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Org. Synth. 1949, 29, 68
DOI: 10.15227/orgsyn.029.0068
1-METHYLAMINO-4-BROMOANTHRAQUINONE
[Anthraquinone, 1-methylamino-4-bromo-]
Submitted by C. V. Wilson
Checked by G. L. Evans and R. S. Schreiber.
1. Procedure
In a 2-l. three-necked flask having ground-glass joints and equipped with a mechanical stirrer, a condenser (Note 1), and a dropping funnel are placed 119 g. (0.5 mole) of 1-methylaminoanthraquinone (p. 573) and 600 ml. of pyridine (Note 2) and (Note 3). The stirrer is started, and 90 g. (29 ml., 0.56 mole) of bromine is added over a period of 9–10 minutes. The flask and contents are now heated on the steam bath for 6 hours with continuous stirring. At the end of this period the hot mixture is transferred from the flask to a beaker and allowed to cool. The solid that separates (Note 4) is collected on a Büchner funnel and is washed thoroughly with hot water to remove a considerable portion of pyridine hydrobromide which is precipitated along with the desired product. The resulting deep red 1-methylamino-4-bromoanthraquinone, after thorough drying, weighs 111–117 g. (70–74%). It melts at 193–195° and is pure enough for most purposes (Note 5).
2. Notes
1. An air condenser of any type is sufficient.
2. A good grade of pyridine is essential. Very poor results are obtained with the practical or technical grades.
3. Larger volumes of pyridine have been used, but the yield drops progressively with increasing amounts.
4. Some of the solid separates during the heating on the steam bath.
5. It may be recrystallized, if desired, from pyridine, by the use of 3.5 ml. per g.; the melting point is raised to 195–196°.
3. Discussion
4-Bromo-1-methylaminoanthraquinone has been prepared from 4-bromo-1-nitroanthraquinone and methylamine at 60°,1 and from 1-methylaminoanthraquinone in pyridine solution by treatment with two moles of bromine.2 This procedure is based on the latter method.

References and Notes
  1. Ger. pat. 144,634 [Frdl., 7, 201 (1902–1904)].
  2. Ger. pat. 164,791 [Frdl., 8, 280 (1905–1907)].

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

bromine (7726-95-6)

pyridine hydrobromide (18820-82-1)

pyridine (110-86-1)

methylamine (74-89-5)

1-METHYLAMINOANTHRAQUINONE (82-38-2)

1-Methylamino-4-bromoanthraquinone,
Anthraquinone, 1-methylamino-4-bromo-,
4-Bromo-1-methylaminoanthraquinone (128-93-8)

4-bromo-1-nitroanthraquinone