Preparation of tri-iodo benzene compounds

Abstract

The invention provides a process by which ultra low salt content triiodinated aromatic compounds may be isolated from a highly acidic hot triiodination raction reaction medium in a straightforward fashion. The process involves increasing the pH to above 5 a value in the range of 3 to 7 with sodium hydroxide, addition of sodium bisulphite and/or sodium dithionite, addition of seed crystals, cooling slowly, and washing the collected precipitate with water.

1. A process for the preparation of a 2,4,6-triiodinated benzene ring containing compound which comprises iodinating a 2,4,6-unsubstituted benzene ring containing compound with an iodine halide iodinating agent in an aqueous reaction medium at a pH below 4 and precipitating the triiodinated reaction product, characterised in that precipitation of the triiodinated reaction product is effected by: adding an aqueous base to the reaction medium while this is at a temperature in the range of 70 to 95° C., thereby to bring the pH of the reaction medium to above  5 a value in the range of 3 to 7 ; adding a reducing agent to the reaction medium while agitating the reaction medium, adding seed crystals of the triiodinated reaction product to the reaction medium; cooling the reaction medium to a temperature below 35° C. over a period of 10 to 30 hours, at a cooling rate of 1.5 to 5° C./hour during the period during which precipitation occurs; filtering the reaction medium to collect the precipitated triiodinated reaction product; and washing the precipitated triiodinated reaction product with from 70 to 200% by weight relative to the weight of the precipitated triiodinated reaction product of water, whereby to yield a product having a salt content of less than 0.1% by weight. 
     
     
       2. A process as claimed in  claim 1  wherein said 2,4,6-unsubstituted compound is a 5-amino-benzamide. 
     
     
       3. A process as claimed in  claim 2  wherein said 5-amino-benzamide is a 5-amino-N,N′-bisalkyl-isophthalamide. 
     
     
       4. A process as claimed in claim  1   2  wherein said 5-amino-benzamide is a 5-amino-N,N′-bis(2,3-dihydroxypropyl)-isophthalamide. 
     
     
       5. A process as claimed in  claim 1  wherein said iodine halide is iodine chloride. 
     
     
       6. The process of  claim 1  wherein said product has a salt content of less than 0.05%.