Dye intermediates and their preparation and use in the synthesis of methine dyes

The method of preparing 3-methyl-2-methylenebenzothiazoline which comprises adding 13.4 g. 2,3-dimethylbenzothiazolium p-toluenesulfonate to an ice bath solution essentially consisting of 75 ml. tetramethyl guanidine and 75 ml. ligroine containing about 0.06 mole sodium hydride, said reaction being conducted under anhydrous conditions and with stirring, the 2,3-dimethylbenzothiazolium p-toluenesulfonate being added slowly to the reaction solution over a period of 3 hours, and stirring the reaction mixture thereafter for about 20 hours at about 20.degree.C.

The method of preparing a monomeric methylene base which comprises reacting a heterocyclic quaternary salt selected from the group consisting of a 2-methylthiazolium salt, a 2-methylbenzothiazolium salt, a 2-methylnaphthothiazolium salt, a 2-methylbenzoselenazolium and a 2-methylnaphthoselenazolium salt, with:

• 1. a non-hydroxylic base selected from the group consisting of 1,4-diazabicyclo-2,2,2-octane and tetramethyl guanidine to convert said heterocyclic quaternary salt to the corresponding methylene base, and
• 2. a proton acceptor which prevents formation of the hydro salt of the non-hydroxylic base;
• said reaction being conducted under anhydrous conditions in a non-hydroxylic liquid in which said heterocyclic quaternary salt is sufficiently insoluble to prevent formation of dimer by reaction between the quaternary salt and the methylene base.