Reductive Desulfurization Research Articles

Comparative investigation on the chemical pre-desulfurization process of a high sulfur coal through orthogonal experiments: a case study

ABSTRACT The effect of different chemical pre-desulfurization processes were compared to achieve the utilization of high sulfur coal efficiently and economically and its total sulfur content is 2.19%. The major influence factors were the reagent dosage, desulfurization temperature, and time. Compared with single-factor experiments, orthogonal experiments can greatly reduce the number of experiments and ensure the rationality of experimental data. The desulfurization rate of acid leach, alkali leach, oxidation, and catalytic reduction were 41.67%, 17.16%, 26.96%, and 27.45%, respectively, and the total sulfur after the pre-desulfurization process were 1.19%, 1.69%, 1.49%, and 1.48%, respectively. Range analysis and variance analysis were employed for the crucial operational parameters. In acid and alkali leaching desulfurization process, the acid/alkali concentration had the greatest influence on the desulfurization effect. In oxidation desulfurization process, the desulfurization time had the greatest influence on the desulfurization effect. In catalytic reduction desulfurization, the reducing agent dosage was the most important factor. The main factor for the results above was that the desulfurization mechanisms were different. Therefore, the research of different desulfurization mechanisms is the main direction of future work. The consequence of this paper would provide data support for the selection of the desulfurization method for high sulfur coal.

One-step electrolytic reduction desulfurization of Sb2S3 in different molten salts

A comparative analysis of different molten salt systems was conducted, including NaCl−KCl, NaCl−CaCl2, NaCl−Na2CO3, NaCl−KCl−CaCl2, and NaCl−KCl−Na2CO3. The phase diagrams, thermal stability, and solubility of Sb2S3 in molten salt systems were investigated. Based on the distribution of the element antimony, current efficiency, energy consumption, and the characterization of the residue, the most suitable molten salt for the electrical reduction of Sb2S3 was verified. The results show that all molten salt systems have good thermal stability and can realize the electrolytic reduction of Sb2S3. The system with CaCl2 is not conducive to the dissolution of Sb2S3, and the system with Na2CO3 can react with Sb2S3. In addition, the current efficiency of the NaCl−KCl system is the highest (75.68%), and the energy consumption ratio is the lowest (2.18 kW·h/kg).

Protein desulfurization: Sodium tetraethylborate makes it fast

Today, the development of powerful one-pot techniques combining native chemical ligation and cysteine reductive desulfurization is central to the production of proteins by chemical synthesis. In the September issue of <i>Chem</i>, Xuechen Li and co-workers achieved this goal by combining sodium tetraethylborate and a phosphine as a post-ligation treatment.

Total Synthesis of Euonymine and Euonyminol Octaacetate.

Euonymine (1) and euonyminol octaacetate (2) share the core structure of euonyminol (3), the most hydroxylated member of the dihydro-β-agarofuran family. In 2, eight of the nine hydroxy groups of 3 are acetylated, and 1 has six acetyl groups and a 14-membered bislactone comprising a pyridine dicarboxylic acid with two methyl groups. The different acylation patterns provide distinct biological activities: 1 and 2 display anti-HIV and P-glycoprotein inhibitory effects, respectively. The 11 contiguous stereocenters and 9 oxygen functionalities of the ABC-ring system of 1 and 2 represent a formidable challenge, which is further heightened by the macrocyclic structure of 1. Here we disclose an efficient synthetic strategy for enantioselective total synthesis of 1 and 2. Starting from (R)-glycerol acetonide, we constructed the B-ring by an Et3N-accelerated Diels-Alder reaction, the C-ring by intramolecular iodoetherification, and the A-ring by ring-closing olefin metathesis. The 10 stereocenters were installed through a series of substrate-controlled stereoselective C-C and C-O bond formations by exploiting the three-dimensional structures of judiciously designed substrates. These newly developed reaction sequences led to protected euonyminol 5, which served as a common intermediate for assembling 1 and 2. Global deprotection of 5 and subsequent acetylation produced 2. Alternatively, the discriminative protective groups of 5 allowed for site-selective bis-esterification to generate bislactone. Combining [3 + 2]-cycloaddition and reductive desulfurization introduced the last remaining stereocenters of the two methyl groups on the macrocycle. Finally, deprotection and acetylation gave rise to fully synthetic 1 for the first time.

