Hydroquinone acetate

Those methods of purifying vinyl acetate which involve washing of the monomer usually seem to be concerned with the removal of hydroquinone, acetic acid, and acetaldehyde. The use of aqueous solutions for these procedures actually is somewhat questionable in view of the ease of hydrolysis of vinyl acetate (comparable in rate to the hydrolysis of ethyl acetate). In aqueous alkali, the hydrolysis rate of this monomer is said to be 370 times as fast as in water [2]. Nevertheless, such procedures have been suggested and are given here for information only as a typical example of this method. 

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. 

Method 1. Cool a solution of 33 g. of hydroquinone in 150 ml. of 60 per cent, acetic acid contained in a 600 ml. beaker to below 5° in an ice bath. Dissolve 42 g. of chromic anhydride in 70 ml. of water, and add 30 ml. of glacial acetic acid. By means of a separatory funnel with bent stem and supported over the beaker, add the chromic anhydride solution... 

A solution of 2,3-dimethylindole (145 g, 1 mol) in dry dioxan containing hydroquinone (100 mg) was treated with JV,JV,JV-trimethylbenzylammonium ethoxide (5 ml of a 40% solution in MeOH) and warmed to 35 C. Freshly distilled acrylonitrile (150 ml, 2.5 mol) was added at a rate such that the temperature did not rise above 40°C. The solution was then stirred overnight and diluted with 10% aq. acetic acid (11). The solution was extracted with CH Clj and the extract was washed with water and dried (MgS04). extract was then mixed with silica gel (800 g) and the solvent removed in vacuo. The silica was placed in a Soxhlet extractor and extracted with cyclohexane. The extract deposited the product as colourless needles (125 g, 63% yield). 

Acrolein is a highly toxic material with extreme lacrimatory properties. At room temperature acrolein is a Hquid with volatiUty and flammabiUty somewhat similar to acetone but unlike acetone, its solubiUty in water is limited. Commercially, acrolein is always stored with hydroquinone and acetic acid as inhibitors. Special care in handling is required because of the flammabiUty, reactivity, and toxicity of acrolein. 

Acrolein produced in the United States is stabilized against free-radical polymerization by 1000—2500 ppm of hydroquinone and is protected somewhat against base-catalyzed polymerization by about 100 ppm of acetic acid. To ensure stabiUty, the pH of a 10% v/v solution of acrolein in water should be below 6. 

Since the principal hazard of contamination of acrolein is base-catalyzed polymerization, a "buffer" solution to shortstop such a polymerization is often employed for emergency addition to a reacting tank. A typical composition of this solution is 78% acetic acid, 15% water, and 7% hydroquinone. The acetic acid is the primary active ingredient. Water is added to depress the freezing point and to increase the solubiUty of hydroquinone. Hydroquinone (HQ) prevents free-radical polymerization. Such polymerization is not expected to be a safety hazard, but there is no reason to exclude HQ from the formulation. Sodium acetate may be included as well to stop polymerization by very strong acids. There is, however, a temperature rise when it is added to acrolein due to catalysis of the acetic acid-acrolein addition reaction. 

The synthesis of chlorarul [118-75-2] (20) has been improved. The old processes starting from phenol or 2,4,6-trichlorophenol have been replaced by new ones involving hydroquinone chlorination. These processes allow the preparation of chlorarul of higher purity, avoiding traces of pentachlorophenol. Different types of chlorination conditions have been disclosed. The reaction can be performed according to the following stoichiometry, operating with chlorine in aqueous acetic acid (86,87), biphasic medium (88), or in the presence of surfactants (89). 

Methyl Vinyl Ketone. Methyl vinyl ketone [78-94-4] (3-buten-2-one) is a colorless Hquid with a pungent odor. It is stable only below 0°C, and readily polymerizes on standing at room temperature. It can be inhibited for storage and transportation by a mixture of acetic or formic acid and hydroquinone or catechol (266). This ketone is completely soluble in water, and forms a binary azeotrope with water (85 MVK 15 H2O vol %) at 75.8°C. 

Vinyl acetate [108-05-4] M 86.1, b 72.3 , d 0.938, n 1.396. Inhibitors such as hydroquinone, and other impurities are removed by drying with CaClj and fractionally distilling under nitrogen, then refluxing briefly with a small amount of benzoyl peroxide and redistilling under nitrogen. Stored in the dark at 0 . 

A solution of hydroquinone (11.0 g) in 50 ml of acetic acid containing 1.1 g of 5 % rhodium on alumina is hydrogenated at 50 psi in a Parr apparatus. Three equivalents of hydrogen are rapidly absorbed. The catalyst is removed by filtration through celite. 

The reaction mixture was removed from the vessel and distilled at a pressure of 30-60 mm, and a bath temperature of 30°C to 50°C until the methanol had all been removed. The extremely viscous tarry residue remaining in the still pot was given a very crude distillation, the distillate boiling at B2°C to 1 32°C/2 mm. In an attempt to purify this distillate by a more careful distillation, 5.3 g of a liquid distilling from 53°C to 150°C/5 mm was collected. At this point, much solid sublimate was noted not only in this distillate but in the condenser of the still. 7 g of the solid sublimate was scraped out of the condenser of the still. Recrystallization of the sublimate from ethyl acetate containing a small amount of petroleum ether gave beautiful crystals melting at 175°C to 177°C (5 g). Infrared analysis confirmed that this compound was hydroquinone (9% conversion). 

Stage B Preparation of 17j -HydroxyEstra-4,9,11-Trien-3-one — 3 g of 17/3-benzoyloxy-estra-4,9,11 -trien-3-one, obtained as described in Stage A are dissolved in 15 cc of methanol. 0.03 g of hydroquinone is added, and the mixture Is taken to reflux while bubbling in nitrogen. Then 1.2 cc of 11% methanolic caustic potash is added and reflux is maintained for three hours, after which the reaction product Is acidified with 0.36 cc of acetic acid. 

By the oxidation of hydroquinone in 60 per cent acetic acid with chromic acid. Craven and Duncan, J. Chem. Soc. 127, 1489 (1925). 

Vinyl Acetate CH3COOCH=CH2 OH compds, HCN, Halides, Halogens, Mer-cap tans, Amine, Silanes Oxygen Vap in Air 2.6 to 13.4% > Ambient > Ambient Inhibitor—Methyl Ether of Hydroquinone or 3-5ppm Diphenylamine. Store in a dry, cool place shield from light impurities 20.9-21.5 402 427 Free-radical polymerization initiated by Benzoyl Peroxide... 

A. 2-Chloro-2,3,3-trijluorocyclobutyl acetate (Note 1). A mixture of 1.0 g. of hydroquinone, 3 drops of a terpene inhibitor (Note 2), and 140 g. (1.63 moles) of inhibited redistilled vinyl acetate (Note 3) is placed in a 400-ml. high-pressure shaker tube lined with stainless steel (Note 4). The shaker tube is closed,... 

Ordinary commercial-grade vinyl acetate is redistilled. One gram of hydroquinone per 100 g. of vinyl acetate is added to inhibit polymerization of the latter, which is then stored at 0-4° until needed. 

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