C-Butadiene

Draw stick structures to represent each of the following species (a) 2,2.3,3-tetramethylhexane, CH C(CH3),C(CH )2CH,CH2CH3 (b) the trityl cation, (C6Hj)3Ci (c) butadiene, CH2CHCHCH2. 

Cyclopentadiene (6) reacted with 105 at 0°C to give 108 (entry 1). At 100°C, butadiene (12) afforded 109 (entry 2). No [2 + 2] cycloadduct was formed in either reaction. Perfluoromethylenecyclopropane (105) failed to react with cis,cis- or cis,trans-2,4-hexadiene at 100 °C, although 110 was readily formed from trans,frans-2,4-hexadiene (106) under these conditions [29] (entry 3). Anthracene (107) added to 105 at 100 °C. The dienophilicity of 105 is exceptional when compared with the reactivity of simple fluoroolefins, such as perfluoro-isobutylene, which require 150 and 200 °C to undergo cycloaddition to cyclopentadiene [30] and anthracene, respectively. 

Another large use of normal butenes in the petrochemical industry is in the production of 1,3-butadiene (CH2 = CH = CH = CH2). In the process, a mixture of n-butenes, air, and steam is passed over a catalyst at a temperature of 500°C to 600°C. Butadiene is used extensively to produce synthetic rubbers (see Isoprene) in polymerization reactions. The greatest use of butadiene is for styrene-butadiene rubber, which contains about a 3 1 ratio of butadiene to styrene. Butadiene is also used as a chemical intermediate to produce other synthetic organics such as chloroprene, for adhesives, resins, and a variety of polymers. 

Table 18. Butadiene metabolites in urine of mice and rats exposed to 800 ppm 1770mg/m ] [l,2,3,4- C]butadiene...

Sun, J.D., Dahl, A.R., Bond, J.A., Bimbaum. L.S. Henderson. R.F. (1989) Characterization of hemoglobin adduct formation in mice and rats after administration of [ C]butadiene or [ C]isoprene, Toxicol, appl. Pharmacol.. 100, 86-95... 

IonomerM Polyurethane[Pg.44]

Fig. 1. The temperature programmed desorption profiles for a-Fe203 (a) Blank desorption without adsorbates (b) ris-2-butene adsorption (c) butadiene adsorption (d) cis-2-butene adsorption from a catalyst depleted of selective oxidation sites. From ref. 5, reprinted with permission, copyright 1979 by the American Chemical Society.

When the 250°C calcined sample was tested for the butene oxidation reaction at 250°C, butadiene was produced very selectively (>80%). The selectivity decreases from about 90% initially to 80% after 12 hr of reaction (Fig. 13). The initial activity is high, but decreases rapidly in the first 2 hr. Regeneration of a catalyst after 13 hr of use by 02 at 250°C recovers the selectivity, but only half of the initial activity. Specific magnetization of the deactivated sample is lower than for a fresh sample, but the shapes of the magnetization curves are the same. 

Since the objective was the preparation of a modified PVC containing a relatively few appended chains of polybutadiene, the reaction was carried out heterogeneously by suspending the PVC in chlorobenzene. The suspension was cooled to 5°-10°C, butadiene, a cobalt compound, and Et2AlCl were added, and the mixture was stirred at 5°-10°C for 30-60 minutes before the addition of methanol to terminate the reaction. 

Fig. 17. Perspective view showing the siting of Cu(III) cations at the pore entrance to the supercage (Cu2 +-exchanged faujasite, dehydrated at I50°C, butadiene adsorbed). The occupancy factors are such that there is approximately one Cu(III) cation per two pore entrances.

C. butadiene and the butenes were almost entirely converted to butane, though the C4 product from thiophene contained only 21% butane, the other 79% being butene. 

AG ii c = 14.3 kcal/mol). ( -c -Butadiene)- and -2,3-substituted buta-diene)zirconocene complexes exhibit markedly lower barriers (Table III) 50-52). In general, the corresponding bis(Tj-cyclopentadienyl)hafnium... 

Figure 1.10. Schematic representation and symmetry labels of n MOs a) of s-trans- and 5-c -butadiene and b) of benzene.

When is in excess of 60 kcal/mol,. s-rm/i.r-butadiene ( V = 60 kcal/ mol), which strongly predominates in the thermal equilibrium, is excited and produces mainly divinylcyclobutanes. When the V of the sensitizer is not high enough to excite. r-rran.s-butadiene, energy transfer to j-c -butadiene ( V = 54 kcal/mol) occurs instead, yielding vinylcyclohexene. If V < 50 kcal/mol, non vertical energy transfer to a twisted diene triplet is believed to occur (Liu et al., 1%5). 

When first-order configuration interaction is taken into account, the contributions from these two transitions add in-phase for excitation into the plus state and out-of-phase for excitation into the minus state cf. Equation (1.26). From the coordinates and or and depicted in Figure 1.9, it is easy to see that for. r-/rawj-butadiene M, - Af, = 0. Accordingly AT- = 0, the transition probability is zero and the transitions into the plus and the minus states are both forbidden. For 5-c -butadiene, which does not possess a center of symmetry, Af, = 0, but M, 0. The transition moment differs from zero and is oriented perpendicular to the long axis of the molecule. The transition into the plus state is therefore allowed. For excitation into the minus state the two contributions cancel each other and this transition is forbidden irrespective of the molecular geometry. (Cf. also Example 1.9.)... 

Irradiation of 5-ci5-2,3-dimethylbutadiene yields both electrocyclic ring closure and double-bond isomerization products (Scheme 28). While the ring closure in j-c -butadiene, isoprene, 2-isopropylbutadiene, and 1,3-penta-diene is considerably less efficient than s-cis-s-trans isomerization, in s-cis-2,3-dimethylbutadiene it is about 50 times faster (Squillacote and Semple, 1990). This effect is counterintuitive, since the two methyl groups appear to hinder the rotation about the central C—C bond in butadiene. 

Complexes XVII are labile, in particular in halogenated solvents, and must be prepared at —10 to — 40°C . Butadiene, isoprene, cyclohexadiene, etc., may be used. In contrast, the niobium hydride XVIH reacts smoothly with butadiene to give XK ... 

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