Fuel composition

Gasoline compositions containing methylcyclopentadienylmanganesetricarbonyl (hereinafter MCMT) are stabilized against oxidation by the addition of 2-ethylhexanoic acid.

BACKGROUND OF THE INVENTION 
This invention relates to gasoline compositions containing additives for 
improving the octane rating of said gasoline, and more specifically to 
gasoline compositions containing stabilizers for said additives. 
MCMT is presently being used as a component of gasoline fuels to improve 
the octane number thereof. However, in the proportions in which it is 
present in the gasoline fuels, usually between about 0.05 and 0.20 gm/gal 
(as manganese), MCMT is unstable. In the presence of sunlight, or other 
source of ultra-violet radiation, MCMT rapidly oxidizes to components that 
precipitate, with the rate of oxidation being dependent upon the 
concentration of dissolved oxygen in the gasoline. Thus, when gasoline 
containing 0.1 gm/gal MCMT (as manganese) is exposed to sunlight, within 
about 2-3 hours nearly complete oxidation of MCMT occurs, and a 
precipitate of oxidation products is formed. Similar oxidation takes place 
in the absence of sunlight, but at a somewhat slower rate. Cnsequently, 
gasoline compositions containing MCMT which are placed in storage for even 
few weeks suffer a significant decrease in octane rating and form a solid 
precipitate capable of clogging valves, transfer lines, etc. 
SUMMARY OF THE INVENTION 
In accordance with this invention 2-ethylhexanoic acid has been found to be 
effective as an anti-oxidant for gasoline fuels containing MCMT. The 
addition of 2-ethylhexanoic acid to such fuels prevents oxidation of the 
MCMT even in the presence of sunlight and oxygen. The invention thus 
consists in gasoline fuels containing MCMT and 2-ethylhexanoic acid in an 
amount sufficient to inhibit the oxidation of the MCMT. The addition of 
2-ethylhexanoic acid to gasoline fuels also aids in preventing the MCMT 
from being evaporated in vessels open to the atmosphere. 
DETAILED DESCRIPTION OF THE INVENTION 
Gasoline fuels containing MCMT as an octane rating additive usually contain 
said MCMT in an amount sufficient to provide between about 0.05 and about 
0.2, preferably between about 0.1 and about 0.15 grams per gallon of 
manganese. The amount of 2-ethylhexanoic acid required to stabilize such 
fuels against oxidation will depend upon the length of time the fuel will 
be stored prior to use and the condition of storage. Ordinarily, such 
amount will be at least 0.05 volume percent, and preferably between about 
0.5 and 2.0 volume percent. If the fuel is to be stored over an extended 
period of time, or under unusually adverse conditions, the 2-ethylhexanoic 
acid content may be increased to as much as 3 volume percent. 
2Ethylhexanoic acid is highly soluble in light hydrocarbons; consequently, 
preparation of the composition of this invention is simply a matter of 
dissolving the additive in the gasoline, either before, after, or 
concurrently with addition of the MCMT, employing conventional fuel 
blending equipment.

The following Example demonstrates the effectiveness of 2-ethylhexanoic 
acid for stabilizing MCMT. 
EXAMPLE 
One fuel composition containing gasoline and MCMT and four fuel 
compositions containing gasoline, MCMT, and 2-ethylhexanoic acid were 
exposed to sunlight during the daylight hours of four consecutive days. 
Each of the compositions contained 0.1 gm MCMT (as manganese) per gallon 
of the liquid compositions. The 2-ethylhexanoic acid was present in 
proportions ranging as follows: 0, 0.01, 0.1, 0.5, and 1.0 volume percent 
of the liquid compositions. 
The results were as follows. After 3 hours of sunlight exposure, the 
composition containing no 2-ethylhexanoic acid developed a precipitate, 
thereby indicating that the MCMT had been oxidized to undesirable 
products. After one day (about 10 hours of sunlight exposure) the 
composition containing 0.01 volume precent of 2-ethylhexanoic acid had 
turned dark brown, showing an initial stage of MCMT oxidation; the other 
compositions containing 2-ethylhexanoic acid were only slightly brown, 
with the intensity of the brown color decreasing with increased proportion 
of the 2-ethylhexanoic acid in the respective compositions. After four 
days (about 40 hours of sunlight exposure) the compositions containing 
0.01 and 0.1 volume percent of 2-ethylhexanoic acid had developed a 
precipitate while the compositions containing 0.5 and 1.0 volume precent 
of 2-ethylhexanoic acid were of medium brown color but contained no 
precipitate. 
The data in this Example show that the addition of sufficient 
2-ethylhexanoic acid to gasoline so as to produce a composition containing 
at least 0.5 volume percent of 2-ethylhexanoic acid insures that the MCMT 
in said composition remains unoxidized during long exposure to direct 
sunlight. 
Although the invention has been described in conjunction with a specific 
example thereof, it is evident that many alterations, modifications, and 
variations will be apparent to those skilled in the art in light of the 
foregoing description. Accordingly, it is intended to embrace all such 
alternatives, modifications, and variations that fall within the spirit 
and scope of the appended claims.