The synthesis of peracids
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I thought it wouldn't be a bad idea to start a digest on the topic of peracid synthesis. The two most commonly used peracids by us, bees, are performic (HCOOOH) and peracetic (CH3COOOH) acid. However, there are some others with potential, although the easiness of performic acid formation and the OTC-ness of the ingredients of peracetic acid are hard to beat.
This digest will contain several peracid synthesis methods, ranging from in situ formation to the synthesis of highly concentrated peracids. I will add all the procedures from my personal collection over time. It's just too much to add at once...
1. Synthesis of peracids using carboxylic acids as precursor
2. Synthesis of peracids using acid chlorides as precursor
3. Synthesis of peracids using acid anhydrides as precursor
4. Synthesis of peracids using boric acid anhydrides as precursor
5. Other peracid synthesis methods
6. Interesting details about peracids and related subjects
According to Houben-Weyl (Methoden der organischen Chemie, Houben-Weyl, Band VIII, Sauerstoffverbindungen III. 4. Auflage, Georg Thieme Verlag Stuttgart, 1952, p 38-43), there are 4 general methods to obtain peracids:
1. from carboxylic acids (-COOH), as they form peracids when reacted with hydrogen peroxide: RCOOH + H2O2 <--> RCOOOH + H2O;
2. from acid chlorides (-COCl). This is a very useful method for the synthesis of perbenzoic acid;
3. from acid anhydrides, especially popular for the synthesis of peracetic acid;
4. from boric acid anhydrides, only applied in few cases since the methods 1-3 are easier to perform.
1. SYNTHESIS OF PERACIDS USING CARBOXYLIC ACIDS AS PRECURSOR
Performic acid - A 10 mL flask is charged with 2 g formic acid (98-100%) (0.0435 mol) and cooled down to -10°C. 2.55 g hydrogen peroxide (98.5%, obtained by filtering 90% H2O2 over anhydrous Na2SO4) is added. Also at -10°C, 0.65 g concentrated H2SO4 is added to the flask. The temperature of the reaction mixture rised up to 5°C! After standing for 14 h in a closed flask, the reaction mixture is distilled on a waterbath at 50° and 100 mmHg. Yield: 1.7 g, contains 91.3% peroxides (iodometric determination). Yield, calculated from formic acid: 63%. Attention: in one case, a violent explosion was observed when stopping the vacuum distillation. [from: J D'Ans, A Kneip. Berichte 48 (1915) 1137]
Performic acid in situ applied to propenyl benzenes - Rh's famous review on the peracid oxidation of isosafrole. (../rhodium/chemistry /peraci
2. SYNTHESIS OF PERACIDS USING ACID CHLORIDES AS PRECURSOR
Perbenzoic acid via benzoyl peroxide - (1) Immerse a 600 mL beaker, containing 50 mL of "40-volume" hydrogen peroxide and equipped with a mechanical stirrer, in an ice bath. Support two dropping funnels, containing respectively 30 mL of 4 N sodium hydroxide solution and 30 g (25 mL) of redistilled benzoyl chloride, with their stems inside the beaker. Add the two reagents alternately a few drops at a time, taking care that the temperature does not rise above 5-8°C and that the solution is maintained faintly alkaline throughout. When all the reagents have been added, stir the solution for a further half an hour; by this time the odour of the benzoyl chloride should have disappeared. Filter off the flocculent precipitate at the pump, wash it with a little cold water, and dry upon filter paper. The yield of benzoyl peroxide is 12 g. It may be purified by dissolving in chloroform at room temperature (!) and adding twice the volume of methyl alcohol. It should not be recrystallised from hot chloroform as serious explosion may result. the compound melts at 106°C with decomposition. Like all organic peroxides, benzoyl peroxide should be handled with care.
