2-Tridecanone → 2,3-Dihydroperimidine

1,8-Diaminonaphthalene of 26.05 g, 32.66 g of 2-tridecanone, 55 mg of p-toluenesulfonic acid monohydrate, and 250 ml of toluene were mixed with stirring. The reaction mixture was refluxed with heating under a nitrogen atmosphere and was allowed to react for 5 hrs. using Dean-Stark trap to remove water from the reaction mixture Thereafter, the mixture was washed with aqueous saturated sodium hydrogen carbonate solution, dried using potassium carbonate anhydride, filtered and solvent was removed under reduced pressure. The product was distilled to obtain 46.50 g of dihydroperimidine intermediate, exhibiting a boiling point of 192 to 213° C./0.3 to 0.4 Torr. The thus prepared dihydroperimidine intermediate of 8.00 g, 1.48 g of squaric acid, 64 ml of n-butanol and 64 ml of toluene were mixed with stirring. The reaction mixture was refluxed with heating under a nitrogen atmosphere and was allowed to react for 3 hrs. using Dean-Stark trap to remove water from the reaction mixture Thereafter, the mixture was filtered, run into petroleum ether and allowed to stand at a temperature of 5° C. for 18 hrs. The product was filtered out, washed with petroleum ether and air-dried to obtain 6.00 g of squarylium dye SS-1. The dye was recrystalized from the mixture of tetrahydrofuran and petroleum ether to refine the product. exhibiting an maximum absorption wavelength (?max) of 802 nm (e=1.8×105) in ethyl acetate.