Ozone precautions


A full treatment of this important—and indeed exciting—area of chemistry belongs to physical chemistry. Here, we are chiefly concerned with two fundamental questions about a chemical reaction—why does it proceed, and why does it give one product rather than another There are many processes, both physical and chemical, which proceed spontaneously. Consider first two flasks, one containing only oxygen and the other only nitrogen, which are connected by opening a tap. The two gases mix spontaneously and the mixture is eventually uniform in both flasks—there has been no chemical reaction but spontaneous mixing has occurred. When anhydrous aluminium chloride is added to water the reaction described on p. 45 occurs with the evolution of a great deal of heat— a strongly exothermic spontaneous reaction. Addition of solid ammonium nitrate to water leads to solution with the absorption of heat—a spontaneous endothermic reaction. These reactions are all spontaneous, but clearly there are wide differences in the apparent energy changes involved.  [c.62]

The combination of sulphur dioxide and oxygen to form the trioxide is slow and does not proceed to completion  [c.297]

Quinoline may be prepared by heating a mixture of aniline, anhydrous glycerol and concentrated sulphuric acid with an oxidising agent, such as nitrobenzene. The reaction with nitrobenzene alone may proceed with extreme violence, but by the addition of ferrous sulphate, which appears to function as an oxygen carrier, the reaction is extended over a longer period of time and Is under complete control.  [c.828]

Nitrogen is a better electron parr donor than oxygen and amides have a more stabilized carbonyl group than esters and anhydrides Chlorine is the poorest electron pair donor and acyl chlorides have the least stabi lized carbonyl group and are the most reactive  [c.874]

Biodegradabihty of a product may be evaluated by extended-term biochemical oxygen demand (BOD) tests. This procedure permits comparison of the amount of oxygen consumed by microorganisms in the oxidation of the test material to the theoretical oxygen requited to completely oxidize the chemical to carbon dioxide and water. Laboratory BOD tests using unacclimated biomass show that ethylene glycol (2,31,32) is readily biodegraded in a system which attempts to simulate the dilute biological conditions of a river or lake. The mean of several BOD deterrninations on ethylene glycol for 5, 10, and 20 days are 51, 78, and 97% biooxidation, respectively (2). Ethylene glycol can be treated effectively in conventional wastewater treatment plants and does not persist in the environment under expected conditions. Eor the higher molecular weight glycols (32) the laboratory BOD tests, using acclimated biomass which should occur in a wastewater treatment plant, show the 20-day value for diethylene glycol (3), triethylene glycol (4), and tetraethylene glycol (5) to be 67, 86, and 88% biooxidation, respectively. Consequendy, in an acclimated environment, the higher molecular weight glycols (tetraethylene glycol is the highest molecular weight studied) readily biodegrade and do not persist in the environment.  [c.360]

Electron beam melting of hafnium in a high vacuum removes those impurities having partial pressure at the surface of the melt greater than the vapor pressure of hafnium, about 0.1 Pa (0.075 p.m Hg) at 2500 K. Some oxygen is removable because hafnium monoxide is more volatile than hafnium. Only nitrogen and higher melting point metals, such as tantalum and tungsten, are not removed. To obtain the very purest hafnium, both refining procedures are used in sequence. Typical analyses of as-produced and refined hafnium are shown in Table 3.  [c.442]

Animal metaboHsm is based on the reactions of oxygen and organic compounds containing carbon, hydrogen, oxygen, and nitrogen and other heteroatoms. Enzymes catalyze these biochemical oxidations, which are accompHshed at about 30—40°C and frequendy proceed stepwise to produce  [c.476]

