alldketacidderacid
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Aldehydes,
ketones,
carboxylic acids,
and derivatives of carboxylic acids
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Aldehydes and ketones
An aldehyde is an organic compound containing carbonyl group >C=O bonded to one, or two
hydrogens.
CO
CO
HCHO
C
O
HH C
O
HR C
O
HAr
carbonyl group
(found in aldehydes and ketones)aldehyde group
or
methanal
(formaldehyd)any other aldehyde
A ketone has a carbonyl group bonded to two alkyls groups, or to two aryl groups, or one of each. A ketone does
not contain a hydrogen bonded to the carbonyl group.
C
O
RR C
O
RAr
dialkyl aldehyde aryl alkyl aldehyde diaryl aldehyde
C
O
ArAr
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Aldehydes and ketones cont.!
Aldehydes and ketones are common naturally occurring compounds.
CH
O
CH
O
HO
OH3C
C CC HH
H H
O
CH
CH3
CH3 O
H3C
H3C
H3C
CH3
O O
O
OH
OH
O
H3C
H3C
benzaldehyd
(in oil of bitter almonds)
vanillin
(in vanilla beans)cinnamaldehyde
(in cinnamon)
citral(in lemon grass)
camphor
(camphor trees)
cortisone
(andrenal hormone)
"he word aldehydewas coined by as a contraction of the #atin alcohol dehydrogenatus
dehydrogenated alcohol!. "he term formyl groupis derived from the #atin word formica= ant."his
word can be recogni$ed in the simplest aldehyde, formaldehyde methanal!,and in the simplest
carboxylic acid, formic acidmethanoic acid, an acid, but also an aldehyde!.
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%tructure and bonding in aldehydes and ketones
"he carbon in >C=O group issp&hybridi$ed and forms three sigma
! bonds that lie in a plane.
"he bond angle between two the sigma bonds is approximately '&(O. )n the C=O group, one of the
atoms bonded to the carbon by a sigma bond is an oxygen atom. "he carbon and the oxygen are
also *ointed by pi
! bond.
+ecause oxygen is more electronegatively than carbon, a C=O
bond is polar. "he >C=O bond in a carbonyl group, with its and
electrons is more polar than the CO- bond in alcohols. "he
reason for this is that the electrons of the carbonyls pi ! bond
are farther from the nuclei, less tightly held, and more easily
polari$ed. "he carbonyl oxygen has an unshared lone pair of
valence electrons that can react with the proton to increase the
positive charge on the carbonyl carbon. /rotonation is important inmany reactions of >C=O group.
C
O
H C
OH
e!dra"n to"ard positive o#ygen
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/hysical properties of aldehydes and ketones
+ecause aldehydes and ketones do not contain -O bonds they cannot undergo hydrogen
bonding as do alcohols. On the other hand, they are polar and can form relatively strong
electrostatic attractions between molecules, the positive portion of one molecule being attracted
to the negative portion of another.
C O
C O
electrostatic attraction
0or this reason, aldehydes and ketones have boiling points
intermediate between those of hydrogenbonded compounds and
unpolar compounds
C-1C-&C-&C-1 C-1C-& C-O C-1C-&C-&O-
+p, oC (.2 34 45
)ncreasing boiling point
Although pure aldehydes and ketones cannot form hydrogen
bonds, these compounds can form hydrogen bonds with the
hydrogen of water and or alcohols. +ecause of this type of
hydrogen bonding, the water solubility of aldehydes and ketones is
parallel that of alcohols. 6thanal and acetone are miscible withwater. +utanone and butanal are partly soluble in water.
COR
R$
OH R$$
COR
R$
OH H
hydrogen bond
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"automerism of aldehydes and ketones
An aldehyde or a ketone with at least one alpha
! carbon hydrogen is in e7uilibrium with an enol
form8 an isomer that contains a >C=C9 bond en! and a hydroxyl group ol!.
"hese structures are a special type of isomers called tautomers:reek tautos8;the same;!.
"he enol tautomer differs from the aldehyde or keto tautomer in the location of the double bondand hydrogen. 0or tautomerism to occurs, a stucture must contain a double bond to a
heteroatom an atom other than carbon, usually oxygen or nitrogen! and
hydrogen.
