AlldKetAcidDerAcid

7/24/2019 AlldKetAcidDerAcid

1/34

Aldehydes,

ketones,

carboxylic acids,

and derivatives of carboxylic acids


2/34

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


3/34

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


5/34

/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


6/34

"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.


7/34

?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.


8/34

?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


9/34


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


10/34


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


11/34

%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


12/34

%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.


13/34

/reparation of aldehydes and ketonesAldehydes. )n laboratory an aldehyde is prepared by oxidation of a primary alcohol.


14/34

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


15/34

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.


16/34

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 ',&ethanediol to aldehyde.

RCH HOCH%CH%OH

O O

O

R


17/34

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


18/34

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.


19/34

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


20/34

"ollens test


21/34

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


22/34

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


23/34

/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.


24/34

/hysical properties of some carboxylic acids

0ormula )@/AC name


25/34

?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!"#$


26/34

"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


27/34

?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 ,


28/34

?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


29/34


-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.


30/34

: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



31/34


Oxidation of primary alcohols and aldehydes. %trong oxidi$ing agents CrO1, D


32/34

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


33/34

%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


34/34

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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