Phenylenediamines, disubstitute

Ai,Af-Disubstituted- -phenylenediamines, such as A/-phenyl-Af -(l,3-dimethylbutyl)-/)-phenylenediamine [793-24-8] (10), are used in greater quantities than other classes of antioxidants. These products protect unsaturated elastomers against oxidation as well as ozone degradation (see Antiozonants). 

The best oxidation inhibitors are not usually the best antio2onants (qv). A disubstituted i ra-phenylenediamine such as AJ-isopropyl-AT-phenyl- -phenylenediamine is often selected for that purpose. -Phenylenediamine derivatives iaterfere with cure chemistry and scorchiness, and can stain objects ia contact with the vulcani2ate (114). On balance, /V-(1,3-dimethy1buty1)-/V-phenyl- -phenylenediamine and phenyl /to1y1- -pheny1enediamines have the best combination of properties. They are less scorchy and provide excellent o2one and heat resistance. Additional protection is gained ia blends with a small amount of EPDM mbber (126). 

Quinone is produced in small yield by direct oxidation of benzene itself with silver peroxide, but better by the action of oxidising agents on a large number of its p-disubstitution products. Thus, in addition to quinol, p-aminophenol (experiment, p. 176), p-anisidine, p-toluidine, and sulphanilic acid as well as p-phenylenediamine and many of its derivatives yield quinone in this way. 

Attempts to directly iodinate quinoxaline failed, and the synthesis of 2,3-diphenyl-5,8-dibromoquinoxaline is somewhat more involved (Scheme 9) [61]. Starting from ort/zo-phenylenediamine, reaction with SOCI2 gives benzothia-diazole in high yield. Bromination in HBr furnishes 4,7-dibromobenzothiadi-azole, which can be alkynylated or directly reduced [62]. Reduction of the dibromide with sodium borohydride leaves the halide substituents unmolested but opens the ring to furnish l,4-dibromo-2,3-diaminobenzene. Reaction of this intermediate with a 1,2-dione furnishes a 2,3-disubstituted 5,8-dibromo-quinoxaline. Pd-catalyzed alkynylation finishes the sequence off and removal of the TMS groups yields the desired 5,8-diethynylquinoxaline monomers (Table 9, entries 13,14). 

A variety of methods have been developed for the preparation of substituted benzimidazoles. Of these, one of the most traditional methods involves the condensation of an o-phenylenediamine with carboxylic acid or its derivatives. Subsequently, several improved protocols have been developed for the synthesis of benzimidazoles via the condensation of o-phenylenediamines with aldehydes in the presence of acid catalysts under various reaction conditions. However, many of these methods suffer from certain drawbacks, including longer reaction times, unsatisfactory yields, harsh reaction conditions, expensive reagents, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity. Bismuth triflate provides a handy alternative to the conventional methods. It catalyzes the reaction of mono- and disubstituted aryl 1,2-diamines with aromatic aldehydes bearing either electron-rich or electron-deficient substituents on the aromatic ring in the presence of Bi(OTf)3 (10 mol%) in water, resulting in the formation of benzimidazole [119] (Fig. 29). Furthermore, the reaction also works well with heteroaromatic aldehydes. 

N-Substituted quinoxalines are obtained from N-substituted o-phenylenediamines. Thus methyl 2,3-dibromopropionate condenses with (V,A -bis(/7-toluenesulfonyl)-o-phenylenediamine to give l,4-bis(p-tolu-enesulfonyl)-2-methoxycarbonyl-1,2,3,4-tetrahydroquinoxaline (20).25 AVV -Disubstituted cyclohexane-1,2-diamines with suitable a/7-dihalides yield decahydroquinoxalines.26 Condensation of cyclohexane- 1,2-diones with glycine amide gives 2-oxo-5,6,7,8-tetrahydroquinoxalines.27... 

The intramolecular 1,3-dipolar cycloadditions of homochiral nitrilimines derived from methyl esters of glycine, L-alanine, L-phenylalanine, and (S)-2-phenylglycine produced enantiopure 2,3,3a,4,5,6-hexahydropyrrolo[3,4-c]pyrazoles in fair to good overall product yields.50 The thermal reaction of diphenylnitrilimine with N-substituted benzimidazoles (47) produced lV,AP-disubstituted o-phenylenediamines (51). The reaction involved two 1,3-dipolar cycloadditions with two nitrilimine moieties yielding adducts (48-50), followed by a ring opening of the azolic ring of (50) (Scheme 13).51... 

Several 2- and 2,3-disubstituted benzodiazepines have been prepared by reactions involving o-phenylenediamine and 3-ketoaldehydes/2-hy-droxymethyleneketones (67JPR166 70JOU450 70ZOR450 79MI1), and a... 

Benzodiazepines 392 are generally prepared from the appropriately o-disubstituted benzene (e.g., 0-phenylenedia-mine) and a 1,3-bis carbon electrophile (Scheme 210) . For example, acetylated derivatives of BaylisHillman adducts 393 derived from ethyl acrylate and aromatic or heteroaromatic aldehydes readily react with 0-phenylenediamine under the influence of base to provide l,4-benzodiazepin-2-ones 394 in good overall yields (Scheme 211) <2006S4205>. 

Jacob et al. [22] presented an improved green solvent free methodology for the selective synthesis of 1,2-disubstituted benzimidazoles (xiii) by the condensation of o-phenylenediamine and aldehydes using solid-supported catalyst (Si02/ZnCl2). 

The reaction between o-phenylenediamine and an equimolar amount of an aromatic or heterocyclic aldehyde has been shown to proceed by initial formation of a monoanil (74). In the presence of oxidizing agents (e.g. nitrobenzene, which also acts as the solvent) this can form the 2-substituted benzimidazole. With two moles of aldehyde the bis-anil (75) forms, giving rise to a 1,2-disubstituted benzimidazole (Scheme 42). This aldehyde route to benzimidazoles is particularly suited to the synthesis of compounds with a heterocyclic group (e.g. 2-thienyl-, 2-pyridyl-) at C-2. Reaction of 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dithietane with o-phenylenediamine gives 2,2-bis(trifluoromethyl)benzimidazoline (7430785). 

A class of related copolymers (8 to 13 in Table 5.2) interesting from the view point of chemistry and properties are the copolymers (produced as Technora by Teijin Ltd.) based on 1,4-phenylenediamine, tereph-thaloyl chloride and the third monomer 3,1 -d i a min od i p he ny I e t he r (Ozawa et al, 1978). The polymerization can be carried out at 0°C-80°C in an amide solvent (NMP or DMAc) with a small amount of salt (CaCL or LiCl). The incorporation of 3,4 -diaminodiphenylether moieties in the chain makes the polymer less rigid than PPD-T and it has a slightly lower decomposition temperature (500 °C as compared to 550 °C for PPD-T). However, as shown in Figure 5.1, except for side-steps the polymer can take a fully extended linear chain conformation because of the unique 3,4 -disubstitution of the diphenylether unit. If the two substitutions are in... 

Dichloroquinoxaline has been converted into a number of polycyclic derivatives by reaction with o-disubstituted benzenes. Thus reaction with o-phenylenediamines gives tetraazanaphthacenes (17), and the corresponding reaction with 2,3-diaminoquinoxaline gives fluorubin derivatives (18). Quinoxalino[2,3-h]benzothiazine derivatives (19) result from the reaction of dichloroquinoxaline and o-aminobenzenethiol and... 

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