Sulfur-containing Carboxylic Acids As Corrosion Inhibitors

Abstract

Organic compositions comprising a liquid hydrocarbon have improved corrosion inhibiting properties when an alkyl thiohydrocarbyl acid, or amine salt thereof, is present in the composition.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the inhibition of corrosion caused by compositions comprising hydrocarbon liquids in contact with metals. More particularly, the invention relates to inhibiting such corrosion by adding to the composition an additive which will impart the desired properties thereto.

2. Discussion of the Prior Art

Most hydrocarbon liquid, or compositions comprising same, will cause corrosion when in contact with metals. The extent of such corrosion will, of course, depend to a large extent upon the system on or in which the hydrocarbon liquid is to be used or upon the environmental conditions of such use. In metal working systems, for example, corrosion might be quite severe, even at low temperatures, if the aqueous emulsions of the hydrocarbon liquid does not contain an inhibitor.

In other systems, such as in the automotive engine, where hydrocarbon liquids of lubricating viscosity are required, the problem of corrosion becomes even more severe because of the high temperatures of operation. Here, unless corrosion is controlled, sludge and stain can form on the lubricated parts. These deposits can drastically reduce the efficiency of an engine, and in fact can destroy it if allowed to remain in the engine over long operating periods.

The use of certain acids and oil-soluble acid salts in lubricants is known. U.S. Pat. No. 2,223,129, for instance, discloses hydrocarbon oil lubricating compositions containing such compounds as phenylmercapto stearic acid as an extreme pressure agent. In addition, U.S. Pat. No. 2,281,676 discloses turbine oils (principally a light, moderately refined, solvent treated petroleum distillate having 150-160 viscosity at 100.degree.F.) and fatty acids having from 10-20 carbon atoms (e.g., lauric, myristic, palmitic and stearic acids). The acids are taught to be corrosion agents.

U.S. Pat. No. 2,474,604 discloses the use of certain alkylthio carboxylic acids, among them cetylthio acetic acid as a rust inhibiting additive for mineral oils. U.S. Pat. No. 2,477,356 teaches that alkylthio acetic acids, as for example, octadecylthio acetic acid, may be used as anticorrosion agents.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided an organic composition comprising a hydrocarbon liquid and a corrosion inhibiting amount of (1) an acid of one of the formulas

1. R - S - R' - COOH

and

2. [-R" - S - R'" - COOH].sub.2

wherein R is alkyl of from about two to about 16 carbon atoms, R' is a straight or branched hydrocarbylene group, such as alkylene, arylene, or an aryl-substituted alkylene, each containing from four to about 22 carbon atoms, R" is alkylene of from about two to about 16 carbon atoms and R'" is the same as R', or of (2) an amine salt of such acid. In the above formulas, since R' may be branched, R' may be ##SPC1##

such that the whole unit has the number of carbon atoms designated, i.e., from four to about 22 carbon atoms.

DESCRIPTION OF SPECIFIC EMBODIMENTS

As is evident from the above formulae, the sulfur-bridged hydrocarbyl or hydrocarbylene must be an alkyl or alkylene group, and according to the discovery herein, such group will contain a minimum of 2 carbon atoms and a maximum of about 16. The other hydrocarbylene group (R' and R'" in the formula) may be an alkylene or an arylene group. This will become apparent from the data presented herein.

The alkylthiohydrocarbyl acids (formula (1) above) of this invention may be synthesized in good yields using known methods. In general aspect, derivatives of acetic and propionic acids may be made by reacting the appropriate thiol salt with the appropriate chloro acid, thus:

Rsm + c1 r' - cooh.fwdarw.r - s - r' - cooh + mc1

this method is described in detail in an article reported in J. Am. Chem. Soc., 69, 693 (1947). German patent 840,966 describes a method for preparing butyric acid derivatives by reacting a thiol salt with gamma-butyrolactone.

The dimer acid (the acid of formula (2) above) may be prepared by reacting a dithiol with a lactone in the presence of an alkali metal alkoxide. Example 3 below will outline this method in more detail.

When the additives of this invention are used with hydrocarbon liquids, they are preferably used as the free acid, but may be used in the form of their liquid-soluble amine salts to impart corrosion inhibiting properties. The amines may be primary, secondary or tertiary and will include alkylamines, where the alkyl contains from about four to about 40 carbon atoms, or they may be arylamines, such as aniline and the like, or they may be of a type wherein the nitrogen is part of a ring system, e.g. pyridine. Such salts are prepared by mixing one mole of the amine with one mole of the acid.

