C3 Alkylation Research Articles

Unveiling the enhanced catalytic performance of low-Si/Al-ratio beta-zeolite on C4 alkylation combing with experiments and molecular simulations

The acidity and pore structure of zeolite catalysts play a crucial role in the selectivity and stability of C4 alkylation due to the synergistic effect of reaction activity and diffusion. Herein, the effect of three acidic beta zeolites with different Si/Al ratios on adsorption, diffusion, and catalytic performance was studied using experiments and molecular simulations. The beta zeolite with the lower Si/Al ratio leads to the faster relative diffusion of isobutane to 1-butene and the smaller adsorption amount of alkylate products. Furthermore, the diffusion of molecules in the zigzag channel along the z direction of beta zeolites is much slower than other two directions. The experimental results indicate that lower Si/Al ratio cause the higher content of strong BAS in the zeolite, resulting in the higher hydride activity and the longer catalytic lifetime. This work provides a theoretical basis for the development of high catalytic activity zeolite catalysts.

Merging Quinoxalin-2(1H)-ones Excitation with Cobaloxime Catalysis: C3 Alkylation of Quinoxalin-2(1H)-ones with Unactivated Alkyl Iodides and Carboxylic Acids under Light.

Reported herein is a practical, economical, and efficient construction of 3-alkylated quinoxalin-2(1H)-ones with alkyl carboxylic acids and alkyl iodides by quinoxalin-2(1H)-one excitation and cobaloxime catalysis. Primary, secondary, and tertiary alkyl iodides and carboxylic acids all could be efficiently transferred into target products with excellent functional group tolerance. Mechanism studies reveal that the quinoxalin-2(1H)-one derivatives could be directly excited and yield alkyl carbon radicals from alkyl carboxylic acids and alkyl iodides with the aid of the cobaloxime complex.

Acidity Quantification and Structure Analysis of Amide-AlCl3 Liquid Coordination Complexes for C4 Alkylation Catalysis

Liquid coordination complexes (LCCs), which are formed between metal halides and donor molecules, represent promising catalysts. Six amide-AlCl3 LCCs were successfully synthesized, followed by their characterization through NMR, Raman, and UV-visible spectroscopy. The acidity of these LCCs was quantified by performing computational modelling of fluoride ion affinities (FIA) and experimental Gutmann–Beckett measurements. Spectroscopic analysis indicated bidentate coordination between amide ligands and Al, which induced asymmetric splitting of Al2Cl6 into diverse ions such as [AlCl2L2]+, [AlCl4]−, [AlCl3L], and [Al2Cl6L]. The computed FIA was found to align well with the experimental acidity trends, thereby confirming the proposed structure of the LCC. In the alkylation tests, the LCC with a high acidity demonstrated an increase in the yields of C5-C7 alkylates. These results provide an in-depth understanding of the tuneable structures of amide-AlCl3 LCCs. The acidity of LCCs can be controlled by tuning the ratio of the organic ligand to AlCl3, which allows bidentate coordination to facilitate asymmetric splitting of Al2Cl6. The LCCs demonstrate a high degree of potential as versatile and sustainable acid catalysts in alkylation reactions. These findings may advance the foundational knowledge of LCCs for the purpose of targeted acid catalyst design.

Metal-Free Late-Stage Alkylation of Tryptophan and Tryptophan-Containing Peptides with 1,3-Dithiane Derivatives.

Late-stage diversification of structurally complex peptides has enormous potential for drug discovery and molecular imaging. We report a simple, metal-free, late-stage reductive C2 alkylation of tryptophan and tryptophan-containing peptides using readily available 1,3-dithianes. This alkylation protocol has a wide substrate scope and an excellent tolerance for reactive functional groups.

Aqueous Flavin Photoredox Catalysis Drives Exclusive C3-Alkylation of Indolyl Radical Cations in Route to Unnatural Tryptophan Mimetics.

One way to build chemical diversity into indoles is to oxidize them to indolyl radical cations (Ind•+). These intermediates can accept new functional groups across C2-C3 bonds or independently at C2. Less encountered is selective diversification at C3, a position plagued by competing dearomative side reactions. We disclose an aqueous photoredox-catalyzed method for transforming Ind•+ into C3-substituted tryptophan mimetics that uses water as a transient protecting group to guide site-selective C3 alkylation.

