Systems containing Sulphur

The sulphur-bridged naphthalene (93) has been prepared by photolysis and thermolysis of naphtho[l,8- ]l,2,3-thiadiazine (94). The presumed intermediate (95) can be intercepted by CS2 to give (96), which is also formed in low yield when (93) is heated or irradiated in CS2. Oxidation of thiadiazine (94) with peracid gives the mono-5-oxide of (93) by spontaneous extrusion of nitrogen from the thiadiazine S-oxide.  

The thiazolium salts (99 R = Me or PhCH2) undergo ring-opening and -contraction to the methylenethietans (100) on treatment with aqueous base. Electrochemical reduction of (101) gives the radical anion of the isomeric compound (102).  

Addition of sulphenes to electron-rich alkenes is a well-known route to thietan dioxides.Iminosulphenes are intermediates in base-promoted reactions of 

Other work on four-membered heterocycles containing one sulphur atom includes a study of the vacuum-u.v. photodecomposition of thietan 1,1-dioxide and the formation of a thietanone from a xanthate and diphenylketen, and reports of several thiets. There is evidence that photolysis of (107) in a matrix at 77 K leads to the o-thiobenzoquinone (108), which is interconvertible with the 

L abbe, J. P. Dekerk, J.-P. Declercq, G. Germain, and M. Van Meerssche, Tetrahedron Lett., 

The thieten 1,1-dioxide (48) has been prepared by cycloaddition of an enamine and sulphene at 0°C. Mild thermolysis causes a ready retrocyclo-addition to occur. Additional stable 3-sultines have been isolated, by the reaction of the anion of a sulphoxide with a ketone and cyclization of the resulting j3-hydroxy-sulphoxide with sulphuryl chloride. Treatment of 2-methylthietan (49) with alumina at 150-350 °C results in the formation of tetrahydrothiophen and but-3-enethiol.  

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Take a system which contains nearly perfect gases and where an exothermic compoimd may be produced or dissociated for instance, a system containing sulphur in liquid and vapor states, hydrogen and hydrogen sulphide let a be the ratio between the mass of the compound the system contains and the mass of this same compound it would contain if the combination of its elements were pushed as far as possible heat the system either at constant pressure or at constant volume. The line VV (Fig. 123) of veritable equilibria has, in the plane TOx, a form we have already traced in Fig. Ill as far as pqint B, of abscissa d, it remains practically identical with the line A A, parallel to OT, and having as constant ordinate x=l it then detaches itself and descends from left to right. 

Thus below 250 a mixture containing only selenium and hydrogen, without trace of selenhydric acid, remains in a state of false equilibrium no reaction is produced in it below 215 a system containing sulphur and hydrogen is in the state of false chemical equilibrium. 

Thus, whatever the initial composition of a system containing sulphur, hydrogen, sulphuretted hydrogen, the reaction-point always corresponds to the beginning of combination. 

Systems containing Sulphur as the only Heteroatom. - A variety of sulphur-containing cyclophanes were synthesized by the dilution principle, using an improved apparatus. The equipment will prove valuable in the preparation of many macrocyclic systems. The iron-catalysed reaction between bis-(2,4-dimethoxyphenyl) sulphide and S2CI2 gave four macrocyclic systems, including (47). The formation of (47) occurs by the unusual electrophilic cleavage of C-aryl-S bonds. 

Systems Containing Sulphur as the Only Heteroatom.- A novel... 

Most passenger car tyre tread compounds are based on SBR or SBR/BR blends and crosslinked with a cure system containing sulphur and various accelerators. Synthetic rubber vulcanisates are not as sensitive to reversion as NR vulcanisates but nevertheless they are subject to alterations due to changes in the crosslink... 

Reactions of contaminants in the fuel or air in the combustion zone can result in the formation of compounds which can condense as molten salts onto cooler components in the system. This type of process can occur when fuels containing sulphur or vanadium are burnt. In the case of sulphur contaminants, alkali sulphates form by reactions with sodium which may also be present in the fuel or in the combustion air, and for vanadium-containing fuels low-melting-point sodium vanadates or vanadium pentoxide are produced, particularly when burning residual oils high in vanadium. Attack by molten salts has many features in common which will be illustrated for the alkali-sulphate-induced attack, but which will be subsequently shown to be relevant to the case of vanadate attack. 

Although the first industrial application of anodic protection was as recent as 1954, it is now widely used, particularly in the USA and USSR. This has been made possible by the recent development of equipment capable of the control of precise potentials at high current outputs. It has been applied to protect mild-steel vessels containing sulphuric acid as large as 49 m in diameter and 15 m high, and commercial equipment is available for use with tanks of capacities from 38 000 to 7 600000 litre . A properly designed anodic-protection system has been shown to be both effective and economically viable, but care must be taken to avoid power failure or the formation of local active-passive cells which lead to the breakdown of passivity and intense corrosion. 

