Linear alkenes (C8 to C18) undergo concurrent oligomerization and double bond isomerization on the commercially available acid-washed bentonite clay F-24X at 120 degrees C. Oligomers from dimers to heptamers form in substantial quantities. Linear 1-alkenes rapidly isomerize to mixtures of linear internal alkenes, which also react to form oligomers. Kinetic data show that double bond isomerization occurs on a site where the adsorption coefficients of C8 to C18 linear alkenes are all similar and <= 1.0. Oligomerization, however, occurs on a site where alkene adsorption coefficients are all similar but >= 10, likely close to 100. A comprehensive model for isomerization and oligomerization of 1-hexadecene fit observed data over several hours and showed that internal alkenes react with internal alkenes at about half the rate that 1-alkenes react with 1-alkenes. Oligomerization occurs by an Eley-Rideal mechanism in which bulk monomers and dimers react with alkenes adsorbed on active sites. Reaction of bulk alkenes with activated adsorbed species is competitive with release of activated oligomers from active sites, resulting in the formation of even heptamers at short reaction times. Oligomers compete strongly for active oligomerization sites and inhibit further oligomerization. Double bond isomerization was not substantially inhibited by the presence of oligomers.

On dry Amberlyst®15 catalyst at 80 °C, 2-octanol undergoes irreversible dehydration to water and octenes. Ether formation is negligible, and reversible alkene double bond isomerization is slow. Kinetic data indicate that two different types of catalytic sites are active. On one site, all adsorbates have large (> 10) adsorption coefficients, and dehydration occurs here by a single site mechanism; on the second site, all adsorbates (except water) have small (< 0.2) adsorption coefficients. Dehydration and alkene double bond isomerization occur on both sites but at separate rates on each site. The site with weak adsorption loses activity rapidly as water forms, while the site with strong adsorption remains active much longer than the other and catalyzes most of the dehydration. Water adsorbs strongly to both sites and inhibits dehydration and double bond isomerization both by competing for vacant active sites and by displacing adsorbed 2-octanol (but not alkenes) directly from the active sites. The existence of two different types of active sites that lose activity at substantially different rates early in the reaction sometimes confounds the interpretation of initial rate data.

The double-bond isomerization of 1-octene to an equilibrium distribution of all seven linear octene isomers on a dry Amberlyst15 catalyst was followed at 90 degrees C using gas chromatography to resolve five of the seven isomers. The simplest kinetic models that fit observed data over several hours indicated that carbenium ions are likely intermediates in these isomerizations. The C2 octyl carbenium ion appeared to be more stable than the C3 and C4 octyl carbenium ions, leading to a lower equilibrium trans to cis ratio in 2-octene than in 3-octenes and 4-octenes. At equilibrium, [2-octyl carbenium ion] / [3-octyl carbenium ion] = 1.6. The octene adsorption coefficient for double-bond isomerization on this catalyst was 0.4-0.5, indicating a rather weak adsorption. However, the concurrent dimerization of octene to branched hexadecene isomers required an adsorption coefficient of similar to 40, indicating octene adsorbs onto two different types of sites on this catalyst. The primary alcohol 2-ethyl-1-hexanol was added to reaction mixtures to suppress octene dimerization, and the active isomerization site in this work was a molecule of 2-ethyl-1-hexanol adsorbed onto a supported sulfonic acid group of the initial resin. This new site was less active than the original acid site.

Relative initial reaction rates for both double bond isomerization and direct esterification with heptanoic acid were determined for the series of linear 1-alkenes from 1-octene to 1-octadecene. In competitive reactions between two 1-alkenes on Amberlyst (R) 15 catalyst at 90 degrees C, rates for both double bond isomerization and esterification decreased with increasing carbon chain length. Data suggested each 1-alkene had two different adsorption coefficients on the catalyst, one for an isomerization site and one for a site for the addition reaction. Results were consistent with previous data suggesting that Amberlyst (R) 15 catalyst has two different types of active sites.

Linear 1-alkenes undergo concurrent dimerization and double bond isomerization on the solid acid catalyst Amberlyst (R) 15. Kinetic data show that double bond isomerization occurs on a site where the alkene adsorption coefficient is small, whereas alkene dimerization occurs on a site where the alkene adsorption coefficient is large. The fraction of isomerization sites occupied by alkene is small, whereas the dimerization sites are practically saturated with alkene. Logically, two different types of acid sites must exist on the surface of Amberlyst (R) 15 catalyst. On the dimerization sites, substantial skeletal rearrangement occurs, likely via rapidly isomerizing carbenium ions, pi-complexes, and/or protonated cyclopropyl intermediates.

