Process for the preparation of a quinoline carboxylic acid

1. A process for the preparation of a carboxylic acid of formula (IV)

wherein R 1 is hydrogen or chlorine,

comprising the steps of:

(i) subjecting a compound of formula (V)

wherein: R 1 is as defined above; and R 2 is C 1 -C 18 alkyl; C 1 -C 6 alkoxyC 1 -C 8 alkyl-; or phenyl or benzyl, wherein the phenyl or benzyl is optionally substituted on the ring by 1, 2 or 3 of independently fluorine, chlorine, C 1 -C 2 alkyl, C 1 -C 2 alkoxy, C 1 fluoroalkyl, or C 1 fluoroalkoxy;

to hydrolysis under acidic conditions to give a solution of a quinolinium salt whose cation is of formula (VI)

wherein R 1 is as defined above; and

(ii) adding base to the solution obtained in step (i) to give the free carboxylic acid (IV).

2. A process as claimed in claim 1 , wherein R 1 is chlorine.

3. A process as claimed in claim 1 wherein R 2 is straight-chain C 1 -C 10 alkyl or non-tertiary branched C 3 -C 10 alkyl.

4. A process as claimed in claim 1 wherein the acid hydrolysis step (i) is carried out under aqueous conditions and uses an acid having a pK a of less than 1.

5. A process as claimed in any preceding claim 1 wherein, in the hydrolysis step (i), the reaction is conducted at a temperature ranging from 50 to 120° C.

6. A process as claimed in claim 1 wherein, in step (ii), the base comprises a group (I) or group (II) metal hydroxide or carbonate.

7. A process as claimed in claim 1 wherein the base added in step (ii) is aqueous lithium hydroxide, aqueous sodium hydroxide or aqueous potassium hydroxide.

8. A process as claimed in claim 1 wherein the base in step (ii) is added until a pH in the range of 1.8 to 3.8 is achieved.

9. A process as claimed in claim 8 wherein the base in step (ii) is added until a pH in the range of 2.5 to 3.1 is achieved.

10. A process as claimed in claim 1 wherein R 2 OH, which is produced in hydrolysis step (i) as a by-product, is continuously removed from the reaction mixture.

11. A process as claimed in claim 1 comprising the further step of combining compound (IV) with a herbicide and optionally one or more agriculturally acceptable carriers, adjuvants and/or excipients.

12. A process as claimed in claim 1 wherein the carboxylic acid (IV) obtained has a volume average particle size distribution such that DV 10 is in the range of between 1 and 15 micrometers, DV 50 is in the range of between 15 and 35 micrometers, and DV 90 is in the range of between 35 and 70 micrometers.

13. A compound of the formula

wherein n is 1, 2 or 3, R 1 is as defined in claim 1 , and A n− is an n valent anion.

14. Particulate carboxylic acid of formula (IVa):

wherein R 1 is chlorine,

having a volume average particle size distribution such that DV 10 is in the range of between 1 and 15 micrometers, DV 50 is in the range of between 15 and 35 micrometers, and DV 90 is in the range of between 35 and 70 micrometers.

15. Particulate carboxylic acid of formula (IVa), as claimed in claim 14 , having a volume average particle size distribution such that DV 10 is between 5 and 10 micrometers, DV 50 is between 20 and 30 micrometers, and DV 90 is between 40 and 60 micrometers.

16. A herbicidal composition comprising particulate carboxylic acid (IVa), as defined in claim 14 , together with at least one herbicide, and optionally one or more agriculturally acceptable carriers, adjuvants and/or excipients.

17. A herbicidal composition as claimed in claim 16 , wherein the herbicide is selected from pyroxsulam, pinoxaden, clodinafop-propargyl, and combinations thereof.