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United States Patent 3,655,559
Holt April 11, 1972

ALKYLATED DIPHENYLAMINES AS STABILIZERS

Abstract

The use of tris 2,4,4'-alkyldiphenylamines for stabilizing organic material and compositions thereof especially synthetic lubricating oils. Such compositions are stabilized against oxidative deterioration.


Inventors: Holt; Brian (Royton, Lancs., EN)
Assignee: CIBA-GEIGY Corporation (Ardsley, NY)
Appl. No.: 05/027,176
Filed: April 9, 1970


Foreign Application Priority Data

Apr 11, 1969 [GB] 18,617/69

Current U.S. Class: 508/493 ; 252/401; 508/485; 524/258; 564/409; 564/433
Current International Class: C10M 133/12 (20060101); C10M 133/00 (20060101); C08K 5/00 (20060101); C08K 5/18 (20060101); C09K 15/00 (20060101); C09K 15/18 (20060101); C09K 15/16 (20060101); C10m 001/34 ()
Field of Search: 252/50,51.5,56,51.5A,401 260/576

References Cited

U.S. Patent Documents
3052632 September 1962 Loeffler
3282840 November 1966 Foster et al.
2009480 July 1935 Craig
Primary Examiner: Wyman; Daniel E.
Assistant Examiner: Cannon; W.

Claims



I claim:

1. A method of stabilizing synthetic carboxylic acid ester lubricating oils which comprises incorporating in said synthetic carboxylic acid ester lubricating oils a compound having the formula:

wherein

R' is a tertiary alkyl group having from four to 12 carbon atoms,

R" is hydrogen or a straight or branched chain alkyl group having from two to four carbon atoms, and

R'" is a straight or branched chain alkyl group having from two to four carbon atoms.

2. A method of claim 1 wherein R' has from four to eight carbon atoms in the alkyl chain.

3. A method of claim 1 wherein R' is a tertiary butyl, tertiary pentyl, tertiary hexyl, tertiary octyl or a nonyl group derived from propylene trimer.

4. A method of claim 1 wherein R" and R"' are ethyl, isopropyl or tertiary butyl.

5. A method of claim 1 wherein said compound is 2:2'-diethyl-4:4'-di-t-butyldiphenylamine.

6. A method of claim 1 wherein said compound is 2:2'-diethyl-4:4'-di-t-octyldiphenylamine.

7. A method of claim 1 wherein said compound is 2:2:4'-tri-t-butyldiphenylamine.

8. A method of claim 1 wherein said compound is 2:2':4:4'-tetra-t-butyldiphenylamine.

9. A method of claim 1 wherein said compound is 2-t-butyl-4:4'-di-t-octyldiphenylamine.

10. A composition comprising a synthetic carboxylic acid ester lubricating oil susceptible to oxidative deterioration and, as an antioxidant, a compound of claim 1.

11. A composition as claimed in claim 10 wherein the proportion of the compound of claim 1 is within the range of from 0.001 percent to 5 percent by weight based on the weight of the synthetic carboxylic acid ester lubricating oil.

12. A composition as claimed in claim 10 wherein the proportion of the compound of claim 1 is within the range of from 0.1 percent to 4.0 percent by weight based on the weight of the synthetic carboxylic acid ester lubricating oil.

13. A composition as claimed in claim 10 wherein the synthetic carboxylic acid ester lubricating oil is intended for use at temperatures at or above 400.degree. F.

14. A composition as claimed in claim 10 wherein the synthetic carboxylic acid ester lubricating oil is based on a diester of a dibasic acid and a monohydric alcohol; on a triester of 1:1:1-trimethylolpropane and a monobasic acid or a mixture of such acids; on a tetraester of pentaerythritol and a monobasic acid or mixture of such esters; or on complex esters derived from 1:1:1-trimethylolpropane, caprylic acid and sebacic acid; or on mixtures thereof.
Description



DETAILED DESCRIPTION

The present invention relates to the use of alkylated diphenylamines and to organic material stabilized by the presence therein of the alkylate diphenylamines.

