Fuel compositions containing tetracoordinated cobalt compounds

Hydrocarbon fuel compositions containing at least one divalent tetracoordinated cobalt compound represented by the structure ##STR1## wherein: R.sub.1, R.sub.2 and R.sub.3 are each independently selected from hydrogen and C.sub.1-6 alkyl, and PA1 R.sub.4 is a branched C.sub.3-6 alkyl wherein the branching is on either or both of the number 1 and 2 carbon atoms of said alkyl group.

BACKGROUND OF THE INVENTION 
This invention concerns hydrocarbon fuel compositions containing divalent 
tetracoordinated cobalt complexes, referred to for simplicity as Co(II) 
bis(.beta.-acetyl-N-alkylvinylimines). 
One of the most important performance properties of a gasoline for internal 
combustion engines is its antiknock quality. Antiknock quality determines 
the maximum power, efficiency, and economy that an engine can provide. 
Antiknock quality, indicated by the octane number of a gasoline, can be 
improved by increasing the amount of high octane quality hydrocarbons such 
as benzene, toluene, etc. in the gasoline. However, because of their 
flexibility and economy, antiknock additives such as tetraalkyllead 
compounds have been used regularly by gasoline refiners to improve 
antiknock quality of hydrocarbon fuels. 
With the advent of automobiles equipped with catalytic converters for 
exhaust emission control purposes has come the attendant requirement for 
lead-free gasolines. Reliance upon blending more of the high octane 
hydrocarbon components to improve the octane quality of the fuel is 
uneconomical since these hydrocarbon components are more valuable when 
utilized as solvents and as chemical feedstocks in the petrochemical 
industry. 
Numerous nonlead antiknock additives, both metal-containing and metal-free, 
have been suggested in the art but have not attained practical 
significance because of insufficient antiknock activity, hydrolytic or 
oxidative instability, insufficient solubility or combinations of these 
deficiencies. Accordingly, there is a need for an effective and stable 
non-lead octane improving additive for the production of lead-free 
gasolines of good antiknock quality. 
Cobalt-containing compounds are known for use in internal combustion 
engines as antiknocks, antipreignition agents and the like. Disclosures of 
such cobalt-containing compounds can be found in U.S. Pat. Nos. 2,023,372; 
2,086,775; 2,737,932; 2,902,983; and 2,235,466, and in British Pat. No. 
287,192. These patents do not, however, suggest the particular 
cobalt-containing compounds employed in this invention. 
The complexes described herein are known from Everett and Holm, J. Am. 
Chem. Soc. 88 2442 (1966). Nowhere in the art, however, is there any 
suggestion that the Everett and Holm complexes might be useful as 
antiknock agents. More importantly, there is no suggestion that such 
compounds would be characterized by good antiknock activity, good 
hydrolytic and oxidative stability, and good solubility in hydrocarbon 
fuels. 
SUMMARY OF THE INVENTION 
This invention concerns hydrocarbon fuel compositions comprising liquid 
hydrocarbons boiling in the range of about 20.degree. C. to 400.degree. C. 
and an amount to provide about 0.02 to 5 grams of cobalt metal per U.S. 
gallon of said hydrocarbon fuel composition of at least one divalent 
tetracoordinated cobalt compound represented by the structure 
##STR2## 
wherein: R.sub.1, R.sub.2 and R.sub.3 are independently selected from 
hydrogen and C.sub.1-6 alkyl, and 
R.sub.4 is a branched C.sub.3-6 alkyl wherein the branching is on either or 
both of the number 1 and 2 carbon atoms of said alkyl group. 
The R.sub.1, R.sub.2 and R.sub.3 alkyl groups are selected from methyl, 
ethyl, propyl, butyl, pentyl and hexyl, as well as the corresponding 
isomeric alkyl groups such as isopropyl, tertiary butyl, neopentyl and the 
like. The preferred compounds have methyl, ethyl, isopropyl or tertiary 
butyl groups as R.sub.1, and R.sub.2 =R.sub.3 =hydrogen. 
The R.sub.4 branched alkyl groups include 1-methylethyl(isopropyl), 
1-methylpropyl(sec.-butyl), 1,1-dimethylethyl(tert.-butyl), 
2-methylpropyl(isobutyl), 1-methylbutyl, 1,2-dimethylpropyl, 
2,2-dimethylpropyl(neopentyl), 1,1-dimethylpropyl(tert.-amyl), 
1-methylpentyl, 1,2,2-trimethylpropyl and 1-methyl-1-ethylpropyl. The 
preferred cobalt complexes are those wherein R.sub.4 is isopropyl or 
t-butyl, i.e., Co(II) bis(.beta.-acetyl-N-isopropylvinylimine), and Co(II) 
bis(.beta.-acetyl-N-t-butylvinylimine). 
