Sulfur- nitrogen compounds

Sulfur-nitrogen chemistry is an area that has seen major developments over the last few decades, in part because of the conductivity of the polymer (SN). The following discussion is necessarily selective, and more detailed accounts are listed at the end of the chapter. Probably the best known of the sulfur-nitrogen compounds is tetrasulfur tetranitride, S4N4. It has traditionally been obtained using reaction 16.119, but a more convenient method is reaction 16.120. Tetrasulfur tetranitride is a diamagnetic orange solid (mp 451 K) which explodes when heated or struck pure samples are very sensitive (see exercise 1 at the end of the section). It is hydrolysed slowly by water (in which it is insoluble) and rapidly by warm alkali (equation 16.121). 

S —N polar bonds. A resonance structure for S4N4 that 

Equations 16.122 and 16.123 show convenient routes to [NS2][SbF6] this product is soluble in liquid SO2 and is readily separated from AgCl which precipitates out of solution. The [NS2] ion (16.73) is isoelectronic (in terms of valence electrons) with [N02] (see structure 15.50). The [N 2] ion is a useful synthon, undergoing cycloaddition reactions with, for example, alkynes, nitriles and alkenes. 

The structure of S4N4, 16.63, is a cradle-Uke ring in which pairs of S atoms are brought within weak bonding distance of one another (compare with Fig. 16.8). The S—N 

No members of this family with adjacent NH groups in the ring are known. 

The Lewis acid-mediated reaction of A -phenyl-5 -(4-methylphenyl)sulfonimidoyl chloride (352) with 1,1-disubstituted alkenes yields benzothiazines (353) with low stereoselectivity in moderate yields (33-57%).  

The kinetics of the hydrolysis reactions of 4-amino-2-phenethyl- (354 R = PhCH2CH2) and 4-amino-2-cyclohexyl-2,3-dihydro-3-oxo-l,2,5-thiadiazole 1,1-dioxide (354 R = CeHii) have been investigated in the pH range 1-10 at 24-73 °C. The products are the corresponding new compounds 2-anuno-2-[(A -substituted-sulfamoyl)imino]acetic acid salts (355 R = PhCH2CH2 or CeHn) which hydrolyse further, in a slow reaction, to the sulfamide and oxalic acid derivatives.  

The dithionite ion has a remarkable eclipsed stmcture of approximate C2v symmetry (Fig. 15.32b). The extraordinarily long S-S distance (239 pm) and the almost parallel SO2 planes (dihedral angle 30°) are other unusual features. Electron-spin-resonance studies have shown the presence of the S02 radical ion in solution ( 300ppm), suggesting the establishment of a monomer-dimer equilibrium 8204  

Consistent with this, air-oxidation of alkaline dithionite solutions at 30-60° are of order one-half with respect to [8204 ]. Acid hydrolysis (second order with respect to [8204 ]) yields thiosulfate and hydrogen sulfite, whereas alkaline hydrolysis produces sulfite and sulfide  

Hydrated dithionites can be dehydrated by gentle warming, but the anhydrous salts themselves decompose on further heating. For example, Na28204 decomposes rapidly at 150° and violently at 190°  

Dithionites are strong reducing agents and will reduce dissolved O2, H2O2,12,103 and Mn04.  

Likewise Cr is reduced to Cr and TiO + to Ti Heavy metal ions such as Cu Ag Pb 8b and Bi are reduced to the metal. Many of these reactions are useful in water-treatment and pollution control. 

Nitride S4N4 is an air-stable compound that can be prepared by passing NH3 gas into a warm solution of S2CI2 in CCI4 or benzene. It is a thermochromic crystal colorless at 83 K, pale yellow at 243 K, orange at room temperature, and deep red above 373 K. 

Structure of (a) S2N2 and (b) polymeric chains in one layer of (SN) and the important structural parameters (bond lengths in pm). 

The homolog realgar, AS4S4, has an analogous but different structure with the electronegative S atoms at the vertices of a square and the electropositive As atoms at the vertices of a tetrahedron. The As atoms are linked by normal single bonds, as shown by the solid lines between them in Fig. 16.7.1(b). The As-As distance is 249 pm, which is nearly equal to the calculated value of 244 pm (Table 3.4.3). 

