Nitrous oxides

Nitrous oxide can be made by the careful thermal decomposition of molten NH4NO3 at about 250°C  

Although the reaction has the overall stoichiometry of a dehydration it is more complex than this and involves a mutual redox reaction between N and N. This is at once explicable in terms of the volt-equivalent diagram in Fig. 11.9 which also interprets why NO and N2 are formed simultaneously as byproducts. It is probable that the mechanism involves dissociation of NH4NO3 into NH3 and HNO3, followed by autoprotolysis of HNO3 to give N02, which is the key intermediate  

Consistent with this NNO can be made from NH4N03, and N NO from NH4 N03. Alternative preparative routes (Fig. 11.9) are the reduction of aqueous nitrous acid with either hydroxylamine or hydrogen azide  

Colourless paramagnetic gas (bp -151.8°) liquid and solid are also colourless when pure 

Blue solid (mp -100.7°), dissociates reversibly in gas phase into NO and NO2 

Nitrous oxide is manufactured by heating very pure ammonium nitrate to 200 to 260°C in aluminum retorts, 

It is purified by treatment with caustic to remove nitric acid and with dichromate to remove nitric oxide. 

Nitrous oxide (N2O, see Section 2.11) is a colorless, odorless gas with mildly anaesthetic properties (laughing gas). It is formed in Nature by bacterial reduction of nitrates. The electronic structure of this linear molecule is best understood by noting that it is isoelectronic with CO2, which is also linear. It is rather easily decomposed into N2 and O2, and so can support combustion. 

Nitrous oxide is nontoxic—it used as the propellant in whipped-cream spray cans—and so might seem to be an unlikely pollutant. However, as noted earlier, it may contribute significantly to greenhouse warming. Furthermore, on diffusing to the stratosphere, N2O becomes involved in the ozone cycle (reactions 8.2, 8.3, and 8.6) following its conversion to nitric oxide (NO)  

There is therefore concern that the ever-increasing use of synthetic nitrate fertilizers may result in further depletion of the ozone layer. Eventually, stratospheric NO is returned to the Earth as nitric acid (see Section 8.4.2), but the overall dynamics of the complex atmospheric chemistry are still not fully understood. 

Nitrous oxide (NYE-truss OX-side) is also known as dinitrogen oxide, dinitrogen monoxide, nitrogen monoxide, and laughing gas. It is a colorless, nonflammable gas with a sweet odor. Its common name of laughing gas is derived from the fact that it produces a sense of light-headedness when inhaled. The gas is widely used as an anesthetic, a substance that reduces sensitivity to pain and discomfort. 

Nitrous oxide. Red atom is oxygen and blue atoms are nitrogen. The nitrogen atoms share a triple bond. 

The public found other uses for the gas as well. During the Victorian period in England, members of the upper class often held laughing gas parties at which people gathered to inhale nitrous oxide as a recreational drug, rather than for any therapeutic purpose. In the United States, the showman 

Barnum (1810-1891) created a sideshow exhibit in which people were invited to test the effects of inhaling nitrous oxide. After seeing a demonstration of this kind, the American dentist Horace Wells (1815-1848) first used nitrous oxide as an anesthetic on his patients. 

Humphry Davy proposed In the 1830s, Samuel Colt 

Nitrous Oxide. For the reaction of H with N2O two paths, (80) and (81), arc possible. Integral reaction probabilities for both processes have been determined 

Nitrous oxide (N2O), a clear, colorless, and oxidizing liquefied gas, possesses a slightly sweet odor. The product remains stable and inert at room temperature. While classified by the DOT as a nonflammable gas, nitrous oxide will support combustion and can deteriorate at temperatures in excess of 1202 F. Nitrous oxide is blended with oxygen when used in anesthesia applications. Pure nitrous oxide will cause asphyxiation. The painkilling and numbing qualities of inhaled nitrous oxide begin to take effect at concentrations of 10%. The CGA and National Welding Supply Association identify initiatives to address the NjO abuse issues. 

Virtually, aU healthcare and industrial facilities generate hazardous wastes as defined by the Resource Conservation and Recovery Act. Each facility must develop effective waste management plans. Effectively managing inventory provides the next best opportunity to reduce hazardous waste generation. The land should be updated as required. Never discard any hazardous chemical down the drain, in a toilet, or on the ground outside. Never attempt to bum chemical waste under any circumstances. Never place hazardous chemicals in trashcans or garbage containers destined for landfills. 

Always read the label, check the SDS, and follow established facility procedures. Even a small amount of some chemicals when left in a container can pose danger. Dispose of aU waste containers according to required procedures. Wastes can react with one another and bum, release toxic vapors, or explode (Table 7.15). 