(2) To synthesize perbenzoic acid (benzoyl hydrogen peroxide), place 5.2 g of sodium in a 500 mL dry conical flask provided with a reflux condenser, and add 100 mL of absolute methyl alcohol; slight cooling may be necessary to moderate the vigour of the reaction. Cool the resulting solution of sodium methoxide to -5°C in a freezing mixture of ice and salt: remove the condenser. Add a solution of 50 g of freshly recrystallised benzoyl peroxide(*) in 200 mL of chloroform, with shaking and cooling, at such a rate that the temperature does not rise above 0°C. Keep the mixture in the ice-salt bath for 5 minutes. with continuous shaking; it turns milky but no precipitate appears. Transfer the reaction mixture to a 1 litre separatory funnel and extract the sodium perbenzoate with 500 mL of water containing much crushed ice. [it is essential that the preparation be carried out as rapidly as possible and the temperature kept as near 0°C as feasible, especially before the free acid is liberated from the sodium salt.] Separate the chloroform layer, and extract the aqueous layer twice with 100 mL portions of cold chloroform to remove the methyl benzoate. Liberate the perbenzoic acid from the aqueous solution by the addition of 225 mL of ice-cold N sulfuric acid and extract it from solution with three 100 mL portions of cold chloroform. Dry the moist chloroform solution (about 308 mL) with a little anhydrous sodium or magnesium sulfate, and keep it in an ice box or a refrigerator until required; it contains about 24 g of perbenzoic acid.
(*) It is essential to use freshly recrystallised benzoyl peroxide. The commercial material usually gives poor results. Commercial benzoyl peroxide may be recrystallised from a small amount of hot chloroform, or by dissolving in chloroform and precipitating with absolute methyl alcohol. The m.p. is not always a safe criterion of purity [...] [from: A Vogel. A text-book of practical organic chemistry. 3rd Edition, Longmans Green and Co, London 1961. p. 807 + 808]
3. SYNTHESIS OF PERACIDS USING ACID ANHYDRIDES AS PRECURSOR
Peracetic acid - A well stirred mixture consisting of 4500 g of acetic anhydride (97.5%) and 1000 g hydrogen peroxide (26-30%) was maintained at 40°C with external cooling. Samples were withdrawn at intervals, and the peracetic acid content of the solution was determined by Smit's method for the determination of peracetic acid in the presence of hydrogen peroxide and diacetyl peroxide. After the mixture reacted about four hours at 40°C and stood overnight at room temperature, the concentration of peracetic acid reached a maximum (about 1 M, 60-80% yield). This solution is quite stable and may be stored for several weeks at 5°C without appreciable reduction in the peracetic acid content. The peracetic acid also may be prepared by Smit's method, in which a sulfuric acid catalyst is used. This reaction, however, may be extremely vigorous and exothermic, owing to the rapid rate of hydrolysis of acetic anhydride in the presence of sulfuric acid. In this preparation, we prefer to add the acetic anhydride-sulfuric acid solution dropwise to the well-stirred hydrogen peroxide solution at 40°C, instead of at 0 to 10°C as recommended by Smit, and to maintain the temperature at 40°C by means of a cooling bath as well as by adjustment of the rate of addition of the acetic anhydride-sulfuric acid solution. The peracetic acid prepared this way has the advantage over the peracetic acid prepared in the absence of a catalyst in that the acetyl peroxide concontration is often exceedingly low. Before this peracetic acid solution can be used for epoxidation, however, it must be treated with a slight excess of sodium acetate in acetic acid solution to neutralize the sulfuric acid present. Sulfuric acid catalyzes the opening of the oxirane ring by acetic acid. [from: TW Findley, D Swern, JT Scanlan. JACS 67 (1945) 412]
Peracetic acid - Peracetic acid can be synthesized by combining hydrogen peroxide (30%) with a mixture of sulfuric acid and acetic anhydride: Post 351495 (GC_MS: "Enhance oxidative strenght of 30% H2O2", Methods Discourse)
Peracetic acid - The synthesis of peracetic acid with acetic anhydride and sulfuric acid, according to d'Ans: Post 404486 (GC_MS: "Peracetic acid synthesis according d'Ans", Methods Discourse). The original documents also contains procedures to synthesize other peracids, such as perpropionic acid.