Initial reaction rate data for the direct esterification of 1-tetradecene with heptanoic acid on dry Amberlyst®15 catalyst permitted the identification of the surface reaction mechanism, as well as the adsorption coefficients of all reactants and products. Three different surface reaction mechanisms were considered, a two-site Langmuir–Hinshelwood mechanism and two single-site Eley–Rideal mechanisms. All the mechanisms considered competitive adsorption by all reactants and products. For each model, an error surface was calculated above the two-dimensional space of possible reactant adsorption coefficients. The error surface identified the best adsorption coefficients for each model and revealed the most likely mechanism for the surface reaction. The best mechanism was Eley–Rideal with adsorbed tetradecene reacting with heptanoic acid in the bulk phase. To explain initial rate responses to changes in initial reactant concentrations, both tetradecene and heptanoic acid must adsorb strongly to the active sites, and heptanoic acid must rapidly equilibrate between monomer and dimer forms. Data also revealed that adsorption and desorption rates were sometimes competitive with the rate of the surface reaction; equilibrium between adsorbed species and those in solution was not always maintained during short reaction times. Proper distinction between Langmuir–Hinshelwood and Eley–Rideal mechanisms required initial rate data for extreme ranges of initial reactant concentrations.

Kinetics for the reaction between 1-tetradecene and heptanoic acid to make tetradecyl heptanoates on dry Amberlyst® 15 catalyst at 90 °C are extremely complex. Observed kinetics of simultaneous double bond isomerization and esterification cannot be reconciled with a single type of catalytic site. Esterification and most of the double bond isomerization must occur on separate sites. Relative rates of esterification for tetradecene isomers suggest that adsorption coefficients on the esterification sites follow 1-tetradecene > 2-tetradecene > 3+-tetradecenes. These relative adsorption coefficients imply that, on this esterification site, 2-tetradecene isomerizes to 3-tetradecene faster than 3-tetradecene isomerizes to 2-tetradecene or 4-tetradecene, a truly novel finding not previously reported for any other acidic site. The site where most of the double bond isomerization occurs does not display this behavior, and isomerization of linear tetradecenes proceeds to thermodynamic equilibrium. Kinetic data indicate that esters form when carboxylic acid traps rapidly isomerizing carbenium ions on the catalyst’s surface. Competition is fierce for esterification sites among olefins, carboxylic acid, and esters, and olefins occupy few esterification sites. Contrastingly, olefins triumph in competition for isomerization sites, and olefin isomerization is much faster than esterification. Heptanoic acid exists primarily in dimer form, but the monomer form reacts to make esters. A complex kinetic model fit experimental data for double bond isomerization, conversion of olefin to esters, and the distribution of secondary esters that formed over 22 h.

On Amberlyst® 15 catalyst (dry) at 85 °C, 1-dodecene underwent concurrent double bond isomerization and alkylation with p-xylene. The alkylation reaction appeared to occur by an Eley–Rideal mechanism in which adsorbed olefin reacted with bulk phase p-xylene. Kinetic data showed that alkylation was irreversible and that the intermediate complex between olefin and p-xylene underwent isomerization in which the aromatic ring moved between adjacent carbons on the dodecyl chain. Given enough reaction time, the dodecyl p-xylene isomers always reached the same equilibrium distribution, regardless of catalyst loading. Kinetic modeling of concurrent olefin isomerization and alkylation showed that these two reactions must occur on two different catalytic sites. Alkylation was inhibited by the formation of dodecyl p-xylenes, while double bond isomerization was not.

On Amberlyst® 15 (dry) at 75 °C, 2-octanol undergoes concurrent esterification and dehydration in the presence of heptanoic acid in the liquid phase. Kinetic data and 18O labelling studies show that the esterification reaction most likely occurs by an Eley–Rideal (ER) mechanism between adsorbed carboxylic acid and bulk phase alcohol, while the dehydration reaction occurs by a Langmuir–Hinshelwood (LH) mechanism requiring interaction of adsorbed alcohol with a vacant site. The two reactions occur on two different types of catalytic sites: while all the sites are sulfonic acid groups, kinetic data suggest that not all of the acidic sites are positioned appropriately to a neighboring site to assist with dehydration. A kinetic model fits the observed data for the simultaneous ER and LH reactions over at least 23 h of observation.

