Optical brightening agents
View Patent ↗The instant invention relates to stilbene optical brightening agents which combine a high solubility in water while providing superior fluorescent whitening effects when applied to the surface of paper in either the size-press or in a pigmented coating composition and which show a reduced anionic charge. The instant optical brighteners may also be used for finishing of textiles.
1. A compound of formula (I)
wherein
M is hydrogen, an alkali metal cation, ammonium or ammonium which is mono-, di- or trisubstituted by a C 2 -C 3 -hydroxyalkyl radical,
n is 1 or 2,
R 1 is hydrogen, a straight-chain C 1 -C 8 alkyl or branched C 3 -C 8 alkyl group which is not substituted by a heteroatom, and
R 2 and R 3 are each, independently of one another, a straight-chain C 1 -C 8 alkyl or branched C 3 -C 8 alkyl group which is not substituted by a heteroatom, and does not form a ring.
2. A compound according to claim 1 wherein
M is hydrogen, an alkali metal cation or ammonium,
n is 1 or 2,
R 1 is hydrogen, a straight-chain C 1 -C 4 alkyl or branched C 3 -C 5 alkyl group which is not be substituted by a heteroatom, and
R 2 and R 3 are each, independently of one another, a straight-chain C 1 -C 4 alkyl or branched C 3 -C 6 alkyl group which is not substituted by a heteroatom, and does not form a ring.
3. A compound according to claim 2 wherein
M is hydrogen, sodium or potassium,
n is 1 or 2,
R 1 is hydrogen, methyl, ethyl, propyl or i-propyl, and
R 2 and R 3 are each, independently of one another, methyl, ethyl or propyl, or i-propyl, i-butyl, i-pentyl or i-hexyl.
4. A compound according to claim 3 wherein
M is hydrogen or sodium,
n is 1 or 2,
R 1 is hydrogen or methyl, and
R 2 and R 3 are each, independently of one another, methyl or ethyl.