Hydrogen peroxide of crystallization

K2C03 3 H202 contains hydrogen peroxide of crystallization and the solid phase decomposition involves the production of the free radicals OH and HOi, detected by EPR measurements [661]. a—Time curves were sigmoid and E = 138 kJ mole-1 for reactions in the range 333—348 K. The reaction rate was more rapid in vacuum than in nitrogen, possibly through an effect on rate of escape of product water, and was also determined by particle size. From microscopic observations, it was concluded that centres of decomposition were related to the distribution of dislocations in the reactant particles. 

The peroxy acids and their salts generally hydrolyze in water to H2O2 and the parent (desoxy) acid. In those cases where such hydrolyses are very rapid (as with the alkali prorates )> chemists often assume that the peroxy linkage in the compound is present as hydrogen peroxide of crystallization. There are a number of more complicated peroxy compounds formed by the heavy metals, but these are described in more advanced texts. 

This chapter is concerned with the thermal decompositions of oxides and peroxides. There are obviously very important connections with the reactions of hydroxides (Chapter 8) and so-called peroxysalts, which contain hydrogen peroxide of crystallization (included in Chapter 7 on hydrates). Hydrated oxides vary from compounds accurately represented by the stoichiometric formula M(OH) , to phases which contain discrete HjO molecules. The chemistry of oxides should also be considered in the context of the other binary compounds (e.g. hydrides, nitrides, carbides, sulphides etc.) dealt with in Chapter 10. 

It is important to make the distinction between true peroxo compounds, which contain —O—O— groups, and compounds that contain hydrogen peroxide of crystallization such as 2Na2C03,3H202 or Na4P207,nH202. Esr studies of peroxoborates and blue peroxocarbonates have shown the presence of free radicals, but it is not yet certain what species are responsible. 

The study of the chemical behavior of concentrated preparations of short-Hved isotopes is compHcated by the rapid production of hydrogen peroxide ia aqueous solutions and the destmction of crystal lattices ia soHd compounds. These effects are brought about by heavy recoils of high energy alpha particles released ia the decay process. 

Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known (82,89). The crystal stmctures of a number of these have been deterrnined. Perhaps the best known are uranium peroxide dihydrate [1344-60-1/, UO 2H20, and, the uranium peroxide tetrahydrate [15737-4-5] UO 4H2O, which are formed when hydrogen peroxide is added to an acid solution of a uranyl salt. 

Peroxohydrates are usually made by simple crystallization from solutions of salts or other compounds in aqueous hydrogen peroxide. They are fairly stable under ambient conditions, but traces of transition metals catalyze the Hberation of oxygen from the hydrogen peroxide. Early work on peroxohydrates has been reviewed (92). 

Other Peroxohydrates. Potassium, mbidium, and cesium carbonates all form peroxohydrates having the general formula M2CO2 3H20. Crystal stmctures have not been estabflshed Raman spectra (31) confirm the presence of molecular hydrogen peroxide in the crystal. These compounds are unstable and have no commercial appHcation. 

Urea forms a 1 1 adduct with hydrogen peroxide. Urea peroxohydrate [124-43-6] CO(NH2)2 202, is made simply by mixing powdered urea and 35% hydrogen peroxide in the presence of stabili2ers, and crystaUi2ing the product by cooling or concentration. It is available in the form of crystals or tablets. The former contain about 35% H2O2, the latter about 34%. The solubihty in water is 510 g/L at 20°C. The solution decomposes above 55°C. 

Commercial preparation of sodium perborate tetrahydrate is by reaction of a sodium metaborate solution, from sodium hydroxide and borax pentahydrate, and hydrogen peroxide followed by crystallization of tetrahydrate (95). The tnhydrate and monohydrate can be formed by reversible dehydration of the tetrahydrate. 

Sodium perborate tnhydrate, NaBO 3H2O or Na2B2(02)2(0H)4 4H2O, triclinic, contains 11.8 wt % active oxygen (96). It has been claimed to have better thermal stabiUty than the tetrahydrate but has not been used commercially. The tnhydrate can be made by dehydration of the tetrahydrate or by crystallization from a sodium metaborate and hydrogen peroxide solution in the present of tnhydrate seeds. Between 18 and 50°C the tnhydrate is more stable but slower to crystallize than the tetrahydrate. Below 15°C the tnhydrate is spontaneously converted into the tetrahydrate. 

The ease of oxidation varies considerably with the nature and number of ring substituents thus, although simple alkyl derivatives of pyrazine, quinoxaline and phenazine are easily oxidized by peracetic acid generated in situ from hydrogen peroxide and acetic acid, some difficulties are encountered. With unsymmetrical substrates there is inevitably the selectivity problem. Thus, methylpyrazine on oxidation with peracetic acid yields mixtures of the 1-and 4-oxides (42) and (43) (59YZ1275). In favourable circumstances, such product mixtures may be separated by fractional crystallization. Simple alkyl derivatives of quinoxalines are... 

A solution of testosterone (54 10 g) in 300 ml methanol is cooled to 0° and treated successively with 60 ml of cold 30 % hydrogen peroxide and 20 ml of cold aqueous 10% sodium hydroxide. The reaction mixture is stored for 48 hr at 0° and then poured into ice water. The resultant oil is extracted with methylene dichloride (or ether) and the extract is dried (MgS04). Removal of the solvent affords the crude product, a mixture of 4a,5a- and 4, 5 -isomers, which is purified by chromatography. A sample of pure 17j5-hydroxy-4/3,5 -oxidoandrostan-3-one, mp 157-158°, crystallizes after trituration of the crude product with ether. 

Hydroxycortisone BMD) (48) A solution of 4 g of 17a,20 20,21-bis-methylenedioxypregn-4-ene-3,l 1-dione (cortisone BMD) (46) dissolved in 300 ml of t-butanol and 5 ml of water is treated with 34 ml of 35 % hydrogen peroxide and 0.45 g of osmium tetroxide predissolved in 36 ml of /-butanol. The resulting mixture is allowed to stand at room temperature for 2 days. Diol (47) which crystallizes during the reaction is collected by filtration and washed with /-butanol and water. The filtrate is diluted with ethyl acetate and washed sequentially with aqueous sodium chloride, aqueous 10% sodium bisulfite, aqueous 10% sodium bicarbonate and finally with water to neutrality. The solvent is evaporated and a second crop of the diol (47) is collected, providing a total of about 3.8 g. 

Bordwell and Boutan (BB)81 carried out extensive work on the methylsulfmyl group in 1957. It must be emphasized that they found that the preparation of pure arylmethyl sulfoxides from arylmethyl sulfides by oxidation was not a trivial matter. The frequently recommended reagent, hydrogen peroxide in acetic acid, tended to give sulfoxides contaminated with appreciable quantities of sulfones, which could not be removed by fractional crystallization. Oxidation by nitric acid was found to be more satisfactory. 

Hydrogenation, of gallic add with rhodium-alumina catalyst, 43, 62 of resorcinol to dihydroresorcinol, 41,56 Hydrogen peroxide, and formic acid, with indene, 41, 53 in oxidation of benzoic add to peroxy-benzoic add, 43, 93 in oxidation of ieri-butyl alcohol to a,a/r, a -tetramcthyltetra-methylene glycol, 40, 90 in oxidation of teri-butylamine to a,<, a, a -tetramethyltetra-methylenediamine, 40, 92 in oxidation of Crystal Violet, 41, 2, 3—4... 

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