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Carboxylic acids: R-COOH, R-CO 2 H, Common names: HCO 2 Hformic acidL. formica ant CH 3 CO 2 Hacetic acidL. acetum vinegar CH 3 CH 2 CO 2 Hpropionic acidG.

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Presentation on theme: "Carboxylic acids: R-COOH, R-CO 2 H, Common names: HCO 2 Hformic acidL. formica ant CH 3 CO 2 Hacetic acidL. acetum vinegar CH 3 CH 2 CO 2 Hpropionic acidG."— Presentation transcript:

1 Carboxylic acids: R-COOH, R-CO 2 H, Common names: HCO 2 Hformic acidL. formica ant CH 3 CO 2 Hacetic acidL. acetum vinegar CH 3 CH 2 CO 2 Hpropionic acidG. “first salt” CH 3 CH 2 CH 2 CO 2 Hbutyric acidL. butyrum butter CH 3 CH 2 CH 2 CH 2 CO 2 Hvaleric acidL. valerans

2 Carboxylic acids, common names: … CH 3 (CH 2 ) 4 CO 2 Hcaproic acidL. caper goat CH 3 (CH 2 ) 5 CO 2 H--- CH 3 (CH 2 ) 6 CO 2 Hcaprylic acid CH 3 (CH 2 ) 7 CO 2 H--- CH 3 (CH 2 ) 8 CO 2 Hcapric acid CH 3 (CH 2 ) 9 CO 2 H--- CH 3 (CH 2 ) 10 CO 2 Hlauric acidoil of lauryl

3 C—C—C—C—C=O δ γ β αused in common names

4 special names

5 IUPAC nomenclature for carboxylic acids: parent chain = longest, continuous carbon chain that contains the carboxyl group  alkane, drop –e, add –oic acid HCOOHmethanoic acid CH 3 CO 2 Hethanoic acid CH 3 CH 2 CO 2 Hpropanoic acid CH 3 CH 3 CHCOOH2-methylpropanoic acid Br CH 3 CH 2 CHCO 2 H2-bromobutanoic acid

6 dicarboxylic acids: HOOC-COOHoxalic acid HO 2 C-CH 2 -CO 2 Hmalonic acid HO 2 C-CH 2 CH 2 -CO 2 Hsuccinic acid HO 2 C-CH 2 CH 2 CH 2 -CO 2 Hglutaric acid HOOC-(CH 2 ) 4 -COOHadipic acid HOOC-(CH 2 ) 5 -COOHpimelic acid Oh, my! Such good apple pie!

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8 salts of carboxylic acids: name of cation + name of acid: drop –ic acid, add –ate CH 3 CO 2 Nasodium acetate or sodium ethanoate CH 3 CH 2 CH 2 CO 2 NH 4 ammonium butyrate ammonium butanoate (CH 3 CH 2 COO) 2 Mg magnesium propionate magnesium propanoate

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10 physical properties: polar + hydrogen bond  relatively high mp/bp water insoluble exceptions: four carbons or less acidic turn blue litmus  red soluble in 5% NaOH RCO 2 H + NaOH  RCO 2 - Na + + H 2 O stronger stronger weaker weaker acid base base acid

11 RCO 2 HRCO 2 - covalentionic water insolublewater soluble Carboxylic acids are insoluble in water, but soluble in 5% NaOH. 1.Identification. 2.Separation of carboxylic acids from basic/neutral organic compounds. The carboxylic acid can be extracted with aq. NaOH and then regenerated by the addition of strong acid.

12 Carboxylic acids, syntheses: 1.oxidation of primary alcohols RCH 2 OH + K 2 Cr 2 O 7  RCOOH 2.oxidation of arenes ArR + KMnO 4, heat  ArCOOH 3.carbonation of Grignard reagents RMgX + CO 2  RCO 2 MgX + H +  RCOOH 4.hydrolysis of nitriles RCN + H 2 O, H +, heat  RCOOH

13 1.oxidation of 1 o alcohols: CH 3 CH 2 CH 2 CH 2 -OH + CrO 3  CH 3 CH 2 CH 2 CO 2 H n-butyl alcohol butyric acid 1-butanol butanoic acid CH 3 CH 3 CH 3 CHCH 2 -OH + KMnO 4  CH 3 CHCOOH isobutyl alcohol isobutyric acid 2-methyl-1-propanol` 2-methylpropanoic acid

14 2.oxidation of arenes: note: aromatic acids only!

15 3.carbonation of Grignard reagent: R-X RMgXRCO 2 MgX RCOOH Increases the carbon chain by one carbon. Mg CO 2 H + CH 3 CH 2 CH 2 -Br CH 3 CH 2 CH 2 MgBr CH 3 CH 2 CH 2 COOH n-propyl bromide butyric acid Mg CO 2 H +

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17 4.Hydrolysis of a nitrile: H 2 O, H + R-C  N R-CO 2 H heat H 2 O, OH - R-C  N R-CO H +  R-CO 2 H heat R-X + NaCN  R-CN + H +, H 2 O, heat  RCOOH 1 o alkyl halide Adds one more carbon to the chain. R-X must be 1 o or CH 3 !

