Carboxylic Acid & Their Derivatives Key Points

CARBOXYLIC ACID & THEIR DERIVATIVES KEY POINTS Separation of 1°, 2° and 3° amines : 1°, 2°, 3° amine + R4NX distillation Mixture of 1°, 2°, 3° amine R4NX does not undergo distillation. Mixture of 1°, 2°, 3° amine can be separated by following methods. (i) Fractional distillation : The mixture of amines may be separated by fractional distillation because their boiling points are quite different. It is used in industry. (ii) Hinsberg method : In this method mixture of amines is seperated by using benzene sulphonyl chloride (Hinsberg's reagent). C6H5SO2Cl + 1° amine  Product KOH dissolve C6H5SO2Cl + 2° amine  Product KOH insoluble 3° amine does not react with benzene sulphonyl chloride. (iii) (4) Hofmann method : In this method mixture of amines is separated by using ethyl oxalate. 1° amine + ethyl oxalate  solid product 2° amine + ethyl oxalate  liquid product 3° amine + ethyl oxalate  No reaction ACETYLATION : Acetylation takes place when alkyl amine combines with acetyl chloride or acetic anhydride. RNH2 + ClCOCH3  RNHCOCH3 + HCl (N –alkyl acetamide) RNH2 + (CH3CO)2O  RNHCOCH3 + CH3COOH (N –alkyl acetamide) (5) BENZOYLATION (SCHOTTEN BAUMANN REACTION) : CONHR COCl + H NH R + HCl NaOH Benzoylchloride (6) N–alkyl benzamide ACIDIC NATURE : Amines are very weak acids only 1° and 2° amines show acidic nature. R—NH2 + Na (7)  1 H 2 2 N– alkyl sodamide   RNHNa + REACTION WITH TILDEN REAGENT : When alkylamine reacts with nitrosyl chloride (Tilden reagent) alkyl chloride is formed. This reaction is important in interconversion. R—NH2 + NOCl   RCl + N2 + H2O (8) REACTION WITH PHOSGENE :   R—NH2 + COCl2 R N C O + 2HCl Alkyl isocyanate (9) REACTION WITH HALOGEN : The hydrogen atoms of the amino group are replaced by halogen atoms in presence of alkali solution. NaOH or KOH R—NH2 + Br2 R—NH—Br + HBr N– bromo alkylamine R—NH—Br + Br2 NaOH R—NBr2 + HBr N, N–dibromo alkyl amine (10) REACTION WITHALDEHYDES : Alkylamine reacts additively with aldehydes to form  - hydroxyl amines which are changed to schiff bases with elimination of water molecule. H H H H2O R NH2 + O C R  R N C R RCH NR (Schiff's base) OH (11) MANNICH REACTION : O O R—CH2NH2 + CH2O + HCH2 C C6H5 H2O R CH2NHCH2 CH2 C C6H5 Acetophenone (12) Mannich base OXIDATION : KMnO4 / H+ : Alkylamine on oxidation with acidified potassium permaganate forms aldimine which on hydrolysis gives aldehyde and ammonia. R—CH2NH2 R2CHNH2 R3CNH2 [O] + KMnO4/H R—CH NH (Aldimine) [O] R2C NH (Ketimine) [O] With H2SO5 (Caro's acid) Or H2O2 H 2O H RCHO + NH3 + H 2O H + R2C O + NH3 (Ketone) R3CNO2 (Nitroalkane) +2 /Fe (Fenton reagent) : O RCH2NH2 [O] R—CH2—NH—OH + RCH NOH + R C NHOH N-alkyl hydroxylamine Aldoxime R2CH NH2 [O] R3CNH2 [O] R2C N OH (Ketoxime) RCNO (Nitroso compound) Hydroxamic acid CARBOXYLIC ACID & THEIR DERIVATIVES (13) CARBYLAMINE REACTION (ISO CYANIDE TEST) : When alkyl amine's heated with chloroform and alc. KOH alkyl isocyanide is formed which has very bad smell. This test is also given by aniline . This is a test for p– amines. R—NH2 + CHCl3 + 3 KOH  R—N C + 3KCl + 3H2O Nucleophile RNH2 attacks electrophilic intermediate [:CCl2] dichlorocarbene. MECHANISM : (14) HOFMANN'S MUSTARD OIL TEST : When alkyl amine is heated with carbon disulphide and mercuric chloride alkyl isothiocyanate is formed which has smell like mustard oil. S S R NH2 + C S  R NH C SH HgCl2 R N C S + HgS + 2HCl Alkyl