Insights into the effect of Si/Al ratio on Isobutane/1-butene ratio in the pore of H-BEA zeolite in C4 alkylation process

The isobutane/butene (I/O) ratio in the pore is a crucial factor for enhancing the catalytic stability of zeolitic catalysts in C4 alkylation process. In this work, the influence mechanism of the Si/Al ratio on the I/O ratio in the pore for H-BEA zeolite was investigated via CB-GCMC methods under realistic alkylation conditions. It is found that the I/O ratio in the pore decreases dramatically with decreasing the Si/Al ratio due to the higher adsorption heats of 1-butene over the acid sites than that of isobutane. Therefore, there will be an optimal Si/Al ratio for C4 alkylation, which is in good agreement with the experimental results. Furthermore, the relationship between the I/O ratio in the pore and feedstock over the H-BEA zeolite with different Si/Al ratios was built. We found that increasing the I/O ratio in the pore by improving the I/O ratio in the feedstock is limited, when the Si/Al ratio is much low. The external surface modification of catalyst will be an effective method to improve the I/O ratio in the pore. These results are of great significance to the rational design of high-efficiency C4 alkylation catalysts.

Visible Light Induced C2 Alkylation of 2H‐Benzoxazoles with Cycloalkanes and Ethers via Selectfluor‐Mediated Oxidation

AbstractAn efficient selectfluor‐oxidative protocol was developed for the direct C2‐alkylation of 2H‐benzoxazoles with cycloalkanes and ethers. Selectfluor can effectively promote the oxidative cross‐coupling without an external catalyst under the visible light irradiation at room temperature. This alkylation reaction tolerates a wide range of functional groups affording 48 examples of the C2‐alkylated 2H‐benzoxazoles in moderate to good yields.

Elucidating effect of acid strength on isomerization mechanisms of butene over solid acid catalysts in C4 alkylation

Understanding the effect of acid strength on butene isomerization mechanisms is essential in C4 alkylation process. Herein, the double bond, trans-cis, and skeleton isomerization mechanisms of butene over acid sites with different acid strengths were investigated utilizing density functional theory (DFT) calculations. It is demonstrated that the acid strength significantly affects the isomerization mechanisms of butene. The stability of carbonium ions as reaction intermediates follows the order: tert-butyl cation > cis-butyl cation > trans-butyl cation, which is more sensitive to acid strength than that of butoxide species. Therefore, the reaction pathways of double bond and trans-cis isomerizations changed with varying the acid strength. Based on the analysis of activation energy barriers, it is found that 1-butene and 2-butene can be easily converted into each other over strong acid site. Thus, for reactants, C4 alkylation has no selectivity to 1-butene and 2-butene over strong acid site, which is consistent with experimental study. This work provides mechanistic insights into the relationship among acid strength, type of butene, and quality of alkylate in the C4 alkylation process.

C4 Alkylation of Pyridines Enabled by the Use of a Bulky Aluminum Lewis Acid and Nickel Catalysis

C4 Alkylation of Pyridines Enabled by the Use of a Bulky Aluminum Lewis Acid and Nickel Catalysis

K2S2O8 Mediated Three‐component Radical Cascade C3 Alkylation of Quinoxalin‐2(1H)‐ones with Vinylarenes and 4‐Hydroxycoumarins/4‐Hydroxy‐6‐methyl‐2‐pyrone

AbstractQuinoxalin‐2(1H)‐ones undergo a three‐component radical cascade C3 alkylation reaction with 4‐hydroxycoumarins/4‐hydroxy‐6‐methyl‐2‐pyrone by using vinyl arenes as intermediary radical acceptors. K2S2O8 in dimethylsulfoxide (DMSO) works as the best reagent‐solvent combination, which promotes the reaction under metal‐, photocatalyst‐ and light‐free conditions producing the three‐component products in moderate yields. We also prove the involvement of radicals in the course of the reaction by performing several radical scavenging experiments with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), diphenyl ethylene, and butylated hydroxytoluene (BHT).

Elucidating Effect of Acid Strength on Isomerization Mechanisms of Butene Over Solid Acid Catalysts in C4 Alkylation

Elucidating Effect of Acid Strength on Isomerization Mechanisms of Butene Over Solid Acid Catalysts in C4 Alkylation

Metal-free visible-light-initiated direct C3 alkylation of quinoxalin-2(1H)-ones and coumarins with unactivated alkyl iodides

A visible-light-mediated direct C3-alkylation of quinoxalin-2(1H)-ones and coumarins with unactivated alkyl iodides under metal- and external photocatalyst-free conditions is described.

