6784664 carbonyl compounds

7/31/2019 6784664 Carbonyl Compounds

1/23

Carbonyl Compounds

(Chapter 35)


2/23

Carbonyl compounds

C O Carbonyl group

sp2

hybridized carbonCoplanar bonds, 120 o bond anglep-p overlap bond

Two types of compounds

Aldehyde Ketone C O

R

R

C O

H

R


3/23

Polarity of carbonyl bondDipole moment

propan-1-ol 1.69Dpropanone 2.88ethanal 2.72

C+ O

-

-bond -ve inductive effect

-bond readily polarizable(mesomeric effect)

C+

O-

C+

O:-


4/23

Chemical reaction

No electrophilic additions (why?)

C O

H-Br

C+ OH

:Br -

C OH

Br


5/23

Chemical reaction


C OH

BrH

Big +ve,unstableproduct

Energetic Factor

(Unstable)


6/23

Chemical reaction


Ea

Big +ve E a ,

unstableTransitionstate

Kinetic Factor

(Unstable)

C+ OH


7/23

Chemical reaction

No nucleophilic substitution

C ONu -:

C O -

Nu


8/23

Nucleophilic Addition

C O

Nu-

:

H/R

R

Reactivity:1. Electrophilicity of C atom

of the C=O group.2. Strength of Nu: - 3. Steric effect at the carbonyl

group

C O -

Nu

H/R

R

E+ C E

CN

H/R

R


9/23

Addition of HCN

C O

H/R

R+ H-CN C OH

CN

H/R

R

Reactivity: HCHO > CH 3CHO > ArCHO > CH 3COCH 3 > CH 3COR > RCOR > ArCOAr


10/23

Nucleophilic Addition

Addition of HCN (using KCN+H +)

C OCN -:

C O -

CN

H/R

R

H/R

HCN

R

C OH

CN

H/R R

Cyanohydrin(2-hydroxynitrile)

Note:HCN is NOTused.Because1. Toxic2. Weak acid

little CN -

slow

fast


11/23

Usefulness in organic synthesis

C OHCN

H/R

R H2O,H+

refluxC OH

COOH

H/R

R

c.H 2SO 4,heat

-C=C-COOH( , -unsaturated acid)

+1 carbon (longer carbonchain)

2 functional group


12/23

Addition of sodium

hydrogensulphate(IV)

C O -

SO 3H

R

RRoom temp. Na +

C OH

SO 3- Na +

R R

Sodiumhydrogensulphate(IV)adduct, isolated ascolourless crystals

C O

R

RNa+ HSO 3-

..

C-S bond is formed as S is more nucleophilic than O


13/23

Addition of sodium

hydrogensulphate(IV)Limit to aliphatic aldehydes and sterically

unhindered ketones (steric effect)

% product from 1mol NaHSO 3 in 1 hour:

C=OCH 3

H89%

C=O

CH 3

CH 3 56%

C=OCH 3

C2H5

36%

=O

35%

C=O

(CH 3)2CH

CH 3 12%

C=O

(CH 3)3C

CH 3 6%

C=O

C2H5

C2H

5

2%

C=OPh

CH 3 1%


14/23

Addition of sodium

hydrogensulphate(IV)Reversible (can be reversed by aq. Alkali oracid by shifting eqm. position to LHS byHSO 3- + H +=> SO 2 , HSO 3- + OH - => SO 32-)

Use to purify liquid or gaseous carbonyl

compounds which are difficult to purifyby direct recrystallization.


15/23

Addition-elimination

(condensation)

C O

R

RN:HO

H

H(Hydroxylamine)

HO N+

C O-

H

H

R

R

HO N C OH

H R

R

-H 2OHO N C

R

R(Oxime)


16/23

Addition-elimination

C O

R

RNH-NH

2

....

NO 2

NO 2

2,4-dinitrophenylhydrazine(Bradys reagent)

NH-N=C....

NO 2

NO 2

2,4-dinitrophenylhydrazone(yellow or light orange crystals)

R

R


17/23

Phenylhydrazone

Products have sharp and characteristicmelting point.

Used as the identification of the originalaldehyde and ketone

Note:

1. NH 3 does not react2. Predict the product obtained byadding H 2N-NH 2 to propanal.


18/23

Oxidation

1. KMnO 4 /H+

, K 2Cr 2O7 /H+

(Strong oxidizing agent)

RCHO => RCOOHRCH 2COCH 2R => RCOOH + R CH 2COOH +

RCH 2COOH + R COOHC6H5CHO => C 6H5COOH requiring reflux for hours


19/23

Oxidation2. Tollens reagent (silver mirror test)

Reagent: 2Ag + + 2OH - => Ag 2O + H 2OAg 2O + 4NH 3 + H 2O => 2Ag(NH 3)2OH

2[Ag(NH 3)2]+ + RCHO + 3OH -

=> RCOO-

+2H 2O + 4NH 3 + 2Ag (mirror)

No reaction with ketone

(Tollens reagent is a mild O.A.)


20/23

Oxidation

3. Fehlings reagent

Reagent: alkaline solution of copper(II) tartrate

RCHO + 2Cu 2+ + 5OH - => RCOO - + 3H 2O + Cu 2O(Fehling) (brick-red)

Note: No reaction with Ketones and Aromatic Aldehydes


21/23

Reduction

Reducing agent: LiAlH 4 Lithium TetrahydridoaluminateNaBH 4 Sodium Tetrahydridoborate

Both equivalent to a source of hydride ion, H-

.

RC O

H/RH -

R O - C

H/R H

R OHC

H/R H

H+


22/23

Reduction

LiAlH 4 must be kept dryi.e. in solution of dry ether

LiBH 4 is less powerful,can be used in aqueous solution.

Reducing agent: H2 /Ni, similar to alkene

RC O

H/R

H2 /NiRCH 2OH


23/23

Triiodomethane reaction

(RCOCH 3 + I 2 /OH - => RCOO - + CHI 3 ,yellow ppt.)

CH 3 C O

H/R

OH -

-H 2O

-CH 2 C O

H/R

X2 CH 2XC O

H/R-X -

CX 3 C O

H/R

CX 3

HO C O -

H/RCX 3- + R/HCOOH CHX 3 + RCOO -

X2

-X -

X2

-X -

OH -

6784664 carbonyl compounds

Documents