PROCESS FOR PREPARING 5-AMINO-2,4,6-TRIIODOISOPHTHALIC ACID DICHLORIDE BY CHLORINATION OF THE CORRESPONDING ACID IN THE PRESENCE OF A TERTIARY AMINE SALT OR QUARTERNARY AMMONIUM SALT

Abstract: A process for the preparation of 5-amino-2,4,6-triiodoisophthalic acid dichloride by chlorinating 5-amino-2,4,6-triiodoisophthalic acid with thionyl chloride in the presence of a suitable solvent and of a tertiary amine salt or quaternary ammonium salt in a molar ratio from 1;1 to 1;2 with respect to 5-amino-2,4,6-triiodoisophathalic acid is described. 5-amino-2,4,6-triiodoisophthalic acid dichloride is an intermediate useful for the preparation of iodinated contrast agents.

Description: PROCESS FOR PREPARING 5-AMIN0-2.4.6-TRII0D0IS0PHTHALIC ACID DICHLORIDE BY CHLORINATION OF THE CORRESPONDING ACID IN THE PRESENCE OF A TERTIARY AMINE SALT OR QUARTERNARY AMMONIUM SALT ************************* The present invention relates to a process for the preparation of an intermediate useful in the synthesis of organic compounds and, more particularly, it relates to a process for the preparation of 5-amιno-2,4,6-tnιodoιsophthahc acid dichloride 5-Amιno-2,4,6-tnιodoιsophthalιc acid dichloride is a known compound useful for the preparation of lodinated contrast agents among which Iopamidol (British patent No 1,472,050 - Savac AG) and Ioversol (European patent application No 0083964 - Mallinckrodt Inc ) can be αted Several examples of synthesis of 5-amιno-2,4,6-tnιodoιsophthahc acid dichloride are reported in the literature and all of them foresee the chlonnation of 5-amιno-2,4,6-tnιodoιsophthahc acid with thionyl chlonde In particular, we can ate the syntheses descπbed in the already mentioned British patent No 1,472,050, in the Belgian patent No 852,418 (Mallinckrodt Inc ) and in the U S A patent No 3,655,752 (Sterling Drug Inc ) which use a strong excess of thionyl chlonde and which require a long and cumbersome work up, hardly suitable under an industrial viewpoint, even if in some cases they allow to afford the desired dichlonde with high yields The synthesis descnbed in the European patent application No 0118347 (Guerbet S A ) foresees the use of excess thionyl chlonde too, but in the presence of catalytic amounts of N,N-dιmethylformamιde The yields are high but the work up requires the removal of excess thionyl chlonde by evaporation also in this case The use of solvents such as ethyl acetate, as descnbed in the International patent applications No WO 91/09007 (Mallinckrodt Inc ) and No WO 93/10825 (Mallinckrodt Inc ) or in the already mentioned European patent application No 0083964, does not allow to obtain the desired dichlonde with satisfactory yields We have now found that, by carrying out the chlonnation reaction of 5-amιno-2,4,6- tniodoisophthahc aαd with thionyl chlonde in a suitable solvent in the presence of a tertiary amine salt or quaternary ammonium salt, the corresponding dichlonde is obtained not only in high yields but also substantially free from impunties and in crystalline form by simple dilution of the reaction mixture with water Therefore, object of the present invention is a process for the preparation of 5-amιno-2,4,6- tniodoisophthalic aαd dichlonde by chlonnation of 5-aπuno-2,4,6-tnιodoιsophthalιc aαd with thionyl chlonde in the presence of a solvent characterized m that the reaction is earned out in the presence of a tertiary amme salt or quaternary ammonium salt m a molar ratio from 1 1 to 1 2 with respect to 5-amιno-2,4,6-tnιodoιsophthalιc aαd The 5-anuno-2,4,6-tnιodoιsophthalιc aαd dichlonde obtained according to the process of the present invention is useful as intermediate in the synthesis of lodinated contrast agents The amount of thionyl chlonde used in the process object of the present invention is generally from 2 to 8 moles with respect to 5-amιno-2,4,6-tnιodoιsophthalιc aαd Preferably, from 4 to 6 moles of thionyl chlonde by mole of 5-amιno-2,4,6-tnιodoιsophthalιc aαd are used Tertiary anune salts which can be used in the process object of the present invention are generally hydrohalides, preferably hydrochloπdes or hydrobromides Quaternary ammonium salts which can be used in the process object of the present invention are generally halides, preferably chlorides or bromides The tertiary amines are generally tnalkylamines, preferably tnethylamine Quaternary ammonium salts are generally tetraalkylammonium salts, preferably tetraethylammomum or tetrabutylammomum salts Examples of tertiary anune salts and of quaternary ammomum salts used in the process object of the present invention are tnethylamine hydrochlonde, tnethylamine hydrobromide, tetrabutylammonium