Alkyl Nitrates and Nitrites

Many compounds have been tested as ignition quality improvers—additives which shorten the ignition delay to a desirable duration. An extensive review in 1944 (6, 43) listed 303 references, 92 dealing with alkyl nitrates and nitrites 61 with aldehydes, ketones, esters, and ethers 49 with peroxides 42 with aromatic nitro compounds 29, with metal derivatives 28 with oxidation and oxidation products 22 with polysulfides 16 with aromatic hydrocarbons nine with nitration and four with oximes and nitroso compounds. In 1950, tests at the U. S. Naval Engineering Experiment Station (48) showed that a concentration of 1.5% of certain peroxides, alkyl nitrates, nitroaikanes, and nitrocarbamates increased cetane number 20 or more units. 

The alkyl nitrate and nitrite esters contain four different elements and as such may be expected to show a very complex kinetic behavior. This is certainly the case with the nitrate esters, the pyrolysis of which is accompanied by varying amounts of oxidation. For the nitrites, however, the pyrolysis seems to be less complex. The principal reaction products from the pyrolysis of C HsONO are CH3CHO + NO together with lesser amounts of N2O + H2O and much smaller amounts of C2H6OH, HCN, CO, and CII2O. 

The use of the direct thermal decomposition method has been fairly widespread, and the values obtained by it will be discussed in the appropriate sections of this book. The O - N bond in alkyl nitrates and nitrites, and the G N bond in nitromethane are among those whose dissociation energy has been measured by this method, but in view of the possible kinetic complexities which may be encountered, such as those already mentioned in connection with the pyrolysis of organic iodides (see Section 4.2.4) the values obtained are often at best only tentative. 

Additives may be used to improve the fuel performance, and additives such as alkyl nitrates and nitrites (ASTM D-1839, ASTM D-4046) can improve ignition quality. Pour point depressants can improve low-temperature performance. Antismoke additives reduce exhaust smoke, which is of growing concern as more and more attention is paid to atmospheric pollution. Antioxidant and sludge dispersants may also be used, particularly with fuels formulated with cracked components, to prevent the formation of insoluble compounds that could cause line and filter plugging (ASTM D-2068, ASTM D-6371, IP 309). 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

Analysing the products of reaction between alkyl nitrates and hydrazine they detected nitrate and nitrite ions, a corresponding alcohol, alkyl hydrazine, nitrogen oxides, ammonia and traces of aldehyde. If the reaction is performed without solvents in an excess of hydrazine, reduction occurs. In an aqueous solution of alcohol the process of substitution predominates particularly when the concentrations of reagents are low. 

Investigating the types of reaction between nitric acid esters and hydrazine Merrow and van Dolah endeavoured first of all to solve the problem of how nitric acid is formed since the answer could in effect make it possible to establish the position of the linkage to be broken off in an ester molecule. They have established experimentally that during the reaction between alkyl nitrates and hydrazine the nitrite ion is produced very quickly. Later it dwindles away as reaction proceeds. The creation of NO in this process can never arise from the removal of a hydrogen atom in the a-posi-tion, since only an insignificant amount of ester can follow the reaction (31) to form an aldehyde ... 

Amyl nitrite is generally sold in small glass bottles or, in rare cases, small vials or ampoules. It is chemically related to nitroglycerine. It is part of a group of closely related chemicals known as alkyl nitrites. In street terminology, amyl, butyl, isobutyl, isoamyl, isopropyl, and cyclohexyl nitrates and nitrites are collectively... 

The presence of carbon dioxide among the products of the reaction of teff-butyldifluoramine with excess nitric acid is a clear indication that C—C bond cleavage occurred. The nitrate and nitrite esters produced in this experiment were mixtures of various alkyl derivatives, and not solely tert-butyl derivatives as in the other cases where nitrate esters were detected. The relative stability of tritvldifluoramine toward oxidative cleavage is fully in accord with known differences between aromatic and aliphatic systems. 

In summary, the main products derived from these photochemical reactions are O3, peroxides (e.g., PAN, PBN, and H202), hydroperoxides, aldehydes, ketones, alcohols, nitro compounds (alkyl and benzyl nitrates and nitrites), and acids such as sulfuric, nitric, and nitrous acid. 

The alkyl nitrites have the chemical formula R-ONO. They are associated with the production of the alkyl nitrates and the PANs. However, the alkyl nitrites absorb light quite strongly in the actinic region and are very rapidly photolyzed to form RO and NO. These are not generally seen in the atmosphere at significant levels. 

Because of these problems, neither the alkyl nitrites nor the peroxy nitrates will be dealt with here. We will focus here on the alkyl nitrates and their analysis. Other multifunctional organic nitrates (e.g., hydroxynitrates, ketonitrates) will be included with the alkyl nitrates, because these are determined with the same analytical methods. 

Rate constants for the reactions of OH radicals with n-nitroalkanes, n-alkyl nitrates and n-alkyl nitrites have been determined at 298 K and 1 atmosphere total pressure using both pulse radiolysis combined with kinetic spectroscopy and a conventional relative rate method. In order to provide more mechanistic information for these reactions, rate constants for the reaction of Cl atoms with these compounds were determined using the relative rate method. The data indicate that the reaction of OH radicals with these nitrogen-containing compounds involves both an abstraction and an addition channel. These results are discussed in terms of reactivity trends and compared with the data from the literature. 

In the absence of oxygen in the rigid PTFE matrix, the reverse reaction of these radical proceeds efficiently. In the presence of oxygen, the terminal alkyl macroradicals can be oxidised to form terminal peroxy radicals which interact with double bonds much slower. Under the action of NO on samples containing neighbouring terminal double bonds and peroxy radicals, the latter are converted into macromolecular nitrates and nitrites [47] ... 

Alkyl nitrates and alkyl nitrites can be formed by the reaction of alkoxyl radicals (RO ) with nitrogen dioxide and nitric oxide, respectively ... 

Ungnade, H.E., and R.A. Smiley (1956), Ultraviolet absorption spectra of nitroparaffins, alkyl nitrates and alkyl nitrites, J. Org. Chem., 21, 993-996. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Alkyl halides are often used as substrates instead of alcohols. In such cases the salt of the inorganic acid is usually used and the mechanism is nucleophilic substitution at the carbon atom. An important example is the treatment of alkyl halides with silver nitrate to form alkyl nitrates. This is used as a test for alkyl halides. In some cases there is competition from the central atom. Thus nitrite ion is an ambident nucleophile that can give nitrites or nitro compounds (see 0-60).731 Dialkyl or aryl alkyl ethers can be cleaved with anhydrous sulfonic acids.732... 

When olefins are treated with N204 in an ether, ester, or alkane as solvent, vtc-dinitro compounds and 3-nitro alkyl nitrites are produced.803 The reaction can be successfully performed with all kinds of olefins and acetylenes. Generally, both products are produced. The dinitro compound is usually stable, but the ester is quite reactive. Upon addition of water or alcohol it is hydrolyzed to a 3-nitro alcohol. If oxygen is added, it is oxidized to a 3-nitro alkyl nitrate or an a-nitro aldehyde or ketone. 

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