Barium £-butoxide-hydroxide

Preparation and Properties of Barium Salt. The catalyst used to prepare this new class of crystallizing polybutadienes consists of a barium t-butoxide-hydroxide salt in combination with an organolithium ( 8, 9, 10). Rather specific preparative techniques must be used in forming this barium salt, as shown in Figure 1. The use of an amine solvent provided quantitative conversion of the metal to barium salts. 

Mole Ratio of Barium t-Butoxide-Hydroxide to n-BuLi. 

Catalyst Concentration. The concentration of the catalyst has a marked effect on the trans-1,4 content of polybutadienes prepared with BuLi and barium t-butoxide-hydroxide in toluene at 30°C, as shown in Figure 5. The trans-1,4 content increases with a decrease in the molar ratio of the initial butadiene to BuLi concentration [(M)/(BuLi)]. The trans-1,4 content approaches a limiting value of about 807., for polybutadienes prepared with large amounts of this catalyst. 

Polymerization Temperature. The stereoregularity of polybutadienes prepared with the BuLi-barium t-butoxide-hydroxide catalyst in toluene is exceedingly temperature dependent. Figure 6 compares the trans-1,4 dependence for polybutadiene prepared with BuLi, alone, and with the BuLi-barium t-butoxide-hydroxide complex in toluene (the molar ratio of the initial butadiene to BuLi concentration was 500). The upper curve demonstrates that the percent trans content increased rapidly from 627. to 807. trans-1,4 as the temperature decreased from 75°C to 22°C. From 22°C to 5°C, the microstructure does not change. The increase in trans-1,4 content occurred with a decrease in cis-1,4 content, the amount of vinyl unsaturation remaining at 5-87.. For the polybutadienes prepared using BuLi alone, there is only a very slight increase in the trans-1,4 content as the polymerization temperature is decreased. 

The amount of both low and high molecular weight polymer produced, as a function of polymerization temperature, can be seen in Figure 7. In this Figure, the MWD s of polybutadienes prepared with barium t-butoxide-hydroxide and BuLi in toluene at 30°C and 5°C are compared. Although both polymers show a broad MWD, the fraction of low molecular weight polymer present in the polybutadiene prepared at 5°C is greatly decreased. 

The polybutadienes prepared with these barium t-butoxide-hydroxide/BuLi catalysts are sufficiently stereoregular to undergo crystallization, as measured by DTA ( 8). Since these polymers have a low vinyl content (7%), they also have a low gl ass transition temperature. At a trans-1,4 content of 79%, the Tg is -91°C and multiple endothermic transitions occur at 4°, 20°, and 35°C. However, in copolymers of butadiene (equivalent trans content) and styrene (9 wt.7. styrene), the endothermic transitions are decreased to -4° and 25°C. Relative to the polybutadiene, the glass transition temperature for the copolymer is increased to -82°C. The strain induced crystallization behavior for a SBR of similar structure will be discussed after the introduction of the following new and advanced synthetic rubber. 

The preparation of high trflns-l,4-polybutadiene ( 80%) is of current interest because it has been reported that these polymers can exhibit strain-induced crystallization analogous to natural mbber. One class of initiators that form high trans-1,4-polybutadiene contain barium salts. For example, a polybutadiene with 79% tram-1,4- and 7% vinyl microstructure (Tg = -91 °C) was prepared from an initiator from n-butyllithium with 0.5 equivalents of a barium (t-butoxide-hydroxide) salt with 9mol% hydroxide ion in toluene at 30 The trans-l,4-content decreased at higher temperamres. A more recent modification utilizes a catalyst formed from a barium(t-alkoxide-hydroxide) or a barium (t-alkoxide)2 salt with the complex of a dialkylmagnesium and a trialkylaluminum. Polybutadienes with 90% 1,4-content were prepared when the ratio of [Ba]/[Mg] was approximately 0.20 and the [Mg]/[A1] ratio was 6 for polymerizations in cyclohexane at 50 The trans-... 

Bromination of 8 followed by dehydrobromination afforded completely unsaturated compound 10. Barium hydroxide and zinc reduction of 10 yielded 11 (69JOC3237). ( >1,2-Diazacyclooctene 12 (R1 - R4 = Me) was synthesized by oxidative cyclization of 2,7-dimethyl-2,7-octanediamine with iodine pentafluoride (78CB596). [For preparation of the stereoi-someric Z compounds, see Section II,A,3,a.] Stetterand Koch reacted bis(Af-bromoamino)biadamantyl 13 with potassium terf-butoxide and isolated a molecule containing a 1,2-diazocine sandwiched between two ada-mantane moieties (14) [see also Section II,A,3,c] (75LA1357). 

Chalcones are important intermediates in the synthesis of flavanoids and are used industrially in bactericides, antibiotic drugs and UV-stabilisers in plastics. Other base catalysts such as magnesium /-butoxide and barium hydroxides have been used to perform the synthesis.31 However, the Cs+-exchanged zeolites offer a more environmentally friendly alternative route. 

Reduced Thiopyrans.—The tetrahydrothiopyran-3,5-dione (73) has been synthesized by treatment of the keto-diester (72) with butoxide, and it is cyclized by barium hydroxide to the furothiopyrone (74), which is a potential synthon for natural furans. Partial reduction of the dione (73) and dehydration gave the dihydrothiopyrone (75). 

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