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Unit – I - Carboxylic Acids and Their Derivatives - Scy1315 SCHOOL OF SCIENCE AND HUMANITIES DEPARTMENT OF CHEMISTRY UNIT – I - CARBOXYLIC ACIDS AND THEIR DERIVATIVES - SCY1315 1 1. CARBOXYLIC ACIDS AND THEIR DERIVATIVES Structure and nomenclature - General methods of preparation of carboxylic acids – acidity – Effect of substituents on acidity – Physical and Chemical properties –Hell-Volhard-Zelinsky Reaction –Dicarboxylic acids - oxalic, malonic succinic, glutaric, adipic, phthalic, acrylic, crotonic and cinnamic acids – Stereospecific addition to maleic and fumaric acids – Derivatives of carboxylic acids – Acid halides, esters, anhydrides and amides – Preparation and Properties – Relative reactivity - Acid and alkaline hydrolysis of esters – trans-esterification. Organic compounds containing carboxylic group are known as carboxylic acids. Their general formulae is RCOOH. NOMENCLATURE H O O HO HO Ethanoic acid methanoic acid O O HO Propanoic acid HO Butanoic acid O (2Z)-3-phenylprop-2-enoic acid O HO Benzoic acid HO O O HO oxo(phenyl)acetic acid 2 ACID DERIVATIVES O O O O H2N Cl benzoyl chloride benzamide ethyl benzoate O O Cl H2N acetyl chloride acetamide O O O Cl H2N H2N butanamide propanoyl chloride propanamide O O O O O O ethyl acetate ethyl butanoate ethyl propanoate 3 DICARBOXILIC ACIDS O O O O HO OH HO OH oxalic acid propanedioic acid O O O O HO OH HO OH butanedioic acid (2E)-but-2-enedioic acid GENERAL PREPARATION METHODS 1. Oxidation of alcohols, aldehydes and ketones CH3CH2OH CH3CHO CH3COOH [O] [O] H [O] OH [O] O O + O HO HO 2. Hydrolysis of cyanides and amides H O+ + 3 H3O CH3CN CH3CONH2 CH3 COOH C H SO K + KCN C H CN 6 5 3 6 5 4 3. Hydrolysis of esters Δ CH3COOC2H5 CH3COOH + C2H5OH KOH 4. Hydroloysis of trihalgen derivates of alkanes CHCl3 CH(OH) 3 HCOOH Cl HO Cl OH Cl HO -H2O O OH 5. Heating dicarboxylic acids O O O Δ H HO OH OH 5 6. Carbonatin of Grignard reagent CH3MgBr + CO2 CH3COMgBr CH3COOH O O 7. Arndt-Eistert Synthesis RCOOH + SOCl RCOCl RCOCHN RCH COOH 2 2 + 2 CH2N2 Ag2O, H3O RCH2COOH H2O EtOH RCOCHN2 RCH2COOC2H5 NH3 RNH 2 RCH2CONH2 RCH2CONHR SPECIAL METHODS OF PREPARATION OF AROMATIC ACIDS 1. Oxidation of alkyl benzene O OH KMnO4 6 2. Friedel Craft reaction O CH3COCl AlCl3 COCl2 AlCl3 O 3. Hydrolysis of Benzotrichloride Cl HO Cl OH Cl HO -H2O O OH 4. Kolbe Reaction OH OH O CO 2 OH NaOH 7 PROPERTIES 1. The first three members are colourless, pungent smelling liquids. C4 to C8 have unpleasant odours. Acids above C7 have no smell. 2. Carboxylic acids are free soluble in water due to hydrogen bonding with water molecule 3. Boiling points of acid lower member are higher than alcohols of comparable molecular masses. 