Mercaptide Ion Research Articles

Mechanism study and determination kinetic of catalytic oxidation of mercaptans in Merox process

Sulfur-containing pollutants lead to reduced quality of end products and environmental problems. Mercaptans are one of those sulfur pollutants which not only are smelly and toxic but also have high corrosive property. Mercaptan catalytic oxidation is the most important method of oil production refining from mercaptan. Thus, cognition of the reaction kinetics and interrogation of effects of various factors on the process are of the most requirements of mercaptan removing units. Due to the inadequate efforts made on reaction kinetics determination of catalytic oxidation of light mercaptans available in liquefied petroleum gas (LPG), this study was done in this regards. First, rate-determining step (RDS) of reactions was determined by analyzing the experimental data obtained from the Merox unit. The experiments were carried out on a cobaltphthalocyanine liquid catalyst in a packed reactor. In order to better understand the process, design, and optimization, the kinetics were defined with respect to the limiting reaction. By investigating the effective parameters of the kinetics, it was determined that the mercaptide ion (RS-) confines the oxidation reaction rate and has the first order in the rate equation. Finally, optimal values were proposed for each of the parameters.

Kinetics of catalytic oxidation of sodium ethyl mercaptide

Catalytic oxidation of mercaptide is a significant way to eliminate waste emission of spent caustic and recycle the resource of caustic. However, the kinetics of mercaptide oxidation for spent caustic regeneration is still unclear, which hinders the reactor design. In this work, mechanism analyses and kinetics experiments were conducted to investigate the kinetics of homogeneous catalytic oxidation of sodium ethyl mercaptide. Ultraviolet visual spectra show that mercaptide ion is superior to oxygen molecule adsorbed on the catalyst, which is in accord with the simulations. Reaction mechanism of two-layer adsorption structure was proposed by density functional theory calculations. By applying the method of decoupling macroscopic kinetics and making pseudo-first-order fast reaction hypothesis, the rate expression of the intrinsic kinetics for the oxidation reaction of sodium ethyl mercaptide was proposed as -dCAdt=6.84×1010exp(-29584RT)CACB. A statistical test was carried out to verify the intrinsic kinetics data, showing that the kinetics data were overall reasonable.

Research on the MgO-supported solid-base catalysts aimed at the sweetening of hydrogenated gasoline

The gas–liquid–solid heterogeneous base-catalyzed oxidation of n-octane thiol and tert-butyl thiol by molecular oxygen was investigated. The activity and stability of MgO-supported NaOH and monometallic Cu, Ni as well as bimetallic Cu–Ni catalysts were studied. The catalysts were further characterized by XRD, FT-IR, XPS and EPR. Compared with commercial cobalt phthalocyanine catalyst (CoPc catalyst), the MgO-supported bimetallic Cu–Ni catalyst displayed an enhanced stability to the oxidation of iso-mercaptan, and the catalytic lifetime is 10h longer than that of CoPc catalyst. It is found that the superoxide anions result from defects and small crystalline size play an important role in conversion of the iso-mercaptans, the more the lattice distortion, the higher the amount of surface adsorbed oxygen, the better was the performance of the sweeten-catalyst. Moreover, compared with commercial CoPc catalyst, the NaOH-rich catalyst is more resistant to deactivation of the oxidation of long chain thiol, and the catalytic lifetime is 26h longer than that of CoPc catalyst. The superbasicity of the NaOH-rich catalyst is responsible for the formation of mercaptide ion, which is the rate-controlling step for the oxidation of long chain thiol. The mercaptans of different structures conform to different reaction mechanisms.

The catalytic action of triethylamine in the reaction of β-hydroxyethyl mercaptan with oxiranes

The formation of an interionically hydrogen-bonded complex during the reaction of triethylamine with β-hydroxyethyl mercaptan, the dissociation of the complex into ions, and the involvement of the mercaptide ion in epoxide ring opening are studied.