Organic Transformation of Benzothiophenes by C−S Bond Cleavage Beyond Reductive Desulfurization

AbstractAs the analogues of indole bicyclic system, benzothiophenes are often overlooked in organic transformation, and synthetic methods developed mostly rely on the acidic protons at C2 or C3 position, known as C−H functionalization. Complementary to the structural modification of benzothiophenes, C−S bond cleavage can realize the skeleton reconstruction. Reduction of benzothiophenes always involves the C−S bond cleavage, especially in the hydrodesulfurization (HDS) of petroleum products. Beyond reductive desulfurization, although C−S bond cleavage of benzothiophenes has been achieved by diverse methodologies, there is no systematic review on such topic. Herein, transformation of benzothiophenes via C−S bond cleavage in organic synthesis will be presented along with briefly delineated mechanism.

Intramolecular Diels-Alder reactions of 1,2,4-triazines. Synthesis of 3-alkylpyridines via Raney nickel desulfurization of thieno[2,3-b]pyridines

Abstract 2-Aryl-2,3-dihydrothieno[2,3-b]pyridines have been prepared via intramolecular Diels-Alder reactions of suitably 3-substituted 1,2,4-triazine intermediates, followed by their reductive desulfurization with Raney Nickel to form 3-substituted pyridines. A one-pot synthesis of 2-aryl-2,3-dihydrothieno[2,3-b]-pyridines from thiosemicarbazide is described as well.

Reductive desulfurization of aromatic sulfides with nickel boride in deep eutectic solvents

Deep eutectic solvents were first used as the solvents in the reductive desulfurization process with nickel boride, and the desulfurization performance of nickel boride was greatly improved.

An Integrated Process of Reductive Desulfurization by Sodium Borohydride and Its Electroreduction Regeneration in Ionic Liquid

In this study, a novel desulfurization method was developed by introducing ionic liquid (IL) into the integrated process of reductive desulfurization by NaBH4 and its regeneration via NaBO2 electroreduction, where ILs play a dual role of electrolyte and extracting agent. Under the conditions of -2.4 V forward pulse voltage, 0.6 V reverse pulse voltage, 0.6 s forward pulse time, 0.4 s reverse pulse time, 0.8 s turn-off time, 80 min electrolytic time, 4/1 IL/oil volume ratio, sulfur removal reached more than 95% for model fuel oil. Therefore, the novel integrated process of reductive desulfurization by NaBH4 and its electroreduction regeneration in IL is feasible and promising.

A study of the desulfurization selectivity of a reductive and extractive desulfurization process with sodium borohydride in polyethylene glycol

The selectivity of a facile reductive and extractive desulfurization process was studied. In this desulfurization method, polyethylene glycol was used as the extractant, and sodium borohydride was used as the reductant. Several different simulated fuels were prepared by dissolving thiophenic sulfides, methylbenzene and hexylene in octane. The results showed that methylbenzene and olefins had different effects on different sulfur compounds during this desulfurization process. The extraction and reduction mechanisms were also explained. Four factors could affect the desulfurization performance: (1) intermolecular hydrogen bonding: (a) active O bonding with aromatic H or (b) S bonding with H atoms in hydroxide radicals, (2) “like-dissolves-like” interactions between polyethylene glycol and thiophenic sulfides, (3) the methyl steric hindrance effect and the electron density of sulfur atoms, and (4) the combination of S atoms with produced nickel boride to form active desulfurization centres. The desulfurization reaction path was also deduced according to the GC/MS results.

DFT study on C-S bond dissociation enthalpies of thiol-derived peptide models

ABSTRACTNative chemical ligation (NCL) and its modified versions (ligation-desulfurization chemistry) have revolutionized the way that large peptides and proteins are obtained by chemical synthesis. Ligation-desulfurization chemistry can generate thiol-derived peptide models, which can generate proteins through reductive desulfurization. The C-S bond cleavages are involved in the process. It is important for us to comprehend the strength of the C-S bond estimated by the homolytic bond dissociation enthalpies (BDEs). Therefore, 25 DFT methods were chosen to calculate the C-S BDEs of the 55 organic sulfides. It is reliable to predict C-S BDEs by M05-2X method with the corresponding root mean square error value of 6.2 kJ/mol. Then, the C-S BDEs of the thiol-derived peptide model and the structure-activity relationships were systematically researched by using this method. Besides, so as to comprehend the nature of the C-S BDE change mode, the analysis comprised of the natural bond orbit and the energies of frontier orbitals were studied.

