Determination of xanthates as Cu(II) complexes by high-performance liquid chromatography – Inductively coupled plasma tandem mass spectrometry

The present study provides a novel, selective analysis method for the determination of low xanthate concentrations. The rising concern over the environmental effects of xanthates demands the development of analysis methods which this study answers. Complex formation in aqueous solution between xanthates and an excess of Co(II), Ni(II), Pb(II), Cd(II), Cu(II), and Zn(II) ions was utilized to selectively determine xanthates by high-performance liquid chromatography–inductively coupled plasma tandem mass spectrometry for the first time. The complexes that were formed were extracted to ethyl acetate using liquid–liquid extraction and separated by high-performance liquid chromatography technique before the quantitative determination of metal ions and sulfur in the xanthate complexes. Good separation and high measurement sensitivity were achieved using Cu(II) as the complex metal ion. The analysis method was optimized for the determination of sodium isopropyl xanthate and sodium isobutyl xanthate with detection limits of 24.7 and 13.3 μg/L, respectively. With a linear calibration range of 0.1–15 mg/L and a total analysis time of 4–5 min, the present method is a fast and sensitive option for selective xanthate determination.     

Adsorption study of xanthates on PbSO<Subscript>4</Subscript> by titration microcalorimetry

Isoperibol (pseudo-adiabatic) titration microcalorimetry was used to study the adsorption of various xanthates [CH₃(CH₂)_nOCS₂^?] at the PbSO₄/aqueous solution interface. The effect of the xanthate alkyl chain length (1n–3n) on the adsorption heat was evaluated. Xanthate adsorption isotherms were also determined. Furthermore, the amount of SO₄ into the aqueous solution was quantified to correlate it with the xanthate uptake by PbSO₄. The adsorption isotherms and the adsorption heat of the xanthates showed two steps. The first step occurred within a sub-monolayer xanthate coverage and was attributed to chemisorption of the xanthates exchanging surface hydroxyls to form CH₃(CH₂)_nOCS₂Pb. Lead xanthate (CH₃(CH₂)_nOCS₂)₂Pb multilayers formed in the second step, which was attributed to an ionic exchange chemical reaction between the xanthates and PbSO₄(aq). In the chemisorption step, the heat was found to be independent of the xanthate alkyl chain length and to linearly decrease in magnitude with the xanthate adsorption. In the multilayer formation step, the magnitude of the integral heat increased with the chain length of the xanthate. Heat contributions due to both the alkyl chain length and the interaction between the xanthate polar group and PbSO₄(aq) for the formation of lead xanthates are presented. Raman spectroscopy was used to characterize the lead xanthate multilayers on PbSO₄.     

Vibrational analysis of alkyl xanthates

Rotational isomers are indicated in the Raman spectra of sodium ethyl and other xanthates. Vibrational bands useful for characterizing xanthate solids and aqueous solutions are given. Vibrational analyses are reported for sodium ethyl xanthate, trans and gauche forms, and the methyl and isopropyl analogs using a Cartesian coordinate force field derived from ab initio molecular orbital calculations.     

A convergent, modular access to complex amines

Various xanthates can be added to N-vinyl phthalimide with little formation of oligomers, if the xanthate is used in excess and the medium slightly diluted. The adduct xanthates thus obtained can in turn undergo radical additions to numerous olefins, providing a convergent and modular access to densely functionalized amines.     

Mechanism of antioxidant action. Transformation involved in the antioxidant function of nickel dithiolates—2

The initial transformation products from nickel dialkyl dithiophosphates and nickel alkyl xanthates have been identified by spectrophotometric and kinetic methods. A common mechanism of action is involved for both nickel complexes and the distribution of products from complexes during their reaction with hydroperoxides suggests a greater contribution from an ionic mechanism in the case of dithiophosphate. Nickel dialkyl dithiophosphate is more stable to u.v. light than nickel alkyl xanthate and its reaction with tert. butyl hydroperoxide in the presence and absence of light is 7–8 times faster than that of the xanthate.     

A New Radical Allylation Reaction of Dithiocarbonates

A radical allylation reaction without tin: The xanthate group in aliphatic xanthates can be replaced by an allyl unit [Eq. (a)]. This radical chain reaction is propagated by ethyl radicals generated by extrusion of sulfur dioxide from ethanesulfonyl radicals, which are themselves derived from allyl ethyl sulfone.     

A practical variation on the Leuckart reaction

S-Aryldiazo xanthates, derived from the corresponding diazonium salts by reaction with potassium O-ethyl xanthate, undergo a radical chain reaction with loss of nitrogen; the intermediate aromatic radical can be captured by an internal olefin to give bicyclic xanthates in good overall yield.     

Phosphonate‐terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end‐capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate‐containing xanthate. Low‐PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Generation and intermolecular capture of cyclopropylacyl radicals

[reaction: see text] Cyclopropylacyl radicals derived from S-cyclopropylacyl xanthates (dithiocarbonates) undergo intermolecular additions to olefins without loss of CO or ring opening. In the presence of a phenyl ring on carbon C-1 of the cyclopropane ring, loss can be made to occur in the absence of an olefinic trap. The adducts from the cyclopropylacyl radical additions are easily converted into enones by base-induced beta-elimination of the xanthate group.     