Typical photopolymer plates comprise a photosensitive layer containing an acrylate monomer a photoinitiation system, eg, a perester and a sensitizing dye, eg, a coumarin (qv). The photosensitive coating is usually covered by a 2-]lni overcoat, generally a water-soluble polymer such as poly(vinyl alcohol), which substantially prevents polymer-chain termination by oxygen. In order to ensure shelf stabiUty at high photographic speeds, laser exposure is used, which provides a free radical that is relatively stable at room temperatures. Only when the plate is heated to over 100°C does the polymerization proceed to completion. Apart from this heating step the processing chemistry is familiar to all plate-making alkaline development followed by appHcation of a hydrophilic polymer layer common to each of the processes described herein.  [c.46]

Sodium is a soft, malleable soHd readily cut with a knife or extmded as wire. It is commonly coated with a layer of white sodium monoxide, carbonate, or hydroxide, depending on the degree and kind of atmospheric exposure. In a strictiy anhydrous iaert atmosphere, the freshly cut surface has a faintiy pink, bright metallic luster. Liquid sodium ia such an atmosphere looks much like mercury. Both Hquid and soHd oxidize ia air, but traces of moisture appear to be required for the reaction to proceed. Oxidation of the Hquid is accelerated by an iacrease ia temperature, or by iacreased velocity of sodium through an air or oxygen environment.  [c.161]

Another method to prepare 19-norsteroids is first to oxidize the C19 angular methyl substituent, followed by reductive decarboxylation or decarbonylation of the resultant C19 lactone, carboxylic acid, or aldehyde. All methods of oxidation of angular methyl groups proceed through high energy intermediates capable of oxidizing unactivated CH bonds. These high energy intermediates are generated from an intramolecular heteroatom in close proximity to the angular methyl group. Practical routes to 19-norsteroids are shown in Figure 13. The addition of hypohalous acid to A -steroids (95) gives 5a-halo-6P-carbinols (96). Cyclization of this 6P-alcohol onto the C19 angular methyl substituent can occur under a variety of different conditions. For example, ether (97) is produced by the treatment of (96) with lead tetraacetate under thermal or photolytic conditions. In addition, treatment of (96) with lead tetraacetate and iodine proceeds though an intermediate hypoiodite (138) that, after homolytic decomposition, results in ether (97) (139). Ether (97) can be either oxidized to lactone (98) or the C3-acetate hydrolyzed and oxidized to the C3-ketone (99). Elimination of the halogen of (99) followed by C6-oxygen reduction yields the C19 alcohol (100). Oxidation of (100) to the aldehyde or carboxylic acid (101), followed by decarbonylation or decarboxylation, respectively, results in the 19-norsteroid (102). Alternatively, acetate hydrolysis, C3-oxidation, and elimination of (98) forms lactone (103). Concomitant C6-reduction and decarboxylation of (103) yield the 19-norsteroid (102) (140). In a similar process, the C19 and C18 angular methyl groups can be oxidized by photolytic activation of a nearly nitrite ester (141). A free-radical activation of the C18-angular methyl moiety has been exploited in a number of synthetic approaches to aldosterone (142,143).  [c.429]

This is typically accompHshed by cooling the titration solution with ice, determining the blank, and titrating rapidly. Another method utilizes deterrnination of the total peroxide and peracid content by use of a ceric sulfate titration to measure hydrogen peroxide followed by a iodide/thiosulfate titration to measure total active oxygen (60).  [c.146]

Equation 1 is referred to as the selective reaction, equation 2 is called the nonselective reaction, and equation 3 is termed the consecutive reaction and is considered to proceed via isomerization of ethylene oxide to acetaldehyde, which undergoes rapid total combustion under the conditions present in the reactor. Only silver has been found to effect the selective partial oxidation of ethylene to ethylene oxide. The maximum selectivity for this reaction is considered to be 85.7%, based on mechanistic considerations. The best catalysts used in ethylene oxide production achieve 80—84% selectivity at commercially useful ethylene—oxygen conversion levels (68,69).  [c.202]

