Chap-05 -Organic compounds containing oxygen

https://docs.google.com/document/d/1q3fojxt_oG7HJNBigiFXM4ZXnFv3LBIi/edit?usp=share_link&ouid=109474854956598892099&rtpof=true&sd=true Organic Compounds Containing Oxygen General methods of preparation, properties, reactions and uses. ALCOHOLS, PHENOLS AND ETHERS Alcohols : Identification of primary, secondary and tertiary alcohols; mechanism of dehydration. Phenols : Acidic nature, electrophilic substitution reactions : halogenation, nitration and sulphonation, Reimer - Tiemann reaction. Ethers : Structure. A ldehyde and Ketones : Nature of carbonyl group; Nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones; Important reactions such as - Nucleophilic addition reactions (addition of HCN, NH3 and its derivatives), Grignard reagent; oxidation; reduction (Wolff Kishner and Clemmensen); acidity of α - hydrogen, aldol condensation, Cannizzaro reaction, Haloform reaction; Chemical tests to distinguish between aldehydes and Ketones. CARBOXYLIC ACIDS Acidic strength and factors affecting it. ALCOHOLS Molecules containing –OH group are termed as alcohols. Classification of alcohols they are classified as primary, secondary or tertiary alcohol according to the carbon that is bonded with –OH. Again when any molecule contain 1, 2 or 3 –OH groups then it is called mono, di or tri hydric alcohols respectively. (as in case of alkyl halides) C H A P T E R THIS CHAPTER INCLUDES Alcohols Phenols OH OH OH OH OH Ethers CH3 – CH2OH Ethyl alcohol (monohydric) CH2 – CH2 Ethylene glycol (dihydric) CH2 – CH – CH2 Glycerol (trihydric) Carbonyl compounds Preparation GENERAL METHODS OF PREPARATION From Alkenes : By direct hydrolysis : OH CH – CH = CH + H O H2SO4 CH – CH – CH Oxymercuration demercuration : CH – CH = CH + H O Hg (OAc)2 Properties Carboxylic acid Derivatives of carboxylic acid Acid Halide 3 2 2 THF OH CH – CH – CH NaBH OH CH – CH – CH Acid Anhydride Ester 2 2 OH– 3 3 Hydroboration oxidation : Hg(OAc) Acid Amide 6CH – CH = CH B2H6 2(CH – CH – CH –) B H2O2/OH OH 6CH3 – CH2 – CH2 + 2H3BO3 Overall result of above reaction is anti Markwonikoff addition of water and with no rearrangement. Oxo process followed by hydrogenation : O CH3 – CH = CH2 + CO + H2 [Co(CO)4]2 high temperature and high pressure CH3 – CH2 – CH2 – C – H H2/Pd CH3 – CH2 – CH2 – CH2 – OH Product has one more carbon. From Alkyl Halides : When alkyl halides are treated with aq. KOH or aq. NaOH or moist Ag2O, alcohols are formed. − R − X + OH ⎯⎯→R − OH + X– Reduction of Carbonyl Compounds, Carboxylic Acids and their Derivatives : O R – C – H red. agent R – CH OH O R – C – R′ red. agent O R – C – OR′ red. agent O OH R – CH2OH + R′ – OH R – C – X O red. agent O R – CH2OH R – C – O – C – R red. agent 2R – CH2OH Table : Reducing nature of different reagents Group Product LiAlH4/H2O NaBH4/C2H5OH B2H6/THF H2/Pt O – C – H – CH2 – OH Yes Yes Yes Yes > C = O > CH – OH Yes Yes Yes Yes – COOH – CH2OH Yes No Yes Yes O – C – Cl – CH2OH Yes Yes No Yes O (R – C – O)2O R – CH2OH Yes No Yes Yes O – C – OR – CH2OH + R – OH Yes No Yes Yes > C = C < > CH – CH < No No Yes Yes (LiAIH4 reduces) C = C only when it is conjugated with Phenylic system Meerwein-Ponndorf-Verley Reduction (MPV Reduction) : Its a name reaction of reduction of O → alcohol Ketones can be reduced to secondary alcohols with aluminium isopropoxide in 2-propanol solution. OH R C = O + CH3 – CH – CH3 [(CH3)2CHO]3Al R R′ CH – OH + (CH3)2C = O Using Grignard Reagent : From aldehydes or ketones : OMgX OH H O/H+ OH – C – + R – MgX – C – R 2 – C – R + Mg X In this reaction Formaldehyde gives 1°-alcohol Other aldehyde gives 2°-alcohol Ketones give 3°-alcohol From carboxylic acid and their derivatives : O Z R – C – R′ + Mg X CH3 – CH — CH + R – MgX OMgX CH3 – CH – CH2 R H O/H+ OH OH CH3 – CH – CH2 + Mg R X Hydrolysis of Ether : Ether undergo acid hydrolysis with dilute H2SO4 under pressure to give corresponding alcohols. R − O − R′ + H2O ⎯⎯dil. 2S⎯O⎯4 →R − OH + R′ − OH Physical Properties Physical state : At ordinary temperature, lower members are colourless liquids with burning taste and a pleasant smell. Boiling Point : The boiling point of alcohols rise regularly with the rise in the molecular mass. Amongst isomeric alcohols, the boiling point decrease in the order. 1° > 2° > 3° Solubility : The extent of solubility of any alcohol in water depends upon the capability of its molecules to form hydrogen bonds with water molecule. Alcohols are lighter than water however, the density increases with the increase in molecular mass. Chemical Properties Reactions involving cleavage of O – H Bond Alcohols are acidic in nature but they are less acidic than water hence they do not give H+ in aqueous solution. They do not change the colour of litmus paper. Their acidic strength increases by increasing–I strength of the groups attached and decreases by increasing +I strength of the groups. Alcohols do not react with aqueous alkali, as it does not give H+ in aqueous solution. Action of active metal : When alcohols are treated with active metal they form alkoxides with the liberation of H2 gas. − + 2ROH + 2Na ⎯⎯→2R − ONa + H2 ↑ Esterification : When carboxylic