Optimal extractive and reductive desulfurization process using sodium borohydride in situ generated via sodium metaborate electroreduction in ionic liquid

In order to lower desulfurization cost, the NaBH4 preparation via NaBO2 electroreduction was introduced into the integrated process of extraction and reductive desulfurization. Accordingly, a novel desulfurization method was developed where NaBH4 can be recycled at the same time as desulfurization. The process of NaBH4 preparation via NaBO2 electroreduction was analyzed by cyclic voltammetry and the effect of pulse parameters on desulfurization efficiency was optimized by orthogonal experiments. Under optimal conditions desulfurization efficiency of more than 97 % was obtained for model fuel oil. Desulfurization mechanism and kinetics was probed. Results showed that the desulfurization of DBT should proceed over direct cleavage of CS bond and desulfurization reaction could be treated as pseudo-first-order reaction. Furthermore, the structures of original and recycled ionic liquids (ILs) were analyzed by nuclear magnetic resonance and the desulfurization performance of the recycled ILs was also investigated. Results showed that ILs maintained their original structures after regeneration and displayed good reusability. In summary, the novel desulfurization process is feasible and promising.

Expanding the Scope of Asinger Chemistry towards Enantiomerically Pure Secondary Amines and β-Aminothiols through Chemoenzymatic Derivatization of 3-Thiazolines

A proof of concept for a novel approach towards enantiomerically highly enriched acyclic secondary amines and β-aminothiols as non-cyclic target molecules when starting from 3-thiazolines as heterocycles is presented. Starting from 2,2,4,5,5-pentamethyl-3-thiazoline, we demonstrated this chemoenzymatic pathway to both of these types of amine molecules, which were isolated as urea derivatives with a non-optimized yield of up to 20%. As a substrate, 2,2,4,5,5-pentamethyl-3-thiazolidine, which was obtained with an enantiomeric excess (ee) of 99% in a biotransformation from the corresponding 3-thiazoline according to a recently developed protocol, was used. For the reductive desulfurization of this substrate leading to a sulfur-free secondary amine, in situ formed Ni2B turned out to be a suitable reducing reagent. However, when using lithium aluminum hydride as a reducing agent, β-aminothiol was obtained.

Effect of removal organic sulfur from coal macromolecular on the properties of high organic sulfur coal

The present work investigated the effect of efficient reduction desulfurization method (potassium tertbutoxide and hydrosilane system) on coal properties. Characteristic changes of high organic sulfur coal were studied utilizing TGA, FTIR and XPS after desulfurization. Results showed that more than 60% organic sulfur was removed, while the calorific value of coal samples decreased slightly and the aromatics in coal macromolecular structure were destroyed little. After treatment, formation of low molecular fragments from aliphatic carbons leaded to the increase of mass loss in TGA. XPS results revealed that some oxygen-containing groups were deoxidized after reduction treatment. The changes of coal properties were mainly attributed to the fracture of branch chain, the reduction of oxidized carbon atoms and side reactions during reduction desulfurization.

Extended Diethylglycine Homopeptides Formed by Desulfurization of Their Tetrahydrothiopyran Analogues.

Diethylglycine (Deg) homopeptides adopt the rare 2.05-helical conformation, the longest three-dimensional structure that a peptide of a given sequence can adopt. Despite this unique conformational feature, Deg is rarely used in peptide design because of its poor reactivity. In this paper, we show that reductive desulfurization of oligomers formed from more reactive tetrahydrothiopyran-containing precursors provides a practical way to build the longest Deg homopeptides so far made, and we detail some conformational studies of the Deg oligomers and their heterocyclic precursors.

Reductive Desulfuration as an Important Tool in Detection of Small Molecule Modifications to Payload of Antibody Drug Conjugates.