Optimized Artificial Neural Network for Evaluation: C4 Alkylation Process Catalyzed by Concentrated Sulfuric Acid.

In this work, an artificial neural network was first achieved and optimized for evaluating product distribution and studying the octane number of the sulfuric acid-catalyzed C4 alkylation process in the stirred tank and rotating packed bed. The feedstock compositions, operating conditions, and reactor types were considered as input parameters into the artificial neural network model. Algorithm, transfer function, and framework were investigated to select the optimal artificial neural network model. The optimal artificial neural network model was confirmed as a network topology of 10-20-30-5 with Bayesian Regularization backpropagation and tan-sigmoid transfer function. Research octane number and product distribution were specified as output parameters. The artificial neural network model was examined, and 5.8 × 10–4 training mean square error, 8.66 × 10–3 testing mean square error, and ±22% deviation were obtained. The correlation coefficient was 0.9997, and the standard deviation of error was 0.5592. Parameter analysis of the artificial neural network model was employed to investigate the influence of operating conditions on the research octane number and product distribution. It displays a bright prospect for evaluating complex systems with an artificial neural network model in different reactors.

Construction of Chiral All‐Carbon Quaternary Stereocenters by Asymmetric Friedel−Crafts Reaction of Isatin Derivatives

Comprehensive SummaryUnder the catalysis of chiral Cu(II) complex, C2 and C3 alkylation of pyrrole and C3 alkylation of indole were realized simultaneously. The chiral oxindole skeleton with an all‐carbon quaternary stereogenic center at the C3‐position could be obtained exclusively with high yields (up to 95%) and excellent enantioselectivities (up to > 99%).

Theoretical study on the C4 alkylation mechanism catalyzed by Cu-containing chloroaluminate ionic liquids

DFT calculations combined with MD simulations have been used to investigate the complicated reaction mechanism of isobutane-isobutylene alkylation catalyzed by the neat chloroaluminate ionic liquid (NIL) and the Cu-containing chloroaluminate ionic liquid (CIL). Transition states of three key elementary reactions were obtained to address the selectivity of the alkylate formation versus the by-product formation in different ionic liquids. The DFT calculations indicate that the Cu species would significantly inhibit the polymerization of C4= olefins and C8+ carbenium ions. Compared to the competitive H-transfer reaction, the reaction rate of polymerization in the NIL was very fast resulting in poor product selectivity. The Mayer bond order (MBO) and electron localization function (ELF) maps reveal that H-transfer from isobutane to C8+ carbenium ion occurs via a concerted H-Cu bond formation between a C8+ and an isobutane to generate the desired isooctane. The Cu complex did engage in the H-transfer of isobutane/C8+, but it did not weaken the catalytic activity in comparison to the neat chloroaluminate anions. The MD simulations show that a combination of high isobutane concentration and low isobutylene concentration at the CIL-hydrocarbon interface can be attributed to the effects of Cu complex, which also leads to the improvement of the alkylation selectivity. An essential role of Cu species in the CIL alkylation is to impede the formation of C12+ carbenium ions and promote the H-transfer between isobutane and C8+ carbenium ion.

The shape selectivity of zeolites in isobutane alkylation: An investigation using CBMC and MD simulations

The adsorption and diffusion behaviors of C8 isomers and C9 component as main products of the isobutane alkylation catalyzed by zeolites with different topologies were investigated using configurational bias Monte Carlo (CBMC) and MD simulations in this work. The adsorption capacity of zeolites at 353 K and 2.0 MPa relies on their pore volume with the order of FAU > BEA > LTL > MOR. The diffusion coefficient of C8 and C9 molecules increases with the decrease of loading and the increase of temperature, and the more compact molecules diffuse slower than the slimmer ones at low loadings while quicker at higher loadings. It was found that for zeolites, small adsorption heat of C8 isomers, or large molecular diffusion coefficient would correspond to a high selectivity of target alkylates. Particularly, BEA zeolite with large RPLD/LCD shows high reaction selectivity, rendering it a good candidate catalyst for C4 alkylation.

