S Rakovsky - Fields of ozone applications - страница 3

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Both methods for ozone treatment (in-situ and on-site) have appeared to be applicable for the degradation of organic substances adsorbed on the solid surface [69].

Wet-scrubber method (based on MnO2) for removing total reduced S-containing compounds such as H2S, mercaptanes, and non-magnetic particles from industrial waste gases using ozone is suggested [21].

3. Industry

3.1. Manufacture of Organic Compounds

We will focus our attention on some of the numerous ozone applications in organic polymer and inorganic productions, passivation, cleanup, and preparation of surfaces for electronics, superconductors, etc.

The reaction of ozone with olefins is the main reaction for ozonides preparation (1, 2, 4-trioxalanes) which can be converted into a mixture of carbonyl compounds, the exact composition of which depends on the olefin structure. This reaction is used for synthetic purposes as with small exceptions the C=C bond is cleaved quantitatively under very mild conditions. Usually the ozonolysis is carried out at low temperatures (as a rule at 203-243 K) as demonstrated in [3], chapters 2 and 3. Mostly, ozonolysis of olefins, except in solid phase, is carried out in various solvents such as paraffins, halogenated hydrocarbons, oxygen, sulfur, and nitrogen containing hydrocarbons like ahcohols, glycols, aldehydes, ketones, acids, ethers, esters, amines, amides, nitriles, sulfoxides, mineral acids, bases, and their mixtures, etc.

In most cases the reaction products are not separated from the reaction mixture except for the purposes of ozonide obtaining, and the oxidates are subject to hydrolysis, reduction, or oxidation [1, 3].

The hydrolysis is applied for preparation of aldehydes [70] and ketones [71]. The reductive decomposition is carried out in the presence of Zn/AcOH,

SO3-2, HSO3-1, LiAlH4, SnCl2, ArP3, Ph3P, SO2, (CH3)2S,

H2/catalyst. The reduction by metal hydrides leads to alcohol formation in the decomposition products mixture while the use of other reductors yields carbonyl compounds. Actually there are no clear requirements to the selection of the most appropriate reductor, but it turned out that dimethylsulfoxide is probably [72] the most preferable reductor in methanol solution. The ozonolysis in the presence of tetracyanoethylene yields directly carbonyl moieties omitting the reduction step [73]. A novel modification of the conventional methods of ozonolysis is exemplified by the ozonolysis of silica gel adsorbed alkenes (acetylenes) [74] and selective ozonolysis of polyalkenes, controlled with the help of dyes introduced in the reaction mixture [73]. Some examples of ozonolysis

Table 6

No.

Preparation of aldehydes, ketones and alcohols during alkenes ozonolysis with consecutive reduction

Substrate

Product

1.

0'

1. EtOAc, 253- 243 K

2. Pd/CaCO3/H2

r^CHO L.'CHO

61

2.

 

1. n-C6H14

2. Zn/HOAc

 

59

3.

N 2

1. MeOH/233 K

2. Na2SO3/H2O

\,/"^CHO N

65

4.

Me(CH2)5CH=CH2

1. MeOH/243-- 213 K

2. Me2S

Me(CH2)5CHO

75

5.

n-Bu-OOCCH=CHCOO-Bu-n

1. MeOH/208-н 203 K

2. (MeO)3P

n-Bu-OOCCHO

78

6.

Me

Me

1. MeOH/238-198 K

2. Nal/MeOH/HOAc

Me

75

7.

Y"X^ Me

4

Me

EtOAc/(CN)2C=C(CN)2,203 K

MeCO(CH2)3COMe +

O

/\

(CN)2C— C(CN)

61

8.

Me(CH2)5CH=CH2

1. n-Pentane/235 - 231 K

2. LiAlH4/Et2O

Me(CH2)5CH2OH

93

9.

H2C=CH(CH2)8COOH

1. MeOH/273 K

2. NaBH4/NaOH/ EtOH/H2O

HOCH2(CH2)8COOH

91

using various reductors for ozonides decomposition are given in Table 6 [75-80].

Ozonolysis is a powerful chemical method for economical and ecologically pure preparation of various carbonyl compounds [81].