4. The even member carbon have markedly high melting points than the odd member preceding or following acid. 5. Acidity of carboxylic acid and substituent’s on acidity REACTIONS OF CARBOXYLIC ACIDS A. INVOLVING HYDROGEN ATOM OF COOH GROUP Reaction with metals CH3COOH +Na CH3COONa + 1/2 H2 CH3COOH +Ca (CH3COO)Ca + 1/2 H2 CH3COOH +Ca (CH3COO)Ca + 1/2 H2 CH3COOH +NaHCO3 CO2 + H2O + CH3COONa CH3COOH +NaOH CH3COONa + H2O C H COOH +NaOH C H COONa + H O 6 5 6 5 2 8 B. INVOLVING –OH OF THE –COOH GROUP i. Reaction with Alcohols (Breakage of Carbonyl and oxygen of –COOH group) O occur's O H + H O O not occur O H + H O anhydrous ZnCl 1 2 1 RCOOH + R OH RCOOR + H2O H2SO4 anhydrous ZnCl2 CH3COOH + CH3OH CH3COOCH3 + H2O H2SO4 Decreasing reactivity order of alcohol CH3OH > C2H5OH > (CH3)2CHOH > (CH3)3OH Decreasing reactivity order of acid HCOOH > CH3COOH> C2H5COOH > (CH3)3COOH H+ C6H5COOH + C2H5OH C6H5COOC2H5 + H2O Decreasing reactivity order of acid O OH O OH O OH > > 9 ii. Rection with PCl5, PCl3 or SOCl2 CH3COOH + PCl5 CH3COCl + HCl + POCl3 CH3COOH + PCl3 CH3COCl + H3PO3 CH3COOH + SOCl2 CH3COCl + SO2 + HCl C6H5COOH + SOCl2 C6H5COCl + SO2 + HCl iii. Reaction with ammonia RCOOH + NH3 RCOONH4 RCONH2 + H2O Δ HCOOH + NH3 HCOONH4 HCONH2 + H2O Δ C6H5COOH + NH3 C6H5COONH4 C6H5CONH2 + H2O Δ iv. Dehydration 2CH3COOH CH3COOCOCH3 P2O5 2C6H5COOH C6H5COOCOC6H5 O O O C. INVOLVING –C=O GROUP OF –COOH GROUP Reduction RCOOH + LiAlH RCH OH 4 2 10 D. INVOLVING ALKYL GROUP OF THE ACID Hell-Volhard-Zelinsky Reaction (HVZ reaction) O O O H Cl2 O H Cl Alc. KOH O KCN O O H NC O H Aq. KOH O O H HO E. DECARBOXYLATION O O O O + Δ O H O 3 keto pentanoic acid O O Δ + O H O 11 – O OH – O O O O + + + + N N – N N – O O O O Δ + + – N – N O O O O F. SALTS OF CARBOXYLIC ACID O O CaO O H NaOH – + O Na O Ag O, Br , Δ 2 2 Br O H 12 ACID CHLORIDES O CHO3COOH + PCl5 CH3COCl + HCl + POCl3 CH3COOH + PCl3 CH3COCl + H3PO3 1 O H R CH3COOH + SOCl2 CH3COCl + SO2 + HCl = X, NH2, OCOR, OR C6H5COOH + SOCl2 C6H5COCl + SO 2 + HCl Preparation: These are prepared by treating caroxylicl acid with SOCl2, PCl5 and PCl3. Chemical Reactions 1. Nucleophilic substitution O O H2O -HCl OH Cl O O C2H5OH O Cl O O NH3 NH2 Cl 13 O O N2H4 NHNH2 Cl O O NH OH 2 NHOH Cl 2. Reduction O Cl LAH O OH H 14 3. Friedel-Craft reaction O CH3COCl AlCl3 COCl2 AlCl3 O 4. Diazomethane O O CH2N2 N2 Cl Ag2O O H2O O OH 15 ACETIC ANHYDRIDE Preparation O O O Pyridine CH COONa 3 O Cl O O O P2O5 Δ O OH O O OH O Δ OH O O O O OH O Δ OH O O 16 Properties: It is a colourless sweet smelling liquid. There is no intermolecular hydrogen bonding in esters. Hence their M.P. and B.P. are low as compared to those of the corresponding carboxylic acids. CHEMICAL REACTIONs a. Hydrolysis in presence of acid b. Hydrolysis in presence of base O O O HOH OH O O HO c. Ammonolysis O O NH2 O NH3 NH2 O O 17 O O O N2H4 O NHNH 2 O O O NH3 O NH 2 d. Alcoholysis O O O C2H5OH O O e. PCl5 O O O PCl5 Cl O 18 f. Claisen Condensation reaction O O O H + O CH3COONa O OH H 19 ACID AMIDES (ACETAMIDE) Preparation 1. Ammonium salts of fatty acids 2. Ammonia and acid chlorides O O – + Δ O NH4 NH2 O O O + O H H N NH H 2 NH2 3. Glacial acetic acid with urea 4. Wilgerdot reaction ALKALINE H2O2 CH3CN +H2O CH3CONH2 COLD H SO 2 4 5. Diazoacetone with ammonia Properties: Among the four derivates of acids, only acid amide molecules are capable of forming hydrogen bonds with each other because they have hydrogen atoms linked to nitrogen. Impure acetamide has mosy odour. Important chemical properties of acied amides are summarized below. 