Stilbene 4-chloro

Here, k( and k0 are the rate constants of the fluorescent and nonactivated radiationless relaxation steps, respectively. Using Eq. (8) Saltiel and D Agostino [9] determined an activation energy of approximately 13kJmol and an zlf-factor of the order of 10 2-1013s for stilbene in nonpolar solvents. Similar results have been reported for halogen- and cyano-substituted stilbenes (Table 12a). As examples, plots of log d>f versus 1/T are shown in Figure 12 for stilbene, 4-chloro-, and 4-bromostilbene. 

Fig. 10.1 Structures ofthe fluorescent whitening agents included in this study. Full names DAS 1,4,4 -bis[4-anilino-6-morpholino-1,3,5-triazin-2-yl)-amino]stilbene-2,2 -disulphonate DSBP, 4,4 -bis(2-sulfostyryl)biphenyl BLS, 4,4 -bis(4-chloro-3-sulfostyryl)biphenyl. Internal standard 4,4 -bis-5-ethyl-3-sulfobenzofur-2-yl)biphenyl.

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

In the triazolopyridine series it has been observed19 that a chloro substituent in an ortho position to the methyl group of tolyl heterocycles exerts an additional activating effect. Thus, in the case of triazolopyridine (19), reaction with Schiff s base from benzaldehyde and p-chloro-aniline yields the expected stilbene (20), whereas no reaction is observed in the case of the analog lacking the chlorine atom. 

Finally, in the azobenzene series it has been found16 that during reaction, exchange of chlorine for hydrogen may occur above 60°C, as illustrated by the case of 3-chloro-4-methyl-4 -dimethylaminoazoben-zene (25), which, depending on reaction temperature, reacts with benzalaniline to yield either the expected stilbene (26) or its dechlorinated analog (27). 

Such reactions have also been carried out on benzofurans carrying benzyl, fluoro, chloro, bromo, methoxy, cyano, and phenyl groups in the benzo ring. Substitution in the stilbene part of the molecule can also be obtained by the use of Schiff s bases derived from differing benzal-dehydes.26,28,29... 

Similar reaction has also been carried out with benzoxazoles substituted in the benzo ring with up to three substituents, such as chloro, alkyl, alkoxy,48 phenoxy,49 phenyl, cycloalkyl, or sulfamoyl10 groups. By employing anils of substituted aromatic aldehydes, varying groups may also be introduced into the stilbene part of the molecule.50 Water-soluble derivatives have also been obtained by the use of sulfonic acid-substituted p-tolylbenzoxazoles and also aromatic aldehyde anils.51... 

Table XII).69 The stilbene part of such molecules may also be further substituted with alkyl, alkoxy, phenoxy, phenyl, chloro, or condensed benzo groups.69 and, as was later reported, carboxylic acid groups and their esters70 in addition to sulfonic acid groups.71,72... 

Of particular interest are cases in which substituents are present in ortho positions to the reacting methyl group. Apart from o-chloro-substituted derivatives, those with methoxy, carbonamido, sulfonamido, and phenylsulfonyl groups have been reported to undergo reaction.68 The 2-(3-chloro-4 methyIphenyl)-5-methoxybenzotriazole (163) has been found to be particularly reactive, yielding, with Schiff s base 98, the stilbene 164.54... 

As previously mentioned, the methyl group of 2-(p-tolyl)-s-triazolo-[l,5-a]pyridine is inert under the conditions of the Anil Synthesis. However, introduction of a chlorine atom in ortho position to this methyl group enables reaction to be carried out at 20°-30°C (Section II,E,3). Thus, for example, from 2-(3-chloro-4-methylphenyl)-j-triazolo[l,5-a]pyridine (19) and Schiff s base 171, the stilbene 172 is formed. In the case of 2-phenyl-7-methyl-j-triazolo[l,5-a]pyridine (173), however, reaction with 171 gives the styryl derivative 174, without additional activation of the methyl group.19... 

Essentially the same substituents as listed above may be present in the alkene being substituted, with the possible exception of chloro, alkoxy and acetoxy groups on vinyl or allyl carbons. These groups, especially chloro, may be lost or partially lost with palladium when the final elimination step occurs. For example, vinyl acetate, iodobenzene and triethylamine with a palladium acetate-triphenylphosphine catalyst at 100 C form mainly (E)-stilbene, presumably via phenylation of styrene formed in the first arylation step (equation 21 ).6 ... 

The epoxy alcohol 47 is a squalene oxide analog that has been used to examine substrate specificity in enzymatic cyclizations by baker s yeast [85], The epoxy alcohol 48 provided an optically active intermediate used in the synthesis of 3,6-epoxyauraptene and marmine [86], and epoxy alcohol 49 served as an intermediate in the synthesis of the antibiotic virantmycin [87], In the synthesis of the three stilbene oxides 50, 51, and 52, the presence of an o-chloro group in the 2-phenyl ring resulted in a lower enantiomeric purity (70% ee) when compared with the analogs without this chlorine substituent [88a]. The very efficient (80% yield, 96% ee) formation of 52a by asymmetric epoxidation of the allylic alcohol precursor offers a synthetic entry to optically active 11 -deoxyanthracyclinones [88b], whereas epoxy alcohol 52b is one of several examples of asymmetric epoxidation used in the synthesis of brevitoxin precursors [88c]. Diastereomeric epoxy alcohols 54 and 55 are obtained in combined 90% yield (>95% ee each) from epoxidation of the racemic alcohol 53 [89], Diastereomeric epoxy alcohols, 57 and 58, also are obtained with high enantiomeric purity in the epoxidation of 56 [44]. The epoxy alcohol obtained from substrate 59 undergoes further intramolecular cyclization with stereospecific formation of the cyclic ether 60 [90]. 

Many fluorescent brighteners are derivatives of 4,4 diamino-stilbene-2,2 -disulfonic acid (59), an example of which is C.I. Fluorescent Brightener 32 (Fig. 13.138). In this case, successive reactions involving diamine 59 with two molecules of cyanuric chloride and two molecules of aniline followed by hydrolysis of the final chloro groups give the target compound. 

Z-stilbene 5 mol% FeCI3-6H20, H202,15 mol% 5-chloro-1-methylimidazole 24%... 

Other new ozonides include those of acenaphthylene and 3,4-di-chloro-3,4-dimethyl-cyclobut-l-ene. They are the cyclic analogs of cis-stilbene ozonide and l,4-dichloro-but-2-ene ozonide, respectively. Altogether, more than 45 ozonides were investigated. 

Results of stereochemical studies with various halohydrins confirm that the oxy-anion attacks the carbon from the opposite side, causing Walden inversion the erythro forms of 3-bromo-2-butanol, stilbene bromohydrin, and chloro malic acid give the trans oxide, and the corresponding threo forms lead to the cis oxides [146]. Furthermore, the frans-halohydrin of cyclohexene reacts 150 times as fast with OH- as the cis compound. Only the reaction of the trans compound yields an epoxide [147] in the reaction of the cis compound, an enol is formed first which then rearranges to the corresponding ketone [148, 149]. 

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