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?omenclature of aldehydes and ketones
Aldehydes. )n )@/AC system, simple aldehydes are named after the parent alkane with the -ane
ending changed to anal-an for a saturated chain and -al for aldehyde!. "he carbonyl carbon in
a simple aldehyde must be carbon '. "herefore, this number is omitted in the name. Othersubstituents, such as alkyl branches, are named by prefixes in the usual manner.
C-1 C-&C-&C-O
CH3 CH CH2CH
CH3 O
1234
3-methylbutanal
carbonyl carbon
is carbon 1
Common aldehydes are often called by their trivial names.
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?omenclature of aldehydes and ketones cont.!
ith trivial names, :reek letters alpha B!, beta !, gamma
!, and so forth are used instead ofnumbers to denote the position of substituent. "he alphacarbon is the one bonded to the
carbonyl >C=O! group, and the betacarbon is the next in line. "he :reek letters are not used in
)@/AC names, only in trivial names
CH3CH2 COH
O
CH3CH COH
O
Cl
ClCH2CH2 COH
O
IUPAC: Propanal 2-chloropropanal 3-chloropropanal
trivial: Propionaldehyde !chloropropionaldehyde !chloropropionaldehyde
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?omenclature of aldehydes and ketones cont.!
Detones. )n the )@/AC system, simple ketones are named with the ending anone.
C=O group.
+ecause it can be at different positions within the carbon chain.
CH3 CCH2CH2CH3
O
CH3CH2 CCH2CH3
OO
2-pentanone 3-pentanone cyclohexanone
( no nu!er needed"
%everal types of trivial nomenclature systems for ketones are used. "he simplest system is
naming the two groups bonded to >C=O group and adding the word ketone.
CH3 CO
ethyl ethyl #etone
ethyl ethyl
CH2CH3
Other common namesE
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?omenclature of aldehydes and ketones cont.!
Other common namesE
CH3CCH3
O
CH3C
O
C
O
acetone
aceto $roup
phenone $roup
acetophenone !en%ophenone
"he :reek letters alphaB! and alpha primeB! are used to denote substituent positions in thetrivial names of some ketones. One alphacarbon is designated as B carbon in order to
differentiate them
Cl2CHCCH3
O
ClCH2CCH2Cl
O
IUPAC: 1&1-dichloro-2-propanone 1&3-dichloro-2-propanone
trivial: ,!dichloroacetone , $!dichloroacetone
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%ome important aldehydes and ketones0ormaldehydemethanal, -&C=O! is a flammable, colorless, toxic gas with suffocating odor. )t
is prepared commercially by the oxidation of methanol. A 15 water solution of
formaldehyde is known as formalin and used as an insecticide, as a fumigantF in embalming
fluidF and in manufacture of explosives, resins, plastics, fabrics, dyes, etc.hen a7ueous solution of methanal is concentrated, a white polymer called
paraformaldehyde is formed. )t is used as a disinfectant and in manufacturing.
C O
H
H
n C O C O C O
H H H
HHH
paraformaldehyde
AcetadehydeC-1C-=O! is flammable, colorless, watersoluble li7uid with a pungent odor. "he
vapors of this compound are narcotic and toxic irritant, )f in large doses these vapors care inhaled,
death can occur by respiratory failure. Acetaldehyde is used in manufacture of dyes, plastics,
synthetic rubber. )t can be polymeri$ed to a cyclic compounds, paraldehyde and metaldehyde.
3 or 4 CH3CH
O
O O
O CH3
CH3
H3C
OO
OOH3C
H3C
CH3
CH3
paraldehyde
( hypnotic" etaldehyde( u'ed a' a 'nail poi'on"
or
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%ome important aldehydes and ketones cont.!
Acetone, C-1!&C=O! is a colorless, volatile, flammable li7uid with the sweet pungent odor. )t isprepared by oxidation of propan&ol. Acetone is relatively nontoxic, it is miscible with water and
the most other organic solvents, and it can dissolve most organic compounds. )t is widely used as
solvent.
"he breath and urine of a person with uncontrolled diabetes sometimes smell of
acetone. )n the body cells, acetone arises from acetoacetate ion in the case when glucose cannot
be properly utili$ed by the bodys cells.
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/reparation of aldehydes and ketonesAldehydes. )n laboratory an aldehyde is prepared by oxidation of a primary alcohol.
