Jacobson catalyst

Asymmetric epoxidation is another important area of activity, initially pioneered by Sharpless, using catalysts based on titanium tetraisoprop-oxide and either (+) or (—) dialkyl tartrate. The enantiomer formed depends on the tartrate used. Whilst this process has been widely used for the synthesis of complex carbohydrates it is limited to allylic alcohols, the hydroxyl group bonding the substrate to the catalyst. Jacobson catalysts (Formula 4.3) based on manganese complexes with chiral Shiff bases have been shown to be efficient in epoxidation of a wide range of alkenes. 

Figure 3.5 Measurement of the chiral purity of commercially available Jacobson s catalyst using a cyclodextrin-based CSP. (a) Lower trace / ,/ -enantiomer product upper trace / ,/ -enantiomer product artificially enriched with S -enantiomer and (b) lower trace S. S -enantiomer product upper trace S. S -enantiomer product artificially enriched with / ,/ -enantiomer. (Conditions CYCLOBOND 1 2000RSP 25 cm X 0.46 cm i.d. mobile phase acetonitrile triethylamine glacial acetic acid [1000 0.5 2.5, v/v] flow rate 1 ml/min temperature ambient detection UV at 240 nm sample preparation 1 mg/ml in acetonitrile injection volume 10 fxl). Reprinted from [19], copyright 1998, with permission of Wiley-Liss, Inc., a subsidiary of John Wiley and Sons, Inc.

Cyclic oligomers with x - 2-9 are found to be present in poly(1,3-dioxolane) samples prepared by monomer-polymer-equilibrations using boron trifluoride diethyl etherate as catalyst. The molecular cyclization equilibrium constants 7fx are measured and the values are in agreement with those calculated by the Jacobson-Stockmayer theory, using an RIS model to describe the statistical conformations of the corresponding chains and assuming that the chains obey Gaussian statistics. 

Jacobson GB, Lee CT, Johnston KP et al (1999) Enhanced catalyst reactivity and separations using water/carbon dioxide emulsions. J Am Chem Soc 121 (50) 11902—11903... 

Despite the numerous polyesters described in the literature, it is only recently that the cyclic populations of ring-chain equilibrates of linear aliphatic polyesters have been characterised. This characterisation was based on the well-known investigations of Carothers 121, 122) and his co-workers and the studies of Billmeyer 123-125) and his group. In particular, Billmeyer s wodc established tetraisopropyltitanate as a catalyst for producing equilibrium between ring and chain molecules in polyester systems. This is in contrast to the catalyst, p-toluene sulphonic acid, used by Jacobson, Beckmann and Stockmayer 127) in what was effectively the first attempt to study experimentally and theoretically the change in the total cyclic population of... 

Jacobson, R.L. Kluksdahl, H.E. McCoy, C.S. and Davis, R.W. "Platinum-rhenium catalysts a major new catalytic reforming development." Proceedings of the American Petroleum Institute, Division of Refining. 49 504-521 1969. 

C. U. Pittman, Jr., S. E. Jacobson, L. R. Smith, W. Clements, H. Hiramoto, Polymer-Anchored Homogeneous Hydrogenation Catalysts and Their Use in Multistep Synthetic Reactions, in Catalysis in Organic Syntheses. P. N. Rylander, H. Greenfield, Eds., pp. 161-180, Academic Press, New York, 1976. 

The results cited above demonstrate that the equilibrium is independent of the nature of the catalyst and involves a range of cyclic species extending to very high molecular weights. Furthermore, for cyclic species other than D3 the position of equilibrium is determined by purely entropic factors. A theory for formation of cyclic compounds in such polymer systems has been developed by Jacobson and Stockmayer6 from which equation (2) for the molar cyclisation constant Kx can be derived,... 

Another initiator for this polymerization is (Me3CO)3W=W(OCMe3)j, but analysis of the products by MS shows that they are macrocyclic oligomers. Their ring-size distribution, as determined by GPC, conforms to the Jacobson-Stockmayer relationship see Ch. 11. It is evident that with the tungsten catalyst... 

Jacobson, K. A. Patchomik, A. Abstracts of the 50th Anniversary Meeting of the Israel Chemical Society, Jerusalem, Israel, April 1984 Jacobson, K. A. Shai, Y. Patchomik, A. Abstracts of the 189th Meeting of The American Chemicd Society, Symposium on Polymeric Reagents and Catalysts, Miami Beach, Florida, May 1985. 

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