Coalescence-adsorption coupling treatment instead of alkaline washing-water washing process for efficient removal of sulfuric acid and sulfates

C4 alkylate oil is an ideal blending component of automotive gasoline, and the green removal of sulfuric acid and sulfates from the high-temperature sulfuric acid alkylation reaction products (SAARP) has always been a hot issue in the field of clean alkylation production. In this paper, a novel coalescence separation-depth adsorption (CS-DA) coupling dry separation technique is introduced to efficiently separate acid-hydrocarbon emulsions, with the aim to supersede the alkaline washing-water washing (AW-WW) process in alkylation unit. Lateral line tests were conducted on the coupling treatment of the alkylation reaction products (ARP) produced in the STRATCO alkylation unit of Sinopec Tianjin Branch. The sulfur morphology analysis shows that the sulfides in the ARP mainly come from C4 feedstocks and alkylation reaction, including mercaptans, thioethers, thiophenes, trace hydrogen sulfide and sulfur dioxide. The mechanism of coalescence separation reveals that the efficient removal process of sulfuric acid by fiber coalescence separation also has a function similar to "pickling extraction" to remove sulfates. In addition, we investigated the influence of CS-DA coupling treatment on the total sulfur and sulfuric acid content in the ARP and performed the copper corrosion and water-soluble acid assays. The research findings indicated that the back sideline of the acid coalescer had the most outstanding separation effect relative to the front and rear lateral lines of the heat exchanger. The total sulfur content in the ARP after separation can be reduced to less than 5 mg/L, without water-soluble acid and copper corrosion (1a). The industrial application shows that the CS-DA coupling dry separation technique can completely replace the AW-WW process, which makes the various indicators of alkylate oil strictly controlled and the sulfur content up to the industrial standard. The novel dry separation technique provides a promising alternative for solving the difficulties in the emulsion treatment of high-temperature sulfuric acid alkylation and promoting the clean production of alkylation.

Computation-guided descriptor for efficient zeolite catalysts screening in C4 alkylation process

Zeolites as the environmentally friendly catalysts for C4 alkylation suffer from rapid deactivation in commercial application. In this work, the intrinsic descriptor (i.e., the i-butane/1-butene ratio in micropores) for catalyst deactivation was proposed by configurational-bias Grand Canonical Monte Carlo (CB-GCMC) calculations. It is found that pore structural topology affects the competitive adsorption between i-butane and 1-butene due to distinct structure of the two adsorbates. The i-butane/1-butene ratios in the pore decreased in the order: BEA > FAU > MOR > MFI. In other words, 3D interconnecting BEA channels formed by 12-membered rings with ordered pore configuration were suggested to have higher i-butane/1-butene ratio, because i-butane has better spatial matching with 12-membered rings on basis of the analysis of the size. Notably, experimental deactivation rate is inversely proportional to calculated i-butane/1-butene ratio inside microproes with good linear correlation. This descriptor for deactivation offers a promising avenue for rational screening of more efficient zeolite catalysts for C4 alkylation.

Cu-Catalyzed Regioselective C-H Alkylation of Benzimidazoles with Aromatic Alkenes.

Herein we report a novel Cu-catalyzed regioselective C2-H alkylation of benzimidazoles with aromatic alkenes. The reaction features exclusive regioselectivity and broad substrate scope in the intermolecular alkylation of benzimidazoles with terminal and internal aromatic alkenes, constituting a modular access toward benzimidazole-containing 1,1-di(hetero)aryl alkanes. The intramolecular C2-H alkylation of benzimidazoles with aromatic alkenes has been achieved in an endo-selective manner. The enantioselective C2 alkylation of benzimidazoles has also been realized with moderate to good stereocontrol.

Visible‐Light‐Induced C2 Alkylation of Heterocyclic N‐Oxides with N‐Hydroxyphthalimide Esters under Metal‐Free Conditions

AbstractA visible‐light‐induced site selective C−H alkylation of heterocyclic N‐oxides with N‐hydroxyphthalimide esters was developed using Eosin Y as the photocatalyst in the presence of Cs2CO3 under redox‐neutral and mild conditions. Using N‐hydroxyphthalimide esters as the radical precursors, quinoline and pyridine N‐oxides were readily coupled with a wide range of primary, secondary, and tertiary radicals to afford the desired alkylated heterocyclic N‐oxides in moderated to excellent yields. Importantly, this reaction protocol also successfully demonstrated its applications for the construction of glycosyl or bioactive natural dehydroabietic acid containing heterocyclic N‐oxides, as well as the pharmaceutical and agrochemical active alkylated quinine‐based functional molecules (potential antimalarial drug).magnified image