The hydrocarbon liquids which may be used in the practice of this invention include mineral oils, both light oils and oils of lubricating viscosity, including naphthenic, paraffinic and aromatic oils. Also included are liquid hydrocarbon fuels, including gasoline, jet fuels, etc., having a boiling range of from about 60.degree.F to about 600.degree.F, as well as synthetic hydrocarbon oils, which may or may not be of lubricating viscosity. These synthetic hydrocarbon oils include those obtained by polymerizing an olefin containing from about three carbon atoms to about 18 carbon atoms. One prominent example of a synthetic hydrocarbon lubricating oil is one prepared by polymerizing decene-1 to the trimer or tetramer. However, any of those liquid polymers containing from about six to about 60 carbon atoms may be used.

The oils mentioned above may be used in a variety of ways. The most obvious of these is as a lubricant, either for applications involving relatively mild conditions, such as in switch contacts, or for applications involving high temperatures. This latter use includes lubrication of an automotive engine. Other areas of use include hydraulic fluids, turbine oils, gear oils and cutting oils.

Another important field involves metal working. The oils used in working metals may or may not be of lubricating viscosity, depending upon the particular application. A metal pre-coat, which is applied prior to storage or to rolling operations, from its very nature will require a fairly viscous oil. HOwever, the oil in coolants, which are generally of the oil-in-water type, need not have lubricating viscosities.

Of those areas mentioned above, one of the more important ones is the field of hyraulics. In this particular field, especially as it applies to aviation, one requirement of the fluid is that it retain its properties at low temperatures. A disadvantage of most known additives is that they are totally insoluble at the required low temperatures, or if they are soluble to any extent, such solubility does not give an effective concentration of the additive. The additives of this invention have been found to be soluble in a decene trimer oil to the extent of 1 percent or better at -12.degree.C, whereas the additives of U.S. Pat. No. 2,747,604 and U.S. Pat. No. 2,477,356 are insoluble in the same oil. For example, 4-(ethylthio)dodecanoic acid was soluble by more than 1 percent at -12.degree.C in a decene trimer oil, whereas N-(dodecylthio)acetic was not soluble at even 0.05 percent at the same temperature.

It has been found that the composition, whether containing a hydrocarbon as the major liquid or a large amount of water, will need from about 0.01 percent to about 5 percent by weight, preferably from about 0.01 percent to about 0.2 percent, of the alkyl thiohydrocarbyl acid or its salt to effectively impart anti-corrosion properties thereto.

When used as an aqueous composition, water will comprise from about 50 percent to about 99 percent of the total composition. If it is desirable or necessary to utilize an emulsion, any of the well-known emulsifiers may be used.

Having described the invention in general terms, the following examples are given to specifically illustrate the practice thereof. It will be understood that such examples are only illustrative and are not intended to place an unnecessary limitation on the invention.

EXAMPLE 1

A one liter flask was fitted with stirrer, thermometer, dropping funnel, and nitrogen inlet tube. To the flask was added 400 ml. of benzene, 63.7 g. of ethane thiol (1.043 mole). Then 53.5 g. of sodium methoxide (0.991 mole) was added with stirring under nitrogen. The mixture was heated and stirred to distil off methanol and benzene. After cooling the dry salt to room temperature, 152 g. (0.770 mole) of .gamma.-n-octyl-.gamma.-butyro-lactone was added. The mixture was heated and stirred under nitrogen for 16 hours at 150.degree.C. Then 400 ml. of 6N. hydrochloric acid was added with stirring and heating. The aqueous layer was separated from the crude product and extracted by two 200 ml. portions of benzene. This extract was combined with the crude product. The benzene was distilled off at atmospheric pressure. Vacuum distillation gave 126 g. of purified 4-(ethylthio) dodecanoic acid distilling at 146.degree.-151.degree.C at 0.2 mm of mercury.

Analysis Calc. Found C 65.17% 64.90% H 10.84% 10.66% S 12.3% 12.2%

example 2

by the method of Example 1, a product was obtained from the reaction of 10.0 g. of sodium methoxide with 34.0 g. of 1-decanethiol in 200 ml. of benzene, followed by 60 g. of .gamma.-phenyl-.gamma.-butyrolactone. The crude sulfide acid (59 g.) was purified by dissolving in a solution of 50 g. of sodium carbonate in 1,500 ml. of water, and extracting this with two 250 ml. portions of n-hexane. The product was liberated from the aqueous solution by the addition of 6N. hydrochloric acid, and collected in ethyl ether. After evaporation of the ether there remained 50 g. of 4-(n-decylthio)-4-phenylbutyric acid.

