Reaction Of Xanthate Research Articles

Simple Synthesis of 1,2-Dideoxy-2-Vinyl Carbohydrates by Tin-Free Radical Reactions of Xanthates.

Vinyl-substituted carbohydrates have been synthesized from glycals derived from hexoses and pentoses. Key step is the radical reaction of xanthates in the presence of triethylborane, a non-toxic reagent. The mechanism has been investigated by isolation of various side products, which speak for a reversibility of the cyclopropylmethyl radical ring-opening. Compared to reactions with tributyltin hydride, higher regioselectivities in favor of the 2-vinyl-substituted sugars have been obtained. Yields are slightly lower with triethylborane, but all products have been isolated in analytically pure form. The new reaction is applicable to benzyl- and silyl-protected carbohydrates, which makes free sugars accessible as well. Overall, more than 15 1,2-dideoxy-2-vinyl carbohydrates have been synthesized from simple precursors in only few steps.

SYNTHESIS AND CHEMICAL MODIFICATION OF NEW HYDROXYBEZALDEHYDE DERIVATIVES

A high pharmacological ability of aromatic benzaldehydes makes them important intermediates for the synthesis of medicinal preparations, such as anticancer, bactericidal, antifungal, and herbicidal drugs. The purpose of this work is the synthesis of biologically active compounds, based on 4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde and the establishment of the structure of the synthesized compounds. Results and discussion. New carbonodithioates, based on O-aromatic systems have been synthesized by the interaction of 4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde with carbon disulfide in the presence of sodium hydroxide in ethanol at the room temperature. As a result of the reactions, sodium O-(4-formylphenyl)carbodithioate (86 %) and sodium O-(4-formyl-2-methoxyphenyl)carbodithioate (80%) have been isolated. The interaction of sodium xanthates with acid chlorides (4-methoxy-, 4-nitro-, 2,4-dinitrobenzoic) in chloroform has led to the formation of aromatic thioanhydrides of carbonodithioic acids in 55-80 % yields. The reactivity of hydroxybenzaldehydes and their dithiocarboxylic derivatives has been studied in the propargylation reaction. Propargylation of 4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde has been carried out with propargyl bromide in the presence of a 3-fold excess of K2CO3 in acetone at the temperature of 60°C. The propargylation reaction of sodium xanthate has been carried out with propargyl bromide in acetone at the room temperature. Conclusion. As a result of the reactions, carbonodithioates, thioanhydrides, acetylenic and thioacetylenic ethers have been synthesized based, on O-aromatic systems (4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde). The structure of the synthesized compounds has been established on the basis of elemental analysis data, IR spectra, 1Н and 13С NMR spectroscopy.

Contribution of ammonia in xanthates adsorption onto copper oxide mineral surface in high-alkaline solution

Ammonia is a useful modifier for enhancing surface sulfurization in copper oxide ore flotation using xanthate as a collector. However, its potential role in the reaction of sulfhydryl collector with sulfurized copper oxide mineral in a complex pulp has been neglected. This work investigates the contribution of ammonia to xanthate adsorption on the sulfurized malachite surface, independent of its effect on sulfurization. Zeta potential measurements indicate that NH3·H2O increases the surface potential of malachite and enhances the proximity of xanthate to the malachite surface in a strong-alkaline solution. Adsorption tests and time-of-flight secondary ion mass spectrometry analysis demonstrate that NH3·H2O can increase the xanthate adsorption density. Spectroscopic analysis reveals copper(I) xanthate and dixanthogen as the primary xanthate products, with their quantities increasing upon NH3·H2O treatment. Thermodynamic analysis of the reaction of malachite, HS−, and xanthate to form copper(I) xanthate and dixanthogen shows that NH3·H2O treatment enhances the stability of the reaction compared to its absence. Thus, NH3·H2O treatment increased the recovery of sulfurized malachite by over 10%. This study offers a comprehensive understanding of ammonia modification for enhancing sulfurization–xanthate flotation of copper oxide minerals and provides a scientific basis for developing high-efficiency collectors.

