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Volumn 2, Issue 6, 2010, Pages 683-693

Minor enantiomer recycling-effect of two reinforcing catalysts on product yield and enantiomeric excess

Author keywords

Asymmetric catalysis; Biocatalysis; Enantioselectivity; Kinetic modeling; Metal catalyst

Indexed keywords


EID: 79957822367     PISSN: 18673880     EISSN: 18673899     Source Type: Journal    
DOI: 10.1002/cctc.200900327     Document Type: Article
Times cited : (14)

References (45)
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    • (Eds.: V. Gotor, I. Alfonso, E. García-Urdiales), Wiley-VCH, Weinheim, Chap.
    • N. J. Turner in Asymmetric Organic Synthesis with Enzymes (Eds.: V. Gotor, I. Alfonso, E. García-Urdiales), Wiley-VCH, Weinheim, 2008, Chap. 5.
    • (2008) Asymmetric Organic Synthesis with Enzymes
    • Turner, N.J.1
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    • C. V. Voss, C. C. Gruber, W. Kroutil, Angew. Chem. Int. Ed.
    • (2008) , vol.47 , pp. 741-745
  • 30
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    • This behavior is analogous to that of an irreversible one-catalyst system which goes to completion with ee = E - 1 / E + 1 and yield = E / E + 1. The recycling system at the limit of high yields thus behaves like a one-catalyst system but with multiplied selectivities.
    • This behavior is analogous to that of an irreversible one-catalyst system which goes to completion with ee = E - 1 / E + 1 and yield = E / E + 1 The recycling system at the limit of high yields thus behaves like a one-catalyst system but with multiplied selectivities.
  • 31
    • 79957870826 scopus 로고    scopus 로고
    • A relatively faster second catalyst can in some cases result in a transiently oscillating behavior similar to what can be seen in feed-back regulated systems. Higher yields and ee values can transiently be achieved, but will be damped to the expected steady state values. The behavior is dependent on the actual values of the kinetic constants. The same behavior can also be seen for sequential systems.
    • A relatively faster second catalyst can in some cases result in a transiently oscillating behavior similar to what can be seen in feed-back regulated systems. Higher yields and ee values can transiently be achieved, but will be damped to the expected steady state values. The behavior is dependent on the actual values of the kinetic constants. The same behavior can also be seen for sequential systems.
  • 32
    • 25444499736 scopus 로고    scopus 로고
    • Poor results have previously been encountered in dynamic kinetic resolutions by PALB-catalyzed acetylation of the cyanohydrin from hexanal
    • Poor results have previously been encountered in dynamic kinetic resolutions by PALB-catalyzed acetylation of the cyanohydrin from hexanal: L. Veum, U. Hanefeld, Synlett 2005, 2382-2384.
    • (2005) Synlett , pp. 2382-2384
    • Veum, L.1    Hanefeld, U.2
  • 33
    • 79957842790 scopus 로고    scopus 로고
    • For simplicity, E is used for both types of catalysts instead of the selectivity factor s for the metal catalyzed process and E for the enzyme-catalyzed kinetic resolution.
    • For simplicity, E is used for both types of catalysts instead of the selectivity factor s for the metal catalyzed process and E for the enzyme-catalyzed kinetic resolution.
  • 34
    • 79957797905 scopus 로고    scopus 로고
    • The titanium dimer is prepared from the monomer by treatment with aqueous buffer Ref. [30].
    • The titanium dimer is prepared from the monomer by treatment with aqueous buffer Ref. [30].
  • 37
    • 79957817558 scopus 로고    scopus 로고
    • 6]benzene in the absence of acetyl cyanide and/or hexanal.
    • 6]benzene in the absence of acetyl cyanide and/or hexanal.
  • 38
    • 79957816631 scopus 로고    scopus 로고
    • The enantiomeric excess decreased until full conversion was reached (ca. 275 min), possibly as a result of changing reaction conditions due to decreasing pH caused by the formation of acetic acid.
    • The enantiomeric excess decreased until full conversion was reached (ca. 275 min), possibly as a result of changing reaction conditions due to decreasing p H caused by the formation of acetic acid.
  • 39
    • 79957804269 scopus 로고    scopus 로고
    • Reactions in the presence of DBU are more complex. Although the processes catalyzed by either Lewis base or Lewis acid are slow at -40°C, they occur with rates similar to that of the Lewis acid-Lewis base catalyzed process at +40°C. The scenario when the amount of titanium catalyst was changed and the amount of DBU was kept constant was therefore less clear, probably as a result of several competing processes: the non-selective background reaction catalyzed by the achiral base being suppressed in the presence of less base, as well as to concentration dependent monomer-dimer equilibria. Reactions performed in the absence of base provided more clear results.
    • Reactions in the presence of DBU are more complex. Although the processes catalyzed by either Lewis base or Lewis acid are slow at -40°C, they occur with rates similar to that of the Lewis acid-Lewis base catalyzed process at +40°C. The scenario when the amount of titanium catalyst was changed and the amount of DBU was kept constant was therefore less clear, probably as a result of several competing processes: the non-selective background reaction catalyzed by the achiral base being suppressed in the presence of less base, as well as to concentration dependent monomer-dimer equilibria. Reactions performed in the absence of base provided more clear results.
  • 41
    • 79957812762 scopus 로고    scopus 로고
    • Use of a sequential "one-catalyst-at-a-time" procedure with the same catalysts (with E values of 2.5 and 10) provides the desired product with higher enantiomeric excess (99%) but with a lower yield (45%). However, if the process is repeated (subsequent to separation of the desired product from scalemic cyanohydrin and racemization of the latter) over and over again, both high yield and high enantiomeric excess may be obtained, provided any substantial chemical and mechanical losses can be avoided.
    • Use of a sequential "one-catalyst-at-a-time" procedure with the same catalysts (with E values of 2.5 and 10) provides the desired product with higher enantiomeric excess (99%) but with a lower yield (45%). However, if the process is repeated (subsequent to separation of the desired product from scalemic cyanohydrin and racemization of the latter) over and over again, both high yield and high enantiomeric excess may be obtained, provided any substantial chemical and mechanical losses can be avoided.
  • 43
    • 0029535737 scopus 로고    scopus 로고
    • J. Kennedy, R. C. Eberhart in Proceedings of IEEE International Conference on Neural Networks, Piscataway, NJ, 1995, 1942-1948.
    • J. Kennedy, R. C. Eberhart in Proceedings of IEEE International Conference on Neural Networks, Piscataway, NJ, 1995, 1942-1948.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.