aldimine Oxo reaction or hydroformylation : In this reaction symmetrical alkene gives 10 aldehyde while unsymmetrical alkene gives isomeric aldehyde (Chain isomers). CH2 CH2 + CO  H E55555F2 CH3CH2CHO Water gas CH3—CH CH2 + CO + H 2 CH3CH2CH2CHO + CH 3 CH CHO CH 3 CARBONYL COMPOUNDS For Ketones only : From Grignard's reagent : RMgX + R—C  R N C NMgX 2H2O R R C O + NH3 + Mg R X OH ; Ketone does not forms. By acylation or benzoylation of aromatic hydrocarbon (Friedel-Crafts Reaction) C6H6 + CH3COCl Dry AlCl3 C6H5COCH3 + HCL Acetophenone C6H6 + C6H5COCl Dry AlCl3 C6H5COC6H5 + HCL C6H6 + COCl2 Dry AlCl3 C6H5COC6H5 + HCL excess Benzophenone Benzophenone From dialkyl Cadmium : RCdR' (dialkyl Cadmium) is a organometallic compound. RCOCl + RCdR'  RCOR' + RCdCl This reaction is superior than Grignard Reaction because the ketones formed, further reacts with Grignard reagent to form 3° alcohols. Example : From R2CuLi : R2CuLi + R'COCl  R'COR + RCu + LiCl By hydrolysis of Aceto Acetic Ester (AAE) : ( - keto acid) (Acetone) Ex. ( –keto acid) (Butanone) PHYSICAL PROPERTIES State : Only formaldehyde is gas, all other carbonyl compounds upto C11 are liquids and C12 & onwards solid. Odour : Lower aldehydes give unpleasant smell, higher aldehydes and all ketones have pleasant smell. Solubility : C1 to C3 (formaldehyde, acetaldehyde and propionaldehyde) and acetone are freely soluble in water due to polarity of bond and can form H—bond with water molecule. C5 onwards are insoluble in water.. Solubility  1 Molecular weight H-bonding Boiling point : Boiling point  Molecular weight Boiling point order is - Alcohol > Carbonyl compounds > Alkane This is because in alcohols intermolecular H-bonding is present but in carbonyl compounds H-bonding doesn't exist, instead dipole-dipole van der waal force of attraction is present. Alkanes are non polar. Density : Density of carbonyl compounds is lower than water. CHEMICAL PROPERTIES : Reactions of both aldehydes and ketones : Due to strong electronegativity of oxygen, the mobile  electrons pulled strongly towards oxygen, leaving the carbon atom deficient of electrons.     C O C O  Carbon is thus readily attacked by N u . The negatively charged oxygen is attacked by electron deficient (electrophile) E+. C O bond in carbonyl group is stronger than C=C bond in alkanes. C C O O Bond energy is 84.0 K Cals Bond energy is 178 K Cals C C C C Bond energy is 83.1 K Cals Bond energy is 146 K Cals 1 Reactivity of carbonyl group Magnitude of +ve charge  – I group  + I group CARBONYL COMPOUNDS Ex. Why carbonyl compound gives nucleophilic addition reaction (NAR) ? Sol. Ex. Arrange the following for reactivity in decreasing order H C O O C O (i) ClCH 2 CHO (ii) NO 2CH 2 CHO (iii) CH 3CHO (iv) CH 3CH 2CHO (III) (i) CH 3CHO (iii) HCCl2 CHO (iv) CCl3CHO (IV) (i) H (iii) CH3 (II) (ii) ClCH 2 CHO CH3CH2 CH3 Sol. C (i) H (ii) CH3 (I) (ii) CH3 (A) I > II > III CH3 C O (iii) (B) II > I > III > IV CH3 (CH3)2CH CH 3 C O (iv) (C) IV > III > II > I [Hint : CH3— is +I group, decreases the intensity of +ve charge on C-atom of (D) C Ex. In Cl O and H Cl Chloral Sol. CH3(+I) C H CH3 C O IV > I > II > III O group. Cl – is –I group increases the intensity of +ve charge on C-atom of Cl (-I) C C CCl3 C O group.] O , which one is more reactive ? I is more reactive than II. CHEMICAL REACTIONS Carbonyl compounds in general under goes