The reversible, direct esterification of 1-hexene and 1-octene with heptanoic acid on Amberlyst (R) 15 (dry) was studied at 75 degrees C to determine kinetics and mechanism. The forward surface reaction occurred by an Eley-Rideal mechanism, in which adsorbed olefin reacted with bulk phase heptanoic acid; the reverse reaction, ester decomposition, required just one surface site. While detailed studies pointed to an Eley-Rideal mechanism, a Langmuir-Hinshelwood mechanism was nearly as good as the Eley-Rideal mechanism for reproducing kinetic data observed across several hours of reaction. Authors conclude that a cursory investigation can support a Langmuir-Hinshelwood mechanism, while a detailed investigation supports an Eley-Rideal mechanism in this system. (C) 2015 Elsevier Inc. All rights reserved.

Rapid isomerization of pi-complex intermediates results in the formation of multiple isomers of alkyl aromatics during AlCl3-catalyzed reactions between linear olefins and aromatic rings. The authors present results of a kinetic study of reactions between p-xylene, 1-dodecene, and linear tetradecenes. Product distributions are well predicted based on a model of reversible pi-complex isomerization. Surprisingly, no double bond isomerization was observed in the linear olefins: All isomerization occurred in the pi-complexes. Copyright (c) 2014 John Wiley & Sons, Ltd.

We investigated acid-catalyzed dimerization for C8 to C24 linear olefins on Amberlyst (R) 15 at 90 degrees C. Double bond position and monomer chain length had no effect on dimerization rate of linear monomers. Dimerization was first order in both monomer and catalyst and occurred via an Eley-Rideal mechanism, in which adsorbed monomer reacted with olefin in the bulk phase. Relative dimerization rates between competing monomers of different chain lengths depended solely upon relative adsorptions of the competing monomers, as all linear olefins reacted equally well with any adsorbed monomer. Relative adsorption onto dimerization sites decreased markedly as chain length increased from C8 to C14, but there was no observed change in adsorption coefficients as chain length increased from C14 to C24. Trimerization occurred when bulk dimer reacted with adsorbed monomer. Dimer molecules competed well for dimerization sites and inhibited the rate of monomer dimerization. The rate-limiting step in dimer formation was the reaction of bulk olefin with adsorbed monomer. (c) 2013 Elsevier Inc. All rights reserved.

A new mechanism for the origin of multiple skeletal isomers observed in the cationic dimerization of 1‐decene is proposed, and products that should form based on this mechanism are predicted. A protonated cyclopropyl intermediate appeared to form directly from combination of 2‐decyl carbocation with 1‐decene; formation of this intermediate did not appear to occur via ring closure of a branched secondary carbocation. The authors propose that rapid, repeated isomerizations of the protonated cyclopropyl intermediates lead to multiple skeletal isomers in decene dimers. The proposed mechanism can account for structures previously identified in mixtures of decene dimers and butene dimers. Copyright © 2012 John Wiley & Sons, Ltd.

We followed the concurrent double bond isomerizations of 1-dodecene (C12 NAO) and 11-dococene (C22 IO) on Amberlyst (R) 15 at 90 degrees C, observing the movement of the double bond from the middle of a C22 chain to its end and the movement of the double bond from the end of a C12 chain to its middle. Double bond migration was stepwise for both chains, and the kinetics were consistent with a common isomerization rate for all olefins of the same chain length, regardless of location of the double bond. Internal dodecenes isomerized 1.35 times faster than internal dococenes, suggesting a higher adsorption coefficient for dodecenes than for dococenes onto Amberlyst (R) 15 at 90 degrees C. (c) 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 745752, 2012

We developed a kinetic model for the reversible direct addition of propionic acid to linear tetradecences and linear hexadecenes on Arnberlyst 15 at 93 degrees C. The model addresses concurrent double bond isomerization of the olefins and assumes carbenium ion formations to be rate limiting for all conversions; it is detailed enough to include terms for multiple isomers of esters and olefins. The reaction was first order in olefin and in ester but was one-half order in propionic acid. Gas chromatography was the analytical method employed to follow the reactions, and this study represents a novel use of this analytical method to elucidate carbenium ion behavior. The model includes five rate-determining steps and five fast steps. (C) 2010 Wiley Periodicals, Inc. Int I Chem Kinet 42: 354-371, 2010