The oxidation of carbon on the catalyst surface (coke burning) is beheved to proceed through the formation of soHd surface oxides, which decompose to give both CO and CO2 as primary products (21). In an early study on the burning of graphite, it was shown that the CO2/CO ratio is constant throughout the burning cycle, independent of oxygen partial pressure, and dependent only on the combustion temperature (22). The burning of carbonaceous deposits from porous oxides produced CO2/CO ratios at the burning site in exact agreement with the ratios of the earlier study (22) over the temperature range 450—600°C (23). Diffusion effects in the pores of large catalyst particles influence the CO2/CO ratio in the bulk vapor phase (23). However, for particle sizes typical of FCC operations (60—70 p.m average particle size), diffusion is not a factor, and thus particle size would not influence the CO2/CO ratio. Consequendy, this molar ratio remains relatively constant at a value of about 1.0 for many regenerators operating in the region below 700°C and in the absence of a CO combustion promoter.  [c.211]

Purity. Electrolytic copper is one of the purest of the materials of commerce. The average copper content of ETP copper, for instance, is over 99.95%, and even the highest level of impurities other than oxygen are found only to the extent of 15—30 ppm. Up to 0.05% oxygen is present in the form of copper(I) oxide. Even at these low impurity levels, properties of interest to fabricators are affected in varying degree.  [c.210]

The ions, M , formed by this reaction at a rate, may be carried into a bulk solution in contact with the metal, or may form insoluble salts or oxides. In order for this anodic reaction to proceed, a second reaction which uses the electrons produced, ie, a reduction reaction, must take place. This second reaction, the cathodic reaction, occurs at the same rate, ie, = 7, where and are the cathodic and anodic currents, respectively. The cathodic reaction, in most cases, is hydrogen evolution or oxygen reduction.  [c.274]

Cathodic Inhibitors. Cathodic inhibitors act to retard or poison the cathodic reaction or selectively precipitate onto cathodic areas producing diffusion barriers to cathodic reactants, thereby reducing the rate of the cathodic reaction. There are three types of cathodic inhibitors (/) hydrogen poisons, (2) oxygen scavengers, and (3) cathodic precipitates. Hydrogen poisons are chemical species such as arsenic or antimony that retard the hydrogen reduction reaction. Because the hydrogen poison slows the cathodic reaction, and because the cathodic and anodic reactions must proceed at the same rate, the whole of the corrosion process is slowed. A potentially serious drawback upon use of hydrogen poisons is that the hydrogen on the surface can be  [c.282]

Composition. Acceptable composition limits for titanium dental castings have not yet been estabHshed, but current practice favors the use of commercially pure or unalloyed titanium. Unalloyed titanium is sold in four grades of purity with grade 1 being the purest and grade 4 the least pure. ASTM specifications govern the maximum allowable content of certain critical elements in each grade. Oxygen is by far the most critical solute element in determining the properties of titanium because of its tendency to produce brittleness. Hardness is a sensitive indicator of the oxygen content of titanium, and limitations on maximum hardness are likely to be part of any future specification.  [c.486]

Ah these polymerizations proceed only in the absence of oxygen or water, which react with the highly reactive propagating species. Polymerization is usuahy carried out in an inert, hydrocarbon solvent and under a nitrogen blanket. Under these conditions, polymers with narrow molecular-weight distributions and precise molecular weights can be produced in stoichiometric amounts.  [c.15]

On the other hand, an oxide such as NiO is oxygen-rich, in the sense that occasional Ni ions are missing, electroneutrality being preserved by some of the nickel being in the +3 valence state. These Ni ions t e electrons from the otherwise filled conduction bands, thus again providing the condition needed for electrical conductivity. Oxygen adsorption according to Eq. XVlIl-31 can draw on the electrons in the slightly depleted band (or, alternatively, can produce unlimited additional Ni ) and so should be able to proceed to monolayer formation. Furthermore, since adsorption will make for more vacancies in a nearly filled band, electrical conductivity should rise. Again, the predictions are borne out experimentally [183].  [c.718]

