Carbonium Research Articles

Alkylation Kinetics of Isobutane by C4 Olefins Using Sulfuric Acid as Catalyst

The alkylation kinetics of isobutane with butene using sulfuric acid as catalyst was investigated by batch experiments in the conditions of industrial interest. More than 16 alkylates were identified and quantified by GC-MS. On the basis of the classic carbonium ion mechanism, the kinetic model was established, which can predict the concentration change of three groups of key alkylates including trimethylpentanes (TMPs), undesirable dimethylhexanes (DMHs), and heavy ends (HEs). The agreement between experimental and model calculated data was quite satisfactory. The rate constants were found to be constant with the varied temperatures (276.2 to 285.2 K) except those accounting for the addition of H+ to isobutene and its reversible reaction. An anti-Arrhenius behavior was observed for the addition reaction of H+ to isobutene, in which the corresponding rate constant falls with the increasing temperatures. The kinetic model was confirmed by the simulation of the industrial alkylation reactor. Hopefully, the ...

Impact of the lignin structure of three lignocellulosic feedstocks on their organosolv delignification. Effect of carbonium ion scavengers

Effect of autohydrolysis and aromatic scavengers on delignification patterns were evaluated using miscanthus (MxG), empty palm fruit bunch (EFB) and typha grass residue as feedstocks. Autohydrolysis was carried out without naphthol and in the presence of naphthol followed by delignification by ethanol organosolv process. Despite their close chemical composition, the three feedstocks demonstrated quite different patterns of delignification under the same condition of pretreatment. Nuclear magnetic resonance (NMR) spectroscopic characterization of ethanol organosolv lignins (EOLs) extracted from the three feedstocks revealed information concerning syringyl, guaiacyl and hydroxyphenyl content (S/G/H ratios) which underpinned the differences among the feedstock behavior. The (S + H)/G ratios for MxG, EFB and typha were determined as ̴1.27, ̴2.33 and 2.70 respectively. The major cause of difference in behavior of feedstock during the pretreatment process was attributed to the variation in lignin composition. A good relationship was observed between S/G ratio and the scavenging effect of 2-naphthol. The effect of four additional aromatic scavengers viz. p-cresol, o-cresol, hydroquinone and dihydroxyanthraquinone (DHAQ) tested in miscanthus demonstrated a significant enhancement on delignification; the effect of p-cresol and DHAQ was tantamount to that of naphthol. Cellulolytic enzyme lignin (CEL) extracted from typha grass was also subjected to 13C NMR characterization in order to obtain a more complete picture of typha lignin. Comparison of NMR spectra of CEL and EOL from TC was performed for determining the processing effect in lignin structure.

Electronic structures of bisnoradamantenyl and bisnoradamantanyl dications and related species

The highly pyramidalized molecule bisnoradamantene is extremely reactive toward nucleophiles and dienes. In this work, we studied the electronic structure of bisnoaradamantene, as well as those of its cation and dication, which are previously unreported carbonium ions. According to QTAIM and MO analysis, there is a 3c-2e bonding system in the bisnoradamantenyl cation and a 4c-2e bonding system in the bisnoradamantenyl dication. A topological study indicated that, on going from bisnoradamantene to its dication, π-bond interaction with the bridgehead carbon atom increases. Additional study of the bisnoradamantanyl dication also indicated that it has two multicenter bonding systems. Comparison of the D3BIA and NICS aromaticity indices of these molecules and other derivatives indicates that these indices are well correlated, and analysis of these indices shows that the cationic and dicationic bisnoradamantenyl species are homoaromatic.

Evidence for concerted processes in the course of the homoallenylic transposition

The hydrolysis of β-allenic tosylates produces mainly 2-methylenecyclobutanols resulting from a homoallenylic participation along with isomeric 2-methylenecyclobutanol minor products coming from a 1234–1243 rearrangement. Structures of various cyclopropylvinyl carbocations involved in the course of the hydrolysis have been determined by computational studies.For acyclic tosylates, the hydrolysis of one β-deuterated allenic tosylate confirmed the nucleophilic attack on the corresponding nonclassical carbonium ion before its evolution to a more stable cyclopropylvinyl carbocation. In the case of one cyclic β-allenic tosylate, the structure of the products has been checked by the use of deuterated isotopomer.

Charge-transfer inclusion complex formation of tropylium cation with pillar[6]arenes

The complexation behavior of pillar[6]arene hosts towards a carbonium ion, tropylium tetrafluoroborate (T·BF4), and the formation of novel charge-transfer (CT) inclusion complexes are described. In contrast, smaller pillar[5]arenes and larger pillar[7]arenes cannot form such complexes due to the unsuitable cavity dimensions.

