Butadiene, formation form 1-butene

The most important reaction is the oxidative addition of two moles of acetic acid to butadiene to form 1,4-diacetoxy-2-butene (21) with the reduction of Pd2+ to Pd°. In this reaction, 3,4-diacetoxy-l-butene (127) is also formed. In order to carry out the reaction catalytic with regard to Pd2+, a redox system is used. This reaction attracts attention from the standpoint of industrial production of 1,4-butanediol. For this purpose, the formation of 127 should be minimized. Numerous patent applications have been made (examples 113-115), but no paper treating the systematic studies on the reaction has been published. 

Marked decreases of the primarily formed butenes and butadiene with ethylene conversion suggest that these olefins play an important role forming secondary products. In fact, subsequent experiments showed that the addition of butadiene, 3-5 mole %, to ethylene accelerates the formation of cyclopentene, cyclohexene, cyclohexadiene, and benzene (Table I). It seems reasonable, therefore, to propose the following reaction scheme for the formation of cyclic compounds from olefins. 

The results for butene isomerization are controversial. Kemball et reported that the isomerization of 1-butene occurred readily at temperatures ca. 300 K, with concomitant formation of significant amounts of butadiene. The initial cis/lrans product ratio was 1.2 — 1.5. They postulated the reaction mechanism involving a butadiene surface species formed by the simultaneous loss of two hydrogen atoms from adjacent carbon atoms on the adsorbed Tbutene molecule. They observed different characteristics on the rti -2-butene isomerization. Exclusive cis-trans isomerization was observed with no detectable double-bond migration or butadiene formation. An intramolecular mechanism involving a secondary carbonium ion as an intermediate was assumed for the isomerization of m-2-butene. 

In order to explain the competitive formation of the 1 1 and 1 2 adducts and the formation of the 2,6-octadienyl rather than the 1,6-oc-tadienyl chain, a mechanism was proposed (62, 69) in which the insertion of one mole of butadiene to the Pd—H bond gives the 77-methallyl complex (68) at first, from which 1-silylated 2-butene is formed. At moderate temperature and in the presence of a stabilizing ligand, further insertion of another molecule of butadiene takes place to give C5-substituted n-allyl complex 69. The reductive elimination of this complex gives the 1 2 adduct having 2,6-octadienyl chain. In the usual telomerization of the nucleophiles, the reaction of butadiene is not stepwise and the bis-n--allylic complex 20 is formed, from which the l, 6-octadienyl chain is liberated. 

The conjugated diene (including the trans-trans, trans-cis, and cis-cis isomers) can further add ethylene to form Cg olefins or even higher olefins (/). The mechanism of isomerization is proposed to be analogous to butene isomerization reactions (4, 8), i.e., 1-butene to 2-butene, which involves hydrogen shifts via the metal hydride mechanism. A plot of the rate of formation of 2,4-hexadiene vs. butadiene conversion is shown in Fig. 2. 

The mechanistic studies were carried out mainly with butadiene and two mechanisms were suggested depending first of all on the trans/cis ratio of the formed 2-butene. On Pd and sometimes on Co catalysts the trans/cis ratio is high and the mechanism is based on formating of syn- and awfi -jr-allyl intermediates which cannot interconvert on the surface. On other metals, where the trans/cis ratio is about unity, the intermediates are Tt-alkenes or cr-alkyls that may interconvert more freely36. 

Crotonaldehyde was formed NADPH-dependently as a minor metabolite of butadiene (partial pressure of 48-52 cm Hg = 660 000 ppm) in microsomes obtained from liver, lung or kidney of male B6C3Fi mice (Sharer et al., 1992) or human liver (Duescher Elfarra, 1994), the formation rate being 20-50 times lower than that of epoxybutene. 3-Butenal was suggested as an intermediate metabolite. No crotonaldehyde formation was observed with microsomes from mouse testis or with microsomes of testis, liver, lung or kidney of male Sprague-Dawley rats (Sharer et al., 1992). 