So far, discussions have been limited to oxide film growtli at low temperatures, where tlie model of Cabrera and Mott [58 usually applies. Oxide growtli, controlled by tlie electric field across the film, follows an inverse logaritlnnic growtli law (equation (C2.8.19)). At elevated temperature, scales can grow much tliicker in water, air or oxygen, for example, or otlier more aggressive gases containing sulphur or chlorine. Mechanistically, tlie processes are similar to tlie passivation discussed earlier in tenns of oxidation, reduction, ion transport and electron transfer, as outlined in figure C2.8.5(a). The main difference is tliat elevated temperatures promote ionic diffusion and, tluis, oxide fonnation can proceed to a much greater extent tlian at low temperatures where only tliin layers are fonned by tlie high-field mechanism. The most common growtli law observed at higher temperatures is tlie so-called parabolic rate law [128]  [c.2728]

This class of methods differ from inverse micelle methods in that the reactions are completed in organic solvents. Such solvents penult the reactions to proceed at much higher temperatures, leading to nearly perfect crystalline solids [55]. In addition, the use of organic solvents penults nanocrystals to be prepared from a wide variety of molecular precursors under oxygen-free and water-free conditions. Metal [12, 56, 52, 58, 59, 60, 61, 62, 63, 64, 65 and 66], semiconductor [62, 68, 69, 20, 21, 22, 23, 24, 25, 26, 22 aiid 28] aiid ceramic nanocrystals [29, 80] have been generated using this basic strategy. These stringent controls over reaction conditions are important in the synthesis of covalent semiconductors, which require reactive organometallic starting materials. This can also be an advantage in the preparation of metal nanocrystals free from oxide or hydroxide contamination. Precursor methods have also shown remarkable success in producing highly monodisperse (a < 5%) nanocrystals, especially for II-VI semiconductor nanocrystals [10, 81]- For these reasons, this particular approach to nanocrystal synthesis is becoming a popular strategy despite the fact that it requires more involved synthetic methodology.  [c.2901]

I his approach to the calculation of free energy differences. Equation (11.6), is gener attributed to Zwanzig [Zwanzig 1954]. To perform a thermodynamic perturbation calculal we must first define and and then run a simulation at the state X, forming ensemble average of exp[—(jfy — x)/ bT] as we proceed. Analogously, we could ru simulation at the state Y and obtain the ensemble average of exp[-(jfx - JifY)/kBT]- T1 if X corresponds to ethanol and Y to ethane thiol, the free energy difference could obtained from a simulation of ethanol in a periodic box of water as follows. For e configuration we calculate the value of the energy for every instantaneous conformat of ethanol in which the oxygen atom is temporarily assigned the potential energy p meters of sulphur. Alternatively, we could simulate ethane thiol and for each configurat calculate the energy of the system in which the sulphur is mutated into oxygen.  [c.581]

This arrangement, known as the pinacol pinacolone rearrangement, is general for 1 2 glycols RR C(OH) CIOHIR R ". The striking feature of the change is the shifting of a methyl group from one of the glycol carbon atoms to the other. This interesting transformation is believed to proceed as follows. The glycol reacts with a proton to give the oxonium ion (I) elimination of water affords the carbonium ion (II) the carbonium ion may undergo a re-arrangement involving a 1 2 shift of the methyl group with its electron pair (carbanion) to give the new carbonium ion (III) the latter loses a proton to give the product of the rearrangement, pinacolone (IV).  [c.349]

Peracids convert ketones into esters in high yield. The peracid adds to the carbonyl group, and one carbon substituent migrates to the positively polarized peroxy oxygen (C.H. Hassall, 1957 W.D. Emmons, 1955 B. Plesnicar, 1978). The migration tendency follows the order f-alkyl > s-alkyl > benzyl > phenyl > /i-alkyl > methyl, if no steric effects are counteracting. This Baeyer-Villiger oxidation is particularly useful with bridged polycyclic ketones. From these compounds lactones are formed, in which the new ester bond replaces a C—C single bond with complete retention of configuration. Thus, upon hydrolysis of the lactone, a cis-disubstituted ring results (J. Meinwald, 1960 R.R. Sauers, 1961). Aldehydes are converted into sensitive formate esters by selenous peracid (F. Nakatsubo, 1970). Ketones may also be converted into amides or lactams via the similar Beckmann rearrangement of ketoximes (W.Z. Heldt, 1960).  [c.136]