According to the present invention, there is used a compound having the formula:

wherein

R' represents a tertiary alkyl group having from four to 12 carbon atoms,

R" is hydrogen or a straight or branched-chain alkyl group having from two to four carbon atoms, and

R'" is a straight or branched chain alkyl group having from two to four carbon atoms,

For stabilizing organic material.

The alkyl substituent R' preferably contains from four to eight carbon atoms and may be, for instance a tertiary-butyl, tertiary-pentyl (1:1-dimethylpropyl), tertiary-hexyl (1:1-dimethylbutyl), tertiary-octyl (1:1:3:3-tetramethylbutyl) or a nonyl or dodecyl group, derived from propylene trimer or tetramer respectively which are commercially-available mixtures of isomeric nonenes or dodecenes. The substituents R" and R'" may be, for example, an ethyl, isopropyl or a tertiary-butyl group.

Examples of preferred used compounds of formula I include 2:2'-diethyl-4:4'-di-t-butyl-diphenylamine, 2:2'-diethyl-4:4'-di-t-octyl-diphenylamine, 2:4:4'-tri-t-butyl-diphenylamine and particularly 2:2':4:4'-tetra-t-butyl-diphenylamine.

The compounds having the formula I are produced by orthoalkylating in a first stage, diphenylamine with a straight- or branched-chain olefine having from two to four carbon atoms per molecule in the presence of a catalyst comprising aluminum, and in a second stage, contacting the thus orthoalkylated diphenylamine with a secondary olefine having from four to 12 carbon atoms per molecule in the presence of a Friedel-Crafts or Bronsted acid catalyst.

The compounds of formula I are thus conveniently produced for instance, by first alkylating diphenylamine in one or both of the ortho- (2 and 2' positions) of the diphenylamine molecule, and subsequently alkylating the orthoalkylated material in both of the para- (4 and 4') positions.

The proportion of olefine to that of diphenylamine in the ortho-alkylation reaction mixture is desirably substantially the stoichiometric proportion required to react one or two molecules of olefine respectively per molecule of diphenylamine. Thus for the reaction of olefine at only one ortho-position in the diphenylamine molecule, the proportion of olefine to diphenylamine is desirably within the range of from 1.0 to 1.1 moles per mole of diphenylamine. However, if reaction at both ortho-positions is desired, the proportion of olefine to diphenylamine is advantageously within the range of from 2.0 to 2.5 moles of olefine per molecule of diphenylamine.

The catalyst used in the orthoalkylation step may be, for example, aluminum metal itself; aluminum amalgam alone or in combination with an alloy for instance, aluminum and nickel; or aluminum or aluminum amalgam in combination with mercury salts for instance, mercuric chloride. A preferred form of catalyst is aluminum metal or a compound of aluminum, with diphenylamine containing a Friedel-Crafts catalyst or Fuller's earth, especially mixtures of aluminum metal with diphenylamine containing aluminum chloride, boron tri-fluoride or Fuller's earth. A particularly preferred form of catalyst for the orthoalkylation step consists of a mixture of aluminum chloride with an alkali metal, especially sodium metal which provides a particularly active form of orthoalkylation catalyst probably consisting of aluminum metal in combination with aluminum chloride.

Normal catalytic amounts of the catalyst are desirably employed in the orthoalkylation process, for example, an amount of catalyst within the range of from 0.1 percent to 10 percent by weight based on the weight of diphenylamine starting material. The total content of aluminum in the catalyst, where a mixed catalyst is used, may vary widely but is preferably within the range of from 10 percent to 90 percent by weight based on the total weight of the catalyst.

If desired, the orthoalkylation reaction may be carried out at substantially atmospheric pressure but is advantageously effected at superatmospheric pressure and at an elevated temperature. The reaction is preferably conducted in a pressure reactor, optionally equipped with an agitating device. The reaction temperature may be, for example, within the range of from 150.degree. to 400.degree. C.

