Reactivities hydrocarbons and

To examine parametrically the influence of inventory levels, we altered the rate of emission for ground level. Halving the nominal NO-fluxes is suggested by the departures of the CO/NOa,-ratios and the C2H2/NOa,-ratios obtained for high oxidant days (87). Subsequent halving of reactive hydrocarbon and nitric oxide fluxes results in the adjustment represented by f = 1/4 in Figures 30, 31, and 32 but preserves the HC/NOa -ratio. In both cases the full propylene oxidation rates were used. 

Experiments conducted in the large 335-ft irradiation chamber also showed that in most cases the effect of ambient concentrations of CO on the oxidation rate of NO to NO2 is negligible. The results for three series of runs, one involving only paraffins, one involving paraffins and more reactive hydrocarbons, and one involving no hydrocarbons, are shown in Table III. The various hydrocarbons and their relative concentrations were chosen to represent the Los Angeles atmosphere as determined by Kopczynski and co-workers 14). All runs were conducted at 50% relative humidity. 

Internal combustion engines used in automobiles and trucks produce reactive hydrocarbons and nitrogen oxides, two of the three key ingredients required for smog to form. Therefore, automotive air emissions are discussed next. 

Figure 16.12 shows the overall reaction scheme for smog formation, which is based upon the photochemically initiated reactions that occur in an atmosphere containing nitrogen oxides, reactive hydrocarbons, and oxygen. The time variations in levels of hydrocarbons, ozone, NO, and NO2 are explained by the following overall reactions ... 

The role of clouds as transporters of chemical constituents such as CO, NOx, reactive hydrocarbons, and their oxidation products from the boundary layer to the middle and upper troposphere (and possibly into the lower stratosphere) should be better understood and quantified, so that they can be parameterized for inclusion in large scale photochemical models of the atmosphere. Similarly the production of NO by lightning and its vertical redistribution by convective storms should also be much better understood and quantified, both for marine and continental conditions. 

Hydrocarbons emitted into the atmosphere react with OH and other transient oxidants (NO3 radicals, O3, Cl-atoms) to form oxygenates. Hydrocarbons have a wide variety of atmospheric lifetimes. Methane is the least reactive hydrocarbon and has an atmospheric lifetime with respect to OH radicals of about 10 years. The lifetimes (days) of ethane, propane, n-butane, and n-decane are about 47, 11, 4.9, and 1, respectively. Alkenes are more reactive than alkanes of the same carbon number and are transformed into oxygenates much more quickly by reactions with OH and O3. For example, the lifetimes for reaction with OH for ethene, propene, and trans-2-butene are about 1.3 days, 10 h, 4.3 h, respectively. In addition, the alkenes react rapidly with ozone to form oxygenates. In the presence of 60 ppb of O3, the lifetimes of ethene, propene, and trans-2-butene with repect to reaction with ozone are 4.9 days, 18 h, and 1.0 h, respectively. Of course, the nature of the products formed by reactions of the hydrocarbons with... 

In addition to inorganic radicals, which profoundly modify the properties of a paraflSn hydrocarbon residue, there is a whole series of organic groupings which are distinguished by exceptional reactivity, for example, the ethylene and acetylene groupings, and the phenyl and naphthyl radicals. Thus the characterisation of unsaturated hydrocarbons and their derivatives, e.g., the aromatic compounds, becomes possible. 

Reactivity numbers of the most reactive positions have been used to correlate the reactivities in nitration (see below) and other substitutions of a series of polycyclic aromatic hydrocarbons, and they give somewhat better correlations than any of the other commonly used indices of reactivity. The relationship shown below, which was discussed earlier ( 7.1.1),... 

The relative rates of reaction of ethane toluene and ethylbenzene with bromine atoms have been measured The most reactive hydrocarbon undergoes hydrogen atom abstraction a million times faster than does the least reactive one Arrange these hydrocarbons in order of decreasing reactivity... 

The nonbonding electron clouds of the attached fluorine atoms tend to repel the oncoming fluorine molecules as they approach the carbon skeleton. This reduces the number of effective coUisions, making it possible to increase the total number of coUisions and stiU not accelerate the reaction rate as the reaction proceeds toward completion. This protective sheath of fluorine atoms provides the inertness of Teflon and other fluorocarbons. It also explains the fact that greater success in direct fluorination processes has been reported when the hydrocarbon to be fluorinated had already been partiaUy fluorinated by some other process or was prechlorinated, ie, the protective sheath of halogens reduced the number of reactive coUisions and aUowed reactions to occur without excessive cleavage of carbon—carbon bonds or mnaway exothermic processes. 

Maleic anhydride has been used in many Diels-Alder reactions (29), and the kinetics of its reaction with isoprene have been taken as proof of the essentially transoid stmcture of isoprene monomer (30). The Diels-Alder reaction of isoprene with chloromaleic anhydride has been analy2ed using gas chromatography (31). Reactions with other reactive hydrocarbons have been studied, eg, the reaction with cyclopentadiene yields 2-isopropenylbicyclo[2.2.1]hept-5-ene (32). Isoprene may function both as diene and dienophile in Diels-Alder reactions to form dimers. 

Because di-/ fZ-alkyl peroxides are less susceptible to radical-induced decompositions, they are safer and more efficient radical generators than primary or secondary dialkyl peroxides. They are the preferred dialkyl peroxides for generating free radicals for commercial appHcations. Without reactive substrates present, di-/ fZ-alkyl peroxides decompose to generate alcohols, ketones, hydrocarbons, and minor amounts of ethers, epoxides, and carbon monoxide. Photolysis of di-/ fZ-butyl peroxide generates / fZ-butoxy radicals at low temperatures (75), whereas thermolysis at high temperatures generates methyl radicals by P-scission (44). 

The regulation Hsts 137 toxic and reactive substances and a threshold quantity for each. The regulation also appHes to flammable Hquids and gases in quantities of 10,000 lb or more (>4.5 metric tons), except hydrocarbon fuels and Hquids stored in unpressuri2ed, ambient temperature tanks, as weU as to the manufacture of any quantities of explosives (see Exlosives and propellants) and pyrotechnics (qv). 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

Wax usually refers to a substance that is a plastic solid at ambient temperature and that, on being subjected to moderately elevated temperatures, becomes a low viscosity hquid. Because it is plastic, wax usually deforms under pressure without the appHcation of heat. The chemical composition of waxes is complex all of the products have relatively wide molecular weight profiles, with the functionaUty ranging from products that contain mainly normal alkanes to those that are mixtures of hydrocarbons and reactive functional species. 

The unit parts per million by carbon takes into account the number of carbon atoms contained in a specific hydrocarbon and is the generally accepted way to report ambient hydrocarbons. This unit is used for three reasons (1) the number of carbons atoms is a very crude indicator of the total reactivity of a group of hydrocarbon compounds, (2) historically. 

It is not feasible to model the reaction of each hydrocarbon species with oxides of nitrogen. Therefore, hydrocarbon species with similar reactivities are lumped together, e.g., into four groups of reactive hydrocarbons olefins, paraffins, aldehydes, and aromatics (32). 

---