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THIADIAZOLE STABILIZERS FOR DITHIOCARBAMATES

By Thomas J. Karol, Ph.D. and Steven G. Donnelly (Manager of Technical Services)

ABSTRACT OF THE DISCLOSURE

Stabilized metal and sulfurized metal dithiocarbamate compositions are described which are stabilized with 2,5-dimercapto-1,3,4-thiadiazole dimer (e.g. VANLUBE 829, VANLUBE^® 972) and its hydrocarbyl or oxygen containing hydrocarbyl derivatives.

Lubricating oil compositions containing the stabilized compositions exhibit improved oxidation and corrosion inhibiting properties.

The present disclosure concerns stabilization of derivatives of dithiocarbamic acid with thiadiazole stabilizers. Another aspect of the disclosure relates to thiadiazole stabilized dithiocarbamate compositions and lubricating compositions containing the stabilized dithiocarbamates.

Derivatives of dithiocarbamic acid are useful additives for lubricants, hydraulic fluids, functional fluids and fuels. In particular, salts of dithiocarbamic acid provide improved functional characteristics such as wear, friction and oxidative resistance to lubricants under extreme pressure conditions.

When dithiocarbamates are incorporated into lubricants, the lubricating compositions may darken upon heating and at elevated temperatures may corrode copper and/or copper alloys. Theses factors could reduce the commercial use of the formulated lubricating compositions in certain applications.

In the prior art, U.S. Pat. No. 2,665,285 discloses stabilization of fungicidal derivatives of dithiocarbamic acid with inorganic sulfites, bisulfites or hyposulfites. U.S. Pat. No. 3,630,897 discloses stabilization of dithiocarbamate salts with poly (phenylene sulfide) polymers and the use of the stabilized dithiocarbamates in lubricating formulations.

Unexpectedly, it has been discovered that thiadiazole dimers (e.g. VANLUBE 829) stabilize salts of dithiocarbamic acid against corrosion (especially copper). The thiadiazole dimers hereto have been known to impart antiwear and antioxidant properties to formulated lubricating compositions as disclosed in U.S. Pat. No. 4,517,103 and U.S. Pat. No. 5,194,621.

SUMMARY OF THE DISCLOSURE

In accordance with the disclosure, we are providing stabilized compositions and a method for protection of metal surfaces from oxidation and corrosion, the improvement of which comprises stabilizing salts of dithiocarbamic acid of the formula



wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2 and the salts are polyvalent metal salts and sulfurized metal salts by adding a stabilizing amount of a thiadiazole dimer having the structural formula



wherein n = 1-2 and R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, and aralkyl groups in which the alkyl groups contain 1 to 16 carbon atoms and may be substituted with oxygen containing groups having alcohol, ether or keto functionality, and adding the stabilized composition to a lubricating base oil which optionally contains other additives.

DETAILED DESCRIPTION OF THE DISCLOSURE

Derivatives of dithiocarbamates can have limited stability and a tendency to decompose which can lead to corrosion.

The stabilized dithiocarbamates of the disclosure are metal salts of at least one dithiocarbamic acid of the formula

wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2 and ranges to 22 or higher. The hydrocarbyl groups may be alkyl, cycloalkyl, aryl, alkaryl or aralkyl groups. R1 and R2 taken together may represent polymethylene forming a cyclic compound with the nitrogen. The alkyl groups may be straight or branched chain as for example ethyl, pentyl, 2-ethylhexyl, dodecyl, tridecyl, hexadecyl groups. Examples of cycloalkyl groups include cyclohexyl and cycloheptyl groups, and examples of aralkyl groups include benzyl and phenylethyl.

The metal salt of the stabilized dithiocarbamate may be monovalent or polyvalent. The polyvalent metals include, among others, Group II, IV, V, VI and VIII metals. For lubricating applications, particularly preferred are molybdenum, zinc, cadmium, antimony and lead salts.

The stabilized compositions can be mixtures of different metal salts of dithiocarbamates or of different dihydrocarbyldithiocarbamates.

The stabilized dithiocarbamates of the disclosure can be sulfurized polyvalent salts of the structural formula



wherein R1, R2, R5 and R6 may be the same or different hydrocarbyl groups as defined above and X represents a sulfur or oxygen atom (e.g. MOLYVAN A).

The thiadiazole dimer stabilizers of the disclosure may be either,

1. a thiadiazole dimer having the structural formula:



wherein n = 1-2 and R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, and aralkyl groups in which the alkyl groups contain 1 to 16 carbon atoms and may be substituted with oxygen containing groups having alcohol, ether, or keto functionality.

OR

2. The thiadiazole dimer may also be substituted in the two position by hydrocarbon groups. Preferred are alkyl, cycloalkyl and aralkyl groups. Particularly preferred are groups in which the alkyl group contains 1 to 16 carbon atoms. Useful stabilizers of the disclosure are thiadiazole dimers containing alkyl groups substituted with oxygen containing groups with alcohol, ether or keto functionality. Such dimers are described in U.S. Pat. No. 5,194,621 and are characterized by the structural formula:



wherein R9, R10, R7 and R8 may be same or different and represent hydrogen, alkyl having 1 to 20 carbon atoms, phenyl and alkyl substituted phenyl. The alkyl groups may be selected from straight and branched chain alkyls. Representative groups include, among others, methyl, ethyl, propyl, butyl, isobutyl, 2-ethylhexyl, 2-heptyl, octyl, 2,5-t-butylphenyl, octylated and nonylated phenyl groups.