The ozonolysis of cyclic alkenes in protic solvents followed by reductive decomposition of the formed hydroperoxides is a classical method for dialdehydes synthesis [82]. This method is applied for the preparation of 3-ethoxycarbonylglutaric dialdehyde by ozonolysis of ethyl 3-cyclopentenecarboxylate. The dialdehyde is an intermediate in the synthesis of dolazetrone mesitilate, which is an active medical substance in ANZEMET anti-emetic. Zn/AcOH, phosphines, amines, and sulfides such as 3, 3'-thiodipropionic acid and its salts are the most suitable reductors for this system. Their efficiency is comparable to that of methyl sulphide but without its shortcomings. The polymer immobilized 3,3'-thiodipropionic acid is also very active in this reduction reaction [82].

The efficient conversion of oximes into the corresponding carbonyl compounds can be also carried out through ozone oxidation [83].

The application of ozone is a new and convenient way for the preparation of cyanoacetylaldehyde (3-oxopropylonitrile) (1) and its stable dimethyl acetal (3,3-dimethoxypropylonitrile) (2) used as valuable intermediates for organic synthesis [84]. For this purpose the ozonolysis of (E)-1,4-dicyano-2-butene or 3-butylonitrile is carried out. Then the oxidates are treated by DMS yielding (1). Further, compound (1) can be used either directly in the next reactions or is transformed into (2). The (2) output amounts are from 67 to 71 %. The acetal can be again hydrolyzed to (1) by treatment with ion-exchange resin Amberlyst-15 [84].

The easily available allylphenyl ethers are ozonized at 233 K, treated with DMS giving solutions of the corresponding phenoxyacetaldehydes which are purified by column chromatography. Their reaction with 1-methyl-1-phenylhydrazine yields the corresponding hydrazones [85].

Quinolinealdehyde derivatives can be synthesized by ozonolysis of the respective quinolineolefins at 213­201 K in methanol or ethanol solution with consecutive reduction of DMS at the same temperatures. Then the reaction mixture is heated to room temperature for 1 h. The yield of the products amounts to 29 %. [86].

6-Chloro-2-hexanone is prepared from 1-methylcyclopentane via three-step scheme: a) ozonolysis of 1-methylcyclopentane in carboyilic acid solution to 1-methylcyclopentanol; b) conversion of 1-methyl-cyclopentanol into 1-methylcyclopentyl hypochloride using NaClO; c) cyclization of 1-methylcyclopentyl hypochloride in 6-chloro-2-hexanone [87].

Ozonation is a stage in the synthesis of optically pure (R)-(+)-4-methyl-2 cyclohexen-1-one from (R)-(+)-pulegone and hydroxy ketone from (-)-cis-pulegol [88].

Polycarbonyl compounds and aldehyde-acids are the ozonolysis products of (+)-4a-[1-(triethylsiloxy)-ethenyl]-2-carene [89].

Carbonyl oxides obtained from vinyl ethers ozonolysis undergo rapid [3+2] cycloaddition with imines giving the corresponding 1,2,4-dioxazolidines in yields of

14-97 % [90].

Carbonyl oxides can be also used for the synthesis of 3-vinyl-1,2,4-trioxalanes (a-vinylozonides) by a [3+2] cycloaddition with a-, ^-unsaturated aldehydes. However, a-, ^-unsaturated ketones are practically inactive in this reaction. The reaction of 3-vinyl-1,2,4-trioxalanes with ozone leads to the formation of the corresponding dizonides [91].

The carbonyl oxides prepared from the ozonolysis of enol ethers (e.g., 1-metoxy-4,8-dimethylnone-1,7 diene) undergo stereoselective intramolecular cycloaddition with inactivated alkenes yielding bicyclic dioxalanes. The latter are easily converted into j8-hydroxycarbonyl species and 1,3-diols by catalytic hydrogenation thus providing a new approach to the synthesis of 1,3-oxygenated products [92].

The ozonolysis of vinyl ethers is discussed in detail

in [93].