Synthesis, characterization, and humidity-responsiveness of guar gum xanthate and its nanocomposite with copper sulfide covellite

A novel conjugation of guar gum with xanthate groups via facile aqueous xanthation reaction has been reported. Density of grafted xanthate on guar gum product (GG-X) is as high as 4.4%, thus GG-X is conceivably characterized and confirmed by various spectrometric, electrochemical, thermogravimetric, and microscopic methods. Complexation of GG-X with numerous borderline and soft metal ions (e.g. Fe2+, Co2+, Ni2+, Cu2+, Pb2+, Pt2+ and Cd2+) yields hydrophilic gel-like materials and shows good agreement with hard and soft acid and base (HSAB) theory. This indicates tremendous potential of GG-X in metal ion extraction, removal and hydrogel cross-linking. GG-X is also employed to formulate an aqueous colloidal dispersion of copper sulfide covellite (GG-X/CuS) nanocomposites. GG-X therefore behaves as a surfactant, allowing formation of electronically conductive nanocomposites. XRD indicates apparent beneficial effects of GG-X in the synthesis of CuS with a crystallite size of 15.6 nm. This novel nanocomposite is a promising material for humidity sensing, showing reversible linear responses to relative humidity changes within 10 to 80% range. The interaction between GG-X and water might cause changes in electrical permittivity of GG-X/CuS nanocomposite and/or electrical hopping conductivity between CuS nanoparticles.

Xanthate modified magnetic activated carbon for efficient removal of cationic dyes and tetracycline hydrochloride from aqueous solutions

The removal of cationic dyes and hydrochloride tetracycline from aqueous solutions has attracted more attention. In this paper, magnetic activated carbon (mAC) was first prepared by one-step co-precipitation method, and xanthate was grafted onto the surface of magnetic activated carbon by xanthation reaction, and the x-mAC functionalized magnetic activated carbon material (x-mAC) was successfully synthesized. x-mAC is used to remove cationic dyes and tetracycline hydrochloride. The physical and chemical properties of AC, mAC and x-mAC were characterized by FTIR, SEM, TEM, XRD, BET and VSM. It is found that x-mAC has good removal ability on malachite green (MG), methylene blue (MB), crystal violet (CV) and tetracycline hydrochloride (TC). The adsorption process of x-mAC on cationic dyes and tetracycline hydrochloride obeys Langmuir adsorption model and pseudo-second-order kinetic model. The kinetic data has a good correlation with the pseudo-second-order equation. The Langmuir and Freundlich models are suitable for isotherm data. The calculated adsorption capacities of MG, MB, CV and TC are 595.24 mg/g, 314.3 mg/g, 394.14 mg/g and 210.94 mg/g, respectively. The results of thermodynamic research (△G <0, △H> 0, △S> 0) showed that the adsorption process was endothermic and spontaneous proceeding. The adsorption-desorption process went through five cycles. After five cycles, the removal rates of MG, MB, CV and TC remained above 81.40 %, 91.78 %, 93.69 % and 91.29 %, respectively. The results showed that due to the good adsorption performance and simple preparation process, x-mAC has potential application prospects in the field of wastewater treatment.

The reaction of potassium xanthates with five-membered cyclic carbonates: selectivity of the underlying cascade reactions and mechanistic insights.

In this paper we describe the reaction between various potassium xanthates (potassium O-methyl xanthate, potassium O-isobutyl xanthate, xanthate functionalized MPEGs, etc.) and common five-membered cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). The reaction was carried out under catalyst-free conditions. Intensive evolution of both CO2 and COS and the simultaneous formation of a rich precipitate were found to be the characteristic features of the studied reaction. It was determined that the precipitate consists of various alkoxides, including potassium ethane-1,2-bis(olate) (EC-based reaction) and potassium propane-1,2-bis(olate) (PC-based reaction) and alkoxide-terminated sulfides. It was also demonstrated that the resulting liquid phase (the mother liquor) contains polyalkylene sulfides whose number average molecular weight (Mn) was found to be in the range 400–550 Da and 300–400 Da for EC- and PC-based oligomers, respectively. Further studies revealed that the distribution between major products varies considerably with variation in the parameters of the reaction. Thus, by applying reduced pressure conditions and a temperature equal to 90 °C, up to 95% selectivity towards the formation of alkoxide-terminated sulfide (e.g., potassium 1,1′-thiobis(propan-2-olate)) was achieved. On the other hand, selectivity towards alkoxide formation equal to 98% was achieved for the reactions carried out in the presence of water. As a general trend, it was also established that a shift in balance between products towards the formation of sulfur-containing products (sulfides) occurs with an appropriate increase in the temperature of the reaction. Based on the obtained experimental data supplemented with quantum-chemical calculations (NBO analysis and scanning of the potential energy surface), the mechanisms of the cascade reactions underlying the formation of key intermediates and final products were also proposed.