chlonde, tetrabutylammomum bromide, tetraethylammomum bromide and tetraethylammomum chlonde Preferably tnethylamine hydrochlonde, which can be optionally prepared m situ, is used The amount of tertiary anune salt or quaternary ammomum salt is preferably equimolar (molar ratio 1 1 ) with respect to 5-amιno-2,4,6-tnιodoιsophthahc aαd Suitable solvents are ethyl acetate, methylene chlonde, chloroform and 1 ,2-dιchloroethane Preferably methylene chlonde is used A preferred practical embodiment of the present invention is the following Thionyl chlonde is added to a suspension of 5-amιno-2,4,6-tπιodoιsophthalιc aαd, tnethylamine and methylene chlonde and the reaction mixture is heated under reflux for some hours At the end of the addition, water is added and the preαpitation of a crystalline product is observed By simple filtration and washing, 5-amιno-2,4,6-tπιodoιsophthalιc aαd dichlonde is obtained m pure form The charactenzing feature of the process object of the invention is the presence of amounts at least equimolar of a tertiary anune salt or of a quaternary anune salt The use of said salt in the above indicated amounts allows to obtain the desired produrt with extremely high yields and, above all, free from impurities which should make difficult its isolation with a puπty degree suitable for its use as intermediate in the synthesis of lodinated contrast agents It is worth underlining that the substantial absence of by-products in the reaction of preparation of 5-amιno-2,4,6-tnιodoιsophthahc aαd dichlonde according to the process object of the present invention does not result exclusively in an improvement of the overall yield of the process with respect to the known methods, but allows also the isolation of the desired product with simple operations of dilution in water of the reaction mixture It is evident to the man skilled in the art the advantage denvmg from the possibility of carrying out a process for the synthesis of an intermediate with high yields, high puπty, through extremely simple operations, without reqiunng either the removal of thionyl chlonde by evaporation or repeated purification operations for isolating the desired product in pure form As already underlined, contrary to what descnbed in the known processes for the preparation of 5-armno-2,4,6-tnιodoιsophthalιc aαd dichlonde, the isolation of the pure product is earned out by simple dilution with water of the reaction mixture As far as we know, a mechanism able to explain the unexpected advantages denvmg from the use of a tertiary anune salt or of a quaternary ammomum salt according to the process object of the present invention cannot be assumed Probably, the salt forms an adduct with thionyl chlonde In this connection, it is worth noting that the literature (European patent application No 0026281 - Bracco Industna Chimica S p A ) desenbes the preparation of 5-methylamιno- 2,4,6-tπιodoιsophthahc aαd dichlonde by reaction with thionyl chlonde in the presence of small amounts of quinoline, without reporting the yields yet However, the use of quinoline or of a tertiary anune salt or quaternary ammonium salt in molar amounts significantly lower than 1 1 with respect to 5-amιno-2,4,6-tnιodoιsophthalιc aαd does not allow to obtain the desired product with high yields .and, above all, with a suitable punty degree In particular, by using quinoline in catalytic amounts as descnbed in the European patent application No 0026281, the desired dichlonde is obtained in admixture with not negligible amounts of by-products and then with a puπty degree not suitable for the use as intermediate in the subsequent steps of the process for the preparation of lodinated contrast agents In order to illustrate the present invention the following examples are now given Example 1 Methylene chlonde (280 g), tnethyiamine (25 5 g, 0 25 moles) and water (2 25 g, 0 125 moles) were charged in this order into a reactor After addition of thionyl chlonde (14 9 g, 0 125 moles) dropwise while keeping the temperature below 30°C, 5-amιno-2,4,6-tnιodoιsophthalιc aαd (140 g, 0 25 moles) and, in about 1 5 hours, thionyl chlonde (143 g, 1 2 moles) were added while keeping the internal temperature below 36°C and adjusting the addition rate with the gas emission At the end of the addition, the reaction mixture was kept under reflux (43°C) for 28 hours After coolmg to about 30°C, methylene chlonde (65 g) and, in small portions, water (100 g) were added At about half of the addition, the formation of a crystalline preαpitate was observed After filtration, the resultant product was reduced to pulp with water (200 g) and then dπed in oven