acid is treated with alcohols in the presence of acid as catalyst, esters are formed. O R – C – OH + H – O – R′ H O R – C – OR′ + HOH Reaction with Grignard Reagent : When Grignard reagents are treated with alcohol (or any proton donor) they form alkanes. R – MgX + H – OR′ R – H + R′ – OMgX Other proton donors can be carboxylic acids, phenols, alkynes, H2O, Amines, NH3 etc. Reactions Involving Cleavage of C– O Bond Reaction with HX : Most alcohols undergo SN1. (a) R − OH + HCl(g) ⎯⎯⎯⎯⎯⎯2 →R − Cl + H2O (b) R − OH + HBr H+ / H2SO4 conc. R − Br + H2O (c) R − OH + HI H+ / H2SO4 conc. R − I + H2O Reactivity order of HX is HI > HBr > HCl Dehydration : Alkyl chlorides can also be prepared by following methods : R – OH + PCl5 R – Cl + POCl3 + HCl 3R – OH + PCl3 3R – Cl + H3PO3 R – OH + SOCl2 R – Cl + SO2 + HCl (Darzen's process) Darzen’s process is the best method as the other products are gases. Reduction : Alcohols are reduced to alkanes when they are treated with Zn-dust or red P + HI. R − OH ⎯⎯Zn d⎯u⎯st →R − H + ZnO Oxidation : O O CH3OH [O] H – C – H [O] [O] H – C – OH CO2 3°-alcohols can’t be oxidised. Strong oxidising agent like KMnO4 or K2Cr2O7 cause maximum oxidation as above. If 1°-alcohol has to be converted into aldehyde PCC + CH2Cl2 or CrO3 should be used among which PCC + CH2Cl2 is the best. 2°-alcohol can converted to ketone best by PCC + CH2Cl2 or CrO3 or H2CrO4 in aq. acetone (Jones reagent). MnO2 selectively oxidises the –OH group of allylic and benzylic 1° and 2° alcohols to aldehydes and ketones respectively. Action of Heated Copper : (i) (ii) CH3 – CH2 – OH OH CH3 – CH – CH3 Cu 573K Cu 573K O CH3 – C – H + H2 (Dehydrogenation) O CH3 – C – CH3 + H2 (Dehydrogenation) (iii) Tertiary alcohols undergo dehydration to give alkene under similar condition. CH3 CH – C – OH Cu CH2 CH – C + H O 3 CH3 573 K 3 2 CH3 Distinction Between 1°, 2° and 3° Alcohols Lucas Test : Any alcohol is treated with Lucas reagent (HCl + an hyd. ZnCl2) at room temperature if Solution becomes cloudy immediately, alcohol is 3°. Solution becomes cloudy after 5-min, alcohol is 2°. In solution cloud does not form at room temperature, alcohol is 1°. Victor Meyer’s Method : R – CH2OH (1°-alcohol) P + I2 R – CH I AgNO2 R – CH – NO + HNO –H2O R – C – NO2 N OH (Nitrolic acid) NaOH blood red colour R2CH – OH (2°-alcohol) P + I2 R – CH – I AgNO2 R CH – NO + HNO –H2O R2C – NO2 NO R – C – OH P + I2 R C – I (3°-alcohol) Pseudonitrol NaOH blue colour AgNO2 R C – NO HNO2 No reaction NaOH Colourless PHENOLS OH and their derivatives are called phenols. In phenol R– of alcohol is replaced by aryl ring. Comparison of bond Angles in Phenols, Alcohols and Ethers : H H–C H .. O H 108.5° 109° H H H–C H .. H C 111.7° H H Bond angle increases with the increase in hindrance. Method of Preparation 1. From Aryl Sulphonic Acids : When aryl sulphonic acids are fused with NaOH at 570 – 620 K followed by hydrolysis phenols are formed. SO3H SO3Na Δ ONa OH H+/H O Cl (aq.) 623 K 320 atm + ONa OH From Benzene Diazonium Salts : NH2 + N2 Cl OH + N2 + H–Cl Cumene Process : H H PO CH3 CH3 C H light CH3 CH3 C–O–O–H OH O +CH – C = CH 3 4 + O2 + CH —C—CH 3 2 Propene Benzene 3 3 Cumene Cumene hydroperoxide Grignard's Synthesis : 1 H2O / H+ OH C6H5MgBr + 2 O2 ⎯⎯→ C6H5OMgBr ⎯⎯⎯⎯→ C6H5OH + Mg Br From Salicylic Acid : OH OH COOH + NaOH Chemical Properties Acidic Nature : COONa + NaOH OH CaO, Δ –Na2CO3 Phenol behave as a weak acid forming phenoxide ion with strong alkalies. C6H5OH Phenol + NaOH → C6H5ONa Sodiumphenoxide + H2O It also reacts with sodium metal to form sodium phenoxide and hydrogen is evolved C H OH + Na → + + 1 H 6 5 C6H5 ONa 2 2 Phenol Effect of substituents on the acidity of phenols : It should be noted that the presence of electron withdrawing groups like –NO2, – CN, –CHO,–X, –COOH, etc. increases the acidic strength (because of the greater polarity of O–H bond the greater stability of the phenoxide ion by the dispersal of –ve charge, by –R effect). On the other hand, electron-releasing groups like –CH3, –NH2, –OH, etc., tend to destabilize the phenoxide ion by intensifying its –ve charge by +R effect and hence decreases the acidic strength. o - chlorophenol > m - chlorophenol > p - chlorophenol Ka = 7.7 × 10–9 1.6 × 10–9 6.3 × 10–10 In case of haloarenes –I effect of halogens dominates over it's +M effect. (except for fluorine) p-nitrophenol > o-nitrophenol > m - nitrophenol > phenol Steric Effect : 3, 5 -dimethyl-4-nitrophenol is weaker acid than the isomeric 2, 6-dimethyl - 4 - nitrophenol. Alkylation or Etherification : When sodium phenoxide is treated with alkyl halides (but not with aryl halides as they are inert) form phenolic ethers. C6H5OH ⎯⎯NaO⎯H →C6H5ONa ⎯⎯CH⎯3I → C6H5OCH3 NaI Phenol −H2O Sodium phenoxide Methyl phenylether (Anisole) C6H5OH ⎯⎯NaO⎯H →C6H5ONa ⎯⎯C2H⎯5B⎯r →C6H5OC2H5 + NaI Phenol Sodium phenoxide Ethyl phenyl ether (Phenetole) Claisen rearrangement : C6H5ONa + BrCH2 – CH = CH2 → C6H5 − O − CH2CH = CH2 + NaBr Allyl phenyl ether When aryl allyl ether is heated to 475 K, the allyl group of the ether migrates from ethereal oxygen to the ring carbon at ortho position. O–C* H2–CH = CH2 ⎯⎯475⎯K → OH CH –CH = C* H