The invention provides molybdenum-zinc dialkyldithiophosphates useful as friction-reducing, anti-wear and oxidation-inhibiting agents in lubricants, in particular, in fuel economy oils.

BACKGROUND OF THE INVENTION 
Field of the Invention 
This invention relates to novel lubricant additives which contain both zinc 
and molybdenum. It also relates to a lubricant composition which reduces 
fuel consumption of an internal combustion engine owing to the presence 
therein of these additives. 
DISCUSSION OF THE PRIOR ART 
A number of additives already have been suggested and tried in oils to 
reduce friction in an internal combustion engine thereby allowing a 
reduction in its energy requirement. Oils so modified are called fuel 
economy oils. 
Heretofore certain molybdenum compounds have been incorporated in oils and 
greases. The U.S. Pat. No. 3,400,140 describes antiwear agents of the 
formula 
EQU [(RO).sub.2 PS--S].sub.2 Mo.sub.2 S.sub.2 O.sub.2 
wherein R is hydrocarbyl. U.S. Pat. No. 4,208,292 discloses lube oil 
additives consisting of phosphomolybdates of the formula: 
##STR1## 
where R is hydrocarbyl. In preparing these compounds the quinquavalent 
molybdenum atom is reduced with SO.sub.2 before reacting it with a 
dialkyldithiophosphoric acid. Neither of these patents teaches or suggests 
bimetallic molybdenum-zinc salts of dialkyldithio phosphoric acid nor 
could their preparative methods produce such compounds. 
SUMMARY OF THE INVENTION 
The invention provides lubricant additives represented by the generic 
formula ZnMo.sub.2 O.sub.x [S.sub.2 P(OR().sub.2 ].sub.y wherein x is 0 
to 3; y is 6 to 12; R is a straight-chained or branched hydrocarbyl group 
having from 3 to 30 carbon atoms or a mixture of at least two such 
hydrocarbyl groups (a,b,c; etc.) where each group can have values from 1 
to 99 molar percents and whose sum must equal 100. 
Preferred compounds are those where x is 3, y is 6; R is 2-ethylhexyl; 
where R is a mixture of 2-ethylhexyl (a); isobutyl (b); and isopropyl (c) 
in a ratio of a:b:c=about 0.3:0.1:0.6; where R ranges from C.sub.4 to 
C.sub.8 ; a mixture of 4-methyl-2-pentyl (a) and 2-propyl (b) in a ratio 
of about a:b=0.47:0.53 and a mixture of 4-methyl-2-pentyl (a); 
2-methyl-1-propyl (b) and 2-propyl (c) in a molar ratio of about 
a:b:c=0.32:0.39:29. The invention also provides lubricants containing 
these additives. Further, the invention provides a method for reducing 
fuel consumption in an internal combustion engine by treating the moving 
surfaces thereof with the composition containing the additives of the 
invention. 
DISCLOSURE 
The oil-soluble molybdenum/zinc dialkyldithiophosphates of this invention 
are prepared by zinc metal reduction of a hexavalent molybdic acid or 
molybdenum salt such as acidified sodium molybdate prior to reaction with 
sufficient dialkyldithiophosphoric acid to convert both metals to their 
dialkyldithiophosphate salts. The product is isolated with no attempt to 
separate the metal salts. 
The products of this invention differ from those prepared from non-reduced 
hexavalent molybdenum in: (1) color: the subject products are brown, while 
dialkyldithiophosphates prepared from the MO.sup.VI reagent (using the 
U.S. Pat. No. 3,400,140 procedure) are blue or blue-green; while those 
prepared according to U.S. Pat. No. 4,208,292 are violet and (2) 
oil-solubility: the subject compositions, when made from mixed 
dialkyldithiophosphoric acids which contain high proportions (30-60%) of 
lower alkyl groups (e.g. isopropyl) are oil-soluble, while the reaction 
products obtained using the non-reduced MO.sup.VI reagents (as in U.S. 
Pat. No. 3,400,140) and the same mixed acid possess major amounts of 
insoluble component(s). 
The ability to prepare oil-soluble molybdenum dialkyldithiophosphates 
containing major amounts of low molecular weight alkyl groups provides 
advantages in cost and in performance as anti-wear agents and 
anti-oxidants. The wear-inhibiting properties of zinc 
dialkyldithiophosphates are known to be inversely related to the molecular 
weight of the alkyl groups employed. 