Preferably, the orthoalkylation step is effected by reacting the diphenylamine and the gaseous olefine reactant in a sealed reactor at a superatmospheric pressure within the range of from 2 to 400 atmospheres. The progress of the reaction may be followed by observing the degree of the drop in pressure as the gaseous olefine is consumed.

On completion of the orthoalkylation reaction, the desired 2- and/or 2:2'-di-ortho-alkylated diphenylamine may be separated from the reaction mixture by conventional techniques, for example by fractional distillation under reduced pressure.

Subsequent to the orthoalkylation step, the orthoalkylated compound is further alkylated by contacting said orthoalkylated diphenylamine with the secondary olefine having from four to 12 carbon atoms per molecule in the presence of a Friedel-Crafts or Bronsted acid catalyst, and preferably at atmospheric pressure. It is particularly preferred to use a Friedel-Crafts catalyst in the further aklylation step. Suitable Friedel-Crafts catalysts include ferric chloride, stannic chloride, zinc chloride, boron trifuloride and diethyl ether complexes thereof, titanium tetrachloride and, preferably, aluminum chloride especially in a substantially anhydrous form.

Suitably secondary olefines include iso-butylene, 2-methyl pentene-1, diisobutylene and propylene trimer.

If a Bronsted acid catalyst is employed it may be, for example, sulphuric acid, phosphoric acid, an organic sulphonic acid, a dialkyl sulphate or a mixture of two or more thereof.

If sulphuric acid is present as a catalyst, it may be for example, in the form of concentrated sulphuric acid, oleum or an aqueous solution of the acid, but is preferably sulphuric acid monohydrate, namely an equimolar mixture of concentrated sulphuric acid (H.sub.2 SO.sub.4) and water. If phosphoric acid is present as catalyst, it may be, for example, in the form of orthophosphoric acid or an aqueous solution of the orthophosphoric acid, for instance a substantially equimolar mixture of orthophosphoric acid (H.sub.3 PO.sub.4) and water.

The proportion of Friedel-Crafts or Bronsted acid catalyst which is employed in the process of the present invention is conveniently within the range of from 0.01 to 1.5 moles of catalyst per mole of orthoalkylated diphenylamine compound, a proportion of Friedel-Crafts or Bronsted acid catalyst within the range of from 0.1 to 0.5 mole of catalyst per mole of orthoalkylated diphenylamine compound being especially preferred.

The para-alklylation step is advantageously carried out in the absence of an added inert solvent. Thus if the olefine is a liquid olefine such as diisobutylene the para-alkylation step is conveniently effected by charging the reactants into a reactor and using excess liquid olefine as the reaction solvent. On the other hand, if the olefine reactant is gaseous, the reaction mixture is desirably charged into a reactor and the gaseous olefine blown through the molten orthoalkylated diphenylamine starting material containing the Bronsted acid or Friedel-Crafts catalyst. The rate at which the gaseous olefine is blown through the reaction melt is advantageously within the range of from 50 milliliters to 300 milliliters per minute, per mole of o-alkylated diphenylamine.

If the para-alkylation step is effected using a liquid olefine reactant, the reaction temperature is preferably within the range of from 80.degree. to 200.degree. C. If, however, the para-alkylation reaction step is effected using a gaseous olefine the reaction temperature is preferably the minimum temperature which is sufficient to maintain a reaction melt through out the reaction period. In the latter case, normally and preferably the temperature of the reaction melt is within the range of from 100.degree. to 200.degree. C. and the reaction is also preferably conducted in an inert atmosphere, for instance a nitrogen atmosphere.

The para-alkylation step is preferably concluded in the presence of a substantial excess of the secondary olefine reactant over the stoichiometric proportion required. Thus, for example, the proportion of secondary olefine is preferably within the range of from 2.0 to 3.0 moles per mole of orthoalkylated diphenylamine.