A high resolution accurate mass LC-MS method was developed to facilitate the characterization of a subset of antibody drug conjugate (ADC) biotherapeutics, where the payload is linked to the antibody by a thioether bond. Desulfuration of the thioether linker was optimized for release of the payload to take advantage of the high resolution and high mass accuracy of the Orbitrap to characterize metabolism of the payload. Two model ADCs, trastuzumab emtansine (T-DM1) and SigmaMAb dansyl-cadavarine-SMCC (SigmaMAb ADC mimic) were selected for optimization of the desulfuration reaction as a function of reaction time, pH, organic solvent, and chaotropic reagents (urea, guanidine HCl) by monitoring the yield of released desulfurated DM1 from T-DM1 and desulfurated dansyl-cadaverine-SMCC from SigmaMAb ADC mimic, respectively. The optimized desulfuration technique was successfully applied to enable characterization of the ADC following its incubation in hepatocytes, liver microsomes, and buffers, as illustrated by the identification of a hydrolyzed thiosuccinimide ring of SigmaMAb ADC mimic following incubation in buffer for 48 h. The results from this study demonstrate that the chemical cleavage of thioether bond by desulfuration is simple, efficient, and specific. This technique is useful in characterization of metabolism on the payload of ADC to provide guidance for improvement of its biopharmaceutical profile. This is the first report on characterization of modification to payload of ADC following desulfuration.

Dithiane-directed Rh(iii)-catalyzed amidation of unactivated C(sp3)-H bonds.

An oxidant-free Rh(iii)-catalyzed direct amidation of alkyl dithianes via C(sp3)-H bond activation utilizing diverse and robust dioxazolone reagents is reported. The reaction hinges on use of a Cp*Rh(iii) complex in combination with an essential amino-carboxylate additive to generate usefully protected 1,3-aminoaldehyde derivatives. The scalability of the reaction was demonstrated as was a series of downstream product functionalizations, including dithiane deprotection, anion alkylation and reductive desulfurization, highlighting the general applicability of this transformation in the synthesis of novel scaffolds and building blocks.

Super electron donor-mediated reductive desulfurization reactions.

The desulfurization of thioacetals and thioethers by a pyridine-derived electron donor is described. This methodology provides efficient access to the reduced products in high yields and does not require the use of transition-metals, elemental alkali-metals, or hydrogen atom donors.

A Traceless Tether Strategy for Achieving Formal Intermolecular Hexadehydro-Diels-Alder Reactions.

A synthetic strategy formally equivalent to an intermolecular hexadehydro-Diels-Alder (HDDA) reaction is described. Sulfur-based linkers were designed and constructed by joining terminal alkynes or diynes using alkyne thiolate chemistry. The resulting tetraynes and triynes successfully underwent HDDA cyclization and benzyne trapping. Linker removal by reductive desulfurization was uneventful. The strategy was also found suitable for the tetradehydro-Diels-Alder (TDDA) reaction.

Feasibility study of reduction removal of thiophene sulfur in coal

The present work investigated an effective reductive desulfurization method for thiophene sulfur in high organic sulfur coal utilizing the potassium tert-butoxide/hydrosilane. Maximum decreases of 65.8% and 64.2% in organic sulfur for Xinyu coal and Guxian raw coals were, respectively obtained under the optimized conditions of the molar ratio of reductive assistant to sulfur of coal (15), treatment time (80 min), temperature (215 °C). According to the results of XPS, more than 80% mercaptan, sulfoether and thiophene on the raw coals surface were removed without destroying the macromolecular structure of coal. Sulfur on treated coal surface samples mainly existed in the form of sulfonate and sulfone due to the hydrolysis and oxidation of intermediate products generated in the reduction desulfurization reaction. These findings confirmed the possibility of effective removal for thiophene sulfur in coal utilizing the reductive system, which could give a reference for thiophene sulfur removal of high organic sulfur coal.

Thioether macrocycles of the microbisporicins via reductive desulfurization

The microbisporicins are the most potent lantibiotics isolated to-date. Cyclic tetra-, hexa- and octapeptides, inspired by this family of antimicrobial agents, have been synthesized from linear peptides. Generalized reaction conditions are reported for the two-step conversion of linear peptides to thioether macrocycles: formation of a disulfide followed by reductive desulfurization. 1H NMR analysis of the reduction reaction mixture indicated the intermediacy of a dehydroalanine when excess hexamethylphosphorus triamide (HMPT) was employed for the reduction. Maintaining a stoichiometric amount of HMPT, in dilute methanolic solution, gave the corresponding thioethers, retaining stereochemical integrity.