The invention discloses a preparation method of high-purity
sulfanilamide. The preparation method specifically comprises the following steps that (1) a chlorosulfonation reaction is conducted, specifically, m-chloroaniline,
chlorosulfonic acid and
phosphorus trichloride are mixed at the
molar ratio of 1:(2.8-3.6):(1-1.8),
chlorosulfonic acid is added dropwise within 1.5-2 hours in m-chloroanilinewith the temperature being 35-55 DEG C, after dripping is ended, the mixed liquid is maintained for 10-30 minutes, and first mixed liquid is obtained;
phosphorus trichloride is added dropwise into thefirst mixed liquid; and heating is conducted to make the temperature of the mixed product rise to 100-115 DEG C, and heat preservation is conducted for 1.5-3.5 hours at the temperature of 100-115 DEGC; (2) standing is conducted; (3) a chlorosulfonated substance is obtained; (4) an ammoniation reaction is conducted; and (5) refining is conducted, specifically, the obtained
amide is subjected to
dissolution decoloration and
crystallization and purification. By controlling the adding sequence, frequency and amount requirements of the reactants, the reaction can be conducted more sufficiently and
safer, the generated by-products are less, obtaining of high-purity
sulfanilamide can be ensured, and the main component (4-amino-chloro-1,3-benzendisulfonamide) of high-purity
sulfanilamide can beas high as 99.9% or above.