Because of their very similar boiling points and azeotrope formation, the components of the C4 fraction cannot be separated by distillation. Instead, other physical and chemical methods must be used. 1,3-Butadiene is recovered by complex formation or by extractive distillation.143-146 Since the reactivity of isobutylene is higher than that of n-butenes, it is separated next by chemical transformations. It is converted with water or methyl alcohol to form, respectively, tert-butyl alcohol and tert-butyl methyl ether, or by oligomerization and polymerization. The remaining n-butenes may be isomerized to yield additional isobutylene. Alternatively, 1-butene in the butadiene-free C4 fraction is isomerized to 2-butenes. The difference between the boiling points of 2-butenes and isobutylene is sufficient to separate them by distillation. n-Butenes and butane may also be separated by extractive distillation.147... 

A single chloro compound, trans-1 -phenyl-3-chloro-1 -butene (7), is formed in hydrochlorination of isomeric 1-phenyl-1,3-butadienes in AcOH135 (Scheme 6.2). The observation is interpreted by the formation of different isomeric allylic carbo-cations (6c and 6t). Rapid rotation of 6c to 6t before captured by the chloride ion ensures selective formation of 7. 

For specific cases such as olefin oxidation over Bi-Mo oxide combinations some information concerning the oxidation mechanism is available. The work of Adams and Jennings (2), of Sachtler (16), and of Adams (1) has led to the general acceptance of an allylic intermediate. The discoverers of the Bi-Mo catalyst system (21) showed that propene is converted to acrolein, while Hearne and Furman (9) proved that butene forms butadiene. The allylic intermediate therefore can in principle react in two different ways (1) formation of a conjugated diene... 

Unlike propene oxidation to acrolein or butene oxidation to maleic anhydride, oxygen is not incorporated into the selective oxidation product butadiene. However, water is formed together with butadiene, and it could conceivably be formed with lattice oxygen. There have been no isotopelabeling experiments to elucidate this. Similarly, it is not known whether the formation of any of the combustion products involves lattice oxygen. 

The molecular mechanism of the selective oxidation pathway is believed to be the one shown in Scheme 2 (Section I). Adsorbed butene forms adsorbed 7r-allyl by H abstraction in much the same way as xc-allyl is formed from propene in propene oxidation (28-31). A second H abstraction results in adsorbed butadiene. Indeed, IR spectroscopy has identified adsorbed 71-complexes of butene and 7t-allyl on MgFe204 (32,33). On heating, the 7r-complex band at 1505 cm 1 disappears between 100-200°C, and the 7t-allyl band at 1480 cm-1 disappears between 200-300°C. The formation of butadiene shows a deuterium isotope effect. The ratio of the rate constants for normal and deuterated butenes, kH/kD, is 3.9 at 300°C and 2.6 at 400°C for MgFe204 (75), 2.4 at 435°C for CoFe204, and 1.8 at 435°C for CuFe204 (25). The large isotope effects indicate that the breaking of C—H (C—D) bonds is involved in the slow reaction step. 

A detailed study of the oxidation of alkenes by O on MgO at 300 K indicated a stoichiometry of one alkene reacted for each O ion (114). With all three alkenes, the initial reaction appears to be the abstraction of a hydrogen atom by the O ion in line with the gas-phase data (100). The reaction of ethylene and propylene with O" gave no gaseous products at 25°C, but heating the sample above 450°C gave mainly methane. Reaction of 1-butene with O gives butadiene as the main product on thermal desorption, and the formation of alkoxide ions was proposed as the intermediate step. The reaction of ethylene is assumed to go through the intermediate H2C=C HO which reacts further with surface oxide ions to form carboxylate ions in Eq. (23),... 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

The methylvinyl radical (IV) can abstract a hydrogen atom from a feed or product molecule to form propylene or it can lose a hydrogen atom to form allene or propadiene as products. For the 2-butenes, steric factors inhibit methyl radical addition thus C5 products are formed to a far lesser extent than from 1-butene. While ethylene may be formed by a sequential decomposition of propylene, this cannot be the only path for its formation, as the yield of ethylene in the high conversion region increases about twice as rapidly as does the methane yield. An additional source of ethylene is the symmetrical cleavage of butadiene to vinyl radicals. 

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