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Supplement F2: The Chemistry of Amino, Nitroso, Nitro and Related Groups.

Edited by Saul Patai Copyright 1996 John Wiley & Sons, Ltd.

ISBN: 0-471-95171-4

CHAPTER 25

Environmental aspects

of compounds containing nitro, nitroso and amino groups

H. K. CHAGGER and A. WILLIAMS

Department of Fuel and Energy, University of Leeds, Leeds, LS2 9JT, UK Fax: +44 113 244 0572; e-mail: FUEAW@LEEDS.AC.UK

I. ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1170 II. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1171 III. ENVIRONMENTAL EXPOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173 A. Nitro Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173 B. Nitroso Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182 1. Leather and tanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183 2. Rubber industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184 3. Metal and machining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185

IV. ENVIRONMENTAL EXPOSURE TO PREFORMED

NITROSAMINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186 A. Sunscreens and Cosmetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186 B. Pharmaceutical Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186 C. Agricultural Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186 D. Packing Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187 E. Foods and Beverages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187 F. Endogenous Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1189

V. AMINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196 A. Hydrazine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196 B. Azo Dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197

VI. CONTROL AND LEGISLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197 VII. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212

 

I. ABBREVIATIONS

BCG

Bacillus Calmette-Guerin

BCNU

bischloroethyl-nitrosourea

CCNU

1-chloroethyl-3-cyclohexyl-1-nitrosourea

1169

1170

 

H. K. Chagger and A. Williams

C-PAH

C-polyaromatic hydrocarbons

DNA

deoxyribonucleic acid

EPA

 

environmental Protection Agency

HO2NO2

peroxy nitric acid

HNO2

nitric acid

LPS

 

lipopolysaccharide

N/C

 

nitrogen/Carbon

NCO

isocynate radical

NDBA

N-nitrosodibutylamine

NDEA

N-nitrosodiethylamine

NDELA

N-nitrosodiethanolamine

NDMA

N-nitrosodimethylamine

NDPhA

N-nitrosodiphenylamine

NEMA

N-nitrosoethylmethylamine

NHMTCA

N-nitroso-2-hydroxymethylthiazolidine-4-carboxylic acid

NHMTHZ

N-nitroso-2-hydroxymethylthiazolidine

NH2O

oxyamine radical

NHPRO

N-nitroso-4-hydroxyproline

NHPYR

N-nitroso-3-hydroxypyrrolidine

Nitro-PAH

nitro-polyaromatic hydrocarbons

NMAMBA

N-nitroso-N-(1-methylacetonyl)-3-methylbutylamine

NMAMPA

N-nitroso-N-(1-methylacetonyl)-2-methylpropylamine

NMOCA

N-nitroso-5-methyloxazolidine-carboxylic acid

NMOR

N-nitrosomorpholine

NMPABOA

2-ethylhexyl 4-(N,N-dimethylamino) benzoate (Padimate O)

NMPhA

N-nitrosomethlyphenylamine

NMPZ

N-nitrosomethlyphenylamine

NOC

N-nitroso compounds

NO

 

nitric oxide

NO2

 

nitrogen dioxide

NO3

ž

nitrate radical

NO2

ž

nitrite radical

N2O3

nitrogen trioxide

NOx

 

mixture of oxides of nitrogen like nitric oxide and nitrogen dioxide

N2O

 

nitrous oxide

N2O3

nitrogen pentaoxide

NOCA

N-nitrosooxazolidine-4-carboxylic acid

NPAH

polyaromatic compounds containing nitrogen

NPIP

N-nitrosopiperidine

NPRO

N-nitrosoproline

NPYR

N-nitrosopyrrolidine

NSAR

N-nitrososarcosine

NTCA

N-nitrosothiazolidine-4-carboxylic acid

NTHZ

N-nitrosothiazolidine

PAH

polynuclear aromatic hydrocarbons

PAC

 