Photochemical and thermal transformations of carboxylic dithiocarbamic anhydrides and acyl xanthates

The reaction of diphenylchloroacetyl chloride with different dithiocarbamates gave the corresponding dithiocarbamic anhydrides. Under analogous conditions, dithiocarbamyl phenylacetic acids and dithiocarbamyl acetic acids were formed from the reaction of dithiocarbamates with phenylchloroacetyl chloride and chloroacetyl chloride, respectively. O-Ethyl S-acyl xanthates were formed from the reaction of potassium O-ethyl xanthate with diphenylacetyl chloride, diphenylchloroacetyl chloride, cyclopentylphenylacetyl chloride and triphenylacetyl chloride. Photolysis of dithiocarbamic anhydrides gave a mixture of products consisting of 1,2-dichlorotetraphenylethane, carbon monoxide and the corresponding thiocarbamoyl sulfides. Acyl xanthates, on the other hand, gave carbon monoxide and the corresponding substituted ethane derivatives. When dithiocarbamic anhydrides were refluxed in hydroxylic solvents such as methanol, ethanol and n-propanol, the corresponding dithiocarbamyl acetates were formed. Thermal decomposition of acyl xanthates gave carbon disulfide and the corresponding esters.     

Nonaqueous redox determination of xanthates and organotrithiocarbonates with copper (II) nitrate in acetonitrile

N, N'-Diphenylbenzidine has been employed as an indicator in the titrations of xanthates and organotrithiocarbonates with copper(II) nitrate in acetonitrile medium. The color-changes from light yellow to blue in case of xanthates and red to blue in case of trithiocarbonates at the endpoints are very sharp. The compounds have also been titrated potentiometrically with copper(II) nitrate in acetonitrile using a bright platinum wire indicator electrode and a modified calomel or antimony electrode as reference electrode. The oxidation of xanthates and trithiocarbonates has been found to proceed in two stages. The first stage corresponds to the formation of dixanthogen and cuprous xanthate in case of xanthate and bis (alkyl/aryl mercaptothiocarbonyl) disulfide and cuprous trithiocarbonate in case of trithiocarbonates. The second stage corresponds to the oxidation of cuprous xanthate or cuprous trithiocarbonate. The proposed methods are simple, accurate, reliable, and widely applicable.     

Intramolecular ring opening of a 2,3-epoxy alcohol by a xanthate anionic center; stereospecific preparation of 2-mercapto-1,3-diol units

Stereospecific ring openings of optically active 2,3-epoxy alcohols were performed by the reaction of 1 , 3 , 5 , and 7 with carbon disulfide and sodium hydride to give the five-membered xanthates 2 , 4 , 6 , and 8 . Both enantiomers of 2-mercapto-1,3-diol triacetates, 11 and 14 , were derived from 4 and 6 , respectively. The ring opening reaction proceeded at −78°C to −30°C, and the yields were around 80%. However, at a higher temperature between 0°C to room temperature, a complicated reaction took place and led to the formation of two isomers of the cyclic thiol carbonates 15 and 16 from 1 or 5 . These processes were also stereospecific, and mechanisms have been proposed. In the case of the 3,4-epoxy alcohol 20 , the epoxide ring opening gave the six-membered xanthate 21 stereospecifically.     

A Novel Method for Analysis of Xanthate Group Distribution in Viscoses

Analytical monitoring of xanthation in the viscose process along with xanthate group analysis in the viscose material is a long-debated problem in cellulose chemistry. The task is rendered extremely intricate by the lability of the starting material and the harshness of the reaction medium, which adds to a lack of suitable analytical approaches. In a four-years' endeavor in our lab, a method is being developed which allows to analyze the distribution of xanthate groups in viscoses relative to the anhydroglucose units and along the cellulose chain. In a first step the xanthate groups are stabilized by alkylation, which was optimized towards quantitative conversion. In a second step, the remaining free hydroxyl groups are protected by carbanilation, followed by selective removal of the stabilized xanthate groups. Steps two and three thus generate an inverse image of the initial xanthate pattern. In the forth and fifth step, the liberated hydroxyl groups are methylated, and the carbanilates are removed, so that in the overall process the xanthates were replaced by methyl groups. All reaction steps have been comprehensively tested with regard to completeness of conversion and orthogonality of the protecting groups.     

Determination of the xanthate group distribution on viscose by liquid-state <Superscript>1</Superscript>H NMR spectroscopy

An analytical method for determination of the xanthate group distribution on viscoses based on liquid-state NMR spectroscopy was developed. Sample preparation involves stabilization of the xanthate group by allylation followed by derivatization of the remaining free hydroxyl groups at the glucose unit. The method was applied for studying (1) the γ-value (number of xanthate groups per 100 glucose units) of viscose, (2) the distribution of the xanthate groups on the anhydroglucose unit (AGU), and (3) changes of the xanthate group distribution during ripening. Results of the γ-value determination are well comparable with reference methods. Elucidation of the xanthate group distribution on the AGU gives the percentage at the C-6 position and a cumulative share of the positions C-2 and C-3. During ripening, xanthate groups at C-2 and C-3 degrade first, while xanthates at C-6 decompose at a slower rate.     

beta-Nitro xanthates as olefin precursors

[reaction: see text] Potassium O-ethyl xanthate readily adds to alpha,beta-unsaturated nitro compounds to give stable beta-nitro xanthates, which undergo tin-free elimination to form olefins in good yield and good E selectivity upon simple heating with lauroyl peroxide in refluxing 1,2-dichloroethane.     

