Method and composition for hardening gelatin

Abstract

A method for hardening gelatin which comprises using as a hardening agent a compound represented by formula (I): ##STR1## wherein R.sub.1, when taken along, may be alkyl of 1 to 20 carbon atoms, aralkyl of from 7 to 20 carbon atoms, aryl of from 6 to 20 carbon atoms, and alkenyl of from 2 to 20 carbon atoms. R.sub.1 and R.sub.2 can also combine with each other to form a heterocyclic ring of 5 to 8 atoms. The R.sub.1 -R.sub.2 ring contains the nitrogen atoms to which R.sub.1 and R.sub.2 are attached, and may also contain an additional nitrogen atom. R.sub.2 and R.sub.3 can combine to form either a 5 or 6 membered ring. The R.sub.2 -R.sub.3 ring contains the nitrogen atom to which R.sub.2 is attached, and may also contain one or two additional nitrogen atoms. R.sub.4 may be hydrogen or alkyl of 1 to 4 carbon atoms. R.sub.5 may be hydrogen or one or more substituents at any of positions 3 through 6 on the pyridine ring, including alkyl of 1 to 20 carbon atoms, aryl of from 6 to 20 carbon atoms, aralkyl of from 7 to 20 carbon atoms, or alkenyl of from 2 to 20 carbon atoms, alkoxy of 1 to 20 carbon atoms, aryloxy of from 6 to 20 carbon atoms, carboxy, halogen, nitro, or sulfo. R.sub.5 may be in a fused ring structure such as in quinoline. X.sup.- represents an anion or an anionic portion of compounds of formula (I) effectively harden gelatin with little or no afterhardening. These compounds are useful in hardening gelatin in photographic elements.