A substituent directed regioselective synthesis of aryl/pyronyl pendant unusual adipate and tetrahydronaphthalene

An efficient regioselective synthesis of pyronyl pendant ethyl methylthiocarbonylalkanoates 5 has been delineated from the base catalyzed reaction of suitably functionalized 2-pyranone 1 and 2-carbethoxycycloalkanones 2, 6 through successive substitution and regioselective ring opening by in situ generated mercaptide ion. To assess the effect of C-4 substituent on regioselectivity, reactions of 6-aryl-3-cyano-4-(piperidin-1-yl)-2-oxopyran 8 with 2-carbethoxycyclohexanone 6a and 2-carbethoxy-2-methylcyclohexanone 6b were carried out separately under analogous reaction conditions but the compounds isolated were identical and characterized as 4-aryl-8-methyl-2-piperidin-1-yl-5,6,7,8-tetrahydronaphthalene-1-carbonitriles 9. Ethyl 2-(5-amino-4′-bromo-4,6-dicyanobiphenyl-3-yl)-5-methylsulfanylcarbonylpentanoate 10 has also been prepared through base catalyzed ring transformation of ethyl 2-[6-(4-bromophenyl)-3-cyano-2-oxo-2 H-pyran-4-yl]-5-methylsulfanylcarbonylpentanoate 5d by malononitrile in DMF.

S-Allylmercaptoglutathione: the reaction product of allicin with glutathione possesses SH-modifying and antioxidant properties

The reaction between allicin (diallylthiosulfinate), the active component of garlic and reduced glutathione was investigated. The product of this reaction, mixed disulfide S-allylmercaptoglutathione (GSSA) was separated by high performance liquid chromatography and identified by 1H and 13C nuclear magnetic resonance and mass spectroscopy. The reaction is fast (with an apparent bimolecular reaction rate constant of 3.0 M −1 s −1). It is pH-dependent, which reveals a direct correlation to the actual concentration of mercaptide ion (GS −). Both GSSA and S-allylmercaptocysteine (prepared from allicin and cysteine) reacted with SH-containing enzymes, papain and alcohol dehydrogenase from Thermoanaerobium brockii yielding the corresponding S-allylmercapto proteins, and caused inactivation of the enzymes. The activity was restored with dithiothreitol or 2-mercaptoethanol. In addition, GSSA also exhibited high antioxidant properties. It showed significant inhibition of the reaction between OH radicals and the spin trap 5,5′-dimethyl-1-pyroline N-oxide in the Fenton system as well as in the UV photolysis of H 2O 2. In ex vivo experiments done with fetal brain slices under iron-induced oxidative stress, GSSA significantly lowered the production levels of lipid peroxides. The similar activity of GSSA and allicin as SH-modifiers and antioxidants suggests that the thioallyl moiety has a key role in the biological activity of allicin and its derivatives.

Covalent binding between bucillamine derivatives and human serum albumin.

To clarify the mechanism of covalent binding between human serum albumin (HSA) and drugs containing thiol groups, we studied the interactions between HSA and bucillamine (BA) and its derivatives. To determine the concentration of HSA-drug conjugate, we used columns of N-methylpyridium polymer cross-linked with ethylene glycol dimethacrylate (4VP-Me), and analyzed the reaction between HSA and BA derivatives kinetically. Following pseudo first-order reaction kinetics, the rate constants of reduction of non-mercaptoalbumin (HNA) to mercaptoalbumin (HMA) (ka) and formation of HSA-drug conjugate (kc) were determined. Formation of HSA-drug conjugate was observed only for drugs containing one thiol group. In compound IV, the plots of ka and kc against pH were found to be linear. The HSA-drug conjugate was affected by various factors such as pKa, pH, temparture and the microenviroment of Cys34. The increases in ka and kc against pH were mainly due to the increase in mercaptide ion concentration. Further, fatty acid affected the microenviroment of Cys34, which increased HSA-drug formation. Cys34 located in a crevice on the surface of the protein plays an important role on the formation of HSA-drug conjugate. These results may be useful for elucidating the reaction mechanisms between various proteins and thiol compounds.

Models for in Vivo Deiodination of 2-Iodohistidine

A variety of simple thiols fully deiodinate 2-iodohistidine within 24 h at 25°C (at pH 7.2; t1/2 = 23.5 min). Deiodination of 2,4-diiodoimidazoles occurs specifically at C-2. but at 16 therate for the 2-iodo compound, while 4-iodoimidazoles are completely stable. N-alkylation does not prevent deiodination but strong electronegative substituents at C-4 or C-5 do block the reaction. Bromoimidazoles are totally stable under the specified conditions. The proposed mechanism involves a nucleophilic attack by the soft mercaptide ion on the soft iodine in the protonated imidazole, with the imidazole ylid-carbene as the leaving group. This facile nonenzymatic delodination provides an explanation for the failure of 2-iodohistidine to maintain its strong antimalarial activity in owl monkeys beyond a 24-h period.