o-Allyl phenol Acylation and benzoylation : O O C6H5 OH + CH3 – C – Cl ⎯⎯Pyr⎯idin⎯e → Acetyl chloride C6H5 – O – C – CH3 Phenol Phenyl acetate Fries Rearrangement : When heated with anhydrous aluminium chloride, phenyl esters undergo Fries rearrangement forming a mixture of o- and p-hydroxy ketones. O O – C – CH3 ⎯⎯He⎯at → AlCl3 OH O OH C – CH3 + Phenyl acetate o-hydroxyacetophenone O = C – CH3 p-Hydroxyacetophenone The para isomer is formed predominantly at low temperature while at higher temperatures o - isomer is predominant. Reactions due to C–O Bond : Reaction with PCl5 : C6H5OH + PCl5 → C6H5Cl + POCl3 + HCl 3C6H5OH + PCl3 → P(OC6H5 )3 + 3HCl Triphenyl phosphate The yields of C6H5Cl is very poor due to the formation of triaryl phosphate. Reaction with Ammonia : C6H5OH+ NH3 ⎯⎯ZnC⎯l2 →C6H5NH2 + H2O Phenol 573 K Aniline Reaction with Zinc Dust : C6H5OH+ Zn ⎯⎯Δ → C6H6 + ZnO Phenol Benzene Reaction with Neutral FeCl3: ( Test for phenol) 3C6H5OH + FeCl3 ⎯⎯→ (C6H5O)3 Fe + 3HCl Ferric phenoxide (Violet) Electrophilic Substitution Reaction on the Benzene Ring : From the contributing structure of phenol, it is clear that ortho- and para-position on it become rich in electron density. Thus the electrophilic attack at these positions is facilitated. Again benzene ring is the very powerful ring activator towards electrophilic aromatic substitution. present on the Bromination : OH + 3Br2 ⎯⎯H2⎯O → OH Br Br + 3HBr Phenol Br 2,4, 6-Tribromophenol (yellow ppt.) OH SO3H p-Phenolsulphonic acid + 3Br2 (aq.) → OH Br Br Br 2,4, 6-Tribromophenol (yellow ppt.) + 3HBr + H2SO4 Nitration : OH (a) Phenol + dil HNO3 ⎯⎯293⎯K → OH OH NO2 + NO o-Nitrophenol (40% yield) 2 p-Nitrophenol (13% yield) (b) With concentrated nitric acid and sulphuric acid, it forms 2, 4, 6-trinitrophenol (Picric acid). OH + 3HNO3 ⎯⎯H2S⎯O4⎯co⎯n⎯c. → (conc.) O2N OH NO2 NO2 2,4, 6-trinitrophenol (Picric acid) Sulphonation : When heated with conc. sulphuric acid, phenol forms hydroxy benzene sulphonic acid. OH H H2SO4, 298 K 3 –H2O OH –H2O SO3H p-Hydroxy benzene sulphonic acid Friedel-Crafts Alkylation and Acylation : Phenol undergo both these reaction to form mainly p-isomer. OH + CH3Cl A⎯nh⎯yd. A⎯lC⎯l 3 → OH OH + CH3 Phenol CH3 (Major product) p–Cresol o-Cresol OH + CH3COCl A⎯nh⎯yd. A⎯lC⎯l 3 → OH COCH3 + OH COCH3 o- p- Hydroxy acetophenone Kolbe’s reaction Riemer Tiemann Reaction : On heating with chloroform and alkali phenols are converted to phenolic aldehydes OH + CHCl3 + 3NaOH ⎯⎯333⎯−34⎯3 → (aq.) H+ OH CHO + 3NaCl + 2H2O In this reaction dichloro carbene is formed as intermediate which attack on benzene ring as electrophile. If instead of chloroform, carbon tetrachloride is used, salicylic acid is formed. Some para isomers is also formed. OH + CCl4 ⎯N⎯aO⎯H → 340 K ONa CCl3 ⎯3⎯Na⎯OH(⎯a⎯q.)→ –3NaCl ONa COONa ⎯⎯Dil. ⎯H 2S⎯O 4 → OH COOH In this reaction ⊕ CCl3 is formed as intermediate which attack on benzene ring as electrophile. Coupling with Diazonium Salts : C H N Cl + C H OH ⎯⎯0−5⎯°⎯C → N = N OH 6 5 2 6 5 pH 9−10 p-Hydroxy azobenzene (An orange dye) Test for phenol Neutral FeCl3 test → Aqueous solution of phenol gives a violet colouration with FeCl3. Br2 water test → Aqueous solution of phenol gives a yellow precipitate of 2, 4, 6-tribromophenol with bromine water. Phenol gives Liebermann's nitroso reaction. Phenol ⎯⎯NaN⎯O⎯2 → Red colour ⎯⎯NaO⎯H →blue colour (in conc. H SO ) excess of water excess 2 4 ETHERS Ethers are those organic compounds which contain two alkyl groups attached to an oxygen atom, i.e., R–O–R. They are regarded as dialkyl derivatives of water or anhydrides of alcohols. H – O – H ⎯⎯–2⎯H → R – O – R ←⎯⎯⎯ R – OH + HO – R Water 2R Ether −H2O Alcohol (2 moles) Ethers may be of two types : (i) Symmetrical or simple ether are those in which both the alkyl groups are identical and (ii) unsymmetrical or mixed ethers are those in which the two alkyl groups are different. CH3–O–CH3; C6H5–O–C6H5 CH3–O–C2H5; CH3–O–C6H5 Symmetrical (simple) ethers Unsymmetrical (mixed)ethers Like water, ether has two unshared pair of electrons on oxygen atom, yet its angle is greater than normal tetrahedral (109°28´) and different from that in water (105°). This is because of the fact that in ethers the repulsion between lone pairs of electrons is overcome by the repulsion between the bulky alkyl groups. Preparation of Ethers : By dehydrating excess of alcohols : Simple ethers can be prepared by heating an excess of primary alcohols with conc. H2SO4 at 413K. Alcohol should be taken in excess so as to avoid its dehydration to alkenes. C2H5 – OH + HO – C2H5 ⎯⎯Con⎯c. ⎯H2S⎯O⎯4 → C2H5 – O – C2H5 + H2O Ethanol (2 molecules) 413 K Diethyl ether Dehydration may also be done by passing alcohol vapours over heated catalyst like alumina under high pressure and temperature of 200 – 250°C. By heating alkyl halide with dry silver oxide (only for simple ethers) : C2H5I + Ag2O + IC2H5 → C2H5OC2H5 + 2AgI Dry Remember that reaction of alkyl halides with moist silver oxide (Ag2O + 2H2O = 2AgOH) gives alcohols C2H5I + Ag2O (moist) → C2H5OH + AgI By heating alkyl halide with sod. or pot. alkoxides (Williamson synthesis): C2H5ONa + ICH3 → C2H5OCH3 + NaI ONa + BrCH3 