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Heactions aldehydes and ketones
Heagents can add to a carbonyl double bond. Carbonyl compounds can undergo
hydrogenation. )n this reaction aldehyde is reduced to'o alcohol, while a ketone is reduced to &o
alcohol.
eneral reaction C
O
R R$+ H
H
catalystCR
R$
H
OH
aldehyde or
ketone
primary or
secondary alcohol
A carbonyl group>C=O is polar and can be attacked by either a nucleophile at the carbonyl
carbon or an electrophile at the carbonyl oxygen.
C
O
u
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Addition of water
Addition of water is reversible reaction. Only the most reactive aldehydes, such a formaldehyde
or chloral Cl1CC-=O! form stable hydrates.
HCH
O
HCH
OH
H
H%O HCH
OH
OHH
!H
HCHOH
OH
stable hydrate in solution
RCR$
O
H%O RCR$
OH
OH
non stable
Addition of alcohol. Alcohol are weak electrophiles, and trace of acid is necessary to cataly$e
the reversible reaction. "he product of the addition ' mole of aldehyde is a hemiacetal, a
compound with one 8O- and 8OH on one carbon. A hemiacetal reacts further with an alcohol to
yield an acetal, a compound in which two 8OH groups are bonded to one carbon.
RCH R$OH
O
RCH
OH
OR$
R$OHRCH
OR$
OR$
hemiacetal acetal
"his reaction is reversible, and the e7uilibrium lies of the aldehyde side of the e7uation.
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Addition of alcohol to ketone
0or the less reactive ketones , the e7uilibrium favors the carbonyl side of e7uation even more.
RCR$ R$$OH
O
RCR$
OH
OR$&
R$$OHRCR$
OR$$
OR$$
hemiketal ketal
Above e7uilibriums favor the aldehyde. -owever, if a fivemembered ring or sixmembered ring
cyclic hemiacetal or acetal can be formed, the cyclic product is favored. Cyclic product can be
obtain by addition an ',ðanediol to aldehyde.
RCH HOCH%CH%OH
O O
O
R
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Addition of hydrogen cyanide
Hydrogen cyanide (HCN), a toxic liquid or gas at RT, is very weak acid !n the
"resence of CN# , HCN adds to the $C%& grou" of an aldehyde or ketone to yield
cyanohydrin, a co'"ound with &H and CN onded to the sa'e caron
RCR
O
RCR
C
OH
+ HCC
-
-OH and -C-
on the same carbon
aldehyde
or ketonecyanohydrin
Cyanohydrins are found in nature. 0or example, the millipede manylegged arthropod! carries the
cyanohydrin mandelonitrile in defensive gland. hen this millipede is attacked , the mandelonitrile
is decomposed en$ymatically to a mixture of ben$aldehyde and -?C, which is s7uirted at the
predator. A single millipede can produce sufficient -C? to kill a mouse.
CH C
OH
CH
O
+ HCenzyme
mandelonitrile
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Additionelimination reactions of aldehydes and ketones
Compounds that contain 8?-&groups such as primary amines H?-& or Ar?-&! and
hydra$ines ?-&, Ar?-?-&, etc.! can undergo addition reactions with aldehydes and ketones.
-owever, the addition products are unstable and undergo elimination of water.
C
O
* H2+ ) C
OH
+H )
C
OH
+)
- H2O
addition product
( un'ta!le"
eliination product
)f ammonia is one of the reactants, the product is called an imine. )f primary amine is one of the
reactants, the product is also called an imine but is fre7uently referred to as a %chiff base.
CH
O
* H2+CH3 CH
OH
+CH3
H
CH
+CH3
H*& addition - H2O
eliinationethylaine
a 10amine
iine
or Schiff base
A variety of 8?-&can react with aldehydes and ketones. )n the next slide *ust two examples will be
show.
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Additionelimination reactions of aldehydes and ketones cont.!
"he product of the reaction of hydroxyamine -O?-&!with aldehyde or ketone is
called anoxime.
CH3CCH3 H% OH
O
CH3CCH3 H%O
OH
o#ime
hen a hydra$ine H?-?-&! reacts with an aldehyde or a ketone the product is a hydra$one.
CH3CCH3
O
H%H H
CH3CCH3phenylhydrazine
phenylhydrazone
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"ollens test
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0ehling test
"he 0ehling test depends on the oxidation of an aldehyde by copper))! ions. )n
this test, the deep blue color of Cu&I
changes to a red precipitate of Cu&O.
RCH
O
%Cu%
+OH! RCO
!