On completion of the para-alkylation reaction the desired tri- and/or tetra-alkylated diphenylamine may be isolated from the final reaction mixture by any conventional technique. For instance, the final reaction mixture may be dissolved in an organic solvent, such as toluene or xylene and washed with aqueous sodium hydroxide and then with water, to neutrality. Removal of the organic solvent then provides the crude reaction product which may be further purified, if desired, by distillation, for instance under reduced pressure and/or by recrystallisation from a suitable solvent such as ethanol.

The compounds having the formula:

wherein R is hydrogen or a teriary-butyl group, can be also produced by contacting in a single stage diphenylamine with iso-butylene in the presence of a Friedel-Crafts or Bronsted acid catalyst.

The process of producing a compound of formula II is conveniently effected by charging the diphenylamine starting material and the Friedel-Crafts or Bronsted acid catalyst into a reactor and heating the mixture to a temperature above its melting point, for instance to a temperature within the range of from 60.degree. to 200.degree. C. more preferably within the range of from 100.degree.to 200.degree. C., and passing the iso-butylene through the reaction melt. The rate at which the iso-butylene is passed through the melt is desirably within the range of from 50 milliliters to 300 milliliters per minute. Desirably the process is conducted in an inert atmosphere, especially in an atmosphere of nitrogen.

In order to produce predominantly the preferred used compound of Formula II, that is 2:2':4:4'-tetra-tertiary butyl diphenylamine, the iso-butylene gas is advantageously passed through the molten reaction mixture until the iso-butylene ceases to be absorbed by the melt. The time required to achieve the maximum absorption of isobutylene at the preferred rate of passage through the melt, defined hereinbefore, is normally within the range of from 2 to 10 hours. If, however, it is desired to produce predominantly 2:2':4-tri-t-butyl dipehnylamine, the passage of iso-butylene is desirably terminated when substantially three molecules of iso-butylene have been absorbed per mole of diphenylamine starting material.

On completion of the reaction, the desired tri- or tetra-t-butyl diphenylamine may be separated from the other components of the reaction mixture by conventional methods. For example, the crude reaction mixture may be dissolved in an organic solvent such as toluene or xylene, washed with aqueous alkali, especially aqueous sodium hydroxide, and water to neutrality, and subsequently fractionally distilling the washed residue. The product so obtained may be further purified, if desired, by fractional crystallization from an organic solvent, particularly methanol or ethanol.

While the reaction may be effected at an elevated pressure if desired, it is preferred that the reaction is conducted at substantially atmospheric pressure in order to avoid the use of expensive pressure equipment.

The Friedel-Crafts or Bronsted catalyst employed in the process of producing the compound of Formula II may be any of the catalysts within the groups specified hereinbefore. However, it is particularly preferred to use aluminum chloride in any form of this catalyst which possesses a high degree of activity in promoting Friedel-Crafts alkylation processes. A particularly preferred form of the catalyst consists of the freshly-prepared, substantially anhydrous material. The catalyst is desirably employed in conventional catalytic amounts, for example in a proportion within the range of from 0.1 percent to 10 percent by weight based on the total weight of the diphenylamine starting material.

The compositions obtained by the present invention preferably contain a proportion of antioxidant of the present invention within the range of from 1.001 percent to 5.0 percent by weight based on the weight of the organic material. More preferably, the compositions contain a proportion of antioxidant within the range of from 0.1 percent to 4.0 percent by weight based on the weight of the organic material. The amount of antioxidant employed in any particular organic material will depend not only on the nature of the organic material but also on the external conditions under which the material is to be used. Thus organic materials to be used at normal temperatures will usually require a smaller proportion of antioxidant than organic materials, such as synthetic lubricants, designed for use at elevated temperatures.

A particular class of organic material susceptible to oxidative deterioration for which the compounds used according to the present invention are particularly valuable as antioxidants is that consisting of synthetic lubricants, especially those derived from carboxylic esters and intended for use at temperatures at or above 400.degree. F.

