Date of Award
Master of Science in Chemical Engineering - (M.S.)
James A. Bradley
The work described in this thesis was undertaken with the view of exploring a reaction sequence suggested by early French investigators to synthesize 2-amino-4-chlorophenol-6-sulfonic acid especially in reference to the German claim that a low yield of product would result following this preparation, In particular, a successful application of this procedure would afford a relatively direct and inexpensive route to the sulfonic acid which is used as an azo dyestuff intermediate and could possibly find application in medicinal chemistry.
It was found that sulfonation and nitration of p-dichlorobenzene gave a high yield of the sodium-2-nitro-1,4-3 dichloro-benzene-6-sulfonate (91%) when using the "salting out" procedure. Rate studies on the hydrolysis of this product indicate that high purity of the sulfonate as roll as concentration and strength of base are essential for conversion to the sodium-2-nitro-4-chlorophenol-6-sulfonate. Use of a pure starting material afforded a substantial increase in yield (10-20%) over use of crude sodium-2-nitroo-1,4-dichloro-benzene-6-sulfonate, Purification may be accomplished by recrystallization from absolute ethanol. A ratio of four moles of sodium hydroxide per mole of the sodium-2- nitro-1,4-dichloro-benzene-6-sulfonate in aqueous medium gave the maximum yield of the sodium-2-nitro-4-chlorophenol-6-sulfonate (73%) during four hours at a temperature of 95?, This was in contrast to the German claim of a preponderance of their undesired "3-nitro isomer" along with the formation of sodium nitrite which could not be detected by several analytical methods,
The employment of inorganic reducing agents for the conversion of sodium-2-nitro-4-chlorophenol-6-sulfonate to 2-amino-4-chlorophenol-6-sulfonic acid resulted in either failure or poor yields except for stannous chloride and hydrochloric acid which gave a yield of 81% and sine and hydrochloric acid which gave 57%. Catalytic hydrogenation in either aqueous acid or alkaline media afforded a smooth means of reduction, yields of 70 to 83% being experienced with 0 palladium on charcoal, platinum oxide, and palladium oxide, Raney nickel gave only 38% of product.
By a careful study of reaction conditions it was possible to obtain the 2-amino-4-chlorophenol-6-sulfonic acid in overall yields of 51 to 55%.
Bronner, Herman Albert, "The synthesis of 2-amino-4-chlorophenol-6 sulfonic acid" (1951). Theses. 2170.