Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

SALVAKSAN 295
hydroxide solution, adding approximately one equivalent of sodium
nitrite, cooling the solution by addition of ice and acidifying with
hydrochloric acid. The diazonium solution when mixed with an
alkaline solution of j8-naphthol produces the corresponding red
azo-dye. (Formulate!)
The introduction of the arsinic acid group into the aromatic nucleus
is of great interest in connexion with the therapeutic application of
arsenic compounds in combating certain infectious diseases (atoxyl =
sodium arsanilate ; salvarsan).
Arsanilic acid was first synthesised, in very poor yield, by melting
arsenic acid with aniline :
Compare this process with sulphonation and nitration, and note
especially the difference between nitrogen and arsenic, which are introduced
respectively as the neutral nitro-group and the corresponding
hydrate, viz. the dibasic arsinic acid group.
The reduction of the arsinic acids to arsenobenzenes corresponds to
that of the nitro-compounds to azo-compounds :
^ < f + 6 H2O .
OH \ / \ /
If the y-hydroxy-compound, obtained by boiling diazotised arsanilic
acid with water, is nitrated, and the nitro-group so introduced is reduced
to the amino-group, further reduction yields the corresponding arsenocompound,
salvarsan. (Formulate these reactions !)
The introduction of the arsinic acid group into the benzene ring,
which generally takes place in Bart's reaction as above described,
probably involves the formation of an intermediate product having a
structure analogous to that of diazosulphonate (p. 297, footnote). This
intermediate product does not undergo rearrangement to the stable
anti-ioma. so rapidly as does the diazosulphonate, but decomposes with
evolution of nitrogen.
C6Hs.N=N + NaAs^-ONa —> C6H5.N=N.As^-ONa + NaCl
Cl M)H \
>- C6Hs.As^-ONa + N2 .
M)H