Examples of such esters include lubricants based on a diester of a dibasic acid and a monohydric alcohol, for instance dioctyl sebacate or dinonyl adipate; on a triester of 1:1:1-trimethylol propane and a monobasic acid or mixture of such acids, for instance 1:1:1-trimethylol propane tripelargonate, 1:1:1-trimethylol propane tricaprylate or mixtures thereof; on a tetraester of pentaerythritol and a monobasic acid or mixture of such acids, for instance pentaerythritol tetracaprylate; or on complex esters derived from 1:1:1-trimethylol propane, caprylic acid and sebacic acid; or on mixtures thereof.

In addition to the compound of formula I, the synthetic lubricant may also contain other additives such as further antioxidants, metal passivators, rust inhibitors, viscosity index improvers, pour-point depressants, dispersants or detergents, extreme pressure or antiwear additives, antifoams, antiknock additives and antiicing additives or carburetor detergents.

Suitable examples of further antioxidants include those contained in the following groups (a) to (h):

a. Alkylated and non-alkylated aromatic amines and mixtures thereof, for example dioctyldiphenylamine; mono-t-octylphenyl-.alpha. and .beta.-naphthylamines; dioctylphenothiazine; Phenyl-.alpha.-naphthylamine;

b. Hindered phenols, for example 2,6di-tertiarybutyl-p-cresol; 4,4'-bis-(2,6-diisopropylphenol); 2,4,6-triisopropylphenol; 2,2' thio-bis-(4-methyl-6-tert-butylphenol);

c. Alkyl, aryl or alkaryl phosphites, for example, triphenyl-phosphite; trinonylphosphite; diphenyldecylphosphite;

d. Esters of thiodipropionic acid, for example, dilaurylthiodipropionate;

e. Salts of carbamic and dithiophosphoric acids, for example, antimony diamyldithiocarbamate, zinc diamyldithiophosphate;

f. Metal salts, complexes of organic cholating agents for example, copper bis (trifluoroacetylacetonates), copper phthalocyanines, tributyl ester of EDTA, monosodium salt;

g. Free radical antioxidants and their precursors, for example, amine oxides and nitroxides;

h. Combinations of two or more antioxidants from any of the above sections, for example, an alkylated amine and a hindered phenol.

Examples of suitable metal passivators include those of the following types:

a. for copper, for example, benzotriazole, 5,5'-methylene-bisbenzotriazole, tetrahydrobenzotriazole, 2,5-dimercaptothiadiazole, salicylidene-propylenediamine, salts of salicylalaminoguanidine; and quinizarin;

b. for magnesium, for example, propyl gallate;

c. for lead, for example, sebacic acid.

Rust inhibitors which may be employed in the lubricant compositions include those of the following groups:

a. Organic acids, and their esters, metal salts, anhydrides for example, N-oleoyl sarcosine, sorbitan mono-oleate, lead naphthenate and dodecenylsuccinic anhydride.

b. Nitrogen-containing materials, for example,

i. primary, secondary or tertiary aliphatic or cycloaliphatic amines and amine salts of organic and inorganic acids, for example, morpholine, stearyl amine and triethanolamine caprylate.

ii. heterocyclic compounds, for example, imidazolines, and oxazolines.

c. Phosphorous-containing materials, for example, inorganic phosphates, phosphonic acids and amine phosphates.

d. Sulphur-containing materials, for example, barium dinonylnaphthalene sulphonates.

Suitable viscosity index improvers or pour-point depressants are, for instance, polyacrylates, polybutenes and polyvinyl pyrrolidones.

Examples of dispersant or detergents include metal sulphonates especially calcium, barium and magnesium salts, metal phenates and polybutenyl succinimides.

Extreme pressure or antiwear additives appropriate for use in the lubricant composition include sulphur and/or phosphorus and/or halogen containing materials, for instance, sulphurized sperm oil, tritolyl phosphate and chlorinated paraffins.