The synthesis of 1,2-dioxalanes is carried out by ozonolysis of 1,1-disubstituted nonactivated olefins. Thus the ozonolysis of cyclopropyl-1,1-disubsituted olefins does not produce carbonyl oxides, but formaldehyde oxide. The latter can react with the initial olefin leading to the formation of 2-dioxalanes with 10 % yield. At the addition of "foreign" olefins or aldehydes other dioxalanes and normal ozonides can be obtained [94].

The cycloalkenes ozonolysis in the presence of methyl pyruvate results in tri-substituted ozonides formation. The latter contain three reaction centers (peroxides, proton on the ozonides cycle and methoxy-carbonyl group) accessible for various functionalization. The cyclohexene ozonolysis in the presence of methylpyrovate gives ozonide whose treatment with PPh3

or Et3N yields CHO(CH3)4CHO and CHO(CH3)4COOMe

(after esterification), respectively. This method proved to be a very convenient and practical way for the synthesis of linear compounds containing various terminal groups from symmetrical cycloalkenes, in two steps and with good yields [95].

The direct conversion of olefins into esters is accomplished during mono-, di- and thi-substituted olefins ozonolysis in 2.5M methanol sodium hydroxide-dichloromethane solution. The methyl esters are obtained in high yields. Thus, 3-benzyloxy-1-nonene (5b) is transformed into 78 % yield 2-benzyloxyoctanoate (7b)

in [96].

The ozonolysis of acyclic alkenes including terpenes is reviewed in [97].

The role of ozonolysis as ecological process for the selective and specialized oxidation of petrochemical olefins and cyclic alkenes, for the manufacture of

biologically active substances and normal organic compounds is thoroughly discussed in [98].

In [99] the data on ozonolysis of acyclic and cyclic mono-, di- and trienes in the various stages of the synthesis of insect pheromones and juvenoids are summarized.

#-acylated esters of (cyclohexa-1,4-dienyl)-Z-alanine are ozonized aiming at the synthesis of novel unnatural amino acids. The combined reduction and ozonolysis followed by condensation with a suitable nucleophile results in transformation of the aromatic ring of Z-Phe to isooxasolyl, /V-phenylpyrazolyl and to bicyclic pyrazolo[1,5-a]pyrimidine groups. The preparation of heterocyclic alanine derivatives is reported [100].

Thymidine diphospho-6-deoxy-a-Z>-ribo-3-hexulose synthesized by Z>-glucose ozonolysis of methyl-glucophosphate is used as a central intermediate in the biosynthesis of di- and tridioxy sugars [101].

The ozonolysis of vinyl halides followed by reductive regio- and stereo-controlled intramolecular cyclocondensation is a key stage in the synthesis of amino sugars [102].

The ozonolysis of pyrols, oxazoles, imidazoles, and isooxazoles demonstrates another application of this reaction to the organic synthesis. Pyrols are efficient protective groups of the amino functions in the synthesis of a-aminoalcohols, a-aminoketones, a-aminoaldehydes and some peptides. The oxazole ring is also known as a protective group in the peptide synthesis [103].

The 1-substituted imidazoles ozonolysis leads to the formation of the corresponding /V-acylamides, which are important amine or acyl derivatives [104].

Some novel tetraacetal oxa-cages and complex tetraquinone oxa-cages are synthesized from alkylfuranes by a three-stage reaction. Oxo rings in the tetraacetals are obtained by the ozonolysis of cz's-endo-1,4-diones (norbornene derivatives) in dichloromethane solution at 195 K and consecutive reduction with DMS. The tetraquinone oxa-cages are obtained in the cis-endo-1,4-diones ozonolysis in dichloromethane solution at 195 K and TEA treatment [105].

A method for cleavage and oxidation of C8-30 olefins to compounds containing terminal carboxylic acid groups is reported in [106]. The process is promoted by oxidation catalysts, such as Cr, Mn, Fe, Co, etc.

The conversion of ethane to methanol and ethanol by ozone sensitized partial oxidation at near atmospheric pressure has been quantitatively studied. The effect of temperature, oxygen concentration in the inlet gas, contact time in the reactor, and ozone concentration in oxygen has been evaluated. The selectivity in regard to ethanol, methanol, as well as the combined selectivity towards formaldehyde-acetaldehyde-methanol-ethanol is also discussed [107].

