US3158576A - Polyhydric alcohol esters of alkyl mercapto fatty acids and oil compositions containing said esters - Google Patents

Description

- are also rust reventives.

United States Patent 3,15%,576 PQLY TYDRHC ALQUHGL ETER 0F ALKYL MER- CAPTQ FATTY AGlDS AND 01L CQMPGSITEQNS CQNTAlNlNG SAM) lid-TEES Harry W. Rudel, Roselle, and William Seitz, Union, NJ assignors to Essa Research and Engineering Company, a corporation of Delaware No Drawing. Filed Jan. 4, 1960, Ser. No.78 4 Claims. (Cl. 25248.6)

This invention relates to polyhydric alcohol esters of alkyl merca-pto fatty acids and to oil compositions containing them. Particularly, the invention relates to esters which are useful as rust reventives in oil compositions and are prepared by partially esterifying a polyhydric alcohol withian alkyl thioether of a saturated fatty acid.

In US. Patent 2,884,379, it was disclosed that certain alkyl mercapto fatty acids were oil soluble and showed excellent rust inhibition in an oil vehicle. However, the use of these acids are limited since they are not particularly suitable, or must be employed in very low concentrations, in many applications where acidic additives are not desirable. Thus, use of these acids, excepting in very low concentrations, is not generally desirable in stationary steam turbine oils, marine E.P. turbine oils, gencral purpose industrial oils, certain types of hydraulic oils, greases, middle distillate fuels and dyed motor and aviation gasolines. The use of an acidic type of inhibitor may be detrimental in applications involving high temperature contact with non-ferrous metals because of their corrosive action. Their use with dyes in gasolines and materials that are color sensitive to acid-base reactions, is also undesirable. Their use in distillate fuels as pipe line rust inhibitors provokes the formation of soluble iron soaps that subsequently form induction system deposits in internal combustion engines.

It has now been found that by further reacting alkyl mercapto fatty acids with a polyhydroxy compound to form an alcoholic compound, that theresulting esters not only retain the excellent rust inhibition of the acids per se, but are superior in that they are neutral in reaction and may be employed in any desired concentration in lubricants without adversely affecting non-ferrous metal corrosion. They may also be employed in motor fuels without romotin the above inade uacies relative to color reaction and iron soap formation.

It has been further found that the additives of the invention are superior in certain respects, such as emulsion forming tendency, to other polyhydric alcohol esters which This undesirable emulsionforming tendency is surprisingly slight with the mercapto acid esters of the invention, particularly when compared to fatty acid esters of polyhydroxy materials, such as; sorbitan monooleate, pentaerythritol dioleate, glyceryl mono-stearate, polyoxyethylene sorbitan mono-laurate and unsubstituted fatty acid esters of trimethylol propane.

The esters of the invention have the general formula:

wherein R is a straight or branched chain alkyl radical containing 4 to 22, preferably-8 to 18 carbon atoms; R is a C to C aliphatic saturated hydrocarbon radical; while R" contains 2 to 18, preferably 3 to 10 carbon atoms and is an aliphatic, saturated hydrocarbon radical or an ether-interrupted aliphatic, saturated hydrocarbon radical, which hydrocarbon radicals may be substituted with 1 to hydroxy groups.

, The esters of the above formula can be prepared by esterifying alkyl thioether fatty acids of the general formula:

RSR'COOH wherein R is an alkyl radicalof 4 to 22 carbon atoms 3,l58,575 Patented Nov. 24, 1964 and R is a saturated aliphatic hydrocarbon radical of 1 to 4 carbon atoms. Examples of such acids include lauryl mercapto acetic acid, C OX0 mercapto acetic acid, hexyl beta mercapto propionic acid, and Z-ethylhexyl alpha mercapto valeric acid. Methods of preparing such acids are described in detail in US. Patent 2,884,379.

The polyhydric alcohols, which may be utilized in forming the desired esters, include trimethylol propane, pentaerythritol, hexitol, sorbitan, glycerin, etc.

The esterification is carried out by reacting 0.25 to 1.0 moles of the polyhydric alcohol per mole of the acid, depending upon the hydroxyl groups in the alcohol, under conventional esterification conditions. If desired, 0.1 to 5.0 wt. percent based on the totfl amount of acid and alcohol reactants, of an esterification catalyst can be used. Suitable catalysts include toluene sulfonic acid, sulfuric acid, hydrogen fluoride, sulfo salicylic acid and sodium acid sulfate. However, generally the reaction will proceed sufficiently fast without a catalyst. Also, it may be desirable to use 25 to 200 wt. percent, based on the total amount of acid and alcohol reactants, of an inert water entraining agent such as toluene, xylene, mesitylene, Varsol, kerosene, halogenated solvent such as perchloroethylene, or any other liquid solvent which is immiscible with water and has the desired boiling temperature.

The esterification is carried out in a conventional manner by heating the reactants and driving off the water. When the stoichiometric amount of water is removed, then the reaction mixture maybe stripped at a pressure of about 10 to 760 mm. Hg and a pot temperature of to 400 F. to remove the entraining agent any other volatile materials. The remaining ester residue can be used without further purification if made without an acid catalyst. If a catalyst has been used, it will usually be desirable to wash the reaction product with aqueous sodium hydroxide, or sodium carbonate and water, followed by drying over a desiccant such as sodium sulfate or anhydrous calcium chloride and filtering prior to the stripping step.

The ester can be dissolved in hydrocarbons, to inhibit rusting, in amounts varying from about 0.03 to 10.0 wt. percent, preferably 0.05 to 6.0 wt. percent, based on the total composition. The hydrocarbon may be a mineral oil such as lubricating oils, slushing oils, kerosene, or it may be a fuel such as motor gasoline, aviation gasoline, jet fuel, furnace oil, or it may be a grease.

