Monoperphthalic acid

To prepare crystalline monoperphthahc acid, place the thoroughly dry ethereal solution (4) in a distiUing flask equipped with a capillary tube connected with a calcium chloride or cotton wool drying tube, and attach the flask to a water pump. Evaporate the ether without the appUcation of heat (ice will form on the flask) to a thin syrup (about 150 ml.). Transfer the syrup to an evaporating dish, rinse the flask with a little anhydrous ether, and add the rinsings to the syrup. Evaporate the remainder of the ether in a vacuum desiccator over concentrated sulphuric acid about 30 g. of monoperphthahc acid, m.p. 110° (decomp.), is obtained. 

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Monoperphthalic acid. This is obtained by adding finely-powdered phthalic anhydride to a well-stirred solution of 30 per cent, hydrogen peroxide in alkali at —10° the solution is acidified and the per acid is extracted with ether ... 

Owing to the greater stability and the easier preparation, monoperphthalic acid is generally preferred to benzoic acid. 

D. ci - -Thiabicyclo[4 .. Q]nonan S,S-Dioxide [Benzo[c]thiophene 2,2-dioxide, cis-octahydro-]. A solution of the sulfide (43.0 g., 0.303 mole) in 11. of ether is cooled to 0° and treated dropwise while magnetically stirred with 1.01. of 0.65iV ethereal monoperphthalic acid (0.65 mole). The mixture is kept overnight at 0°, after which time the precipitated phthalic acid is separated by filtration and the filtrate concentrated with a rotary evaporator. Bulb-to-bulb distillation of the residual oil at 0.05-0.1 mm. affords the sulfone as a eolorless liquid (48.5-50 g., 92-95%) (Note 11). This product is crystallized from ether-hexane to give a colorless solid, m.p. 39-41° (Note 12). 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

Several steroid olefins, especially A -steroids, do not give exclusive a-epoxidation. The a-oxirane usually predominates in the epoxidation mixture, its proportion varying from 50% to 90% or greater when either perbenzoic acid or monoperphthalic acid is employed. The claims that the ratio of a- to p-epoxide is high in compounds containing a keto group d or a j5-substituent at may be misleading since epoxidation of 17a,20 20,... 

Perbenzoic acid and monoperphthalic acid are used in the same manner as MCPBA but a fresh solution of these reagents is usually required syntheses for these reagents can also be found in Fieser and Fieser s Reagents for Organic Synthesis. A microtechnique for perbenzoic acid epoxidation has also been described. ... 

Epoxidation of the A -enol acetate was originally carried out with per-benzoic acid. Monoperphthalic acid has also been used, but is apparently more susceptible to steric and conformational factors. The commercially available peracetic acid is generally most convenient. Based on the expected backside attack, the derived epoxides have the 17a configuration, and hydrolysis always produces the 17a-hydroxy group. 

A solution of 10 g (0.023 mole) of cholesteryl acetate (mp 112-114°) in ether (50 ml) is mixed with a solution containing 8.4 g (0.046 mole) of monoperphthalic acid (Chapter 17, Section II) in 250 ml of ether. The solution is maintained at reflux for 6 hours, following which the solvent is removed by distillation (steam bath). The residue is dried under vacuum and digested with 250 ml of dry chloroform. Filtration of the mixture gives 6.7 g of phthalic acid (87% recovery). The solvent is evaporated from the filtrate under reduced pressure and the residue is crystallized from 30 ml of methanol, giving 6.0 g (58% yield) of -cholesteryl oxide acetate. Recrystallization affords the pure product, mp 111-112°. Concentration of the filtrate yields 1.55 g (15% yield) of a-cholesteryl oxide acetate which has a mp of 101-103° after crystallization from ethanol. 

The dried ether solution contains about 30 g (65%) of monoperphthalic acid and is approx. 0.26 to 0.28 M. It may be used directly for oxidation reactions (cf. Chapter 1, Section IV), or stored under refrigeration. Evaporation of the ether under reduced pressure (no heat) affords the crystalline product, mp 110° (dec). 

Bohme77 employed excess monoperphthalic acid in diethyl ether to oxidize dibenzyl and benzyl ethyl sulphoxides. Reaction time was 24 h at - 15 to + 10 °C, after which he added potassium iodide and water and titrated the iodine set free with thiosulphate. Dickenson78 oxidized dimethyl sulphoxide in malt, wort or beer with Na2S2Os. In... 

Pyridine-N-oxide has been prepared by oxidation of pyridine with perbenzoic acid,4 with monoperphthalic acid,6 with peracetic acid (hydrogen peroxide and acetic acid),6-7 and with hydrogen peroxide and other carboxylic acids.7... 

The oxidative cyclization of vinylallenes need not be directed by a pendant hydroxyl group in order to succeed. The higher reactivity of the allene compared with the exocyclic methylene group in 73 (Eq. 13.23) with monoperphthalic acid leads primarily to the allene oxide which rearranges to cydopentenone 74 [27]. Inevitably some epoxidation of the alkene also takes place during the reaction. When m-CPBA is used as the oxidant, another side reaction is associated with m-chlorobenzoic add-mediated decomposition of the intermediate epoxide. It is possible to overcome this problem by performing the epoxidation in dichloromethane in a two-phase system with aqueous bicarbonate so as to buffer the add [28]. 

If ether is not suitable for the oxidation reactions in which the peracid is to be used, the material can be dissolved in another solvent after removal of the ether. An excellent solvent for monoperphthalic acid oxidations is dioxane, and a solution of the peracid in dioxane is readily prepared by adding dioxane to the dried ether extract and then removing the ether under reduced pressure at 150. The dioxane must be peroxide-free.1... 

Monoperphthalic acid has been prepared by hydrolysis of phthalyl peroxide with sodium hydroxide2 and by shaking phthalic anhydride with excess alkaline peroxide solution.2 The method described here is a modification of this latter process.3... 

If the ether is evaporated under reduced pressure (Note 5), crystalline monoperphthalic acid is obtained. It is more convenient, however, to use the ether solution directly (Note 6). Its peracid content is determined by adding to 2 cc. of the solution 30 cc. of 20 per cent potassium iodide solution and titrating the iodine after ten minutes with 0.05 N thiosulfate solution. The yield is 60-65 g. (65-70 per cent of the theoretical amount based on the phthalic anhydride) (Note 7). 

If crystalline monoperphthalic acid is desired, it may be orepared conveniently as follows The dried ether solution is placed in a distilling flask equipped with a capillary tube connected with a drying tube (p. 9), and the flask is connected with... 

Convergine (101) and hippodamine (102) are an V-oxide/free base pair, since monoperphthalic acid oxidation of 102 gives convergine (101) and 101 can be reduced with lithium aluminum hydride to yield 102. The structure and absolute configuration of 101 and 102 have been established by X-ray diffraction analysis... 

The oxidation may be carried out by Caro s acid (per monosulphuric acid, H2S05) or with perbenzoic, peracetic or monoperphthalic acid. 

The sulfur in alkylthio groups of 1,2,4-thiadiazoles may be oxidized successively to the sulfoxide and sulfone stage. Thus, 5-amino(or anilino)-3-alkylthio- 1,2,4-thiadiazoles (321 R = NH2 or PhNH)85,133 and 3-alkylthio-1,2,4-thiadiazoles (321 R = H),90 on treatment with one or two moles of monoperphthalic acid, yield the appropriate oxidation products (322 and 323). Hydrogen peroxide or chlorine may replace the less convenient per-acid as the oxidizing reagent.86 By careful... 

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