Upon studying the ozone-induced oxidative conversion of methane to methanol and ethane to ethanol it has been established that these reactions do not occur in the absence of ozone which clearly suggests that the partial oxidation is initiated by the oxygen atoms generated from the ozone decomposition [87, 108].

Ortho-selective nitration of acetanilides with nitrogen dioxide in the presence of ozone, at low temperatures results in ortho-nitro derivatives formation

in high yields [109].

The ozone mediated reaction of nonactive arenes with nitrogen oxides in the presence of suitable catalysts is reported as a new method for the synthesis of the corresponding nitro derivatives with high yields [110].

The ozone induced reaction of polychloro benzenes and some related halogeno compounds with nitrogen dioxide is a novel non-acid methodology for the selective mono nitration of moderately deactivated aromatic systems [111]. In the presence of ozone and preferably with methanesulfonic acid as a catalyst, the polychloro benzenes undergo mononitration with nitrogen dioxide at low temperatures giving polychloronitrobenzenes in nearly quantitative yields [111].

The ozone mediated reaction of aromatic acetals and acylal with nitrogen dioxide is suggested as a novel methodology for the nuclear nitration of acid sensitive aromatic compounds under neutral conditions [112].

Mineral and acid-free nitro compounds are prepared from CH2Cl2 soluted pyridine or its derivatives treated with NO2/O2/O3-mixture for 8 h [113].

The nitration of aromatic compounds with nitrogen oxides in the presence of ozone is a catalytic process [114].

The stereoselective synthesis of vinyl ethers is accomplished by #-(arylidene (or alkylidene) amino)-2-azetidinones reaction with ozone and NaBH4 treatment resulting in di- and trisubstituted olefins derivatives [90].

The steroeselective synthesis of (2s, 3s) norstatine derivatives is carried out through aldehydes ozonolysis in the presence of lithium methoxyallene [94].

An interesting method of succinic acid preparation from butadiene rubber ozonolysis is suggested [115].

The preparation of a-phenyl ketone, ft>carboxylate-ended telehelic methyl methacrylate oligomers by the ozonolysis of regioregular methyl methacrylate-phenylacetylene copolymers is described in [116]. The oligomers have molecular mass varying from 1600 to 4500 (with respect to the initial copolymers) and polydespersity less than 2.

Ozone is also a very convenient agent in the manufacture of organic ceramics [117].

The ability of ozone to destroy the double C=C bonds in organic compounds is the reason for its wide application in the preparation of bifunctional compounds. This is the principle that lies in the organization of the manufacture of dodecanedicarboxylic acid (1) and azelaic acid (2). The initial substrate for the preparation of (1) is cyclododecane, which is obtained from the trimerization

of butadiene and partial hydrogenation and (2) is prepared on the base of oleic acid:

CH3(CH2)7CH=CH(CH2)7COOH + 03   —-    CH3(CH2)7CH CH(CH2)7COOH

CH3(CH2)7CH      CH(CH2)7COOH   —     CH3(CH2)7COOH  + HOOC(CH2)7COOH

The main part of dicarboxylic acids is used in the manufacture of polyester fibers, and the azelaic acid esters (и-hexyl, cyclohexyl-, z'so-octyl- and 2-ethylhexyl ester) are excellent plastisizers and synthetic lubricants.

The action of ozone is also used in pharmaceuticals in the preparation of valuable hormone products. Thus the C=C bond at C17 in the side chain of stigmasterol is destroyed by ozone yielding progesterone - an initial source for many hormones such as cortisone, male and female sex hormones, etc.

The method of selective decolorization of fabrics containing cellulose materials, such as cotton and oxidizing dyes [118], includes the following steps: application of oxidation blocking agent to the fibers; contact of the fibers with the oxidizing reagent in gas or evaporated state in the presence of moisture till the oxidation and decolorization of the dyer is carried out; interruption of this contact before the beginning of a substantial destruction of the fiber. The oxidizing agents are selected among ozone, chlorine and nitrogen oxides and sulfur dioxide flow. The application of ozone for decolorizing indigo-painted cotton jeans after this procedures results in jeans material which does not turn yellow for 6 months while the untreated goes yellow much more rapidly [118].

