Surfactants as Catalysts for Organic Reactions in Water Atefeh Garzan 11/07/07

Surfactants as Catalysts for Organic Reactions in

Water

Atefeh Garzan

11/07/07

Homogeneous catalysts:

Brønsted acid catalysis:

Lewis acid catalysis:

- Advantages: high activity, selectivity - Disadvantages: separation and recycling problems

Homogeneous catalysis: catalyst is in the same phase as reactants.

+AlCl3H

R

O

R Cl

O

OR

H

H2O+ ROH

O

Heterogeneous catalysts: Heterogeneous catalysis: catalyst is in a different phase than reactants.

- Metals alone

- Metals plus other component

- Advantages: easy separation and recovery- Disadvantages: less activity and selectivity

Other catalysts:

New Methods to combine the benefits:

- high activity, selectivity

- easy separation and recovery

Transfer a homogeneous catalyst into a multi phase system:

- surfactant - phase transfer system- organic or inorganic support:

H. Turkt, W. Ford, J. Org. Chem. 1991, 56, 1253. C. Starks, J. Am. Chem. Soc. 1971, 93, 195.

NaOCl

1

O

N

N

N

N

ClNaO3S

ClSO3Na

ClCl

Cl Cl

ClSO3Na

ClNaO3S

MnII

ClBr + NaCN(n-Bu)4P Cl

CN + NaBr

Surfactant:

surfactant

Surface Active Agent

Surfactants have amphiphilic structure:

HydrophobicHydrophilic

Classification of surfactant:

Anionic

Cationic

Amphoteric

Nonionic

Sodium dodecylsulfate (SDS)

Cetylpyridinium bromide

Dipalmitoylphosphatidylcholine (lecithin)

Polyoxyethylene 4 lauryl ether

N

Br

SO Na

O

O

O

O

O

OP

OCH2CH2N(CH3)3

OO

OO

OO

OH

Behavior of surfactants:

When a molecule with amphiphilic structure is dissolved in aqueous medium, the hydrophobic group distorts the structure of the water.

As a result of this distortion, some of the surfactant molecules are expelled to the surfaces of the system with their hydrophobic groups

oriented to minimize contact with the water molecules.

Nonpolar tail

Polar head

Micelle formation:When the water surface is or begin to be saturated, the overall energy reduction may continue through another mechanism:

Micelle formation

Hunter, Foundations of Colloid Science, p. 572, 1993.

Driving force:Hydrophobic effect

Formation of the micelle No formation of the micelle

Electrostatic repulsion

Critical Micelle Concentration (CMC):

CMC decreases with increasing alkyl chain length CMC increases as the polar head becomes larger. CMC of neutral surfactants lower than ionic

CMC

Hydrophobic effect Electrostatic repulsion

Krafft temperature: For surfactants there exists a critical temperature above which solubility rapidly increases

(equals CMC) and micelles form Krafft point or Krafft temperature (TK )

Krafft point strongly depends on the size of head group and counterion.

Surfactant Tk (oC)

C12H25SO3-Na+

C12H25OSO3-Na+

n-C8F17SO3-Na+

n-C8F17SO3-K+

38

16

75

80

D. Myers, surfactant science and technology, p.111, 2006.

Surfactant aggregates:

Monomers

Spherical Micelles

Polar Solvent

Bilayer Lamella

Cylindrical Micelles

Nonpolar Solvent

Reverse Micelles Inverted Hexagonal Phase

Easy separation and recovery, high activity, selectivity.

Surfactant in organic reaction:

In this system, we can use water as solvent; in water, surfactants can:

- Act as a catalyst

- Help to solubilize the organic compounds in water

In comparison to organic solvents, water is:

- Cheap

- Safe

- Less harmful

Micellar catalysis:

Electrostatic interaction:

M. N. Khan, N. H. Lajis, J. Phys. Org. Chem. 1998, 11, 209.

Additive Conc. (M) 103 Kobs (s-1) - - 1.83

0.01 1.28

0.01 1.78

0.01 2.05

Na ( )11SOO

O

O

N

O

O

OH

Kopen N

OHO

O

N

Br

13

OO

OH99

Micellar catalysis:

N

N

N

N

N

OH

O

OOOH

OBr

Br

Br

Br

Br

Br

Br

OH

OH

OH

OH

OH

OH

N

O

O

OH

Kopen N

OHO

O

Micellar catalysis:

Electrostatic interaction:

M. N. Khan, N. H. Lajis, J. Phys. Org. Chem. 1998, 11, 209.

Additive Conc. (M) 103 Kobs (s-1) - - 1.83

0.01 1.28

0.01 1.78

0.01 2.05

Na ( )11SOO

O

O

N

O

O

OH

Kopen N

OHO

O

N

Br

13

OO

OH99

Micellar catalysis:

A + B A_B

Rate= k [A][B]

The reactants are concentrated through insertion to the micelle.

The TS≠ can be stabilized by interaction of polar head group.

A catalyst is a substance that increases the rate of a chemical reaction

without itself being changed in the process.

A+B

A_B

[A---B] ≠

energy

time

activation energy

activation energy

uncatalyzed reactioncatalyzed reaction

Lewis acid catalysis:

Lewis acid catalysis is generally carried out under strictly

anhydrous conditions because of the water-labile nature of most

Lewis acids.

Some metal salts such as rare earth metal triflates can be used

as water-stable Lewis acids.

PhCHO +

(1 equiv.) (1.5 equiv.)

(0.1 eq)

H2Ort, 4h 88%

OSiMe3

Ph

Sc(OTf)3

SDS (0.2 eq)Ph

OH

Ph

O

S. Kobayashi, T. Wakabayashi, S. Nagayama, H. Oyamada, Tetrahedron Lett. 1997, 38, 4559.

Lewis acid surfactant

K. Manabe, Y. Mori, T. Wakabayashi, S. Nagayama, S. Kobayashi, J. Am. Chem. Soc. 2000, 122, 7202.

“Lewis acid-surfactant-combined catalyst (LASC)”, acts:

-as a Lewis acid to activate the substrate molecules

-as a surfactant to help to solubilize the organic compounds in water

Lewis Acid Surfactant Catalyst:

ScCl3 + SOO

O

O3 Na

H2O

SOO

O

OSc3+

3+3 NaCl


Colloidal Dispersion

Organic Compounds

:

Lewis Acid Surfactant Catalyst:

SOO

O

OSc3+

3

Size of surfactant aggregates:

0.1 1.0 10.0 100.0 1000 10000

SolutionsMicelles

Microemulsion

Colloidal dispersion

Emulsion

size (nm)

So

lub

ilit

y

NaO3SOC12H25

Sc(O3SOC12H25)3

Aldol reaction:

92%

83%

76%

19%

PhCHO +


(10 mol%)

H2Ort, 4h

OSiMe3

Ph

LASC

Ph

OH

Ph

O

Sc3+ ( )11SOO

O

O

3

Sc3+ ( )11OS

3

O

O

Sc3+( )12O

S3

O

O

Sc3+ ( )13OS

3

O

O

>1.0 µm

0.5-1.0 µm

<0.5 µm

High stability

Medium stability

Low stability

(92%) (83%)

(~1.5 µm) (1.1 µm)

(76%) (0.7 µm)

(19%) (0.4 µm)

CMC decreases as the polar head becomes smaller CMC decreases with increasing alkyl chain length

Stability of colloidal dispersion:

Sc3+ ( )11SOO

O

O

3 Sc3+ ( )11OS

3

O

O

Sc3+( )12O

S3

O

O

Sc3+ ( )13OS

3

O

O

Effect of solvents:

solvent yield (%)

H2O 92

DMF 14

DMSO 9

CH2Cl2 3

PhCHO +


(10 mol%)

H2Ort, 4h

OSiMe3

Ph

1

Ph

OH

Ph

O

1: Sc(O3SOC12H25)3


0

5

10

15

20

25

30

0 2 4 6 8

Time (h)

Yie

ld (

%)

Series1

Series2

Kinetics for aldol reaction:

Aldol reaction in water was found to

be 130 times higher than that in

CH2Cl2.