The preparation of the present products can be represented as follows: 
##STR2## 
The subject process employs the reduction by zinc metal of Mo.sup.(VI) to 
Mo.sup.(V) prior to reaction with a dialkyldithio-phosphoric acid, in 
order to prevent the undesired side reaction of Mo.sup.(VI) (a known 
oxidant) with the acid to form bis-dialkylthiophosphoryl-disulfides and 
other oxidation products. The side reaction consumes a significant portion 
of the dialkyldithiophosphoric acid, thus decreasing the conversion to the 
desired molybdenum dialkyldithiophosphates as well as introducing 
undesired side-reaction products. Also the reducing agent, zinc, is 
incorporated into the product and therefore is utilized and not wasted. 
Broadly stated, the method of the invention comprises acidifying a 
hexavalent alkali metal or ammonium molybdate with 3 hydrogen equivalents 
of mineral acid to form a solution containing a polymolybdic acid mixture; 
cooling the acidified solution to around ambient temperature; adding 
finely divided zinc to the solution in a 0.5:1 g. atomic ratio of Zn:Mo; 
agitating the solution until the hexavalent molybdenum has been reduced; 
adding 1.0 hydrogen equivalent of base and then 3.0-6.0 moles of a 
dialkyldithiophosphoric acid; refluxing the mixture and azeotroping to 
remove the water of reaction. Then the mixture is cooled to ambient 
temperature; filtered, the filtrate is distilled under reduced pressure 
and a liquid or solid residue is collected as the useful product. 
The dialkyldithiophosphoric acids used in the above synthesis are prepared 
by the conventional procedure of reacting P.sub.2 S.sub.5 with four or 
more moles of the desired alcohol or alcohol mixture at 
70.degree.-80.degree. C., in the presence of an inert solvent (usually 
cyclohexane, n-heptane or other hydrocarbon). The reaction mixture is 
filtered to remove small amounts of sulfur and unreacted P.sub.2 S.sub.5, 
and the filtrate containing the dialkyldithiophosphoric acid is employed 
in the preparation of the Mo/Zn dialkyldithiophosphate.

Preparation of the subject compositions is illustrated in the following 
examples which are representative but not limitative of the best mode of 
carrying out the invention. 
EXAMPLE I 
This example illustrates the preparation of molybdenum/zinc 
di-2-ethylhexyldithiophosphate. 
A solution of 24.20 g. (0.10 mole) Na.sub.2 MoO.sub.4.2H.sub.2 O in 50 ml 
water is stirred while adding 15.0 g (0.15 mole) conc. H.sub.2 SO.sub.4, 
the temperature rising from room temperature to a maximum of 60.degree., 
cooling being used. When the mixture is cooled to about 30.degree., 3.63 
g. (0.05 g. atom) of zind dust is added over 15 minutes. The temperature 
rises to about 45.degree.-50.degree. C. The mixture is stirred 4 hrs. at 
30.degree., forming a blue solution and blue solids, the color change 
indicating that hexavalent molybdenum has been reduced to a lower valence. 
Next 4.00 g. (0.10 mole) NaOH is added, and the mixture stirred at 
50.degree. C., max. for 1 hr. (the color having now turned brown). 
Thereafter, 25 ml. ethyl acetate and 210 g. of a n-heptane solution 
containing 0.30 mole of bis-(2-ethylhexyl)dithiophosphoric acid are added 
to the reaction flask. The mixture is stirred for 1/2 hr. at ambient 
temperature before being heated to the reflux temperature of the solvent 
mixture. The water is removed by azeotropic distillation into a Dean-Stark 
trap, recycling the supernatant hydrocarbon distillate back into the 
reaction flask. A total of 51 ml water was collected after refluxing for 4 
hours at 79.degree.-100.degree. C. The mixture is then cooled and 
filtered, and the filtrate is stripped at reduced pressure (.about.10 mm 
Hg) to 80.degree. C. The yield was 116 g. of a clear, deep brown liquid 
which had the following analyses: % Mo=7.04, % Zn=2.6, % P=7.5, % S=13.3, 
and % Na=0.0055. These analyses correspond to atomic ratios of 
Mo:Zn:P:S=1:0.54:3.30:5.67, which closely approaches the 1:0.5:3:6 ratio 
calculated for the Mo/Zn dialkyldithiophosphate ZnMo.sub.2 [S.sub.2 
P(OR).sub.2 ].sub.6. 