The changes in the composition and chemistry of UV/ozone modified wool fiber surfaces [119] are investigated by means of photoelectronic spectroscopy (XPS). The oxidation of the disulfide sulfur to sulfone groups (-SO3H) containing S6+ approaches almost 90 % conversion. This is much more than the conversion levels by using oxygen plasma. Ozonolysis results in rise of C-O groups content, particularly of the carbonyl ones [119].

The process for producing cellulose fibers and moldings such as fibers, filaments, threads (yarn), films, membranes in the form of flat, pipe and empty fibrous membranes, etc. is carried out using ozone [120]. They are produced by extrusion of cellulose solutions in tertiary amine aminooxides and in some cases in water (particularly N-methylformaline N-oxide and water); regenerating bath and water for washing by treatment with hydrogen peroxide, peracetic acid and ozone or chlorine dioxide for the regeneration of tertiary amines oxides. The introduced compounds can be enzymatically or catalytically destroyed before solvent and water regeneration.

Pitch-based carbon or graphite fibers of high tensile strength are manufactured by primary treatment of the pitch-based fibers with high concentrated ozone for a short period; then the treatment by ozone-free gases follows; in the next step they are subject to carbonization of graphitization to give elliptical fibers of long wool similar structure. Upon treatment in the absence of ozone the fibers stitched during graphitization [121].

The EPR analysis of thermal decomposition of peroxides in ozonized polypropylene fiber for grafting shows that the decomposition of the peroxide groups begins at about 343 K. The generation of several peroxides radicals is registered; the access of the fiber to the spin sample is enhanced through oxidation. Small amounts of RO2 radicals with lifetime of a couple of weeks have been identified. The integral intensity of the EPR-signal rises with time and ozonation temperature [122].

Ozonolysis modifies the diffusion pattern of liquid monomers in polypropylene matrix as their addition occurs in the amorphous phase. The appearance of intra-morphological structure and peroxides localization upon ozonolysis of polypropylene (granules and fibers) is monitored using electron spin resonance and transmission electron microscopy [123].

Upon ozonolysis, UV-radiation and plasma treatment polymer peroxides are generated on the surface of films from polypropylene, polyurethanes and polyester fibers [124]. Their thermal and reductive-oxidative decomposition have been studied by means of functional analysis using peroxidase and iodide. However, their disposition in the polymer specimen is quite various thus impeding their analysis and depends on the treatment agent. For example, the treatment with plasma generates easily accessible peroxides in polyurethane films while the UV-radiation and ozonation leads to formation of peroxides incapable of reacting with aqueous solution of peroxidase. The redox decomposition of the peroxide groups by ferro-ions at 298 K has shown that less than 50 % of the peroxides may react with ferro-ions at rate constants similar to those of hydrogen peroxide in aqueous solution. The thermal degradation of peroxides does not follow first order kinetics, most probably because of the generation of various peroxide species, characterized by different rates of decomposition. The lowest rate constant of decomposition is observed at 335 K is 3.10-3 min-1, which does not depend on the polymer nature and the method of peroxides generation [124].

Ozone-induced graft polymerization onto polymer surface is an important and convenient method for polymer modification [125].

Ozone-induced graft copolymerization of polyethylene glycol monomethyl ether methacrylate onto poly(etherurethane) improves the hydrophility and water absorption. The autoaccelerated effect in ozone-induced polymerization has been also discussed [126].

The modification of the surface properties of polypropylene and block copolymer is carried out by ozone

treatment. Thus, the wet ability of the polymers is improved - the contact angle of water becomes £ 670. The break of the polymer chain and carboxyl groups formation are accelerated by using high ozone concentrations. The cut-off fragments resulting from the ozone treatment are removed from the surface by ultrasound and organic solvents [127].

