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| | Process for making quinacridone and its derivatives - Patent 4064129 |
 | | A commercially important process for making quinacridones involves the acid catalyzed ring closure of 2,5-diarylaminoterephthalic acids in polyphosphoric acid which is usually a preferred solvent for effecting the ring closure since it functions as both solvent and acid catalyst and is exemplified in U.S. Pat. |
 | | The acid catalysts that may be used include, but are not limited to, the mono- or di-sulfonic acids of benzene, toluene, xylene, paradichlorobenzene, naphthalene, nitrobenzene and chloroparaxylene. |
 | | Generally, the acid catalyst is used in a range of about 0.1 to about 4 parts per part of 2,5-diarylaminoterephthalic acid, the preferred range being from about 0.2 to 1.5 parts per part of 2,5-diarylaminoterephthalic acid. |
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