Butene reaction

Reactions with isobutene led to channels (5), (7), and (8), but no evidence for process (6) was observed. Time-of-flight (TOF) spectra for all four isomers were similar, so only data for the Y + cis-2-butene reaction will be shown. A Newton diagram for this reaction is shown in Fig. 33. 

Fig. 34. Sample TOF spectra for YC4H6 products at indicated lab angles for the Y + cis-2-butene reaction at fJcoii = 26.6 kcal/mol (open circles). Solid-line fits generated using CM distributions shown in Fig. 38.

Upon examining the data for the reactions of all four butene isomers (Fig. 37), the most striking observation is that the data for all four isomers are quite similar, except that there is no YH2 formed from isobutene. In addition, the branching ratios for each isomer are similar, except that 4>ych2 OyCiHe, is approximately a factor of two greater for isobutene than for the other isomers, and for propene, YCH2 is a much more important channel than is YH2 (Fig. 40), a situation that is exactly the opposite to that for the butene reactions (Fig. 37). 

Fig. 39. Time-of-flight spectra for rn/e values corresponding to (a) YC4H6, (b) YH2, and (c) YCH2 products from the Y + cis-2-butene reaction at the CM angle for, n = 11.0 kcal/mol.

Note that the total product intensity for H2 elimination was similar for the Y + propene and Y + butene reactions. 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

Unimolecular reactions induced by electromagnetic radiation are often further divided into direct and indirect reactions. In a direct reaction, the unimolecular reaction is over within the order of a vibrational period after the initial excitation. In an indirect reaction, the unimolecular reaction starts long after the initial excitation, since a long-lived intermediate complex is formed. Evidently, the cyclo-butene reaction is not... 

Ene-additions of alkenes and dienes to silene 6 are considerably slower than [2 + 4]-cycloadditions. cA-Substitution in the ene component of the reaction causes a small acceleration in rate relative to fraws-substitution, as illustrated in Table 2 by the relative rate constants for reaction of 6 with cis- and rraws-2-butene. Reaction with cis, trans-2,4-hexadiene produces only a single adduct (66 equation 51), corresponding to selective ene-reaction with the cA-methyl group in the diene. 

Normal Butene Reactions. Under alkylation conditions, all four butene isomers are believed to undergo isomerization, dimerization, and co-dimerization when first coming in contact with HF catalyst, i.e., immediately following protonation. These are very rapid, Ionic reactions and take place competitively along with isobutane alkylation. Alkylate compositions from the four butenes are basically similar (see Table VII). However, l-butene produces a C3 fraction containing nearly two times... 

Differences of opinion still exist when sulfuric acid Is use as the catalyst as to the main route for production of DMH s (the precursors for DMH s). Although both Hofmann and Schrleshelm (8) and Albright and LI (11) have Indicated reasons why the reaction In which 1-butene reacts with a t-butyl cation to form DMH Is generally of little or no Importance, recent authors still refer to the 1-butene route as an Important one but without rebutting the earlier arguments. An even more complete sutrmary of reasons why the 1-butene reaction Is of little Importance when sulfuric acid Is the catalyst Is reported below. 

The above discussion was devoted to alkylations with sulfuric acid. In the case of HF alkylations, considerable amounts of DMH s are produced however by means of the 1-butene reaction as will be considered in detail later. 

Results from this laboratory for steam pyrolysis of isobutene were reported earlier (I), and this chapter describes the pyrolysis of the three normal butene isomers 1-butene, m-2-butene, and trans-2-butene. Reaction schemes are derived from the product distributions, and kinetic parameters are established. 

Fig. 9. Experimental (a and b) and simulated (c and d) partial pressure oscillations for the CO/02/propylene reaction (a and c), and the CO/O2/1-butene reaction (b and d), both over Pt. The simulated curves are obtained by an elementary-step model. (From Ref. 207.)...

The general kinetic characteristics of all of the butene reactions are very similar, and it should be further noted that none of them forms vinylic mercaptans. 

Fig. 13. Butene reaction catalyzed by ferrierite in a pulse reactor at 623 K. Conversion (A) and isobutylene/X all butenes (O) versus the number of pulses (49).

P. B. Venuto (Mobil Oil, Paulsboro, N. J. 08066) Even though your butene reactions occur at low temperatures—relative to thermal free radical reactions—with the presence of polyvalent transition metal ions, radical-type or electron unpairing-type reactions may certainly occur. In your reactions of butene over CeX at 190 °C, did you notice any evidence of an intermolecular hydrogen (hydride) type reaction, as evidenced by light paraffins in the gas phase and hydrogen-deficient species (aromatics) within pores ... 

These assumptions lead to the major products actually observed if the product-forming step involves y-attack by hydrido complex on the allylic group. At a high cyanide concentration, such an attack would produce 1-butene (Reaction 21), while at low cyanide concentration, trans-2 hutene would be formed (Reaction 22). 

In-Sitii C NMR Studies of 1-Butene Reactions on Acid Catalysts without Magic Angle Spinning... 

The next propagation step involves propylene coordination to the surface carbene with formation of n-butene reaction (3) or isobutene reaction (4). The high selectivity for n-olefin, in our experiments as well as in conventional Fischer-Tropsch catalysts, must be accounted for by a selective coordination and (or) reaction of the olefin (21) according to reaction (3) which is probably due to the electrophilic character of the surface... 

The mole fractions, xj, thus calculated are shown in a triangular graph, and the set of curves which correspond to the change of the mole fraction with time obtained is called the n-butenes reaction profile. 

Tsuchiya and Imamura [1] calculated a lot of n-butenes reaction profiles as a function of X (=kic/kit) and y (=kct/ku) on the basis of the Wei-Prater method [3]. In view of the acid-base catalysts, they classified these profiles into four types (1) cis-convex, (2) rake, (3) trans-convex and (4) tree. The reaction profiles for base catalysts are of the cis-convex type. Reaction profiles of the trans-convex type are obtained by acid catalysts. 

This section summarizes the chemistry of the SC isobutane regeneration process. To understand the nature of the hydrocarbons that remain adsorbed on the surface of the USY zeolite catalyst both before and after SC isobutane regeneration, a series of ex-situ temperature-programmed oxidation (TPO), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and ultraviolet-visible (UV-vis) analyses was performed on samples submitted to different TOS 10 under isobutane/butene reaction conditions. 

---