324 HANDBOOK OF PHOTOGRAPHY 



NH2 



1 : 2-Diaminobenzene (o-phenylenediamine) 



is formed. 



Two amino and one hydroxyl group may be substituted into the benzene nucleus 

 with the formation of 



OH 



NHo 



2 : 4-Diaminophenol 



NH.2 



which is marketed in the form of the hydrochloride salt as Amidol. 



By substituting another benzene ring for one of the amino hydrogens of p-amino- 

 phenol, the p-hydroxydiphenylamine developers are formed: 



H 



^—< >0H 



which were marketed as developers under the trade name of Duratol. 



The product resulting from the substitution of a hydroxy phenyl group for one of 

 the amino hydrogens of p-aminophenol, which is designated as 



H 



H0< > — N — < >0H 4:4'-Dihydroxydipheny]amine 



appeared in the photographic developer market as Pyramidol. 



Another class of developing agents is found in hydroxy-substituted benzidine or 



H2N<^^ y\ \XH-2 4:4'-Diamino-o-hydroxydiphenyl 



OH 



which appears to be the Diphenal developer of prewar days. 



Instead of the amino group, ring structures may be substituted for a nuclear 

 hydrogen of phenol or aniline. Examples of these ring compoimds include 



H. H2 



/ \ 



O NH Morpholine 



Ho H2 



H2 H2 

 C— C 



/ \ 



H2C NH Piperidine 



\ / 



G— C 

 H2 H2 