An example of a scale-up project is the pressurized, fluid-bed Renugas plant in HawaH (159). The gasifier is designed for 63.5 t/d of sugarcane bagasse. In addition to bagasse, other feedstocks such as wood, waste biomass, and RDE may be evaluated. The demonstration provides process information for both air- and oxygen-blown gasification at low and high pressures. Renugas will be evaluated for both fuel gas and synthesis gas production, and for electric power production with advanced power generation schemes.  [c.46]

The mechanism of oil oxidation is thought to proceed by a free-radical chain reaction. Reaction-chain initiators are formed from unstable oil molecules, and these react with oxygen to form peroxy radicals which in turn attack the unoxidized oil and form new initiators and hydroperoxides. The hydroperoxides are unstable and divide, thereby forming new initiators and continuing the reaction. Oxidation inhibitors may not entirely prevent oil oxidation when conditions of exposure are severe, and only some types of oils are inhibited to a great degree. Two general types of oxidation inhibitors are those that react with the initiators, peroxy radicals and hydroperoxides, to form inactive compounds, and those that decompose these materials to form less reactive compounds. At temperatures below 93°C, oxidation proceeds slowly and inhibitors of the first type are effective. Examples are hindered (alkylated) phenols, eg, 2,6-di(/ f2 -butyl)-4-methylphenol [128-37-0] C H240, also known as 2,6-di(/ f2 but5i)- -cresol (DBPC), and aromatic amines, eg, /V-phenyl-CX-naphthylamine [90-30-2] These are used in turbines, circulation, and hydrautic oils that are intended for extended service at  [c.266]

Sta.rting from Phenol. Phenol can be selectively oxidized into -benzoquinone with oxygen. The reaction is catalyzed by cuprous chloride. At low catalyst concentration, the principal drawback of this method is the high pressure of oxygen that is required, leading to difficult safety procedures. It appears that a high concentration of the catalyst (50% of Cu(I)—phenol) allows the reaction to proceed at atmospheric pressure (58).  [c.489]

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45).  [c.265]

AU. epoxy resias contain compounds from the epoxide, ethoxylene, or oxirane groups, ia which an oxygen atom is bonded to two adjacent (end) bonded carbon atoms. In electrical and electronic appHcations, three types of epoxy resias are commonly used diglycidyl ethers of bisphenol A (DGEBA) or bisphenol F (DGEBF), phenoHc and cresol novolaks, and cycloaliphatic epoxides. DGEBF is less viscous than DGEBA. Liquid DGEBAs synthesized from petrochemical derivatives are most common and are readily adaptable for electrical and electronic device encapsulation. The epoxy novolaks, essentially synthesized ia the same way as DGEBA, are primarily soHds because of their relatively superior performance at elevated temperatures, they are widely used as mol ding compounds. The cycloaliphatic epoxides or peracid epoxides, usually cured with dicarboxyhc acid anhydrides, offer excellent electrical properties and resistance to environmental exposure. Reference 10 compiles the mechanical and electrical properties of the various epoxies (see also Epoxy resins).  [c.531]