Kinetic characteristics of reactions of mercaptide ions of the ?-hydroxyethyl mercaptan-triethylamine system with olefin oxides at 15?45�C

The kinetics of the reaction of ethylene, propylene, and 1-butene oxides with β-hydroxyethyl mercaptan was studied in the presence of a triethylamine catalyst, and the rate constants of the attack of the β-hydroxyethyl mercaptide ion in the limiting step at the olefin oxide molecule were determined.

Chemistry of alkenyl azlactones. VII. Preparation and properties of multiazlactones derived from mercaptan‐functional compounds and oligomers

AbstractThe reaction of polymercaptans and 2‐alkenyl azlactones has been further investigated, and several new multiazlactones which are liquids at room temperature have been prepared and characterized. Michael addition yielding the multiazlactones was found to take place slowly in the absence of and rapidly in the presence of acid catalysts. If basic impurities capable of forming mercaptide ion were present, however, the reaction underwent a substantially different course producing primarily ring‐opened products. A source of these basic impurities was determined to be the method of preparation of the alkenyl azlactone itself. When the azlactone was prepared from its acyclic N‐substituted aminoacid precursor by cyclodehydration by use of ethyl chloroformate and triethylamine, a small amount of triethylamine remained that dramatically altered the course of reaction. Nonbasic cyclodehydration agents such as dicyclohexylcarbodiimide were effective at eliminating this side reaction, as well as was the practice of adding excess acid to the reaction system to neutralize the basic impurities.

Macroscopic and microscopic ionization constants of the thiol and amine groups in 1-methyl-4-mercaptopiperidine

The acid dissociation constants of 1-methyl-4-mercaptopiperidine (p K 1 = 9.51, p K 2 = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (p K A = 9.59) and 1-methyl-4-(methylthio)piperidine (p K B = 10.18) have been determined potentiometrically in 3 M sodium perchlorate (10% methanol) medium. The ultraviolet absorption of the mercaptide ion has been used to determine the relative proton affinity of the sulphur and nitrogen functions in 1-methyl-4-mercaptopiperidine under the same conditions, and its four microscopic constants (p K a = 9.49, p K b = 10.23, p K c = 11.34, p K d = 10.60) have been calculated; p K A has also been determined spectrophotometrically. From the results obtained, it can be concluded that the thiol group is more acidic than the amine group and that the Adams relation, K a + K b = K 1, holds very well when it is assumed that the spectrophotometric values for K a, and K b, can be replaced by K A and K B respectively.

Assay of the enzymatic hydrolysis of pantetheine

Four rapid, independent assays of enzymatic pantetheine hydrolysis are described and compared using an enzyme partially purified from pig kidney. Two assays detect specifically the hydrolysis products: cysteamine (2-aminoethanethiol) is measured by the absorbance of its fluoropyruvate adduct at 300 nm and pantothenate is measured by radioimmunoassay. Methods of [ 14C]pantethine synthesis are discussed and the labeled substrate employed in a third enzymatic assay. A fourth assay continuously monitors the absorbance of mercaptide ion at 240 nm. The mercaptide ion concentration increases proportionally with hydrolysis at a buffered pH because of a difference in p K(-SH) between pantetheine (9.9) and cysteamine (8.1) at 37°C. The enzyme shows a pH optimum of ca. 9 and an apparent K m of 20 μ m.

The Desulfurization of Diphenyl Disulfide with Triphenylphosphine

Abstract When diphenyl disulfide and triphenylphosphine are fused (neat) at 250–300°C in an inert atmosphere, diphenyl sulfide and triphenylphosphine sulfide are produced. This reaction has also been carried out under reflux in tetralin, M-Pyrol, tetradecane, and hexadecane. Probable mechanisms for the desulfurization involve nucleophilic attack of triphenylphosphine at sulfur to form a phosphonium mercaptide, followed by either nucleophilic attack of the mercaptide ion at the aromatic carbon atom bearing sulfur or formation of a phosphorane with subsequent intramolecular collapse to form products.