Analysis Calc. Found C 71.38% 71.59% H 9.59% 9.48% S 9.5% 9.3%

example 3

a dimer acid of the formula

[HOOC(CH.sub.2).sub.2 CH(n-C.sub.8 H.sub.17)-S-CH.sub.2 CH.sub.2 ].sub.2

is prepared as follows:

10.0 parts of 1,4-butanedithiol is added to 100 cc of benzene, and, while stirring vigorously and adding N.sub.2, 8.86 parts of sodium methoxide is added. The benzene and methanol are stripped off, and, when the residue has cooled, 40.0 parts of .gamma.-n-octyl-.gamma.-butyrolactone is added and the reactants are heated at 150.degree.C overnight.

250 parts of water are added, the whole is transferred to a separatory funnel and ethyl ether is added. All materials are placed in a beaker and acidified with concentrated hydrochloric acid in 100 cc of benzene. The organic layers are combined and evaporated on a hot plate under N.sub.2.

EXAMPLE 4

4-(n-dodecylthio)butyric acid was prepared similarly to Example 1 from n-dodecyl mercaptan, sodium methoxide, and .gamma.-butyrolactone.

EVALUATION OF PRODUCTS

The above products were evaluated as rust preventatives in the presence of synthetic sea water as directed by the procedure outlined in ASTM D665-60, procedure B.

The products, tested in accordance with the above procedure, gave the following results. The oil used was 150 SUS (100.degree.F) citronelle Turbine Base oil.

Weight % Compound 0.06 0.03 Ex. 1 Pass Pass Ex. 2 Pass Pass Ex. 3 Pass Fail (Severe rust) Ex. 4 Pass Fail (Medium rust)

These results show that good inhibition can be obtained with the sulfur atom at various positions in the acid chain. Also, it is shown that aryl groups can be present in the molecule.

It has been surprisingly found that (1) although R may have the requisite number of alkyl carbon atoms, if R' is alkyl of less than about 4 carbon atoms or (2) if R is an aromatic hydrocarbyl group, the product fails as a rust inhibitor. This is shown by the following data, found under same conditions and in same oil as above.

Weight % Compound 0.06% 0.03% (n-Butylthio)acetic acid -- Fail (n-Octadecylthio)acetic acid -- Fail 3-(phenylthio)propionic acid Fail -- 4-(n-Octadecylthio)butyric acid -- Fail 4-(Phenylthio)butyric acid Fail -- 4-(Phenylthio)dodecanoic acid Fail (severe -- rust)

Another thing apparent from the second set of data is the fact that when the R chain length exceeds about 16 or 17 carbon atoms, the additive fails as an anti-rust agent. It would seem from this data, then, that R must be an alkyl and it must be of a prescribed length for acceptable activity. It seems also that, whereas an aromatic group can be associated with R', R must not be aromatic.

Although the present invention has been described with certain specific embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of this invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims.

Claims

We claim:

1. An organic composition comprising a major proportion of a hydrocarbon liquid and a corrosion inhibiting amount of an acid of one of the formulas

R - s - r' - cooh

and

[-R" - S - R'" - COOH].sub.2

wherein R is alkyl of from about two to about 16 carbon atoms, R' is arylene of up to about 22 carbon atoms, R" is alkylene of from about two to about 16 carbon atoms and R'" is hydrocarbylene of from four to about 22 carbon atoms.

2. the composition of claim 1 comprising from about 0.01 to about 5 percent by weight of said acid salt.

3. The composition of claim 1 wherein the hydrocarbon liquid is a mineral oil, a synthetic oil or a liquid hydrocarbon fuel.

4. The composition of claim 3 wherein the oil is a lubricating oil.

5. The composition of claim 3 wherein the oil is a turbine oil.

6. The composition of claim 4 wherein the lubricating oil is a polyolefin fluid.

7. An aqueous emulsion comprising the composition of claim 1 and from about 50 to about 99 percent by weight thereof of water.

8. The composition of claim 1 wherein the acid is n-decylthio-phenylbutyric acid.

9. The composition of claim 1 wherein the acid has the formula

[HOOC(CH.sub.2).sub.2 CH(C.sub.8 H.sub.17) - S - CH.sub.2 CH.sub.2 ].sub.2