Processes for Chelating Agents

All of the processes used to make aminopolycarboxylic acid chelating agents are similar. They can be illustrated by the route to the tetrasodium salt of 

The manufacturing processes are all variations of the conversion of ethylenediamine to a cyanomethyl (-CH2CN) derivative and hydrolysis of this intermediate. Two processes go directly from ethylenediamine to the final product in a single step. They differ in that one used sodium cyanide (see Eq. 16.3) while the other used hydrogen cyanide and caustic soda (see Eq. 16.4)250. 

Several by-products are formed in these processes. They include ammonia, sodium salts ofNTA (nitrilotriacetic add), iminodiacetic add (IDA), glycolic acid and some partially substituted EDTA compounds. 

A third, two-step synthesis route produces the cyanomethyl derivative in a distinct step. This process uses formaldehyde, hydrogen cyanide and ethylenediamine250. 

The resulting cyanomethyl compound is insoluble in water and is therefore easily separated from excess reactants and by-products that remain in the water. The ammonia by-product is removed by distillation. The purified cyanomethyl compound is then hydrolyzed with caustic soda in a separate step to make pure tetrasodium EDTA250. 

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