DETAILS OF THE INVENTION 
The cobalt complexes are prepared from .beta.-acetyl-N-alkylvinylamines 
represented by the formula 
##STR3## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are as defined. The 
.beta.-acyl-N-alkylvinylamines are known and can be prepared, for example, 
by the method of Benary, Berichte 63 1573 (1930). Briefly, that method 
involves condensation of a sodium salt of a .beta.-dicarbonyl compound 
with a salt of an amine in an inert solvent such as absolute alcohol. 
The cobalt complexes are prepared by condensing the appropriate 
.beta.-acyl-N-alkylvinylamine with 
bis(tetraalkylammonium)tetrabromocobaltate, (R.sub.4 N).sub.2 CoBr.sub.4, 
under anaerobic and anhydrous conditions as described by Everett and Holm, 
J. Am. Chem. Soc. 88 2442, (1966). Preparation A, infra, was conducted 
basically according to the Everett and Holm procedure. The (R.sub.4 
N).sub.2 CoBr.sub.4 can be prepared according to the procedure of 
Inorganic Synthesis, Volume IX, page 140, S. Y. Tyree, Jr. Ed. 
McGraw-Hill, N.Y. 1967, which preparation involves mixing cobaltous 
bromide with two molar equivalents of tetraalkylammonium bromide in 
absolute alcohol. 
In the cobalt compounds described and depicted herein, the broken line 
curve within each of the six-membered rings represents resonating 
structures of the .beta.-acyl-N-alkylvinylamine anion. By resonating 
structures of the .beta.-acyl-N-alkylvinylamine anion is meant that the 
actual structure is a hybrid structure of the two more important anion 
structures 
##STR4## 
For simplicity, the cobalt complexes can be referred to as Co(II) 
bis(.beta.-acyl-N-alkylvinylimines) wherein Co(II) designates a divalent 
cobalt metal ion and .beta.-acyl-N-alkylvinylimine refers to the anion of 
.beta.-acyl-N-alkylvinylamine. 
The hydrocarbon fuels into which the cobalt complexes are incorporated to 
improve their combustion characteristics include petroleum hydrocarbons 
such as motor gasoline, aviation gasoline, jet fuel, diesel fuel, light 
distillates, fuel oil, gas oil and the like. Improved combustion 
characteristics lie in the areas of antiknock efficiency, modified 
combustion chamber deposits, octane requirement increase control, reduced 
smoke, reduced carbon formation and the like. The cobalt complexes are 
characterized by good fuel solubility and by good hydrolytic and oxidative 
stability. 
The motor gasolines are generally mixtures of paraffinic, olefinic, 
cycloaliphatic and aromatic hydrocarbons including such fractions and 
refinery products obtained by distillation, cracking, reforming, 
alkylation and polymerization processes. Normally, gasolines boil in the 
range of about 20.degree. C. to 225.degree. C. The fuel can also contain 
other additives normally used in commercial gasolines such as detergents, 
oxidation inhibitors, gum inhibitors, anti-icing additives, metal 
deactivators, dyes, solvents and the like. 
In lead-free gasolines designed for use in catalyst-equipped automobiles, 
the octane number improvement desired over the base gasoline is usually up 
to about 3 Research Octane Numbers and thus the gasoline will contain 
about 0.025 to 0.3 gram of cobalt per gallon. Higher concentrations of 
cobalt can be used to obtain even greater octane improvement. 
The cobalt complexes described herein can also be employed in gasolines 
containing lead antiknock compounds to provide additional improvements in 
octane numbers. Such gasolines can contain about 0.1 to 3 grams of lead 
metal and about 0.02 to 5 grams of cobalt metal per gallon. The lead 
antiknock compound can be tetraethyllead, tetramethyllead, mixtures of 
tetraethyllead and tetramethyllead or redistributed mixtures of 
tetraethyllead and tetramethyllead. The lead antiknock-containing gasoline 
can also contain scavengers normally used with lead antiknocks such as 
ethylenedichloride, ethylenedibromide or mixtures of these. 