polynuclear aromatic compounds

PAN

peroxy acetyl nitrate

PANH

nitrogen containing polyaromatic hydrocarbons

RNO3

alkyl nitrate

VOC

volatile organic compounds

25. Environmental aspects of compounds

1171

II. INTRODUCTION

The nitro, amino and nitroso derivatives of organic compounds constitute a large and varied group of compounds which are used widely in industry but can also be formed in the atmosphere by chemical reactions. This series is characterized chemically by substitution of an amino group (NH2) or nitro group (NO2) for a hydrogen atom of an organic (usually aromatic) compound. Nitroso compounds can be placed into two categories, the N-nitroso and the C-nitroso compounds. The N-nitroso compounds result from typical free radical reactions or by the reaction of secondary amines with nitrous acid. The C- nitroso compounds can be derived from aliphatic compounds by free radical reactions, or from aromatic compounds when, e.g., nitrosation of the aromatic ring of a tertiary amine occurs at either the para or the ortho position. Beside these routes, NOx , which is present in the atmosphere as a result of combustion processes, reacts with volatile organic compounds (VOC) to give rise to various organic NO and NO2 compounds. Ammonia in the atmosphere plays a very minor role, although high levels of ammonia or hydrazine in the work place can produce some very toxic compounds.

The nitro compounds which are products of direct nitration can undergo subsequent reduction yielding amines; these amines can be converted into more versatile class of organic compounds as shown in Figure 1. This sequence provides a route to formation of dozens of aromatic compounds.

The amino, nitro and nitroso compounds are often used in bulk as intermediates in synthesis of dyes, pharmaceuticals, antioxidants and accelerators for the rubber industry and are also produced during the manufacture of different industrial commodity foods beverages and agricultural products. The nitrosamine production seems to be an unsolved problem, although there has been a reduction in concentration of nitrates in cured meats and other products over the decades. Several new nitrosamines have been identified in tobacco products, while cosmetic and personal care products have been found to be contaminated with nitrosodiethanolamine. Increased use of diesel fuel because of its higher efficiency has led to problems due to emission of high polyaromatic compounds (PAC) which react with either the nitrogen present in the fuel or in the lubricating oil, with NO and NO2 being formed and in term forming nitro-PAH. These nitro-PAH have been found to be even more potent than their parent PAH in terms of mutagenecity and carcinogenecity (Table 1).

Legislation and control have been implemented on concentration levels of NOx arising from industries and combustion processes in developed nations (USA, Canada, Europe). Still nitroso compounds are formed invariably as intermediates either during manufacturing cycles or in the atmosphere. Exposure from most compounds occurs during handling of the chemicals, inhalation and ingestion are also becoming prominent routes for exposure. There is sufficient evidence to indicate that the large majority (90%) of these compounds

Sources

Automobiles Combustion processes

Laboratories Industrial processes

Atmospheric reactions and transformations

Reaction during combustion

Nitro-PAH

NPAH

C-PAH

Most of them classified as mutagens and carcinogens

Reaction in the

atmosphere NOC

e.g. NDMA, NDELA, NDEA, NDPA

FIGURE 1. Formation and reduction of nitro compounds

1172 H. K. Chagger and A. Williams

TABLE 1. Structure, sources and effects of nitrogen-containing organic compounds1,2

Structure Sources Effects

Nitro ( NO2) Aliphatic ( C NO2) Examples: Nitromethane, nitroethane, nitropropane etc.

Nitro-PAH,

Nitrophenols

C-nitroso compounds (C NDO)

Nitrogen Oxides Nitric oxide (NO)

Amines

Hydrazine

Nitroso (N NDO) (NOC)

Solvents for cellulose esters, resins, oils, fats, waxes, dyes, vasodilators in medicine, industrial and military explosives

Combustion processes, atmospheric reactions, diesel engines

Combustion products, atmospheric reactions

Fossil flue combustion systems, biomass burning

Aniline

Tobacco plants, polymerization catalysts, pharmaceutical products, corrosion inhibitor in boiler water, propellant fuels

Pesticides, industrial waste, drying of foods in combustion gases, e.g. brewing industry, soup mixes, tea, spices, powdered formulations, soy protein isolates, cereal products, dairy products and cured meat products etc.