Other additive materials may also be added to the hydrocarbon along with the ester to enhance other desirable characteristics of the compositions. Such materials as oiliness agents, extreme pressure additives, thickening agents, pour point depressors, detergents, dyes, and the like which are frequently added to various oil products may be used in conjunction with the ester of the invention to obtain the desired final composition.

The invention will be understood by reference to the following examples which include a preferred form of the invention.

a EXAMPLE I 289 grams (1 mol) of C 0x0 (tridecyl) mercapto acetic acid having a neutralization number of 194, 134 grams (1 mol) of trimethylol propane and about 500 grams of Xylene were added to a flask equipped with condenser, stirrer and thermometer; No catalyst was used. The reaction mixture was heated and maintained at a temperature of about 300 F. until 1 mol of water was recovered, which required about 2 hours. The solvent was then substantially removed by distillation at a pressure of about 50 mm. mercury. The last traces of solvent were removed at 15 mm. pressure and a final pot temperature of 370 F. 395 grams of ester remained as residue. The ester showed the following analysis:

Sulfur8.0%, neutralization number-99 mg. KOH/ gm. ester, and saponification number-141.8 mg. KOH/ gm. of ester.

parts by weight of the above ester was added to 95 parts by weight of an acid treated naphthenic lubricating oil having a viscosity of :150 SUS at 100 F.

For comparison purposes, a second blend was made up consisting of 5 wt. percent of sorbitan monooleate in the same oil.

A Humidity Cabinet test was run on the above two oil blends as well as the base oil per se, i.e. without additive. This test was carried in a Standard ]ANH792 Humidity Cabinet. Briefly, this test is conducted by dipping sandblasted steel panels into the oil composition to be tested at room temperature, allowing the panels to drain for two hours, and then suspending them in the Humidity Cabinet operating at a temperature of 120 F. and 100% relative humidity. The panels were periodically examined and the test was considered complete when the first three significant specks of rust appeared on the panel. In this test, a 5 wt. percent oil blend of sorbitan monooleate is accepted as a standard of satisfactory performance.

The results or" this test are summarized in the following table:

Table I HUMIDITY CABINET TESTS Additive: Days Protection 5 wt. percent mercapto acetic acid ester of Example I 5 wt. percent sorbitan monooleate 10 None 1 EXAMPLE 11 Three blends were prepared in a deasphalted, dewaxed, phenol-treated, mid-continent lubricating oil having a viscosity of 165 SUS. at 10 F. These blends were prepared by simple mixing of the additive into the oil while warming to a temperature of about 70 to 150 F. The blends contained the mercapto acetic acid ester of Example I, sorbitan monooleate, and a monooleate ester of trimethylol propane, respectively, in amounts of 0.1 wt. percent, based on the weight of the oil. These blends were evaluated as rust preventives for steam turbine oils in the presence of both distilled water and synthetic sea water. The test was carried out in accordance with the ASTM D-66546T test procedure. Briefly described, in this test a standard steel spindle is maintained in contact with a rapidly stirred oil composition (300 cc.) and Water cc.) mixture for 24 hours at 140 F. At the end of this time the extent of rusting of the panel is noted.

The blends were also subjected to the Herschel Emulsion test in which ml. of oil and 40 ml. of water are brought to test temperature (180 F.) in a 100 ml. graduated cylinder, agitated with a paddle stirrer at 1500 RPM, allowed to stand at the test temperature, and then noting the time and extent of emulsion breaking. A satisfactory oil will show less than 3 m1. of interface emulsion after 30 minutes standing.

The results obtained and the compositions tested are summarized in Table II, which follows:

As seen from the preceding tbale, the ester of the invention was very effective as a rust inhibitor and did not have excessive emulsifying tendencies. On the other hand sorbitan monooleate forms a much more stable emulsion (which is undesirable in many oils, e.g. steam turbine oils) While the trimethylol propane monooleate was a poor rust inhibitor.

What is claimed is:

1. A rust inhibited composition comprising a major amount of liquid mineral hydrocarbon and a rust inhibiting amount of an ester of the general formula:

RSRCOOR"OH wherein R is a C to C alkyl radical, R is a C to C aliphatic saturated hydrocarbon radical and R is a hydroxy substituted radical selected from the group consisting of hydroxy substituted aliphatic saturated hydrocarbon radicals and hydroxy substituted ether interrupted hydrocarbon radicals, said hydroxy substituted hydrocarbon radicals containing 1 to 5 hydroxy groups and a total of 2 to 18 carbon atoms.

2. A composition according to claim 1, comprising a major amount of mineral oil and 0.05 to 6.0 wt. percent of said ester.

3. A composition according to claim 2, wherein R is a C to C alkyl radical, R is a C hydrocarbon radical and R" contains 3 to 10 carbon atoms.

4. A mineral oil composition comprising a major amount of a mineral oil and about 0.05 to 6.0 wt. percent of the ester of equimolar amounts of C alkyl mercapto acetic acid and trimethylol propane.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,604 \Vasson et a1. June 28, 1949 2,503,401 Mattano et a1 Apr. 11, 1950 2,540,093 Brooks Feb. 6, 1951 2,603,653 Kosmin et al July 15, 1952 2,603,654 Kosmin July 15, 1952 2,884,379 Rudel et a1. Apr. 28, 1959

Claims (1)

1. A RUST INHIBITED COMPOSITION COMPRISING A MAJOR AMOUNT OF LIQUID MINERAL HYDROCARBON AND A RUST INHIBITING AMOUNT OF AN ESTER OF THE GENERAL FORMULA: