carboxylic acids dr akm shafiqul islam school of bioprocess engineering
TRANSCRIPT
Carboxylic acidsCarboxylic acids
Dr AKM Shafiqul IslamDr AKM Shafiqul Islam
School of Bioprocess EngineeringSchool of Bioprocess Engineering
Carboxylic AcidsCarboxylic Acids
The functional group of a carboxylic acid is a The functional group of a carboxylic acid is a carboxyl groupcarboxyl group, , CarbonylCarbonyl with with hydroxyhydroxy
represented in one of three waysrepresented in one of three ways
CO2HCOOHC-OHO
Fill in the table below.
formic acid methanoic acidacetic acid ethanoic acidpropionic
acidpropanoic
acidbutyric acid butanoic acidvaleric acid pentanoic acidcaproic acid hexanoic acidbenzoic acid benzoic acid
2. Carboxylic acids that have branches are often given IUPAC names, where the numbering of the longest carbon chain begins at the Carbonyl carbon. Name the following compounds.
2-bromopropanoic acid
3-chlorobutanoic acid
4-amino-3-methylhexanoic acid
Carboxylic Aromatic AcidsCarboxylic Aromatic AcidsC
OHO
benzoic acid
COHO
CO
OH
o-phthalic acid(benzene-1,2-dicarboxylic)
OH
COHO
salicylic acid(2-hydroxybenzenecarboxylic)
OH
OH
HO
COHO
gallic acid(3,4,5-trihydroxy
-benzenecarboxylic)
CH3O
OH
COHO
vanillic acid(4-hydroxy-3-methoxy-benzenecarboxylic)
CCH
CHO
OH
cinnamic acid{(2E)-3-phenylprop
-2-enoic}
Carboxylic acids and their derivatives:Carboxylic acids and their derivatives:
Tart taste of citrus fruits, vinegar, and rhubarbTart taste of citrus fruits, vinegar, and rhubarb
Sharp sting of red antsSharp sting of red ants
Unsavory smell and taste of rancid butterUnsavory smell and taste of rancid butter
Vitamin C is a carboxylic acidVitamin C is a carboxylic acid
Pleasant taste and odor of fruits are due to carboxylic acid Pleasant taste and odor of fruits are due to carboxylic acid
derivatives: estersderivatives: esters
Where are they to be found?Where are they to be found?
Physical PropertiesPhysical Properties The carboxyl group contains three polar The carboxyl group contains three polar
covalent bonds; C=O, C-O, and O-Hcovalent bonds; C=O, C-O, and O-H the polarity of these bonds determines the major the polarity of these bonds determines the major
physical properties of carboxylic acidsphysical properties of carboxylic acids
δδ--O – HO – Hδδ++ δδ++C=OC=Oδδ--
RR
RRCC
OOHH
OO••••
•••• ••••
•••• RRCC
OOHH
OO••••
•••• ••••
••••++••••
––
Electron DelocalizationElectron Delocalization
stabilizes carbonyl groupstabilizes carbonyl group
RRCC
OOHH
OO••••
•••• ••••
•••• RRCC
OOHH
OO••••
•••• ••••
••••++••••
–– RRCC
OOHH
OO••••
••••
••••
++
••••
––
Electron DelocalizationElectron Delocalization
Physical PropertiesPhysical Properties The carbonyl group has a large dipoleThe carbonyl group has a large dipole The hydroxy group is capable of hydrogen The hydroxy group is capable of hydrogen
bonding.bonding. The molecules can H-bond to each otherThe molecules can H-bond to each other How does this affect boiling point?How does this affect boiling point?
Higher than aldehydes and ketone – no H-bondsHigher than aldehydes and ketone – no H-bonds Higher than alcohols – H-bonds, not strong Higher than alcohols – H-bonds, not strong
dipoledipole
H3C C
O
O
H
CH3C
O
O
H- +
+ -
hydrogen bondingbetween two molecules
HH33CCCC
OO HH OO
OOHHOO
HH
HH
HH
Solubility in WaterSolubility in WaterCarboxylic acids are similar to alcohols in Carboxylic acids are similar to alcohols in respect to their solubility in waterrespect to their solubility in waterForm hydrogen bonds to waterForm hydrogen bonds to water
Physical PropertiesPhysical Properties carboxylic acids are more soluble in water than are carboxylic acids are more soluble in water than are
alcohols, ethers, aldehydes, and ketones of comparable alcohols, ethers, aldehydes, and ketones of comparable molecular weightmolecular weight
CH3COOHCH3CH2CH2OHCH3CH2CHO
CH3(CH2)2COOHCH3(CH2)3CH2OHCH3(CH2)3CHO
acetic acid
1-propanolpropanal
60.5
60.158.1
1189748
16388.1butanoic acid1-pentanol 88.1 137
103pentanal 86.1
Structure NameMolecularWeight
Boiling Point (°C)
Solubility(g/100 mL H2O)
infinite
infinite
16infinite
2.3slight
Copyright© 2005, Michael J. Wovkulich. All rights reserved.