isothiocyanate S R2NH + C S S  RN 2  No reaction C SH HgCl2 No reaction S R3N + C (15) S REACTION WITH HNO2 (NaNO2 + HCl or H2SO4) : (A) (B) Primary amines react with nitrous acid to produce nitrogen gas [seen as bubbles] R—NH2 + HONO  R—OH + N2  + H2O CH3 NH2 + HNO2  CH3—O—CH3 R2 NH + HONO  R2 N—NO + H2O N–nitroso amine (Yellow oily layer) This is called libbermann's nitroso test (C) R3N + HONO  R3NHNO 2 Trialkyl ammonium nitrite (Soluble in water) KEY POINTS KEY POINTS (i) Nitrosoamines are carcinogens (Cancer causing agents) (ii) Amines can have chiral N-atom but cannot be resolved into enantiomeric forms because of rapid inversion of one enantiomeric form into the other. (iii) The Schiff's bases formed by reaction of 1°-amines and aldehyde/ketones are also called anils. (iv) The mixture of 1°, 2°, 3° amines can be distinguished by Hoffmann's test or Hinsberg's reagent or carbylamine test or nitrous acid test. (v) In Hoffmann test CS2 + HgCl2 are used and in Hinsberg test benzene sulphonyl chloride (C6H5SO2Cl) is used. Aniline is also called aminobenzene or phenyl amine. Aniline was first prepared by Unverdon 1826 by the distillation of indigo which is called anil in spanish and hence the name aniline. In aniline —NH2 group is directly attached to benzene ring. GENERAL METHODS OF PREPARATION : (1) Lab method : Aniline is prepared in the lab by reduction of C6H5NO2 with Sn + HCl. C6H5NO2 (2) (i) Fe + HCl (ii) NaOH ZnCl2 300° C C6H5 —NH2 + H2O C6H5NH2 + H2O From benzamide (Hofmann's reaction): Aniline is formed when benzamide is treated with Br2 and KOH. C6H5CONH2 + Br2 + 4KOH (5) C6H5NH2 + H2O From Phenol : Aniline is obtained when phenol is treated with ammonia in presence of ZnCl2 at 300°C. C6H5OH + NH3 (4) (ii) NaOH Industrial method : Aniline is obtained by reduction of nitrobenzene in presence of Fe/HCl. C6H5—NO2 (3) (i) Sn + HCl  C6H5NH2 + K2CO3 + 2KBr + 2H2O From benzoic acid (Schmidt reaction) : Benzoic acid is dissolved in conc. H2SO4 and hydrazoic acid is dissolved in chloroform. When both solutions are mixed aniline obtained. C6H5COOH + N3H conc. H 2SO 4 C6H5NH2 + N2 + CO2 (Hydrazoic acid) (6) From chloro benzene : Aniline can be manufactured by the action of ammonia on chloro benzene in presence of cuprous oxide (Cu2O). 2C6H5Cl + Cu2O + 2NH3  2 C6H5NH2 + 2CuCl + H2O CARBOXYLIC ACID & THEIR DERIVATIVES (7) From Grignard reagent : C6H5MgBr + ClNH2  (8) From Benzene: C6H6 + NH2OH (9) FeCl3 C6H5NH2 + H2O From phenyl isocyanide : C6H5N (10) C6H5NH2 + Mg Br Cl C + 2H2O  C6H5NH2 + HCOOH From phenyl isocyanate:C6H5N C O + 2KOH  C6H5NH2 + K2CO3 Similarities and Differences between Aromatic and Aliphatic amines : (A) (B) Similarities : (i) Both are basic, although aliphatic amines are more basic than the aromatic amines. (ii) Both form salts with acids, however salts of aromatic amines are easily hydrolysed. (iii) Both undergoes alkylation and acylation. (iv) Both react with Grignard reagents forming hydrocarbons. (v) Both forms schiff's bases. Differences : (i) Aniline is insoluble in water while aliphatic amines are soluble in water (due to H-bonds) (ii) Aniline gives diazonium salt with HNO2 while aliphatic amines gives alcohol and nitrogen (except CH3NH2) (iii) Aniline undergoes coupling and electrophilic substitution reactions in benzene ring while aliphatic is not. (iv) Aniline has characteristic aromatic smell while aliphatic amines have smell like ammonia (v) Aniline gives aniline black dye with acidic K2Cr2O7 while aliphatic does not form dye. (vi) Aniline gives violet colour with NaOCl while aliphatic amines does not give. CHEMICAL PROPERTIES : CARBOXYLIC ACID & THEIR DERIVATIVES (B) Reactions due to benzene ring : Note : (i) In aniline 2, 4, 6 or ortho and para positions are electron rich so electrophile attacks here.In aniline 3, 5, or meta position is electron deficient so nucleophile attacks here. (1) (ii) The benzene ring of aniline undergoes halogenation, sulphonation and nitration. (iii) The NH2 group is o-, p-directing. Halogenation : Chlorine and bromine react with aniline and form trichloro and tribromo aniline respectively NH2 + 3Br2 or 3Cl2 Polar solvent e.g. H2O Br NH2 Br or Br 2,4,6– Tribromo aniline Cl NH2 Cl Cl (white ppt.) NH2 NH2 + Br2 Non polar solvent (CS2 or CCl4) Br NH2 + Br o– and p–Bromoaniline Note : However, monobromo or chloro derivative of aniline can be prepared if -NH2 group is first protected by acetyl group. Here the reactivity decreases due to -I effect of acetyl group. (2) Nitration : (a) Direct nitration : The direct nitration of aniline by conc. HNO3 and conc. H2SO4 give meta-nitroaniline. Due to positively charged N, m-position becomes electron rich as compared to o, p–position.  NH2  NH3HSO4 + +NO2  H2SO4 H2SO4 HNO 3 (b) NH2 NO2 Indirect nitration : In indirect nitration amino group is protected by acetylation to give acetanilide, which on nitration and subsequent hydrolysis give o- and p- nitro-aniline. Ex. Azo dye test is given by (A) All amines (B) Only secondary amine (C) Only primary aliphatic amine (D) Only primary aromatic amine Sol. (D) (3) Sulphonation : Aniline reacts with fuming H2SO4 to give sulphanilic acid.(p-Amino-benzene sulphonic acid)  NH2  NHSO3H NH3HSO4 + H2SO4 (Fuming)  H2 O    180  C NH2 Rearrangement SO3H Sulphanilic acid Note : (i) This process is called baking. (ii) Sulphanilic acid is an important intermediate in the manufacturing of dyes and drugs. (iii) The compounds in which both proton donating & proton accepting groups present are called ampholite (dipolar ion). CARBOXYLIC ACID & THEIR DERIVATIVES (4) Catalytic hydrogenation : Aniline undergoes hydrogenation in presence of Ni at high temp. to form amino cyclohexane. NH2 NH2 + 3H2 (5) Ni High temp. Mercuration : When treated with alc. solution of mercuric acetate aniline undergoes mercuration. NH2 NH2 + (CH3COO)2Hg HgOCCH3  O  + CH3COOH o– Amino phenyl mercuric acetate TESTS OF ANILINE : Carbylamine test : Aniline gives carbylamine test or Isocyanide test. C6H5NH2 + CHCl3 + KOH  C6H5NC (Bad smelling) Dye test : Aniline is first diazotised. On adding alkaline soln. of -naphthol to the diazotised product a scarlet red dye is formed. On heating with bromine water, a ppt. is formed. Test for HCOOH and CH3COOH Test (i) HCOOH CH3COOH Tollen reagent Silver mirror – Fehling solution Cu2O red – Reducing character Reducing agents - HgCl2 (ii) – Corrosive sublimate Hg2Cl2 Calomel – K2Cr2O7 Cr+3 – Na2CO3 + H2 CH4 Decarboxylation. (iii) Heating at 1600C (iv) Heating sodium COONa salts of acids COONa COOH (vi) (vii) –  HCl COOH (v) –  at 3600C CO2 + H2 + NaCl Conc.H2SO4 CO + H2O Dissolve – Anhydride Cl2 / P CO2 + 2HCl Products are mono, di, HCHO CH3COCH3 P2O5 (viii) Ca salt heat BENZOIC ACID (C6H5COOH) GENERAL METHOD OF PREPARATION : tri chloro acetic acid. CARBOXYLIC ACID & THEIR DERIVATIVES CHEMICAL PROPERTIES