4. SYNTHESIS OF PERACIDS USING BORIC ACID ANHYDRIDES AS PRECURSOR
5. OTHER PERACID SYNTHESIS METHODS
Perbenzoic acid via benzaldehyde autooxidation - In a five-liter, three-neck, Pyrex flask, equipped with a thermometer and two fritted-glass discs, 518.5 g of benzaldehyde (4.89 moles) was dissolved in 4000 mL of acetone. The flask was immersed in an ice-bath and irradiated with three 125-Watt, Hg vapor lamps while a constant stream of dry air was passed through the solution for 25 hours (reaction temperature, 5-10°C). The peroxide content of the solution was determined at frequent intervals; after about 25 hours the rate of peroxide formation decreased considerably. At the end of this period, 3700 mL of solution containing 1.9 moles of active oxygen was obtained. The yield of peroxide (calculated as perbenzoic acid) from benzaldehyde was about 40%. [from: D Swern, TW Findley, JT Scanlan. JACS 66 (1944) 1925]
Peracetic acid synthesis using solid superacid catalysts - (Abstract: A new method for the preparation of peroxyacetic acid from acetic acid and hydrogen peroxide in the presence of solid superacids as a catalyst under mild conditions has been proposed. The preparation of peroxyacetic acid could be carried out in a batchwise operation as well as in a flow-system operation. Nafion-H was found to be active and very stable catalyst for the preparation of peroxyacetic acid and to be regenerated without the loss of catalytic activity.). DOI:10.1016/S0040-4039(03)01276-0 MS Saha et al. A new method for the preparation of peroxyacetic acid using solid superacid catalysts. Tetrahedron Letters 44 (2003) 5535-5537.
Formation of peracids via percarbonate or perborate - (Taken from: Sodium perborate and sodium percarbonate in organic synthesis. J Muzart. Synthesis (1995) 1325) To the best of our knowledge, the oldest organic reaction reported with SPB concerns the formation of peracids. The oxidation of benzoic acid by SPB was observed more than 70 years ago (CA 1925, 19, 1134). In 1946, a preparative method, using water as solvent at 0°C, was disclosed for the preparation of peracetic and monoperphthalic acids from the corresponding anhydrides (MA Stahmann et al. JOC 11 (1946) 586; L Fieser. Reactants for Organic Synthesis. Wiley, NY, Vol 1 (1967) p820) while the formation of sodium salts of various organic peroxy acids using a similar procedure was included in a patent (Patent DE893049). Later, it was shown that the formation of peracetic acid from SPB and GAA was more rapid under anhydrous conditions (Y Ogata et al. Bull Chem Soc Jpn 52 (1979) 635). The formation of peracids as the effective oxidizing species has often been proposed for oxidations with SPC in the presence of organic acids or acid anhydrides (R Gonsalves et al. J Chem Res Syn (1991) 208; WW Zajac Jr et al. Synthesis (1988) 808). Similarly, acetonitrile would lead to peroxyimidic acid (R Gonsalves, cf previous; T Ando et al. Chem Lett (1986) 665.
6. INTERESTING DETAILS ABOUT PERACIDS AND RELATED SUBJECTS
Acid reagents in general - Thread by Aurelius, containing many links to other forum threads with information of a wide variety of helpful acid reagents: Post 398337 (Aurelius: "Compilation of Acid Reagents", Chemistry Discourse)
pKa-values of some aliphatic peroxy acids - Taken from Patai's The Chemistry of Functional Groups, Peroxides. [format: peracid, pKa, temperature]
H-COOOH, 7.1, 19.5°C
Me-COOOH, 8.2, 20.0°C
Et-COOOH, 8.1, 23.0°C
n-Pr-COOOH, 8.2, 21.5°C
ClCH2-COOOH, 7.2, 25°C
t-Bu-COOOH, 8.23, 25°C
Peracetic acid - Post 10279 (strangespice: "Proper forming of peracetic acid", Serious Chemistry)
Performic and peracetic acid concentrations in function of reaction time - Post 452068 (Rhodium: "Peracid concentrations", Methods Discourse); the article also displays the preparation of said peracids. A must-read!
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