in water

in CH2Cl2


Necessity to use water:

solvent yield (%)

none 10

DMF 21

pyridine 23

Et2O 14

H2O 80

S. Kobayashi, I. Hachiya, J. Org. Chem., 1994, 59, 3590.

PhCHO +

(10 mol%)

THF, rt, 19h

OSiMe3Yb(OTf)3

Ph

OH OAdditive (500 mol%)

Mechanism of catalytic reaction:

-

-

-

---

-

-

-

-- -

-Sc3+

Sc3+

Sc3+

Sc3+[Sc(H2O)n]3+

[Sc(H2O)n]3+

[Sc(H2O)n]3+

[Sc(H2O)n]3+

H2O

H2O

OSiMe3

Ph

PhCHO

Ph

OH

Ph

O

Role of water:

Hydrophobic interactions in water lead to increase the local

concentration of substrates, resulting in the higher reaction rate in

water.

Hydration of Sc(III) ion and the counterion by water leads to

dissociation of the LASC salt to form highly Lewis acidic species

such as [Sc(H2O)n]+3.

.Manabe, Y. Mori, T. Wakabayashi, S. Nagayama, S. Kobayashi, J. Am. Chem. Soc. 2000, 122, 7202.

Mechanism of catalytic reaction:

-

-

-

---

-

-

-

-- -

-

[Sc(H2O)n]3+

[Sc(H2O)n]3+

[Sc(H2O)n]3+

[Sc(H2O)n]3+

H2O

H2O

OSiMe3

Ph

PhCHO

Ph

OH

Ph

O

Interface:

The rate of the reaction depends on the total area of the interface.

Stirring of the reaction would increase the total area of the interface.

0

10

20

30

40

50

60

70

80

90

100

0 2 4

Time (h)

Yie

ld (

%)

1400 rmp

0 rmp

LASC-catalyzed Aldol reactions:

Ph Me Ph 92

PhCO Me Ph 86

Ph Me2 SEt 98

PhCH=CH Me Ph 91

R1 R2 R3 yield (%)


1a: Sc(O3SOC12H25)3

R1CHO +OSiMe3

R3


1a(10 mol%)

H2O, rt, 4hR1

OH O

R3

R2

R2

Workup:

After centrifugation at 3500 rpm for 20 min, the colloidal mixture became a tri-phasic system.

water

LASC

Mixture of organic compounds

Friedlander synthesis of Quinolines:

L. Zhanga, J. Wua, Adv. Synth. Catal. 2007, 349, 1047. M. Zolfigol, P. Salehi, A. Ghaderi, M. Shiri, Z. Tanbakouchian, J. Mol. Cat. A 2006, 259, 253.

LASC (catalyst) yield (%)

Sm(O3SOC12H25)3 82

Ce(O3SOC12H25)3 91

Sc(O3SOC12H25)3 90

Ph

O

NH2

+ H3C OEt

OOcat. (10 mol%)

N CH3

CO2EtPh

Water, rt, air

Rhodium catalyst:

Cationic rhodium catalysts are frequently employed as homogeneous

catalysts for:

- hydrogenation

- hydrosilylation

B. Wang, P. Cao, X. Zhang, Tetrahedron Lett. 2000, 42, 8041.

- hydride transfer

- cycloaddition

Rh(dppb) SbF6

CH2Cl2, 10 minO

Ph

HO

Ph

99%

dppb= diphenylphosphanylbutane

Add surfactant

[{RhCl(cod)}2]-tppts

H2O, 50oC, 12h

O

Ph

O

Ph

H

51%

+ O

Ph

14%

O

Ph


H2O, 50oC, 2hO

Ph

H

32%

Oct3NMeCl(cationic)


H2O, 50oC, 2hO

Ph

H

27%

TritonX-100(nonionic)


H2O, 50oC, 2h

O

Ph

H

91%

Na(O3SOC12H25)3(anionic)

tppts= tris(m-sulfonatophenyl) phosphane cod= cyclooctadiene

D. Motoda, H. Kinoshita, H. Shinokubo, K. Oshima, Angew. Chem. Int. Ed. 2004, 43, 1860.

[4+2] annulation of dienynes:

Decreasing

temperature

The Krafft temperature is strongly dependent on the head group and counterion and increases by increasing the size of counterion.