OCH3 + NaBr Sod. phenoxide Methoxybenzene (Anisole) However CH3 + | CH3 | CH3–Cl + NaO–C–CH3 | CH3 CH3–O–C–CH3 + NaCl | CH3 If alkyl halide is other than methyl halide and it is treated with tertiary alkoxide ion, Hoffmann elimination takes place instead of Williamson's ether synthesis. CH3–CH2–CH=CH2 + HCl (Major) Methyl ethers can be prepared by treating primary or secondary alcohol or phenol with diazomethane in presence of BF3. C2H5OH + CH2N2 ⎯⎯B⎯F3 → Chemical Properties : C2H5OCH3 Ethylmethyl ether N2 Properties due to Alkyl Groups : Halogenation : When ethers are treated with chlorine or bromine in the dark, substitution occurs at the α-carbon atom. The extent of substitution depends upon the reaction conditions. β α α´ β´ dark CH3 – CH2 – O – CH2 – CH3 + Cl2 ⎯⎯⎯→ CH3 .CHCl – O – CH2.CH3 α– Chlorodiethyl ether ↓ Cl2 CH2Cl.CHCl – O – CH2 .CH3 + CH3CHCl – O – CHCl.CH3 α, β–Dichlorodiethyl ether α, α´–Dichlorodiethyl ether CH3CH2 – O – CH2 .CH3 + 10Cl2 ⎯⎯lig⎯ht → CCl3 .CCl2 – O – CCl2 .CCl3 Perchlorodiethyl ether Combustion : C2H5.O.C2H5 + 6O2 4CO2 + 5H2O Properties due to Ethereal Oxygen : Chemical inertness : Since ethers do not have an active group, in their molecules, these do not react with active metals like Na, strong bases like NaOH, reducing or oxidising agents. Formation of peroxide (Autoxidation) : On standing in contact with air and light ethers are converted into unstable peroxides (R2O O) which are highly explosive even in low concentrations. Basic nature : Owing to the presence of unshared electron pairs on oxygen, ether behave as Lewis bases. Hence they dissolve in strong acids (e.g. conc. HCl, conc. H2SO4) at low temperature to form oxonium salts. (C2H5 )2 O + H2SO4 → Diethyl ether [(C2H5 )2 OH]+HSO– Diethyloxonium hydrogen sulphate On account of this property, ether is removed from ethyl bromide by shaking with conc. H2SO4. Being Lewis bases, ethers also form coordination complexes with Lewis acids like BF3, AlCl3, RMgX, etc. R2O + BF3 R2O BF3 2R2O + RMgX R2O R Mg R2O X It is for this reason that ethers are used as solvent for Grignard reagents. Properties due to carbon-oxygen bond : Hydrolysis : C2H5 – O – C2H5 + H2O ⎯⎯H2S⎯O⎯4 → 2C2H5OH Ethyl alcohol The hydrolysis may also be effected by boiling the ether with water or by treating it with steam. Action of conc. sulphuric acid : C2H5 – O – C2H5 + H2SO4 (conc.) → C2H5OH + Ethyl alcohol C2H5HSO4 Ethyl hydrogen sulphate C2H5OH + H2SO4 (conc.) → C2H5HSO4 + H2O Action of hydroiodic or hydrobromic acid : In cold, ether react with HI or HBr to give the corresponding alkyl halide and alcohol. In case of mixed ethers, the halogen atom attaches itself to the smaller alkyl group. C2H5 – O – C2H5 + HI → Ethyl ether C2H5I Ethyl iodide C2H5OH Ethyl alcohol The order of reactivity of halogen acids is : HI > HBr > HCl If one of the the group around oxygen is aryl group then I– will always attack on the group other than aryl group. O–CH3 + HI OH + CH I CH3 CH | | 3 O–C–CH3 + HI OH + I–C–CH | CH3 Properties Due to Benzene Nucleus : | 3 CH3 Alkoxy group, being o-, p- directing, anisole undergoes substitution in o- and p- positions. However, –OR group is less activating than the phenolic group. Nitration : OCH3 OCH3 conc. HNO3 conc. H2SO4 NO2 + OCH3 Methylphenyl ether (Anisole) Bromination : Methyl 2-nitrophenyl ether or o-Nitroanisole NO2 Methyl 4-nitrophenyl ether or p-Nitroanisole OCH3 Br Br2/Fe OCH3 Br Br Anisole 2, 4, 6, Tribromoanisole OCH3 + Br2 CS2 OCH3 Br + OCH3 Br Anisole 2-Bromoanisole 4-Bromoanisole Sulphonation : OCH3 OCH3 OCH3 H2SO4 SO3 SO3H SO3H Anisole p-Methoxybenzene sulphonic acid o-Methoxybenzene sulphonic acid CARBONYL COMPOUNDS (ALDEHYDES AND KETONES) Aldehydes and ketones are the compounds containing carbonyl group (>C=O). O – C – Carbonyl group O R – C – H An aldehyde O R – C – R Ketone Structure of the carbonyl group: Like the carbon-carbon double bond of alkenes, the carbon-oxygen double bond of the carbonyl group is composed of one σ and one π bond. In the carbonyl group, carbon atom is in state of sp2 hybridisation. The C–O σ bond is produced by overlap of an sp2 orbital of carbon with a p-orbital of oxygen. On the other hand, the C–O π bond is formed by the sideways overlap of p orbitals of carbon and that of p orbital of oxygen. The remaining two sp2 orbitals of carbon form σ bonds with the s orbital of hydrogen or sp3 orbital of carbon of the alkyl group. p p X X O O Y Y (a) (b) The polar nature of the carbonyl group causes intermolecular attraction (dipole-dipole attraction) in aldehydes and ketones and hence accounts their higher boiling points than that of hydrocarbons and ethers of comparable mol. wt. However, the high values of dipole moments (2.3 - 2.8 D) of aldehydes and ketones can’t be accounted for, only by inductive effect; this can be accounted for if carbonyl group is a resonance hybrid of the following two structures. + − C = O ↔ > C — O GENERAL METHODS OF PREPARATION OF ALDEHYDES AND KETONES From Alcohols : By Oxidation : Primary alcohols gives aldehyes, while secondary alcohols give ketones. CH3 .CH2OH ⎯⎯K2C⎯r2O⎯7 +⎯di⎯l.H2⎯SO⎯4 → CH3 .CHO + H2O Ethyl alcohol Δ (Pr imary