nucleophilic addition reaction : Addition of a nucleophile and a proton across the (C = O) double bond. The reactivity of the carbonyl group arises from the electronegativity of the oxygen atom and the resulting polarization of the carbon-oxygen double bond. The electrophilic carbonyl carbon atom is sp2 hybridized and flat, leaving it relatively unhindered and open to attack from either face of the double bond. Mechanism a b – Nu C == O Planar slow step 1 Nu a b Nu + O— Tetrahedral intermediate H fast step 2 a b OH Addition product Nucleophile (Nu-) attacks the carbonyl group perpendicular to the plane of sp2 hybridised orbitals of carbonyl carbon. In the process, hybridisation of carbon changes from sp2 to sp3. A tetrahedral alkoxide is formed as intermediate. Reactivity : Aldehydes are more reactive than ketones in nucleophilic addition reactions. H C=O > R C=O > H There are two factors which influence the reactivity of ketone and aldehyde. H (i) Inductive effect (ii) steric factor (i) + I effect of alkyl group decrease the amount of charge on C+ (C+ – O–). in ketones. (ii) Steric effect also causes the less reactivity of carbonyl group. Nucleophilic addition reactions : (1) Addition of HCN : CARBONYL COMPOUNDS (2) Addition of NaHSO3 : This reaction is utilized for the separation of carbonyl compounds from non - carbonyl compounds. C O + NaHSO3  C OH H 3O  Carbonyl compounds. *(Regain) SO3 Na Sodium bi sulphite Mechanism : C (3) Bisulphite compound (Crystalline) NaHSO3 ‡ˆ ˆˆ ˆ† ˆˆ Na + + HSO 3 HSO 3 ‡ˆ ˆˆ ˆ† ˆˆ H + + SO 3–2 O + SO3 –2 Reaction with ammonia derivatives : These are condensation or addition elimination reaction. These proceeds well in weakly acidic medium. NH3 C O + H2N Z NH2Z (Ammonia derivative)  H +Z C Addition - elimination (Condensation) Mechanism : N Z + H2O Ammonia derivatives (NH2Z) : Z = OH  NH2OH (Hydroxyl amine) Z = NH2  NH 2NH2 (hydrazine) Z = NHC6H5  NH2NHC6H5 (Phenyl hydrazine) Z = 2, 4–Dinitro phenyl hydrazine (DNP) Brady's reagent. Z = NHCONH2  NH2NHCONH2 Semi Carbazide. (Aldoxime) (Hydrazone) (Phenyl hydrazone) (Semi Carbazone) (4) With alcohol and thioalcohol : H R C O + ROH HCl(g) H R C OH ROH HCl(g) OR Hemi-acetal R R C O + 2ROH HCl(g) R R C OR OR H R C OR OR Acetal + H2O Ketal Tri ethoxy methane [HC(OC2H5)3] remove the water formed during the reaction and so the reaction proceeds in forward direction. CARBONYL COMPOUNDS R H C R HCl(g) H2O O + 2RSH H Thioalcohol R R C SR SR R [O] H R R C SR SR R [O] CH3 C SO2R CH3 SO2R C2H5 Sulphonal (5) C C R Mercaptal (Thio Ketal) All sulphones compounds are hypnotic compounds. CH3 C SO2R SO2R Mercaptal HCl(g) H2O O + 2RSH C SO2 R SO2 R Sulphones Compound SO2R C2 H5 SO2R C2H5 Trional C SO2R SO2R Tetronal Reaction with glycol (group protection) : C O+ H O CH2 H O CH2 (neutral) (6) Reaction with sodium alkynide : (7) Reaction with Grignard reagent : HCl(g) H2O C O CH2 O CH2 Cyclic acetal / ketal Ethanol (1° alcohol) CH3CHO + CH3Mgl 2–Propanol (2° alcohol) 2–Methyl–2–propanol (3° alcohol) (8) Reaction with H2O : It is a reversible reaction. C weak acid O + H 2O C H2O OH OH (neutral) Ex. unstable hydrate Which compound form more stable hydrate with H 2O? (A) HCHO (B) CH3CHO (C) CH3COCH3 (D) CH3COC2H5 [Hint : HCHO since it is more reactive towards this reaction.] Ans. (A) Ex. Which carbonyl compound not gives reversible reaction with water ? Sol. Chloral