EXAMPLE 2 
This example illustrates the preparation of a Mo/Zn dialkyldithiophosphate, 
using a dialkyldithiophosphoric acid prepared from a mixture of higher and 
lower alcohols. 
The procedure of Example 1 was followed, charging the same materials, 
except for using 168.3 g (0.3 mole) of a heptane solution of a 
dialkyldithiophosphoric acid prepared from a mixture of 
2-ethylhexanol:isobutanol:isopropanol in a mole ratio of 0.3:0.1:0.6. The 
product (78 g) was, again, brown and had the following analyses: 
______________________________________ 
Mo Zn P S 
______________________________________ 
%, wt 8.55 3.55 9.8 16.9 
At. Ratio 1 : 0.61 : 3.55 : 5.93 
______________________________________ 
The product was completely soluble at 0.93% (wt) in a fully formulated 
10W-40 motor oil. 
EXAMPLE 3 
This example illustrates the preparation of a molybdenum 
dialkyldithiophosphate as in Ex. 2 with the omission of zinc metal. 
A solution of 36.30 g (0.15 mole) Na.sub.2 MoO.sub.4.2H.sub.2 O in 40 ml. 
water was treated with an equivalent amount of H.sub.2 SO.sub.4 (15.00 
g.=0.15 mole). Then 168.3 g of a heptane solution containing 0.3 mole of 
the mixed dialkyldithiophosphoric acid used in Ex. 2 was added, along with 
150 ml additional n-heptane and 300 ml. ethyl acetate. After reaction at 
reflux as in Ex. 1, the stripped product was a mixture of a blue-green 
liquid and some blue solids. The liquid portion was only partially soluble 
at 0.5% wt. when added to a commercial SAE 10W-40 motor oil. The color and 
solubility differences between the products of Ex. 2 and 3 illustrate the 
uniqueness of the compositions of subject invention. 
EXAMPLE 4 
This example illustrates the preparation of the Ex. 2 product, without 
using ethyl acetate. 
The procedure of Ex. 2 was followed, using heptane as the primary solvent 
and adding 12 ml. cyclohexane to depress the initial boiling point to that 
obtained in Ex. 2 using heptane/ethyl acetate. The other materials were 
identical to those in Ex. 2 in composition and quantity. The product has 
the following analyses: % Mo=7.85, % Zn=3.9, % P=10.0, % S=22.6. 
The following examples illustrate the preparation of Mo/Zn 
dialkyldithiophosphates, employing a number of different alcohols or 
mixtures in the preparation of the dialkyldithio-acid solution. The Ex. 4 
procedure was followed except that cyclohexane was omitted. 
TABLE I 
______________________________________ 
OTHER Mo/Zn DIALKYLDITHIOPHOSPHATE 
PREATIONS 
Alcohol 
Ex. Mole Analysis of Products 
No. Alcohol(s) Ratio.sup.1 
% Mo % Zn % P % S 
______________________________________ 
5 "Alfol 1214" 
(n-C.sub.12 :n-C.sub.14) 
55:45 4.0 1.6 4.8 9.0 
6 "HCO Alcohol" 
(C.sub.4 -C.sub.8) 
60: 8.11 3.46 9.84 18.9 
2-Propanol 40 
7 4-Methyl-2- 
pentanol 47: 11.4 3.60 10.1 18.2 
2-Propanol 53 
8 4-Methyl-2- 
pentanol 32: 
2-Methyl-1- 
propanol 39: 9.89 3.43 12.3 19.5 
2-Propanol 29 
______________________________________ 
.sup.1 Ratio of alcohols charged in the preparation of 
dialkyldithiophosphoric acid. 
The above examples 5-8 demonstrate the applicability of the subject 
invention to the preparation of Mo/Zn dialkyldithiophosphates from a 
variety of alcohol mixtures. 
The products of the above examples were blended into motor oil compositions 
and tested by various tests. Of these, the Bench L-38 Test simulates the 
engine test environment of Federal Test Method No. 791a, Method 3405.1, 
and provides a method for studying the copper-lead bearing corrosion 
characteristics of crankcase oils. In carrying out this test, a journal 
bearing is rotated in a journal bearing rig, (JBR), which contains a 
preweighed connecting rod bearing along with 500 ml of test oil. The oil 
is heated to 200.degree. F. and the journal rotated at 1725 rpm for 2 
hours, an activator is added and the temperature increased to 305.degree. 
