Replacement of oxygen by sulfur groups

Treatment of alkyl halides with alkali thiocyanates leads to replacement of the halogen with formation of thiocyanic esters (organic thiocyanates). However, it is impossible to foretell whether thiocyanic esters or the isothiocyanic esters ( mustard oils ) will be products by this method but in all cases the latter is the more stable, so that thiocyanates can be converted into isothiocyanates by heat. 

There are also preparatively important methods for preparation of thiocyanic esters that start from dithiocyanogen, which behaves in its reactions as a pseudohalogen, so that it can add to olefinic double-bond systems and substitute aromatic compounds. Kaufmann362 and also Wood363 have reviewed the preparation of organic thiocyanates, which has been described previously (pages 203, 213 ) in the present volume. 

Thiocyanic esters can also be obtained by treating arene-364 or alkane-sulfenyl chlorides,365 including trichloromethanesulfenyl chloride,366 with potassium cyanide  

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Sulfur or the thiol group may be substituted for functional groups as well as for hydrogen in the presence of nickel sulfide catalysts. Simultaneous replacement of oxygen by sulfur in carbonyl compounds and hydrogenation to thiols may be carried put over nickel sulfide catalysts. 

The replacement of oxygen by sulfur results in a red shift of the first absorption band of around 0.21 eV. However, the substitution of the terminal hydrogen for the methyl group does not modify the band position, fir the four derivatives there is a flux of charge from the phenolic part toward the rest of the molecule. This flux is larger in pCA and pCMe, 0.22 e, than in pCTA and pCTMe , 0.13 e. Consequently, the delocalization of the charge is larger in the excited state of the 0X0 derivatives that becomes more stable than the thio derivatives. 

Bivalent Sulfur. The prefix thio, placed before an affix that denotes the oxygen-containing group or an oxygen atom, implies the replacement of that oxygen by sulfur. Thus the suffix -thiol denotes — SH, -thione denotes —(C)=S and implies the presence of an =S at a nonterminal carbon atom, -thioic acid denotes [(C)=S]OH [(C)=0]SH (that is, the O-substituted acid and the 5-substi-... 

In the parent unsubstituted ring systems cf. first column of Table 32) replacement of a —CH=CH— group with a sulfur atom has little effect, and replacement of a —CH=CH— group with an oxygen atom lowers the boiling point by ca. 40 °C. 

Carius (8) replaced the oxygen in phosphoryl chloride by sulfur. This may be somewhat analogous to the replacement of oxygen in a carbonyl group by sulfur using phosphorus pentasulfide. Prinz (8) used thionyl chloride in his reaction with phosphorus sulfide and De Fazi (2) used carbon tetrachloride in a very interesting preparation of this important intermediate. 

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