T.Butylthiirane

All attempts to oxidize either cis- or trans-di-t-butylthiirane oxides failed122 (see equation 20). Reagents investigated included m-chloroperbenzoic acid, sodium peroxide, hydrogen peroxide, ozone and aqueous potassium permanganate. The cis oxide was resistant to oxidation (apparently steric hindrance), and the trans isomer was consumed with excess oxidizing agent but no identifiable products could be isolated. 

When compared, optically pure and racemic polymers reveal some significant differences in their properties such as crystallization, solubility or crystalline structure. The way of racemiza-tion of a polymer could be realized either by intercrystallite compensation, as in the case of polymethylthiirane (56) or by formation of a racemic lattice, as observed for monomers with bulky substituents such as t-butylthiirane (57). The properties of the racemic polymer are then very different of those of the optically pure one, for example, the melting points could differ of more than 50 C. A similar behaviour was recently observed in the case of substituted 6 propiolactones (58-60). Therefore the preparation of pure optically active polymers remains of inte-... 

Other thiiranes that have heen polymerized with stereoselective and/or stereoelective initiator systems include isopropylthiirane, t-hutylthiirane, ° and cis- and tram-2,S-dimethylthiirane. ° ° The polymerization of t-butylthiirane gives pure isotactic chains with most stereospedfic initiators. An exceptionally high stereoelection was observed in the polymerization of methyl- or ethylthiirane with optically active atropisomeric initiator systems. For example, zinc (S)-l,l-hi-2-naphtholate gave an r-value of 15-20. ° ° At 67% conversion a residual monomer with an optical activity of [a]D24 = 51.77° (neat, 1 dm) was obtained (Scheme 28). 

---