Copolymerization of Carbon–carbon Double-bond Monomer (Styrene) with Cyclic Monomer (Tetrahydrofuran)

We reported in this work that the cationic copolymerization in one step takes place between carbon–carbon double-bond monomer styrene with cyclic monomer tetrahydrofuran. The comonomers studied belong to different families: vinylic and cyclic ether. The reaction is initiated with maghnite-H+ an acid exchanged montmorillonite as acid solid ecocatalyst. Maghnite-H+ is already used as catalyst for polymerization of many vinylic and heterocyclic monomers. The oxonium ion of tetrahydrofuran and carbonium ion of styrene propagated the reaction of copolymerization. The acetic anhydride is essential for the maintenance of the ring opening of tetrahydrofuran and the entry in copolymerization. The temperature was kept constant at 40°C in oil bath heating for 6 hours. A typical reaction product was analyzed by 1H-NMR, 13C-NMR and IR and the formation of the copolymer was confirmed. The reaction was proved by matched with analysis. The maghnite-H+ allowed us to obtain extremely pure copolymer in good yield by following a simples operational conditions. © 2012 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Acidic and Catalytic Properties of Modified Clay for Removing Trace Olefin from Aromatics and Its Industrial Test

The commercial clay modified with zeolite and La2O3 was characterized by thermoprogrammed desorption (t.p.d.) of NH3 and pyridine adsorption followed by Fourier transform infrared spectroscopy (FTIR). The result showed that the weak Lewis acid plays an important role in the alkylation reaction between olefin and aromatics which obeyed the carbonium ion mechanism. The industrial test was conducted in the 450kt/a industrial PX device at Sinopec Zhenhai Company for removing trace olefins from aromatics. It has been proved that the life cycle of the catalyst was 5.3 times that of the commercial clay. The kinetics formula for deactivation rates was explored and the result showed that the rate of clay was much higher than the catalyst deactivation rate.

Commercial test of the catalyst for removal of trace olefins from aromatics and its mechanism

Twenty-two tons of catalyst was used in the 130kt/a industrial PX device at Sinopec Qilu Company for removing trace olefins from aromatics. The result showed it had an effective running time about 3 times as long as that of the commercial clay. The reaction mechanism was explored and it indicated that the weak L acid was the main reason for the enhancement of the catalyst activity. In addition, the process of the olefins reacted with the aromatics via the carbonium ion mechanism can be generalized by the alkylation reaction.

Superacid-Promoted Ionization of Alkanes Without Carbonium Ion Formation: A Density Functional Theory Study

The carbonium ion has been suggested to be the intermediate in superacid-promoted reactions (SbF(5)-HF) such as hydrogen-deuterium exchange and in the electrophilic C-H cleavage into hydrogen and the carbenium ion. In this study, the superacid-promoted C-H cleavage into hydrogen and the carbenium ion was studied using density functional theory (B3LYP and M062X) and ab initio methods (MP2 and CCSD). The calculations suggest that the superacid-promoted C-H cleavage proceeds via a concerted transition state leading to hydrogen (H(2)) and the carbenium ion without the formation of the elusive carbonium ion. The reactivity for the superacid-promoted C-H cleavage decreases upon going from isobutane (tertiary) > propane (secondary) > isobutane (primary) > propane (primary) > ethane >> methane.

Benzene adsorption and protonation in perfluorosulfonic membrane

Benzene adsorption in a perfluorosulfonic membrane was performed through deep dehydration of the latter over the phosphoric anhydride. The subsequent UV irradiation is accompanied by a gradual transition of the benzene π-complexes in the protonated form C6H7+ that allows us to consider the perfluorosulfonic membrane as a solid superacids. The photoexcitation on the absorption band of adsorbed carbonium ion causes its fluorescence in the region of 450–600 nm.

A carbonium pseudo ionic liquid with excellent extractive desulfurization performance

Lewis hard acid AlCl3 was softened by some butyl halides forming highly polarized liquids. These liquids are similar to the ionic liquids (ILs) with metallic complex anion and varying composition, and thus termed here as carbonium pseudo ILs (CPILs). The CPILs, that is, t‐C4H9Cl‐AlCl3, n‐C4H9Cl‐AlCl3, and t‐C4H9Br‐AlCl3, show very strong desulfurization activity for various thiophenic compounds like 3‐methylthiophene, benzothiophene, and dibenzothiophene. The above thiophenic compounds can be removed completely from model oils within 20 min by a very small amount of CPILs reactive extractant. The extractive mechanism is deemed as an acid–base complexation along with alkylation of the thiophenic compounds, and the Lewis acidity comes from both carbonium ion (borderline acid) and the dissolved AlCl3 (hard acid). The t‐C4H9Cl‐AlCl3 shows good selectivity for three thiophenic compounds even in toluene‐containing system. Further, some CPILs show satisfactory desulfurization performance for the model gasoline that mimics the composition of real one. © 2012 American Institute of Chemical Engineers AIChE J, 59: 948–958, 2013

