94 Chap 17 : Carboxylic Acids 17.1 Structure 17.2 Nomenclature 17.3 Physical properties 17.4 Acidity 17.5 Preparation of carboxylic acids 17.6 Reducti

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1 94 Chap 17 : Carboxylic Acids 17.1 Structure 17.2 Nomenclature 17.3 Physical properties 17.4 Acidity 17.5 Preparation of carboxylic acids 17.6 Reduction 17.7 Esterification 17.8 Conversion to acid chlorides 17.9 Decarboxylation 17.1 Structure Carboxylic acid : Alkyl or aryl + carboxyl group - RCH or ArCH sp 2 C H sp Nomenclature A. IUPAC System Aliphatic carboxylic acid ( 지방족카복실산 ) 의명명법 : 1) Carboxyl기를갖는가장긴탄소사슬을선정하고알케인의어미 -e를 -oic acid로교체함. 2) 카복실산이 C=C 혹은 C C을포함할때는이름중의 -an-을 -en- 혹은 -yn-으로교체하고, 숫자를사용하여다중결합의위치를표시함. 3) 다른작용기를포함하는카복실산의경우는 -CH 작용기가최우선권을가지므로다른작용기는접두어를붙여서명명함. 4) Dicarboxylic acid는두개의 carboxyl기를갖는탄소사슬의이름에 -dioic acid를붙여서명명함. 즉, Alkane + dioic acid 5) 고리에직접 carboxyl기가결합된경우는고리명에 -carboxylic acid를붙여서명명하며, 고리의원자위치는 -CH기가결합된탄소부터번호를붙인다.

2 95 HCH CH 3 CH H Methanoic acid Ethanoic acid 3-Methylbutanoic acid (Formic acid) (Acetic acid) H H trans-2-butenoic acid H (R)-5-Hydroxyhexanoic acid H H Ethanedioic acid (xalic acid) H Hexanedioic acid (Adipic acid) H CH HC CH 2-Cyclohexenecarboxylic acid trans-1,3-cyclopentanecarboxylic acid Aromatic carboxylic acid ( 방향족카복실산 ) 의명명법 : 1) 가장간단한방향족산은 benzoic acid ( 벤조산 ) 이며, 치환체가결합된경우는치환체를접두어로명명하고, 치환체의위치는 -CH를기준으로하여숫자로표기함 2) Dicarboxylic acid는 benzene + dicarboxylic acid로명명하며, 숫자를사용하여 -CH기의위치를표기함 CH CH CH H CH Benzoic acid 2-Hydroxybenzoic acid 1,4-Benzenedicarboxylic acid (Salicylic acid) (Terephthalic acid) B. Common Names ( 관용명 ) 지방족카복실산의관용명은출처에따라명명되었으며, 치환기의위치를나타내기위하여그리스문자 α, β, γ, δ, ε 등이흔히사용된다. Table 17.1 : Common names of several aliphatic carboxylic acids H NH 2 (S)-α-Aminopropionic acid [(S)-2-Aminopropanoic acid] H β-ketobutyric acid (3-xobutanoic acid)

3 Physical Properties 카복실산의물리적성질 : 1) 액체나고체상태에서카복실산은분자상호간의수소결합에의하여 dimer ( 이량체 ) 로존재한다. 2) 카복실산은알코올, 알데하이드, 케톤과같은비슷한분자량을갖는다른형태의 유기화합물보다매우높은끓는점을갖는다. 3) 카복실산은카보닐기와하이드록시기사이의수소결합에의하여물분자와상호 작용하므로비슷한분자량을갖는알코올, 에터, 알데하이드, 케톤화합물보다 물에잘녹는다. 4) 수용액에서카복실산의물에대한용해도는분자량이증가함에따라감소한다. Table 17.2 : Boiling point and solubility in H 2 of several carboxylic acid, alcohol, and aldehyde of comparable molecular weight

