Dr. Wolf's CHM 201 & 202 19-1 19.16 -Halogenation of Carboxylic Acids: The Hell-Volhard-Zelinsky...
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Transcript of Dr. Wolf's CHM 201 & 202 19-1 19.16 -Halogenation of Carboxylic Acids: The Hell-Volhard-Zelinsky...
19-1Dr. Wolf's CHM 201 & 202
19.16-Halogenation of Carboxylic
Acids:The Hell-Volhard-Zelinsky
Reaction
19-2Dr. Wolf's CHM 201 & 202
analogous to analogous to -halogenation of aldehydes and -halogenation of aldehydes and ketonesketones
key question: Is enol content of carboxylic key question: Is enol content of carboxylic acids high enough to permit reaction to occur acids high enough to permit reaction to occur at reasonable rate?at reasonable rate? (Answer is NO) (Answer is NO)
-Halogenation of Carboxylic Acids
-Halogenation of Carboxylic Acids
++ XX22 ++ HHXXRR22CCOHCCOH
OO
HH
RR22CCOHCCOH
OO
XX
19-3Dr. Wolf's CHM 201 & 202
reaction works well if a small amount ofreaction works well if a small amount ofphosphorus or a phosphorus trihalide is added tophosphorus or a phosphorus trihalide is added tothe reaction mixturethe reaction mixture
this combination is called the Hell-Volhard-this combination is called the Hell-Volhard-Zelinsky reactionZelinsky reaction
But...But...
++ XX22 ++ HHXXRR22CCOHCCOH
OO
HH
RR22CCOHCCOH
OO
XX
P or PXP or PX33
19-4Dr. Wolf's CHM 201 & 202
ExampleExample CHCH22COHCOH
OO
PClPCl33 benzenebenzene80°C80°C
CHCOHCHCOH
OO
BrBr
(60-62%)(60-62%)
++ BrBr22
19-5Dr. Wolf's CHM 201 & 202
ValueValue
CHCH33CHCH22CHCH22COHCOH
OOBrBr22
PPCHCH33CHCH22CHCOHCHCOH
OO
BrBr
(77%)(77%)
-Halogen can be replaced by nucleophilic -Halogen can be replaced by nucleophilic substitutionsubstitution
19-6Dr. Wolf's CHM 201 & 202
ValueValue
CHCH33CHCH22CHCH22COHCOH
OOBrBr22
PPCHCH33CHCH22CHCOHCHCOH
OO
BrBr
CHCH33CHCH22CHCOHCHCOH
OO
OHOH
(77%)(77%)
(69%)(69%)
KK22COCO33
HH22OO
heatheat
19-7Dr. Wolf's CHM 201 & 202
Synthesis of -Amino AcidsSynthesis of -Amino Acids
(CH(CH33))22CHCHCHCH22COHCOH
OOBrBr22
PClPCl33(CH(CH33))22CHCHCOHCHCHCOH
OO
BrBr
(CH(CH33))22CHCHCOHCHCHCOH
OO
NHNH22
(88%)(88%)
(48%)(48%)
NHNH33
HH22OO
19-8Dr. Wolf's CHM 201 & 202
19.17Decarboxylation of Malonic
Acidand Related Compounds
19-9Dr. Wolf's CHM 201 & 202
Decarboxylation of Carboxylic Acids
Decarboxylation of Carboxylic Acids
Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.
RHRH ++ COCO22RCOHRCOH
OO
19-10Dr. Wolf's CHM 201 & 202
Decarboxylation of Carboxylic Acids
Decarboxylation of Carboxylic Acids
Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.
But malonic acid does.But malonic acid does.
RHRH ++ COCO22RCOHRCOH
OO
150°C150°CCHCH33COHCOH
OO
++ COCO22HOCCHHOCCH22COHCOH
OO OO
19-11Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other. OO OO
OHOHHOHO
HH HH
OO
HOHO OO
OO
HH HH
HH
19-12Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation
This compound is This compound is the enol form of the enol form of acetic acid.acetic acid.
OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
19-13Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCH33
OO
19-14Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
HH HH HH
HH
OHOH
HOHO
OO
HOHO OO
OO
HH HH
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCH33
OO
These hydrogens play no role.These hydrogens play no role.
19-15Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
RR R'R' RR
R'R'
OHOH
HOHO
OO
HOHO OO
OO
RR R'R'
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
HOCCHHOCCHR'R'
OO
Groups other than H may be present.Groups other than H may be present.