Explosives, dyes, pigments, insecticides, textiles, plastics, resins, elastomers, pharmaceuticals, fuel additives, plant-growth regulators, rubber accelerators and antioxidants Azo dyes, used in textiles, leather, printing, paper making, drugs and food industry

Cause toxic narcosis, liver damage, depressive effect on central nervous system;

industrially 30 ppm can cause nausea, vomiting, diarrhea, irritation of the respiratory system, dizziness. Repeated exposure causes cyanosis and may act as potential carcinogens

Mutagenic and carcinogenic

Mutagenic and carcinogenic

Cause bronchitis, pneumonia and lung infections, asthma Photochemical smog, acid rain

Production of NO2

Some substances were considered to induce cancer of oesophagus, stomach and nasopharynx

Skin irritants, cause cyanosis and methaemoglobinanemia

Mutagenic and carcinogenic

represent a serious health hazard, and are known for their toxic, mutagenic and carcinogenic effects. The simplest of these toxic, compounds are aniline, hydrazine and mononitrobenzene. In most cases the symptoms appear over a period of time usually many years. This causes difficulties in assessing the carcinogenecity of these chemicals and the implication of regulatory activities in order to minimize the exposure to these chemicals. The Occupational Safety and Health Administration in many countries divides these chemicals into three classes, namely potential suspected carcinogens where there is good scientific evidence of human carcinogenesis; suspected carcinogens where there is suggestive evidence of carcinogenecity in man, and experimental carcinogens. Some countries have totally banned the production and use of the first category of these chemicals, and in other cases the production and use are controlled by legislation. A list of some chemical carcinogens is given in Table 2.

25. Environmental aspects of compounds

1173

TABLE 2. Different categories and possible control of chemical carcinogens3

 

Chemicals

Control

 

 

 

 

Human carcinogens

 

 

2-Naphthylamine

Importation and use in manufacture of these

 

Benzidine

are prohibited by legislation, e.g. in the

 

4-Aminobiphenyl

U.K., except if present at less than 1% in

 

4-Nitrobiphenyl

another material

 

1-Naphthylamine

Use of this is controlled by legislation, e.g.

 

 

in the U.K.

 

Acrylonitrile

Threshold limit values (TLV) awaiting

 

 

reassignment when new data becomes

 

 

available; no exposure permitted

 

Suspected human carcinogens

Assigned maximum operating levels (TLV)

 

3-Amino-1,2,4-triazole

0.5 ppm (1 mg m 3)

 

1,1-Dimethylhydrazine

 

2-Chloroaniline

0.2 ppm (0.35 mg m 3)

 

Methylhydrazine

 

2-Nitropropane

25 ppm (90 mg m 3)

 

Experimental carcinogens

2-Acetylaminofluorene Diazomethane 4-Dimethylaminoazobenzene Ethyl diazoacetate Ethylenethiourea

Ethyl N-nitroso carbamate

In general carcinogenic activity has also been observed in certain structural classes3:

žBiological alkylating agents, bis(chloroethyl)amines, ethyleneimines

žPolycyclic hydrocarbons or heterocycles, monoand di-benzanthracenes, -pyrenes, -acridines

žAromatic amines, two rings or more, napthylamines, amino- (or nitro-), acetylaminofluoroene

žNitroso compounds, nitrosoamines, nitrosoamides

žAzo compounds and hydrazines, azo alkanes, azo aromatics, aminoazobenzenes, diazonium salts, diazomethane, hydrazine and its methyl derivatives

This review does not deal specifically with all the categories mentioned above, but takes into account compounds which are formed at the work place and result in direct exposure and preformed nitroso compounds. The latter are formed from amines or contain high concentrations of amino compounds. The contamination may arise as a result of contaminated starting material, in particular amines or from the formation of NOC during the manufacturing cycle.