Alcohol) Acetaldehyde CH2OH CHO Benzyl alcohol K2Cr2O7 + H2SO4 [O], Δ Benzaldehyde Controlled oxidation of 1°-alcohol and 2°-alcohol with PCC + CH2Cl2 or CrO3 forms aldehyde and ketone respectively. Ketones in good yield can be prepared by Oppenauer oxidation of secondary alcohols. R CHOH + R´ CH3 CH3 [(CH3)3CO]3Al C = O (Aluminium t-butoxide) R C = O + R´ CH3 CH3 CHOH Sec. alcohol Acetone Ketone Isopropanol By catalytic dehydrogenation of alcohols : 1° Alcohols yield aldehyde in this method. CH3OH ⎯⎯C⎯u →HCHO + H2 Methanol 573 K Formaldehyde Secondary alcohols, on similar treatment, give ketones. CH3 CH3 CHOH Cu CH3 C = O + H2 573 K CH Isopropanol Acetone From Fatty Acids : By dry distillation of calcium salts of fatty acids : Pyrolysis (heating) of calcium salts of fatty acid or a mixture of two fatty acids leads to the formation of aldehydes and/or ketones depending upon the nature of the fatty acid. Distillation of calcium formate to formaldehyde H COO O OCH Ca + Ca 2HCHO + 2CaCO3 H COO O OCH Formaldehyde Calcium formate (2 moles) Distillation of mixture of Ca(CH3COO)2 and Ca(HCOO)2 CH3 COO Ca + Ca O OCH 2CH3CHO + 2CaCO3 CH3 COO O OCH Acetaldehyde Calcium acetate Calcium formate Yield is generally poor due to side reactions ; i.e., formaldehyde from calcium formate and acetone from calcium acetate. Distillation of the calcium salt of a fatty acid other than formic acid gives ketones (simple ketones). CH3–COO CH3–COO Ca + Ca OOC–CH3 OOC–CH3 2CH3–CO–CH3 + 2CaCO3 Acetone Calcium acetate From gem-dihalides : CH3 CHCl2 aq. KOH OH CH3 CH CH3 CHO + H2 O Ethylidene chloride OH Unstable Acetaldehyde gem-Dihalides having two halogen atoms to a non-terminal carbon atom give ketone on alkaline hydrolysis. Cl | CH3–C–CH3 | Cl aq. alkali OH | CH3–C–CH3 | OH O || CH3–C–CH3 Acetone + H2O 2, 2-Dichloropropane (Isopropylidene chloride) From Alkynes : CH ≡ CH + H2O ⎯⎯dil. ⎯H2S⎯O⎯4 → [CH2 = CHOH] → CH3CHO Acetylene HgSO4 Vinyl alcohol (Unstable) Acetaldehyde CH3C ≡ CH + H2O H2SO4 HgSO4 OH CH3.C CH2 Tautomerisation O CH3 C CH3 From Grignard Reagents : Unstable CH3 CH3 Acetone H – C ≡ N + CH3MgI H – C = NMgI H2O H – C = O + NH2MgI Acetaldehyde By Reducitve Ozonolysis of Alkenes : O O3 C C C C H2O, Zn C O + O C + H2O2 O O O H C = CH + O CH CH H2O, Zn CH O + CH O 3 2 3 2 2 2 2 O O Methods giving only Aldehydes : Formaldehyde (2 moles) From Acid Chlorides (Rosenmund Reduction) : O R C Cl Acid chloride H2/Pd + BaSO4, S Boiling xylene R CHO + HCl CH3 O C Cl Pd/BaSO4,S Boiling xylene CH3 CHO + HCl Acetyl chloride From nitriles (Stephen's reduction) : Acetaldehyde CH3.C ≡ N SnCl2 + HCl OH– CH3.CH = NH H O/OH– CH3CHO + NH3 Methyl cyanide Aldimine Methods for Aromatic Aldehydes and Ketones : Aromatic Aldehydes : CH3 CH(OCOCH3)2 CHO CrO3 (CH3CO)3O alkaline hydrolysis + CH3COONa + H2O Aromatic Ketones : (Friedal-craft's acylation) (i) C6H6 CH3COCl ⎯⎯anh⎯y. → C6H5COCH3 + HCl Benzene AlCl3 Acetophenone Here instead of acid chloride we can use anhydrides also (ii) C6H6 + C6H5COCl ⎯⎯anh⎯y. → C6H5COC6H5 + HCl Physical Properties AlCl3 Benzophenone Methanal is gas at room temperature, ethanal is liquid at room temperature. Other carbonyl compounds are liquids or solids at room temperature. Lower members have sharp pungent odours. As the size of the molecule increases, the odour becomes less pungent and more fragrant. They can form H-bonding with water that's why lower members are miscible with water. With the increase in the size of the alkyl group their solubility in water decreases. However higher members are soluble in non polar organic solvents. Their boiling point is greater than comparable molecular weight of hydrocarbon or ether because of their polarity but less than alcohol because alcohol has H-bonding. Trend of Boiling Point : O || CH3–CH3–OH > CH3CH2CHO > CH3CCH3 > CH3CH2CHO > CH3–O–CH2–CH3 > CH3–CH2–CH2–CH3 Chemical Properties Both aldehydes and ketones contain a carbonyl group in the structure and hence show marked similarity in their chemical behaviour. Nucleophilic addition reactions Aldehydes are more reactive than ketones because greater the alkyl group (as in ketone) more will be electron density and hindrance hence lesser will be chance for the attack of nucleophile and hence lesser will be ease of nucleophilic addition. Addition of hydrogencyanide : Aldheydes and ketones react with hydrogen cyanide to form cyanohydrins. CH3 H C = O + HCN CH3 OH C H CH Acetaldehyde Acetaldehyde cyanohydrin CH3 C = O + HCN CH3 OH C CH3 CH3 CN Acetone Acetone cyanohydrin C6H5 C = O + HCN C6H5 OH C CH3 CH3 CN Acetophenone Acetophenone cyanohydrine Benzophenone does not react with hydrogen cyanide because of steric hindrance. On the other hand, aromatic aldehydes (e.g., C6H5CHO) when refluxed with alcoholic potassium cyanide solution undergo dimerization to form benzoin. 