Microwave-assisted Tertiary Carbon Radical Reaction for Construction of Quaternary Carbon Center

Microwave-assisted tertiary carbon radical reaction was developed. The reaction of tertiary xanthates with electron deficient alkenes was prompted by microwave irradiation, and various coupling products possessing quaternary carbon centers were obtained in good yields. The reaction was conducted under simple and common radical condition except for microwave irradiation, and the reaction completed within 5 min.

Mechanism of xanthation reaction in viscose process

Xanthation reaction in viscose process is heterogeneous reaction (gaseous CS2-wet alkaline cellulose) complicated with side reactions. Commercial requirement of CS2 in viscose process is 32–34%, which is significantly higher than the stoichiometric requirement (23.5% w/w of the cellulose) due to formation of byproducts. Detailed xanthation reaction kinetics study was performed to understand the xanthate and by-products formation mechanism along with effect of mass transfer and its possible impact on CS2 consumption. Heterogeneous nature of the xanthation reaction offers significant mass transfer resistance and was hypothesized to be driven by CS2 partitioning into wet alkali cellulose and its unstable complex (DTC—dithiocarbonate) formation with alkali. Xanthation reaction mechanism in the form of physico-chemical process steps has been proposed with experimental justification.

Uptake of trivalent chromium from aqueous solutions by xanthate pine bark: Characterization, batch and column studies

Abstract In this study, the performance of chemically modified pine bark for removal of Cr(III) from solutions was investigated. Initially, several chemicals were tested (NaOH, C5H9NO4, H3PO2 and CS2). The xanthate pine bark (XPB) obtained with CS2, was screened as the best adsorbent and thus, it was characterized in respect to morphological and textural properties. Sulfur groups after xanthation reaction were identified on XPB by FTIR and EDS spectroscopies. Equilibrium isotherm and kinetics were determined. The equilibrium data were well described by the Langmuir isotherm allowing to calculate the maximum adsorption capacity (56.5 mg/g). The kinetics is fast and follows a pseudo-second order model. Furthermore, an ion-exchange sorption mechanism between Cr(III) and Na+ was proposed. Among the desorbing agents tested, the best results were achieved with 2.0 M H2SO4. Moreover, in the column tests, a reduction on the breakthrough time and the stoichiometric time from 36.5 and 22.8%, respectively, was observed, when the feed concentration increased from 230 to 500 mg/L. The breakthrough curves were well modeled by Bohard-Adams, Thomas or Yoon-Nelson equations. Globally, XPB revealed to be a promising adsorbent for uptake Cr(III). The scale-up design and the economic assessment indicated potential applicability for the treatment of real effluents.

Determination and application of the solubility product of metal xanthate in mineral flotation and heavy metal removal in wastewater treatment

The reactions of ethyl and butyl xanthates with Pb2+, Cd2+ and Zn2+ were investigated to determine the solubility products of metal xanthates using UV/Visible spectroscopic method and software WinSGW and MEDUSA. The effects of solution pH, chemical reactions and ionic strength on the determination of solubility products of metal xanthates were investigated. For a given metal, the solubility product of metal xanthate was found to decrease with the increase of the carbon chain length of the alkyl group. The determined solubility products of metal xanthates were in the order of ZnX2 > CdX2 > PbX2 and M(EX)2 > M(BX)2. The accurate Ksp constant allowed more accurate calculation of the minimal concentration of xanthate ions for treating heavy metal-containing waste water to selectively separate metal ions, avoiding the potential presence of toxic xanthates in the treated water.

Effective production of sodium isobutyl xanthate using carbon disulfide as a solvent: Reaction kinetics, calorimetry and scale-up

