Fluorescent whitening agent

The principle of fluorescent whitening was described in 1929 (1), but the industrial use of FWAs began about 10 years later. Since that time FWAs have found increasing use in the most diverse fields (2—5). The toxicological properties of fluorescent whiteners have been summarized (6). Commercial products investigated thus fat have been found to be completely harmless. Mote than 2000 patents for FWAs exist, there ate several hundred commercial products, and approximately one hundred producers and distributors. 

Many chemical compounds have been described in the Hterature as fluorescent, and since the 1950s intensive research has yielded many fluorescent compounds that provide a suitable whitening effect however, only a small number of these compounds have found practical uses. Collectively these materials are aromatic or heterocycHc compounds many of them contain condensed ring systems. An important feature of these compounds is the presence of an unintermpted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds ate derivatives of stilbene [588-59-0] or 4,4 -diaminostilbene biphenyl 5-membeted heterocycles such as triazoles, oxazoles, imidazoles, etc or 6-membeted heterocycles, eg, coumarins, naphthaUmide, t-triazine, etc. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Stilbene Derivatives. Most commercial brighteneis aie bistria2inyl derivatives (1) of 4,4 -diarmnostilbene-2,2 -disulfonic acid (Table 1). The usual compounds are symmetric preparation begias with reaction of 2 moles of cyanuric chloride derivatives with 1 mole of 

4 -diamiQostilbene-2,2 -disulfonic acid [81-11-8J. Asymmetric derivatives can be synthesized via 4-amiQO-4 -nitrostilbene-2,2 -disulfonic acid however, thek preparation is more expensive, and they show Htde advantage over the symmetrical compounds (see Stilbene dyes). The principal effects of stmctural variations are changes ki solubiUty, substrate affinity, acid fastness, etc. The bistriazinyl compounds are not stable toward hypochlorite however, some compounds show some fastness after appHcation to the fiber. Mono(azol-2-yl)stilbenes arose from efforts to find hypochlorite-stable products with neutral fluorescence. The bistriazinyl brigbteners are employed principally on ceUulosics, such as cotton or paper. Some products also show affinity for nylon at the weaMy alkaline pH of most commercial detergents. 

---

Table 1. Symmetrical Stilbene Derivatives used as Fluorescent Whitening Agents...

Other Heterocyclic Systems. Naphthalimides (15), where R = —NHCOR, are derivatives of 4-anTinonaphthalimide (69) and are used in plastics. The alkoxynaphthalimides (15, R = OCH ) (70,71) are of particular interest as fluorescent whitening agents. 

Initially, fluorescent whitening agents (FWAs) were used exclusively in textile finishing the detergent and paper industries followed thereafter. These products are also used in fiber spinning masses, plastics, and paints. 

Table 5. Fluorescent Whitening Agents in the Detergent Industry...

Table 6. Fluorescent Whitening Agents Used in the Synthetic Fibers and Plastics Industries...

Fluorescent Whitening Agents," in F. Coulston and F. Korte, eds.. Environmental Quality and Safety Suppl. Vol. 4, Georg Thieme Vedag, Stuttgart, and Academic Press, Inc., New York, 1975. 

Blueing agents, which are dyes, provide another approach to maintaining fabric whiteness by a mechanism in which a yellow cast of washed fabrics is covered by the blue dye. Since this approach reduces reflectance, it is less desirable than the use of fluorescent whitening agents that increase reflectance. 

Dye Intermedia.tes, Dye intermediates are defined as those precursors to colorants that are manufactured within the dyes industry, and they are neady always colodess. Colored precursors are conveniendy termed color bases. As distinct from primaries they are only rarely manufactured in single-product units because of the comparatively low tonnages requited. Fluorescent brightening agents (FBAs) are neither intermediates nor tme colorants. Basic manufacturing processes for FBAs are described in Reference 18 (see Fluorescent whitening agents). 

---