Method of preparing lubricant additives

The invention provides a molybdate compound that is useful in lubricants, especially hydrocarbyl lubricating oils, to reduce friction and to decrease fuel consumption in internal combustion engines.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is directed to lubricant additives useful as friction 
modifiers or reducers. It is further directed to a method of reducing fuel 
consumption in internal combustion engines by adding the above-referred to 
additives, hydrocarbyl molybdates to the lubricating oil used therein. 
2. Discussion of the Prior Art 
Efforts to reduce the amount of fuel consumed by automobile engines and the 
like have revolved around finding lubricants that reduce the overall 
friction in the engine, thus allowing a reduction in the engine's energy 
requirements. 
Many of the solutions have been strictly mechanical, as for example, 
setting the engine for a leaner burn or simply building smaller cars and 
smaller engines. On the other hand, a considerable amount of work has been 
done with mineral lubricating oils and greases by modifying them with 
additives to enhance their friction properties. New synthetic lubricants 
also have been prepared and compounded for use in today's modern engines. 
U.S. Pat. No. 3,400,140 discloses the use of phosphomolybdates as extreme 
pressure additives. The ethyl homologue of the additive compounds embodied 
herein has been reported in the literature L. Malatesta, Gazz. Chem. 
ital., 69, 408 (1939), and R. N. Jowitt and P. C. H. Mitchell, J. Chem. 
Soc. A, 1702 (1970). However, it is oil insoluble and we are not aware of 
any disclosures in the art of any oil soluble homologues. So far as is 
known the hydrocarbyl molybdates in accordance with this invention are 
neither taught nor suggested by any prior reference or combination of 
references, patent or literature. 
SUMMARY OF THE INVENTION 
Compounds in accordance with the invention have the general formula: 
##STR1## 
wherein R may be the same or different and is a C.sub.2 -C.sub.30 
hydrocarbyl group. Accordingly R may be alkyl or cycloalkyl of at least 2 
carbon atoms, aryl or alkaryl. R is preferably C.sub.3 to C.sub.30 alkyl 
and more preferably butyl, pentyl, hexyl, 2-ethylhexyl or dodecyl, etc. 
When R is aryl, it preferably has from 6 to 14 carbon atoms and when 
alkaryl from 7 to 18 carbon atoms such as nonylphenyl or dodecylphenyl. 
Accordingly hydrocarbyl is interpreted herein to mean alkyl, cycloalkyl, 
aryl or alkaryl as defined above. Usually to ensure oil solubility the 
total number of carbon atoms in the R groups will not exceed 30. For 
example, the alkyl group in "alkaryl" is selected such that the total 
carbon atoms in the aryl and alkyl portions together will not exceed 30. 
The invention also provides lubricant compositions containing such 
compounds and a method for reducing fuel consumption in an internal 
combustion engine by treating the moving surfaces thereof with the said 
composition. 
Generally speaking the subject additive compounds are prepared by the 
reaction of an alkali metal, preferably sodium or potassium, or an 
ammonium alkyldithiocarbonate with a soluble molybdenum (VI) compound in 
the presence of a suitable reducing agent. 
The molybdenum (VI) compound is preferably selected from the following 
non-exhaustive list sodium molybdate (or hydrates thereof), potassium 
molybdate, ammonium heptamolybdate tetrahydrate and molybdic oxide 
(MoO.sub.3) solubilized in a base such as sodium or potassium hydroxide 
and ammonium hydroxide. 
Preparation is usually carried out within the following ranges: 
temperature, from 5.degree. to 60.degree. C.; pressure ambient to 50 psi; 
reaction time from 1/2 hr. to 5 hours and in a molar or weight ratio of 
from 1:1 to 4:1 of alkyldithiocarbonate to molybdenum. 
The amount of compound in the lubricant will usefully range from about 0.1% 
to about 10% by weight of said lubricant, preferably from about 1% to 
about 5% by weight. 
The lubricants contemplated for use with the esters herein disclosed 
include both mineral and synthetic hydrocarbon oils of lubricating 
viscosity, mixtures thereof with other synthetic oil and the greases 
therefrom. The synthetic hydrocarbon oils include long chain alkanes such 
as cetanes and olefin polymers such as trimers and tetramers of octane and 
decene. The synthetic oils with which these can be mixed include (1) ester 
oils such as pentaerythritol esters of monocarboxylic acids having 2 to 20 
carbon atoms, (2) polyglycol ethers, (3) polyacetals and (4) siloxane 
fluids. Especially useful among the synthetic esters are those made from 
polycarboxylic acids and monohydric alcohols. More preferred are the ester 
fluids made from pentaerythritol, or mixtures there with di- and 
tripentaerythritol, and an aliphatic monocarboxylic acid containing from 1 
to 20 carbon atoms, or mixtures of such acids.

Having described the invention in general terms, the following are offered 
to specifically illustrate the development. It is to be understood they 
are illustrations only and that the invention is not thereby limited 
except as by the appended claims. 