Comparison of metabolism-mediated effects of pyrrolizidine alkaloids in a HepG2/C3A cell-S9 co-incubation system and quantification of their glutathione conjugates

Toxicity of pyrrolizidine alkaloids (PAs) largely depends on their metabolic activation by hepatic enzymes, including cytochrome P450s, to become chemically reactive pyrrolic derivatives. These then spontaneously release the esterifying acids to generate carbonium ions that form covalent adducts with cellular nucleophiles to exhibit toxicity.In our investigation, metabolism-mediated toxicity of monocrotaline, retrorsine, lycopsamine, echimidine (retronecine-type PAs), heliotrine (a heliotridine-type PA) and senkirkine (an otonecine-type PA) was studied using an in vitro co-incubation assay.Human hepatocarcinoma (HepG2/C3A) cells were incubated with PAs in the presence and absence of rat liver S9 fraction and the toxicity was assessed as lowered mitochondrial activity.Bioactivation potential was measured by incubating PAs with rat liver S9 fraction, NADPH and GSH in a cell free system. Pyrrolic metabolites generated were entrapped as glutathione conjugates (7-GSH-DHP and 7,9-di-GSH-DHP) which were quantified using LC-MS-MS analysis.Our results indicated that PAs were metabolized by rat liver S9 fraction into reactive pyrrolic derivatives which were toxic to HepG2/C3A cells. This approach can be used to determine and compare bioactivation potential and metabolism-mediated toxicity of various PAs.

Physiologically based kinetic modeling of bioactivation and detoxification of the alkenylbenzene methyleugenol in human as compared with rat

This study defines a physiologically based kinetic (PBK) model for methyleugenol (ME) in human based on in vitro and in silico derived parameters. With the model obtained, bioactivation and detoxification of methyleugenol (ME) at different doses levels could be investigated. The outcomes of the current model were compared with those of a previously developed PBK model for methyleugenol (ME) in male rat. The results obtained reveal that formation of 1′-hydroxymethyleugenol glucuronide (1′HMEG), a major metabolic pathway in male rat liver, appears to represent a minor metabolic pathway in human liver whereas in human liver a significantly higher formation of 1′-oxomethyleugenol (1′OME) compared with male rat liver is observed. Furthermore, formation of 1′-sulfooxymethyleugenol (1′HMES), which readily undergoes desulfonation to a reactive carbonium ion (CA) that can form DNA or protein adducts (DA), is predicted to be the same in the liver of both human and male rat at oral doses of 0.0034 and 300mg/kg bw. Altogether despite a significant difference in especially the metabolic pathways of the proximate carcinogenic metabolite 1′-hydroxymethyleugenol (1′HME) between human and male rat, the influence of species differences on the ultimate overall bioactivation of methyleugenol (ME) to 1′-sulfooxymethyleugenol (1′HMES) appears to be negligible. Moreover, the PBK model predicted the formation of 1′-sulfooxymethyleugenol (1′HMES) in the liver of human and rat to be linear from doses as high as the benchmark dose (BMD10) down to as low as the virtual safe dose (VSD). This study shows that kinetic data do not provide a reason to argue against linear extrapolation from the rat tumor data to the human situation.

Studies on the Aromatization Reaction of LPG and Gasoline: Reaction Behaviors and Mechanistic Pathways

The aromatization reaction of liquefied petroleum gas (LPG) and gasoline on the different catalysts was investigated in a confined fluidized bed. As for the aromatization reaction of LPG and gasoline, four feedstock (first aromatization reaction product, four fractions of gasoline, high olefin's LPG, and high paraffin's LPG) have significant influence on product yields and product distribution. The aromatization index (AI) and competent parameter (CP) are proposed to study the mechanistic pathways of the aromatization reaction of LPG and gasoline. Furthermore, the relative ratio of the free radical mechanism and that of the carbonium ion mechanism are obtained. The greater the AI value, the greater the aromatization reaction. When the CP value is more than 1.5, the aromatization reaction mainly occurs. When the CP value is less than 0.6, isomerization reaction mainly happens. When the CP value is between 0.6 and 1.5, the aromatization reaction and the isomerization reaction happen at the same time.