1. Hydrolysis H+ CH CONH CH COOH + NH 3 2 3 3 20 2. HNO2 HNO2 CH3CONH2 CH3COOH + N2 + H2O 3. Dehydration ` CH3CONH2 CH3CN + H2O 4. Hofmann degradation reaction CH3CON2 + Br2 + 4KOH CH3NH2 + 2KBr + K2CO3 + H2O ESTERS (ETHYL ACETATE) Preparation O O + OH OH O O O + Br O O Ag O O + CH2N2 OH O O O Al(OC H ) 2 5 3 O H 21 Esterification and hydrolysis of ester O O + OH H+ OH O O O + OH O NaOH O Na REACTIONS OF ESTERS O OH O + + NH 3 NH O 2 O OH O + + H2N NH O O H7C3 H7C3 + O HO O O O + O OH O OH + O DIBAH HO O O + Cl Cl O PCl5 POCl3 22 REFERENCES 1. O. P. Agarwal, Unified Chemistry text book, Volume 1; Jai Prash Nath Publication, Meerut, India. 2. O. P. Agarwal, Unified Chemistry text book, Volume 2; Jai Prash Nath Publication, Meerut, India. 3. O. P. Agarwal, Unified Chemistry text book, Volume 3; Jai Prash Nath Publication, Meerut, India. 4. O. P. Agarwal, Unified Chemistry text book, Volume 4; Jai Prash Nath Publication, Meerut, India. Question Bank 1. Write the any four Synthetic methods for Aliphatic carboxylic acids? 2. Write the any four Synthetic methods for Aromatic carboxylic acids? 3. Write a short note on Arndt Eistert Synthesis 4. Write a short note on Hell-Volhard-Zelinsky Reaction? 5. Write an essay on chemical properties of carboxylic acid group? 6. Write a short note derivatives of carboxylic acids. 7. Write an essay on dicarboilic acids and their synthesis, properties and applications. 23 SCHOOL OF SCIENCE AND HUMANITIES DEPARTMENT OF CHEMISTRY UNIT – II - Reactive Methylene Groups – SCY1315 1 UNIT-2 REACTIVE METHYLENE GROUPS 2.0 INTRODUCTION When a methylene group is presentr between two electronegative groups such as CO or CN, the hydrogen atoms of methylene group becomes acidic. Such compounds exhibit keto-enol equilibrium. The migration of hydrogen atoms to keto group depends on the inductive effect of the alkyl group or other groups on either side of the –CH2-group. Example 1: Other Examples: Another example of unsymmetrical compound- When a compound containing active methylene groups reacts with a strong base the proton removal takes place from both keto and enol form and the resulting enolate is stabilised by resonance. 2 Reactions of EAA with strong base: 2.1 KETO-ENOL TAUTOMERISM Compounds of structurally distinct molecules which are present as equilibrium mixture and the two forms are readily interconvertible and the removal of one form from the mixture results in the conversion to other from in order to restore equilibrium. The term Tautomerism is coined by Laar in 1885 to describe the phenomemon of substance reacting chemically according to the two possible structures.
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