Process of concentration and purification of organic compounds

Details Process of concentration and purification of organic compounds Process of concentration and purification of organic compounds

1993-08-20

1995-09-05

Spear, Frank

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210641, 210651, 210259, B01D 6114

Patent

active

054476356

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process aimed at concentrating and purifying raw aqueous solutions of water-soluble non-ionic organic compounds, preferably those which are useful as contrast enhancing agents in diagnostic procedures, such as for example X-ray, NMR and ultrasound diagnosis, through the use of techniques of tangential filtration on membranes. This process also allows the recovery of valuable reactants in excess and of reaction solvents, if any. It is particularly useful for purifying expensive non-ionic iodinated compounds, which now have been widely used in X-ray imaging.
The introduction in X-ray diagnosis of contrast media containing non-ionic iodinated compounds as opacifying agents represented a remarkable progress in the state of this field, so these media will eventually substitute the traditional iodinated ionic products (see: Grainger and Dawson, Clinical Radiology, 1990, 42, 1-5).
However the synthetic processes and, particularly, the final purification of these products are more complex and expensive than those previously used to obtain the ionic contrast media. In fact, neutral iodinated opacifying agents differ from the ionic ones because they cannot be isolated and purified by precipitation from water due to their high solubility in this solvent. Hence, the following problems must still be conveniently solved: the removal of ionic species, usually inorganic salts, present in the final reaction mixture, the recovery of valuable reagents in excess and of the water-soluble reaction media. A preferred technique to be performed (see patents: DE 1909439, GB 1472050, EP 26281) is the one based on the submission of the raw solutions of the contrast media to a complex series of operations such as:
preliminary removal of the solvent, usually dimethylacetamide (DMAC) or dimethylformamide (DMF), by evaporation,
dilution by water of the residue,
extraction of the residual reaction medium, preferably with a chlorinated solvent,
elution of the aqueous phase on a system of columns of cationic and anionic ion-exchange resins,
concentration of the eluate by evaporation,
crystallization of the crude residue from hydroalcoholic mixtures in order to remove the last neutral impurities.
The drawbacks connected with this type of process are clear. For instance, large purification plants for ion-exchange resins are needed and their running is extremely complex and expensive. In addition, a large quantity of thermal energy is required for the concentration of the considerable volumes of water to be used. It is also necessary to use, to recover and to remove polluting and toxic organic solvents such as the chlorinated ones. Last but not least, the concentration of extremely dilute solutions causes the corresponding concentration of impurity traces and the submission of the final product to a long-lasting thermal treatment.
Another process which can be carried out (see patents: EP 83964, WO 8908101) implies the purification of raw solutions of non-ionic contrast media through preparative liquid chromatography. This technique is extremely complex and expensive too, and in addition it is not suitable for industrial application.
EP 0391621 generically mentions the possibility to use ultrafiltration or column chromatography as an optional further purification step in the preparation of iodized hydroxyethyl starch.
A general treatise of ultrafiltration and reverse osmosis techniques is found in Handbook of Separation Process Technology, R. W. Rousseau ed., John Wiley and Sons, 1987.
The diafiltration process is described for example in Separation Techniques for Chemical Engineers, P. A. Schweitzer ed., McGraw Hill Book Company, 1988.
The process of this invention involves this method on highly concentrated solutions of water-soluble neutral iodinated contrast agents, by obtaining extremely favourable and absolutely unexpected results if compared to the state of the art.
It is known that organic impurities with low relative mass and/or inorganic salts can be removed from aqueous dilute solutions through tangential

REFERENCES:
patent: 5114703 (1992-05-01), Wolf et al.
patent: 5312615 (1994-05-01), Schneider et al.

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