Isoalkyl cations

For the experiments in which the first-step reaction products of isobutylene were employedt reactions between high molecular weight olefins and isobutane were of major importance. Presumably a first step in the overall process was the protonation of the heavier olefins to form heavier isoalkyl cations. These cations apparently fragmented to a large extent to form mainly... 

Some t-CaHg s are also formed by related reactions (fragmentation of heavier isoalkyl cations, as shown in Table III). 

Reaction D Includes reactions of Isoalkyl cations (C5 and higher cations) with Isobutane to form Isoparaffins (that become part of the alkylate) and t-C4Hg . This reaction Is thought to be of some but not major Importance for sulfuric acid alkylations, as will be discussed In more detail later. Most Isoparaffins are. however, probably formed by the reaction of Isoalkyl cations with RH (acid-soluble polymers). 

High ratios for these two reactants promote high ratios of TMP s to LE s. This Is because production of l-Cio and heavier Isoalkyl cations (Reactions K) are minimized. Of Interest, there was a high TMP s/LE s ratio In the alkylate of two-step alkylations (6). 

C 2 i-Cie, or other heavy Isoalkyl cations fragment via 8-sc1ss1on. A wide variety of isoalkyl cations... 

Trimethylpentenes protonate rapidly to form TMP s. As Indicated above, trimethylpentenes can be formed by fragmentation of heavy Isoalkyl cations. Furthermore the protonations of trimethyl pentenes and other olefins are to some extent at lease reversible. Hence, small concentrations of trimethyl pentenes are present in alkylation reactors during especially the initial stages of alkylation Mosby and Albright (1) for example found small amounts of olefins when the alkylation product was quenched and neutralized. 

S-scIsslon of 2,2,4-TMP as shown In Reaction E Is an example. Isoalkyl cations that frequently fragment are thought to Include l-Cig and l-Cis . Examples of how they might fragment are as follows ... 

Olefins rapidly protonate to form Isoalkyl cations, e.g. 

Note Isoalkyl cations formed by fragmentation and protonation of olefins generally contain 4 to 10 carbon atoms. Some t-C.Hg+ s are formed In this manner, as are both DfH+ s and T s. This method Is thought to be the major method for production of the precursors for LE s and for DMH s (when sulfuric acid Is used as the catalyst). 

Isoalkyl cation + RH - Isoalkane + R (polymer cations) From Isobutane and Other Isoalkanes Isoalkyl cation + 1-C H j ... 

Transfer of a hydride Ion to an Isoalkyl cation Is often the rate controlling step In the overall reaction scheme (16). Isoalkyl cations Including C5 and higher ones react forming the various Isoparaffin molecules found In alkylate, e.g., IMP+ s react to form TMP s. 

I-C12 heavier isoalkyl cations are produced during alkylation primarily because of polymerization reactions involving olefins. The C results of Hofmann and Schriesheim (8) indicating that higher levels of olefin reacted during production of DMH s and LE s as compared to TMP s is consistent with this postulate. 

Production of Heavy Ends and Acid-Soluble Hydrocarbons. Heavy ends (HE S) are produced In large amounts by reactions involving primarily olefins these reactions are primarily polymerization-type reactions. The olefins are quite soluble in the acid phase, but isobutane is not. High ratios of isobutane to olefins and high levels of agitation are necessary to minimize formation of heavy ends (3). The large Isoalkyl cations formed by polymerization-type reactions obviously frapent to some extent to produce some Cg and Cio isoparaffins (found In appreciable quantities In... 

Cracking the larger isoalkyl cations can undergo P-scission to form smaller olefins and isoalkyl cations. 

When HF is used as the catalyst, some re-C4Hio is always detected in the product stream and equations (4) and (5) are obviously of at least some importance. When sulfuric acid is, however, used at typical operation temperatures of about 10°C, no re-C4Hio is produced and equations (4) and (5) are of little or no importance. Instead, conjunct polymers (CPs) act as intermediates. They contain tertiary C—H bonds (1) which act as intermediates both in the production of t-C4C9+ and alkylate molecules. Conjunct polymers serve as a reservoir for hydride ions, with an inflow from mainly isobutane and an outflow to the numerous isoalkyl cations. The CP cations (CP+) thus produced react as shovra in Equation (6) to give -C4Cg+. 

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