Preparation A--Co(II) bis(.beta.-acetyl-N-isopropylvinylimine) 
A five liter reaction flask equipped with a thermometer, an agitator, a 
condenser, an addition funnel and a nitrogen sweep system was dried by 
heating the flask under a dry nitrogen sweep. Dry tertiary butyl alcohol 
(2800 ml) containing 154.9 g of potassium tertiary butoxide was added to 
the flask, heated to 50.degree. C. and .beta.-acetyl-N-isopropylvinylamine 
(139.9 g), prepared according to Benary, Berichte 63 1573 (1930), was 
added. Over a period of about 1 hour, 
bis(tetraethylammonium)tetrabromocobaltate (539 g), prepared according to 
Inorganic Synthesis, Volume IX, page 140, was added while maintaining the 
reaction temperature at 50.degree. C. After 2 hours at 50.degree. C., the 
contents of the flask was allowed to cool to room temperature and 
agitation was continued for about 15 hours. The contents of the flask was 
filtered under nitrogen atmosphere and the precipitate was washed with dry 
tertiary butyl alcohol (800 ml). 
The combined filtrate was concentrated at 20 to 40 mm pressure and 
40.degree. to 50.degree. C. to a semisolid brown mass. The semisolid mass 
was dissolved in 1500 ml of n-heptane by heating under a nitrogen 
atmosphere. The heptane solution was filtered, cooled in an ice bath and 
again filtered giving 97.5 g (57% theory) of Co(II) 
bis(.beta.-acetyl-N-isopropylvinylimine) as a red solid melting in the 
range of 120.5.degree. to 121.degree. C. An additional 21 g of the product 
was obtained by cooling the above filtrate in a dry ice-acetone bath and 
filtering. The cobalt(II) bis(.beta.-acetyl-N-isopropylvinylamine) was 
stable to air oxidation both as a solid and as a solution. The following 
elemental analyses were obtained: carbon, 54.7%; hydrogen, 7.7%; nitrogen, 
9.0%; and cobalt, 18.7%. Theoretical values for Co(II) 
bis(.beta.-acetyl-N-isopropylvinylimine) are: carbon, 54.1%; hydrogen, 
7.7%; nitrogen, 7.7% and cobalt, 18.6%. 
Using the procedure essentially as described above, the following CO(II) 
bis(.beta.-acyl-N-alkylvinylimines) were prepared: 
______________________________________ 
##STR5## 
Prepara- Stability 
tion R.sub.1 R.sub.2 
R.sub.3 
R.sub.4 to Air 
______________________________________ 
B CH.sub.3 H H C(CH.sub.3).sub.3 
good 
C (CH.sub.3).sub.3 C 
H H C(CH.sub. 3).sub.3 
good 
______________________________________ 
In addition, the following complexes excluded from the scope of this 
invention by reason of the unbranched character of R.sub.4 were also 
prepared by the procedure of Preparation A: 
______________________________________ 
Prepara- Stability 
tion R.sub.1 R.sub.2 R.sub.3 
R.sub.4 
to Air 
______________________________________ 
X CH.sub.3 H H C.sub.2 H.sub.5 
poor 
Y CH.sub.3 H H CH.sub.3 
v. poor 
______________________________________ 
Thermogravimetric characterizations were made of the cobalt complexes of 
Preparations A, B, X and Y using a Du Pont 990 Thermal Analyzer coupled to 
a Du Pont 951 Thermogravimetric Analyzer. A 20 mg sample of the cobalt 
complex was heated over a temperature range of 25.degree. to 500.degree. 
C. at a heating rate of 5.degree. C./minute with either nitrogen or air as 
the carrier gas at a gas flow rate of 40 ml/minute. The analysis with 
nitrogen as the carrier gas indicates thermal stability of the cobalt 
complex whereas the analysis with air as the carrier gas indicates thermal 
and oxidative stabilities. Both the complexes of Preparation A (R.sub.1 
=CH.sub.3, R.sub.2 =R.sub.3 =H and R.sub.4 =CH(CH.sub.3).sub.2) and 
Preparation B (R.sub.1 =CH.sub.3, R.sub.2 =R.sub.3 =H and R.sub.4 
=C(CH.sub.3).sub.3) were found to be oxidatively and thermally stable. 
With either nitrogen or air as the carrier gas, the complex of Preparation 
A showed initiation of volatilization at about 125.degree. C. and complete 
volatilization at about 210.degree. C. With the complex of Preparation B, 
volatilization was initiated at about 155.degree. C. and was completed at 
about 240.degree. C. The results showed that the complex of Preparation X 
(R.sub.1 =CH.sub.3, R.sub.2 =R.sub.3 =H and R.sub.4 =C.sub.2 H.sub.5) was 
thermally stable with volatilization initiated at about 75.degree. C. and 
completed at about 220.degree. C. With air as the carrier gas, oxidative 
degradation of the complex of Preparation X took place at about 
200.degree. C. with about 60% of the sample volatilized. The complex of 
Preparation Y (R.sub.1 =CH.sub.3, R.sub.2 =R.sub.3 =H and R.sub.4 
=CH.sub.3) underwent oxidative degradation upon exposure to air at room 
temperature.