Commercial fermentations are conducted ki large bioreactors which are usually referred to as fermentors and are designed for operation ki batch, fed-batch, or continuous fermentation (qv) modes (19). The organism is grown at constant temperature ki a sterile nutrient medium, containing a carbon source, a nitrogen source, and a small amount of inorganic salts, under controlled conditions of aeration (qv) and agitation. The media for commercial fermentations are usually complex mixtures containing relatively kiexpensive nutrients such as molasses, com steep Hquor, or soy meal. A batch fermentation is a closed system containing sterilised medium kioculated with the desked microorganism. Incubation is allowed to proceed under optimal physiological conditions and nothing is added durkig the course of the fermentation except oxygen, an antifoam agent (see Defoamers), and acid or base to control the pH. In the fed-batch process, nutrients are added ki increments as the fermentation progresses. In the continuous fermentation, nutrient solution is added to the bioreactor continuously as an equivalent volume of converted nutrient solution with microorganisms is simultaneously removed from the system for processkig.  [c.475]

Hydrothermal Treatment of Wastes. Hydrothermal processing (qv) of materials appears to be a promising method of disposal for many noxious materials and of conversion of some wastes to valuable by-products. This method consists of mixing reactants and water pressurizing, heating to reaction temperatures, and cooling the products and then carrying out secondary processiag of the products. For efficient oxidation, oxygen is added to the water. Typical pressures and temperatures are 22 MPa (3190 psi) and 550°C (1022°F) for destmction of wastes. Somewhat lower pressures and temperatures are used for conversions. Contact times are on the order of a few minutes. Organic chemicals are oxidized to carbon dioxide and water. Because the processes are below 1000°C, nitrogen is usually reduced to the elemental state. Other common heteroatoms are converted to corresponding acids, such as HCl and H2SO4. Reaction at high temperatures and pressures is an active field of research. There is consensus that the hydrothermal oxidation processes proceed by free-radical mechanisms.  [c.369]

Vinyhdene chloride polymers are highly resistant to oxidation, permeation of small molecules, and biodegradation, which makes them extremely durable under most use conditions. However, these materials are thermally unstable and, when heated above about 120°C, undergo degradative dehydrochlorination. For this reason, the superior characteristics of the homopolymer caimot be exploited. Furthermore, it degrades with rapid evolution of hydrogen chloride within a few degrees of its melting temperature (200°C). As a consequence, the copolymers of VDC with vinyl chloride, alkyl acrylates or methacrylates, acrylonitrile or methacrylonitrile, rather than the homopolymer, have come to commercial prominence. Such copolymers have often served as substrates for a study of the degradation reaction (99—102). The thermal degradation of vinyhdene chloride copolymers occurs in two distinct steps. The first involves degradative dehydrochlorination via a chain process to generate poly(chloroacetyiene) sequences (101,103). Subsequent Diels-Alder-type condensation between conjugated sequences affords a highly cross-linked network, which, upon further dehydrochlorination, leads to the formation of a large surface area, highly absorptive carbon (1). The initial dehydrochlorination occurs at moderate temperatures and is a typical chain process involving distinct initiation, propagation, and termination phases (104,105). Initiation is thought to occur via carbon—chlorine bond scission promoted by a defect stmcture within the polymer. An effective defect site in these polymers is unsaturation (100). Introduction of a random double bond produces an aHyUc dichioromethylene unit activated for carbon—chlorine bond scission. Initiation by the thermally induced cleavage of this bond, followed by propagation by successive dehydrochlorination along the chain, ie, the so-called unripping reaction, can then proceed readily. The thermal stabiUty of these polymers is decreased by pretreatment with ultraviolet irradiation (106), electron-beam irradiation (107), and basic solvents or reagents (108,109) by an atmosphere of oxygen (106,110) or nitric oxide (106) and by the presence of either peroxide linkages within the polymer (110,111), residues of emulsifying agents (110), organometaUic initiator residues (110), ash from a previous decomposition (110), peroxide initiator residues (106—115), or metal ions (116). AH the foregoing are sufficient to introduce random double bonds into the polymer stmcture. This can be demonstrated by examination of the treated sample by ultraviolet and infrared spectroscopic methods (107). Prolonged treatment of the polymer with basic reagents leads to more extensive dehydrohalogenation (116—121) x- or y-irradiation promotes carbon—carbon bond scission (106). The principal steps in the thermal degradation of VDC polymer are formation of a conjugated polyene sequence followed by carbonization.  [c.437]

