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Surfactants as Catalysts for Organic Reactions in Water. Atefeh Garzan 11/07/07. Homogeneous catalysts:. Br ø nsted acid catalysis: Lewis acid catalysis: - Advantages: high activity, selectivity - Disadvantages: separation and recycling problems.

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Surfactants as Catalysts for Organic Reactions in Water

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Surfactants as Catalysts for Organic Reactions in Water

Atefeh Garzan

11/07/07


Homogeneous catalysts l.jpg

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.


Heterogeneous catalysts l.jpg

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 l.jpg

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.


Surfactant l.jpg

Surfactant:

surfactant

Surface Active Agent

  • Surfactants have amphiphilic structure:

Hydrophilic

Hydrophobic


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Classification of surfactant:

  • Anionic

  • Cationic

  • Amphoteric

  • Nonionic

Sodium dodecylsulfate (SDS)

Cetylpyridinium bromide

Dipalmitoylphosphatidylcholine (lecithin)

Polyoxyethylene 4 lauryl ether


Behavior of surfactants l.jpg

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 orientedto minimize contact with the water molecules.

Nonpolar tail

Polar head


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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 l.jpg

Driving force:

Hydrophobic effect

Electrostatic repulsion

Formation of the micelle

No formation of the micelle


Critical micelle concentration cmc l.jpg

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 l.jpg

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 l.jpg

Surfactant aggregates:


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Surfactant in organic reaction:

  • Easy separation and recovery, high activity, selectivity.

  • 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 l.jpg

Micellar catalysis:

  • Electrostatic interaction:

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

- - 1.83

0.01 1.28

0.01 1.78

0.01 2.05

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


Micellar catalysis15 l.jpg

Micellar catalysis:


Micellar catalysis16 l.jpg

Micellar catalysis:

  • Electrostatic interaction:

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

- - 1.83

0.01 1.28

0.01 1.78

0.01 2.05

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


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Micellar catalysis:

  • 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

  • Rate= k [A][B]

energy

activation energy

activation energy

  • The reactants are concentrated through insertion to the micelle.

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

A+B

uncatalyzed reaction

catalyzed reaction

A_B

time


Lewis acid catalysis l.jpg

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.

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


Lewis acid surfactant catalyst l.jpg

Lewis Acid Surfactant Catalyst:

Lewis acid surfactant

  • “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

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


Lewis acid surfactant catalyst20 l.jpg

Lewis Acid Surfactant Catalyst:

Colloidal Dispersion

:

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


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Size of surfactant aggregates:

Solutions

Micelles

Microemulsion

Solubility

Colloidal dispersion

Emulsion

0.1 1.0 10.0 100.0 1000 10000

size (nm)


Aldol reaction l.jpg

Aldol reaction:

92%

76%

83%

19%


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Stability of colloidal dispersion:

  • CMC decreases as the polar head becomes smaller

  • CMC decreases with increasing alkyl chain length

High stability

>1.0 µm

0.5-1.0 µm

<0.5 µm

(92%)(83%) (~1.5 µm) (1.1 µm)

Medium stability

(76%) (0.7 µm)

Low stability

(19%) (0.4 µm)


Effect of solvents l.jpg

Effect of solvents:

solvent yield (%)

H2O 92

DMF 14

DMSO 9

CH2Cl2 3

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


Kinetics for aldol reaction l.jpg

Kinetics for aldol reaction:

  • Aldol reaction in water was found to be 130 times higher than that in CH2Cl2.

in water

in CH2Cl2

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


Necessity to use water l.jpg

Necessity to use water:

solvent yield (%)

none 10

DMF 21

pyridine 23

Et2O14

H2O 80

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


Mechanism of catalytic reaction l.jpg

Mechanism of catalytic reaction:

H2O

H2O


Role of water l.jpg

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 reaction29 l.jpg

Mechanism of catalytic reaction:

H2O

H2O


Interface l.jpg

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.


Lasc catalyzed aldol reactions l.jpg

LASC-catalyzed Aldol reactions:

R1 R2 R3 yield (%)

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


Workup l.jpg

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.jpg

Friedlander synthesis of Quinolines:

LASC (catalyst) yield (%)

Sm(O3SOC12H25)3 82

Ce(O3SOC12H25)3 91

Sc(O3SOC12H25)3 90

L. Zhanga, J. Wua, Adv. Synth. Catal.2007, 349, 1047. M. Zolfigol, P. Salehi, A. Ghaderi, M. Shiri, Z. Tanbakouchian, J. Mol. Cat. A2006, 259, 253.


Rhodium catalyst l.jpg

Rhodium catalyst:

  • Cationic rhodium catalysts are frequently employed as homogeneous catalysts for:

    - hydrogenation

    - hydrosilylation

- hydride transfer

- cycloaddition

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


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Add surfactant

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


4 2 annulation of dienynes l.jpg

[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.

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


4 2 annulation of dienynes37 l.jpg

[4+2] annulation of dienynes:

No ligand

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


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Decreasing the amount of catalyst


Formation of micellar catalyst l.jpg

Formation of micellar catalyst:

Ion-electrode analysis:

- concentration of Cl- (obs.):

2.54 × 10-3 molL-1

- concentration of Cl- (cal.):

2.50 × 10-3 molL-1

Formation of micelle:

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


Slide40 l.jpg

[4+2] annulation in water:

Dienyne t[min] Product Yield (%)

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


Br nsted acid catalyst l.jpg

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


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Dehydration reactions in water:

Remove Water

Add excess amount of substrates


Br nsted acid surfactant catalyst l.jpg

Brønsted acid surfactant Catalyst:

: Brønsted acid surfactant catalyst

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


Esterification with various catalysts l.jpg

Esterification with various catalysts:

Catalyst Yield (%)

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


Initial rate of esterification in water l.jpg

Initial rate of esterification in water:

DBSA catalyzed the reaction 2.3 times faster than OBSA and 59 times faster than TsOH


Various amounts of dbsa l.jpg

Various amounts of DBSA:

amount of DBSA (mol %) yield (%)

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


Size of particles l.jpg

Size of particles:

10 (mol%)

200 (mol%)

10 µm

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


Effect of substrates l.jpg

Effect of substrates:

n yield (%)

a: ethanol was used.


Esterification of various substrates l.jpg

Esterification of various substrates:

R R` yield (%)

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


Etherification l.jpg

Etherification:

  • Williamson ether synthesis:

  • Lewis acid catalyze:

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


Etherification51 l.jpg

Etherification:

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


Etherification52 l.jpg

Etherification:


Surfactant asymmetric organocatalyst l.jpg

Surfactant, asymmetric organocatalyst:

Na+

a)

X-

+

+

-NaX

STAO

H+

OH-

+

b)

+

-H2O

STAO

: Chiral imidazolium cation

: Anion of surfactant

+

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


Slide54 l.jpg

Michael addition of cyclohexanone:

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

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


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Michael addition of cyclohexanone:

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

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


Conclusions l.jpg

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


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