Sulfur base ligation to iron(II) and cobalt(II) porphyrins

Equilibrium constants for the binding of sulfur bases to cobalt(II) porphyrins were measured in toluene solution by a spectrophotometric method. The order of decreasing binding strength of sulfur ligands to cobalt(II) porphyrins was found to be mercaptide ions >> thioethers > mercaptans. It is suggested that a similar stability order of these sulfur ligands should exist towards iron(II) porphyrins, but formation constants could be obtained only for the mercaptide ions.

ChemInform Abstract: OLEFIN‐FORMING ELIMINATION INDUCED BY MERCAPTIDE IONS. VARIATION OF TRANSITION‐STATE CHARACTER AS INDICATED BY SUBSTITUENT EFFECTS ON RATE

Chemischer InformationsdienstVolume 10, Issue 35 Preparative Organic Chemistry ChemInform Abstract: OLEFIN-FORMING ELIMINATION INDUCED BY MERCAPTIDE IONS. VARIATION OF TRANSITION-STATE CHARACTER AS INDICATED BY SUBSTITUENT EFFECTS ON RATE J. F. BUNNETT, J. F. BUNNETTSearch for more papers by this authorS. SRIDHARAN, S. SRIDHARANSearch for more papers by this authorW. P. CAVIN, W. P. CAVINSearch for more papers by this author J. F. BUNNETT, J. F. BUNNETTSearch for more papers by this authorS. SRIDHARAN, S. SRIDHARANSearch for more papers by this authorW. P. CAVIN, W. P. CAVINSearch for more papers by this author First published: August 28, 1979 https://doi.org/10.1002/chin.197935093Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue35August 28, 1979 RelatedInformation

ChemInform Abstract: STEREO‐ AND REGIO‐SPECIFICITY IN ORGANIC SYNTHESIS PROMOTED BY METAL IONS

AbstractReview: Bericht über einen Vortrag, der auf dem "26th International Congress of Pure and Applied Chemistry" in Tokyo v. 4.9.

Olefin-forming elimination induced by mercaptide ions. Variation of transition-state character as indicated by substituent effects on rate

Olefin-forming elimination induced by mercaptide ions. Variation of transition-state character as indicated by substituent effects on rate

Stereo- and regio-specificity in organic synthesis promoted by metal ions

Abstract

Effect of the immediate environment on the reactivity of the essential -SH group of papain.

The effect of the microenvironment on the reactivity of the essential -- SH group of papain was studied by alkylation with methyl iodide and with the more polar iodoacetamide. Rate and activation parameters for these reactions were determined with two forms of the -- SH group: the free mercaptide ion at pH 10.0, and the mercaptide-imidazolium ion-pair at pH 5.5. The ion-pair of papain reacts with methyl iodide at a rate 1470 times less than that of thiolsubtilisin. This surprising difference between the reactivities of the two enzymes suggests that in contrast to thiolsubtilisin, where a non-polar environment enhances the rate, in the case of papain a more polar environment somewhat inhibits the reaction with the non-polar methyl iodide. The positive activation entropy for the papain reaction may indicate an 'ordered' structure of bound water around the sulfur atom. The high rate and the low activation entropy (organized transition state) of the reaction of papain with iodoacetamide can be explained in terms of hydrogen-bond formation between the enzyme and the amide group of the alkylating agent.

Facile alkylation of methionine by benzyl bromide and demonstration of fumarase inactivation accompanied by alkylation of a methionine residue.

Benzyl bromide is a selective alkylator of sulfur nucleophiles including methionine and cysteine. Only the mercaptide ion is a more efficient nucleophile than is the sulfur ether of methionine. Alkylation rates relative to methionine are 200: less than or equal to 0.03: less than or equal to 0.03: less than or equal to 0.02 for GS-, histidine, tryptophan, and GSH, respectively. Alkylation of methionine by benzyl bromide is more than 50 times faster than alkylation by iodoacetate. Fumarase is readily inactivated by exposure to benzyl bromide at pH 6.6 to 6.8 accompanied by alkylation of close to 1 methionine residue/subunit. Fumarase fully inactivated by exposure to benzyl bromide shows no detected alkylation of amino acid residues other than methionine. The rate of inactivation of fumarase by benzyl bromide is decreased about 4-fold by the presence of excess substrates. Denaturation of fumarase in 6 M urea at pH 6.5 exposes additional methionine as well as cysteine residues to alkylation.