Process for the preparation of cyanine dyes with polysulfonate anions

A method for preparing infrared absorbing cyanine dyes of the structure:

• in which:
• R1 is hydrogen, or R1 is one or more alkyl, alkoxy, carboxyl, nitro, cyano, trifluoromethyl, acyl, alkyl or aryl sulfonyl, or halogen groups, or R1 is the atoms necessary to form a substituted or unsubstituted benzo group;
• R2 is alkyl, aryl, or aralkyl;
• Nu is halogen, substituted or unsubstituted phenoxy, substituted or unsubstituted thiophenoxy, or substituted or unsubstituted diphenylamino;
• Y is O, S, NR′, or C(R′)2, where R′ is hydrogen or alkyl;
• m is zero or one;
• n is two, three, or four;
• and
• A is an aromatic group that has n sulfonate groups;
• the method comprising the steps of:
• a) reacting an activated methylene group containing a heterocyclic base of the structure:
• with a compound of the structure:
• and forming an intermediate in a reaction mixture;
• in which W is O or Ar—N, Ar is an aromatic group, X− is an anion, and m is zero or one, and
• b) adding a salt of A to the reaction mixture;
• and
• c) isolating the infrared absorbing cyanine dye;
• in which the infrared absorbing cyanine dye is the only compound isolated in the method.