BP Nitrous oxide JP Nitrous oxide PhEur Dinitrogenii oxidum USP Nitrous oxide 

Dinitrogen monoxide E942 laughing gas nitrogen monoxide. 

Nitrous oxide and other compressed gases such as carbon dioxide and nitrogen are used as propellants for topical pharmaceutical aerosols. They are also used in other aerosol products that work satisfactorily with the coarse aerosol spray that is produced with compressed gases, e.g. furniture polish and window cleaner. 

The advantages of compressed gases as aerosol propellants are that they are inexpensive, of low toxicity, and practically odorless and tasteless. In contrast to liquefied gases, their pressures change relatively little with temperature. However, there is no reservoir of propellant in the aerosol, and as a result the pressure decreases as the product is used, changing the spray characteristics. 

Misuse of a product by the consumer, such as using a product inverted, results in the discharge of the vapor phase instead of the liquid phase. Since most of the propellant is contained in the vapor phase, some of the propellant will be lost and the spray characteristics will be altered. Additionally, the sprays produced using compressed gases are very wet. However, recent developments in valve technology have reduced the risk of misuse by making available valves which will spray only the product (not propellant) regardless of the position of the container. Additionally, barrier systems will also prevent loss of propellant. 

CHEMICAL NAME = nitric monoxide nitrogen dioxide dinitrogen oxide 

equilibrium, the color of the gas fades from brown toward colorless. 

Nitric oxide is a free radical that quickly reacts in air to produce nitrogen dioxide. It is also an important biological messenger and transmitter. Nitrous oxide is a colorless, nonflammable, nontoxic gas with a slightly sweet odor and taste. Nitrous oxide is called laughing gas and has been used as a recreational inhalant, anesthetic, oxidizer, and propellant. 

Source Edgar Fahs Smith Collection, University of Pennsylvania. 

Nitrogen oxides play a key role in ozone chemistry. Paul Crutzen (1933—) received the 1995 Nobel Prize in chemistry for research that helped define the role of nitrogen oxides in ozone depletion. 

The compound profile of nitrous oxide is given in Table 16.4. N2O goes by a variety of names including the older nitrous oxide and the more modem dinitrogen oxide. 

Names Dinilrogen oxide (lUPAC) Nitrous oxide Laughing gas 

Physical descriplion Colorless, fairly unreactive gas with pleasing odor and sweet taste will support combustion once reaction has started 

History /application note Discovered in 1772 by Priestley surgical anesthetic first used in 1837 now used in dental and other minor surgery as well as a propellant gas 

The effecb of laughing gas being passed around a classroom. A drawing by George Cruikshank from the book Chemistry No Mystery, published in London, 1839. 

Several oxides of nitrogen have been well characterized. These are described in Table 12.2. 12.6.1 Nitrous Oxide, NzO 

The N20 molecule is linear as a result of it being a 16-electron triatomic molecule. Three resonance structures can be drawn for this molecule  

N2O3 Dinitrogen trioxide Blue solid, dissoc. in gas 

Nitrous oxide is rather unreactive, but it can function as an oxidizing agent, and it reacts explosively with H2, 

Nitrous oxide is quite soluble in water. At 0 °C, a volume of water dissolves 1.3 times its volume of N20 at 1 atm pressure. It is used as a propellant gas in canned whipped cream, and it has been used as an anesthetic (laughing gas). The melting point of N20 is -91 °C and the boiling point is -88 °C. 

In the following, the atmospheric cycle of gaseous nitrous oxide will first be discussed. As we shall see, the pathway of this compound is related to the NOx cycle. After the discussion of N20, the abundance of ammonia gas (ammonium particles) will briefly be presented these can also be converted in the air to nitrogen oxides. Finally, the atmospheric cycle of NO will be outlined, including particulate nitrate. 

Schiitz et al. (1970) estimated, on the basis of their measurements, a N20 column concentration of 3.30x10 4 g cm-2 in the troposphere. The corresponding stratospheric figure is 0.625 x 10 4 gem2. Taking into account the surface of the 

Earth (5.1 x 10 8 cm2), a rounded-off value of 1700 x 1061 can be calculated for the whole of the troposphere, while the global atmospheric NzO burden is equal to 2000 x 1061. The data of Rasmussen and Pierotti (1978) lead to a somewhat higher total quantity in the troposphere. However, on the basis of several recent vertical profile measurements, Ehhalt et al. (1977) give a global tropospheric nitrous oxide mass of 1660 x 106 t which is in excellent agreement with Schutz s estimate. 

