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If picrylsulphide is heated on the waterbath with nitric acid of 
1.52 sp. gr. the unchanged substance is obtained on diluting with 
water, while tetranitrodiphenylsulphide (1. 3. 4) when treated in 
the same manner, is entirely converted into the corresponding sulphone. 
Picrylsulphide may even be heated with the same nitric acid for 
some hours at 200° in a sealed tube without undergoing any 
change. 
If we look into the formula of picrylsulphide we notice that 
four nitro-groups occupy an ortho-position in regard to the sulphur 
atom. It was therefore probable that the sulphur atom is protected 
by these nitro-groups against the oxidising action of the nitric acid; 
a case, therefore, of so-called sterical obstacle (iindrance). 
After this had been confirmed the following questions arose: 
1°. Are perhaps two nitro-groups, when occupying an ortho-position 
in regard to the sulphur atom in one of the benzene nuclei, alone 
sufficient to prevent the oxidising action of the nitric acid? This 
was not quite improbable after VicroR MeyYER’s researches on 
esterification and those of HOLLEMAN on the protective action of 
ortho-placed nitro groups during the action of Cl and Br on 2.6. 
dinitrotoluene etc. !). 20. Are there other atoms or atomic groups 
which exercise the same influence ? 
To answer the first question trinitrothioanisol, prepared by the 
action of methyliodide on sodium thopicrate, was treated with 
nitrie acid. The trinitrothioanisol m.p. 98° was converted into a sub- 
stance with m.p. 210° whilst the analysis showed that oxygen had 
indeed been absorbed; the two ortho-placed nitro-groups alone were 
consequently insufficient to protect the sulphur atom against the 
action of the nitric acid. 
To answer the second question two of the ortho-placed nitro- 
groups in the picrylsulphide were replaced by cyanogen in such a 
manner that a CN-group was present in each of the benzene nuclei. 
This compound seemed also to be stable towards nitric acid. After- 
wards the compound was tested in which two nitro-groups of the 
picrylsulphide were replaced by CH; This compound also was not 
changed by heating on the waterbath with nitric acid of 1.52 sp.gr. 
It therefore appears that the cyanogen and the methyl-group as 
well as the nitro-group can protect the sulphur atom against the 
oxidising action of the nitric acid. 
nnn end 
1) Compare ScroLtz, Raumerfüllung der Atomgruppen. 
18* 