III. ENVIRONMENTAL EXPOSURE

A. Nitro Compounds

A variety of nitrogen oxides (NOx ) such as nitric oxide (NO) and nitrogen dioxide (NO2) as well as nitrous oxide (N2O) are present in the atmosphere. The sources of these oxides are biological actions and organic decomposition in the soil and in the ocean

1174

H. K. Chagger and A. Williams

(mainly N2O) or from activities through combustion. The combustion generated NOx mainly consists of NO initially but is rapidly converted into NO2 in the atmosphere. These oxides react with the VOCs in the atmosphere leading to the formation of photochemical oxidants and of smog, when as part of the reaction sequence the hydrocarbon radicals also produce RNO and RNO2.

The major route of formation of these nitro compounds is via the reaction of VOCs with the NOx arising from hot flue gases, such as automobile exhaust gases and gas streams used for drying food stuffs, etc. In these combustion systems the aliphatics can react with nitro compounds or arenes to produce nitro-PAH and nitroarenes. Some of the NOx produced are thus converted into C-nitroso compounds. The interactions and reaction chemistry of these compounds is complex and difficult to interpret.

During combustion processes the molecular nitrogen in the combustion air and the fuel nitrogen that may be present in the fuel is converted into nitric oxide and some nitrogen dioxide4 when NO and residual O2 are cooled together. The NO formation is also controlled by (1) thermal NO, (2) prompt NO and (3) N2O to NO routes5 7.

The amount of prompt NO produced in combustion systems is relatively small compared with the total NOx formation. However, prompt NOx is still formed at low temperatures and is one of the features in producing ultra-low NOx burners. The nitric oxide reacts with other species in the atmosphere to give various other nitrogen oxides, namely NO2 and nitrogen pollutants.

Figure 2 shows the nitric oxide cycle resulting in the emission of NOx and pollutants arising from it at atmospheric temperatures8.

Apart from NOx , ammonia also occurs in the atmosphere which is largely formed by the natural ecosystem. In industrial regions it can undergo a series of reactions to produce ammonium sulphate aerosol in presence of sulphuric acid, or alternatively form NH2, N2O and NO. These species are responsible for the destruction of ozone in the

troposphere9.

 

 

 

 

NH3 C OH ! NH2 C H2O

 

 

 

NH2 C NO ! N2O C H2O

 

 

 

NH2 C O3 ! NH2O C O2

 

 

 

NH2 C NO2 ! N2O C H2O

 

 

NH2O C NO ! NH2 C NO2

 

 

Combustion

 

 

RNO3

NO, NO2

HONO

 

 

HO2NO2

 

Cloud

PAN

NO3

HNO3

 

 

 

VOC

Aerosol NO3

Gas phase reactions

 

N2O5

 

Photochemical reactions

 

 

Precipitate

Gas/surface reactions

 

 

 

 

 

FIGURE 2. Nitric oxide cycle and pollutants

25. Environmental aspects of compounds

1175

The NH2O formed in the series of chain reactions is anticipated to be a short-lived intermediate which could interact with polyaromatic hydrocarbons (PAH) in atmosphere to give nitroarenes or nitro-PAH.

A typical fuel combustion process in air produces 50 1000 ppm of NOx in flue gases. The level of NOx occurring during combustion can be reduced considerably by using low or ultra-low NOx burners and such burners have also been produced for food drying. These burners consist of fuel-lean pre-mixed flames burning in a stream of ducted dilutionary air. In such flames, formation of NOx occurs partly via the thermal NOx route and nitrous oxide route. These burners are fuel-lean and hence produce insignificant levels of PAH (0.2 mg/m3) and almost no NOx in case of some burners10,11. Low temperature catalytic combustion of lean natural gas mixtures is another method of eliminating NOx and PAH generated during combustion. Low cost and highly active nickel-cobalt or ironbased catalysts have a great potential in this field12,13. Application of reburn process, i.e. staging of the fuel to react with NO formed in the flame with hydrocarbon radicals, CHi, and converting it to molecular nitrogen thereby reduce the NOx concentration levels14. Gas turbines are being used to generate electric power because of their effect on energy conservation and low cost of installation. Gas turbine combustors are now designed to use low NOx burners and typical emissions at full load are around 15 25 ppm only15. These techniques not only resolve the problem of NOx and PAH, but also that of nitroso compounds which are formed during the combustion process or are formed atmospherically.