It was shown by experiments carried out under laboratory conditions that nitrous oxide can be liberated from different soils since under some conditions bacterial denitrification processes lead to the formation of NzO gas (Delwiche, 

It has been mentioned in Section 1.1 that for atmospheric constituents the residence time linearly increases with the decrease of the variability of the concentration. Junge (1974) speculates that the product of the residence time and the relative standard deviation of the concentration is constant and equal to 0.14. By using this relation Rasmussen and Pierotti (1978) estimate, on the basis of their measurements, residence times of between 25 and 30 years, which is in acceptable agreement with the above figure. 

Enhanced radiation cross-linking in polyethylene, polypropylene, and poly-isobutylene and in copolymers of ethylene and propylene was found when nitrous oxide was incorporated into the polymer matrix. Mechanisms of fhis process have been proposed by several workers.  

Bonds resonate between single/triple and double 

Nitrous oxide is used as a foaming agent and propellant in whipped cream. It dissolves easily in fats under pressure, and comes out of solu- 

Nitrous oxide dissolves in the fats that sheath the nerve cells, and produces numbing and mild intoxication. It is the laughing gas dentists use to make patients less aware of pain. 

Many gases dissolve in fats and make good propellants. However, most are flammable or toxic, or they react with the fats. Other possible propellants, such as the propane used in hairsprays or in Freon, also cause intoxication when they dissolve in the fats around nerve cells. These substances are not used, since their flammability, safety, cost, or taste makes them less desirable than nitrous oxide for spray cans of whipping cream. 

There was equivocal evidence of carcinogenic activity in male and female mice based on increased incidences of hemangiosarcoma, carcinoma of the intestine (cecum), and hepatocellular neoplasms (females only). There was equivocal evidence of carcinogenic activity of p-nitrotoluene in male rats based on increased incidences of subcutaneous skin neoplasms, and there was some evidence of carcinogenic activity in females based on increased incidences of clitoral gland neoplasms. There was equivocal evidence of carcinogenic activity in male mice based on increased incidences of alveolar/bronchiolar neoplasms, and there was no evidence of carcinogenic activity in female mice exposed to 1250, 2500, or 5000 ppm in the diet. 

Metabolism and genetic toxicity have been reported to differ with the isomer of nitro-toluene. p-Nitrotoluene was not mutagenic in bacterial assays, but it did increase sister chromatid exchange frequencies and chromosomal aberrations in vitro-, in vivo it did not increase the frequency of micronuclei in bone marrow of treated rodents. Similar findings were reported for the ortho isomer, except that it did not induce chromosomal aberrations in vitro. Only the ortho isomer induces DNA excision repair in the in vivo-in vitro hepatocyte unscheduled DNA synthesis assay. Furthermore, ort/jo-nitrotoluene binds to hepatic DNA to a much greater extent than meta- or para-nitrotoluene, and investigators suggest that it may act similarly to the rodent hepatocarcino-gen 2,6-dinitrotoluene.  

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for nitro-toluene is 2 ppm (11 mg/m ) with a notation for skin absorption. 

Dunnick JK, Elwell MR, Bucher JR Comparative toxicities of o-, m-, and -nitrotoluene in 13-week feed studies in F344 rats and B6C3F1 mice. Fundam Appl Toxicol 22 411-421, 1994 

Ciss M et al Toxicological study of nitro-toluenes Long-term toxicity. Dakar Med 25 293, 1980 

FIGURE 4.16 Absorption spectrum of NO, at 298 K [adapted from DeMore et al., 1997 based on data from Ravishankara and Mauldin (1986), Sander (1986), and Canosa-Mas et al. (1987)]. 

For a solar zenith angle of 0°, the photolysis rate constants are estimated to be in the range 0.17-0.19 s for (18a) and 0.016-0.020 s l for (18b) at the earth s surface in the absence of clouds (Orlando et al., 1993 Johnston et al., 1996). The 0(3P) that is formed in the predominant path will add to 02 to generate 03, which can then react with N02 to regenerate NO,. 

Wavelength (nm) 102V (cm2 molecule ) Quantum yield Wavelength (nm) io2V (cm2 molecule 1) Quantum yield  

Absorption of N2O starts below about 210 nm (2). The absorption spectrum in the 172-197 nm region has recently been studied by Selwyn and Johnston (96). The spectrum consists of a weak continuum superimposed on diffuse bands of v-J bending mode which increased in intensity with temperature. The transitions observed are probably X- -E+ and lA - xl +. Photodissocia- 

Reactions 40 and 41 are almost equally important. Reaction 40 is a major source of NO in the stratosphere. The branching ratio, k g/(k g+k ), has recently been reported in several 

The photolysis of N2O with focussed 193 nm laser light produced NO in the highly excited D and E states (102). The excited NO is apparently formed by three sequential steps involving processes 39 and 40 and photoexcitation of NO produced by (40). 