Silicones are particularly suitable as antifoams and lead alkyls are eminently suitable as antiknock additives for the lubricant compositions of the invention.

Examples of antiicing additives or carburetor detergents include, for instance, glycol ethers, imidazolines and amine phosphates.

Other organic materials susceptible to oxidative degradation for which the compounds used according to the present invention are valuable antioxidants, include, for instance, substances falling within the following groups:

a. materials consisting of, or based on, aliphatic or other hydrocarbons, for instance, gasoline, lubricating oils, lubricating greases, mineral oils and waxes.

b. natural and synthetic polymeric materials, for instance, natural rubber; synthetic addition polymers such as homopolymers and co-polymers of vinyl and vinylidene monomers including ethylene, propylene, styrene, butadiene, acrylonitrile, vinyl chloride or vinyl acetate; synthetic polymers derived from condensation reactions and containing either ester, amide or urethane groups, for instance, alkyd and polyamide resins and fibers.

c. non-polymeric oxygen-containing substances, for instance, aldehydes such as n-heptaldehyde, and unsaturated fatty acids or esters thereof, for instance, methyl oleate and ricinolcic acid.

d. organo-metalloid substances such as silicone polymers. for instance, polydimethylsiloxanes, polymethylphenylsiloxanes and chlorinated derivatives thereof; silanes, for instance, tetra-alkyl and tetra-aryl silanes; and organo-metallic substances such as organo-metallic polymers.

e. vitamins, essential oils, ketones and ethers.

The compounds of Formula I may be employed in multi-ingredient compositions, that is compositions containing at least one organic substance susceptible to oxidative deterioration or a mixture thereof and one or more organic or inorganic compounds, for instance, an alcoholic or aqueous emulsion of an organic material susceptible to oxidative deterioration.

The present invention is further illustrated by the following examples. Parts and percentages expressed therein are by weight unless otherwise stated.

EXAMPLE 1

69 Parts of 2:2'-diethyldiphenylamine and 0.7 part of anhydrous aluminum chloride were charged into a reactor and the mixture heated to 130.degree. C., cooled to 100.degree. C. At this temperature 85.9 parts of diisobutylene were added to the mixture over a period of 2 hours and the mixture was then heated under reflux conditions until the temperature of the reflux mixture reached 160.degree. C. After cooling, the reaction mixture was taken up in 500 parts of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum furnished 110.7 parts of a crude product as an oil. This oil was distilled to give a product which solidified on cooling. Recrystallization of this solid from ethanol gave 2:2'-diethyl-4:4'-di-t-octyl diphenylamine having melting point of 63.degree. C. and having the following elemental analysis by weight:

Found Calculated(for C.sub.32 II.sub.51 N) carbon 85.70% 85.46% hydrogen 11.51% 11.43% nitrogen 3.18% 3.11%

EXAMPLE 2

169 Parts of diphenylamine and 4.4 parts of anhydrous aluminum chloride were charged into a reactor and the mixture heated to a temperature of 140.degree. C. under an atmosphere of nitrogen to give a liquid melt. Isobutylene was then passed through the melt at a rate of 200 milliliters per minute until absorption of isobutylene ceased, after a period of 5.5 hours. After cooling, the reaction mixture was taken up in 500 parts of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum to give a viscous brown oil which slowly solidified. Recrystallization of this solid from ethanol gave 2:2':4:4'-tetra-t-butyl diphenylamine having melting point of 161.degree. to 162.degree. C. and the following elemental analysis:

Found Calculated (for C.sub.28 H.sub.43 N) carbon 85.48% 85.43% hydrogen 10.84% 11.01% nitrogen 3.65% 3.56%

EXAMPLES 3-5

A synthetic ester-based lubricant was formulated and subjected to the Pratt and Whitney Type II oxidation-corrosion test. The base fluid was a complex ester derived from sebacic acid, caprylic acid and trimethylol propane, the complex ester being described and claimed in British Pat. No. 971,901. Each test was carried out for 48 hours at a temperature of 425.degree. C. using dry air at a rate of 5 liters per hour and in the presence of specimens of magnesium alloy, aluminum alloy, copper, silver and steel.

