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Chapter 10 Carboxylic Acids and Their Derivatives Nomenclature Physical properties Acidity Some reactions Introduction -carboxyl = carbonyl + hydroxyl -acids around us: taste of vinegar, sting (독아) of an ant (formic acid), rancid (악취나는) smell of butter aspirin, ibuprofen(iso-butyl-propanoicphenolic acid), resilience (탄성) of polyester and nylon fabric, Velcro (fabric hook-and-loop fasteners), softness of silk, strength of bacterial cell wall (N-acetylmuramic acid),our own membrane (fatty acids) Aspirin Ibuprofen Nomenclature -IUPAC system: “e” of alkane Æ -oic acid -substituted acid 1)IUPAC: the chain is numbered beginning with carboxyl carbon atom, and substituent (치환체) are located in usual way 2)common name: substituents are located with Greek letters, beginning with α-carbon atom e.g., 2-bromopropanoic acid (α-bromopropionic acid), propenoic acid (acrylic acid), 3-hydroxybutanoic acid (β-hydroxybutyric acid) -carboxyl group has priority over alcohol, aldehyde, ketone, and prefix “oxo-” is used to locate carbonyl group of aldehyde and ketone e.g., 3-oxopropanoic acid, 2-bromo-4-oxopentanoic acid Nomenclature Pelagonium spp (Geranium) Nomenclature -cyclic carboxylic acids: parent cycloalkane name + carboxylic acid (e.g., cyclopentanecarboxylic acid, trans-3-chlorocyclobutanecarboxylic acid) -aromatic acid: -oic or -ic acid e.g., benzoic acid (benzenecarboxylic acid), p-chlorobenzoic acid (4-chlorobenzenecarboxylic acid), o-toluic acid (2-methylbenzenecarboxylic acid), 2-naphthoic acid (2-naphthalenecarboxylic acid) -aliphatic dicarboxylic acid: -dioic acid (IUPAC) butanedioic acid, butynedioic acid, cis-2-butenedioic acid (maleic acid), trans-2-butenedioic acid (fumaric acid) -benzenedicarboxylic acids: phthalic acid, isophthalic acid, terephthalic acid -functional group: acyl, formyl, acetyl, propanoyl, benzoyl Nomenclature Sorrel (괭이밥) Physical properties -Colorless liquid with sharp (찌르는) or unpleasant (불쾌한) odor e.g., acetic acid in vinegar, butyric acid-rancid butter, goat acids, 3-methyl-2-hexenoic acid-offensive (자극적인) odor from armpit (겨드랑이) -form H-bonding with themselves and with other molecules Æ high bp (even higher than alcohol), e.g., glacial acetic acid -form dimers by two H-bonds Acidity and acidity constant -Carboxylic acids dissociate in water, yielding a carboxylate anion and a hydronium ion (generally considered as weak acids) -Ka; acidity constant What makes carboxylic acids acidic? -More acidic for two reasons (compare dissociation of ethanol and acetic acid, Fig 10-3, 4) 1)carbonyl carbon atom carries substantial (상당한) positive charge Æmake it much easier to place a negative charge on adjacent (인접한) oxygen atom 2)acetate ion is stabilized by resonance (see Fig in p292) -In addition, C-O bond in ionized acids is shorter (see Fig in P293) Fig 10.1 compare acetate ion and ethoxide ion Effect of structure on acidity -Acidity can vary depending on what other groups are attached to the molecule -compare acidities of mono-, di-, trichloroacetic acids (see the Fig in p293) Æ inductive effect -recall (상기하다) that electron-withdrawing groups enhance acidity and electron-releasing groups reduce acidity Preparation of acids -Can be prepared in many ways 1) oxidation of primary alcohols or aldehydes (Fig 10.6) 2) oxidation of alkyl side chains on aromatic rings (Fig 10.6 - 11) 3) reaction of Grignard reagents with carbon dioxide (Fig 10.12) 4) hydrolysis of alkyl cyanide (Fig 10.13-14) Carboxylic acid derivatives -Compounds in which –OH of –COOH is replaced by various other groups (e.g., ester, acyl halide, acid anhydride, primary amides) -many esters and amides occur naturally Esters -OH is replaced by –OR -Named in a manner analogous (유사한) to carboxylic acid salt i.e., the R part of –OR group is named first, followed by the name of acid, with “–ic” ending changed to “–ate” e.g., methyl acetate (methyl ethanoate), ethyl acetate (ethylethanoate), methyl butanoate phenylacetate methylbenzoate Preparation of esters: mechanism, nucleophilic Acyl substitution -carboxylic acid react with alcohol in the presence of acid catalyst to form ester (Fischer esterification) -Mechanism (6 steps, see Fig 10-19) 1) protonation of carboxyl group 2) alcohol, as a nucleophile, attacks carbonyl carbon of protonated acid 3), 4) equlibria on oxygen between proton loss and gain 5) water formation (as a leaving group) 6) deprotonation and ester formation Lactones -lactones: cyclic ester, can be formed from hydroxy acids (HO-R-COOH), mostly five or six-membered rings -lactone compunds around us: coumarin (newly mown hay), nepetalactone (catnip), erithromycin (antibiotics, a macrocyclic lactone) (p303) Coumarin Nepetalactone Penicillin catnip