The Bunsen solubility of N2O (CnjO in mol L ) in seawater in equilibrium with moist air at P = 1 atm can be calculated with the polynomial given by Weiss and Price (1980)  

It was not until the advent of the electron capture detector (BCD) and the development an appropriate BCD cahbration routine when precise and rehable N2O measurements were made possible (Cohen, 1977 BUdns, 1980 Rasmussen et al, 1976 Weiss, 1981). Up to now the use of an BCD in connection with equilibration or purge-and-trap techniques followed by gas chromatographic separation is state of the art for the determination of dissolved NoO (Butler and BUdns, 1991). 

N2O is in mainly produced by two microbial processes, namely denitrification and nitrification (see Fig. 2.1)  

As can be seen from the denitrification reaction sequence, N2O is a obligatory intermediate. Thus, N2O originating from denitrification is resulting from the interplay of its formation and its consumption step to N2. Denitrification is a 

N2O depth profiles from regions with oxic water masses such as found in the major parts the Atlantic (Fig. 2.2), Pacific, and Indian Oceans are characterized by a subsurface N2O maximum which coincidents with the minimum of dissolved O2 and the maximum of N03 (Butler et al., 1989 Cohen and Gordon, 919 Oudot et al., 1990, 2002). The N2O subsurface maximum is less pronounced or even absent 

In the atmosphere, HNO would presumably transfer the odd hydrogen atom to other receptors, such as 02, rather than react with itself. Until the products of this reaction are firmly established, one must treat the conversion of NH2 to N20 as one of several conceivable reaction pathways. 

Atmospheric N20 was discovered in 1938 by Adel via infrared absorption features in the solar spectrum. For the next 30 yr, N20 aroused little interest, presumably because it is neither a hazardous pollutant nor does it display any particular chemical activity. In fact, there are no gas-phase reactions that remove it from the troposphere as far as we know. In the stratosphere (see Chapter 3), N20 undergoes photodecomposition, and it reacts with O( D). The second reaction is the major source of higher nitrogen oxides in that region, and since these reduce ozone catalytically via chain reactions, N20 is an important agent in controlling the stratospheric ozone balance. The recognition of this relationship by Crutzen (1970, 1971) and McElroy 

The earlier studies, particular those of Goody (1969) and Schiitz et al. (1970) indicated a much larger variability (about 40 ppbv), which in the light of the recent data is likely to have resulted from instrumental effects. The insufficient sensitivity of thermal conductivity detectors then in use required a preconcentration procedure, which gave rise to larger errors. The difficulties of instrument calibration, influence of temperature, etc. also were underrated at that time. 

Investigators Dectector6 Locations Years Average mixing ratio (ppbv) 

Singh et al. (1979a) ECD Various locations 1975-1978 Northern hemisphere 311 2.3 

Chemical Name Synonyms Chemical Formula CAS number Molecular Weight Boiling point(l atm) 

Molar specific heat, 38.63 J/gmole °C constant pressure (25°C, 1 atm)  

NFPA hazard identification health U flammability 0 reactivity 0 

Simple asphyxiant and central nervous system depressant. Poisoning may affect the hver, kidneys and blood. Asphyxiant, narcotic, high concentrations without oxygen can cause headache, anoxia, cardiac arrhythmias, cerebral edema. Chronic exposure has resulted in loss of pain and temperature sensation, muscle weakness and other effects which may be permanent. 

It was Robert Southey (1774-1843), who was the Poet Laureate of the United Kingdom for the last 30 years of his life. 

The French chemist Charles-Louis Berthollet (1748-1821) made NgO by heating ammonium nitrate in 1785. Sir Humphry Davy repeated this in 1800, and it remains the current industrial method for making NgO, by heating ammonium nitrate at 245-270°C, with a risk of explosion if heated above 290°C. 

After initial trials, Priestley thought that NgO could be used as a preserving agent, but this proved unsuccessful. Priestley noted that it would support combustion of a candle, but a mouse exposed to it would die. 

He even administered the gas to visitors to the institute, and after watching the amusing effects on people who inhaled it, coined the term laughing gas For the next 40 years or so, the primary use of NjO was for recreational enjoyment and public shows. The so-called nitrous oxide capers took place in traveling medicine shows and carnivals, where the public would pay a small price to inhale a minute s worth of the gas. People would laugh and act silly until the effect of the drug came to its abrupt end, when they would stand about in confusion. Many famous people (of their 

And it goes on to say, The gas will be administered only to gentlemen of the finest respectability. The object is to make the entertainment in every respect, a genteel affair . 

