Process for the preparation of cyanine dyes with polysulfonate anions
View Patent ↗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.
1. A method for preparing infrared absorbing cyanine dyes of the structure:
in which:
R 1 is hydrogen, or R 1 is one or more alkyl, alkoxy, carboxyl, nitro, cyano, trifluoromethyl, acyl, alkyl or aryl sulfonyl, or halogen groups, or R 1 is the atoms necessary to form a substituted or unsubstituted benzo group;
R 2 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.
2. The method of claim 1 in which R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; Nu is chloro, phenoxy, thiophenoxy, or diphenyl amino; and Y is C(CH 3 ) 2 , O, or S.
3. The method of claim 2 in which A is selected from the group consisting of biphenyl-4,4′-disulfonate; diphenyl ether-4,4′-disolfonate; stilbene-2,2′-disulfonate; 2,2′-dihydroxy-4 ,4′-dimethoxybenzophenone-5,5′-disulfonate,
4. The method of claim 2 in which n is 2 and A is 4,5-dihydroxy-1,3-benzenedisulfonate.
5. The method of claim 1 in which Nu is chloro.
6. The method of claim 5 in which R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; and Y is C(CH 3 ) 2 , O, or S.
7. The method of claim 6 in which n is 2 and A is 4,5-dihydroxy-1,3-benzenedisulfonate.
8. The method of claim 7 in which Y is C(CH 3 ) 2 .
9. The method of claim 8 in which n is 2 and A is 4,5-dihydroxy-1,3-benzenedisulfonate.
10. The method of claim 1 additionally comprising, after step a) and before step b), an additional step of adding a substituted or unsubstituted phenoxy, a substituted or unsubstituted thiophenoxy, or a substituted or unsubstituted diphenylamino compound to the reaction mixture.
11. The method of claim 10 in which R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; Nu is phenoxy, thiophenoxy, or diphenyl amino; and Y is C(CH 3 ) 2 O, or S.
12. The method of claim 11 in which A is 4,5-dihydroxy-1,3-benzenedisulfonate.
13. The method of claim 12 in which Y is C(CH 3 ) 2 .
14. The method of claim 13 in which n is 2 and A is 4,5-dihydroxy-1,3-benzenedisulfonate.
15. The method of claim 1 in which the dye is isolated by filtration.
16. The method of claim 15 in which R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; Nu is chloro, phenoxy, thiophenoxy, or diphenyl amino; and Y is C(CH 3 ) 2 , O, or S.
17. The method of claim 16 in which A is 4,5-dihydroxy-1,3-benzenedisulfonate.
18. The method of claim 1 in which:
R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; Nu is chloro; Y is C(CH 3 ) 2 , O, or S; and A is 4,5-dihydroxy-1,3-benzenedisulfonate; and
the method consists essentially of steps a), b), and c).
19. The method of claim 1 in which:
R 1 is hydrogen; R 2 is methyl, ethyl, n-propyl, or n-butyl; Nu is phenoxy, thiophenoxy, or diphenyl amino; R 2 is methyl, ethyl, n-propyl, or n-butyl; Y is C(CH 3 ) 2 , O, or S; and A is 4,5-dihydroxy-1,3-benzenedisulfonate; and
the method consists essentially of steps a), b), c), and an additional step of adding a substituted or unsubstituted phenoxy, a substituted or unsubstituted thiophenoxy, or a substituted or unsubstituted diphenylamino compound to the reaction mixture.