US2619464A - Lubricant containing high molecular weight alkyl monothiocyanates - Google Patents

Description

Patented Nov. 25, 1952 LUBRICANT CONTAINING HIGH MOLECU- LAR WEIGHT ALKYL MONOTHIOCYA- NATES Ferdinand P. Otto, Woodbury, N. J., assignor to Socony-Vacuum Oil Company, Incorporated, a.

corporation of New York No Drawing. Application March 25, 1949, Serial No. 83,522

This invention relates to mineral lubricating oil compositions, and it is more particularly concerned with mineral lubricating oils containing corrosion inhibitors, namely, high molecular weight alkyl monothiocyanates.

As is well known to those familiar with the art, what are known as hard metal alloy bearings, such as copper-lead, cadmium-nickel, and cadmium-silver bearings, are used to a great extent in place of so-called soft metal bearings, such as Babbitt metal bearings, in modern internal combustion engines. However, the highly-refined mineral lubricating oils which are used to lubricate these engines tend to corrode such bearings. This corrosive action is usually attributed to the fact that mineral lubricating oils oxidize under the operating conditions of the engine to form corrosive oxidation products. Various substances have been proposed as addition agents for these oils for the purpose of inhibiting oxidation and the attendant corrosive action of the oxidation products. For example, in United States Letters Patent, No. 2,168,674, to Loane et al., mineral oils containing fatty acid thiocyanates, such as lauroyl thiocyanate and stearoyl thiocyanate, have been suggested. In a later patent, No. 2,169,700, the same inventors have disclosed mineral oils containing polythiocyanates having the formula, R(SCN)1L, wherein R. is an aliphatic radical or an aromatic radical, and n is an integer greater than one. The patentees specifically taught that there must be at least two thiocyanate groups in the additive molecule.

It has now been discovered that mineral lubricating oils containing small amounts of high molecular Weight alkyl monothiocyanates, such as paraiiin wax monothiocyanates, are resistant to oxidation and have a reduced tendency to corrode hard metal alloy bearings. It has also been found that the corresponding high molecular Weight alkyl polythiocyanates are not effective for the purposes of this invention, due to their substantial insolubility in mineral lubricating oils.

Accordingly, it is abroad object of this invention to provide mineral lubricating oils which are resistant to oxidation and which have a reduced tendency to corrode hard metal alloy bearings. Another object is to provide mineral lubrieating oils containing high molecular weight alkyl monothiocyanates. A specific object is to provide mineral lubricating oils containing parafiin Wax monothiocyanates, which oils are resistant to oxidation and which have a reduced tendency to corrode hard metal alloy bearings. Other objects 1 Claim. (01. 252-47) and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.

Broadly stated, the present invention provides a mineral lubricating oil containing a minor amount, sufficient to reduce the tendency thereof to corrode hard metal alloy bearings, of a high molecular weight alkyl monothiocyanate having more than about twenty carbon atoms per alkyl radical, and preferably between about 21 carbon atoms and about 34 carbon atoms per alkyl radical.

The high molecular weight alkyl monothiocyanates contemplated herein can be relatively pure compounds, or they can be mixtures of alkyl monothiocyanates having more than about twenty carbon atoms per alkyl radical. These compounds can be prepared by any methods for the preparation of alkyl thiocyanates which are well known to those skilled in the art. For example, they can be prepared by reacting an inorganic salt of thiocyanic acid with an alkyl halide. This is the method used in the preparation of the additives of the present invention. I

In general, any alkyl halide, or mixture of alkyl halides, containing more than about twenty carbon atoms, and preferably between about 21 and about 34 carbon atoms, per molecule can be used to prepare the additives of this invention. The alkyl radicals of these alkyl halides may be straight-chain or branched-chain. Especially preferred are the high molecular weight alkyl chlorides. Non-limiting examples of the alkyl chlorides useful in preparing the additives contemplated herein are heneicosyl chloride; docosyl chloride; tricosyl chloride; 2-methyltricosyl chloride; tetracosyl chloride; isohexacosyl chloride; triacontyl chloride; tetratriacontyl chloride; tetracontyl chloride; and pentacontyl chloride.