The low temperature nonelectrolytic nickel plating onto three types of polypropylene is carried out by substrate pretreatment with ozone. The latter modifies the polymer surface for galvanization while the combination of polar with anchor effect as a result of the ozone etching enhances the adhesive properties of the polymer surface. The washing of the material after ozonolysis is obligatory to ensuring proper adhesion of the material [128].

The surface properties of polypropylene (I), 100 mm films from (I), ethylene-propylene block polymer (II), or ethylene-propylene polymer prepared by the random method (III) can be improved by ozonation at concentrations of 1.38, 0.64, and 0.41 mol %, respectively. The adhesion of dyes, coloring agents, dye layers, on (I) is substantially improved and depends on the substrates in the following order: (II) > (III) > (I). It has been found that for each sample there are optimum conditions of ozonation. Reactive dyes such as epoxy and acrylo urethane resins impart a better adhesion force than the conventional nonreactive acrylic or vinylchloride resin [129].

Freshly extruded, 50 mm C2H4-ethyl acrylate-maleic anhydride copolymer film is treated by 500 ml/m2 oxygen containing 10 g/m2 ozone and is calendered with 200 mm monolayer C2ClF3 - polymer film at 288 K to produce moisture-proof packaging material with intra-layer adhesion of 800 g/15 mm and thermosealing force of 3.6 kg/15 mm against 250 and 1.3, respectively in the absence of ozone treatment [130].

Methylmethacrylate polymers with good thermal degradation resistance are prepared by ozonolysis [131] whereby the end unsaturated groups are converted into carbonyl or carboxyl ones. Ozone/air mixture is blown through a 10 g Acrypet VH solution in CH2Cl2 at 195 K followed by exposure only to air for 60 min and after solvent removal the solid residue is dried in vacuum at 570 K for 8 h. The polymer thus obtained is characterized by an initial temperature of thermal degradation of 588 K against 570 K for the polymer without ozone treatment [131].

The surfaces of propene polymer moldings are treated with ozone to improve their hydrophility. The ozone treatment of the surfaces for 8 h reduces the contact angle

of water from 100 to 810 [132].

Ozonation of PVC latex is also carried out for removal of vinyl chloride residues. The aqueous dispersions of saturated polymers are treated with ozone and the vinyl monomers are removed [133].

Graft polymerization of vinyl monomers onto Nylon 6 fiber is carried out after ozone oxidation of the fibers or films from Nylon 6 with vinyl monomers such as acrylamide, methylmethacrylate and vinyl acetate. The molecular mass of Nylon 6 decreases slightly upon ozonation. For acrylamide graft polymerization system the preliminary treatment in air or vacuum by g-rays radiation prior ozonation results in higher graft percentage. For methyl methacrylate the apparent graft percentage does not rise with the ozonation time. However the apparent graft percentage for vinyl acetate is increased with the ozone time treatment [134].

The adhesion of PVC-, fluropolymer or polyester-coated steel panels is improved by treatment with 5-50 % solution of H2O2 or ozone [135].

Synthesis of water-soluble telehelic methyl-ketone-ended oligo- V,V-dimethylacrylamides by the ozonolysis of poly(VV,VV-dimethylacrylamide-stat-2,3-dimethyl-butadiene) is reported in [136].

The synthesis of telehelic methylmethacrylate and styrene oligomers with fruorophenyl ketone end groups is accomplished by the ozonolysis of copolymers containing 4-flurophenyl butadiene units [137].

Graft polymerization of acrylic acid is carried out into preliminary ozonized siloxane matrixes [138].

The manufacture of base discs for laser recording material is realized by covering of the plastic substrates surface with solid polymer layer possessing directing channels and/or signal holes. The surface of the plastic substrate is preliminary cleaned by UV/ozone exposure before the formation of the hardened polymer layer [139].