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Dinitrogen oxide, nitrous oxide, N2O. Colourless gas, m.p. —9T C, b.p. —88-5°C (heat on NH4NO3). Decomposes to N2 and O2 above SOO C can be detonated. Linear molecule NNO. Used as a mild anaesthetic. 

Johnston H S 1951 Interpretation of the data on the thermal decomposition of nitrous oxide J. Chem. Phys. 19 663-7... 

Margottin-Maclou M, Doyennette L and Henry L 1971 Relaxation of vibrational energy in carbon monoxide, hydrogen chloride, carbon dioxide and nitrous oxide App/. Opt. 10 1768-80... 

Data for the several flame methods assume an acetylene-nitrous oxide flame residing on a 5- or 10-cm slot burner. The sample is nebulized into a spray chamber placed immediately ahead of the burner. Detection limits are quite dependent on instrument and operating variables, particularly the detector, the fuel and oxidant gases, the slit width, and the method used for background correction and data smoothing. 

Dimethylhydrazine Air, hydrogen peroxide, nitric acid, nitrous oxide... 

Thermal energy in flame atomization is provided by the combustion of a fuel-oxidant mixture. Common fuels and oxidants and their normal temperature ranges are listed in Table 10.9. Of these, the air-acetylene and nitrous oxide-acetylene flames are used most frequently. Normally, the fuel and oxidant are mixed in an approximately stoichiometric ratio however, a fuel-rich mixture may be desirable for atoms that are easily oxidized. The most common design for the burner is the slot burner shown in Figure 10.38. This burner provides a long path length for monitoring absorbance and a stable flame. 

The main problem in this technique is getting the atoms into the vapour phase, bearing in mind the typically low volatility of many materials to be analysed. The method used is to spray, in a very fine mist, a liquid molecular sample containing the atom concerned into a high-temperature flame. Air mixed with coal gas, propane or acetylene, or nitrous oxide mixed with acetylene, produce flames in the temperature range 2100 K to 3200 K, the higher temperature being necessary for such refractory elements as Al, Si, V, Ti and Be. 

Propellants. The propellant, said to be the heart of an aerosol system, maintains a suitable pressure within the container and expels the product once the valve is opened. Propellants may be either a Hquefied halocarbon, hydrocarbon, or halocarbon—hydrocarbon blend, or a compressed gas such as carbon dioxide (qv), nitrogen (qv), or nitrous oxide. 

Considerable developmental effort is being devoted to aerosol formulations using the compressed gases given in Table 4. These propellants are used in some food and industrial aerosols. Carbon dioxide and nitrous oxide, which tend to be more soluble, are often preferred. When some of the compressed gas dissolves in the product concentrate, there is partial replenishment of the headspace as the gas is expelled. Hence, the greater the gas solubiUty, the more gas is available to maintain the initial conditions. 

Property Carbon dioxide Nitrous oxide Nitrogen... 

Tracer Type. A discrete quantity of a foreign substance is injected momentarily into the flow stream and the time interval for this substance to reach a detection point, or pass between detection points, is measured. From this time, the average velocity can be computed. Among the tracers that have historically been used are salt, anhydrous ammonia, nitrous oxide, dyes, and radioactive isotopes. The most common appHcation area for tracer methods is in gas pipelines where tracers are used to check existing metered sections and to spot-check unmetered sections. 

The narcotic potency and solubiUty in oHve oil of several metabohcaHy inert gases are Hsted in Table 10. The narcotic potency, ED q, is expressed as the partial pressure of the gas in breathing mixtures requited to produce a certain degree of anesthesia in 50% of the test animals. The solubiUties are expressed as Bunsen coefficients, the volume of atmospheric pressure gas dissolved by an equal volume of Hquid. The Hpid solubiHty of xenon is about the same as that of nitrous oxide, a commonly used light anesthetic, and its narcotic potency is also about the same. As an anesthetic, xenon has the virtues of reasonable potency, nonflammability, chemical inertness, and easy elimination by the body, but its scarcity and great cost preclude its wide use for this purpose (see Anesthetics). 

Other uses of oxyacetylene flames in mill operations are in building up or hardfacing metal, lancing (piercing a hole in a metal mass), and a variety of metal cleaning procedures. A minor but interesting fuel use of acetylene is in flame spectrophotometry where oxygen and nitrous oxide are used as oxidants in procedures for a wide variety of the elements. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

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