As is well known to those familiar with the art, it is diflicult and not commercially feasible to produce these alkyl chlorides in a relatively pure state. A practical method for obtaining satis-, factory mixtures of them is by partial chlorination of a paraffin wax melting between about 40 C. and about 72 (3., such as paraflin wax, ozokerite, ceresin wax, slack wax, and scale wax. The chlorination of such waxes results in mixtures of monochloro waxes and polychlcro waxes. Accordingly, the monochloro waxes must be separated from the chlorinated Wax mixture, since polychloro waxes ultimately produce polythiocyanates which, as stated hereinbefore, are insoluble in mineral lubricating oils. A suitable method for the chlorination of wax and the separation of monochloro wax has been fully described in United States Letters Patent, No. 2,238,790, to Davis et al.

Any inorganic salt of thiocyanic acid can be reacted with the alkyl chloride reactant to produce the alkyl monothiocyanates. Sodium thiocyanate, strontium thiocyanate, potassium thiocyanate, and ammonium thiocyanate may be mentioned by way of non-limiting example. Ammonium thiocyanate is the preferred inorganic salt reactant.

The reaction between the inorganic salt reactant and the alkyl chloride reactant can be effected in several ways, such as, for example, by fusing the reactants. Suitably, the reaction can be efiected by refluxing a mixture of the monochloro wax reactant and an excess of the inorganic salt reactant in a solvent. such as fusel oil and butanol-l, at a temperature of about 130 C. for between about 5 and about 25 hours.

The use of a solvent in the reaction between the inorganic salt reactant and the alkyl chloride reactant is not essential. In order to effect a homogeneous reaction mixture, it is preferable to use an alcohol solvent combination in which the inorganic salt reactant is soluble and which has a. relatively high reflux temperature. The preferred combination of alcohols comprises a low molecular weight alcohol, such as methanol, ethanol, the propyl alcohols, and the butyl alcohols, and a higher molecular weight alcohol, such as the amyl alcohols, the hexyl alcohols and the octyl alcohols. The low molecular weight alcohol acts as a solvent for the inorganic salt reactant, and the higher molecular Weight alcohol serves to increase the reflux temperature of the reaction mixture. The relative amount of each alcohol in such a combination will be that suflicient to produce a combination which refiuxes at temperatures of about 100 C. or higher. Such temperature conditions favor greater yield of the monothiocyanate reaction products. Non-limiting examples of alcohol combinations utilizable herein are isopropanol-fusel oil; ethanol-octane]; ethanol-fusel oil; methanol-hexanol; and t-butyl alcohol-amyl alcohol. If desired, only one alcohol can be used as the solvent. The relative yield of product, however, will usually be lower. Alcohols which are utilizable alone include methanol; ethanol;propanol-1; propanol-Z; butanol-l; pentanol-l; 2-ethylhexanol-1; and octanol-l.

When the high molecular weight alkyl monothiocyanates are produced by the methods described hereinbefore, product separation is easily effected. If solvents are employed, they may be removed by well known methods, such as by evaporation or distillation. The unreacted inorganic thiocyanate salts and the ammonium chloride formed during the reaction can be removed by filtration. The reaction product thus isolated is in a substantially pure form and it is entirely satisfactory for the purposes of this invention.

Non-limiting examples of the high molecular weight 'alkyl monothiocyanates contemplated herein are heneicosyl thiocyanate; docosyl thiocyanate; 2-methy1tricosyl thiocyanate; tetracosyl thiocyanate; isohexacosyl thiocyanate; :triacontyl thiocyanate; tetratriacontyl thiocyanate; tetracontyl thiocyanate; pentacontyl thiocyanate; paraffin wax monothiocyanate; ozokerite monothiocyanate; and ceresin wax monothiocyanate. These materials can be added to mineral lubricating oils in amounts varying between about 0.1 per cent and about per cent by weight. It is preferable, however, to use amounts .4 varying between about 0.25 per cent and about 2.0 per cent by weight.

The following specific examples are given to exemplify the high molecular weight alkyl monothiocyanates used in accordance with this invention, and to demonstrate the advantages of mineral lubricating oils containing them. It is to be strictly understood that this invention is not to be limited to the particular high molecular weight alkyl monothiocyanates described therein. Other high molecular weight alkyl monothiocyanates, as set forth hereinbefore, may be used in the mineral lubricating oil compositions contemplated herein, as those skilled in the art will readily understand.

