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Synlett 2003(13): 2083-2085  
DOI: 10.1055/s-2003-41484
LETTER
© Georg Thieme Verlag Stuttgart · New York

Novel Synthesis of Metal-Free Phthalocyanines from Phthalimides and Phthalic Anhydrides with Hexamethyldisilazane

Hitoshi Uchida, Hideyuki Yoshiyama, Paidi Yella Reddy, Shuichi Nakamura, Takeshi Toru*
Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, Japan
Fax: +81(52)7355217; e-Mail: toru@ach.nitech.ac.jp;
Further Information

Publication History

Received 30 July 2003
Publication Date:
08 October 2003 (online)

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Abstract

Metal-free phthalocyanines and their peripherally sub­stituted derivatives have been synthesized from unsubstituted and substituted phthalimides, phthalic anhydrides, and naphthalimide on heating with hexamethyldisilazane under mild conditions.

Key words

phthalocyanine - naphthalocyanine - phthalimide - phthal­ic anhydride - hexamethyldisilazane

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The results will be published in J. Org. Chem.

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Typical Procedure for the Preparation of 3a. A glass tube was charged with phthalimide (100 mg, 0.68 mmol), p-TsOH·H2O (13 mg, 0.07 mmol), HMDS (560 µL, 438 mg, 2.7 mmol) and DMF (50 µL, 0.68 mmol) under argon atmosphere. Then the tube was sealed. The mixture was heated at 150 °C, when a dark purple solid immediately appeared. After heating for 10 h, the mixture was cooled and filtered. The solid was washed with MeOH, and then dissolved in conc. H2SO4 (5.0 mL). The resulting solution was poured into H2O (100 mL) and the blue precipitates were filtered and washed with H2O. The solid was further purified by extraction by soxhlet extractor with methanol to give 62 mg (58%) of 3a as a blue solid.

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Metal-free phthalocyanines are not formed in the absence of either p-TsOH or DMF. p-TsOH probably plays a role to activate HMDS as a silylating agent as well as phthalimides and DMF is requisite for dissolving substrates, although the role of these reagents is not clear enough.

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We also found that metal-free phthalocyanines were obtainable from phthalonitriles by the action of HMDS. The results will be reported in due course.