The invention provides a process for the preparation of a carboxylic acid of formula (IV) (which is useful as a safener for herbicides): wherein R1 is hydrogen or chlorine, comprising the steps of: (i) subjecting a compound of formula (V) wherein: R1 is as defined above； and R2 is C1-C18 alkyl； C1-C6 alkoxyC1-C8 alkyl-； optionally substituted phenyl； or optionally substituted benzyl； to hydrolysis under acidic conditions to give a solution of a quinolinium salt； and (ii) adding base to the solution obtained in step (i) to give the free carboxylic acid (IV). The invention also provides a solid (e.g. particulate) form of one quinoline carboxylic acid compound within formula (IV) defined by R1 being chlorine； and novel intermediates useable in the above process.
