1. Surfactants as Catalysts for Organic Reactions in Water
Atefeh Garzan
11/07/07
I’m working on the Condor-WS project which is a collaboration between the Condor team, UCL & Cambridge

2. Homogeneous catalysts:
Homogeneous catalysis: catalyst is in the same phase as reactants.
Brønsted acid catalysis:
Lewis acid catalysis:
- Advantages: high activity, selectivity
- Disadvantages: separation and recycling problems

3. 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

4. Other catalysts: - surfactant 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, C. Starks, J. Am. Chem. Soc. 1971, 93, 195.

5. Surfactant: surfactant Surface Active Agent
Surfactants have amphiphilic structure:
Hydrophilic
Hydrophobic

6. Classification of surfactant:
Anionic
Cationic
Amphoteric
Nonionic
Sodium dodecylsulfate (SDS)
Cetylpyridinium bromide
Dipalmitoylphosphatidylcholine (lecithin)
Polyoxyethylene 4 lauryl ether

7. 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

8. 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.

9. Driving force: Hydrophobic effect Electrostatic repulsion
Formation of the micelle
No formation of the micelle

10. Critical Micelle Concentration (CMC):
Hydrophobic effect Electrostatic repulsion
CMC decreases with increasing alkyl chain length
CMC increases as the polar head becomes larger.
CMC of neutral surfactants lower than ionic

11. 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.

12. Surfactant aggregates:

13. 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

14. Micellar catalysis: Electrostatic interaction:
Additive Conc. (M) Kobs (s-1)
M. N. Khan, N. H. Lajis, J. Phys. Org. Chem , 11, 209.

15. Micellar catalysis:

16. Micellar catalysis: Electrostatic interaction:
Additive Conc. (M) Kobs (s-1)
M. N. Khan, N. H. Lajis, J. Phys. Org. Chem , 11, 209.

17. Micellar catalysis: A + B A_B
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

18. 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.

19. Lewis Acid Surfactant Catalyst:
“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.

20. Lewis Acid Surfactant Catalyst:
Colloidal Dispersion
K. Manabe, Y. Mori, T. Wakabayashi, S. Nagayama, S. Kobayashi, J. Am. Chem. Soc. 2000, 122, 7202.

21. Size of surfactant aggregates:
Solutions
Micelles
Microemulsion
Solubility
Colloidal dispersion
Emulsion
size (nm)

22. Aldol reaction:
92%
76%
83%
19%

23. Stability of colloidal dispersion:
CMC decreases as the polar head becomes smaller
CMC decreases with increasing alkyl chain length
High stability
>1.0 µm µm
<0.5 µm
(92%) (83%) (~1.5 µm) (1.1 µm)
Medium stability
(76%) (0.7 µm)
Low stability
(19%) (0.4 µm)

24. 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.

25. 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.

26. Necessity to use water:
solvent yield (%)
none
DMF
pyridine
Et2O
H2O
S. Kobayashi, I. Hachiya, J. Org. Chem., 1994, 59, 3590.

27. Mechanism of catalytic reaction:
H2O
H2O

28. 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.

29. Mechanism of catalytic reaction:
H2O
H2O

30. 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.

31. LASC-catalyzed Aldol reactions:
R R R yield (%) Ph Me 92
PhCO 86
Me2
SEt 98
PhCH=CH 91
K. Manabe, Y. Mori, T. Wakabayashi, S. Nagayama, S. Kobayashi, J. Am. Chem. Soc. 2000, 122, 7202.

32. Workup:
After centrifugation at 3500 rpm for 20 min, the colloidal mixture became a tri-phasic system.
water
LASC
Mixture of organic compounds

33. Friedlander synthesis of Quinolines:
LASC (catalyst) yield (%)
Sm(O3SOC12H25)
Ce(O3SOC12H25)
Sc(O3SOC12H25)
L. Zhanga, J. Wua, Adv. Synth. Catal. 2007, 349, M. Zolfigol, P. Salehi, A. Ghaderi, M. Shiri, Z. Tanbakouchian, J. Mol. Cat. A 2006, 259, 253.

34. 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.

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

36. [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.

37. [4+2] annulation of dienynes:
No ligand
D. Motoda, H. Kinoshita, H. Shinokubo, K. Oshima, Angew. Chem. Int. Ed. 2004, 43, 1860.

38. Decreasing the amount of catalyst

39. 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.

40. [4+2] annulation in water:
Dienyne t[min] Product Yield (%) 25 93 10 97
120
(24 h) 95 71
D. Motoda, H. Kinoshita, H. Shinokubo, K. Oshima, Angew. Chem. Int. Ed. 2004, 43, 1860.

41. 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

42. Dehydration reactions in water:
Remove Water
Add excess amount of substrates

43. Brønsted acid surfactant Catalyst:
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

44. Esterification with various catalysts:
Catalyst Yield (%)
NaO3SC6H4C12H25 2
Sc[O3S(CH2)11CH3]3 15
H2SO4 1
TsOH 4
OBSA 39
DBSA 60
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

45. Initial rate of esterification in water:
DBSA catalyzed the reaction 2.3 times faster than OBSA and 59 times faster than TsOH

46. Various amounts of DBSA:
amount of DBSA (mol %) yield (%) 10 84 50 71
100 58
200 32
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

47. Size of particles: 10 (mol%) 200 (mol%) 10 µm
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

48. Effect of substrates: 5 2 39 4 72 6 8 10 10a 78 81 84 15 n yield (%)5 2 39 4 72 6 8 10
10a 78 81 84 15
a: ethanol was used.

49. Esterification of various substrates:
R R` yield (%) 89 92
>99 91
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

50. Etherification: Williamson ether synthesis: Lewis acid catalyze:
G. V. M. Sharma, T. Rajendra Prasad, A. K. Mahalingam, Tetrahedron Lett. 2001, 42, 759.

51. Etherification:
K. Manabe, S. Iimura, X. Sun, S. Kobayashi, J. Am. Chem. Soc. 2002, 124,

52. Etherification:

53. Surfactant, asymmetric organocatalyst:
Na+ a) + X- +
-NaX
STAO H+ b) +
OH- +
-H2O
STAO
: Chiral imidazolium cation
: Anion of surfactant +
S. Luo,X. Mi, S. Liu, H. Xu, J. Cheng, Chem. Commun., 2006, 3687.

54. Michael addition of cyclohexanone:
Catalyst t/h yield (%) syn : anti ee (%) 1 12 np — 2 20 nd 3 93
97 : 3 97
S. Luo,X. Mi, S. Liu, H. Xu, J. Cheng, Chem. Commun., 2006, 3687.

55. Michael addition of cyclohexanone:
R Time/h Yield (%) syn : anti ee (%) Ph 12 93
97 : 3 97
3-NO2Ph 36 83
2-ClPh
>99
99 : 1 98
4-MePh 90 95
4-MeOPh 15 84 94
2-Naphthyl 96
S. Luo,X. Mi, S. Liu, H. Xu, J. Cheng, Chem. Commun., 2006, 3687.

56. 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

57. Dr. Smith Dr. Jackson Dr. Baker Dr. Walker
Dr. Borhan
Dr. Smith Dr. Jackson Dr. Baker Dr. Walker
Chrysoula
Marina, Aman, Calvin, Dan, Sing, Mercy, Roozbeh, Stewart, Toyin, Wenjing, Xiaofei, Xiaoyong
I’m working on the Condor-WS project which is a collaboration between the Condor team, UCL & Cambridge
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