4 Acidity ( 산성도 ) A. Acid Ionization Constant ( 산이온화상수 ) Carboxylic acid : Weak acid, K a = 10-4 ~ 10-5 pk a = 4 ~ 5 pk a of RH = 16 ~ 18 e.g. K a of CH 3 CH : CH 3 CH + H 2 K' a CH 3 C - + H 3 + K' a = [CH 3 C - ][H 3 + ] [CH 3 CH][H 2 ] K a = K' a [H 2 ] = [CH 3 C - ][H 3 + ] [CH 3 CH] = 1.76 x 10-5 at 25 o C K a 가증가할수록강산, K a 가감소할수록약산 pk a = -logk a pk a 가감소할수록강산, pk a 가증가할수록약산 Acidity of RCH 1) Resonance 효과에의하여 carboxylate anion의음전하가 delocalization ( 비편재화 ) 되며, carbonyl기가 electron withdrawing inductive effect를통하여음이온을안정화시킴. 2) 탄소보다전기음성도가더큰원자가치환된경우는 inductive effect에의하여음이온의전자를끌어당기므로카복실산의산성도가증가한다. CH 3 CH ClCH 2 CH Cl 2 CHCH Cl 3 CCH pk a : ) Benzoic acid는벤젠고리의 sp 2 로혼성된탄소의전자끌기유도효과가나타 나므로 sp 3 혼성된카복실산보다산성도가더증가한다. CH 3 CH C 6 H 5 CH pk a :

5 98 예제 17.2 : Stronger acid * 수용액속에서의카복실산의존재형태 카복실산이수용액에용해될때존재하는카복실산의형태는용액의 ph 에 의존한다. R C H 용액의 ph 가 2 이하일때우세한종 H H + R C H + R C 용액의 ph 가산의 pk a 와같을때같은농도로존재 H H + R C 용액의 ph 가 7 이상일때우세한종 B. Reaction with Bases 모든카복실산은수용성이든지비수용성이든지관계없이 NaH, NaHC 3 등의 염기와반응하여수용성염을생성한다. CH + NaHC 3 H 2 C Na + + H 2 C 3 Sodium benzoate (60 g/100 ml H 2 ) 예제 17.3 : Acid-base reaction H H + NaHC 3 (S)-Lactic acid Figure 17.1 : Flow chart for separation of benzoic acid from benzyl alcohol

6 Preparation of Carboxylic Acids A. Addition of Carbon Dioxide to a Grignard Reagent RMgX 시약에 C 2 를 carboxylation시킨 magnesium carboxylate 염을산성화시켜카복실산을제조함 MgBr + C THF 0 o C C MgBr + HCl/H 2 CH Cyclopentanecarboxylic acid B. Industrial Synthesis of Acetic Acid H H C C H + H 2 H 2S 4 HgS 4 CH 2 C H CH 3 C H 2 Co 3+ CH 3 C H 2 CH 2 CH Pd 2+, Cu 2+ 2 CH 3 CH (Wacker 공정 ) 17.6 Reduction RCH : 환원되기가장어려운작용기중의하나임. LiAlH 4 와같은강환원제로가열조건에서환원되어 1차알코올을생성. A. Lithium Aluminum Hydride Carboxylic acid를 Et 2 혹은 THF 용매에서 LiAlH 4 를첨가하여가열한후, H 2 로처리하면 1 o alcohol이높은수율로생성된다. C H + LiAlH 4 Et 2 H 2 CH 2 H + LiH + Al(H) 3 4-Hydroxymethylcyclopentene B. Selective Reduction of ther Functional Groups Carboxyl 기는일반적으로 catalytic hydrogenation (H 2 /Ni, Pt, Pd 등 ) 이일어나지 않으며, 약환원제인 NaBH 4 와도반응이일어나지않는다. H + H 2 Pt 25 o C, 2 atm H H 5-Hydroxyhexanoic acid H H 1) NaBH 4 2) H 2 H 5-Hydroxy-5-phenylpentanoic acid

Organic Chemistry

Organic Chemistry Carboxyl Acid 의중요한화학적성질 : 산도 Carboxylic Acid 의주요유도체 : Ester, Amide, 산무수물, 산할로젠화물 Hankyong National University 17-1 Carboxyl 기 ( CH) 의구조작용기 : CH(Carboxyl 기 : carbony기 + hydroxyl기 ) 지방족 Carboxylic Acid :