OR

3. A COMBINATION of 1 and 2 ABOVE.

Dithiocarbamates can be stabilized by adding about 0.5 to 5.0 percent of thiadiazole dimer based on the weight of the dithiocarbamate. Preferred range of the thiadiazole is about 0.9 to 3.0 percent.

The stabilized compositions of the disclosure can be incorporated into lubricating compositions to produce improved corrosion protection.

The amount of the stabilized dithiocarbamate additive required to effectively impart antioxidant properties to lubricating compositions may range from 0.01 to 10.0 percent of the lubricating composition. The preferred range is about 0. 1 to 5.0 percent of the additive based on the lubricating composition.

The lubricating compositions contemplated herein include lubricating oils, engine oils and lubricating greases containing a major amount of base oil. The base oil may be selected from naphthenic, aromatic, paraffinic, mineral and synthetic oils. The synthetic oils may be selected from, among others, alkylene polymers, polysiloxanes, carboxylic acid esters and polyglycol ethers.

The lubricating compositions may contain the necessary ingredients to formulate the composition, as for example emulsifiers, dispersants and viscosity improvers. Greases may be prepared by adding thickeners, as for example, salts and complexes of fatty acids, polyurea compounds, clays and quaternary ammonium bentonite complexes. Depending on the intended use of the lubricant, other functional additives may be added to enhance a particular property of the lubricant. The lubricating compositions may further contain extreme pressure agents, metal passivators, rust inhibitors, dispersants and other known antioxidants and antiwear agents.

The following examples are given for the purpose of further illustrating the disclosure. All percentages and parts are based on weight unless otherwise indicated.

EXAMPLE 1

Copper corrosion test was conducted by the ASTM D-4048 method at 100⁰C for 24 hours. Polyurea base grease was formulated with sulfurized oxymolybdenum dibutyldithiocarbamate (e.g. MOLYVAN A) with and without 5,5’-dithiobis-1,3,4-thiadiazole-2(3H)-thione (e.g. VANLUBE 829). The test sample containing the dithiocarbamate stabilized with thiadiazole composition of the disclosure showed considerable improvement of copper corrosion as compared to unstabilized dithiocarbamate. The test results are compiled in Table I herein.

Table I

Sample	Active Ingredient	Mass Percent	Cu Strip Rating
1	Mo dithiocarbamate	3.0	4a
2	Mo dithiocarbamate	2.85	1b
	& Thiadiazole	0.15
3	Polyurea Base Grease	100	1a

The above embodiments have shown various aspects of the present disclosure. Other variations will be evident to those skilled in the art and such modifications are intended to be within the scope of the disclosure as defined by the appended claims.

WHAT IS DISCLOSED

1. A stabilized composition containing (1) a salt of dithiocarbamic acid of the formula



wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2 and the salts are polyvalent metal salts and sulfurized metal salts and (2) a stabilizing amount of a thiadiazole dimer having the structural formula



wherein n = 1-2 and R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, and aralkyl groups in which the alkyl groups contain 1 to 16 carbon atoms and may be substituted with oxygen containing groups having alcohol, ether or keto functionality.

2. A stabilized composition of claim 1 wherein the sulfurized polyvalent salt has the structural formula



wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2, R5 and R6 are each independently hydrocarbyl groups in which the number is at least 2 and may be the same or different than R1 and R2, X represents a sulfur or oxygen atom.

3. A stabilized composition of claim 1 wherein the metal salt is molybdenum dibutyldithiocarbamate.

4. A composition of claim 1 wherein the thiadiazole dimer has a structural formula



wherein R7, R8, R9 and R10 may be the same or different and represent hydrogen, alkyl having 1 to 20 carbon atoms, phenyl and alkyl substituted phenyl groups.

5. A stabilized composition of claim 1 wherein the thiadiazole dimer is present in an amount of 0.5 to 5.0 percent.

6. A composition of claim 1 wherein the thiadiazole dimer is 5,5-dithiobis- 1,3,4thiadiazole-2(3 H)-thione.

7. A lubricating composition comprising a major amount of base oil of lubricating viscosity and 0.1 to 10.0 percent by weight of a stabilized antioxidant composition containing (1) a salt of dithiocarbamic acid of the formula



wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2 and the salts are polyvalent metal salts and sulfurized metal salts and (2) a stabilizing amount of a thiadiazole dimer having the structural formula



wherein n = 1-2 and R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, and aralkyl groups in which the alkyl groups contain 1 to 16 carbon atoms and may be substituted with oxygen containing groups having alcohol, ether or keto functionality.

8. A lubricating composition of claim 7 wherein the stabilized antioxidant composition consists of molybdenum dibutyldithiocarbamate and 5,5'-dithiobis-1,3,4-thiadiazole-2(3H)-thione.

9. A lubricating composition of claim 7 wherein the stabilized antioxidant composition consists of molybdenum ditridecyldithiocarbamate and 2,2'-di(1-propoxypropylthio)-5,5'-dithiobis- 1,3,4-thiadiazole.

10. A method for protection of metal surfaces from oxidation and corrosion, the improvement of which comprises the steps of stabilizing salts of dithiocarbamic acid of the formula



wherein R1 and R2 are each independently hydrocarbyl groups in which the number of carbons is at least 2 and the salts are polyvalent metal salts and sulfurized metal salts by adding 0.5 to 5.0 percent by weight of a thiadiazole dimer having the structural formula



wherein n = 1-2 and R3 and R4 are independently selected from hydrogen, alkyl, cycloalkyl, and aralkyl groups in which the alkyl groups contain 1 to 16 carbon atoms and may be substituted with oxygen containing groups having alcohol, ether or keto functionality and

(b) adding the stabilized composition to a lubricating base oil and

(c) optionally adding other lubricating additives.

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