The Karl Fischer procedure has now been simplified and the accuracy improved by modification to a coulometric method (Chapter 14). In this procedure the sample under test is added to a pyridine-methanol solution containing sulphur dioxide and a soluble iodide. Upon electrolysis, iodine is liberated at the anode and reactions (a) and (b) then follow the end point is detected by a pair of electrodes which function as a biamperometric detection system and indicate the presence of free iodine. Since one mole of iodine reacts with one mole of water it follows that 1 mg of water is equivalent to 10.71 coulombs. 

The thiazole ring system is found in many types of dye. Thiazole-containing sulphur dyes and primuline were considered in section 6.4-2. Quaternised dehydrothio-p-toluidine 6.133 is available as Cl Basic Yellow 1 (6.152). Other derivatives of this intermediate are used as direct dyes, such as Cl Direct Yellow 8 (4-58). The benzothiazole ring appears in various azo disperse dyes [14], quatemisation of which gives useful cationic dyes, an important example being Cl Basic Blue 41 (4.99). Another example containing a quaternised thiazole ring is Cl Basic Red 29 (4-102). 

The system styrene-sulphuric acid merits some special discussion. Gandini and Plesch [6, 7] were unable to reproduce the results of Pepper and his collaborators [8]. When a phial containing styrene was broken into a solution of sulphuric acid in methylene or ethylene dichloride at 20 °C only traces of polymer were obtained, apparently very rapidly, and thereafter no further polymerisation and no colour developed. These results are in essential agreement with those of Tsuda [9] who also found the polymerisation to be inhibited by water. 

Oxazole, imidazole and thiazole systems contain a five-membered ring and two hetero-atoms, one of which is a nitrogen atom. The hetero-atoms are separated by a carbon atom in the ring. The second hetero-atoms are oxygen, nitrogen and sulphur for oxazole, imidazole and thiazole systems, respectively. 

The flame photometry detector is specific for compounds containing sulphur or phosphorous. Compounds eluting from the column are burned in a flame hot enough to excite these elements and induce photonic emission, which is detected by a photomultiplier (see Fig. 2.12). Optical filters are used in the detection system to... 

A comparison of ELISA, HPLC, and HPLC-ELISA methods was published for the determination of SAL in chicken liver tissue. Samples were homogenized with MeOH and extracted with methylenechloride. Some samples were analyzed by HPLC using the isocratic solvent system and postcolumn derivatization (vanillin in MeOH containing sulphuric acid), with the eluent monitoring at 520 nm. The HPLC-ELISA system was used to characterize nonspecific effects analyzing column fractions by ELISA, since this detection is over 1000 times more sensitive than the spectrophotometric one. This alleviated the need to derivatize the drug prior to the detection (104). 

The parent saturated three-membered ring systems containing nitrogen, or oxygen, or sulphur as the heteroatom are known as aziridine (1), oxirane (2) and thiirane (3). 

Any ring system containing at least one heteroatom (i.e. an atom other than carbon - typically nitrogen, oxygen, or sulphur) can be described as heterocyclic. This broad definition encompasses both aromatic heterocycles (such as pyridine 5.1) and their non-aromatic counterparts (piperidine 1.7). 

In the light of the foregoing discussion it may be expected that fluoroalkenes participate in cycloaddition reactions with unsaturated systems containing heteroatoms [260], e.g. nitroso compounds [261], sulphur trioxide [262], sulphur dioxide [263], nitriles [264] and so on (Figure 7.78). 

Raghavan V. (1988) Phase Diagrams of Ternary Iron Alloys Part 2. Ternary Systems Containing Iron and Sulphur. Indian Institute of Metals, Calcutta. 

The choice of the active orbital space for the CASSCF calculations is a crucial step, and has turned out to be especially difficult in these proteins and other systems containing a Cu-thiolate bond. From earlier studies it was known that in complexes with first-row transition metal ions with many 3d electrons, the active space should include one correlating orbital for each of the doubly occupied 3d orbitals [28]. Therefore the starting active space contains 10 orbitals 3d and 3d"). In addition, it is necessary to add the 3p orbitals on Scys to describe correctly the covalent character of the Cu-Scys bond and also 2p and 3p orbitals on nitrogen and sulphur to describe charge-transfer states. The final active space therefore contain 11 or 12 active orbitals (12 active orbitals are at present the upper limit for the CASPT2 method). 

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