F. for 22 hrs. The bearings are then removed, cleaned with pentane and 
reweighed. The difference in weight is then reported as the bearing wt. 
loss (BWL) in mg. The activator is prepared by grinding 2 g of lead 
chloride with a motorized mortar and pestle and adding 5 ml. of test oil 
until a paste forms; an additional 25 ml. of test oil is added and the 
mixture is ground for 5 minutes. The mixture is then transferred to a 
beaker using approximately 70 ml. of pentane. The mixture is then added to 
the JBR using pentane in the transfer. The test duration is 24 hrs, the 
air flow rate is 1480 ml/minute. 
The second test employed was the Four Ball Wear Test described in U.S. Pat. 
No. 3,384,588 which measures the amount of wear a lubricating oil permits 
at selected test conditions with and without additives to be tested. The 
greater amount of wear, the poorer the ability of the test oil composition 
to prevent such wear. This wear is measured in terms fo millimeter wear 
scar diameter. This test was run for 1 hour at 1800 rpm/200.degree. F./40 
kg load. The friction coefficient was measured at the end of the test when 
the anti-friction film is fully developed. 
The "Small Engine Friction Test" (SEFT) is a single cylinder engine test 
which measures the frictional characteristics of an oil. The values given 
in Table II are based on the torque required to motor an engine containing 
the oil under test. The results of this test have been found to correlate 
with field experience using a large fleet of cars under varied on-the-road 
driving conditions as the percentage change in torque correlates with a 
percent change in fuel economy. 
The Bench IIID Test measures the oil thickening tendencies of motor oils 
under high temperature conditions. The test consists of oxidizing a sample 
of oil in the presence of air with an iron and copper catalyst at 
340.degree. F. After 24, 48 and 72 hours the percent increases in 
viscosity at 40.degree. C. and milliliters evaporation loss are determined 
on the oxidized oil. After 24 and 48 hours fresh make-up oil is added to 
the oxidized oil. 
The utility of Mo/Zn dialkyldithiophosphates as multi-purpose additives in 
lubricating oil formulations is demonstrated in the following Tables II 
and III. The performance of the subject additives in the tests indicated 
in the tables show that the additives are extremely effective 
friction-reducing agents which also impart oxidation, corrosion, and 
wear-preventative properties to lubricant formulations. 
The data in Table II shows that very large reductions in friction are 
obtained by use of the subject Mo/Zn dialkyldithiophosphates. This effect 
is observed at very low Mo concentrations, and varies somewhat with the 
nature of the dialkyldithiophosphate. From Table II it can be seen that, 
compared to a commercial zinc dialkyldithiophosphate, the subject 
additives are superior in preventing oxidative thickening of the oil, are 
equivalent or superior in bearing corrosion, and are superior in anti-wear 
properties. Surprisingly, the molybdenum dialkyldithiophosphate prepared 
according to Example 3 (omitting the zinc metal reduction step of Example 
2) was not sufficiently soluble at 0.5 weight percent in the base oil to 
permit evaluation thereof in the evaluation tests and therefore must be 
considered unsuitable as a lubricant additive. This solubility and hence 
the performance difference illustrates the novelty and advantage of the 
subject invention as in Example 2. 
The commercial zinc dialkyldithiophosphate used in oil A was prepared from 
the same mixture of alcohols used in the preparation of the Example 6 
product. Comparison of the test results with oils A and E demonstrates the 
effectiveness of the mixed Mo/Zn salt vs. zinc alone. 
TABLE II 
______________________________________ 
SMALL ENGINE FRICTION TEST SCREENING OF 
Mo/Zn DIALKYLDITHIOPHOSPHATES.sup.1 
Small Engine 
Friction Test 
Metal Dialkyldithiophosphates 
% Friction 
Mo/Zn DTP Zn DTP Total % Decrease.sup.2 
Oil Ex. No. (% Wt) % Wt Mo Zn at 280.degree. F. 