H2O, 50oC, 2h

O

Ph

H

91%

O

Ph

Na(O3SOC12H25)3


H2O, 25oC, 2hO

Ph

H

0%

O

Ph

Na(O3SOC12H25)3

[{RhCl(cod)}2] (2.5 mol%)tppts (20 mol%)

[4+2] annulation of dienynes:

No ligand


[{RhCl(cod)}2] (2.5 mol%)tppts (20 mol%)

[{RhCl(cod)}2] (2.5 mol%)

[{RhCl(cod)}2]

H2O, 25oC, 1h

O

Ph

H

96%

O

Ph

Na(O3SOC12H25)3


H2O, 25oC, 2hO

Ph

H

0%

O

Ph

Na(O3SOC12H25)3

Decreasing the amount of catalyst

nbd= norbornadiene

[{RhCl(cod)}2]

H2O, 25oC, 1h

O

Ph

H

96%

O

Ph

Na(O3SOC12H25)3

[{RhCl(cod)}2]

H2O, 25oC, 20min.

O

Ph

H

26%

O

Ph

Na(O3SOC12H25)3

[{RhCl(nbd)}2]

H2O, 25oC, 20 min.O

Ph

H

93%

O

Ph

Na(O3SOC12H25)3

[{RhCl(cod)}2] (2.5 mol%)

[{RhCl(cod)}2] (1.25 mol%)

[{RhCl(nbd)}2] (1.25 mol%)

Formation of micellar catalyst:

Formation of micelle:

Ion-electrode analysis:

- concentration of Cl- (obs.):

2.54 × 10-3 molL-1

- concentration of Cl- (cal.):

2.50 × 10-3 molL-1


SDS + [Rh(nbd)(H2O)n]+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+

Rh+Rh+

-

-

-

---

-

-

-- -

-

-

[{RhCl(nbd)}2] + H2O [Rh(nbd)(H2O)n]+ + [Cl(H2O)m]-

[4+2] annulation in water:

Dienyne t[min] Product Yield (%)

25 93

10

97

120

(24 h)

95

71


O

Ph

NBn

O

OH

Ph

CO2EtCO2Et

O

Ph

H

O

H

HO

NBn

H

Ph

HCO2Et

CO2Et

Brønsted acid catalyst:

The use of a Brønsted acid is one of the more convenient and

environmentally benign methods of catalyzing organic reactions in

water.

The advantage of water over organic solvents in Brønsted-catalyzed

reactions is that the:

- nucleophilicity of the corresponding base may be of less concern

due to extensive solvation of charge by hydrogen-bonding water

molecules.

Brønsted acid surfactant combined catalyst

Dehydration reactions in water:

Remove Water

Add excess amount of substrates

R OH

O

+ R'OH R O

OR' + H2O

R OH

O

+ R'OH R O

OR' + H2O

R OH

O

+ R'OH R O

OR' + H2O

Brønsted acid surfactant Catalyst:

RCO2H

R'OH

: Brønsted acid surfactant catalyst

K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124, 11971.

RCO2R'

H2O

H2O

H2O

Esterification with various catalysts:

NaO3SC6H4C12H252

Sc[O3S(CH2)11CH3]315

H2SO41

TsOH 4

OBSA 39

DBSA 60

Catalyst Yield (%)

catalyst(10 mol %)

H2O40 oC, 24 h

OH

O+ HO Ph

1 : 1

O

O

Ph( )10 ( )10

SO

OOH

SO

OOH

SO

OOH

11

7

TsOH:

OBSA:

DBSA:


0

2

4

6

8

10

12

14

16

18

20

0 20 40 60

Time (h)

Yie

ld (

%) DBSA

OBSA

TsOH

Initial rate of esterification in water:

DBSA catalyzed the reaction 2.3 times faster than OBSA

and 59 times faster than TsOH

SO

OOH

SO

OOH

SO

OOH

11

7

TsOH:

OBSA:

DBSA:

Various amounts of DBSA:

10 84

50 71

100 58

200 32

amount of DBSA (mol %) yield (%)


catalyst(10 mol %)

H2O40 oC, 24 h

OH

O+ HO Ph

1 : 1

O

O

Ph( )10 ( )10

Size of particles:

10 (mol%) 200 (mol%)


10 µm

Effect of substrates:

0 5

2 39

4 72

6

8

10

10a

78

81

84

15

n yield (%)

a: ethanol was used.

