The present invention provides a novel polymorphic form of olopatadine hydrochloride ([(Z)-3-(dimethylamino)propylidene]-6,11-dihydrodibenz[b,e]oxepin-2-acetic acid hydrochloride), a selective histamine H1-receptor antagonist that is used for the treatment of ocular symptoms of seasonal allergic conjunctivitis. The present invention also provides novel methods for producing olopatadine on a large scale, and in a manner that is cost effective, provides a low level of impurities and eliminates the need to use the costly and dangerous base, butyllithium, which is used in prior art reactions for making olopatadine. The present invention further provides novel processes for carrying out a large scale production of 3-dimethylaminopropyltriphenylphosphonium bromide and its corresponding hydrobromide salt, which are employed in the production of olopatadine, and pharmaceutically acceptable salts of olopatadine.