hydrate. (Chloral) (Chloral hydrate) Stable by intra molecular hydrogen bonding. Wittig Reaction : Wittig reaction affords an important and useful method for the synthesis of alkenes by the treatment of aldehydes or ketones with alkylidenetriphenylphosphorane (Ph3P = CR2) or simply known as phosphorane Ph Ph P Ph + CH2 Ph Ph Ph O Ph CH2 Ph (1-phenylvinyl) benzene + Ph P O Ph triphenylphosphine oxide The wittig reagent, alkylidenetriphenylphosphorane (ylide), is prepared by treating trialkyl or triarylphosphine usually the latter with an alkyl halide in either solution. The resulting phosphonium salt is treated with strong base (such as C6H5Li, BuLi, NaNH2, NaH, C2H 5ONa, etc.) Cannizaro's reaction : Those aldehydes which do not contain are Salt of carboxylic acid + alcohol.  -H atom give this reaction, with conc. NaOH or KOH; Products In this reaction one molecule of carbonyl compounds is oxidised to acid, while other is reduced to alcohol, such type of reactions are called disproportionation reaction. (Redox reaction) HCHO + HCHO conc. NaOH HCOONa + CH3OH CARBONYL COMPOUNDS Mechanism : (Cannizaro reaction) (a) Rapid reversible addition of OH to one molecule of HCHO. OH H C OH H H C H O O 1 (b) Transfer of hydride ion H to second molecule of HCHO (c) Proton exchange HCOO 1 + Na  HCOO 1 + CH3OH  HCOONa When molecules are same Two different molecules Simple cannizaro reaction Mixed cannizaro reaction In mixed or crossed cannizaro reaction more reactive aldehyde is oxidised and less reactive aldehyde is reduced. HCHO + C6H5CHO NaOH HCOONa Oxidized + (Sodium formate) Ex : CH3CHO + HCHO Ca(OH)2 C6H5CH2OH Reduced (Benzyl alcohol) C(CH2OH)4 + (HCOO)2 Ca, explain mechanism ? 2, 2-Dihydroxy methyl –1, 3–propane diol.(Penta erythritol) Tishchenko reaction : It is a modified cannizaro reaction. All aldehydes undergo this reaction in presence of (C2H5O)3Al, to form ester. O 2RCHO (R'O) 3 Al  RCH2 O C R Ester Ex. CH 3CHO + CH 3CHO (C 2H5O) 3 Al CH COOH + CH CH OH 1 4 43 4 4 4 2 4 43 4 42 43 Esterification  CH3—COOCH2CH3 (Ethyl acetate) Reaction With Halogen : Replacement of -H atoms : This reaction is not shown by formaldehyde (HCHO), since  -H atoms are absent, as enolisation does not takes place in HCHO. Ex. Ex. Ex. Ex. Replacement of O-atom of C O group : It takes place by PCl5 or SOCl2. C O + PCl5 C  Cl Cl + POCl3 Phosphorus penta chloride C O + SOCl2  C Cl Cl + SO2 Thionyl chloride Haloform reactions : Chlorine or bromine replaces one or more -hydrogen atoms in aldehydes and ketones, e.g., acetone may be brominated in glacial acetic acid to give mono bromoacetone : CH3COCH3 + Br2  CH3COCH2Br + HBr (43–44%) The halogenation of carbonyl compounds is catalysed by acids and bases. Let us consider the case of acetone. In alkaline solution, tribromo acetone and bromoform are isolated. Thus, the introduction of a second and a third bromine atom is more rapid than the first. In aqueous sodium hydroxide, the rate has been shown to be independent of the bromine concentration, but first order with respect to both acetone and base i.e., Rate = k [acetone] [OH1] CARBONYL COMPOUNDS Aldol Condensation : Two molecules of an aldehyde or a ketone undergo condensation in the presence of a base to yield a hydroxyaldehyde or a -hydroxyketone. This reaction is called the aldol condensation. In general Carbonyl compounds which contain -H atoms