2C6H5CHO Benzaldehyde CN– ethanol OH O C6H5 – CH – C – C6H5 Benzoin Above reaction is known as benzoin condensation. Addition of sodium bisulphite : Aldehydes and methyl ketones react with a saturated aqueous solution of bisulphite to form crystalline sodium bisulphite derivatives. CH3 H C = O + NaHSO3 CH3 H OH C SO3Na Acetaldehyde Sod. bisulphite Acetaldehyde sod. bisulphite C6H5 H C6H5 C = O + NaHSO3 C H OH SO3Na Benzaldehyde Benzaldehyde sod. bisulphite Aromatic ketones and aliphatic ketones having higher alkyl groups do not react with sodium bisulphite. This is due to the fact that the large SO2− ion cannot attack the carbonyl carbon atom when it is surrounded by larger substituents (steric hindrance). Thus C2H5COC2H5, C6H5COCH3, C6H5COC6H5 do not react with sodium bisulphite. Methyl ketones give this reaction. Addition of Grignard reagents : H C = O + CH3MgI H H CH3 C H OMgI H2O H CH3 C H OH Formaldehyde Ethyl alcohol (primary alcohol) CH3 H CH3 C OMgI H2O CH3 H CH3 C OH Isopropyl alcohol (Sec. alcohol) CH3 H3C H3C C = O + CH3MgI CH3 C ⎯⎯H2⎯O → CH3 | C − OH H3C Acetone H3C OMgI | CH3 ter. butyl alcohol (ter. alcohol) Addition of alcohols (Acetal formation) : Aldehydes (not Ketones) react with alcohols in presence of dry HCl gas to form hemi-acetals (hemi means half) which being unstable immediately react with another molecule of alcohol to form stable acetals. For example, CH3 H C=O + C2H5OH dry HCl gas CH3 C H OC2H5 OH dry HCl (–H2O) CH3 C H OC2H5 OC2H5 Acetaldehyde hemiacetal (1-Ethoxyethanol) Acetaldehyde acetal (1, 1-diethoxyethane, Gem diether) HO — CH2 3 R 2 O — CH2 C = O + C R′ HO— CH2 1 O — CH2 (cyclic compound) Ethanol Ethylene glycol Ethylene glycol ketal Reduction by metal hydrides such as lithium aluminium hydride CH3 C=O LiAlH4 CH3 C H or CH CH OH 3 2 H H OH Acetaldehyde Ethyl alcohol Similar product are also formed by NaBH4 , H2 — Pt, H2 — Ni or metal-acid. However, aldehydes and ketones can be reduced to the corresponding alkanes by means of red phosphorus and hydroiodic acid, or amalgamated zinc and concentrated hydrochloric acid (Clemmensen reduction) or reacting hydrazine solution followed by treatment with alkaline solution of ethylene glycol (Wolf-kishner reduction). The basic reaction in all these reductions is the reduction of carbonyl group to methylene group. Nucleophillic Substitution Replacement of Carbonyl Oxygen : Reaction with Ammonia Derivatives : Aldehydes and ketones react with a number of ammonia derivatives like NH2OH, NH2NH2, C6H5NHNH2 etc. in weakly acidic medium. Such reactions take place in slightly acidic medium and involves nucleophilic addition of the ammonia derivative followed by dehydration. H —C = O + :N H Z —C—N—Z –H2O –C=NZ H –O H Ammonia der. Addition product Ammonia derivatives Final products H2N — OH Hydroxylamine C=NOH Oximes H2N — NH2 Hydrazine C=NNH2 Hydrazones H2N — NHC6H5 Phenylhydrazine C=NNHC6H5 Phenylhydrazones H2N — NHCONH2 Semicarbazide C=NNHCONH2 Semicarbazones NH2—NH— —NO2 NO2 2, 4 − DNP (also known as Brady's reagent) C=N–NH NO2 NO2 2, 4 − Dinitrophenylhydrazones (These are yellow or orange or red solids) Reaction with thioalcohols (mercaptans) : Aldehydes and ketones react with thioalcohols and form thioacetals (mercaptals) and thioketals (mercaptals) respectively. Reaction involving alkyl as well as carbonyl group (condensation reactions) : Aldol condensation between acetaldehyde molecules : H | CH3–C + HCH2–CHO || O dil alkali CH –CH–CH CHO | OH β-hydroxybutyraldehyde (Aldol) Aldol condensation between acetone molecules : CH3 CH3 Ba(OH)2 C=O + HCH2–COCH3 CH3 CH3 CCH2COCH3 Acetone(2 molecules) Diacetone alcohol (Ketol) Mechanism : Abstraction of acidic hydrogen by base H O CH —C—H + OH– O CH2—C—H + H2 (Enolate ion which is stabilised by resonance) Nucleophilic attack of enolate ion O O O– O CH3—C—H + CH2—C—H CH3—CH—CH2—CH + H2O OH CH3—CH—CH2CHO + OH (β-hydroxy carbonyl compound) Crossed Aldol Condensation : When mixture of two carbonyl compounds having α-hydrogen on at least one of them is treated with dilute alkali the mixture of products is formed and this reaction is called as crossed aldol condensation. For example when mixture of CH3CHO and CH3–CO–CH3 is treated with dilute alkali then four products are formed. OH OH O OH | | || | OH O | || CH3–CH–CH2–CHO, CH3–CH–CH2–C–CH3, CH3–C–CH2CHO | CH3 and CH3–C–CH–C–CH3 | CH3 However if one of them does not have α-hydrogen then the number of products formed will be two OH OH OH– | | CH3–CHO + HCHO CH3–CH–CH2CHO + CH2–CH2–CHO Perkin reaction : Condensation of an aromatic aldehyde with acid anhydride in presence of base (sodium salt of the acid from which the anhydride is derived) to form α, β-unsaturated acid as known as Perkin reaction. For example, C6H5 CHO + (CH3CO)2 O ⎯⎯CH⎯3CO⎯ON⎯a → C6H5CH = CHCOOH Benzaldehyde Acetic anhydride Cinnamic acid Aldehydes are oxidised not only by strong oxidising agents like KMnO4 and K2Cr2O7 but also by much milder oxidising agents like bromine water, Tollen’s reagent, Fehling’s solution and Benedict’s solution. Tollen’s reagent : Tollen's reagent is Ammoniacal silver nitrate solution – + R.CHO + 2[Ag(NH3 )2 ]OH → RCOONH4 + (Tollen's reagent) 2Ag ↓ + H2O + 3NH3 Silver mirror Fehling solution : [Alkaline solution of copper sulphate containing sodium potassium tartarate (Roschelle salt)] R–CHO + 2Cu2+ + 5OH– ⎯⎯→ R–COO– + Cu2O (Reddish brown) + 3H2O Benedict Solution : Its a solution of CuSO4, sodium citrate and sodium carbonate. When heated with aldehyde it gives a reddish brown ppt. of