DBSA(10 mol %)

H2O, 40 oCOH

O+ HO Ph O

O

Ph( )n ( )n

Esterification of various substrates:

89

92

>99

91

R R` yield (%)


(1:2)

DBSA (10 mol %)

H2O, 40 oC, 48 hR OH

O

+ R'OH R O

OR'

CH2-

( )8

CH2-

( )8

PhCH2-

Ph CH2-

PhCH2

-

CH2-

( )9

CH2-

( )9

BrCH2

-( )9

Etherification:

Williamson ether synthesis:

Lewis acid catalyze:

G. V. M. Sharma, T. Rajendra Prasad, A. K. Mahalingam, Tetrahedron Lett. 2001, 42, 759.

ROH + R'XNaOH

ROR'

X= halides, tosylates

PhOH +

Yb(OTf)3/FeCl3 (10 mol%)

CH2Cl2

PhO Ph

PhPhOH

Ph

Etherification:

DBSA (10 mol%)

H2O, 24hOH + O Ph

Ph

89%

( )9 ( )9PhOH

Ph

OH( )9 + OOH O( )9

O77%

DBSA (10 mol%)

H2O, 24h

DBSA (10 mol%)

H2O, 24hPhOH

Ph+

PhOH

Ph

PhO

Ph

PhPh

91%


0

20

40

60

80

100

120

0 50 100 150

Time (h)

Yie

ld (

%)

benzhydrol

benzhydryldodecyl ether

dibenzhydrylether

Etherification:

Ph

OH

Ph

Ph

PhB

OH( )9

Ph

PhA

PhO

Ph

PhPh

DBSA (10 mol%)

H2O, 24hOH + O Ph

Ph( )9 ( )9Ph

OHPh

+

89% 10%

A B

OH( )9

Ph

PhA

B

PhO

Ph

PhPh

Surfactant, asymmetric organocatalyst:

-

-

-

+ X-Na+

-NaX+

STAO

a)

b) + OH-H+

-H2O+

STAO

+ : Chiral imidazolium cation : Anion of surfactant

S. Luo,X. Mi, S. Liu, H. Xu, J. Cheng, Chem. Commun., 2006, 3687.

-

-

Michael addition of cyclohexanone:

1 12 np — —

2 12 20 nd nd

3 12 93 97 : 3 97

Catalyst t/h yield (%) syn : anti ee (%)


O

+ PhNO2

STAO (20 mol%)

H2O, RT

ONO2

Ph

NH

NN

Bu

3

NH

NN

Bu

2

NH

NN

C8H17-n

Br

1

Br S C12H25

O

OO

STAO= Surfactant-type asymmetric organocatalyst

R Time/h Yield (%) syn : anti ee (%)

Ph 12 93 97 : 3 97

3-NO2Ph

36 83

97 : 3 97

2-ClPh 12 >99

99 : 1 98

4-MePh

12 90

97 : 3 95

4-MeOPh

15 84 99 : 1 94

2-Naphthyl 15 84 97 : 3 96


Michael addition of cyclohexanone:

O

+ RNO2

STAO (20 mol%)

H2O, rt

ONO2

R

Conclusions:

Advantages of using of the surfactant combined catalysts in organic

reaction:

- using of water as a solvent

- high activity

- solve the problem of reagent incompatibility

- easy separation and recovery

Disadvantages of using of the surfactant combined catalysts in

organic reaction:

- substrate limitation

- catalyst limitation

Dr. Borhan

Dr. Smith Dr. Jackson Dr. Baker Dr. Walker

Chrysoula

Marina, Aman, Calvin, Dan, Sing, Mercy, Roozbeh, Stewart, Toyin, Wenjing, Xiaofei,

Xiaoyong

Afra, Maryam, Paramita, Behnaz

Documents

Surfactants as Catalysts for Organic Reactions in Water Atefeh Garzan 11/07/07