Alkoxide anions don’t have resonance-stabilization.
Alcohols are weaker acids than carboxylic acids.
R OH H2O H3O+
+ +
acid base alkoxide anion
R O
Physical PropertiesPhysical Properties
Sharp and or sour odor/tasteSharp and or sour odor/taste Vinegar, rancid butter, sweat, sauerkrautVinegar, rancid butter, sweat, sauerkraut
When the carbonyl group is substituted by atoms other than carbon or hydrogen, as in
R C
Z
O
where Z is oxygen, nitrogen, or halogen, the compound becomes a carboxylic acid or a carboxylic acid derivative.
Carboxylic acids derivativesCarboxylic acids derivatives
Ester Acid anhydride AmideEster Acid anhydride Amide Acid halide Acid halide
Carboxylic acid and derivativesCarboxylic acid and derivatives
O
R
X
O
R
O
O
RO
R
R'O
O
R
H2N
Carboxylic Acid Derivatives Carboxylic Acid Derivatives Hydroxy AcidsHydroxy Acids
Beta-hydroxy acidBeta-hydroxy acid
OH
O
OH
Salicylic Acid
exfoliant
oil soluble – penetrates oil containing pores to remove dead skin cells
less irritating than alpha acids
Reactions carboxylic acidsReactions carboxylic acids
1.1. as acidsas acids2.2. conversion into functional derivativesconversion into functional derivatives
a)a) acid chloridesacid chloridesb)b) estersestersc)c) amidesamides
3.3. reductionreduction4.4. alpha-halogenationalpha-halogenation5.5. EASEAS
Reactions : Acid/BaseReactions : Acid/Base Carboxylic acids are weak acidsCarboxylic acids are weak acids
Give up the H bonded to O to water or baseGive up the H bonded to O to water or base Tendency for acid to give up proton (HTendency for acid to give up proton (H++) is indicated by ) is indicated by
pKa; lower pKa indicates stronger acidpKa; lower pKa indicates stronger acid Carboxylic acids: pKCarboxylic acids: pKaa 4.0 - 5.0 4.0 - 5.0
In comparison:In comparison: Hydrochloric acid Hydrochloric acid pKa = -7pKa = -7 Sulfuric acid Sulfuric acid pKa = -3pKa = -3 Alcohol Alcohol pKa = 15-16pKa = 15-16
CH3COH H2O CH3CO H3O+
O O
Comparison Of pKa ValuesComparison Of pKa Values
Hydrochloric acid Hydrochloric acid pKa = -7pKa = -7 Sulfuric acid Sulfuric acid pKa = -3pKa = -3 Alcohol Alcohol pKa = 15-16pKa = 15-16 Carboxylic acidCarboxylic acid pKa = 4 pKa = 4
1. Both acetic acid and ethanol have an acidic hydrogen on the OH group. Why is the pKa value for acetic acid (pKa = 4.74) lower than the pKa for ethanol (pKa = 15.9)? In other words, why are carboxylic acids more acidic than alcohols. Consider resonance-stabilized anions.
R C
O
OH H2O R C
O
O H3O+
+ +
acid base carboxylate anion
Acidity of Carboxylic AcidsAcidity of Carboxylic Acids
=R CO
OR C
O
O
R CO
O
½-
½-
The greater the stability of the carboxylate anion, the farther the shift to the right.
resonance-stabilized carboxylate anion
R C
O
OH H2O R C
O
O H3O+
+ +
acid base carboxylate anion
The farther the shift to the right, the greater the acidity.