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20 carboxylic acids, reactions: 1.as acids 2.conversion into functional derivatives a)  acid chlorides b)  esters c)  amides 3.reduction 4.alpha-halogenation 5.EAS

21 as acids: a)with active metals RCO 2 H + Na  RCO 2 - Na + + H 2 (g) b)with bases RCO 2 H + NaOH  RCO 2 - Na + + H 2 O c)relative acid strength? CH 4 < NH 3 < HC  CH < ROH < HOH < H 2 CO 3 < RCO 2 H < HF d)quantitative HA + H 2 O  H 3 O + + A - ionization in water Ka = [H 3 O + ] [A - ] / [HA]

22 Ka for carboxylic acids  Why are carboxylic acids more acidic than alcohols? ROH + H 2 O  H 3 O + + RO - RCOOH + H 2 O  H 3 O + + RCOO - ΔG o = R T log Keq The position of the equilibrium is determined by the free energy change, ΔG o. ΔG o = ΔH - TΔS ΔG o  ΔH  Ka is inversely related to ΔH, the potential energy difference between the acid and its conjugate base. The smaller the ΔH, the larger the Ka and the stronger the acid.

23 ΔH The smaller the ΔH, the more the equilibrium lies to the right, giving a larger Ka ( a stronger acid ).

24 Resonance stabilization of the carboxylate ion decreases the ΔH, shifts the ionization in water to the right, increases the Ka, and results in carboxylic acids being stronger acids.

25 Effect of substituent groups on acid strength? CH 3 COOH1.75 x ClCH 2 COOH136 x Cl 2 CHCOOH5,530 x Cl 3 CCOOH23,200 x Cl is electron withdrawing and delocalizes the negative charge on the carboxylate ion, lowering the PE, decreasing the ΔH, shifting the ionization to the right and increasing acid strength.

26 Effect of substituent groups on acid strength of benzoic acids? Electron withdrawing groups will stabilize the anion, decrease the ΔH, shift the ionization to the right, increasing the Ka, increasing acid strength. Electron donating groups will destabilize the anion, increase the ΔH, shift the ionization in water to the left, decreasing the Ka, decreasing acid strength.

27 -NH 2, -NHR, -NR 2 -OH -OR electron donating -NHCOCH 3 -C 6 H 5 -R -H -X -CHO, -COR -SO 3 H -COOH, -COOR electron withdrawing -CN -NR 3 + -NO 2

28 Relative acid strength? Ka p-aminobenzoic acid1.4 x p-hydroxybenzoic acid2.6 x p-methoxybenzoic acid3.3 x p-toluic acid4.2 x benzoic acid6.3 x p-chlorobenzoic acid 10.3 x p-nitrobenzoic acid 36 x 10 -5

29 2.Conversion into functional derivatives: a)  acid chlorides

30 b)  esters “direct” esterification: H + RCOOH + R´OH  RCO 2 R´ + H 2 O -reversible and often does not favor the ester -use an excess of the alcohol or acid to shift equilibrium -or remove the products to shift equilibrium to completion “indirect” esterification: RCOOH + PCl 3  RCOCl + R´OH  RCO 2 R´ -convert the acid into the acid chloride first; not reversible

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32 c)  amides “indirect” only! RCOOH + SOCl 2  RCOCl + NH 3  RCONH 2 amide Directly reacting ammonia with a carboxylic acid results in an ammonium salt: RCOOH + NH 3  RCOO - NH 4 + acid base

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34 3.Reduction: RCO 2 H + LiAlH 4 ; then H +  RCH 2 OH 1 o alcohol Carboxylic acids resist catalytic reduction under normal conditions. RCOOH + H 2, Ni  NR

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36 4.Alpha-halogenation: (Hell-Volhard-Zelinsky reaction) RCH 2 COOH + X 2, P  RCHCOOH + HX X α-haloacid X 2 = Cl 2, Br 2

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38 5. EAS: (-COOH is deactivating and meta- directing)

39 spectroscopy: IR: -COOH O—H stretch 2500 – 3000 cm -1 (b) C=O stretch 1680 – 1725 (s) nmr: -COOH 10.5 – 12 ppm

40 p-toluic acid -COO—H stretch C=O

41 c b a

42 Carboxylic acids, syntheses: 1.oxidation of primary alcohols RCH 2 OH + K 2 Cr 2 O 7  RCOOH 2.oxidation of arenes ArR + KMnO 4, heat  ArCOOH 3.carbonation of Grignard reagents RMgX + CO 2  RCO 2 MgX + H +  RCOOH 4.hydrolysis of nitriles RCN + H 2 O, H +, heat  RCOOH

43 carboxylic acids, reactions: 1.as acids 2.conversion into functional derivatives a)  acid chlorides b)  esters c)  amides 3.reduction 4.alpha-halogenation 5.EAS


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