EXAMPLE 1 Preparation of monochloro war:

One thousand grams of a paraflin wax, having a melting point of about 52 C., were heated to C. Chlorine gas was passed into the resulting melt until the wax gained about 111 grams in weight. The reaction mixture was then blown with nitrogen gas to remove occluded hydrogen chloride and residual chlorine, producing a prodnot which contained about ten per cent of combined chlorine by weight. This product was allowed to stand for about 1'7 hours (overnight), at a temperature of 23-30 C. The unreacted paraffin wax solidified and the chlorinated paraifin wax remained liquid at these temperatures. Separation of the two phases was efiected by filtration. Then, a 570 gram portion of the filtrate, consisting, in the main, of monochloro and dichloro wax, was dissolved in ten times its volume of acetone, and the resulting solution was chilled to 23 C. The monochloro wax, which precipitated at this temperature, was removed by filtration and topped at 150 C. under a pressure of about 150 millimeters to remove entrained solvent. The monochloro wax, which was obtained in a 55 per cent yield, contained 9.5 per cent chlorine. The filtrate containing predominantly dichloro wax was freed of acetone by distillation under reduced pressure. The dichloro wax fraction contained 19.3 per cent chlorine,

EXAMPLE 2 Preparation of wax monothiocyanate A mixture of 400 grams of a monochloro wax containing 10.5 per cent chlorine, prepared as described in Example 1, grams of ammonium thiocyanate, 350 cubic centimeters of fusel oil, and 350 cubic centimeters of butanol-l was stirred and refluxed for about twenty hours at 130 C. The ammonium chloride which formed as a result of the ensuing reaction between the monochloro wax and the ammonium thiocyanate, was removed by filtration. The solvents were removed from the filtrate by distillation at C under reduced pressure. After cooling the residue to room temperature, unreacted ammonium thiocyanate was removed by filtration leaving relatively piu'e wax monothiocyanate. This was a light orange oil that became a waxy solid on standing, and which contained 7.58 per cent sulfur, 3.2 per cent nitrogen, and 0.53 per cent chlorine.

EXAMPLE 3 Preparation of war dithiocyanate A mixture of 300 grams of dichlorowax containing 19.3 per cent chlorine, produced in Example l, and grams of ammonium thiocyanate in 400 cubic centimeters of fusel oil and EXAMPLE 4 Preparation of mixed wax monoand poly-thiocyanates In order to determine whether a mixture of wax monoand poly-thiocyanates would be utilizable, such a, mixture was prepared from a chlorowax which consisted of a mixture of monoand di-chloro waxes. A mixture of 300 grams of a 22 per cent chlorinated wax and 211 grams of ammonium thiocyanate were reacted in 500 cubic centimeters of fusel oil and 300 cubic centimeters of butanol-l, in accordance with the procedure described in Example 2. The product was a viscous, brown oil containing 16.1 per cent sulfur, 6.6 per cent nitrogen, and 2.1 per cent chlorine. It was substantially insoluble in mineral lubricating oils.

EXAMPLE 5 Preparation of kerosene thiocyanate In order to determine the effect of an alkyl thiocyanate of lower molecular weight, a product was prepared from a chlorinated, oleum-treated kerosene. The kerosene, which was chlorinated to a chlorine-content of per cent, by the method described hereinbefore, had a boiling range of 237-291 C. and it contained paraflinic hydrocarbons having fewer than twenty carbon atoms. A mixture of 400 grams of the 15 per cent chlorinated kerosene (substantially monochloro kerosene) and 192 grams of ammonium thiocyanate in 400 cubic centimeters of fusel oil and 400 cubic centimeters of butanol-l was reacted, and the product was separated, by the method described in Example 2. The product was a brown liquid which contained 9.5 per cent sulfur, 4.3 per cent nitrogen, and 2.2 per cent chlorine. It was not soluble in mineral lubricating oils.