As acids:As acids:
a) with active metalsa) with active metals
RCORCO22H + Na H + Na RCO RCO22-Na+ + H-Na+ + H22(g)(g)
b) b) with baseswith bases
RCORCO22H + NaOH H + NaOH RCO RCO22-Na+ + H-Na+ + H22OO
c) c) relative acid strength?relative acid strength?
CHCH44 < NH < NH33 < HC < HCCH < ROH < HOH < HCH < ROH < HOH < H22COCO33 < RCO< RCO22H < H < HFHF
d)d) quantitativequantitative
HA + HHA + H22O O H H33OO++ + A + A-- onization in water onization in water
Ka = [HKa = [H33OO++] [A-] / [HA]] [A-] / [HA]
Dehydration of Carboxylic AcidDehydration of Carboxylic Acid
* water must be removed (to avoid hydrolysis)* water must be removed (to avoid hydrolysis)
* limited use* limited use
H3C O CH3
O O+ H2O(g)H3C COOH2 800o
COOH
COOH200o
O
O
O
+ H2O(g)
Reaction With BasesReaction With Bases All carboxylic All carboxylic acidsacids react with strong react with strong basesbases to to
form water-soluble form water-soluble saltssalts
COOH NaOHH2O
COO- Na
+H2O+ +
Benzoic acid(slightly soluble in water)
Sodium benzoate(60 g/100 mL water)
COOH NH3H2O
COO- NH4
++
Ammonium benzoate(20 g/100 mL water)
Benzoic acid(slightly soluble in water)
Reactions with basesReactions with bases
Salts of carboxylic acidsSalts of carboxylic acids Drop the –ic acidDrop the –ic acid Change to –ateChange to –ate
Sodium benzoate & monosodium glutamate Sodium benzoate & monosodium glutamate Sodium benzoate – inhibit moldSodium benzoate – inhibit mold MSG – flavor enhancerMSG – flavor enhancer
OHC
CH
O
NH2
CH2CH2
CO
-
O
Na+
O-
O
Na+
sodium benzoate MSG
R COH
O SOCl2
or PCl3orPCl5
R CCl
O
CO2H + SOCl2 COCl
CH3CH2CH2 CO
OH
PCl3CH3CH2CH2 C
O
Cl
a) acid chlorides
Conversion into functional derivativesConversion into functional derivatives
“direct” esterification: H+
RCOOH + R´OH RCO2R´ + H2O
-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 + PCl3 RCOCl + R´OH RCO2R´
-convert the acid into the acid chloride first; not reversible
)b esters
C CO
O
CH3
+ H2O
SOCl2
CCH3OH
O
OH+ CH3OH
O
Cl
H+
)c amides
“indirect” only!
RCOOH + SOCl2 RCOCl + NH3 RCONH2
amide
Directly reacting ammonia with a carboxylic acid results in an ammonium salt:
RCOOH + NH3 RCOO-NH4+
acid base
OH
O
3-Methylbutanoic acid
PCl3
Cl
O NH3
NH2
O
CO
OH
PCl3C
O
ClC
O
NH2
NH3
NH3
amide
CO
O NH4
ammonium salt
3. Reduction:
RCO2H + LiAlH4; then H+ RCH2OH
1o alcohol
Carboxylic acids resist catalytic reduction under normal conditions.
RCOOH + H2, Ni NR
CH3CH2CH2CH2CH2CH2CH2COOH
Octanoic acid(Caprylic acid)
LiAlH4 H+
CH3CH2CH2CH2CH2CH2CH2CH2OH
1-Octanol
CH2 CO
OH
H2, PtNR
LiAlH4
H+
CH2CH2OH
4. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH + X2, P RCHCOOH + HX X α-haloacid X2 = Cl2, Br2
COOH
Br2,PNR (no alpha H)
CH3CH2CH2CH2COOH + Br2,P CH3CH2CH2CHCOOH
Brpentanoic acid2-bromopentanoic acid
RCH2COOH + Br2,P RCHCOOH + HBr
Br
NH2OH
RCHCOOH RCHCOOH
RCH=CHCOOHRCH2CHCOOH
Br
aminoacid
NaOH;then H+
NH3
KOH(alc)
then H+
5. EAS: (-COOH is deactivating and meta- directing)
CO2H
CO2H
NO2
CO2H
SO3H
CO2H
Br
NR
HNO3,H2SO4
H2SO4,SO3
Br2,Fe
CH3Cl,AlCl3
benzoic acid