The following Examples illustrate the invention. 
EXAMPLES 1 AND 2 
The ability of the disclosed cobalt complexes to increase octane numbers 
was determined in a lead-free motor gasoline having the following 
characteristics: 
______________________________________ 
Composition: 
saturated hydrocarbons, volume percent 
61 
olefinic hydrocarbons, volume percent 
8 
aromatic hydrocarbons, volume percent 
31 
Distillation (ASTM D-86): 
.degree.C. (to nearest 
whole degree) 
Initial Boiling Pt. 38 
5 53 
10 62 
30 97 
50 122 
70 144 
90 179 
95 201 
Max. Temp. 219 
Recovery, volume percent 
98 
Residue, volume percent 1 
Reid Vapor Pressure (ASTM D-323) 
lb. 7.9 
Induction Period (ASTM D-525) 
no break 
Sulfur (ASTM D-3120) weight 
0.034 
percent 
.degree.C. 
Octane Rating 
Research Octane Number (RON) 
91.4 
Motor Octane Number (MON) 
82.0 
(RON + MON)/2 Octane Number 
86.7 
______________________________________ 
The octane numbers of the fuels were determined by the Research Method 
(ASTM D-909) and the Motor Method (ASTM D-357). Generally, Research Octane 
Number (R) is considered to be a better guide of antiknock quality of 
fuels when vehicles are operated under mild conditions associated with low 
speeds while the Motor Octane Number (M) is considered to be a better 
indicator when operating a vehicle at high engine speed or under heavy 
load conditions. For many engine operating conditions, some intermediate 
value between the Research and the Motor Octane Numbers such as an average 
provide the best indication of the antiknock quality of the fuel. 
To separate portions of the base fuel were added cobalt(II) 
bis(.beta.-acyl-N-alkylvinylimine) complexes in the amount to provide 
cobalt metal concentrations as indicated in Table 1 below. The knock 
ratings for the fuel blends were determined in duplicates on duplicate 
samples. The results are summarized below wherein the antiknock quality 
improvements are provided in terms of increase in the octane numbers 
(.DELTA.O.N.) over the Research, Motor and (R+M)/2 octane numbers of the 
base fuel. 
In Example 1, the cobalt complex is that of Preparation A; in Example 2, 
that of Preparation B; and in the Comparative Example, that of Preparation 
X. 
Table 1 
______________________________________ 
Antiknock Response 
Cobalt Increase in Octane Number (.DELTA.O.N.) 
g/gal Research Motor (R + M)/2 
______________________________________ 
Example 1 (Compound = Co(II) bis(.beta.-acetyl-N-iso- 
propylvinylimine) 
0.025 0.2 0.2 0.2 
0.05 0.9 0.5 0.7 
0.10 1.9 1.0 1.5 
0.15 2.3 1.3 1.8 
0.20 2.9 1.1 2.0 
0.25 3.3 1.3 2.3 
0.30 3.1 1.5 2.3 
______________________________________ 
Example 2 (Compound = Co(II) bis(.beta.-acetyl-N-tert.- 
butylvinylimine) 
0.025 0.2 0.2 0.2 
0.05 0.6 0.4 0.5 
0.10 1.7 1.0 1.3 
0.15 2.1 1.1 1.6 
0.20 2.3 1.2 1.8 
0.25 2.8 1.4 2.1 
0.30 3.0 1.5 2.3 
______________________________________ 
Comparison Example Compound = Co(II) bis(.beta.-acetyl- 
N-ethylvinylimine) 
0.025 0.2 0.2 0.2 
0.05 0.5 0.2 0.3 
0.10 1.5 0.6 1.0 
0.15 1.7 0.8 1.3 
0.20 2.0 0.9 1.5 
0.25 2.2 1.2 1.7 
0.30 2.3 0.9 1.6 
______________________________________ 
Examples 1 and 2 responses show that Co(II) 
bis(.beta.-acetyl-N-alkylvinylimine) complexes wherein the alkyl 
substituent on the nitrogen is a branched alkyl group provide superior 
octane improvement over the comparative cobalt complex with a 
straight-chain substituent on the nitrogen. 
Thus, comparison of the increases in Research Octane Numbers obtained using 
the compound of the Comparison vs. those obtained using the compound of 
Example 1 shows that the compound of the Comparison gives results, on the 
average, only about 75% of those obtained with the compound of Example 1. 