______________________________________ 
A -- 1.40 -- .15 0 .+-. 2.sup.(2) 
B 1 (1.10) 1.10 .08 .15 13 
C 2 (.93) .56 .08 .096 12.8 
D .sup. 2.sup.a 
(.57) .94 .05 .116 10.5 
E 6 (.54) .90 .05 .116 19.0 
F .sup. 6.sup.a 
(.51) .90 .04 .116 27.8 
G .sup. 6.sup.a 
(.25) 1.15 .02 .135 10.2 
______________________________________ 
.sup.1 The subject Mo/Zn DTP's were blended into a conventional 10W40 
motor oil formulation, substituted in part for the commercial zinc 
dialkyldithiophosphate normally employed at 0.15% Zn. The other additive 
components were a polybutenylsuccinimide at .08% N + a calcium detergent 
at .23% Ca + about 12% of an oil concentrate of an olefin copolymer VI 
improver + 0.1% of an oil concentrate of a polymethacrylate pour 
depressant + 0.25% of an arylamine antioxidant + 0.15% of an ashless rust 
inhibitor in a paraffinic base oil. 
.sup.2 The mean value of six runs of the reference oil A in the test is 
used as the base upon which to calculate the effect of the experimental 
additives. 
.sup.a Repeat preparations of those given in the examples. 
TABLE III 
__________________________________________________________________________ 
OTHER TESTS ON LUBRICATING OILS CONTAINING Mo/Zn DIALKYLDITHIOPHOSPHATES 
Bench IIID 
Bench 4-Ball 
Mo/Zn Dialkyldithiophosphate 
Commercial, Test, 74 Hrs 
L-38 Test 
Wear Test.sup.4 
Oil Conc. in Oil 
Zinc DTP (% Viscosity.sup.3 
(mg Bearing) 
(mm Scar) 
No. 
Ex. No. 
% Wt 
% Mo 
% P 
% Wt 
% P 
Oil Formulation.sup.2 
Increase) 
(Weight Loss) 
(diameter) 
__________________________________________________________________________ 
H Control 
-- -- -- .75 .08 
10W-40 Too Viscous to 
31.3 .45 
measure 
I 1 1.10 
.08 .08 
-- -- 10W-40 55 32.6 .36 
J 2 .93 .08 .09 
-- -- 10W-40 66 16.4 .36 
K 6 .88 .08 .09 
-- -- 10W-40 71 14.9 .36 
__________________________________________________________________________ 
.sup.1 Zinc dialkyldithiophosphate prepared from the alcohol mixture used 
in the preparation of Ex. 6 (blend 4). 
.sup.2 The test oils differ from a commercial 10W40 formulation only in 
the dosage and/or type of metal dialkyldithiophosphate. The other additiv 
components are a polybutenylsuccinimide at .08% N + a calcium detergent a 
.23% Ca + about 12% of an oil concentrate of an olefin copolymer VI 
improver + 0.1% of an oil concentrate of a polymethacrylate pour 
depressant + 0.25% of an aryl amine antioxidant + 0.15% of an ashless rus 
inhibitor in a paraffinic base oil. 
.sup.3 Viscosity (kinematic) measured at 100.degree. F. 
.sup.4 The 4Ball Wear Test was run 1 hr at 1800 rpm and 40 kg load at 
200.degree. F. 
Lubricating compositions according to the present invention contain at 
least one of the above products in an amount ranging from about 0.1 to 15 
percent; preferably between 0.5 and 2.0 percent by weight, and, especially 
at least 0.5 percent by weight. 
The present compositions can also contain a combination of other well-known 
additives in an amount sufficient to achieve each additive's function. 
Lubricating compositions according to this invention comprise a major 
amount of any of the well-known types of oils of lubricating viscosity as 
suitable base oils. They include hydrocarbon or mineral lubricating oils 
of naphthenic, paraffinic and mixed naphthenic and paraffinic types. Such 
oils may be refined by any of the conventional methods such as solvent 
refining and acid refining. Synthetic hydrocarbon oils of the alkylene 
polymer type or those derived from coal and shale may also be employed. 
Alkylene oxide polymers and their derivatives such as the propylene oxide 
polymers and their ethers and esters in which the terminal hydroxyl groups 
have been modified, are also suitable. Synthetic oils of the dicarboxylic 
acid ester type including dibutyl adipate, di-2-ethylhexyl sebacate, 
dilauryl azelate, and the like may be used. Alkyl benzene types of 
synthetic oils such as tetradecyl benzene, etc., are also included.