Cu2O. Ketones are not oxidised by mild oxidising agents. Oxidation in drastic condition a O b ‘a’ cleavage HCOOH + HOOC – CH2CH3 CH — C — CH CH Methanoic acid Propanoic acid 3 2 3 2-Butanone ‘b’ cleavage CH3COOH + HOOCCH3 Ethanoic acid (2 moles) ⎫ Major ⎭ Oxidation of mixed ketones is governed by Popoff’s rule according to which the carbonyl group of the ketone goes with the smaller alkyl group. Thus in the above case 'b' type of cleavage will decide major products. Reaction with Ammonia : CH3CH = O + HNH2 CH3CH 6HCHO + 4NH3 → (CH2 )6 N4 + 6H2O Hexamethylene −tetramine (Urotropine ) OH NH2 Δ –H2O CH3—CH = NH Acetaldimine Cannizzaro reaction : This reaction is preferentially given by those aldehydes which do not contain α- hydrogen. In Cannizzaro reaction, one molecule of the aldehyde is oxidised to acid at the expense of the other which is reduced to alcohol i.e., disproportionation reaction takes place. The reaction occurs in the presence of concentrated solution of any base. 2 HCHO Formaldehyde NaOH → HCOONa + Sod. formate CH3OH Methyl alcohol Reaction given only by Ketones : Reduction in Neutral or Alkaline Medium : To form Pinacol which undergoes pinacol - Pinacolone rearrangement in acidic medium CH3 CH3 CH3 C = O + O = C Mg — Hg/H O CH3 C — C CH3 + | 2 ⎯ ⎯→H C − C − C− CH CH3 CH3 CH3 | | OH OH CH3 3 | || 3 CH3 O Pinacolone Ketones can be reduced to secondary alcohols with aluminum isopropoxide in 2-propanol solution (Meerwein - Ponndorf Verley reduction). R2C = O ⎯⎯[Me⎯2CH⎯O⎯]3⎯Al → R2CHOH Me2CHOH (Meerwein - Ponndorf Verley reduction). R2C = O ⎯⎯[Me⎯2CH⎯O⎯]3⎯Al → R2CHOH Me2CHOH Condensation with chloroform : CH3 CH3 C = O + CHCl3 NaOH CH3 C CH3 OH CCl3 1, 1, 1-Trichloro-2-methylpropanol-2 (Chloretone) used as hypnotic drug Haloform reaction : Methyl ketones and acetaldehyde react rapidly with halogens (Cl2, Br2 or I2) in the presence of alkali to form haloform. O e.g., R C CH3 + 3Br2 + 4NaOH heat RCOONa + CHBr3 + 3H2O + 3NaBr Bromoform (reddish brown ppt.) Special Reactions of Aromatic Aldehydes and Ketones : Reaction with Ammonia : C6H5CH=OH2NH + O=CHC H C6H5CH=N C6H5CH=OH2NH Reaction with amines : 6 5 CHC6H5 C6H5CH=N Hydrobenzamide C6H5CH = O + H2NC6H5 → C6H5CH = NC6H5 + H2O Benzylidene aniline. (Benzal aniline) Reaction of benzene nucleus CHO CHO conc. HNO3 conc. H2SO4 NO Benzaldehyde m-Nitrobenzaldehyde CHO conc. H2SO3 CHO SO3H Benzaldehyde COCH3 NO2 conc. HNO3 conc. H2SO4 Benzaldehyde sulphonic acid COCH3 Br2 AlCl3 COCH3 Br 3-Nitroacetophenone COCH3 Br /OH– 273K Acetophenone 3-Bromoacetophenone COCH2Br Acetophenone α-Bromoacetophenone CARBOXYLIC ACIDS Preparation : By the oxidation of primary alcohols and aldehydes RCH2OH Primary alcohol ⎯⎯[⎯O] →RCHO ⎯⎯[⎯O] → Aldehyde RCOOH Carboxylic acid CH2OH ⎯⎯[O⎯] → CHO ⎯⎯[⎯O] → COOH Benzyl alcohol RCOCH2R′ → Benzaldehyde RCOOH + R′COOH Mixture of two carboxylic acids Benzoic acid By the hydrolysis of cyanides (nitriles) R–C≡N (+H2O) RCONH H O/OH– RCOO + NH R–COOH By the hydrolysis of esters R–COOH + NH + CH3COOC2H5 + KOH(aq.) ⎯⎯he⎯at → Ethyl acetate CH3COOK Potassium acetate C2H5OH CH3COOK(aq.) + HCl(aq.) ⎯→ CH3COOH (aq.) + KCl(aq.) Acetic acid By the hydrolysis of trihalogen derivatives of alkanes Cl H – C – Cl Cl ⎯⎯3KO⎯H(⎯aq⎯.) → (–3 KCl) OH H – C – OH OH ⎯⎯–H2⎯O → O H – C OH Chloroform Unstable Formic acid By heating malonic acid and their derivative acids. COOH CH2 COOH Malonic acid ⎯⎯he⎯at → CH3COOH + CO2 By the reaction of Grignard reagent with CO2 O CH3MgBr Methyl mag. bromide + CO ⎯⎯D⎯ry → 2 ether CH3 – C O OMgBr ⎯⎯H2⎯O → OH CH3COOH + Mg Br OH C H MgBr + CO → C H – C – OMgBr ⎯⎯H2⎯O → C6H5COOH + Mg 6 5 2 6 5 Phenyl magnesium bromide Benzoic acid Br Product in above reactions have one more carbon than that in Grignard reagent taken. By oxidation of alkyl benzenes R – ⎯⎯⎯⎯⎯⎯ ⎯→ K2Cr2O7 or conc. HNO3 COOH Benzoic acid Physical properties The first three members (C1 to C3) are colourless, pungent smelling liquids, the next three (C4 to C6) have unpleasant odours. Acids with 7 or more carbon atoms have no distinct smell because of low volatility. Two molecules of carboxylic acids are held together not by one but by two strong hydrogen bonds. C6H5 or R – C O -- H – O O -- H – O C – R or C6H5 Dimers of carboxylic acids The behaviour of formic acid is exceptional. It exists as a dimer in vapour state and a polymer in liquid and solid states. Their H-bonding is so strong that even in vapour state they exist as dimer i.e., H-bond is not broken even in vapour state. In normal carboxylic acids, the even members have markedly higher melting points than the odd members preceeding or following it (oscillation or alternation effect). Effect of Substituents on Acidity : We know that the carboxylic acids are acidic in nature because of the stabilisation (i.e., dispersal of negative charge) of carboxylate ion. So any factor which can enhance the dispersal of negative charge of the carboxylate ion will increase the acidity and vice versa. Thus electron-withdrawing substituents (like halogen, –NO2–C6H5, etc.) would disperse the negative charge and hence stabilise the carboxylate ion and thus increase acidity of the parent acid. On the other hand, electron- releasing substituents would increase the negative charge, destabilise the carboxylate ion and thus decrease acidity of the parent acid and vice-versa. e.g., the acidic strength of the corresponding halogen acids also follows the same order i.e. FCH2COOH > ClCH2COOH > BrCH2COOH > ICH2COOH Fluoroacetic acid Chloroacetic acid Bromoacetic acid Iodoacetic acid Orthoeffect : Among derivative of aromatic carboxylic acid, ortho derivative is the most acidic. This effect is called as ortho effect. COOH OH COOH COOH COOH > > > (–I) OH OH (–I < + R) e.g., COOH CH3 COOH COOH COOH > > > CH3 (+I) CH3 (+I, + R) Chemical Properties Reaction involving hydrogen atom of the –COOH group Reaction with metals, alkalies, carbonates and bicarbonates. 