Nitration Hydrocarbons

Titov and co-workers, although conceding the validity of the ionic nitration mechanism for liq phase nitrations with coned acids, believe that many nitrations occur via a free-radical mechanism involving the free radicals (at any rate molecules having an unpaired electron) N02, N03, and NO. For vapor phase nitration of hydrocarbons, nitration of side chains of aromatic compds in... 

A o R + HNO3 followed by R + N02 - RN02. According to Titov the formation of the reactive R radicals explains the many side reactions (eg oxidations, nit ro sat ions etc) observed in hydrocarbon nitrations... 

For soybean-based biodiesel at this concentration, the estimated emission impacts for percent change in emissions of NO,, particular matter (PM), HC, and CO were +20%, -10.1%, -21.1%, and -11.0%, respectively (EPA, 2002). The use of blends of biodiesel and diesel oil are preferred in engines in order to avoid some problems related to the decrease of power and torque, and to the increase of NO, emissions (a contributing factor in the localized formation of smog and ozone) that occurs with an increase in the content of pure biodiesel in a blend. Emissions of all pollutants except NO appear to decrease when biodiesel is used. The use of biodiesel in a conventional diesel engine dramatically reduces the emissions of unbumed hydrocarbons, carbon dioxide, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, ozone-forming hydrocarbons, and particulate matter. The net contribution of carbon dioxide from biomass combustion is small. 

The nitration of aliphatic hydrocarbons with dinitrogen pentoxide and nitronium salts has been described. Topchiev gives an extensive discussion of works related to hydrocarbon nitration conducted prior to 1956. 

The main index headings for search other than the names of specific compounds are Paraffins nitration of Paraffins, nitro Paraffins, from nitration of— Paraffins, dinitro Hydrocaibons, nitration of Nitration of hydrocarbons Nitration of paraffins Petroleum, nitrogen compounds from Olefins, nitro derivatives and Acetylenes, nitro derivatives. These items are not mutually inclusive, e.g., references under Paraffins, nitration of are not necessarily to be found under Nitration of paraffins. In Chemical Abstracts collective index for 1937 to 1946, there are 19 entries under the first heading and 12 entries under the second only 10 are common to both lists. 

Volume 1. Synthesis-Gas Derivatives and Major Hydrocarbons. Volume 2. Major Oxygenated, Chlorinated and Nitrated Derivatives. 

It should be noted that aliphatic compounds (except the paraffins) are usually oxidised by concentrated nitric acid, whereas aromatic compounds (including the hydrocarbons) are usually nitrated by the concentrated acid (in the presence of sulphuric acid) and oxidised by the dilute acid. As an example of the latter, benzaldehyde, CjHsCHO, when treated with concentrated nitric acid gives ffi-nitrobenzaldehyde, N02CgH4CH0, but with dilute nitric acid gives benzoic acid, CgHgCOOH. 

Since aliphatic hydrocarbons (unlike aromatic hydrocarbons, p. 155) can be directly nitrated only under very special conditions, indirect methods are usually employed for the preparation of compounds such as nitroethane, CjHsNO. When ethyl iodide is heated with silver nitrite, two isomeric compounds are formed, and can be easily separated by fractional distillation. The first is the true ester, ethyl nitrite, C,HiONO, of b.p. 17° its identity is shown by the action of hot sodium hydroxide solution, which hydrolyses it, giving ethanol and... 

Aliphatic mono-halides, and aromatic hydrocarbons with halogen in side-chain, precipitate silver hdide on treatment with cold aqueous silver nitrate solution. 

The simpler nitrop>arafIins (nitromethane, nitroethane, 1- and 2-nitroproj)ane) are now cheap commercial products. They are obtained by the vapour phase nitration of the hydrocarbons a gaseous mixture of two mols of hydrocarbon and 1 mol of nitric acid vapour is passed through a narrow reaction tube at 420-476°. Thus with methane at 476° a 13 per cent, conversion into nitro methane is obtained ethane at 420° gives a 9 1 mixture of nitroethane (b.p. 114°) and nitromethane (b.p. 102°) propane at 420° afifords a 21 per cent, yield of a complex mixture of 1- (b.p. 130-6°) and 2-nitropropane (b.p. 120°), nitroethane and nitromethane, which are separated by fractional distillation. 

Unlike aliphatic hydrocarbons, aromatic hydrocarbons can be sul-phonated and nitrated they also form characteristic molecular compounds with picric acid, styphnic acid and 1 3 5-trinitrobenzene. Many of the reactions of aromatic hydrocarbons will be evident from the following discussion of crystalline derivatives suitable for their characterisation. 

NITRATION OF AROMATIC HYDROCARBONS Aromatic hydrocarbons may be nitrated, i.e., the hydrogen atoms replaced by nitro (NOj) groups, with concentrated nitric acid in the presence of concentrated sulpliuric acid, for example ... 

This realization led me to study related possible intermolecular electrophilic reactions of saturated hydrocarbons, Not only protolytic reactions but also a broad scope of reactions with varied electrophiles (alkylation, formylation, nitration, halogenation, oxygenation, etc.) were found to be feasible when using snperacidic, low-nucleophilicity reaction conditions. 

We found a way to overcome charge-charge repulsion when activating the nitronium ion when Tewis acids were used instead of strong Bronsted acids. The Friedel-Crafts nitration of deactivated aromatics and some aliphatic hydrocarbons was efficiently carried out with the NO2CI/3AICI3 system. In this case, the nitronium ion is coordinated to AICI3. 

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),... 

Most correlations of rates with localisation energies have used values for the latter derived from the Hiickel approximation. More advanced methods of m.o. theory can, of course, be used, and fig. 7.1 illustrates plots correlating data for the nitration of polynuclear hydrocarbons in acetic anhydride -" with localisation energies derived from self-... 

Fig. 7.1. Nitration of polynuclear hydrocarbons by nitric acid in acetic anhydride, (i) Plot of login (KijK against N. ,g-AnthryI positions A,

Some information is available about the nitration of polycyclic hydrocarbons and their derivatives, but it is of no quantitative significance. The formation of a cr-complex from anthracene and nitronium ions has been mentioned ( 6.2.3, 6-3)-... 

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