Methyl sorbate group

Methyl sorbate and analogous monomers were polymerized in the presence of (/ )-2-methylbutyllithium or of complexes between butyllithium and optically active Lewis bases (329, 330) (see formulas 32 and 33) the polymers show weak optical activity. The prevailing configuration of the — CH(CH3)— group was determined by the sign of rotation of the methylsuccinic acid obtained from the polymer after ozonization. The low optical purity ( = 6%) found is related to the presence of a remarkable stereochemical disorder (115, 116) and to the fact that the chiral agent is active, at least in the case of methylbutyllithium, only in the initiation reaction. 

R and R groups and an all-trans arrangement of the double bonds. The polymer is named transerythrodiisotactic 1,4-poly (methyl sorbate) or diisotactic poly[eryr/tro-3-(methoxycar-bonyl)-4- -methylbut-1 -ene-1,4-diyl]. 

This work was repeated by several groups " in the reaction of sodium dimethylmalonate with methyl sorbate. Fanner and Metha observed small amounts of the 1,4-adduct besides the 1,6-addition product. Difficulties in conducting the transformations and analyzing the products are evident from reports on malonate additions to ethyl mucouate - " depending on the reaction conditions, the expected 1,4-adduct (equation 4) or isomerization products fonned by double bond displacement were isolated. Nucleophilic 1.4- and 1.6-addition reactions to 2,4-pentadienenitrile were also repor-tedi5-i<... 

The polymers are effective as catalysts of stereoselective hydrogenation of methyl sorbate to c/5-3-hexenoate at 160°C in cyclohexane or tetrahydrofuran. Soluble completes have been isolated after hydrogenation. Then, the catalytic activity decreases this is probably caused by the loss of Cr(CO)3 groups. The results agree with the mechanism involving the dissociation of Cr(CO)3 groups, a considerable amount of which cannot be reassociated with polymeric phenyl groups. 

Thus, by referencing the absorbances of the loaded samples to those of the corresponding unloaded samples, any influence of the sample itself on the IR absorbance is eliminated and the amount of sorbate may be deduced simply from the intensity of the characteristic IR bands. In the case of n-hexane, the asymmetric vibration of the methyl group, 5., is evaluated. 

---