Benzanthrone, reduction

Benzanthrone has been prepared by three general methods, the first of which is generally regarded as the best (i) by heating a reduction product of anthraquinone with sulfuric acid and glycerol,1 or with a derivative of glycerol, or with acrolein. The anthraquinone is usually reduced in sulfuric acid solution, just prior to the reaction, by means of aniline sulfate, iron, , or copper. It has also been prepared (2) by the action of aluminum or ferric chloride on phenyl-a-naphthyl ketone, and (3) from i-phenylnaphthalene-2-carboxylic acid. ... 

An example of industrial interest is the benzanthrone (9) synthesis. Benzan-throne derivatives are manufactured by cathodically reducing anthraquinone derivatives that may contain electronegative substituents [61]. In the cathode compartment the reduction of anthraquinone (7) in 85% H2S04 to oxanthrone (8) occurs which in presence of glycerol reacts to form benzanthrone (9), which is an important dye intermediate [40, 61]. 

Benzanthrone (6.73) is the source of various commercially important violet, blue and green vat dyes. This tetracyclic system can be prepared from a mixture of anthraquinone and propane-1,2,3-triol (glycerol) by heating with iron powder in concentrated sulphuric acid. The reaction involves reduction of anthraquinone to anthrone (6.74) followed by condensation (Scheme 6.14) with propenal (acrolein), the latter compound being generated... 

The electrochemical reduction of carbonyl compounds can also be used for C—C coupling. An example of industrial interest is a new benzanthrone synthesis patented by Ciba 465). If anthraquinone is reduced in 85 % H2S04 in the presence of glycerol, the oxanthrone formed as an intermediate reacts with glycerol to form benzanthrone ... 

Another interesting example of the reduction of an aromatic ketone is the conversion in 60% yield of benzanthrone to 1,10-trimethylenephenan-threne ... 

Attempts to prepare this hydrocarbon from benzanthrone by the Wolff-Kishner method (formation and hydrolysis of the hydrazone) or its modifications, by Raney nickel reduction, or by zinc-dust distillation were either unsuccessful or gave the desired hydrocarbon in poor yield. The successful reduction using synthesis gas demonstrates further the potentialities of this new hydrogenation procedure in problems of synthetic organic chemistry. 

Reduction with aluminum powder, for example, in the preparation of benzanthrone, or of quinizarin from purpurin (seldom used). 

A procedure for the reductive acetylation of a quinone, a benzanthrone, or an a-diketone is as follows. A suspension of 1 g. of substance in 5-6 ml. of acetic anhydride is treated with 1 g. of zinc dust and 0.2 g. of anhydrous sodium acetate until the colored material has disappeared and the supernatant liquor is colorless or pale yellow, depending upon the purity of the starting material. After short boiling to complete the reaction, acetic acid is added as required to dissolve the product and part of the zinc acetate that has separated, the solution is filtered at the boiling point from zinc and zinc acetate, the residue is washed with hot solvent, and the total filtrate is boiled under a reflux condenser and treated cautiously with sufficient water to hydrolyze the excess acetic anhydride and then to produce a saturated solution. 

An optimized design employing a tubular electrode in a cylindrical cavity has been described [638]. The mechanism and kinetics of the electrooxidation of several para-haloanilines and the follow-up reactions in acetonitrile have been investigated with this cell [639]. A similar design that is suitable for low temperature measurements (233 K) has been reported [640]. It has been employed in a study of the temperature dependence of the reduction of bromonitrobenzene in acetonitrile solution. The electroreduction of perinaphthenone in a single electron process has been investigated with this cell [641]. The lifetime of the neutral radical formed by deprotonation of the radical anion has been estimated to be around 1 min. A similar electrochemical behavior of benzanthrone was observed. 

It is generally accepted that this reaction involves the conversion of glycerol into acrolein and reduction of anthraquinone to anthrone, the latter undergoing the Aldol Condensation with acrolein. After that, the consecutive dehydration, cyclization, and oxidation afford the final product of benzanthrone. An illustration of the reaction mechanism is displayed here. 

Procedure. Dissolve 0-3-0-5 g of the sample in 100 ml. of sulphuric acid d = 1 84). Transfer a 2-ml. aliquot portion into a 50-ml. flask, add 40 ml. of methanol and dilute with water. Deoxygenate an aliquot portion of this mixture and record the reduction wave of benzanthrone at — 0 96 V. 

---