Butadiene addition

Co(OCOR)2/AlEt3/H20 initiates polymerization of 1,3-butadiene. Addition of phosphine ligands influences the structure and molecular weight of the polymer [75]. Sterically bulky phosphines decrease catalytic activity. Co(OCOR)2/MAO/f-BuCl is also effective for the polymerization of 1,3-buta-diene to produce the cis- 1,4-polymer [76]. The catalyst preparation procedure and aging time have a critical influence on the cis content and yield of the polymer. The reaction rate is reduced by addition of mesitylene or trimethoxybenzene to the reaction mixture [77]. The concentration of the active species of the catalyst is estimated based on the equilibrium between the Co and Al compounds in the reaction mixture [78]. 

Butadiene reacts readily with oxygen to form polymeric peroxides, which are not very soluble in Hquid butadiene and tend to setde at the bottom of the container because of their higher density. The peroxides are shock sensitive therefore it is imperative to exclude any source of oxygen from butadiene. Addition of antioxidants like /-butylcatechol (TBC) or butylated hydroxy toluene (BHT) removes free radicals that can cause rapid exothermic polymerizations. Butadiene shipments now routinely contain about 100 ppm TBC. Before use, the inhibitor can easily be removed (247,248). Inert gas, such as nitrogen, can also be used to blanket contained butadiene (249). 

The alkylmetal-metal alkoxide combination was first described by Morton [6] for the anionic polymerization of butadiene - addition of an equivalent of sodium iso-propoxide improved the catalytic activity of allylsodium. Fifteen years later the spe-... 

Figure 10. Change in electrical conductivity of ChH7Li Met20 toluene solution on butadiene addition at points A and B...

Our experimental finding supports the view that the active site of butadiene polymerization in the presence of bis(7r-crotylnickel iodide) is the complex with nickel bound to iodide. Thus, the butadiene addition across syn-7r-allyllic bond produces trans-1,4-polybutadiene. 

The subscripts of the rate constants indicate type SB = butadiene addition to a styrene centre, etc. 

The utility of the asymmetric fumarate/butadiene addition in synthesis is highlighted by the conversion of the (f ./ )-cyclohexene (313a) (derived from (+)-( 5)-menthol) to enantiomerically pure (-)-bilobalide (317) (Scheme 78). This conversion involves particularly the annulation of a cyclopentenone ring to (313a) at the acylated centers which govern the topicity of the acylation (313a) - (314) and internal Michael reaction (314) (315). Ozonolysis of the cyclohexene moiety sets the stage for the formation... 

In one of the earliest investigations of regioselectivity in radical addition reactions to polyenes, the addition of hydrogen bromide to 1,3-butadiene was observed to yield mainly the 1,4-addition product in the presence of peroxides. The preference for attack at the Cl position of 1,3-butadiene has subsequently been observed for a large number of radicalsOnly for the addition of the methyl radical has the ratio of addition to the Cl vs C2 actually been measured. A value of Cl C2 = 1.0 0.01 has been found . For all other cases, products arising from attack at C2 have not been reported. This is also true for radical addition to 2,3-dimethyl-l,3-butadiene . Additions to 1,3-pentadiene occur predominantly at the Cl position due to the steric effect exerted by the terminal methyl This is a reflection of the reduced... 

A final example of aqueous media used in the hydrocyanation of butadiene is provided by Waddan at ICI [23]. In this chemistry, copper nitrate salts in aqueous media (among many others) are used for the oxidative dihydrocyanation of butadiene to dicyanobutenes (Eq. 9). Good conversions of butadiene are reported in nonaqueous media but no examples are actually provided in which water is added as a solvent. Moreover, because of problems with alkene and HCN dimerization and the risk of explosion hazards, these reactions appear to work best when conducted stepwise (i.e., HCN addition to catalyst followed by oxidation followed, in turn, by butadiene addition), leading one to wonder about the productivity of these systems. 

These ideas were confirmed by direct studies of kinetics of addition of butadiene to lithium polystyrene and styrene to lithium polybutadiene412,4135. The first reaction was too fast to be followed. An estimate, based on the assumption of its internal first order kinetics in living polystyrene, gives the bimolecular constant of butadiene addition to lithium polystyrene in benzene as 1.3 M-1s-1 at 29 °C, independent of the initial concentration of lithium polystyrene which was varied from 1 - 4 10 3 M412). This is a... 

This hypothesis was disproved by Worsfold413,415) who investigated the effect of butadiene on the rate of addition of styrene to lithium polystyrene. Only qualitative results were reported the rapidity of the butadiene addition prevented quantitative investigation. However, a closely similar system, isoprene - styrene, was more amenable to a quantitative study415) because the addition of isoprene to lithium polystyrene is somewhat slower. The general pattern of co-polymerization is the same as in the butadiene - styrene system. The effect of small amounts of isoprene on the rate of styrene addition was investigated and the retarding effect demanded by the Korotkov mechanism was not observed. ... 

A detailed recent study has been made to try and elucidate whether metallacyclobutanes rearrange to alkenes by p elimination or by a elimination to give an intermediate ylide complex, which can rearrange to an alkene complex. Using deuterium-labeled platinum(IV) platinacyclobutanes it is concluded that the pathway involves a [1,3] H shift (a elimination) rather than a [1,2] H shift ()3 elimination). Platinacyclopentanes have also been formed by an alkene coupling between Pt(cod)2 and butadiene. Addition of PMcs gives complex (66 equation 2(K)). ... 

Metal complexes can occasionally give good results as catalysts in Diels-Alder reactions, as for butadiene and isoprene dimerisations with Fe(CO)2(NO)2 and butadiene addition to 2-butyne in the presence of Fe (cyclooctatetraenela . However, these catalysts usually promote formation of several products in non-specific manner, through a two-step mechan-ism - , not dissimilar to most photochemical processes (see following section). 

There are two types of styrene-butadiene copolymer a random copolymer and a block copolymer. Spectra for the block and random styrene-butadiene copolymers are provided in Reference Spectra 15 and 16, respectively. For a full characterization of SBR it is necessary to determine the composition in terms of the monomer ratios, including the three configurations of the butadiene addition reaction components, and to be able to differentiate random and block copolymerization. 

The "specialty" center (solvents, detergents, butadiene, additives, etc.). 

The end block of SAMS copolymer was polymerized first in some preparations in AMS solvent. In this case, AMS was added and blanked with butyl-lithium as before. Styrene monomer and s-butyllithium for initiation were then added to start the SAMS polymerization at temperatures above 50°C. At the time designated for butadiene addition, a small amount of the butadiene monomer was bled in first. The remaining butadiene was added after the reaction solution was cooled to near 5°C. The reaction solution was then brought back to about 50°C for a period of 70 to 80 minutes for the... 

The classic example is the butadiene system, which can rearrange photochemi-cally to either cyclobutene or bicyclobutane. The spin pairing diagrams are shown in Figure 13. The stereochemical properties of this reaction were discussed in Section III (see Fig. 8). A related reaction is the addition of two ethylene derivatives to form cyclobutanes. In this system, there are also three possible spin pairing options. 

Example Anoth er example of Iron tier orbital theory uses the reaction ol phenyl-butadiene with ph en ylethylene. This reaction is a [4-1-21 pericyclic addition to form a six-membered ring. It could proceed with the two phenyl rings close to each other (head to head) or further away front each other (head to tail). 

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