The compound of the Comparison gives results only about 85% of those 
obtained with the compound of Example 2. These results were computed from 
the increase in antiknock response (RON) obtained at each cobalt 
concentration in the Table when using the compound of the Comparison 
divided by the increase obtained when using the compound of Example 1 and 
Example 2. 
For an additional examination of the importance of the differences in 
Research Octane Number increases obtained with the Comparison Compound 
versus the increases obtained with the compound of Example 1, see the 
discussion following Table 2. 
The differences are more particularly noticeable when the improvements in 
Motor Octane Numbers are compared. This deficiency in Motor Octane Number 
improvement of the complex of Preparation X is believed to be due to its 
lower oxidative stability under the more severe operating conditions of 
the Motor Method. Because of its better volatility as indicated by the 
thermogravimetric analyses described above, it would normally be expected 
that the complex of Preparation X would be a more effective antiknock 
additive than those of Preparations A and B. Thus, the discovery that the 
less volatile complexes (where R.sub.4 is a branched chain alkyl group) 
give better antiknock improvement is a surprising one. 
EXAMPLE 3 
In another series, antiknock performances of the complexes of Preparations 
A (Example 3) and X (Comparison Example) were determined using a modified 
Research Octane Number Method. The modification consisted of using fuel 
injection in place of the usual carburetion, all other conditions 
remaining the same. In this modification, fuel is injected directly into 
the combustion chamber of the engine and is therefore not exposed to air 
and moisture in the induction system as in the usual carburetion 
procedure. The value of using the modified method is that if the results 
obtained thereby are better than the results obtained by the usual 
carburetion procedure, it indicates that the failure of an antiknock 
additive to provide its full potential as an octane number improver by the 
normal method is due to its oxidative or hydrolytic instability in the 
environment of the induction system of the carburated engines. See Table 
2. 
The base fuel used in these Examples had the following characteristics: 
______________________________________ 
Composition: 
saturated hydrocarbons, volume percent 
65 
olefinic hydrocarbons, volume percent 
9 
aromatic hydrocarbons, volume percent 
26 
Distillation (ASTM D-86) 
.degree. C. (to nearest 
whole degree) 
Initial Boiling Pt. 41 
10% 59 
50% 94 
90% 154 
Max. Temp. 176 
Recovery, volume percent 
97 
Residue, volume percent 1 
.degree.C. 
Reid Vapor Pressure (ASTM D-323) 
lb 8.6 
Sulfur (ASTM D-3120) weight 
percent 0.002 
Octane Rating 
Research Octane No. 96.9 
Motor Octane No. 82.7 
(R + M)/2 Octane No. 86.8 
______________________________________ 
Table 2 
______________________________________ 
Antiknock Response by Fuel Injection Method 
Cobalt Increase in Octane Number (.DELTA. O.N.) 
g/gal Research 
______________________________________ 
Example 3 Compound = Co(II) bis(.beta.-acetyl-N-iso- 
propylvinylimine) 
0.25 2.7 
0.50 4.0 
0.75 5.2 
1.0 5.9 
2.0 8.4 
3.0 10.4 
______________________________________ 
Comparison Example Compound = Co(II) bis(.beta.-acetyl- 
N-ethylvinylimine) 
0.25 2.5 
0.50 3.8 
0.75 4.6 
1.0 5.6 
2.0 7.8 
3.0 9.7 
______________________________________ 
It can be seen from Table 2 that the branched chain complex of Preparation 
A provides superior antiknock activity when compared to the unbranched 
complex of Preparation X using a fuel injection procedure. 
As discussed following Table 1, the data summarized therein show that in a 
carbureted engine, Co(II) bis(.beta.-acetyl-N-ethylvinylimide) of the 
Comparison has, on the average, only about 75% of the Research Octane 
Number improving efficiency of the compound of Examples 1 and 3, Co(II) 
bis(.beta.-acetyl-N-isopropylvinylimine) on a comparable metal weight 
basis. The data summarized in Table 2 show that when the fuel is injected 
directly into the combustion chamber, the compound of the Comparison 
exhibits on the average, 93% of the Research Octane Number improving 
efficiency of the compound of Examples 1 and 3. This depreciation of 
relative efficiency of about 93% down to 75% of the compound of the 
Comparison relative to the compound of Examples 1 and 3 (in going from the 
fuel injection engine to the carbureted engine) is attributed to the 
increased degradation of the compound of the Comparison in the induction 
system of the carbureted engine due to its relatively low oxidative 
stability and possibly also due to its relatively low hydrolytic 
stability.