Reaction of tert-butyl hypochlorite with carbonium ion from styrene epoxide in an acidic alcoholic solution

The kinetic regularities of the change in the concentration of tert-butyl hypochlorite in the presence of the binary system (BS) styrene epoxide—p-toluenesulfonic acid in a tert-butanol solution were studied using iodometry and HPLC and compared with the data obtained earlier for hydroperoxide decomposition. The expressions for the rates of transformation of ButOCl, epoxide, and ROOH in the BS through the reactant concentrations are of the same type (the first order for the acid and the zero order for epoxide, ButOCl, and ROOH) and indicate that the reactions are related to epoxide heterolysis. Dioxygen ceases ROOH decomposition in the BS but exerts no effect on the decrease in the concentration of ButOCl, which efficiently inhibits the O2 uptake in the BS and almost an order of magnitude retards the accumulation of benzaldehyde (the product of styrene epoxide oxidation) with a low (up to 15%) decrease in the heterolysis rate. The inhibition effect is due to the heterolytic interaction of ButOCl with the carbocation formed by the cleavage of the three-membered ring of protonated styrene epoxide. The introduction of ButOCl in the BS decreases the stationary concentration of the carbocation and, as a consequence, the stationary concentration of phenylcarbene responsible for O2 uptake.

Green epoxidation of 1-hexene: O2 utilizing cis-MoO2 Schiff base complex

The green epoxidation of 1-hexene using [hydrazine-N-salicylidene-N′-salicyloyl-] cis-dioxomolybdenum(VI) and its zeolite-Y composite as catalyst in DMF in the presence of molecular oxygen as oxidant and in the temperature range 333–363 K is reported. The ‘green’ factor of olefin oxidation catalysis using the Mo(VI) dioxo complex is its ability to use atmospheric oxygen which is non-hazardous and inexpensive and produces no harmful by-products. The effects of the initial concentration of the substrate and Mo complex and the temperature in the range 333–363 K on the rate of reaction are examined. The olefin conversion into different products is monitored using gas chromatography. The formation of 1,2-epoxyhexane, 1-hexanal and 2-hexanone is observed under both homogeneous and heterogeneous catalytic conditions; however, 2-hexanone did not form during the reactions using the zeolite composite. 1-Hexene conversion was found to be nearly complete and the product distribution into 1,2-epoxyhexane, 1-hexanal and 2-hexanone being 1 : 20 : 6 under homogeneous conditions for 6 h; while the final product is 1-hexanal under heterogeneous conditions for 6 h. The rate of 1-hexene oxidation showed first order dependence with respect to the catalyst and substrate concentration and it was an endothermic reaction (activation energy, 10.68 Kcal mol−1). A tentative mechanism for the oxidation of 1-hexene is proposed and the observed product formation was reasoned to involve epoxide isomerisation through participation of adventitious water in the reaction mixture and the resulting carbonium ions.

Revealing the catalytic mechanism of an ionic liquid with an isotope exchange method

The alkylation mechanism catalyzed by an ionic liquid (as a Lewis acid) may be different from the traditional alkylation mechanism catalyzed by Brønsted acid, especially as their initiation steps are still not clear. In this paper, an isotope exchange method is used to investigate the catalytic mechanism of AlCl3/butyl-methyl-imidazolium chloride ionic liquid in the alkylation of benzene with 1-dodecene. The proposed catalytic mechanism was confi rmed by analysis of ionic liquid before and after reaction and of the alkylation products of deuterated benzene (C6D6) with 1-dodecene. The proposed mechanism consists of the equilibrium reaction between [Al2Cl7]−+H+ and [AlHCl3]++[AlCl4]−, in which the Brønsted acid [AlHCl3]+ is supplied by the reaction of 2-H on the imidazolium ring and [Al2Cl7]−. The alkylation reaction is initiated by the Brønsted acid [AlHCl3]+ which reacts with 1-dodecene to form a carbonium ion, then the carbonium ion reacts with benzene to form an unstable σ complex, leading to the formation of 2-phenyldodecane.

Comparative study of the hypercoordinate carbonium ions and their boron analogs: A challenge for spectroscopists

Theoretical and related experimental studies have shown that carbon can extend its bonding from Kekule’s tetravalent methane to five, six or seven coordinated protonated methanes, i.e., CH 5 +, CH 6 2+ and CH 7 3+ and their analogs. Ab initio calculations indicate that higher coordinated, highly charged carbonium ions could be viable species despite the substantial charge–charge repulsion. Structure and bonding of such carbonium ions and the isoelectronic boron analogs were studied and are discussed. These contribute to our general understanding of the electrophilic reactivity of C–H and C–C single bonds.

ChemInform Abstract: Hydration of Olefins into Alcohols

AbstractReview: 43 refs.

Making M–CN bonds from M–Cl in (PONOP)M and (dippe)Ni systems (M = Ni, Pd, and Pt) using t-BuNC

C–N bond activation of tert-butyl isocyanide in methanol using 2,6-bis(di- tert-butylphosphinito)pyridine (PONOP) metal (Ni, Pd, Pt) complexes and (dippe)NiCl 2 are reported. t-BuOMe and t-BuCl were detected as organic products by GC–MS. Substitution of the metal-chloride by one molecule of tert-butyl isocyanide followed by carbonium ion loss/nucleophilic attack by chloride anion or methanol led to formation of a metal-cyanide bond.