Besides nitrogen oxides, PAH are also formed due to incomplete combustion or pyrolysis of organic matter in the combustion systems at high temperatures16 19. Figure 3

log p(species containing N)/(atm) 10

0

 

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

ammonia

2

 

 

 

 

hydrogen cyanide

 

 

 

 

 

3

 

 

 

 

acetonitrile

 

 

 

 

benzothiazole

 

 

 

 

 

4

 

 

 

 

 

5

 

 

 

 

propionitrile

 

 

 

 

 

6

 

 

 

 

CMMO

 

 

 

 

methylamine

 

 

 

 

 

 

 

 

 

 

pyridine

7

 

 

 

 

benzo(f) quinoline

 

 

 

 

 

phenanthridine

 

 

 

 

 

aniline

8

 

 

 

 

picoline

 

 

 

 

 

9

 

 

 

 

ethylamine

 

 

 

 

 

500

600

700

800

900

1000

 

 

T/(K)

 

 

 

FIGURE 3. Variation of nitrogenous species with temperature

1176

H. K. Chagger and A. Williams

illustrates that most nitrogen compounds and nitro-PAH are formed at high temperatures and are produced directly or indirectly during high-temperature combustion processes20. This raises questions regarding the mode of formation of N-nitroso and C-nitroso compounds, as to whether they are formed in the high combustion region or in the other cooling regions involving reaction products at the same time undergoing a quenching process.

Numerous forms of PAH have also been identified in the exhausts from diesel-powered vehicles. Soot generated from combustion processes generally contains about 0.1 mol% of N/C, but the nitrogen content in case of soot deposits in engines is ten times higher than particles found in flames or atmosphere. It was found that the nitrogen-containing PAH (PANH) originated by the reaction of nitrogen oxides (NOx ) with PAH in the hot exhaust gases21. These PANH can dissociate to give rise to NOx or act as a precursor in the formation of the nitro-PAH which are potent mutagens22. The unburnt fuel which is between 0.2 1.0% was found to act as a source for the formation of NPAH. Experiments involving the addition of PAH, e.g. pyrene and phenanthrene, to aliphatic fuels was found to increase the emission levels of the PAH and NPAH corresponding to the concentration of its parent PAH. Hence, the variability of PAC components in diesel fuels can significantly affect the PAH concentrations23. Most commonly found PAH are: naphthalene, fluorene and phenanthrene and their alkyl substituted homologues24. The PAH are distributed in both the gaseous phase and particle phase in the atmosphere. Some of the two to four ring PAH are present in the gaseous phase depending upon their vapour pressure25,26. The nitration of the parent aromatic molecule, as a result of either combustion or atmospheric reaction, results in formation of nitro-PAH or nitroarenes27,28 as shown in Figure 4.

 

 

 

 

 

 

 

 

 

 

 

 

 

Combustion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

emissions from

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Low temperature reactions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

fuel nitrogen

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

in the atmosphere

 

 

 

 

 

 

 

 

 

 

 

 

 

 

and other sources

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cooling and drying

 

 

 

 

 

 

 

 

High temperature chemistry

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

in combustion systems

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOx formation

 

 

 

 

 

 

PAH and soot formation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C2H2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HCN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NCO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOx

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOx + Food Products

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Benzene

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NHi

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Atmospheric reactions with

 

 

NO

 

 

 

NO

 

 

NO2

 

 

 

 

 

 

 

 

 

 

 

 

 

PAH in atmosphere

 

 

 

 

 

 

 

 

 

 

 

PAH

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N2O5-NO3-NO2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N2

 

 

 

 

 

 

 

NOx

 

 

 

PAH + H PAH + H2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nitro-PAH

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 4. Formation of nitro-PAH by association of NOx and PAH compounds

