Sensitizers sulfides

Yield of allenes 47a-e from sulfides unbranched in a-position to sulfur are moderate to high. However, a-branching to sulfur lead to lower yields (allenes 47f-h) and is accompanied by competing formation of sulfoxides by 0-transfer from oxaziridine 44. The metal-free reaction conditions allow synthesis of particularly sensitive allenes or those derived from sensitive sulfides... 

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

Arsenious oxide, trivalent antimony (73), sulfurous acid (74), hydrogen sulfide (75), stannous ion, and thiocianate (76) have been recommended for the titration of iodine. However, none of these appears to have a greater sensitivity for the deterrnination of minute quantities of iodine than thiosulfate. Organic compounds such as formaldehyde (77), chloral hydrate (78), aldoses (79), acetone (70,80), and hydroquinone have also been suggested for this purpose. 

Phosphoms(V) sulfide is a mild skin irritant and may cause dermatitis in sensitive individuals. The primary health ha2ard results from the Hberation of hydrogen sulfide after contact with moisture. Contact with moisture also forms phosphoric acid. A secondary ha2ard is the formation of sulfur dioxide when phosphoms(V) sulfide bums. The oral LD q of in rats is 389 mg/kg the OSHA standard time-weighted average (TWA) is 1 mg /m (33). 

The odor threshold of carbon disulfide is about 1 ppm in air but varies widely depending on individual sensitivity and purity of the carbon disulfide. However, using the sense of smell to detect excessive concentrations of carbon disulfide is unreHable because of the frequent co-presence of hydrogen sulfide that dulls the olfactory sense. 

Sulfide is used for the selective reduction of dinitro compounds to nitroarylamines, and for metal-sensitive systems, such as certain substituted ... 

Potentiometric Titrations. If one wishes to analyze electroactive analytes that are not ions or for which ion-selective electrodes are not available, two problems arise. First, the working electrodes, such as silver, platinum, mercury, etc, are not selective. Second, metallic electrodes may exhibit mixed potentials, which may arise from a variety of causes. For example, silver may exchange electrons with redox couples in solution, sense Ag" via electron exchange with the external circuit, or tarnish to produce pH-sensitive oxide sites or Ag2S sites that are sensitive to sulfide and haUde. On the other... 

Plating Bath Purification. Purification, often needed once a plating bath is made, is used periodically to maintain the plating solutions. Alkaline ziac plating solutions are sensitive to a few mg/L of heavy-metal contamination, which can be precipitated usiag sodium sulfide and filtered out. 

Some studies of potential commercial significance have been made. For instance, deposition of catalyst some distance away from the pore mouth extends the catalyst s hfe when pore mouth deactivation occui s. Oxidation of CO in automobile exhausts is sensitive to the catalyst profile. For oxidation of propane the activity is eggshell > uniform > egg white. Nonuniform distributions have been found superior for hydrodemetaUation of petroleum and hydrodesulfuriza-tion with molybdenum and cobalt sulfides. Whether any commercial processes with programmed pore distribution of catalysts are actually in use is not mentioned in the recent extensive review of GavriUidis et al. (in Becker and Pereira, eds., Computer-Aided Design of Catalysts, Dekker, 1993, pp. 137-198), with the exception of monohthic automobile exhaust cleanup where the catalyst may be deposited some distance from the mouth of the pore and where perhaps a 25-percent longer life thereby may be attained. 

Corrosion products and deposits. All sulfate reducers produce metal sulfides as corrosion products. Sulfide usually lines pits or is entrapped in material just above the pit surface. When freshly corroded surfaces are exposed to hydrochloric acid, the rotten-egg odor of hydrogen sulfide is easily detected. Rapid, spontaneous decomposition of metal sulfides occurs after sample removal, as water vapor in the air adsorbs onto metal surfaces and reacts with the metal sulfide. The metal sulfides are slowly converted to hydrogen sulfide gas, eventually removing all traces of sulfide (Fig. 6.11). Therefore, only freshly corroded surfaces contain appreciable sulfide. More sensitive spot tests using sodium azide are often successful at detecting metal sulfides at very low concentrations on surfaces. 

Fig. 14-7. Distribution of sensitivity to ethylene sulfide odor in 33 individuals. The abscissa is the percentage of the individuals who detected the presence of ethylene sulfide at various levels. Source Dravnicks, A., and Jarke, F., J. Air PoIIut. Control Assoc. 30, 1284-1289 (19801.

The mtroducuon of a tnfluoromethanethio group into an aromatic nng has a synthetic importance The reaction of tnfluoromethanethio copper with aryl bro mides and iodides provides a convenient route to the synthesis of aryltn fluoromethane sulfides The reaction is not sensitive to the type of substituents or the aromahc nucleus Selectivity can be achieved accordmg to the type of halogen or the aromatic rmg, because iodides react at lower temperatures than bromides, whereas chlondes do not react [f J] (equation 12) (Table 5)... 

Another boron sulfide, of stoichiometry BS2, can be made by heating B2S3 and sulfur to 300°C under very carefully defined conditions. It is a colourless, moisture-sensitive material with a porphine-like molecular structure, BgSig, as shown in Fig. 6.29b. An alternative route to BgSie involves the reaction of dibromotrithiadiborolane with trithiocarbonic acid in an H2S generator in dilute CS2 solution ... 

MSH + MOH). Accordingly, solubilities depend sensitively not only on temperature but also on pH and partial pressure of H2S. Thus, by varying the acidity. As can be separated from Pb, Pb from Zn, Zn from Ni, and Mn from Mg. In pure water the solubility of Na2S is said to be 18.06g per 100 g H2O and for Ba2S it is 7.28 g. In the case of some less-basic elements (e.g. AI2S3, Cr2S3) hydrolysis is complete and action of H2S on solutions of the metal cation results in the precipitation of the hydroxide likewise these sulfides (and SiS2, etc.) react rapidly with water with evolution of H2S. 

What about the state of equilibrium for the reaction represented by equation (11)1 Let us place a strip of metallic copper in a zinc sulfate solution. No visible reaction occurs and attempts to detect the presence of cupric ion by adding H2S to produce the black color of cupric sulfide, CuS, fail. Cupric sulfide has such low solubility that this is an extremely sensitive test, yet the amount of Cu+2 formed cannot be detected. Apparently the state of equilibrium for the reaction (11) greatly favors the products over the reactants. 

Catalyst Poisons. Hausberger, Atwood, and Knight (33) reported that nickel catalysts are extremely sensitive to sulfides and chlorides. If all materials which adversely affect the performance of a catalyst were classified as poisons, then carbon laydown and, under extreme conditions, water vapor would be included as nickel methanation catalyst poisons. 

It was used primarily in submarine mines. Because of the sensitivity of the fuse, the main charge was replaced with a mixt of powd graphite and MF. At about the same time, an Austrian, Gen von Ebner, independently invented a fuze resembling Abel s, but contg a priming mixt of Sb sulfide 44, K chlorate 44 and graphite 12%. Both of these fuzees replaced, in Europe, the Statham fuze, which had been in use since 1840... 

---