Alkyl xanthates are by far the most widely used collectors in the froth flotation beneficiation of base metal sulfide and precious metal ores. However, the commercial xanthate production process suffers from low yield, low productivity, poor containment and environmental pollution. To address these issues, an effective method was developed for the synthesis of xanthates using carbon disulfide as both a reactant and the solvent. This study involved the optimization of various process parameters, including solvent dosage, temperature, caustic alkali particle size, and agitation speed, to intensify the conversion of sodium isobutyl xanthate (SIBX) and elucidate the reaction kinetics. The results indicated that carbon disulfide leads to a higher yield and better purity than solvents such as dichloromethane, petroleum ether, acetone, and water. Moreover, the addition of solvent allows the synthesis of high-purity xanthates by employing commercial grainy/sheet caustic soda as the raw material without further pulverization. The rate of the xanthation reaction was controlled by the rate of diffusion through the product layer, and the apparent activation energy was calculated to be 15 kJ∙mol−1. In addition, the thermal behavior of xanthate synthesis in a medium was monitored in a 2 L reaction calorimeter (RC1e) under the optimal conditions. Finally, a pilot-plant process was conducted in a 4000 L stainless-steel-jacketed reactor. The results demonstrated that xanthate production using excess carbon disulfide as a self-solvent gave excellent yield (>95%) and purity (>90%), whereas the kneader approach provided SIBX in only a 91% yield and 84% purity. Furthermore, this technology has widespread adaptability for the preparation of C2 to C8 xanthates. Compared with the traditional kneader approach, this new synthesis technology completely eliminates the required pulverization of caustic alkali, intensifies mass and heat transfer via the solvent, raises the productivity and improves the manufacturing environment, offering an effective and promising approach for the clean production of xanthates.

Radical-Mediated Reactions of α-Bromo Aluminium Thioacetals, α-Bromothioesters, and Xanthates for Thiolactone Synthesis.

Thiolactones have attracted considerable attention in recent years as bioactive natural products, lead compounds for drug discovery, molecular probes, and reagents for polymerisation. We have investigated radical-mediated C-C bond forming reactions as a strategy for thiolactone synthesis. Cyclisation of an α-bromo aluminium thioacetal was investigated under radical conditions. It was found that at low temperature, a radical fragmentation and rearrangement process occurs. A putative reaction mechanism involving a previously unreported aluminium templated thiol-ene step for the rearrangement process is presented. Cyclisation reactions of α-bromo thioesters and α-xanthate thioesters under radical mediated conditions furnished the desired thiolactones in moderate yields.

Radical Deuteration with D2O: Catalysis and Mechanistic Insights.

Selective incorporation of deuterium atoms into molecules is of high interest for labeling purposes and for optimizing properties of drug candidates. A mild and environmentally benign method for the deuteration of alkyl iodides via radical pathway using D2O as source of deuterium has been developed. The reaction is initiated and mediated by triethylborane in the presence of dodecanethiol as a catalyst. This method is compatible with a wide range of functional groups and provides the monodeuterated products in good yields and with a high level of deuterium incorporation. It opens promising opportunities for the development of enantioselective radical reactions. Moreover, a revision of the mechanism of the deoxygenation reaction of xanthates using R3B and water (Wood deoxygenation) is presented.

Dissolving pulp from bamboo-willow

The production of dissolving pulp from bamboo-willow (Salix salicaceae or Zhuliu in Chinese) was investigated. It is one of the new fast-growing tree species with strong cold resistance and can grow well in arid areas. Bamboo-willow chips were prehydrolyzed with phosphoric acid and subsequently pulped via the Kraft process. Phosphoric acid was used to dissolve hemicelluloses from bamboo-willow. The resulting brown stock was bleached using oxygen delignification (O), sodium hypochlorite (H), Peroxide (P) and acid (A). Kraft cooking and O–H–P bleaching effectively removed lignin from prehydrolyzed bamboo-willow. The acid post-treatment decreased the ash and ferric ion content in bamboo-willow dissolving pulp. The obtained bamboo-willow dissolving pulp contained low pentosan and high α-cellulose content, and the pulp had high reactivity. The final ash contents, ferric ion, pentosan and α-cellulose content as well as the degree of polymerization and brightness were 0.0950%, 14.7 mg/kg, 2.86%, 95.1%, 547, and 87.2% ISO, respectively. Reactivity is the most significant quality parameter of dissolving pulp and has a large effect on the xanthation reaction during viscose preparation. The reactivity of the obtained bamboo-willow dissolving pulp reached 5.90 s, which implies that the produced dissolving pulp can be used in rayon production.

Aminopyridine-Borane Complexes as Hydrogen Atom Donor Reagents: Reaction Mechanism and Substrate Selectivity.