O
Cu%O 3H%O
blue red
C b li id
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Carboxylic acidsA carboxylic acid is a compound containing the carboxyl group, a term derived from carbonyl
and hydroxyl. "he carboxyl group is written in different manners.
CO
OHCOH
O
CO%H COOH
"he group bonded to 8COO- can be almost any grouping, even another carboxyl group.
CH3COOH COOH CH% CCOOH
H
HOOC COOH
acetic benzoic acrylic o#alic
acid
)n 8COO- group each oxygen atom carries two pairs of unshared valence electrons. "hese oxygen
atoms are electronegative with respect to the carbonyl carbon and the hydroxyl hydrogen. "hus,
the 8COO- is polar. +ecause of polarity of the O- bond and because carboxylate ion HCOO ! is
resonance stabili$ed, carboxylic acids can lose a proton to a strong or moderate strong base
R C
O
O HR C
O
O H
unshared valence electrons polar bonds
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/hysical properties of carboxylic acidsA carboxylic acid molecule contains an 8O- group and thus can form hydrogen bonds with water.
+ecause of hydrogen bonding, the carboxylic acids containing one to four carbons are miscible
with water.
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/hysical properties of some carboxylic acids
0ormula )@/AC name
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?omenclature of carboxylic acids
"he )@/AC name of simple carboxylic acid is taken from the name of the parent alkane with
the 8ane ending changed to anoic acid. "he carbonyl carbon is numbered as carbon '.
CH3CH%COOH CH3CHCOOH
CH3
3
,%3
,%
propanoic acid %!methylpropanoic acid
"he lowformulaweight carboxylic acids are usually referred by their trivial names, which often
are derived from the acids source or odor."he name formic acid is derived from the #atin word for ants 8 formica.At one time, this acid was
prepared by the distillation of red ants. "he name acetic acidis derived from the #atin acetum,
i.e. Kvinegar;. Linegar is a 2J a7ueous solution of acetic acid. Butyric acidis a principal
odorous ingredient of rancid butter. Laleric acid #atin valere8 Kto be strong;! is not a strong
acid but is a very strongsmelling acid. Of the particular interest are the trivial names of the J, ,
and '(carbon acids, which are foulsmelling compounds found in goat sweat. "he name of allthree acids are derived prom the #atin caper, means 8 Kgoat;. 6nanthic acidis derived from the
:reek oenanthe8 Kvine blossom;. /elargonic acid is derived from its name of its ester found in
geranium Pelargonium roseum. (see next slide).
The name and properties some of important class of carboxylic acids fatty acids will be
discussed in lecture entitled!P!"#$
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"rivial names and derivations of some carboxylic acids
?umberof C
0ormula ?ame Gerivation
* -COO- formic Ants #. formica!+ C-1COO- acetic Linegar #. acetum!
C-1C- &COO- propionic
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?omenclature of carboxylic acids cont.!
:reek prefixes , , , etc.! can be used to indicate a substituentss position in reference to
carbonyl group. "hese :reek prefixes are used only in trivial name. )n the )@/AC system only
numbers are used.
CH3CHCOOH
OHCH3CHCH%COOH
Cl
-./AC0 %!hydro#ypropanoic acid 3!chlorobutanoic acid
*rivial0 !hydro#ypropionic acid !chlorobutyric acid
(also called lactic acid& 12 lac !milk))
hen a 8COO- is bonded to a ring carbon, the cyclic portion of the molecule is named and the
ending 8carboxylic acidis added. %ubstituted ben$oic acid are named in the same fashion as
other substituted ben$enes, with ben$oic acid as a parent name.
COOH
OH
%!hydr#ycyclohe#anecarbo#ylic acid
H% COOH
'!aminobenzoic acid
Carbon ,
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?omenclature of carboxylic acids cont.!
A diacid is named as an 8anedioic acidin the )@/AC system. "he alkane 8eis retain before a
consonant!. "he trivial name of these compounds are more fre7uently encountered than the
)@/AC names.
0ormula )@/AC name "rivial name
-OOCCOO- ethanedioic oxalic
-OOCC-&COO- propanedioic malonic
-OOCC-&!&COO- butanedioic succinic
-OOCC-&!1COO- pentanedioic glutaric
-OOCC-&!3COO- hexanedioic adipic
-OOCC-&!2COO- heptanedioic pimelic
/reparation of carboxylic acids
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/reparation of carboxylic acids
-ydrolysis of carboxylic acid derivatives. %ydrolysis means cleavage of a molecule by water.