undergo aldol condensation with dil. NaOH. Aldol contains both alcoholic and carbonyl group. Mechanism of aldol condensation : It takes place in the following two stages :  Formation of Carbanion  Combination of carbanion with other aldehyde molecule. Formation of Carbanion : -H atom of C O group are quite acidic which can be removed easily as proton, by a base. Carbanion thus formed is stable because of resonance - Combination of carbanion with other aldehyde molecule : Aldol condensation is possible between : 1. Two aldehyde (Same or different) 2. Two ketones (Same or different) 3. One aldehyde and one ketone Identical carbonyl compounds Different carbonyl compounds Simple or self aldol condensation Mixed or crossed aldol condensation Simple or Self condensation : Mixed or Crossed aldol Condensation : Ex : Sol. CH3CHO + CH3CH2CHO OH (WB) OH Total 4 products. Write structure of products ? (Aldol) OH CH3—CH (Aldol) CH—CHO CH3—CH2—CH CH—CHO CARBONYL COMPOUNDS OH (Aldol) OH (Aldol) Intramolecular aldol condensation : ( – Unsaturated Ketone) (Aldol) Here 5 membered ring is more stable than 3 membered ring so above product is formed as a major product. INNTTS S KEEYYPPOOI If in crossed aldol condensation reaction , only one carbonyl compound have –H than total two product formed. OH (WB) CH3CHO + C6H5CHO OH Total 2 product. (Aldol) CH3—CH CH—CHO (Crotonaldehyde) OH (Aldol) C6H5—CH CH—CHO (Cinnamaldehyde) Claisen Condensation : When two molecules of ester undergo a condensation reaction, the reaction is called Claisen condensation. The product of the claisen condensation is a -keto ester. -keto ester After nucleophilic attack, the aldol addition and the Claisen condensation differ. In the claisen condensation, the negatively charged oxygen reforms the carbon oxygen -bond and eliminates the OR group. Mixed Claisen Condensation : Intramolecular Claisen Condensation : Dieckmann condensation : The addition of base to a 1,6-diester causes the diester to undergo intramolecular claisen condensation, thereby forming a five membered ring -keto ester. An intramolecular claisen condensation is called a Dieckmann condensation. Perkin Reaction : In perkin reaction, condensation has been effected between aromatic aldehydes and aliphatic acid anhydride in the presence of sodium or potassium salt of the acid corresponding to the anhydride, to yield , -unsaturated aromatic acids. The acid anhydride should have at least two -H. C6H5CHO + (CH3CO)2O AcONa 170  180°C C6H5—CH=CH—COOH CARBONYL COMPOUNDS Knoevenagel Reaction : Condensation of aldehydes and ketones with compounds having active methylene group in the presence of basic catalyst to form a, b-unsaturated compounds is called Knoevenagel Reaction. The basic catalyst may be ammonia or its derivative. Thus 1°, 2°, 3° amines i.e., aniline, di-or tri - alkyl amines, pyridine or piperidine are used. Reformatsky Reaction : A similar reaction like the addition of organometallic compounds on carbonyl compounds that involves the addition of an organozinc reagent to the carbonyl group of an aldehyde or ketone. This reaction, called Reformatsky reaction, extends the carbon skeleton of an aldehyde or ketone and yields b-hydroxy esters. It involves treating an aldehyde or ketone with an -bromo ester in the presence of zinc metal; the solvent most often used is benzene. The initial product is a zinc