Photochemistry of S-phenacyl xanthates

Various synthetically readily accessible S-phenacyl xanthates are shown to undergo photoinitiated homolytic scission of the C-S bond in the primary step. The resultant fragments, phenacyl and xanthic acid radicals, recombine to form symmetrical 1,4-diketones and xanthogen disulfides, respectively, in high to moderate chemical yields in chemically inert solvents. They can also be efficiently trapped by a hydrogen-atom-donating solvent to give acetophenone and xanthic acid derivatives. The latter compound is in situ thermally converted to the corresponding alcohol in high chemical yields. S-Phenacyl xanthates could thus be utilized as synthetic precursors to the above-mentioned compounds or as photoremovable protecting groups for alcohols in which the xanthate moiety represents a photolabile linker. The photochemically released phenacyl radical fragments efficiently but reversibly add to the thiocarbonyl group of the parent xanthate molecule. The kinetics of this degenerative reversible addition-fragmentation transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) mechanism was studied using laser flash photolysis (LFP) and density functional theory (DFT) calculations. The rate constants of the RAFT addition step, k(add) ～ 7 × 10(8) M(-1) s(-1), and phenacyl radical addition to a double bond of 1,1-diphenylethylene, k(add) ～ 10(8) M(-1) s(-1), in acetonitrile were experimentally determined by LFP. In addition, photoinitiation of the methyl methacrylate polymerization by S-phenacyl xanthate is demonstrated. The polydispersity index of the resulting poly(methyl methacrylate) was found to be ～1.4. We conclude that S-phenacyl xanthates can serve simultaneously as photoinitiators as well as RAFT/MADIX agents in polymerization reactions.     

One‐Step Double Covalent Functionalization of Reduced Graphene Oxide with Xanthates and Peroxides

Radical functionalization of reduced graphene oxide has been achieved by reaction with a xanthate in the presence of peroxide as a radical initiator. X‐ray photoelectron spectroscopy, bulk elemental analyses, and thermogravimetric analyses showed that the xanthate grafting is covalent and efficient. The synthesis and use of seven xanthates and three peroxides showed that the highest grafting yield is obtained when xanthate and peroxide are introduced in stoichiometric amounts. It also revealed that the peroxide used as radical initiator is grafted at the graphenic surface during the functionalization. The method presented in this contribution therefore allows bifunctionalized reduced graphene oxide samples to be easily obtained in one single step. This method leads to undamaged graphene sheets with higher dispersibility than the pristine sample.     

Determination of sulphur functions with N-iodosuccinimide

Titrimetric determination of thioureas, thiols, xanthates and dithiocarbamates with N-iodosuccinimide (NIS) is described. The method for xanthate can be applied to carbon disulphide (converted into xanthate with potassium ethoxide). Acidic and non-aqueous solutions of the oxidizing agent are stable. The procedures are rapid and accurate to 0.1% with a precision of 0.2%. Hydrogen sulphide and thiocarbonyl compounds interfere. The behaviour of N-bromosuccinimide and NIS with thiols in aqueous medium is compared. It is shown that iodine is the oxidizing species in both cases. The limitations of iodine as a reagent for thiol determination are discussed. Cysteine, which cannot be determined with iodine, can be determined with NIS. The role of methanol in non-aqueous determination of thiols is discussed. Methanol accelerates the oxidation, which is otherwise slow in acetonitrile medium.     

Modular approach to saturated and α,β-unsaturated ketones

2-Fluoro-6-pyridinyloxy derivatives of 2-ethoxyvinyl carbinols react with radicals derived from xanthates by an addition-fragmentation pathway to give highly functionalized ketones after acid hydrolysis. 1,4-Diketones are readily accessible by this approach. α,β-Unsaturated ketones can be obtained by starting with geminal acetoxy xanthates prepared by addition of a simpler xanthate to vinyl acetate.     

Xanthates derived from 1,3-dithiane and its monosulfoxide; one-carbon radical equivalents

The behaviour and synthetic scope of the C-2 centred radicals derived from 1,3-dithiane and 1,3-dithiane 1-oxide have been studied. Both radicals are available from the corresponding xanthates and have proved suitable substrates for the xanthate transfer reaction. However, the synthetic scope of the former is severely limited by the fact that it does not add to unactivated olefins. The latter on the other hand is a more promising radical precursor and undergoes smooth radical addition to a wide range of alkenes. Furthermore, subsequent transformations of some of the radical adducts confirm its utility as a synthetic equivalent of both the methyl and the formyl radical.