Process for the preparation of cyanine dyes with polysulfonate anions

摘要

A convenient and economical method for preparing infrared absorbing cyanine dyes useful in lithographic printing plate precursors is disclosed. The reaction is generally carried out by condensation of a heterocyclic base containing an activated methylene group and an unsaturated bisaldehyde or its equivalent in a solvent or solvent mixture at about 20-150° C. All the reactions necessary for production of the infrared absorbing cyanine dye may be carried out in one reaction vessel without isolating any intermediate products.