alkoxide, which must be hydrolysed to yield the -hydroxy ester. Schmidt Reaction : This is the reaction between a carbonyl compound and hydrazoic acid in the presence of a strong acid concentrated sulphuric acid. Aldehydes give a mixture of cyanide and formyl derivatives of primary amines, whereas ketones give amides : RCHO + HN3 H 2SO 4 RCN + RNHCHO + N2 RCOR + HN3 H 2SO 4 RCONHR + N2 Reaction with primary amine : Schiff's Base Benzoin condensation : The benzoin condensation is essentially a dimerisation of two aromatic aldehydes under the catalytic influence of cyanide ions to give benzoin (I). O 2 C6H5CHO KCN H3C OH H5C6 (I) The hydrogen atom attached to the carbonyl group of aldehyde is not active enough to be removed easily but the addition of the cyanide ion to the carbonyl carbon places this hydrogen in the alpha position of the nitrile thus rendering it relatively acidic. The carbanion, thus generated, attacks the carbonyl carbon of the second aldehyde molecule in a rate-determining step forming an unstable cyanohydrin of benzoin which immediately breaks down into benzoin and hydrogen cyanide. Benzilic acid rearrangement : The addition of a strong base to a carbonyl group results in the formation of an anion. The reversal of the anionic charge may cause expulsion of the attached group X, e.g. However, in a 1, 2-diketone the group X may migrate to the adjacent electron-deficient carbonyl carbon forming -hydroxy acid. Thus, benzil on treatment with a strong base forms benzilic acid (salt), hence the name benzilic acid rearrangement. The Beckmann rearrangement : The acid catalysed transformation of a ketoxime to an N-substituted amide is known as the Beckmann rearrangement. C=O + H2N—OH –H2O C=N—OH Oxime CARBONYL COMPOUNDS The rearrangement is catalysed by a variety of acidic reagents such as H 3 PO 2 , H 2 SO 4 , SOCl 2 , PCl5, etc. Oxidation Reactions : By K 2Cr2O 7/H 2SO 4 : On oxidation with K2Cr2O7/H2SO4 1° alc. gives aldehyde, which on further oxidation gives acid with same C-atom. While, 20 alcohol on oxidation gives ketone which on further oxidation gives acid with less C-atom. [O] R—CH2OH R—CH O [O] R—COOH CH 3 [O] (1° alcohol) CH3CH2CH 2 CH CH 3 [O] CH 3CH2CH 2 OH (2° alcohol) C CH3CH2COOH+CH3COOH O (i) 3° alcohol is not oxidised within 2 or 3 minutes. (ii) 1° and 2° alcohol converts orange colour of K 2Cr 2O7 to green in 2-3 minutes. SeO 2 (Selenium Oxide) : Ketones or aldehydes on oxidation with SeO 2 gives dicarbonyl compounds. This reaction is possible only in compounds containing –carbon. HCHO doesn't show this reaction. Baeyer's Villiger oxidation : Both aldehyde and ketones are oxidized by peroxy acids. This reaction, called the Baeyer-villiger oxidation, is especially useful with Ketones, because it converts them to carboxylic esters. For example, treating acetophenone with a peroxy acid converts it to the ester phenyl acetate. O O O OH H5C6 CH3 Mechanism : R H5C6—O O H3C phenyl acetate The product of this reaction show that a phenyl group has a greater tendency to migrate then a methyl group. Had this not been the case, the product would have been C6H5COOCH3 and not CH3COOC6H5. This tendency of a group to migrate is called is migratory aptitude. Studies of the Baeyer-villiger oxidation and other reaction have shown that the migratory aptitude of groups H > phenyl > 3° alkyl > 2° alkyl 1° alkyl > methyl. In all cases, this order is for groups migrating with their electron pairs, that is, as anions. Ex. Sol. Ex. CARBONYL COMPOUNDS CH3 Sol. CH3 C O CH3 C CH3 O Reduction : The wolf kishner reduction : When a ketone or an aldehyde is heated in a basic solution of hydrazine, the carbonyl group is converted to a methylene group this process is called Deoxygenation because an oxygen is removed from the reactant. The reaction is known as the Wolf-kishner Reduction. COCH3 (i) NH2–NH2 (ii) OH/HOCH2–CH2OH CH3 Clemmensen Reduction : The reduction of carbonyl groups of aldehydes and ketones to methylene groups with amalgamated zinc and concentrated hydrochloric acid is known as Clemmensen reduction. COCH3 Zn–Hg, HCl Reflux CH3 The nature of product depends upon the reducing agent used. It can be summarized as. (i) Reducing agents are (ii) — Red P/HI at 150°C — Zn-Hg/HCl [Clemensen's reduction] — NH2—NH2/C2H5OH,OH1 [Wolff Kishner's reduction] Reducing agents are — LiAlH4 (Nicetron brown) — Na/C2H5OH (Bouveault blank) — NaH/Benzene (Darzen reaction) — [(CH3)2CHO]3Al (Aluminium isopropoxide) — (CH3)2 CHOH (Isopropyl alcohol) Reduction with aluminium isopropoxide is excess of isopropanol is called MPV (Meerwein Ponndorf Verley) reduction. Other reducible groups are not attacked like —NO2, —CH CH 3 Example : CH2 CH C O MPV reduction CH2, —C CH 3 CH 2 CH C—. CHOH Reactions given by only aldehydes : Polymerisation : It is a reversible process. Formaldehyde : Evaporation nHCHO (a) (CH 2O) n , H 2O  Paraformaldehyde n = 6–50 Hydrated white crystal Formalin (40% HCHO) Conc. nHCHO (b) (c) 3HCHO Paraformaldehyde is a linear polymer which show reducing character with Tollen's reagent, Fehling solutio n etc. (CH 2O) n , H 2O H2SO4  Allowed to stand at room temp. Poly oxy methylene n > 100 (CH23O) Meta formaldehyde (Trioxane) Cyclic polymer (Trioxy methylene) Cyclic polymer doesn't show reducing (d) Ca(OH)2 6HCHO or Ba(OH)2 CH2 O O H2C CH2 O character with Tollen's reagent etc. C6H12O6 Formose sugar A linear polymer (  -acrose) Acetaldehyde : CH2 CH (a) 3CH3CHO Conc. H2SO4 Room temp. O (CH3CHO)3 H3C HC O CH CH3 O Para acetaldehyde Paraldehyde (cyclic polymer) Pleasent smelling liquid Hypnotic compound (b) 4CH3CHO CH3 CH3 0°C CH3 O O Conc. HSO 2 4 O O CH3 Meta aldehyde White crystalline solid. Cyclic polymer Used as solid fuel or killing snails (CH3CHO)4 CARBONYL COMPOUNDS Reaction with ammonia : Except formaldehyde, all other aldehydes give addition reactions (HCHO give addition elimination i.e. condensation reaction) 6CH2O + 4NH3 Condensation Reaction (CH2)6N4 + 6H2O Urotropine (Hexamine) White crystalline solid Used in preparation of explosive Used in treatment of urine infection diseases CH3 CH + NH2 O Addition Reaction CH3 Conc. H2 SO4 CH NH2 CH3—CH H O 2 Acetaldimine used in preparation of cyclic polymer OH Acetaldehyde ammonia H CH3 CH HN NH 3CH3—CH NH 3H2O Trimerisation H3C . 