under vacuum at 60°C for about 21 hours obtaining 5-amιno-2,4,6-tnιodoιsophthalιc aαd dichlonde (139 g, 93 3% yield) practically pure by HPLC analysis and by thin layer chromatography Example 2 Methylene chlonde (280 g), tnethylamine (51 g, 0 5 moles) and water (4 5 g, 0 25 moles) were charged in this order mto a reactor After addition of thionyl chlonde (30 g, 0 25 moles) dropwise while keeping the temperature below 30°C, 5-amιno-2,4,6-tπιodoιsophthalιc aαd (140 g, 0 25 moles) and, in about 2 hours, thionyl chloride (143 g; 1.2 moles) were added while keeping the internal temperature below 36°C and adjusting the addition rate with the gas emission. At the end of the addition, the reaction mixture was kept under reflux (about 43°C) for 22 hours. After cooling to about 30°C, water (100 g) was added in small portions. At about half of the addition, the formation of a crystalline precipitate was observed. Subsequently, the addition of water (250 g total) was completed and the precipitate was filtered. The resultant product was reduced to pulp twice with water (2x300 g) and then dried in oven under vacuum at 60°C for about 21 hours obtaining 5-aminc-2,4,6-triiodoisophthalic acid dichlonde (140.7 g; 94.4% yield) practically pure by HPLC analysis and by thin layer chromatography. Example 3 Methylene chloride (112 g) and tetrabutylammonium bromide (3.23 g; 0.1 moles) were charged in this order into a reactor. 5-Anuno-2,4,6-triiodoisophthalic acid (55.9 g; 0.1 moles) and, in about 2 hours, thionyl chlonde (57.1 g; 0 479 moles) were added to the mixture while keeping the internal temperature below 36°C and adjusting the addition rate with the gas emission. At the end of the addition, the rea- tion mixture was kept under reflux (43°C) for 27 hours After coolmg to about 20°C, water (60 g) was added in small portions. At about half of the addition, the formation of a crystalline precipitate was observed After filtration, the resultant product was washed with water (5x50 g) and then dned in oven under vacuum at 50°C for about 21 hours obtaining 5-amino-2,4,6-triiodoisophthalic acid dichlonde (49.99 g; 83.8% yield) practically pure by HPLC analysis and by thin layer chromatography.

Claims: Claims 1) A process for the preparation of 5-amιno-2,4,6-tnιodoιsophthalιc aαd dichlonde by chlonnation of 5-anuno-2,4,6-tnιodoιsophthalιc aαd with thionyl -chlonde m the presence of a solvent charactenzed in that the reaction is earned out in the presence of a tertiary anune salt or quaternary ammonium salt in a molar ratio from 1 1 to 1 2 with respect to 5-amιno-2,4,6- tπiodoisophthalic aαd 2) A process according to claim 1 wherem the amount of thionyl chlonde is from 2 to 8 moles by mole of 5-aπunc-2,4,6-tπιodoιsophthalιc aαd 3) A process according to claim 2 wherem the amount of thionyl chlonde is from 4 to 6 moles by mole of 5-amιno-2,4,6-tπιodoιsophthalιc aαd 4) A process according to claim 1 wherem the tertiary anune salts or quaternary anune salts are tertiary anune hydroha des or quaternary ammomum ha des 5) A process accordmg to claim 4 wherem the salts are tertiary anune hydrochloπdes or hydrobromides or quaternary ammomum chloπdes or bromides 6) A process accordmg to claim 1 wherein the tertiary amines are tnalkylaπunes 7) A process according to claim 6 where the tertiary anune is tnethylamine 8) A process according to claim 1 wherem the quaternary ammomum salts are tetraalkylammomum salts 9) A process accordmg to claim 8 wherein the quaternary ammomum salt is selected among tetraethylammomum and tetrabutylammomum salts 10) A process according to claim 1 wherein the tertiary amine salts or quaternary ammomum salts are selected among tnethylamine hydrochlonde, tnethylamine hydrobroπude, tetrabutylammomum chlonde, tetrabutylammomum bromide, tetraethylammomum bromide and tetraethylammomum chlonde 1 1) A process according to claim 10 wherein tnethylamine hydrochlonde is used 12) A process accordmg to claim 1 wherem the amount of tertiary amine salt or quaternary ammomum salt is equimolar with respect to 5-amιno-2,4,6-tnιodoιsophthahc aαd 13) A process accordmg to claim 1 wherem the solvent is selected among ethyl acetate, methylene chlonde, chloroform and 1,2-dιchloroethane 14) A process accordmg to claim 13 wherem the solvent is methylene chlonde

Inventors: BARRECA GIUSEPPE, CANNATA VINCENZO, VELGI CORRADO, BARRECA, GIUSEPPE, CANNATA, VINCENZO, VELGI, CORRADO
Applicants: BARRECA GIUSEPPE, CANNATA VINCENZO, VELGI CORRADO, ZAMBON SPA, BARRECA, GIUSEPPE, CANNATA, VINCENZO, VELGI, CORRADO, ZAMBON GROUP S.P.A.
Application year: 1995
Main classification: C07C227
IPC codes: C07C227, C07C229