EXAMPLE 1 
A solution of ammonium heptamolybdate tetrahydrate (0.1 equiv., 17.6 g) in 
100 ml water was added to a cooled (0.degree. to 5.degree. C.) solution of 
potassium 2-ethylhexyl xanthate (0.2 mol, 48.8 g) in water (100 ml). A 
stream of sulfur dioxide was introduced into the reaction mixture and 
excess SO.sub.2 was allowed to pass through the stirred solution for one 
hour, while it gradually warmed to room temperature. The organic phase was 
taken up in hexane (500 ml), washed twice with 200 ml water, and 
separated. Solvent removal by rotary evaporation yielded 36.5 g (68.9% 
yield) of crude 
-oxo-bis[oxobis(0-2-ethylhexyldithiocarbonato)molybdenum(V)], as a red 
oil, contaminated with an undetermined quantity of the corresponding 
dixanthogen. The subject additives are characterized by carbon-13 NMR and, 
especially, by a charge transfer peak in the visible spectrum. 
Photoelectronic spectrum, .lambda..sub.max 507 nm. The carbon-13 NMR 
spectrum of the alkyl group is summarized below. Predicted values were 
calculated from the rules given by: J. B. Stothers, "Carbon-13 NMR 
Spectroscopy," Academic Press, New York, 1972, pp. 58, 142. 
______________________________________ 
##STR2## 
Calcd. 
.delta..sub.c 
13.8 23.2 32.6 30.5 40.4 78 
Obsvd. 
.delta..sub.c 
14.0 22.9 30.1 28.9 38.9 77 
______________________________________ 
Anal. Calcd. for C.sub.36 H.sub.68 O.sub.7 Mo.sub.2 S.sub.8 : C, 40.74; H, 
6.46; Mo, 18.08; S, 24.17. Found: C, 47.67; H, 8.03; Mo, 11.05; S, 23.69. 
EXAMPLE 2 
The same procedure as Example 1 was used, except that the reaction time was 
three hours. The product was 34.3 g of red oil, with analysis, visible 
spectrum and carbon-13 NMR spectrum substantially the same as Example 1. 
EVALUATION OF THE PRODUCT 
Low Velocity Friction Apparatus (LVFA) 
The Low Velocity Friction Apparatus (LVFA) is used to measure the friction 
of test lubricants under various loads, temperatures, and sliding speeds. 
The LVFA consists of a flat SAE 1020 steel surface (diam. 1.5 in.) which 
is attached to a drive shaft and rotated over a stationary, raised, narrow 
ringed SAE 1020 steel surface (area 0.08 in.sup.2). Both surfaces are 
submerged in the test lubricant. Friction between the steel surfaces is 
measured as a function of the sliding speed at a lubricant temperature of 
250.degree. F. The friction between the rubbing surfaces is measured using 
a torquearm strain gauge system. The strain gauge output, which is 
calibrated to be equal to the coefficient of friction, is fed to the Y 
axis of an X-Y plotter. The speed signal from the tachometer-generator is 
fed to the X-axis. To minimize external friction, the piston is supported 
by an air bearing. The normal force loading the rubbing surfaces is 
regulated by air pressure on the bottom of the piston. The drive system 
consists of an infinitely variable-speed hydraulic transmission driven by 
a 1/2 HP electric motor. To vary the sliding speed, the output speed of 
the transmission is regulated by a lever-cammoor arrangement. 
Procedure 
The rubbing surfaces and 12-13 ml. of test lubricant are placed on the 
LVFA. A 500 psi load is applied, and the sliding speed is maintained at 30 
fpm at ambient temperature for a few minutes. A plot of coefficients of 
friction (U.sub.k) over a range of sliding speeds, 5 to 40 fpm (25-195 
rpm), is obtained. A minimum of three measurements is obtained for each 
test lubricant. Then, the test lubricant and specimens are heated to 
250.degree. F., another set of measurements is obtained, and the system is 
run for 50 minutes at 250.degree. F., 500 psi, and 30 fpm sliding speed. 
Freshly polished steel specimens are used for each run. The surface of the 
steel is parallel ground to 15 to 20 microinches. 
The data obtained are shown in Table 2. 
______________________________________ 
% Change in Coeff. 
of Friction Relative 
Conc. to Base Oil.sup.(a)(b) 
Additive % Wt. 5 ft/min 30 ft/min 
______________________________________ 
Example 1 4 63 59 
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.sup.(a) The base oil is a lubricating oil comprising about 66% by weight 
of a synthetic hydrocarbon fluid (SHC) and about 20% by weight of an este 
fluid. The SHC has a typical viscosity at 210.degree. F. of about 7.0 
cSt., and the ester fluid has a typical viscosity at 0.degree. F. of 10.0 
cSt. The percentages by weight are percentages by weight of the total 
lubricating oil composition, including the usual additive package. 
.sup.(b) The data are percent decrease in friction according to: 
##STR3## 
Thus, the corresponding value for the oil alone would be zero for the for 
of the data used.