Optically active propylene

Another example is illustrated in the relationship between the specific rotation and the microstructure of polypropylene oxide reported by Price. Optically active propylene oxide and racemic propylene oxide-a-d were polymerized under otherwise identical conditions by the freeze-dried ZnEt2-H20 (1 0.7) catalyst system containing varying amounts of ZnEt2. A linear relationship was observed between specific rotation of the former polymer and the tail-to-tail dyad content of the latter (Fig. 14). This result proves quantitatively that the decrease in the specific rotation of polymer prepared by several catalysts is due to the presence of head-to-head and tail-to-tail linkages, and also provides supporting evidence for our microstructure analysis. 

Propylene oxide can be converted into propylene glycol by the action of either dilute acid or dilute base. When optically active propylene oxide is used, the glycol obtained from acidic hydrolysis has a rotation opposite to that obtained from alkaline hydrolysis. What is the most likely interpretation of these facts ... 

If optically active propylene glycol is used, depending on the method of hydrolysis, two different enantiomers are formed. Enantiomers are mirror image isomers whose chemical and physical properties are the same, except for the ability to rotate plane polarized light in opposite directions. 

Sen has synthesized optically active propylene/CO copolymers using more traditional chiral phosphines (108-110).336... 

When the polymerizations of cyclic sulfides are carried out with anionic initiators, many side reactions can occur. On the other hand, common anionic initiators, like KOH, yield optically active polymers from optically active propylene sulfide. An example of a side reaction is formation of propylene and sodium sulfide in sodium naphthalene initiated polymerizations. 

Optical activity in biopolymers has been known and studied well before this phenomenon was observed in synthetic polymers. Homopolymerization of vinyl monomers does not result in structures with asymmetric centers (The role of the end groups is generally negligible). Polymers can be formed and will exhibit optical activity, however, that will contain centers of asymmetry in the backbones [73]. This can be a result of optical activity in the monomers. This activity becomes incorporated into the polymer backbone in the process of chain growth. It can also be a result of polymerization that involves asymmetric induction [74, 75]. These processes in polymer formation are explained in subsequent chapters. An example of inclusion of an optically active monomer into the polymer chain is the polymerization of optically active propylene oxide. (See Chap. 5 for additional discussion). The process of chain growth is such that the monomer addition is sterically controlled by the asymmetric portion of the monomer. Several factors appear important in order to produce measurable optical activity in copolymers [76]. These are (1) Selection of comonomer must be such that the induced asymmetric center in the polymer backbone remains a center of asymmetry. (2) The four substituents on the originally inducing center on the center portion must differ considerably in size. (3) The location... 

Oxirans.—A simple four-stage preparation of (5)-propylene oxide from ethyl L-( —)-maleate has been described (Scheme 2). This work is of importance for the synthesis of nonactin carboxylic acid. Another synthesis of optically-active propylene oxide involves the cyclization of OL-propylene chlorohydrin with a variety of bases in the presence of a cobalt complex the highest optical purity was 27%. Wynberg and co-workers have shown that the base-catalysed epoxidation of electron-poor alkenes is subject to catalytic asymmetric induction hydrogen peroxide and t-butyl hydroperoxide were used as oxidants in the presence of quaternary... 

The mechanism of the polymerization of propylene oxide is considered to be similar to that of ethylene oxide but the rate of the propylene oxide polymerization is 1 — 2 orders lower than the rate of ethylene oxide polymerization. The polymerization of optically active propylene oxide in the presence of powdered KOH or magnesium oxalate leads to the formation of crystalline optically active polymers. 

Optically active propylene oxide was polymerized by potassium hydroxide as a catalyst and the polymer of an osmometric molecular weight of 3200 was obtained [5]. Optical rotation of the polymer was measured in 35 different solvents at ambient temperature at a fixed concentration of 2.5 g/100 ml. 

Fig. 6. Moffitt-type plots of optically active propylene oxide in various solvents. The symbols appended to the curves indicate the solvents listed in Table I.

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