25. Environmental aspects of compounds

1177

Although simpler nitroarenes have been used for decades as industrial chemicals (e.g. nitrobenzene and nitrotolouene) and pharmaceutical chemicals (e.g. nitrofuran), their carcinogenic affects have only come to light in the last two decades. Nitroarenes have also been identified in photocopy toners29,30, diesel exhaust particles31,32, kerosene heater emissions33,34 and ambient air. Specific nitroarenes are formed by different mechanisms. Direct combustion appears to emit nitroarenes formed by direct electrophilic nitration (e.g. 1-nitropyrene, 3-nitrofluranthene)35,36, whereas atmospheric reactions involve multistep reaction of OH radicals in the presence of NOx resulting in different nitroarene isomers. Atmospheric nitroarenes are largely in the vapour phase while the direct nitrated nitroarenes of similar volatility are found in particle extracts distributed between the gas/vapour phase37,38.

Atmospheric reactions

Most of the experimental work on PAH has been conducted on 4 or 6-ring compounds. The PAH undergoes photolysis and reacts with OH and NO3 radicals, N2O5 and ozone. As the ambient atmosphere contains oxides of nitrogen and OH radicals, it was proposed that the gas-phase reactions of PAH with OH occurred in daytime and with N2O5 at night. N2O5 is generated in the atmosphere from the reaction between NO2 with O3 to form NO3 radicals. NO3 then reacts with NO2 to give N2O5 as shown in reactions 1 and 2.

O C NO2 ! NO3

(1)

NO3 C NO2 ! N2O5

(2)

In the presence of sunlight the NO3 reacts rapidly with NO to yield NO2 and it is photolysed via reactions 3 and 4.

NO3 C light

!

NO2 C O

(3)

NO3 C light

!

NO C O

(4)

Hence, the potential for NO3 and N2O5 existing in the atmosphere depends upon simultaneous existence of O3 and NO3 in the absence of nitric oxide and sunlight. The reaction mechanism for the formation of a typical PAH is illustrated in Figure 5. The basic steps involve (i) addition of OH at the site of highest electron density, (ii) addition of NO2 to OH-PAH adduct and (iii) loss of water to form nitroarene as shown below in Figure 7. It was suggested that this mechanism could proceed partly or fully in gas phase, followed by condensation of the products, i.e. nitro-PAH on the surface of the particles39.

Nitroarenes were formed under laboratory conditions when PAH reacted with gas-phase OH radical (in presence of NOx ) and N2O540 45. The atmospheric nitroarene formation rate depends upon the concentration of the individual species N2O5 NO3 NO2 An analogous reaction sequence occurs when PAH reacts in N2O5 NO3 NO2 systems46. Naphthalene reacts with NO3 radical forms NO3 naphthalene adduct, which dissociates or reacts with NO2 to form nitronaphthalene and other products as shown in Figure 6.

Table 3 shows the atmospheric lifetime for eleven PAH with respect to gas-phase reaction with OH and NO3 radicals, O3 and N2O5. This was calculated from the estimated and calculated rate constants. It is evident that most of the nitroarenes formed under ambient atmospheric conditions were produced by reaction of PAH with OH. The PAH reaction with NO3 radical was also considered as an important step because it resulted in the formation of nitroarenes from the N2O5 reaction with gas-phase PAH.

However, it should be noted that the amount of nitrated (NO2 and NO) compounds in diesel exhaust can be correlated with a number of experimental variables. The key

1178

H. K. Chagger and A. Williams

OH

NO2

H2 O

OH

NO2

H2 O

H OH

H

NO2

H OH

H

NO2

H

OH

H

NO2

H NO2

OH

H

FIGURE 5. Gas-phase reactions of PAH with OH radicals and NO2

issue still to be resolved is whether these compounds are formed in the combustion regions (i.e. combustion chambers) or are formed by secondary reaction products in the exhaust soot deposits. Some experimentalist have not found any nitrated products in diesel exhausts48. However, dinitro compounds like 1,3-dinitropyrene, 1,6-dinitropyrene and 1,8-dinitropyrene have been identified in the diesel exhaust by other authors49.

Соседние файлы в папке Patai S., Rappoport Z. 1996 The chemistry of functional groups. The chemistry of amino, nitroso, nitro and related groups. Part 2