Nitroso compounds atmospheric

Secondary and tertiary amines are not generally prepared in the laboratory. On the technical scale methylaniline is prepared by heating a mixture of aniline hydrochloride (55 parts) and methyl alcohol (16 parts) at 120° in an autoclave. For dimethylaniline, aniline and methyl alcohol are mixed in the proportion of 80 78, 8 parts of concentrated sulphuric acid are added and the mixture heated in an autoclave at 230-235° and a pressure of 25-30 atmospheres. Ethyl- and diethyl-anihne are prepared similarly. One method of isolating pure methyl- or ethyl-aniline from the commercial product consists in converting it into the Y-nitroso derivative with nitrous acid, followed by reduction of the nitroso compound with tin and hydrochloric acid ... 

The N-nitroso compounds are a potential source of carcinogenesis in humans. N-nltroso compounds appear to be ubiquitous in our environment, being present in low levels in foods, cosmetics, drugs, atmosphere, etc., and also appear to be formed endogenously in vivo. 

Major emphasis in studies of N-nitroso compounds in foods has been placed upon volatile nitrosamines, in part because these compounds are relatively easy to isolate from complex matrices by virtue of their volatility. Procedures utilizing atmospheric pressure or vacuum distillation have been used by most investigators, with variations of the method of Fine e al. (2) being among the most popular. This procedure employs vacuum distillation of a mineral oil suspension of the sample with optional addition of water to improve nitrosamine recovery from low moisture content samples (6) The usual approach to prevention of nitrosamine formation during analysis involves adding sulfamic acid or ascorbate to destroy residual nitrite at an early stage of sample preparation. 

C-nitroso compounds Combustion products, atmospheric Mutagenic and carcinogenic... 

The nitroso compounds can be formed by reaction with organic compounds present in the atmosphere and include two categories namely N-nitroso and C-nitroso compounds. 

The former are formed by the reaction of aromatic amines and NO in the atmosphere whereas the latter are formed during combustion processes. N-nitroso compounds have been studied extensively and some of them are discussed below. 

Since the hydroxylamine product is readily oxidized by air to the blue nitroso compound, these manipulations should be performed rapidly to minimize exposure of the product to atmospheric oxygen. Any nitroso compound formed at this stage will co-distil with the ether and is difficult to recover. 

Miscellaneous. Volatile nitrosamines can escape into the atmosphere from a variety of other sources. Automobile and diesel engine exhausts may contain N-nitroso compounds, including NDMA at trace levels (5). Nitrosodiethanolamine (NDEIA) is a likely air contaminant in machine shops which use cutting and grinding fluids contaminated with high concentrations of NDElA (10). Several herbicides, known to contain appreciable levels of volatile nitrosamines (9), are applied as aqueous sprays it is likely that worker exposure via inhalation may be appreciable. 

In addition to the need to monitor known problematic compounds, newer compounds are being identified as potential threats to humans and as such need to be monitored in the atmosphere. For example, researchers reported (10) that several chemical and instrumental analyses of HPLC fractions provided evidence for the presence of /V-nitroso compounds in extracts of airborne particles in New York City. The levels of these compounds were found to be approximately equivalent to the total concentrations of polycyclic aromatic hydrocarbons in the air. Since 90% of the N-nitroso compounds that have been tested are carcinogens (10), the newly discovered but untested materials may represent a significant environmental hazard. The procedure involved collecting samples of breathable, particulate matter from the air in New York City. -These samples were extracted with dichloro-methane. Potential interferences were-removed by sequential extractions with 0.2 N NaOH (removal of acids, phenols, nitrates, and nitrites) and 0.2 N H2S04 (removal of amines and bases). The samples were then subjected to a fractional distillation and other treatments. Readers interested in the total details should consult the original article (10). Both thin-layer chromatography (TLC) and HPLC were used to separate the compounds present in the methanolic extract. 

Protonated A-nitroso amines undergo photolytic decomposition from the excited state generating transient aminium radicals and nitric oxide. Aminium radicals, which are electrophilic radicals, initiate the addition to alkenes to give //-amino nitroso compounds or oc-amino oximes (Section 7.2.5.2), however, under an oxygen atmosphere, //-nitryloxy amines (/i-amino nitrates) are produced through peroxynitrites intermediates97-99. 

The catalytic reduction of aromatic nitroso compounds to amines is well documented. Selective reduction of nitro aromatic compounds can be achieved at room temperature and atmospheric pressure using an interlamellar montmorillonitesilylpalladium(II) complex (equation 20)." ... 