EXAMPLE 6 The tendency of a mineral lubricating oil containing a high molecular weight alkyl monothiocyanate to corrode hard metal alloy bearings was determined by means of the well known Bubble Test. In accordance therewith, a weighed piece of a cadmium-silver bearing was placed in a 200 x -millimeter test tube together with a mineral lubricating oil containing a small amount of the wax monothiocyanate product of Example 2. The base oil Was a solvent-extracted Pennsylvania oil having an A. P. I. gravity of 29.3, a flash point of 405 F., and Saybolt Universal viscosities of 305 seconds at 100 F. and 53 sec onds at 210 F. The test tube was maintained at a temperature of 175 C. in a constant temperature bath while air was passed through it by means of a delivery tube inserted in the oil, at a rate of two liters per hour for 22 hours. At the end of this period of time, the cadmiumsilver bearing was carefully reweighed and the loss in weight in millig ams was noted. A sample of the uninhibited base oil was tested concurrently under the same conditions. Tests on two lubricating oil blends containing 0.5 per cent and 0.25 per cent, respectively, of the wax monothiocyanate gave the following results:

I o vt iif onc., eig 0 Inhibitor percent the Bearing, mg.

Product of Example 2 0. 50 0 Do 0. 25 1 26 It will be apparent that mineral lubricating oil compositions of the present invention have little tendency to attack hard. metal bearings.

EXAMPLE 7 In order to determine the stability of the mineral lubricating oil compositions of the present invention under engine operating conditions, a mineral oil containing one per cent by weight of the product of Example 2 was tested in a Lauson single cylinder, four cycle, liquid-cooled gasoline engine provided with jet lubrication. The base oil used was a solvent-treated Pennsylvania oil having an A. P. I. gravity of 31.1, a flash point of 405 R, and Saybolt Universal viscosities of 166 at F. and 45 at 210 F. The test engine was operated at a speed of 1815 R. P. M. for 36 hours, using an oil temperature of 280 F. At the end of the test period, the oil was tested for evidence of acidic oxidation products as indicated by the neutralization number (N. N.=number mg. KOH equivalent to 1 gram oil), and the viscosity was determined. The one per cent blend of the product of Example 2 in the aforedescribed base oil had a neutralization number of 4.8 and a kinematic viscosity of 7.62 at 210 F. A sample of the uninhibited base oil, similarly tested, had a neutralization number of 12.8 and a kinematic viscosity of 11.57 at 210 F. It is evident that the mineral lubricating oil composition prepared in accordance with this invention performs in a manner superior to the uninhibited base oil in actual engine operation.

It will be apparent from the foregoing illustrative examples that the high molecular weight alkyl thiocyanates must be the monothiocyanates. The polythiocyanates, even when in admixture with the monothiocyanates, are not soluble in mineral lubricating oils. It will also be noted that alkyl monothiocyanates having fewer than twenty carbon atoms are not utilizable herein for the same reasons.

Mineral oil concentrates are also contemplated in this invention, such concentrates containing substantially larger amounts of the additives than set forth hereinbefore. Thus, relatively large amounts, i. e., upwards of about ten per cent and up to about 49 per cent by weight, may be incorporated in a mineral lubricating oil. The concentrates thus obtained may thereafter be diluted with a suitable quantity of a mineral lubricating oil prior to use, to produce a mineral lubricating oil composition containing the desired optimum concentration of the additive.

It is to be understood that, in addition to the additives of the present invention, other oil addition agents may be incorporated in the mineral lubricating oil composition, to impart other desirable characteristics thereto. For example, extreme pressure additives, pour point depressants, antirust agents, detergents, and viscosity index improvers may be added to the mineral lubricating oils in addition to the corrosion inhibitors contemplated herein.

7 Although the present invention has been de- REFERENCES CITED scribed with preferred embodiments, it is to be The following references are of record in the understood that modifications and variations f1 f t n may be resorted to without departing from the l e 0 18 pa 8 spirit and scope thereof, as those skilled in the 5 UNITED STATES PATENTS art will readily understand. Such variations and Number Name Date modifications are considered to be within the 2,218,918 Loane Oct. 22, 1940 p rvi w nd s pe f the ppended claim. 2,310,670 Badertscher Feb. 9, 1943 iclaim: 1 1 b t 1 t 2,339,050 Carson Jan. 11, 1944 mmera ll nca mg 01 C011 ainmg a 11111101 10 amount, sufficient to reduce the tendency there- FOREIGN PATENTS of to corrode hard metal alloy bearings, of a Number Country Date paraffin wax monothiocyanatg 514,052 Great Britain Oct. 30, 1939 FERDINAND P. OTTO.