4-Nitrostilbene yield

It was also found that bromonitrophenylmethane (375) reacted with sodium aryl-methanenitronate (374) in DMSO to give the isoxazoline iV-oxide (369) in 60% yield. Both reactions probably involved the formation of a vicinal dinitroethane derivative (376), which lost nitrous acid to give cfs-a-nitrostilbene (368). As mentioned, the reaction of (368) with (374) gave the isoxazoline iV-oxide (369). 

The prototypical organic material with high P (all values of P quoted here are for 1.06 1 light unless noted) is p-nitroaniline (PNA). In electrostatic units (esu), P for PNA is 34.5 x 10 30 esu. (37) It has a dipole moment of 6.8 D. Extension of the chromophore by insertion of a single double bond to produce 4-amino-4 -nitrostilbene increases P dramatically 248 x 10"30 esu. (38) However, both crystalline materials are centrosymmetric, and so no SHG is possible. Most achiral molecules crystallize in centrosymmetric space groups, but some do not. Several materials have been discovered during the last few years which have combinations of hyperpolarizability, crystal growth and habit, and linear spectral properties which make them candiates for useful NLO materials. As will be obvious from the comparison, considerable compromise must be made to yield a practical material. 

Substituted a-nitrostilbenes were hydrogenated to 1,2-diphenylethylamines in 52-87% yields, conveniently in methanol over in situ-prepared Pd-C catalyst (eq. 9.28).53 In these cases the hydrogenation was carried out in presence of the hydrogen chloride formed from palladium chloride, the amount of which, however, was much smaller (-0.0022 mol) for the nitrostilbenes hydrogenated (0.037-0.042 mol). In one instance, a-nitro-4 -methoxystilbene gave rise to a small amount of the corresponding oxime when the hydrogen uptake was less than theoretical. 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Nitro alcohols ate usually isolated (method 102) but are sometimes dehydrated directly to olefinic nitro compounds as in the preparation of co-nitro-2-vinylthiophene from nitromethane, thiophenecarboxaldehyde, and sodium hydroxide (78% yield). Many substituted /3-nitrostyrenes have been obtained by condensation of nitromethane or nitroethane with substituted benzaldehydes. A methyl group on the benzene ring is sufficiently activated by nitro groups in the orlio or para position to cause condensation with aldehydes. A series of nitrostilbenes has been made in this way from substituted benzaldehydes. ... 

According to Pitacco, Valentin and coworkers secondary ketoenamines react generally with nitroolehns to give alkyl- and aryl-substituted tetrahydroindole-7-ones under thermodynamic control in good yield without any catalyst, if the a-ketoenamine is an N-alkyl derivative. The course of the reaction depends on the substituents and the conditions which result in different cleavage or rearrangement reactions. In the case of a-nitrostilbene a Michael adduct is obtained in low yield. If, however, for example, 1-nitrocyclopentene is used in the reaction with iV-t-butylenaminone under kinetic control, an unstable [4 -i- 2]cycloadduct can be isolated. The reaction clearly demonstrates the concurrence of Michael addition and subsequent cyclization to 7-indolones... 

For nitrostilbenes (Table 5d) in nonpolar solvents at ambient temperature the quantum yields of isomerization are comparable to those of stilbene itself. However, 4-nitro-4 -R-stilbenes show a different dependence on solvent properties and temperature. On increasing the solvent polarity, decreases strongly for polar substituents for example, R = OCH3, NH2, and N(CH3)2, 4,4 -NMS, 4,4 -NAS, and 4,4 -NDS, respectively. nonpolar solvents (cyclohexane and benzene) are... 

TABLE 5d Quantum Yields of cis tram Photoisomerization for Nitrostilbenes"... 

Whitten and co-workers [230] have amply investigated stilbene isomerization induced by excited porphyrins. Electron-deficient nitrostilbenes quench excited Zn or Mg etioporphyrins through exciplex formation. Light absorbed by the porphyrin affects isomerization of 4-nitro- or 4,4 -dinitro-stilbene with low quantum yields ((%trans)sens = 99.5), possibly via a stilbene exchange chain mechanism [230]. Azastilbenes coordinate to me-talloporphyrins in both the ground and the excited state (but do not quench it), and isomerize efficiently upon selective excitation of the porphyrin [231]. Complexed 1,4 -NPE gives d , = 6.6, = 0.2, and (%trans)sens = 96,... 

Fluorescence Quantum Yields. For tram-stilbcne 4>f is independent of lexc and the concentration (typically < 10 4 M) and only slightly reduced by the presence of c/s-stilbene [13, 81, 99, 240, 241, 294]. The liquid solutions at room temperature f is about 0.04 for trons-stilbene and 4-bromostilbene, and larger for 4-chlorostilbene and several cyanostilbenes. For nitrostilbenes very small, but there are exceptions in the presence of an electron... 

In liquid solutions in the absence of a sensitizer, T-T absorption has hitherto been observed predominantly with nitro-substituted frans-arylethy-lenes (Tables 16c-e) such as nitrostilbenes [31,200], nitroazastilbenes [172,416], and nitrostyrenes [417], Apparently, the nitro group enhances strongly thioindigo dyes [418,419]. No triplet could be measured for stilbene under direct excitation conditions at room temperature [96,200] because the triplet yield is too small (see Section 1V.B.6). 

Figure 17. Temperature dependence of the triplet yield of traws-4-bromostilbene in GT ( ) and ethanol (O) and rrtms-4-nitrostilbene in GT (A) [114,119].

The 4-nitrostilbenes represent an interesting class of compounds (37). For several of these, the optical density of the triplet-triplet absorption is independent of temperature and medium viscosity, indicating efficient triplet population under all conditions studied (76). For the same solvent the triplet-triplet absorption spectra are also temperature-independent, though the trans->cis quantum yield drops sharply as the temperature is decreased and the medium viscosity is increased (74). These results indicate a transoid equilibrium geometry for the triplets at all temperatures studied (76), consistent with large ferrocene (4.7 X 10 A/ s, cyclohexane) and azulene (4.4 x 10 s , cyclohexane)... 

Various catalyst types were tested with a wide variety of substrates. For example, p-iodonitrobenzene and styrene react according to the Heck cross coupling to p-nitrostilbene with a yield of 99%. This situation is similar for many other reactions of styrene and methylacrylate with other reactants containing iodine and bromine. On the other hand, chlorobenzene reacts with styrene only in trace amounts. 

Synthesis of nitrostilbene polyurethane 19. A20mLheavy walled glass vial was charged with diol 16 (0.1889 g, 0.575 mmol) and 5 mL of dry DMF. Diisocyanate 17 (0.2449 g, 0.748 mmol) in 5 mL of DMF was added. Two drops of Et3N was added to facilitate the polymerization. The polymerization mixture was stirred at 90 X, yielding an orange-r viscous solution. The reaction was stopped after 48 h and added dropwise into cold methanol. Polymer 19 precipitated out as an orange-red solid powder. It was reprecipitated and washed with methanol. UV ... 

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