Azobenzenes preparation

Table III gives data for other unsymmetrically substituted azobenzenes prepared by this technique.

Nishiyama Kand Fujihira M 1988 Cis-trans reversible photoisomerization of an amphiphilio azobenzene derivative in its pure LB film prepared as polyion oomplexes with polyallylamine Chem. Lett. 1257-60... 

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

To prepare the hydrochloride, dissolve about 1 g. of the compound (which need not be perfectly dry) in about 8 ml. of alcohol. Add this solution to boiling dilute hydrochloric acid (10 ml. of the concentrated acid and 80 ml. of water). Boil for 5 minutes, filter the hot solution if necessary, and allow to cool. p-Amino-azobenzene hydrochloride separates in steel-blue crystals. Filter, wash with a little dilute hydrochloric acid, and dry. 

Method 2 (from hydrazobenzene). Prepare a solution of sodium hypobromite by adding 10 g. (3-2 ml.) of bromine dropwise to a cold solution of 6-0 g. of sodium hydroxide in 75 ml. of water immersed in an ice bath. Dissolve 9-5 g. of hydrazobenzene (Section IV,87) in 60 ml. of ether contained in a separatory funnel, and add the cold sodimn hypobromite solution in small portions. Shake for 10 minutes, preferably mechanically. Separate the ether layer, pour it into a 100 ml. distilling flask, and distil off the ether by warming gently on a water bath. Dissolve the warm liquid residue in about 30 ml. of alcohol, transfer to a small beaker, heat to boiling on a water bath, add water dropwise to the hot solution until the azobenzene just commences to separate, render the solution clear again with a few drops of alcohol, and cool in ice water. Filter the orange crystals at the pump, and wash with a little 50 per cent, alcohol. Dry in the air. The yield is 8 g. 

Two moles of diphenylacetylene insert into the benzyl methyl sulfide complex 481 to afford the eight-membered heterocycle 482[440j. The cinnolinium Salt 483 is prepared by the insertion of alkynes into the azobenzene com-plex[44l]. 

Another interesting variation on the linkage holding together two benzocrowns was reported by Shinkai and coworkers In their case, the benzo groups on the crowns were also part of a photolabile azobenzene system. The azo-linked bis-crown was prepared as follows (see Eq. 3.34). 4 -Nitrobenzo-l 5-crown-5 was reductively dimerized... 

Zhu T., Yu H.Z., Wang J., Wang Y.Q., Cai S.M., Liu Z.F., Two-dimensional surface enhanced Raman mapping of differently prepared gold substrates with an azobenzene self-assembled monolayer, Chem. Phys. Lett. 1997 265 334-340. 

Oxidative photocyclization of benzylideneaniline appears to proceed efficiently only in the presence of strong acid. The phenanthridine 31, however, has been prepared by irradiation of the imine 3228 few other examples of the photocyclization of arylimines have been reported.29 Strong acid is also required for successful photocyclization of azobenzenes to benzo-[c]cinnolines. Here, protonation is claimed to lower the reactive n, n excited state below the level of the unreactive n, it state. 2-Phenylazopyridine,... 

Recently, Okuyama et al. succeeded to prepare single crystals of some azobenzene amphiphiles and decided molecular and aggregation structure of single crystals [14-19], The spectral prediction of the chromophore orientation in the bilayer assemblies were very consistent with the X-ray structural analyses of the single crystals. 

In order to verify Okuyama s prediction on molecular orientation in bilayer assemblies, azobenzene amphiphiles having a viologen moiety as a hydrophilic head group, CnAzoCmV2+ 2Br, were newly prepared. Bathochromic shift to 390 nm in the visible absorption band of the... 

Two azobenzene-linked amphiphiles were dissolved in chloroform and mixture solution with various molar ratio were prepared. The mixed monolayers of C180AZON02 and C180AZOCOOH were spread on a 10 4 M aq. BaCl2 solution... 

The mixed liposomal solutions were prepared by the ethanol-injection method(13) in order to obtain completely transparent solutions. It is interesting to note that miscibility of the photochromic amphiphiles with DPPC depend on the position of bulky azobenzene. If azobenzene is incorporated close to the end of long alkyl chain, a stable mixed bilayer state cannot be formed. On the other hand, when the azobenzene moiety is located near the head group or at the center of the hydrocarbon tail, the azobenzene amphiphiles are successfully incorporated into the bilayer membrane. No individual micelle formation nor phase separation in the bilayer was observed at 25 °C by absorption spectroscopy. However, the microstructure of the mixed liposomes depends on the type of azobenzene amphiphiles. 

Weener et al. prepared photo-responsive monolayers from azobenzene modified polypropylene imine) dendrimers which also hold promise in the area of optical data storage [74], A fifth generation polypropylene imine) dendrimer was functionalized with equal amounts of palmitoyl and azobenzene containing alkyl chains, resulting in the formation of an amphiphilic copolymer with a random shell structure (Figure 16.5). 

As follows from the preparation of helianthine, dimethylaniline condenses in exactly the same way as phenol p-dimethylamino-azobenzene is formed. 

The 4,4 -13C2 azobenzene was prepared from the commercially available13C-labelled acetone by the sequence of reactions shown in Scheme 4. 

Some 4,4 -diiodohydrazobenzene labelled with carbon-14 at one of the 4-positions of the phenyl rings was prepared from [4-14C] azobenzene that had been synthesized previously in Shine s laboratory (equation 18). 

Poctova M, Kakac B. 1981. Determination of azobenzene and hydrazobenzene in ketazone (kebuzone) pharmaceutical preparations. Cesk Farm 30 159-161. (Czech)... 

Other new complexes reported are the species [PdL(Bu NC)2], where L is a large variety of unsaturated ligands e.g. azobenzene. All were prepared in a similar manner to the known oxygen complex. 

The experimental procedure was essentially the same for all substances mentioned, namely, the method used in the case of nitrobenzene. Some complication arises, however, due to the fact that the solids do not disperse as easily in the fermentation mixture. Although the materials were always added in alcoholic solution to the yeast preparation, partial precipitation was unavoidable. With 21.4 g. of nitrosobenzene a yield of 4 g. of aniline was obtained addition of the same quantity of phenylhydroxylamine gave 7.5 g. of aniline. In both cases azobenzene appeared as a by-product and could be isolated in the pure state. Its formation can be readily explained by a condensation of the intermediary nitrosobenzene with the end product aniline. 

---