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Carboxylic Acids and Their Derivatives By Dr. Nahed Nasser CARBOXYLIC ACIDS CONTENTS • Structure of carboxylic acids • Nomenclature • Physical properties of carboxylic acids • Preparation of carboxylic acids •Reactions of carboxylic acids •Derivatives of carboxylic acids: a. Acid chlorides b. Esters c. Amides d. Anhydrides •Occurrence and uses of carboxylic acids and their derivatives STRUCTURE OF CARBOXYLIC ACIDS • Carboxylic acids are organic acids contain one or more carboxyl group •A carboxyl group is made up of a carbonyl (C=O) group and a hydroxyl (O-H) group • It is often written in condensed form as –CO2H or –COOH • The general formula of a carboxylic acid is R-COOH or Ar-COOH 3 NOMENCLATURE Of CARBOXYLIC ACIDS IUPAC Nomenclature of carboxylic acids • Find the longest continuous carbon chain contains the COOH group to get the name of the parent hydrocarbon, the ending -e is replaced by the suffix –oic acid. • Number the chain starting with the carbon of COOH group as C-1 • If there are substituents identify their names and positions and list them as prefixes in alphabetical order. Examples: (CH3)2CH - CH(CH3) - CH2 - CH2 - COOH 4,5-Dimethylhexanoic acid is called • Cyclic compounds (Aliphatic or aromatic) containing one or more COOH groups attached to the ring are named by identifying the name of the ring followed by the word carboxylic acid or dicarboxylic acids etc. The carbon atom bearing the carboxylic group is numbered 1 and the substituents are numbered relative to it. COOH COOH Cyclopropanecarboxylic acid CH(CH3)2 2-Isopropyl-cyclobutanecarboxylic acid COOH COOH Br NH2 Cl 3-Amino-cyclohexanecarboxylic acid COOH 2-Bromo-4-chloro-cyclopentanecarboxylic acid COOH COOH OH Benzene carboxylic acid 2-Hydroxybenzene carboxylic acid COOH Benzene-1,2-dicarboxylic acid 5 Common nomenclature of carboxylic acids • Some carboxylic acids are called after characteristic properties or their origin. Formula HCOOH CH3COOH CH3CH2COOH CH3 (CH2)2COOH CH3 (CH2)3COOH IUPAC name methanoic acid ethanoic acid propanoic acid butanoic acid pentanoic aic Common name origin of name formic acid Latin for ant acetic acid Latin for vinegar propionic acid Greek for milk butyric acid Latin for butter valeric acid valerian root • The positions of the carbons present on the acid chain, are located by the Greek letters α indicating the carbon atom next to COOH group (C2), β (C3), γ (C4), δ (C5), etc . -C-C-C-C-C-COOH 6 54 3 2 1 6 CH3 COOH H3C H3C common: IUPAC: -- Dimethyl butyric acid 2,3-Dimethyl butanoic acid • Some aromatic acids have common names. COOH COOH COOH COOH COOH OH COOH Benzoic acid Salicylic acid Phthalic acid Terphathalic acid 7 PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS Solubility • Carboxylic acids are polar, they can form hydrogen bonds with H water molecules O H-Bonds H H O O H C R O H • Smaller carboxylic acids (1 to 4 carbons) are soluble with water • Whereas the solubility of bigger carboxylic acids decrease with size due to the increasing hydrophobic nature of the alkyl chain. •Aromatic acids are insoluble in water 8 Boiling Points • Carboxylic acids have exceptionally high boiling points than alcohols of identical relative molecular masses, For example: M.F. M.W bp / °C 1- Propanol C3H8O 60.01 97.2 Ethanoic acid C2H4O2 60.05 118 • This is due to carboxylic acids usually exist as dimeric pairs by forming two intramolecular hydrogen bonds in nonpolar media O H3 C H O C C O H O Hydrogen bond CH3 Acidity and acid strength • • • • Carboxylic acids are the most acidic simple organic compounds (they are stronger acids by over ten powers of ten compared to alcohols of comparable weights); also they are more acidic than phenols However, they are weak acids compared to inorganic acids (HCl or H2SO4) Adjacent electron withdrawing substituents near the carboxyl group increase the acidity Whereas electron releasing substituents decrease the acidity . • HCOOH > CH3COOH > CH3CH2COOH > CH3CH2CH2CH2COOH ( size of R group) • Cl3CCOOH > Cl2CHCOOH > ClCH2COOH > CH3COOH > (OCH3)CH2COOH ( number of e.w.g. and e.r. g.) • CH3CH2CH2CH(Cl)COOH > CH3CH2CH(Cl)CH2COOH > CH3CH(Cl)CH2CH2COOH > CH2(Cl)CH2CH2CH2COOH ( position of e.w.g. relative to COOH group) COOH • O2 N COOH COOH COOH > > NO2 NO2 > COOH > 10 CH3 Preparation of Carboxylic acids 1- Oxidation of primary alcohols or aldehydes + H2Cr 2O7 or K 2Cr 2O7/ H R CH2 O OH R or KMnO 4 / heat C OH carboxylic acid Primary alcohol + H2Cr 2O7 or K 2Cr 2O7/ H R CH O O R or KMnO 4 / heat Aldehyde C OH carboxylic acid 2- Oxidation of Alkylbenzenes CH3 COOH KMnO Toluene 4 Benzoic acid CH 2 CH 3 COOH KMnO 4 + Benzoic acid CO 2 + H 2O 3- Carbonation of Grignard Reagents H2O H2O 4- Hydrolysis of nitriles R-X NaCN + R C N H3O / heat RCOOH + + NH4 Reactions of Carboxylic Acids 1- Salts Formation KOH or NaOH RCOOH - + RCOO K or Na - + NaHCO 3 RCOO Na NH3 RCOO NH 4 - + + H2O + + H2O CO 2 + - COO Na COOH + + NaHCO 3 Sodium Benzoate OH + NaHCO 3 N. R 2- Substitution of hydroxyl group R'OH / H NH3 RCOOH SOCl2 1) PCL5 2) R''COO Na RCOOR' Ester RCOO NH4 Salt of acid RCOCl Acid chloride RCOOCOR'' Anhydride Carboxylic Acid Derivatives O R C R Cl R C OR' Acid Chloride Ester O O O C R C O O Amide acid anhydride O H3C IUPAC: Common : C Cl C Cl Ethanoyl chloride Acetyl chloride R' N 1-Nomenclature of acid chloride • Replace the -ic acid ending in the name of the parent acid by –yl chloride O C Benzoylchloride Reactions of Acid Chlorides O H2O R + C HCl OH O R'OH R + C HCl OR' O O R R NH3 Cl HCl NH2 + C + C O NH 2R' R + C HCl NHR' O AlCl 3 R C 1) LiAlH 4 2) H 3O + R CH 2OH + HCl Reactions of Esters O R O + + C H H2O R + C OH OR' O R O + + C H R''OH R O + + C H NH3 R O C OR' 1) LiAlH 4 2) H 3O R + CH2 OH + R'OH R" + OR' R'OH NH2 O C + C OR' R R'OH OR" O R + C OR' R R'OH 2 R"MgX 1) Dry ether 2) H 3O + R C R" OH + R'OH Reactions of Amides O R H3O C O + R + C NH2 OH O R O NaOH/ heat C R ONa O 1) LiAlH 4 C NH2 O R NHR' O C NH2 O R 2) H 3O + 1) LiAlH 4 C R + C NH2 R NH3 C NH2 2) H 3O + P 2O 5 R CH2 NH2 R CH2 NHR' R C N - H 2O Br 2 / NaOH or NaOBr R NH2 NH3 R Reactions of Acid anhydride O H2O R + C R'COOH OH O R'OH R + C R'COOH OR' O O C O O C R NH3 R' R'COOH + C NH2 + O NH 2R' R + C R'COOH NHR' O AlCl 3 R 1) LiAlH 4 2) H 3O + R + C CH 2OH + R'CH 2OH R'COOH Occurrence and Uses of Carboxylic Acids and their Derivatives • Carboxylic acids and their derivatives are widespread in nature O O C C OH C OH O Pyruvic acid - a metabolite Butyric acid- a short chain fatty acid C H N H S O CH3 O C SH CH3 O Pencillin G (an antibiotic) COOH O CH3 Isopentyl acetate (banana odour) 20 Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Examples H3C O C O C C OH HO Ibuprofen analgesic and non sterodial anti-inflammatory drug for relief of arthritis O Acetyl salicylic acid aspirin(analgesic, antipyretic and antiinflammatory) O O C OH H O NH2 C H3C OH Acetic acid in vinegar, organic solvent HO OH L-Dopa ( for treatment of parkinson's disease) 21 OH N N H2N N H2 H C N O H COOH C N CH CH2CH2COOH N folic acid H2N COOH p-aminobenzoic acd PABA H2N SO2NH2 sulfanilamide Antibiotic ‘’ Magic bullet’’ • Sulfanilamide It eliminates bacteria that cause infections by stopping the production of folic acid inside the bacterial cells • Para-amino benzoic acid, more commonly known as PABA, is a non-protein amino acid widely available in nature. It can be found in food sources such as liver, eggs (whole), molasses, rice, wheat germ and spinach. PABA is often referred to as Vitamin Bx (part of the Vitamin B complex family) and it has been suggested to contribute to a lot of processes in the body and it marketed as PABA vitamin.. Most Popular Use of PABA: PABA is widely used as a topical sunscreen (i.e. Sunscreen with PABA), as it has the ability to absorb UV rays from the sun ; it is considered as antioxidant, it has been found to reduce wrinkles and even to restore gray hair to its original color, further more play a role in red cells formation and manufacturing of folic acid, may play a role in reducing fatigue and limiting the effects of depression. • 22