Diphenyl-2-pyrazolines

Pyrazolines are a class of FBAs for use on cellulose acetate and more importantly commercially on polyamide fibres. For polyamide, anionic derivatives such as (3.62) are used, applied by pad-thermosol and related methods. 

Although the intense blue fluorescence of l,3-diphenyl-2-pyrazolines had long been known [86], the usefulness of these compounds as optical brighteners was not recognized until 1949 [87], The most valuable brighteners are the 3-(4-chloro-phenyl)-l-(4-phenylsulfonic acid) derivatives because of their ready manufacturing ability, excellent optical properties, and versatility in application. 

Industrial synthesis involves the reaction of f5-chloro-4-chloropropiophenones with phenylhydrazines containing substituents at the 4-position, such as 4-hydra-zinobenzenesulfonamide. The 3-chloro-4-chloropropiophenone needed as starting product can be obtained from the Fricdc 1-Crafts reaction of chlorobenzene with 2-chloropropionyl chloride. 

The tertiary and quaternary amine salts of l,3-diphenyl-2-pyrazoline derivatives (Table 7.9) are brilliant, moderately lightfast brighteners for (modified) polyacrylonitriles. Some can also be used to brighten cellulose acetate. Depending on the structure and nature of the anion, concentrated aqueous solutions with long shelf lives can be obtained such products are needed, for example, in gel brightening. 

The side chains R in Table 7.8 and S02R in Table 7.9 can be added before or after cyclocondensation, for example, by the attachment of NaHS03, amines, or alcohols to vinyl or allylsulfonyl groups. 

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Treatment of (126) with ethanolic hydrochloric acid causes fragmentation to give acetophenone and 3,5-diphenyl-2-pyrazoline (equation 17). 

The salicylaldehydes commonly used have nitro, alkoxy, or halogen substituents, and need no further comment. Some unusual ones have cationic substituents 3-, 4- and 5-methylthio- and dimethylaminosalicylaldehydes have been prepared and methylated to the corresponding dimethylsulfonium and trimethylammonium salicylaldehydes. 1012 The salicylaldehyde substituted in the 4-position with a 3,5-diphenyl-2-pyrazolin-l-yl group gives a series of BIPS and spiro(dipyrans) having highly fluorescent spiro forms and nonfluorescent open forms, which is the reverse of the usual situation. 13... 

Erhan P, Mutlu A et al (2001) Synthesis and antidepressant activities of some 3, 5-diphenyl-2-pyrazolines. Eur J Med Chem 36 539-543... 

Bromo-l-methylbenzo[c]pyrazolo[l,2-a]pyrazole-3,9-dione 4-(p-Chlorobenzal)-l,3-diphenyl-2-pyrazolin-5-one... 

The photoinitiation of polymerization of pentaerythritol tetraacrylate using phenyl-(p-anisyl)-iodonium triflate or triphenylsulfonium hexafluorophosphate, sensitized with either l,6-diphenyl-l,3,5-hexatriene or 1,3-diphenyl-2-pyrazoline, was illustrated by Smith [111b] in 1981. Under his conditions, direct photolysis of the onium initiators failed to initiate polymerization. Baumann and co-workers, however, found conditions for initiation of radical polymerization on direct irradiation of onium salts [18,122], consistent with the hypothesized generation of radicals capable of cage escape in direct photolysis. 

Fluorescence studies of the commercially important l,3-diphenyl-2-pyrazoline derivatives have been extended to a wide range of phenyl- and methyl-substituted derivatives. The fluorescence yields in non-polar solvents are all close to unity, with the exception of l,3,5,5-tetraphenyl-2-pyrazoline. This is not the case in methanol, when a large variation in yields is observed.85 (See the section on oxidation for other photochemical processes in these compounds.) By an examination of the fluorescence spectra and fluorescence excitation spectra of 9-amino-acridine at 4.2 K, the fine-structure fluorescence spectrum of the neutral molecule has been identified and investigated using laser excitation.88... 

The photo-oxidation of the commercially important l,3-diphenyl-2-pyrazolines has been further investigated,281- 282 and the photo-oxidation of 6,6-diarylfulvenes reported.283 Another polymer-bound singlet oxygen carrier has been used to simplify photo-oxidation reactions,284 and the decomposition of bis-(triphenyl-bromoantimonyl) peroxide provides another useful source of singlet oxygen.285... 

A comprehensive comparison among different expressions was done by Koutek, in a remarkable paper of the late 1970s [201] on the basis of the data available for 9 compounds, viz. carbazole, indole, l,3-diphenyl-2-pyrazoline, (hexamethyl-benzene + tetrachlorophthalic anhydride) CT-complex, 4-amino-4 -nitrostilbene, 4-dimethylamino-benzonitrile, 4-dimethylamino-4 -nitrostilbene, 4-dimethylamino-co-nitrostyrene, and 4-dimethylamino-benzylidene-4 -nitroaniline. Unfortunately, the analysis was limited to neutral molecules characterised by the presence of a symmetry axis, or at least by expected co-directional electric dipole moment vectors. 

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