0rom the :reekE hydro meaning water and lysis means Mloosing; or Kbreaking!. A compound
that yield carboxylic acid when it is hydroly$ed is called derivative of a carboxylic acid.
"eri&ati&es of carboxylic acids
CR
O
Cl CR
O
O C R
O
CR
O
OR$ CR
O
H% CR
acid
chloride acid
anhydride
ester amide nitrile
"he >C=O group of carboxylic acid derivative except nitriles! has two bonds. One of thesebonds is to a hydrogen, an alkyl group, or an aryl group. "he other bond is to an electronegative
atomE N, O, or ?!.
CRO
OR$
carbonyl portion of the
derivative contains
H& R& or Ar bonded
to the caronyl group
electronegative atom
hen the derivatives is heated in a7ueous acid
or base, he electronegative atom can be cleaved
from the carbonyl carbon. )f the cleavage is
carried out in acidic solution, the carbonylportion of the acid derivative is converted to a
carboxylic acid. )f the reaction is carried out in
base, the carbonyl portion forms a carboxylate
ion. Carboxylates can be converted to carboxylic
acid by acidification.
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:eneral reaction for hydrolisis
)n acid:
CR
O
H OHH
CR
O
OH H
carbo#ylic
acid
)n base:
CR
O
CR
O
O! H
carbo#ylate
!OH
CR
O
OHH
/reparation of carboxylic acids
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/reparation of carboxylic acids
Oxidation of primary alcohols and aldehydes. %trong oxidi$ing agents CrO1, D
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Acidity of carboxylic acids"he strength of an acid is expressed as the acidity constant Da.Davalues are often converted to
pDavalues, where pDa= log Da.
Acidity constants of some carboxylic acids
0ormula ?ame Da pDa
-COO- formic '. x '(3 1,52
C-1COO- acetic '. x '(2 3.53
C-1C-&COO- propanoic '.1 x '(2 3.5
C-1C-&!&COO- butanoic '.2 x '(2 3.'
ClC-&COO- chloroacetic '.3 x '(1 &.2
Cl&C-COO- dichloroacetic 1.1 x '(& '.3
Cl1CCOO- trichloroacetic &.( x '(' (.5(
C-1C-ClCOO- &chloropropanoic '.2 x '(1 &.1
ClC-&C-&COO- 1chloropropanoic '.( x '(3 1.4
Da '(2 '(& '(( '(& '(1
pDa 2 & ( & 1)ncreasing acid strength
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%alts of carboxylic acids
%trong base such as ?aO- undergo complete reaction with carboxylic acids to yield salts called
carboxylates.
CRO
O H aOH CRO
O a HOH
Carboxylates are salts and behave much like inorganic salts. "hey are odorless, relatively high
melting, and often water soluble. +eing ionic, they are insoluble in organic solvents. "he sodium
and potassium salts of long8hydrocarbonchain carboxylic acids fatty acids! are called soaps.
Carboxylates are named similarly to inorganic salts. "he cation is first, followed by the name of theanion as a separate word. "he name of the carboxylate anion is taken of the parent carboxylic acid
with the 8oic acidending changed to 8oate.
COOH COOa
benzoic acid sodium benzoate
Carboxylic acid also react with ammonia and amines to yield ammonium carboxylates. "his
reaction is especially important in protein chemistry, because the protein molecules are rich in
carbonyl group and amino groups. "reatment of carboxylate with a strong or moderate strong acid
converts the salts back to the carboxylic acids.
Other reactions of carboxylic acids
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Other reactions of carboxylic acids
Carboxylic acids are not reduced by catalytic hydrogenation. Other unsaturated groups in a
molecule can be reduced without concurrent reduction of 8COO- group.
CH3CCH%COH H%
O O
CH3CHCH%COH
OH O
keto group reduced carbonyl group not reduced
Carboxylic acid are readily reduced to primary alcohols with a very reactive reducing agent
lithium aluminum hydride, #iAl-3,. "his reagent reduces other carbonyl group such a keto
groups but does not usually reduce C=C double bonds.
CH3CH%COH
O
CH3CH%CH%
OH1iAlH'
6sterification. "he reaction of a carboxylic acid with an alcohol and a trace of strong acid catalyst
-&
%O3
! yields an ester, HCOOH. "he reaction is called an esterification.
:eneral e7uation for esterification.
RCOR$
O
RCOH R$OH
O
H%O
ester
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