Preparation of tri-iodo benzene compounds
View Patent ↗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%.