RR
19-16Dr. Wolf's CHM 201 & 202
185°C185°C
Decarboxylation is a general reaction for 1,3-dicarboxylic acids
Decarboxylation is a general reaction for 1,3-dicarboxylic acids
160°C160°C
COCO22HH
COCO22HH
COCO22HH
HH
(74%)(74%)
(96-99%)(96-99%)
CH(COCH(CO22H)H)22
CHCH22COCO22HH
19-17Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHHOHO
RR R'R' RR
R'R'
OHOH
HOHO
OO
HOHO OO
OO
RR R'R'
HH ++ CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
This OH group plays no role.This OH group plays no role.
HOCCHHOCCHR'R'
OO
RR
19-18Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHR"R"
RR R'R'
RR
CC
OO
OO
One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.
Groups other than OH may be present.Groups other than OH may be present.
R"R"CCHCCHR'R'
OO
RR
OO
OO
OO
RR R'R'
HH R"R"
R'R'
OHOH
++R"R"
19-19Dr. Wolf's CHM 201 & 202
Mechanism of DecarboxylationMechanism of Decarboxylation OO OO
OHOHR"R"
RR R'R'
This kind of compoundThis kind of compoundis called a is called a -keto acid.-keto acid.
R"R"CCHCCHR'R'
OO
RR
Decarboxylation of a Decarboxylation of a -keto acid gives a -keto acid gives a ketone.ketone.
19-20Dr. Wolf's CHM 201 & 202
Decarboxylation of a -Keto AcidDecarboxylation of a -Keto Acid
CCCHCH33CC
OO
CHCH33
CHCH33
COCO22HH25°C25°C
COCO22
CCCHCH33CC
OO
CHCH33
CHCH33
HH
++
19-21Dr. Wolf's CHM 201 & 202
Section 19.18Section 19.18Spectroscopic Analysis ofSpectroscopic Analysis of
Carboxylic AcidsCarboxylic Acids
19-22Dr. Wolf's CHM 201 & 202
A carboxylic acid is characterized by peaks due toA carboxylic acid is characterized by peaks due toOH and C=O groups in its infrared spectrum.OH and C=O groups in its infrared spectrum.
C=O stretching gives an intense absorptionC=O stretching gives an intense absorptionnear 1700 cmnear 1700 cm-1-1..
OH peak is broad and overlaps with C—H OH peak is broad and overlaps with C—H absorptions.absorptions.
Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy
Dr. Wolf's CHM 201 & 202 19-23
2000200035003500 30003000 25002500 1000100015001500 500500
Wave number, cmWave number, cm-1-1
Figure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acid
C=OC=O
O—H and C—H stretchO—H and C—H stretch
monosubstitutedmonosubstitutedbenzenebenzene
CC66HH55CHCH22CHCH22CHCH22COCO22HH
19-24Dr. Wolf's CHM 201 & 202
proton of OH group of a carboxylic acid is normallyproton of OH group of a carboxylic acid is normallythe least shielded of all of the protons in a the least shielded of all of the protons in a 11HHNMR spectrum: (NMR spectrum: ( 10-12 ppm; broad). 10-12 ppm; broad).
11H NMRH NMR11H NMRH NMR
19-25Dr. Wolf's CHM 201 & 202
Chemical shift (Chemical shift (, ppm), ppm)
Figure 19.9Figure 19.9
CCHH22CCHH22CCHH22COCOHH
OO
01.02.03.04.05.06.07.08.09.010.011.012.0
19-26Dr. Wolf's CHM 201 & 202
1313C NMRC NMR1313C NMRC NMR
Carbonyl carbon is at low field (Carbonyl carbon is at low field ( 160-185 ppm), 160-185 ppm), but not as deshielded as the carbonyl carbon of but not as deshielded as the carbonyl carbon of an aldehyde or ketone (an aldehyde or ketone ( 190-215 ppm). 190-215 ppm).
19-27Dr. Wolf's CHM 201 & 202
UV-VISUV-VISUV-VISUV-VIS
Carboxylic acids absorb near 210 nm, butCarboxylic acids absorb near 210 nm, butUV-VIS spectroscopy has not proven to UV-VIS spectroscopy has not proven to be very useful for structure determination of be very useful for structure determination of carboxylic acids.carboxylic acids.
19-28Dr. Wolf's CHM 201 & 202
Aliphatic carboxylic acids undergo a varietyAliphatic carboxylic acids undergo a varietyof fragmentations.of fragmentations.Aromatic carboxylic acids first form acylium ions,Aromatic carboxylic acids first form acylium ions,which then lose CO.which then lose CO.
Mass SpectrometryMass SpectrometryMass SpectrometryMass Spectrometry
ArCArCOHOH
••••OO ••
••
ArCArCOHOH
••++OO ••
••
ArCArC OO ••••
++ArAr+
+
19-29Dr. Wolf's CHM 201 & 202
End of Chapter 19