Routes to Novel Azo compounds
Iannarelli, Paul M.
Routes to novel heterocyclic azo compounds and components of use as potential inkjet dyes were investigated. A new route to fluorenones from biphenyl acid chlorides using FVP (Flash Vacuum Pyrolysis) has been discovered. Fluorenone and 4-methylfluoren-9-one were prepared by FVP of 2-phenylbenzoyl chloride and 2-methylbiphenyl-2-carbonyl chloride respectively. Xanthen-9-one and thioxanthen-9-one were also prepared by FVP from the corresponding acid chlorides. 9-Phenanthrol could also be prepared via the FVP of biphenylacetyl choride and the application of this method to a heterocylic thiophene system afforded naphtho[1,2-b]thiophen-4-ol. Naphtho[2,1-b]thiophen-4-ol and naphtho[1,2-b]furan- 4-ol could be obtained in low yields by the FVP of (2-thiophen-3-ylphenyl)acetic acid methyl ester and (2-furan-2-ylphenyl) acetic acid methyl ester over a tungsten trioxide catalyst. Coupling of these systems with the diazonium salt of Acid Yellow 9 afforded the corresponding azo compounds. New heterocyclic dyes were also prepared from the condensation of heterocyclic hydrazines with 4,9-disulfophenanthrenequinone. Pyridine, pyridazine, phthalazine, isoquinoline and 2-quinoline disulfophenanthrene quinone metallised 2:1 nickel complexed magenta dyes were prepared. Industrial tests by standard methods revealed the pyridazine dye has a particularly impressive balance of light and ozone fastness over similar magenta dyes. The reaction of an arylnitro compound with 2-aminopyridine appeared to be an attractive and high yielding route to 2-(phenylazo)pyridine. However, application of this reaction to substituted and naphthalene systems failed. This afforded byproducts due to nucleophilic substitution of groups such as methoxy and the relatively uncommon nucleophilic substitution of hydrogen with none of the required azo products obtained. Therefore it appeared that the reaction of a nitro and amine was not a robust and versatile route to heterocyclic azo compounds. An alternate route to heterocyclic azo compounds involved the use of the Mills reaction by the condensation o-anisidine, p-chloroaniline, 2-aminophenol, 3- aminophenol, naphthylamine, 8-amnioquinoline and 2-acetylamino-5-aminobenzenesulfonic acid with 2-nitrosopyridine afforded the heterocyclic azo products in moderate to high yields. The Mills reaction does appear to be the favored route to heterocyclic azo compounds. Several factors were identified which affect the process of bisazo coupling of chromotropic acid and products obtained. Reaction at the ipso position of monoPACAs (2-phenylazochromotropic acid) leading to increased yields of the ipso substitution monoPACA by-product as opposed to the expected bisazo coupling position was a major problem. Studies indicated reactivity at the ipso position was greatly reduced by the presence of electron withdrawing groups around the phenyl ring of the monoPACA. Further study indicated reaction at the bisazo coupling position increased with the strength of the diazonium salt used in bisazo coupling. Therefore the electronic nature of the monoPACA starting material and the diazonium salt used in bisazo coupling greatly affected the products obtained. Reaction pH studies also revealed attack at the bisazo coupling position increases with pH and at lower pH (5.0 – 8.0) attack at the ipso position dominated. Reactivity of the monoPACA starting material also increased with pH. The influence of steric effects upon bisazo coupling revealed, in the cases where ortho sulfonic acid groups were present in the monoPACA, a reduction in attack at the ipso position. Hence the reaction appeared to be directed towards the required bisazo coupling position.