Mercaptans, decomposition

Mercaptans are naturally present in crude oil (Chapters 1 and 8), or they result from the decomposition of other sulfur compounds during thermai or catalytic cracking operations. 

Physical Properties. Trichloromethanesulfenyl chloride [594-42-3] (perchloromethyl mercaptan, a misnomer but used as the common commercial name), CCl SCl, is a strongly acrid, pale yellow Hquid, boiling at 149°C with some decomposition at atmospheric pressure, 68°C at 6.93 kPa (52... 

Materials that promote the decomposition of organic hydroperoxide to form stable products rather than chain-initiating free radicals are known as peroxide decomposers. Amongst the materials that function in this way may be included a number of mercaptans, sulphonic acids, zinc dialkylthiophosphate and zinc dimethyldithiocarbamate. There is also evidence that some of the phenol and aryl amine chain-breaking antioxidants may function in addition by this mechanism. In saturated hydrocarbon polymers diauryl thiodipropionate has achieved a preeminent position as a peroxide decomposer. 

Similar products are obtained from the photosensitized decomposition of the tertiary azides, suggesting that decomposition may result from the triplet azides under both direct and sensitized photolysis/461 Additional evidence for a discrete nitrene intermediate comes from the observation that this intermediate can be trapped by decomposition of the azides in the presence of good hydrogen donors such as tri- -butyItin hydride and jec-butyl mercaptan. Triarylamines result ... 

When added to water as an aquatic herbicide, acrolein undergoes rapid decomposition, especially in sunlight. At the same time, it reacts rapidly with amines, alcohols, and mercaptans of aquatic plants, destroying cell structure and killing the plants (Parent et al. 1992). Mammals drinking acrolein-contaminated water rapidly convert acrolein to saturated alcohol compounds because of the low pH in the upper portion of their GI tracts the primary breakdown product is beta-propionaldehyde (USEPA 1980). 

The free radical polymerization of HPMA in the presence of mercaptans involves two different initiation mechanisms (Scheme 2) [26]. One is the initiation by RS radicals from chain transfer agent the other appears to be the direct initiation by the primary isobutyronitrile (IBN) radicals formed by the decomposition of AIBN [27]. The RS are formed by either the free radical transfer reaction of alkyl mercaptans with the IBN radicals or the chain transfer reaction of an active polymer chain with the mercaptans. The initiation by the RS radicals produces the ST polymers with a functional group at one end of the polymer chain. The initiation by IBN radicals leads to nonfunctional polymer chains with an IBN end group. The presence of the polymers with IBN end groups effects the purity and the functionality of ST polymers. As expected, the production of nonfunctionalized polymer chains is affected by reaction conditions. The polymerization is mainly terminated by chain transfer reaction with the mercaptans, but other termination mechanisms, such as disproportionation and recombination, take place depending on the reaction conditions [26]. 

Baumann next found that cystine, on reduction with zinc and hydrochloric acid, was converted into a new base, which he called cysteine this gave the same products on decomposition as cystine, into which it was easily reconverted by oxidation. He therefore recognised that these compounds were related to each other, as a mercaptan is to a disulphide consequently the formula... 

Hydrogen sulfide and mercaptans Sour crudes formed by decomposition of sulfur compounds during distillation, cracking, reforming, and hydroprocessing... 

The best evidence for the photolytic decomposition of mercaptans and disulfides into free radicals involves photoinitiation of polymerization of olefins. Thus, photolysis of disulfides initiates the copolymerization of butadiene and styrene,154 as well as the polymerization of styrene207 and of acrylonitrile.19 Thiophenol and other thiols promote polymerization upon ultraviolet irradiation.19 Furthermore, the exchange of RS-groups between disulfides and thiols is greatly accelerated by light. Representative examples are benzothiazolyl disulfide and 2-mercapto-thiazole,90 tolyl disulfide and p-thiocresol, and benzyl disulfide and benzylmercaptan.91 The reaction probably has a free radical mechanism. Similar exchange reactions have been observed of RS-groups of pairs of disulfides have been observed.19... 

A solution of 225 g. of sodium hydroxide (Note 3) in 250 ml. of water is poured into the reaction mixture. A heavy brown oil separates, consisting of S-2-furfurylisothiourea, which has already partially decomposed to 2-furfuryl mercaptan. The flask is quickly fitted with a steam-inlet tube and condenser. Steam distillation is continued as long as the distillate contains oily drops. The mercaptan is separated from the aqueous phase by means of a separatory funnel (Notes 7 and 8). The product is dried with calcium chloride yield, 313-340 g. (55-60%). The 2-furfuryl mercaptan so obtained is of a high degree of purity (Note 9) but can be distilled without decomposition in a nitrogen atmosphere b.p. 160°/759 mm., 84°/65 mm., n 1.533. 

Furfuryl mercaptan cannot be prepared according to the classical method using furfuryl chloride and potassium sulfide.2 It has been prepared by reduction of 2-furfuryl disulfide, obtained from furfural and ammonium hydrosulfide.3 The mercaptan has also been obtained in 33% yield 2 by the reaction of furfuryl chloride with thiourea and subsequent decomposition of the intermediate S-2-furfurylisothiourea according to the general method described in Organic Syntheses.4 In the present method, which has been published previously, the use of the very unstable and difficultly available furfuryl halides is avoided.6... 

In the case of PMMA dissolved in acetone, the change of LSI could be correlated both with the separation of fragments and, to some extent, with the lifetime of the intermediates which contribute to the main-chain scission [71]. The LSI decreased in two modes, probably due to the two pathways for the main-chain scission. The fast mode with a lifetime of about 20 ps was influenced neither in its extent nor in its rate by the addition of 02 or mercaptane. Therefore the first mode was ascribed to the diffusional separation of fragments which are generated by the main-chain scission through the direct decomposition of electronically excited or ionic intermediates. The slow mode with a lifetime of 6 ms was suppressed, to an extent, depending on the ( -concentration it was attributed to long-lived polymer radicals. The added 02 reacts with lateral polymer radicals to prevent their decomposition. 

Organosulfur decomposition in soils and sediments yields mercaptans and H2S. Analogous to ammoni-fication, this process is referred to as desulfurization. 

SYN 2-PROPENE-l-THIOL SAFETY PROFILE Poison by inhalation and ingestion. Strong irritant to skin and mucous membranes. When heated to decomposition it emits highly toxic fumes of SOx. Vet " dangerous fire hazard. To fight fire, use water mist or spray, alcohol foam, CO2, or dry chemical. See also ALLYL COMPOUNDS and MERCAPTANS. 

SAFETY PROFILE Poison by intraperitoneal and intravenous routes. Moderately toxic by ingestion. Skin and eye irritant. When heated to decomposition it emits toxic fumes of SO and NOx. See also MERCAPTANS. 

SAFETY PROFILE Suspected carcinogen with experimental carcinogenic and tumorigenic data. Poison by ingestion and intraperitoneal routes. Experimental teratogenic and reproductive effects. Mutation data reported. Incompatible with oxidizers. When heated to decomposition or on contact with acids or acid fumes it emits toxic SOx and NOx. See also MERCAPTANS. 

Experimental teratogenic effects. An eye irritant. Mutation data reported. See also MERCAPTANS and SULFIDES. When heated to decomposition it emits very toxic fumes of NOx and SOx. 

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