Mercaptans determination

Chemical assay is preferably performed by gas—hquid chromatography (glc) or by the conventional methods for determination of unsaturation such as bromination or addition of mercaptan, sodium bisulfite, or mercuric acetate. 

In this work the results of reseai ch common sorbtion-X-Ray-fluorescence analysis of Pb(II), Cd(II), Zn(II) and Mo(VI) with preconcentration on complexing chemical silica gel modified with mercaptane groups and modified with 8-hydroxyquinoline were described. The conditions and limits of determination of the X-Ray-fluorescence method in the thin lawyers ai e discussion. 

Natural gas - Determination of sulfur compounds. Determination of hydrogen sulfide, mercaptan sulfur, and carbonyl sulfide sulfur by potentiometry. Also BS 3156 Subsection 11.4.3 1994 Natural gas - Determination of sulfur compounds. Lmgener combustion method. Also BS 3156 Subsection 11.4.5 1994... 

Other Techniques Continuous methods for monitoring sulfur dioxide include electrochemical cells and infrared techniques. Sulfur trioxide can be measured by FTIR techniques. The main components of the reduced-sulfur compounds emitted, for example, from the pulp and paper industry, are hydrogen sulfide, methyl mercaptane, dimethyl sulfide and dimethyl disulfide. These can be determined separately using FTIR and gas chromatographic techniques. 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

This input to design refers to the long-term stability of the raw material sources for the plant. It is only of importance where the raw materials can or do contain impurities which can have profound effects on the corrosivity of the process. Just as the design should cater not only for the norm of operation but for the extremes, so it is pertinent to question the assumptions made about raw material purity. Crude oil (where HjS, mercaptan sulphur and napthenic acid contents determine the corrosivity of the distillation process) and phosphate rock (chloride, silica and fluoride determine the corrosivity of phosphoric acid) are very pertinent examples. Thus, crude-oil units intended to process low-sulphur crudes , and therefore designed on a basis of carbon-steel equipment, experience serious corrosion problems when only higher sulphur crudes are economically available and must be processed. 

Hence the slope of the plot of log[S] against log[M] must equal Cs-The concentration [S] of unreacted mercaptan regulator may be determined by amperometric titration with silver nitrate,or the combined sulfur in the polymer may be determined radiochemically using mercaptan containing S, and the unreacted mercaptan concentration [S] calculated by difference. Transfer constants for carbon... 

Method 1 refers to determination from the average degree of polymerization using Eq. (42), and 2 refers to determination from the consumption of mercaptan using Eq. (44). 

The water (moisture) content can rapidly and accurately be determined in polymers such as PBT, PA6, PA4.6 and PC via coulometric titration, with detection limits of some 20 ppm. Water produced during heating of PET was determined by Karl Fischer titration [536]. The method can be used for determining very small quantities of water (10p,g-15mg). Certified water standards are available. Karl Fischer titrations are not universal. The method is not applicable in the presence of H2S, mercaptans, sulfides or appreciable amounts of hydroperoxides, and to any compound or mixture which partially reacts under the conditions of the test, to produce water [31]. Compounds that consume or release iodine under the analysis conditions interfere with the determination. 

Electrodes of the first kind have only limited application to titration in non-aqueous media a well-known example is the use of a silver electrode in the determination of sulphides and/or mercaptans in petroleum products by titration in methanol-benzene (1 1) with methanolic silver nitrate as titrant. As an indicator electrode of the second kind the antimony pH electrode (or antimony/antimony trioxide electrode) may be mentioned its standard potential value depends on proton solvation in the titration medium chosen cf., the equilibrium reaction on p. 46). 

Blanchette AR, Cooper AD. 1976. Determination of hydrogen sulfide and methyl mercaptan in mouth air at parts-per-billion level by gas chromatography. Anal Chem 48 729-731... 

Ellman, G.L. (1958) A colorimetric method for determining low concentrations of mercaptans. Arch. Biochem. Biophys. 74, 443—450. 

Leek and Bagander [221] determined reduced sulfide compounds (hydrogen sulfide, methyl mercaptan, carbon disulfide, dimethyl sulfide, and dimeth-yldisulfide) in water by gas chromatography using flame detection. Detection limits ranged from 0.2 ng/1 for carbon disulfide to 0.6 ng/1 for methyl mercaptan. Hydrogen sulfide was determined at the 1 ng/1 level. 

Leek and Baagander [311] determined reduced sulfide compounds in seawater by gas chromatography using a flame ionisation detector. Substances determined include methyl mercaptan, dimethyl sulfide, hydrogen sulfide and carbon disulfide. Detection limits range from 0.2ng/l (carbon disulfide) to 0.6 ng/1 (methyl mercapton). 

In abroad sense, the model developed for the cobaloxime(II)-catalyzed reactions seems to be valid also for the autoxidation of the alkyl mercaptan to disulfides in the presence of cobalt(II) phthalocyanine tetra-sodium sulfonate in reverse micelles (142). It was assumed that the rate-determining electron transfer within the catalyst-substrate-dioxygen complex leads to the formation of the final products via the RS and O - radicals. The yield of the disulfide product was higher in water-oil microemulsions prepared from a cationic surfactant than in the presence of an anionic surfactant. This difference is probably due to the stabilization of the monomeric form of the catalyst in the former environment. 

As esters the alkyl halides are hydrolysed by alkalis to alcohols and salts of halogen acids. They are converted by nascent hydrogen into hydrocarbons, by ammonia into amines, by alkoxides into ethers, by alkali hydrogen sulphides into mercaptans, by potassium cyanide into nitriles, and by sodium acetate into acetic esters. (Formulate these reactions.) The alkyl halides are practically insoluble in water but are, on the other hand, miscible with organic solvents. As a consequence of the great affinity of iodine for silver, the alkyl iodides are almost instantaneously decomposed by aqueous-alcoholic silver nitrate solution, and so yield silver iodide and alcohol. The important method of Ziesel for the quantitative determination of alkyl groups combined in the form of ethers, depends on this property (cf. p. 80). 

The amine-catalyzed mercaptan-epoxide reaction (Equation 4) proceeds exothermally at room temperature (27. 28). The order of average relative nucleophile-displacement rates (Table II) further suggests that mercaptans react significantly faster than amines and that the addition of the mercaptlde (RS ) ion to the epoxide group is the rate determining step (30). 

In a fatal human exposure, a worker engaged in emptying metal gas cylinders of methyl mercaptan was found comatose at the work site he developed expiratory wheezes, elevated blood pressure, tachycardia, and marked rigidity of extremities. Methemoglobinemia and severe hemolytic anemia developed with hematuria and proteinuria but were brief in duration deep coma persisted until death due to pulmonary embolus 28 days after exposure. It was determined that the individual was deficient in erythrocyte glucose-6-phosphate dehydrogenase, which was the likely cause of the hemolysis and formation of methemoglobin. 

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