The controlled degradation of polymers containing ozonides in the main chain takes place in the presence of:

1) periodate suported on Amberlyst A26 (SPIR);

2) diphenylphosphine deposited on polystyrene (SPR);

3) boron hydride supported on Amberlyst A26 (BER) [129]. Poly(butyl)methacrylate-copolymers are prepared by emulsion polymerization. These materials and the homopolymer poly(butyl)methacrylate are ozonized at various temperatures and treated by any of the reagents described above, thus giving telechelic oligomers in 99 % yield. Molecular mass varies when the ozonation temperature is changed. The end aldehyde groups are registered using 1H and 13C -NMR spectroscopy; the end hydroxyl groups are observed by means of FT-IR and 13C-NMR; the presence of hydroxyl groups is confirmed by tosylate formation; the carboxyl groups are identified by FT-IR and 13C-NMR and quantitatively determined by titration; in the SPR-generated oligomers the content of aldehyde groups constitutes about 80 % of the end functional groups. The oligomers obtained in BER and SPIR contain 99 % hydroxyl and carboxyl groups [140].

Polyethylene fibers are subject to ozone treatment to modify their surface [141]. The analysis of the surface is carried out by means of X-ray photoelectron (ESCA) and IR (FT-IR) spectroscopy. Carbon (C) and oxygen (O) were the main atoms monitored with ESCA (C-1s,

O-1s areas) on the treated fibers. The analysis of C-1s peaks (C1, C2 and C3) reveals that the oxidation level depends on the ozonation time. The components of 1s peak (Oo, O1, O2) are very useful for carrying out the surface analysis. They demonstrate the presence of carbonyl groups (1740-1700 cm-1) even on the untreated fibers whose intensity rises with treatment time. Ozonolysis is directed from the surface to the fiber bulk. This is confirmed by the great enhancement of the carbonyl bond band after 3 h ozonation. The thermal analysis suggests structural and morphological changes of the fiber when ozonation time exceeds 2 h [141].

The processing of fiber-reinforced plastics is performed by blowing an ozone-oxygen mixture (flow rate of 0.4 l/min) for 5 h through a CH2CL2 solution containing glass reinforced fiber particles (1mm diameter) filled with CaCO3 and unsaturated polyester. The fibers emerge on the surface till a fine powder is precipitated [142].

The manufacture of laminates through heat-sealing method involves the application of electric crown, UV-radiation or ozone exposure [143].

The manufacture of pour point depressants for oils, particularly useful for diesel oils, is carried out by oxidative degradation of waste polyethylene and/or polypropylene (I) with ozone at 303-423 K. 1000 g Waste (I) is exposed to ozone action at 423 K for 5 h giving the pour point depressant. The addition of 1 % depressant to diesel oil reduces the solidification of the oil from 253 to 238 K and the temperature of filter plugging from 264 to 253 K [144].

3.2. Inorganic Productions

Stainless steel parts are treated by ozone for surface passivation. The parts are heated in oxidative or inert atmosphere at a temperature of condensation lower or equal to 263 K. The unreacted ozone is re-used [145].

The main passivating agent is oxygen in combination at least with ozone. The system is particularly appropriate for passivation of metals (e.g., stainless steel, Ti, etc.) equipment, used in chemical plants and exposed to strong corrosion action at high temperatures and pressures [146].

To increase the corrosion resistance of metals and alloys they were exposed from 1 s to 10 min in cold plasma under pressure 1-103 Pa and 100-5000 V in atmosphere containing O2, O3, N2, H2, air, CO2, CO, N-oxides, H2O (gas), combustible gas and/or inert gas. Thus, 17 % of C0-ferrite stainless steel is subject to plasma treatment for 4 min at 103 Pa, 100 mA, and 250 V in nitrogen-oxygen mixture with 20 % oxygen. The corrosion resistance was evaluated by treatment of the sample with a solution containing 17 ml 28 % FeCl3, 2.5 ml HCl, 188.5 ml H2O, and 5 g NaCl. The sample shows relatively good resistance as compared with the untreated one [147].