Kieselguhr filtration, using different kinds of kieselguhr as filter aid (see Diatomite), is used in various filter constructions, ie, vertical leaf pressure filters, horizontal leaf pressure filters, candle filters, and plate and frame filters (Fig. 13 and Fig. 14). The filter constmctions offered by four to five main producers vary in minor details, but in general the technique is the same. A coarse grade of kieselguhr is used as precoat, ie, it is distributed by recirculation, equally over the total filtration area. After precoating a mixture of beer, sludge, and an appropriate mixture of kieselguhr grades are pumped onto the filter and only the sparkling, brilliant beer mns through the filterbed to a pressure tank for control. In addition to required specifications, the most important consideration is that oxygen uptake during the entire filtration is as tittle as possible.  [c.26]

Per cidDecomposition. Peracids, whether preformed or formed in situwi2i the perhydrolysis reaction, are susceptible to decomposition in an aqueous bleaching bath. The decomposition is caused by the occurrence of one of four reactions. The peracid can decompose as a result of oxidation of the bleachable material. Transition metals present even at extremely low concentration in the bath from the incoming water can decompose the peracid catalyticaHy (143,144). To minimise this effect, metal-sequestering agents have been proposed to prevent the degradation of the peracid in solution (143,144). Peracids can also hydroly2e to the parent acid and hydrogen peroxide because of the large excess of water present in the aqueous bleaching bath. This is generally a kineticaHy slow process (87). A final decomposition mechanism involves the reaction of two moles of peracid generating two moles of parent acid and a mole of oxygen.  [c.149]

The reaction involves the nucleophilic attack of a peracid anion on the unionized peracid giving a tetrahedral diperoxy intermediate that then eliminates oxygen giving the parent acids. The observed rate of the reaction depends on the initial concentration of the peracid as expected in a second-order process. The reaction also depends on the stmcture of the peracid (specifically whether the peracid can micellize) (4). MiceUization increases the effective second-order concentration of the peracid because of the proximity of one peracid to another. This effect can be mitigated by the addition of an appropriate surfactant, which when incorporated into the peracid micelle, effectively dilutes the peracid, reducing the rate of decomposition (4,90).  [c.149]

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27).  [c.481]

Chlorine atoms obtained from the dissociation of chlorine molecules by thermal, photochemical, or chemically initiated processes react with a methane molecule to form hydrogen chloride and a methyl-free radical. The methyl radical reacts with an undissociated chlorine molecule to give methyl chloride and a new chlorine radical necessary to continue the reaction. Other more highly chlorinated products are formed in a similar manner. Chain terrnination may proceed by way of several of the examples cited in equations 6, 7, and 8. The initial radical-producing catalytic process is inhibited by oxygen to an extent that only a few ppm of oxygen can drastically decrease the reaction rate. In some commercial processes, small amounts of air are dehberately added to inhibit chlorination beyond the monochloro stage.  [c.508]

Further pursuit of the isoelectronic substitution principle leads to the identification of a further class of cation formed by replacing the aza-nitrogen by an oxonia group (O ). There is here no possibility of cancelling the charge by further proton removal. Therefore the fundamental heteroaromatic rings containing an oxonia-oxygen are few, and the pyrylium ion (6) and some of its aza and diaza analogues, e.g. the 1,3-oxazinium ion (7), are the only examples in the monocyclic series. Some of the corresponding sulfur analogues, with S in place of O, are also known.  [c.2]


See pages that mention the term Ozone precautions : [c.314]    [c.10]    [c.33]    [c.434]    [c.351]    [c.44]    [c.65]    [c.21]    [c.189]    [c.275]    [c.170]    [c.250]    [c.303]   
Hazardous chemicals handbook Изд.2 (2002) -- [ c.304 ]