2RCOOH + 2Na → 2RCOONa + H2 Reaction involving –OH group of carboxylic acids (Formation of acid derivatives). Reaction with phosphorus halides or thionyl chloride (Formation of acid halides). CH3COOH + PCl5 → CH3COCl + HCl + POCl3 Acetic acid Acetyl chloride Reaction with ammonia RCOOH Carboxylic acid NH3 → RCOONH4 Amm. salt of acid ⎯⎯He⎯at → RCONH2 + H2O Acid amide Reaction with alcohols (esterification). Carboxylic acids react with alcohols in the presence of an acid or alkali to form esters. This reaction is known as esterification 18 + – 18 RCOOH + HOR′ ⎯⎯⎯⎯H ⎯or ⎯OH⎯⎯⎯→RCOOR′+ H2O Presence of dehydrating agent makes the reaction in forward direction. The greater the bulk of the substituent(s) near the –OH group of alcohol and / or – COOH group of acid, the slower the esterification. Thus the rate of esterification decreases in the following order CH3OH > CH3CH2OH > (CH3)2CHOH > (CH3)3COH HCOOH > CH3COOH > (CH3)2 CHCOOH > (CH3)3COOH Dehydration (Formation of anhydrides). Carboxylic acids, when heated in presence of a dehydrating agent like P2O5 or acetic anhydride, undergo dehydration to form acid anhydrides. CH3COOH + HOOCCH3 ⎯⎯P2O⎯5 o⎯r A⎯c2⎯O →CH3COOCOCH3 + H2O heat Acetic anhydride C6H5 COONa+ ClCOC6H5 → C6H5COOCOC6H5 + NaCl Sod. benzoate Benzoyl chloride Benzoic anhydride Reactions involving – CO – part of the –COOH group Hell-Volhard Zelinsky reaction : Carboxylic acids having α-hydrogen when treated with red P + Cl2 or Br2 or I2 followed by hydrolysis form α-chlorinated (or brominated or iodinated) derivative of carboxylic acid. O || CH2–C–OH + red P + Cl2 | H O || CH2–C–OH | Cl This reaction is used to form α-substituted products of carboxylic acid. Reactions of Salts of Carboxylic Acids : Heating of sodium salts with soda lime (NaOH + CaO) to form alkanes. CH3COONa+ NaOH ⎯⎯he⎯at →CH4 ↑ +Na2CO3 Sod. acetate C6H5COONa+ NaOH ⎯⎯He⎯at → C6H6 + Na2CO3 Sod. benzoate Benzene Electrolysis of conc. aqueous solution of sodium or pottasium salts gives alkanes. CH3COONa + H2O ⎯⎯Ele⎯ctro⎯lys⎯is → CH3 − CH3 + 2CO2 + 21K4O4 H2 4+ 4H32 at anode at cathode Heating of ammonium salts CH3COONH4 ⎯⎯He⎯at →CH3CONH2 + H2O Ammonium acetate Acetamide Dry distillation of calcium salts (Formation of aldehydes and ketones). (HCOO)2 Ca ⎯⎯He⎯at → Cal. formate HCHO Formaldehyde CaCO3 Ring substitution in aromatic acids. Since the –COOH group is deactivating and m-directing, it directs the new group at m-position. Further, since the –COOH group is deactivating, electrophilic substitution (halogenation, nitration, and sulphonation) takes place only under drastic conditions. Deactivation by –COOH group is so strong that aromatic acids do not undergo Friedel-Craft reaction. COOH SO3H m - sulphobenzoic acid ←⎯SO⎯3 ⎯ H2SO4 COOH Benzoic acid ⎯⎯B⎯r2 → FeBr3 COOH Br m - bromobenzoic acid Derivatives of carboxylic acids : These are formed by the replacement of –OH group of acid by some other suitable group e.g. RCOCl, RCONH2, RCOOR′ and (RCO)2O. Order of Reactivity Towards Nucleophilic Substitution Reaction : Carboxylic acid derivatives undergo nucleophilic substitution in either acidic or basic medium. O || R–C–Z + Nu H+/OH– O || R–C–Nu + Z Ease of reactivity of different derivative of carboxylic acid depend upon leaving group ability of Z . Weaker the base better is the leaving group as anion. Thus leaving group ability is as O || − − Cl– > R–C–O– > R − O > NH Properties : H2O CH3COOH + HCl Fumes in air CH3COOC2H5 + HCl CH CONH + NH Cl 3 2 4 CH3CHO + HCl CH3COCH3 + CdCl2 C6H5COCH3 + HCl Acid Anhydrides: (RCO)2O, prepared by dehydration of carboxylic acid. H2O C2H5NH2 2CH3COOH CH3COOC2H5 + CH3COOH CH3CONH2 + CH3COOH CH3CONHC2H5 + CH3COOH Benzene, AlCl3 C6H5COCH3+ CH3COOH Esters: RCOOR prepared by reaction of acid with alcohol or acid chloride or anhydrides with alcohol. CH3COOC2H5 H O/H+ NaOH (aq) NH3 CH3COOH + C2H5OH CH3COONa + C2H5OH CH3CONH2+ C2H5OH CH3OH; HCl (aq) CH COOCH + C H OH LiAlH4 CH3CH2OH OH 2C2H5 MgBr CH —C—C H H O / H+ 3 2 5 C2H5 Acid amides: RCONH2 – It is prepared by reaction of carboxylic acid or its derivatives with NH3. It is amphoteric in nature. Acid amides act as weak acids as well as weak bases due to the structures given: O .. ⊕ R —C—N—H R—C=N—H H H HCl Na H2SO4, H2O NaOH P2O5, Δ (NaNO2 + HCl) Br2 + KOH CH3CONH2.HCl CH3CONH Na CH3COOH+ (NH4)2SO4 CH3COONa +NH3 CH3CN + H2O CH3COOH+ N2 + H2O CH3NH2 + K2CO3 + KBr + H2O (Hofmann bromamide reaction) ❑ ❑ ❑