Toluene octane rating

The product of this reaction, toluene (methylbenzene), has an octane rating of 120. 

An arbitrary mixture of hydrocarbons is compared to a mixture of these two compounds, with its octane number that equal to the appropriate mixture of these standard compounds. Some molecules and their octane ratings are indicated in Table 2-6. Aromatics have a high octane number (toluene is 120), and some compounds such as tetraethyl lead have a strong octane enhancement when added to other mixtures (blending octane number). Oxygenates such as ethanol and ethers (MTBE) have fairly high octane numbers and supposedly produce less pollution, either alone or blended with hydrocarbons. 

Benzene, toluene, and p-xylene (BTX) are often added to gasoline to boost octane ratings. What would be observed if a mixture of these three compounds were subjected to GC-MS analysis How many peaks would be present in the gas chromatogram What would be the relative order of the peaks What molecular ions would be observed in the mass spectra ... 

Benzene and toluene, the simplest aromatic hydrocarbons obtained from petroleum refining, are useful starting materials for synthetic polymers. They are two components of the BTX mixture added to gasoline to boost octane ratings. 

Gasoline contains additives such as benzene, toluene and branched hydrocarbons to achieve the necessary octane ratings. Direct emission of these volatile compounds, e.g. at gas stations, forms a significant source of air pollution as well. Unburned gasoline and cracked hydrocarbons such as ethylene and propylene also form a substantial constituent of exhaust. 

One of the compounds used to increase the octane rating of gasoline is toluene (right). 

Since tetraethyllead can no longer be used, other octane enhancers must be added to gasoline to increase the octane rating. These have included benzene, toluene, xylenes, 2-methyl-2-propanol, methyl tertiary-butyl ether (MTBE), methanol, and ethanol. 

Benzene, toluene, and xylenes are important because they raise the octane rating of gasoline. 

Benzene, toluene and xylene can be recovered from pyrolysis gasoline as required. After hydrogenation, principally to saturate diolefins, pyrolysis gasoline is used as a motor fuel and is noted for its high octane rating. 

The economics of this process are determined by the price of the toluene. When there is high demand for aromatics, e.g. for gasoline to increase the octane rating, the consequent increase in the value of toluene makes the process uneconomical in comparison with the cumene route. 

To replace tetraethyllead, oil companies have developed other additives and strategies that will improve the octane rating of gasoline without producing harmful emissions. One approach is to increase quantities of hydrocarbons that have very high antiknock properties themselves. Typical are the aromatic hydrocarbons, including benzene, toluene, and xylene. Such compounds are natural components of most crude petroleum, and additional aromatic compounds can be added to... 

Toluene is sometimes added to gasoline blends to improve octane rating. Much of the toluene that is used for this purpose may not even be isolated from the refinery streams. It is also a very common solvent for the coatings and adhesive industries. It is a common feedstock for explosives such as TNT. It is also a common feedstock to produce other chemical intermediates such as benzene, xylenes, nitrobenzene, and benzyl chloride. 

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