Hydroquinone diacetate

Dihydroxyacetophenone (II) can be prepared in good yield by heating hydroquinone diacetate (I) in the presence of 3-3 mols of aluminium chloride, Hydroquinone cannot be acylated by the Eriedel-Crafts method. 

Dihydroxyacetophenone. Finely powder a mixture of 40 g. of dry hydroquinone diacetate (1) and 87 g. of anhydrous aluminium chloride in a glass mortar and introduce it into a 500 ml. round-bottomed flask, fitted with an air condenser protected by a calcium chloride tube and connected to a gas absorption trap (Fig. II, 8, 1). Immerse the flask in an oil bath and heat slowly so that the temperature reaches 110-120° at the end of about 30 minutes the evolution of hydrogen chloride then hegins. Raise the temperature slowly to 160-165° and maintain this temperature for 3 hours. Remove the flask from the oil bath and allow to cool. Add 280 g. of crushed ice followed by 20 ml. of concentrated hydrochloric acid in order to decompose the excess of aluminium chloride. Filter the resulting solid with suction and wash it with two 80 ml. portions of cold water. Recrystallise the crude product from 200 ml. of 95 per cent, ethanol. The 3 ield of pure 2 5-dihydroxyacetophenone, m.p. 202-203°, is 23 g. 

I) Hydroquinone dIacetate may be prepared as follows. Add I drop of concentrated sulphuric acid to a mixture of 55 g. of hydroquinone and 103 g. (05-5 ml.) of A.R. acetic anhydride in a 500 ml. conical flask. Stir the mixture gently by hand it warms up rapidly and the hydroquinone dissolves. After 5 minutes, pour the clear solution on to 400 ml. of crushed ice. Alter with suction and wash with 500 ml. of water. Recrystallise the solid from 50 cent, ethanol by weight (ca. 400 ml. are required). The yield of pure hydroquinone diacetate, m.p. 122°, is 89 g. 

Apart from examples given by Chakrabarti and Sharma (1993) and Sharma (1995), a number of additional examples can be cited. A reference will be made to the reaction of ketoi.sophorone with AC2O to give trimethyl hydroquinone diacetate where a cationic ion-exchange resin (CIER) works in an elegant and functional way (Eqn. (7)). 

Benzenetetrol has been prepared by the hydrolysis of 2,4,6-triaminophenol with dilute hydrochloric acid and by heating aqueous solutions of <0.2 M 2,4,6-triaminophenol at >130° C (223—225). The acid hydrolysis is improved by copper (226). 1,2,3,5-Benzenetetrol also has been prepared in 46% overall yield by the nitration of hydroquinone diacetate at low temperature to 2,6-dinitrohydroquinone acetate, followed by reduction to the corresponding diamine hydrochloride with tin and hydrochloric acid. The diamine hydrochloride is hydrolyzed to the tetrol with 1 wt % hydrochloric acid at 155—160°C (224). Hydrogenation of 2,6-dibenzoyloxy benzoquinone over Pd—C gives a 90% yield of 1,2,3,5-tetrahydroxybenzene (227). 

Dihydroxyacetophenone (6) (cognate preparation in Expt 6.107), which cannot be prepared by a Friedel-Crafts acetylation of hydroquinone, is obtained in good yield when hydroquinone diacetate (5) is heated in the presence of 3.3 mol of aluminium chloride. 

Naphthyl acetate Benzoin acetate Phloroglucinol triacetate Hydroquinone diacetate Pyrogallol triacetate... 

Terminal epoxides react with DMF in the presence of BiBr3 under an 02 atmosphere to afford cyclic carbonates (Equation (87)).143 Para-quinones react with acetic anhydride under the catalysis of Bi(OTf)3 to give acetoxy-1,4-hydroquinone diacetates (Equation (88)).144... 

Oxides of silver [171, 368], mercury [384], lead [431], and nitrogen [457] react at room temperature. 2,5-Hydroquinone diacetic acid and mercuric oxide in ether, after several hours at room temperature, give p-benzoquinone-2,5-diacetic acid in 90% yield [384]. 

A mixture of 50 g. (0.257 mole) of dry hydroquinone diacetate (p. 68) and 116 g. (0.87 mole) (Note 1) of anhydrous aluminum chloride is finely powdered in a mortar and introduced into a dry 500-ml. round-bottomed flask fitted with an air condenser protected by a calcium chloride tube and connected to a gas-absorption trap. The flask is placed in an oil bath (Note 2) which is heated slowly from room temperature so that at the end of about hour the temperature of the oil reaches 110-120°, at which point the evolution of hydrogen chloride be ns. The temperature is then raised slowly to 160-165° and maintained at that point for about 3 hours (Note 3) at the end of about 2 hours the evolution of hydrogen chloride becomes very slow and the mass assiunes a green color and becomes pasty in consistency (Note 4). 

Dihydroxyacetophenone has been prepared in 54% yield by heating hydroquinone diacetate, hydroquinone, and anhydrous aluminum chloride. It has also been prepared by the reaction of hydroquinone with acetic acid in the presence of zinc chloride. 

Hydroquinone diacetate has been prepared by the treatment of hydroquinone with acetic anhydride, both in the presence and in the absence of strong acid catalysts, by the treatment of the sodium salt of hydroquinone with acetic anhydride, and by the reaction of hydroquinone with acetic anhydride in the presence of sodium acetate. - It has also been prepared from hydroquinone and acetyl chloride the acetylation with acetyl chloride is reported to be improved by the addition of metallic magnesium. ... 

Preparation. The tetraethyleneglycol-linked di-acid monomer is dried under high vacuum for 2 h prior to use. Hydroquinone diacetate is recrystallized from ethanol and dried under vacuum to constant weight. All glassware is dried in the oven at 125°C prior to use. 

The rate of anisole acylation depended on the acetate (Table 2). Initially it was about 1.5 times greater with p-tolyl acetate and with 2-methoxyphenyl acetate than with phenyl acetate, slightly lower with 2-methoxyhydroquinone diacetate, 2.5 times lower with the hydroquinone diacetate and very low with 2,4,6-trimethylphenyl acetate. The low reactivity of this latter acetate can be related to limitations in the rate of diffusion of this bulky compound in the BEA zeolite pores. Furthermore, a greater reactivity of this acetate was found with HFAU zeolites whose pore size is greater. Curiously, with hydroquinone diacetate (but not with the 2-methoxyhydroquinone acetate), there was a quasi immediate deactivation. We are carrying out additional experiments so as to understand how the reactivity of aromatic acetates changes with their nature and the zeolite acidity and porosity. 

---