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ENANTIOSELECTIVE HYDROGENATION WITH ...

RICHARDS, DAVID RONALD.

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ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS.

Record Type:	Electronic resources : Monograph/item
Title/Author:	ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS./
Author:	RICHARDS, DAVID RONALD.
Description:	205 p.
Notes:	Source: Dissertation Abstracts International, Volume: 48-01, Section: B, page: 0115.
Contained By:	Dissertation Abstracts International48-01B.
Subject:	Chemistry, Analytical. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=8710379

ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS.
RICHARDS, DAVID RONALD.

ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS. - 205 p.

Source: Dissertation Abstracts International, Volume: 48-01, Section: B, page: 0115.

Thesis (Ph.D.)--Northwestern University, 1987.

For the synthesis of asymmetric molecules from nonchiral reactants it is desirable to have active and stereoselective heterogeneous catalysts. In the present state of the art, catalysts of moderate enantioselectivity are obtained by impregnating an active metal with an asymmetric "modifier", such as optically active tartaric acid. The objective of our study is to identify the factors which limit the selectivity of such catalysts. In general, modified catalysts have two types of sites, selective and nonselective. The ultimate selectivity is then limited by: (1) the concentration of selective sites, (2) the turnover frequency on either site, and (3) the intrinsic selectivity of the selective sites.Subjects--Topical Terms:

586156
Chemistry, Analytical.

ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS.
LDR:03291nmm 2200241 4500 001 1840128
005 20050714101545.5
008 130614s1987 d
035 $a (UnM)AAI8710379
035 $a AAI8710379
040 $a UnM $c UnM
100 1 $a RICHARDS, DAVID RONALD. $3 1928477
245 1 0 $a ENANTIOSELECTIVE HYDROGENATION WITH (R,R)-TARTARIC ACID MODIFIED NICKEL/SILICON DIOXIDE CATALYSTS.
300 $a 205 p.
500 $a Source: Dissertation Abstracts International, Volume: 48-01, Section: B, page: 0115.
502 $a Thesis (Ph.D.)--Northwestern University, 1987.
520 $a For the synthesis of asymmetric molecules from nonchiral reactants it is desirable to have active and stereoselective heterogeneous catalysts. In the present state of the art, catalysts of moderate enantioselectivity are obtained by impregnating an active metal with an asymmetric "modifier", such as optically active tartaric acid. The objective of our study is to identify the factors which limit the selectivity of such catalysts. In general, modified catalysts have two types of sites, selective and nonselective. The ultimate selectivity is then limited by: (1) the concentration of selective sites, (2) the turnover frequency on either site, and (3) the intrinsic selectivity of the selective sites.
520 $a Through the use of Auger electron spectroscopy and catalyst pellet crushing experiments, modification conditions were optimized to obtain uniform modification throughout the catalyst pellet. The hydrogenation of 1-hexene was then used as a probe reaction to measure the fraction of the surface which remained unmodified. Temperature programmed oxidation was used to quantify the amount of tartaric acid present on the catalyst. By using appropriate modifying conditions a surface concentration of selective sites near 100% was obtained. The overall enantioselectivity then reflects the intrinsic selectivity of the selective sites. Using the hydrogenation of methyl acetoacetate as a test reaction, the intrinsic selectivity is (LESSTHEQ)50%. It follows from our results that the significant enhancement of the enantioselectivity by certain comodifiers, which has been reported by Harada, is due to a change of the intrinsic selectivity. It has been found that the magnitude of the comodifier effect depends on the reaction conditions (temperature, gas or liquid phase) as well as the modification conditions (pH, comodifier concentration). The role of comodifiers was also investigated by studying nickel tartrates which had been prepared with and without sodium bromide. Infrared studies of the nickel tartrate samples revealed no significant structural changes. However, studies using thermogravimetric analysis and temperature programmed oxidation coupled with the results of elemental analysis revealed that the incorporation of sodium bromide into the nickel tartrate resulted in a decrease of the crystal water content. Based on the present findings it appears that both the cation and anion of the comodifier are involved in increasing the intrinsic selectivity of the selective sites.
590 $a School code: 0163.
650 4 $a Chemistry, Analytical. $3 586156
690 $a 0486
710 2 0 $a Northwestern University. $3 1018161
773 0 $t Dissertation Abstracts International $g 48-01B.
790 $a 0163
791 $a Ph.D.
792 $a 1987
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=8710379