To each lubricant sample there was added, prior to commencing the test, a proportion of a new compound of the present invention and a proportion of benzotriazole. For the purposes of comparison, further tests were carried out using a control lubricant composition containing no antioxidant and also using a lubricant composition containing diphenylamine or 4:4'-di-t-octyldiphenylamine and benzotriazole.

The results achieved are summarized in the following Table I: ##SPC1##

The data shown in Table I illustrate well the excellent properties of the lubricant compositions of the present invention especially with respect to low sludge formation and magnesium and copper attack, compared with the control composition and also compositions comprising previously-known additives.

EXAMPLE 6

The following synthetic rubber formulation was made up:

styrene/butadiene copolymer rubber 100.0 parts zinc oxide 5.0 parts stearic acid 2.0 parts titanium dioxide 10.0 parts hydrated silica 50.0 parts dibenzthiazole disulphide 1.5 parts tetramethylthiuram disulphide 0.25 parts sulphur 2.0 parts di-ethylene glycol 3.0 parts product of Example 2 1.0 part

The formulation was prepared on a two-roll mill in the cold using a tight nip initially over a period of 35 minutes according to the following sequential procedure:

1. Bond the copolymer rubber

2. Add zinc oxide and antioxidant

3. Add fillers and diethylene glycol/stearic acid alternately

4. Finally add sulphur and both disulphide ingredients

5. Remove from mill.

The sample was then vulcanized by cutting a 6.0 inch .times. 6.0 inch .times. 0.050 inch sheet from the milled sheet and curing the former for 40 minutes at 153.degree. C.

Various physical properties of both the aged and unaged rubber were then determined, the details of the evaluations being set out in the following Tables II and III. Details of the test methods used are shown at the foot of each of the tables. For the purpose of comparison, results relating to control experiments and to experiments using the same amount of a previously-known antioxidant are also shown in Tables II and III. ##SPC2## ##SPC3##

The results in Tables II and III demonstrate the excellent physical properties of the unaged and aged and/or cured rubber compositions containing a new antioxidant compound of the present invention. Thus, for example it can be seen from the data in Table II that the compositions of the present invention give lower stress and hardness figures than the control and prior art compositions, thus indicating a desirably softer and more flexible product. Similarly, these excellent properties are retained to a much higher degree as indicated by the date in the lower half of Table II.

The data in Table III on the other hand, illustrates well the excellent stain-resistant characteristics of the compositions of the present invention compared with the control composition and the prior art compositions.

EXAMPLE 7

75.12 Parts by weight of 2,2'-di-ethyldiphenylamine and 1.5 parts by weight of anhydrous aluminum chloride were charged into a reactor and the mixture heated to a temperature of 140.degree. C. under an atmosphere of nitrogen to give a liquid melt. Isobutylene was then passed through the melt at a rate of 200 milliliters per minute until absorption of isobutylene ceased, after a period of 3 hours. After cooling, the reaction mixture was taken up in 300 parts by weight of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum yielded 112 parts by weight of 2,2'-diethyl-4,4'-di-t-butyl diphenylamine as a yellow viscous oil having boiling point 154.degree. C. at 0.05 millimeters of mercury pressure and the following elemental analysis:

Found Calculated (for C.sub.24 H.sub.35 N) carbon 85.64% 85.40% hydrogen 10.49% 10.45% nitrogen 3.99% 4.15%

