DIAMMONIUM PHTHALATE

Ammonium phthalate is an organic intermediate obtained by reacting phthalic acid with ammonia, and can be used to prepare phthalimides. Phthalimides and their derivatives are important intermediates in synthetic organic chemistry. For example, they have important uses in the preparation of bioactive compounds (i.e., antibacterial agents, analgesics, antifungal agents, plant growth regulators) and also in the fuel industry.

Step 1: Acid Hydrolysis to Phthalic Acid
318 g of water was added to a 2-liter multi-neck flask equipped with a stirrer and a thermometer and heated to 95 C. At this temperature, 1.524 g of disodium phthalate in water (19.6%) and 301,8 g of sulfuric acid were added simultaneously to the flask over a period of 1 hour. The mixture was then stirred at 95C for 1 hour and then cooled to 20C.
The phthalic acid was crystallized and evacuated at 20C using a suction filter. The phthalic acid was then washed with 215 g of water.
Step 2: Phthalic acid to ammonium phthalate
In this suction filter the freshly washed phthalic acid was mixed with 89g of water under stirring to form a homogeneous mixture. 221 g of 20% ammonia was added to this mixture at 70C over a period of 1 hour. A solution of 545 g of 47% ammonium phthalate (based on a theoretical yield of 90% conversion of disodium phthalate) was then produced. The solution was stored at a temperature higher than 55C in order to prevent crystallization of the ammonium phthalate.