Lewis base-borane complexes are shown to be potent hydrogen atom donors in radical chain reduction reactions. Results obtained in 1 H, 11 B, and 13 C NMR measurements and kinetic experiments support a complex reaction mechanism involving the parent borane as well as its initial reaction products as active hydrogen atom donors. Efficient reduction reactions of iodides, bromides, and xanthates in apolar solvents rely on initiator systems generating oxygen-centered radicals under thermal conditions and pyridine-borane complexes carrying solubilizing substituents. In contrast to tin hydride reagents, the pyridine-boranes reduce xanthates faster than the corresponding iodides.

Effect of the Utilization of Electron Beam Irradiation on the Reactivity of Bamboo Dissolving Pulp

Electron beam irradiation (EBI) was used to improve the reactivity of bamboo dissolving pulp. An EBI treatment with a dose lower than 10 kGy showed that the Fock reactivity of the dissolving pulp noticeably increased from 69.5% to 98.3% with negligible cellulose losses. However, when the irradiation dose was higher than 10 kGy, the Fock reactivity increased with an observable α-cellulose loss, which could result in the lower strength of end-products. The gradual increase of Fock reactivity has a good agreement with the reduction of the degree of polymerization (DP) of cellulose. This suggests that lowering the DP of cellulose could enhance cellulose reactivity. Later analyses confirmed that an EBI treatment creates fiber pores that facilitate a cellulose xanthation reaction. The EBI treatment could randomly destroy cellulose crystalline and amorphous regions. The results indicated that the reactivity improvement was due not only to the DP, but also due to the changes in the fiber morphology and cellulose structure caused by the EBI processing.

Extension to the Silyl-Tethered Radical Cyclization: Cyclohex-2-en-1-oxy Vinyl Silanes in Stereoselective Radical Addition/Cyclization Cascades.

A novel radical cascade reaction of xanthates with 1-[(vinyldimethylsilyl)oxy]cyclohex-2-enes is developed. Due to the steric and electronic differentiation of the two olefinic functions, exclusive regioselectivity and high stereoselectivity of the addition-cyclization are observed. Several methods for modification of both the silicon tether and the xanthate function are reported.

Pb(II) Removal Process in a Packed Column System with Xanthation-Modified Deoiled Allspice Husk

The present research dealt with lead removal using modified Pimenta dioica L. Merrill as biosorbent in a batch and in continuous flow column systems, respectively. The allspice husk residues were modified first with a treatment through the xanthation reaction. For the adsorption tests, the atomic adsorption spectrophotometry method was used to determine the lead concentrations in the liquid samples. In the kinetic batch study (10 mg of sorbent in 10 mL of 25 mg L−1 lead solution), the removal efficiency was 99% (adsorption capacity of 25.8 mg g−1). The kinetic data followed the pseudo-second-order model. The adsorption isotherm was fitted to the Freundlich model, where constants were Kf and 1/n (8.06 mg(1-1/n) g−1 L1/n and 0.52), corresponding to adsorption capacities of 8 and 62 mg g−1, at liquid equilibrium concentration of 1 and 50 mg L−1, respectively. In the continuous flow systems where lead solution of 50 mg L−1 was treated in 2 columns of 5 cm (4.45 g) and 10 cm (9.07 g) bed heights, the dynamic adsorption capacity obtained by fitting the Thomas model was 29.114 mg g−1 and 45.322 mg g−1, respectively.

ChemInform Abstract: Radical Solution to the Alkylation of the Highly Base‐Sensitive 1,1‐Dichloroacetone. Application to the Synthesis of Z‐Alkenoates and E,E‐Dienoates.

AbstractThe reaction of xanthate (I) and various alkenes can provide the access to functionalized gem‐α‐dichloroketones [e.g. (III)], which can be further derived to alkenoates [e.g. (VI) and (VIII)] and dienoates [e.g. (IX)].

Copper-Catalyzed Domino Synthesis of 2-Arylthiochromanones through Concomitant C-S Bond Formations Using Xanthate as Sulfur Source.

An efficient domino process for the synthesis of thioflavanones has been described using a copper catalyst without addition of any external ligand. A variety of thioflavanones have been synthesized from easily accessible 2'-iodochalcones or 2'-bromochalcones in excellent yield through in situ incorporation of sulfur using xanthate as an odorless sulfur source. This domino process proceeds through Cu-catalyzed C(aryl)-S bond formation by the coupling reaction of xanthate with 2'-halochalcones followed by C-S bond cleavage of thioester then S-C bond formation by intramolecular Michael addition.