Preparation of Pentabromophenol and Bromanil from Phenol MORITZ KOHN' Hauaw,Cubo
AS AN example of the preparation of completely brominated aromatic compounds, pentabromophenol and bromanil can be prepared easily as a laboratory exercise. The following procedure is recommended because i t has been used successfully by my collaborators and myself for many years. Phenol (I) is transformed first into 2,4,6-tribromophenol (11); the latter, treated with bromine in the presence of iron as a catalyst, yields pentabromophenol (111). The oxidation of I11 with fuming nitric acid yields the tetrabromoquinone (bromanil) (IV).
All the vessels and materials used for the preparation of pentabromophenol must be completely dry; water, even in small traces, is to be excluded carefully. It is advisable to wear some sort of eye protection. Under a good hood, in a china cup, 20 cc. of bromine Formerly of the,University of Vienna.
(which is more than sufficient because 3 mols of bromine would correspond to only 15 cc. of bromine) are added gradually to 0.9 g. phenol dried, if necessary, by fresh distillation. The tribromophenol formed in this way is melted (the rims of the cup are heated gently also) to prevent admission of moisture from the air. Then one gram of very finely powdered iron is mixed with the product in the cup, the gas burner is removed, and 30 cc. of bromine (three times the quantity required theoretically) are gradually added with care. The temperature of the mixture increases during the formation of pentabromophenol and HBr. The superffuous bromine is evaporated over a boiling water bath, and the dry residue is pulverized in a porcelain mortar and heated with 50 cc. dilute (1:2) hydrochloric acid for half an hour on a water bath. Then the mixture is cooled, the raw material is filtered by suction, washed thoroughly with water, and dried a t a temperature of 120°C. Pure pentabromophenol (melting point 225°C.) can be obtained by crystallization of this raw product from glacial acetic acid. For the preparation of bromanil (IV), 25 g. of raw pentabromophenol, completely dried, are heated carefully and gradually with 100 cc. of concentrated fuming nitric acid until the reaction takes place and brown vapors are developed. The mixture is poured out on pieces of ice, the m d e bromanil is filtered by suction, and washed with warm alcohol. Crystallization from boiling glacial acetic acid yields pure bromanil.
