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Zheng et al.
We have developed an efficient process for the preparation of 2,9-dichloro-1,10-
phenanthroline in three steps from 1,10-phenanthroline in 67% yield. 2,9-Dibromo-
1,10-phenanthroline was also obtained by this method in 81% yield from 3. Moreover,
2,9-diodo-1,10-phenanthroline could be obtained by reaction of 4 with conc. aqueous hy-
driodic acid.13 We believe that this procedure will provide a more practical alternative to
the existing methods for the synthesis of 2,9-dihalo-1,10-phenanthrolines.
Experimental Section
All reagents and solvents were of reagent grade and used without further purification un-
less otherwise specified. 4,7-Dimethyl-1,10-phenanthroline and 3,4,7,8-tetramethyl-1,10-
phenanthroline were purchased from Aladdin Reagent Co. Ltd. The 1,10-phenanthroline
hydrate and other reagents were purchased from Sinopharm Chemical Reagent Co. Ltd.
Melting points (mps) were determined on a WRS-1B digital melting point apparatus and
are uncorrected.1H NMR spectra were obtained on a 300 MHz Varian Mercury VX-300 in
CDCl3 or D2O with TMS as internal standard. Ultrasound-promoted reactions were carried
out in a common ultrasonic laboratory cleaner (JN-5200D).
Compound 2
A mixture of 1,10-phenanthroline monohydrate (10.00 g, 50.5 mmol) in chlorobenzene
(80 mL) was heated at 70◦C with magnetic stirring. To the hot colorless solution, 1,3-
dibromopropane (51 g, 253 mmol) was added dropwise over 15 minutes, and then the
temperature was raised to 120◦C. During the course of the reaction, a yellow powder
precipitated from the reaction mixture. After 4 h, the mixture was allowed to cool to room
temperature and the yellow powder was collected, washed with petroleum ether and dried
in vacuo to yield compound 2 (19.30 g, 100%), mp. >300◦C. 1H NMR (D2O): δ 9.50 (dd,
J = 1.2 and 5.8 Hz, 2H), 9.28 (dd, J = 1.2 and 8.6 Hz, 2H), 8.41 (s, 2H), 8.37 (d, J = 2.7,
2H), 4.99 (t, J = 7.0 Hz, 4H), 3.27 (q, J = 6.7 Hz, 2H).
The filtrate from the isolation of 2 may be re-used after addition of the appropriate
amount of 1,3-dibromopropane.
Anal. Calcd for C15H14Br2N2: C, 47.15; H, 3.69; N, 7.33. Found: C, 47.02; H, 3.65;
N, 7.41.
Compound 2a
In a similar manner to the synthesis of 2, 2a was obtained in quantitative yield as a pale
yellow solid form 1a, mp. >300◦C. 1H NMR (D2O): δ 9.34 (d, J = 6.0 Hz, 2H), 8.66 (s,
2H), 8.31 (d, J = 6.0 Hz, 2H), 4.98 (t, J = 6.6 Hz, 4H), 3.27 (q, J = 6.8 Hz, 2H), 3.13 (s,
6H).
Anal. Calcd for C17H18Br2N2: C, 49.78; H, 4.42; N, 6.83. Found: C, 49.86; H, 4.31;
N, 6.87.