3H2O CH HC N NH CH3 H Trimethyl hexahydro Triazine trihydrate Reducing character : Aldehydes are easily oxidised so they are strong reducing agents. Tollen's reagent : It oxidises aldehydes. Tollen's reagent is ammoniacal silver nitrate solution (AgNO3+NH4OH)  [Ag(NH3)2]OH RCHO+[Ag(NH3)2]OH  RCOOH + Ag + H 2O Silver mirror AgNO3 + NH4OH  AgOH  Ag 2 O RCHO + Ag2O  RCOOH + Ag (Silver mirror) Fehling's solution : It is a mixture of CuSO 4, NaOH and sodium potassium tartrate. Fehling solution A– (aq.) solution of CuSO 4 Fehling solution B– Roschelle salt (Sodium potassium tartrate + NaOH) Fehling solution A + Fehlings solution B(Dark blue colour of cupric tartrate) RCHO + Cu+2 + OH–  RCOOH + Cu2O (Cuprous oxide–Red ppt.) 2+ Cu  Cu+ (Cupric - Blue) (Cuprous - Red ppt.) Benedict's solution : It is a mixture of CuSO 4 + sodium citrate + Na 2CO 3. It provides Cu+2. It is reduced by aldehyde to give red ppt of cuprous oxide. – RCHO + Cu2+ + OH  RCOOH + Cu2O (Cuprous oxide–Red ppt.) Mercuric chloride : HgCl 2 is a corrosive sublimate. It is reduced by aldehyde to give white ppt of mercurous chloride (Calonal) which further react with aldehyde to give black ppt of Hg. RCHO + HgCl2 + H 2O  RCOOH + Hg2Cl 2 + HCl (calomal) RCHO + Hg2Cl 2 + H 2O  RCOOH + Hg + HCl (black ppt) Reaction with schiff's reagent : Schiff's reagent is dil solution of p-roseniline hydrochloride or magenta dye. Its pink colour is discharged by passing SO2 gas and the colourless solution is called schiff's reagent, Aldehyde reacts with this reagent to restore the pink colour. Reaction of only ketones : Reduction : Acetone is reduced by magnesium amalgam and water to give pinacol. Pinacol Reaction with chloroform : Reaction with HNO2 : Oximino acetone Oxidation reaction : According to popoff's rule C O group stays with smaller alkyl group. O CH3 CH2 C CH3 CH3COOH + CH3COOH CARBONYL COMPOUNDS Condensation reaction : (a) In presence of dry HCl - aldol condensation takes place Mesityl oxide (b) In presence of conc.H 2SO 4 Reaction with ammonia : Pyrolysis : HCHO CH3CHO  Pyrolysis  CO + H2 CH4 + CO TEST FOR HCHO, CH 3CHO, CH3COCH 3 S.No. 1 2 Test HCHO Legel's test :Na [Fe(NO)(CN)3 ] sodium nitroprusite (alk.) Only methyl C O Compound gives this test Iodoform test (I2 + NaOH) Pyragallol Red Red – – – yellow ppt – yellow ppt – – – Silver mirror Red ppt Black ppt Pink colour Orange colour Blue 4 Orthonitro benzaldehyde Tollen's reagent Fehling's reagent Mercuric chloride Schiff's reagent - 5 6 white ppt. OH OH – Silver mirror Red ppt Black ppt Pink colour Orange colour DNP CH3 COCH3 – OH 3 CH3 CHO – – – – Orange colour BENZALDEHYDE (C6H5CHO) General Method of Preparation : C6H6 C6H5CH3 C6H5COCl C6H5CN (C6H5 COO)2 Ca C6H5CHCl2 C6H5CH2OH C6H5CH2Cl C6H5MgBr C6H6 Oil of bitter almonds CO/ HCl + AlCl3 CrO2Cl2 Pd/BaSO4 (i) SnCl2 /HCl (ii) H2O (HCOO)2 Ca/D * (Gattermann-kosch reaction) * (Etard reaction) * (Rosenmund reaction) * (Stephen's reaction) C6H5CHO aq. KOH [O] (CH2)6N4 (i) HCOOC2H5 (ii) H2O (i) HCN/HCl (ii) H2O AlCl3 (Gattermann) CARBONYL COMPOUNDS Chemical properties : C6H5CH(OH)CN (Similar) C6H5CH(OH)SO3Na NaHSO3 C6H5CH C6H5COOH N 2C6H5CHO C6H5 CH N 2C6H5CHO C6H5 CH C OH O (CH3CO)2O,CH3 COONa H2 CH PCl5 C6H5CHCl2 NO2 – HO C6H5CHO C6H5 C6H5 C6H5 CH C6H5 Benzoin CH CH Perkin CH CH NO2 Nitrostyrene Br Tollen Silver mirror test C6H5COONa + C6H5CH2 Cannizaro reaction N Ar reagent OH NaOH Ar NH2 Schiff's base Schiff's Pink colour reagent C6H5COOCH2C6H5 Tischenko reachion OH CH CH alc.KCN Oxidation C6H5COCl C6H5 2NH3 NH2 Z N Z C6H5CH3 C6H5 170°/Cl2 HCN Red P + HI C6H5CH (different) (ii) H2O HNO3 /H2SO4 Fuming H2 SO4 Cl2/FeCl3 Cinnamic acid Reformatsky reaction m – nitrobenzaldehyde m–formyl benzene sulphonic acid Chloro benzaldehyde AlCl3 Al(OR)3 C6H5MgBr C6H5 (i) Zn+CH2COOC 2H5 H2 O CH3 C O OH CH3 C6H5CH CH C O CH3 COOH