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ADDITIONS OF AMINES TO CARBONYL GROUPS. Aldehydes and Ketones. MANTRA. (Memorization Jingle). Reactions with C=O :. Primary amines yield imines. Secondary amines yield enamines. Tertiary amines do not react. we will come back to this again and again. AMINES:. . . . primary.

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Presentation Transcript
slide1

ADDITIONS OF AMINES

TO CARBONYL GROUPS

Aldehydes and Ketones

slide2

MANTRA

(Memorization Jingle)

Reactions with C=O :

Primary amines yield imines

Secondary amines yield enamines

Tertiary aminesdo not react

we will come back to this again and again

AMINES:

..

..

..

primary

secondary

tertiary

slide4

Addition-Elimination:The Formation of Imines

ketone or

aldehyde

..

a “carbinolamine”

intermediate

..

+

H

primary

amine

Addition of the amine

is followed by a loss

of water (elimination).

Imines are compounds

with a C=N bond

G is a primary

alkyl group

slide5

H

H-O

H

H

H-O-H

+

H-O-H

+

+

H-O-H

H-O

H

H

Mechanism of Imine Formation

weak base addition - acid catalyzed

2

1

acid-catalyzed

addition

proton exchanges

an imine

..

+

+

loss of water

(elimination)

deprotonation

slide6

Formation of Simple Imines

overall result

remove

These reactions do not favor the formation of the

imine unless:

- the product is insoluble

(crystallizes or precipitates) or

- water is removed to drive the equilibrium

slide7

Hydrolysis of Simple Imines

REVERSAL

In an excess of aqueous acid, simple imines hydrolyze

back to the aldehyde or ketone and the amine from

which they were orginally formed …..

H3O+

Imines that are not soluble, however, are difficult to

hydrolyze.

slide8

CRYSTALLINE IMINES

HYDRAZONE AND OXIME DERIVATIVES

slide9

shown

below

CRYSTALLINE IMINES

There are some special amines that

yield insoluble products (imines)

that are easy to crystallize …..

..

:NH2OH

hydroxylamine

semicarbazine

..

..

R-NH-NH2

various

hydrazine

compounds

2,4-dinitrophenyl-

hydrazine

slide10

Formation of Oximes

hydroxylamine

aldehyde

or ketone

(usually crystallizes)

slide11

Formation of Hydrazones

a hydrazine

aldehyde

or ketone

slide12

insoluble

red, orangeoryellow

precipitate forms

a 2,4-DNP

2,4-Dinitrophenylhydrazones

2,4-dinitrophenylhydrazine

2,4-dinitrophenylhydrazine

aldehyde

or ketone

2,4-dinitrophenylhydrazone

(precipitates)

slide13

Formation of Semicarbazones

semicarbazine

semicarbazide

aldehyde

or ketone

a semicarbazone

(usually crystallizes)

slide14

DERIVATIVES

CRYSTALLINE IMINES CAN BE USED AS DERIVATIVES

A derivative is a solid compound (formed from the

original compound) whose melting point can help

to identify the original compound.

What you will see in the tables of unknowns:

semicarbazone

2,4-dinitrophenyl-

hydrazone

ketones

bp mp

2-undecanone 231 12 12263

4-chloroacetophenone 232 12 204236

4-phenyl-2-butanone 235 - 142127

slide16

Pyridoxyl-5’-phosphate (P-5’-P)

Converts amino acids to a-ketoacids, and vice versa.

Biologically important in transamination reactions.

..

an amino acid

+

- H2O

pyridoxyl-5’-phosphate

( P-5’-P )

continued

formation of

the imine

+

first imine

slide17

:Enz

Enz-H

converts

tautomerism

H-Enz

+

Enz:

a-ketoacid

first imine

H2O

+

new imine

Removing the

amino group

hydrolysis of

the new imine

+

pyridoxamine

slide18

TRANSFERRING THE AMINO GROUP

a different a-ketoacid

pyridoxamine

tautomerism

hydrolysis of the imine

These steps are the

reverse of those on

the previous slides.

a different

amino acid

slide19

SUMMARY

TRANSAMINATION

( has NH2 )

( takes NH2 group )

a-Ketoacid-1 +

Amino Acid-1 +

pyridoxyl-5’-phosphate

pyridoxamine-NH2

( has NH2 )

( has NH2 )

( gives NH2 back )

Amino Acid-2 +

a-Ketoacid-2 +

pyridoxyl- 5’-phosphate

pyridoxamine-NH2

( has NH2 )

is a different

a-ketoacid

than

slide21

Formation of Enamines

b-hydrogen

is required

secondary

amine

..

benzene

“carbinolamine”

generally removed

by azeotropic

distillation

an enamine

slide22

COMPARISON

carbinolamine intermediates

PRIMARY AMINES

SECONDARY AMINES

hydrogen on the

adjacent carbon

..

..

