Phosphorus—Sulphur Links

Electrochemical reduction of a,a -dibromoketones affords the unstable cyclo-propanone, which is in equlibrium with the dipolar intermediate 22. The cyclopro-panone hemiacetal is isolated in yields of 40 - 85 % from reaction in acetonitrile and methanol at -20 °C [99], The dipolar form can be trapped in a cycloaddition process with furan [100], Reaction with acetic acid leads to the a-acetoxy-ketone.[101]. Unstable three membered heterocyclic rings are intermediate in the reduction of sulphur and phosphorus linked dibromo compounds 23. In these reactions, the heteroatom is extruded leaving ci - and trans-stilbenes as the isolated products [102,103],... 

The direct linking of like atoms, such an essential feature of carbon chemistry, occurs to only a limited extent with other elements. Metal-metal bonds are not uncommon but they are always weak examples are found in the polynuclear carbonyls (p. 306) and compounds such as SugRg and PbgRfi (R = alkyl). Among the other non-metals catenation is displayed by boron, silicon, germanium, phosphorus and sulphur none of the substances... 

Because of the strong bonds it makes with oxygen, nitrogen and sulphur, phosphorus forms a large number of polymers. Polyphosphate anions have —P—O—P— linkages and so have the oxygen-linked compounds ... 

N.m.r. data have also been used to show that the compound (C6H6PS)3 has the heterocyclophosphane structure with a five-membered P3S2 ring containing isolated sulphur atoms. One of the directly connected phosphorus atoms is linked to another sulphur atom in an exo-position, in addition to the phenyl group. The above structure has also been confirmed by a second study. ... 

The properties of elastic sulphur, pS, can be stabilised by adding a few percent of phosphorus. A vulcanisation process occurs in which cross-linking is produced via the P atoms, and as more phosphorus is added, the product becomes more brittle and finally vitreous when cross-linking is... 

Spiro cations in which four sulphur atoms are linked directly to the central phosphorus atom, are formed in reactions... 

The alkylation technique successfully explored for linking cis-disposed nitrogen and sulphur donor atoms has been extended to phosphorus. The macrocyclic com-potmd benzo-[15]aneP4, isolated as the complex [Ni(L1203)]Cl2, was synthesised by the template reaction shown in Scheme 5-2. Note that the terminal coordinated phosphorus donor atoms can be involved in the chelate-forming template reaction only after their deprotonation, which is facihtated by the electron-withdrawing effect of the metal ion and the presence of a base (K2CO3). 

Soil polysaccharide also contains phosphorus and sulphur. The latter ranges from one S atom per 40-250 hexose units and it may be in the form of ester sulphate groupswhereas the phosphorus is usually of the order of 1%. It is considered that neither the sulphur nor the phosphorus form would contribute in any special way nutritionally. In fact they may be more closely associated with the peptide which appears to be covalently linked to the polysaccharide and it becomes a matter of definition as to what is encompassed by the term polysaccharide. 

---