Electrochemical tests reveal the influence of dissolved ozone on the corrosion behavior of Cu-30 Ni and 304L stainless steel in 0.5N sodium chloride solutions [148]. These experiments include: measurements of the corrosion potential as a function of the time and ozone concentration; cyclic polarization experiments; isopotential measurements of the current density and study of the film components. The results of these experiments show that for Cu-30 Ni and 304L stainless steel the corrosion potential is shifted to the more noble values (300 mV) at [O3] < 0.2-0.3 mg/l. At higher concentrations it remains unchanged. The dissolved ozone reduces the corrosion level for Cu-30 Ni alloys, which is evaluated by the substantial decrease in the current density at constant applied potential. The improvement of the corrosion resistance should be related to the decrease of the thickness of the corrosion products film and to the higher oxygen fraction as compared with the chloride in the same film. For stainless steel the differences in the passivating films in ozonized and nonozonised solutions are negligible as it is shown by spectroscopy [148].

Laboratory experiments have been carried out to study the ozone application for acid oxidizing leaching of chalcopyrite with 0.5 M H2SO4. For evaluating of the reaction mechanism the effect of particles size distribution, stirring and acid concentration, the dissolution reaction and reaction kinetics on the leaching have been investigated. The reaction rate is governed by ozone diffusion to the reaction mixture. Ozone is an efficient oxidizer and the process is most effective at 293 K [149].

The rate of acid leaching of chalcopyrite depends on the use of ozone as an oxidizing agent in sulfuric acid solutions. The leaching of chalcolyrite follows a parabolic law [150]. The use of ozone as an oxidizer provides conditions for the formation of elemental sulfur on the leached surfaces. The rate of leaching is reduced with temperature as the ozone solubility decreases with temperature. The results show that ozone is the best oxidizing agent for acid oxidizing leaching of chalcopyrite and may be applied in pilot plants for regular manufacture.

We have studied the possibility of using ozone for improvement of Ag extraction from polymers deposits in a flotation plant in the town of Rudozem (Bulgaria). It has been found that upon bubbling of ozone (1 vol % concentration, flow rate - 300 l/h) through flotation machine the degree of Ag extraction is increased by 1­2 % [150].

The redox leaching of precious metals from manganese-containing ores carried out by other authors show also positive results [151].

Molybdenite flotation from copper/molybdenum concentrates by ozone conditioning results in relatively pure copper-free molybdenum. The process including multi-step ozone flotation proves to be a technical and economical profitable method [152].

The manufacture of potassium permanganate is accomplished by melting of Mn-containing compounds

with KOH, dissolution of the melt and the solution oxidation. To reduce the energy consumption Mn(NO3)2 is used as a Mn-containing compound. It can be easily alloyed with KOH in a 1:5-1:10 ratio at 523-573 K. Then the product is dissolved in 20-25 % KOH solution, the solid residues is removed, saluted in 3-5 % KOH and the solution is oxidized by ozone-air mixture [153].

In the manufacture of silicon carbide ceramics melted organosilicon polymer is oxidized with 0.001 vol % ozone. Polycarboxylstyrene is the preferred polymer. The ceramics obtained is characterized by high thermal resistance and acceptable physical properties [117].

Mixtures containing In- and Sn-compounds are molded and sintered in a furnace in air atmosphere containing > 1000 ppm ozone. The ITO ceramics thus obtained are characterized by high density at low temperature sintering for a short time [154, 155].

A method for oxidizing carbonaceous material and especially for bleaching gray kaolin for subsequent use as coating or filler for paper in the presence of ozone is reported in [156].

The manufacture of mercury (I) chloride includes the reaction of Hg with hydrochloric acid in the presence of water and subsequent removal and drying at 368­378 K. Ozone (0.1 g/g product) is bubbled through the reacting mass to increase the product yield and quality [157].

Arsenic acid is prepared from (As2Cl6)2- -ions by ozonolysis [158].

The removal of color and organic matter in industrial phosphoric acid by ozone and the influence on activated carbon treatment is described in [148]. Industrial phosphonic acid containing 42-45 % P2O5 and 220­300 mg/l organic matter (OM) is subject to combined treatment with ozone and activated carbon. The independent ozonation results in removal of the initial dark color of the acid and the organic matter. It is only through absorption on activated carbon that the level of OM could be reduced to 80 % per 25 g/kg P2O5. The ozonation prior to adsorption enhances the efficiency of the activated carbon effect and decreases its specific consumption [159].

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