Butyl nitrite is ineffective by ingestion because it is degraded in the gastrointestinal tract. A 44% uptake of butyl nitrite was observed when rats were atmospherically exposed for 5 min periods. It is very rapidly transformed in the body. The likely products of butyl nitrite in vivo might be butyl alcohol, methemoglobin, nitrite ion, nitrate ion, nitrosothiols, and possibly other nitroso compounds. Butyl nitrite... 

A large number of other substances are also active inhibitors. These include oxygen, NO (one of the most effective inhibitors, so much so that some highly reactive monomers can be distilled only under an atmosphere of NO), aromatic nitro compounds, numerous nitroso compounds, sulfur compounds, amines, phenols, aldehydes, and carbamates. An interesting inhibitor is molecular oxygen. Being a diradical, oxygen reacts with chain radicals to form the relatively unreac-tive peroxy radical ... 

The nitroso complex reacts with CO to give an insertion reaction into the N-Ru bond, generating a metallacyclic complex, the structure of which has been solved by X-ray crystallography in the case in which Ar = 4-chlorophenyl [146]. The CO insertion is fast and, when the reaction between Ru(CO)3(DPPE) and a nitro compound not containing strongly electron-withdrawing substituents is performed in a CO atmosphere, the intermediate nitroso complex is nor even observable. The same type of metallacyclic complexes are also formed by direct reaction of Ru(CO)3(DPPE) with aromatic nitroso compounds. The first steps of the reaction are summarised in Scheme 5 ... 

Because of the low reactivity of pure NO in reactions of atom abstraction as well as addition to double bonds, direct interaction of this reactant with most synthetic polymers does not occur. However, the chemical modification of macromolecules in an atmosphere of NO in conditions of the simnltaneous generation of macroradicals takes place due to spin trapping via the formation of nitroso compounds. The structure of stable nitrogen-containing radicals formed from nitroso compounds in the subsequent reactions gives information on the mechanism of proceeding processes in polymers under the action of various radical-initiating factors. 

A similar procedure was used to obtain spin-labelled TEE-HEP [49]. The presence of hexafluoropropylene (HFP) groups in this polymer leads to disturbance of the structural ordering typical of PTFE to more complex dynamics of their motion. After y-irradiation of powders and films of TFE-HFP copolymer in air, there are three types of stable peroxy macroradicals in the samples end radicals CF -CF O, secondary middle-chain radicals CF -CF(00 )-CF2, and tertiary middle-chain radicals CF2-C(CF3)(00 )-CF2. In contrast to PTFE, prolonged exposure (>100 hours) of these samples in a NO atmosphere at room temperature does not lead to the formation of aminoxyl macroradicals. However, two types of macroradicals are formed if TFE-HFP is heated with evacuation after the decay of radicals in a NO atmosphere. At 90 °C, the ESR spectrum demonstrates the presence of tertiary alkyl macroradicals CF2-C (CF3)-CF2 formed upon decay of the tertiary nitroso compounds [57]. On further increasing of the temperature up to 180 "C, the tertiary alkyl macroradicals... 

The mechanism of the conversion of free radicals in fluorinated polymers reflects the introduction of NO into the middle of the main chain without changing its orientation and the possible formation of CF radicals in the system under the action of light. The ARs appear in the temperature range where the tertiary nitroso compounds decay in the vacuum with the regeneration of tertiary alkyl macroradicals CF2-C (CFj)-CF2 As has been established [58], these tertiary macroradicals decay in an inert atmosphere. Decay of these radicals requires spatial transfer of free valence. The first step of radical decay is P-decomposition by the reaction [59] ... 

The radical R in an atmosphere of NO is converted into nitroso compounds and further into oximes ... 

The y-radiolysis of PMMA at room temperature in an atmosphere of NO as well as photolysis leads to the formation of acylalkylaminoxyl radicals. The evacuation of samples at elevated temperatures gives rise to the appearance of the signal of iminoxyl radicals in the ESR spectrum. As distinct from photolysis, y-radiolysis can stimulate hydrogen-atom detachment from the C-H bonds of macromolecules and, consequently, the formation of primary and secondary macromolecular nitroso compounds takes place in an atmosphere of NO. Such nitroso compounds are rapidly isomerised into oximes [63]. The abstraction of hydrogen atoms from the OH groups of oximes by active free radicals results in the formation of iminoxyl radicals [64]. This viewpoint is confirmed by the observation of ESR spectra of iminoxyl radicals in y-irradiated PMMA and AC in the presence of NO. 

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