-H2O

-H2O

no hydrogen

on nitrogen

hydrogen

on the

nitrogen

imine

enamine

When there is no hydrogen on

nitrogen, one is lost from carbon.

slide23

piperidine

SOME SECONDARY

AMINES FREQUENTLY

USED TO FORM

ENAMINES

pyrrolidine

Water must be removed

morpholine

slide24

H

H-O-H

+

H

H-O-H

+

O-H

H

Enamine Formation

MECHANISM

continued ….

slide25

Enamine Formation (cont)

MECHANISM

+

H2O

H

O-H

water must

be removed

to force the

equilibrium

H3O+

+

enamine

slide26

Nucleophilic Character of Enamines

C

nucleophilic

at carbon

X

SN2

slide27

Reactions of Enamines as Nucleophiles

SN2

an iminium salt

hydrolysis

alkylation

slide28

Az

ALKYLATION OF A KETONE

pyrrolidine

..

iminium

salt

..

+

H+

enamine

H3O+

workup

remove

water

+

slide29

H

H-O-H

+

O-H

H

Hydrolysis of Iminium Salts

MECHANISM

continued ….

slide30

O-H

H

Hydrolysis of Iminium Salts

MECHANISM

slide31

SUBSTRATES FOR ENAMINE ALKYLATION

(and acylation)

alkylation

X = Cl, Br, I

primary

secondary

allylic

acylation

enamine

acyl compounds

may be used

slide32

CHLORIDES, BROMIDES AND IODIDES

In SN2 reactions you learned the rate sequence R-I > R-Br > R-Cl

and that iodides are better substrates than chlorides.

This is true.

Based on this knowledge …..

many students assume that if acid chlorides are good

the acid bromides and iodides must be better.

However …… acid bromides and iodides are difficult to

prepare, and the iodides are quite unstable

….. you should use the chlorides.

They are easily prepared

from the acid by:

R-COOH + SOCl2

slide33

Enamine Reactions -- Summary

secondary

amine

alkyl or

acyl

halide

slide34

TERTIARY AMINES

DO NOT REACT

slide35

H

COMPARISON

PRIMARY AMINE

You need to lose two H’s,

one to form the intermediate,

one to eliminate water.

loses H from N

..

H

SECONDARY AMINE

H is lost to form intermediate

loses H from C

TERTIARY AMINE

:

N-R

H is lost

R

..

:

unstable

The tertiary amine can’t

form the carbinolamine

intermediate because

it lacks an H on N.

reverses

N-R

+

R

R

no H to lose

slide36

FORMING RINGS

SOME GUIDELINES

slide37

DILUTE SOLUTION AND EXACT STOICHIOMETRY

FAVOR RING FORMATION

Problem 16-18 in

in your textbook.

pH = 5

Excess formaldehyde (>2:1)

and a more concentrated

solution favor the diimime.

Also remember

that unstrained

5- and 6-rings

form easily,

other sizes are

difficult.

1:1 molar ratio and

dilute solution favor

the ring formation

In dilute solution the molecule is more

likely to react internally with itself

because encounters with other molecules

will be less frequent.

slide38

HINT ON THE MECHANISM …..

C=N can undergo additions just like C=O

Both are polar multiple bonds

and both can undergo acid-

catalyzed nucleophilic addition.

protonation

first

+

CRUCIAL

STEP

forms ring

..

pH 5

mildly

acidic

….. see if you can figure out the rest of the mechanism

for Problem 16-18 on your own.

slide40

Ylide

-

..

+

A compound or intermediate

with both a positive and a

negative charge on adjacent

atoms.

X

Y

BOND

Betaine or Zwitterion

+

A compound or intermediate

with both a positive and a

negative charge, not on

adjacent atoms, but in different

parts of the molecule.

Y

MOLECULE

-

X

:

slide41

Preparation of a Phosphorous Ylide

( WITTIG REAGENT )

precipitates

benzene

:

heat

-

..

:

O-CH3

..

..

ether

strong base

-

+

..

Triphenylphosphine

( Ph = C6H5 )

an ylide

slide42

Resonance in Ylides

dp-pp BACKBONDING

..

Remember that Phosphorous

is a Period III element (d orbitals).

P

C

Backbonding to phosphorous

reduces the formal charges

and stabilizes the negative

charge on carbon.

3d

2p

slide43

The Wittig Reaction

MECHANISM

-

..

+

ylide

betaine

INSOLUBLE

synthesis of

an alkene

very thermodynamically

stable molecule

oxaphosphetane

(UNSTABLE)

slide44

+

+

:

ylide

-

SYNTHESIS OF AN ALKENE - WITTIG REACTION

slide45

+

Br-

PhLi

..

-

+

ylide

+

..

:

..

-

+

triphenylphosphine

oxide (insoluble)

ANOTHER WITTIG ALKENE SYNTHESIS

slide46

Muscalure

Sex pheromone of the

common house fly.

Musca Domestica

(Z)-9-tricosene

Wittig

The reaction can be made to give the

cis alkene (Z) by correct choice of

solvent and temperature, or by the

separation of a mixture of cis and trans.