When the heated vapor of S4N4 is passed over silver wool at 520 to 570 K, the unstable cyclic dimer S2N2 is obtained. It forms large colorless crystals which are insoluble in water but soluble in many organic solvents. 

The molecular structure of S2N2, as shown in Fig. 16.7.2(a), is aZ)2h square-planar ring with S-N edge 165 pm, somewhat analogous to the isoelectronic cation S + (Fig. 16.4.2). The valence-bond representations of the S2N2 molecule are as follows  

S4N4 and Sg) are all obtained by treating S2CI2 with NH3. No members of this family with adjacent NH groups in the ring are known. 

The reactions of SyNH with SbCl5 in liquid SO2, or S3N3CI3 with SbCl5 and sulfur in SOCI2, lead to the formation of the salt [NS2][SbCl6] containing the [NS2] ion, (15.68) which is isoelectronic (in terms of valence electrons) with [NOy] (see structure 14.50). 

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Gmelin Handbook of Inorganic Chemistry, 8 ed., Sulfur-Nitrogen Compounds, Part 2 Compounds with Sulfur of Oxidation Number IV, Springer-Verlag, Berlin (1985). 

H. W. Roesky, Cyclic Sulfur-Nitrogen Compounds, Adv. Inorg. Chem. Radiochem., 22, 239 (1979). 

R. Gleiter, Stmcture and Bonding in Cyclic Sulfur-Nitrogen Compounds Molecular Orbital Considerations, Angew. Chem. Int. Ed. Engl., 20, 444 (1981). 

T. Chivers, Sulfur-Nitrogen Compounds, in R. B. King (ed.) Encyclopedia of Inorganic Chemistry, Vol.7, John Wiley, pp. 3988-4009 (1994). 

R. P. Sharma and R. D. Vetma, Recent Developments in the Chemistry of Sulfur-Nitrogen Compounds Sulfur-Nitrogen Cyclic Anions, J. Sci. Ind. Res., 40, 34 (1981). 

M. Herberhold, Small Reactive Sulfur-Nitrogen Compounds and Their Transition-Metal Complexes, Comments Inorg. Chem., 7, 53 (1988). 

Some acyclic sulfur-nitrogen compounds also exhibit intense colours. For example, S-nitrosothiols RSNO are either green, red or pink (Section 9.7). Their UV-visible spectra show an intense band in the 330-350 nm region (no it ) and a weaker band in the visible region at 550-600 nm... 

Bonding in Sulfur-Nitrogen Compounds Comparison with Organic Systems... 

Rhenium(VI) complexes, 4,194 alkoxides, 4,196 amides, 4,194 amines, 4,199 carboxylates, 4,199 dimethylformamide, 4,199 dioxane, 4,198 halides, 4,195,199 2-hydroxypyridine, 4,199 imides, 4,194 magnetic behavior, 1,271 mixed sulfur-nitrogen compounds, 4,196 N heterocycles, 4,199 nitrides, 4,194 oxide halides, 4, 195 oxoanions,4,196 pyridine, 4,199 sulfates, 4,198 sulfur compounds, 4,196 tellurates, 4,198... 

The chemistry of elemental sulfur and sulfur-rich molecules including polysulfides in liquid ammonia [82] and in primary as well as secondary amines [83] is complex because of the possible formation of sulfur-nitrogen compounds. Therefore, polysulfide solutions in these solvents will not be discussed here. Inert solvents which have often been used are dimethylfor-mamide (DMF) [84-86], tetrahydrofuran (THF) [87], dimethylsulfoxide (DMSO) [87], and hexamethylphosphoric triamide (HMPA) [86, 88]. 

The electrochemical reduction and oxidation of sulfur and of polysulfide dianions at inert electrodes has been studied in aprotic solvents and in liquid ammonia. In the latter case, sulfur-nitrogen compounds are involved and these systems [90] will not be discussed here. 

Sulfur Compounds with Nitrogen, Oxygen and Halides (in German) 1977 Sulfur-Nitrogen Compounds, Part 1 (in German)... 

H. Tetrasulfur Tetranitride and Related Sulfur-Nitrogen Compounds... 

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