Photoadduct benzene-maleic anhydride

Figure 1. Infrared spectra (KBr) of (A) polyimide prepared by photolysis of benzene solutions of N,N -hexamethylenebismaleimide (B) polyimide prepared from benzene-maleic anhydride photoadduct (2) and 1,6-hexanediamine and (C) the N,N -bis(n-...

Bradshaw [74] reported in 1966 that maleimide undergoes sensitized photochemical addition to benzene, producing the imide analog of the corresponding maleic anhydride photoadduct. The author observed that the reaction probably proceeds by the addition of electronically excited maleimide to benzene. The photoaddition proved successful also with toluene, /-butylbenzene, and ethylbenzene. Simultaneously, Bryce-Smith and Hems [75] reported that 2 1 photoadducts are formed from maleimide, iV-n-butyl-,. V-benzyl-, iV-o-tolyl-, and iV-2,6-xylylmaleimide with benzene.. V-Phenyl, N-p-tolyl-, and A-p-methoxyphenylmaleimide did not form photoadducts. Trifluoroacetic acid was found to be virtually without effect on the photoaddition of N-n - bulyI maleimide No phenyl-A- -butylsuccinimide was detected [36], It was concluded that a dipolar intermediate is not involved. When N-n-bulylmalcimide and benzene were irradiated in the presence of tetra-cyanoethylene, a 1 1 1 adduct was formed [37],... 

Cyclobutane derivatives are formed after exposing a mixture of alkenes and maleic anhydride to light. Photoadducts are formed by reaction of maleic anhydride with ethylene [74-85-1] and benzene (50). 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

Rafikov et al. [35] describe a correlation between the electron-donating capacity of substituted benzenes and the efficiency of adduct formation with maleic anhydride. This is only valid if similar compounds are compared. The ionization potentials of benzene and toluene are 9.246 and 8.820 eV, respectively the yields of adduct formation are 70% and 30%, respectively. In the series of halogenobenzenes, the ionization potentials are as follows fluorobenzene, 9.195 eV chlorobenzene, 9.080 eV bromobenzene, 9.030 eV the yields of adducts are 7%, 2%, and <1%, respectively. Anisole and diphenyl ether, with ionization potentials of 8.220 and 8.090 eV, respectively, do not give adducts with maleic anhydride. It thus seems that an increase in the electron-donating capacity of the benzene derivative leads to a decrease in the yield of photoadducts. 

The present widespread interest in photoaddition reactions of aromatic compounds originates from observations made over 25 years ago that irradiation of maleic anhydride solutions in benzene produced the 2 1 adduct (33). Numerous accounts concerning the mechanism and scope of the reaction have since appeared and a kinetic model for the process has been proposed. "" The rate of reaction was found to be dependent on the concentrations of benzene, sensitizer, and oxygen but was essentially independent of temperature change in this last parameter does, however, have a pronounced effect on the distribution of 2 1 photoadduct isomers produced from maleic anhydride and methylbenzenes. Subsequent to the early findings on the maleic anhydride system several maleimides were also shown to form 2 1 adducts analogous to (33) with benzene. It is therefore most interesting that the 2 1 adduct (34) of... 

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