EXAMPLE 8

169 Parts by weight of diphenylamine and 4.4 parts by weight of anhydrous aluminum chloride were charged into a reactor and the mixture heated to a temperature of 140.degree. C. under an atmosphere of nitrogen to give a liquid melt. Isobutylene was then passed through the melt at a rate of 200 milliliters per minute until absorption of isobutylene ceased, after a period of 5.5 hours. After cooling the reaction mixture was taken up in 500 parts by weight of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum yielded a viscous brown oil which slowly solidified. Recrystallization of this solid from ethanol yielded 112 parts by weight of 2,2',4,4'-tetra-t-butyldiphenylamine having a melting point of 161.degree. to 162.degree. C. Evaporation of the filtrate to dryness yielded an oily solid which was dissolved in ether and saturated with hydrogen chloride gas to remove 48.0 parts by weight of 4,4'-di-t-butyldiphenylamine as the hydrochloride, the ether filtrate was evaporated to dryness and the residual solid recrystallized from methanol to yield 124 parts by weight of 2,4,4'-tri-t-butyldiphenylamine having a melting point of 106.degree. to 107.degree. C. and the following elemental analysis:

Found Calculated (for C.sub.24 H.sub.35 N) carbon 85.30% 85.40% hydrogen 10.75% 10.45% nitrogen 4.34% 4.15%

EXAMPLE 9

169 parts by weight of diphenylamine and 4.4 parts by weight of anhydrous aluminum chloride were charged into a reactor and the mixture heated to a temperature of 140.degree. C. under an atmosphere of nitrogen to give a liquid melt. The reaction mixture was then cooled to 100.degree. C. and 336 parts by weight of diisobutylene were added over a period of 15 minutes, the reaction mixture was then refluxed for a further 48 hours. After cooling, the reaction mixture was taken up in 500 parts of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum furnished 400 parts of a crude product as an oily solid. Recrystallization of this solid from ethanol gave 299.7 parts of 4,4'-di-t-octyldiphenylamine having a melting point of 100.degree. to 102.degree. C. Removal of ethanol under vacuum from the mother liquor yielded 100 parts of a black viscous oil. This oil was distilled under vacuum to yield 55.6 parts of an oil which slowly solidified and was shown by comparison with authentic samples to be a mixture of diphenylamine, 4-t-octyldiphenylamine and 4,4'-di-t-octyldiphenylamine. The residue from the distillation was triturated with 60.degree. to 80.degree. C. petroleum ether to yield 15.3 parts of 4,4' di-t-octyldiphenylamine. The residue was then chromatographed on a basic alumina column using 60.degree. to 80.degree. C. petroleum ether to yield 1.3 parts of a viscous yellow oil which slowly solidified. Recrystallization from ethanol yielded 2-t-butyl-4,4'-di-t-octyldiphenylamine as a pale yellow solid having a melting point of 116.degree. to 118.degree. C. and the following elemental analysis:

Found Calculated (for C.sub.32 H.sub.51 N) carbon 84.56 85.50 hydrogen 11.29 11.44 nitrogen 3.19 3.18

EXAMPLE 10

7.2 parts of 2-isopropyldiphenylamine and 0.14 parts of anhydrous aluminum chloride were charged into a reactor and the mixture heated to 140.degree. C. under an atmosphere of nitrogen to give a liquid melt, cooled to 100.degree. C. and 15.4 parts of diisobutylene were added over a period of 15 minutes. The reaction mixture was then refluxed for a further 15 hours. After cooling, the reaction mixture was taken up in 100 parts of toluene and washed with aqueous 10 percent sodium hydroxide and then with water to neutrality. Removal of the toluene solvent under vacuum furnished 13.9 parts of a crude product as an oil. Separation on a basic alumina column yielded 2-isopropyl-4,4'-di-t-octyldiphenylamine as a pink oil having the following elemental analysis:

Found Calculated (For C.sub.31 H.sub.49 N) carbon 85.13 85.42 hydrogen 11.34 11.34 nitrogen 3.07 3.22

EXAMPLE 11

9.9 parts of 2,2'-di-isopropyldiphenylamine and 0.16 parts of anhydrous aluminum chloride were charged into a reactor and the mixture heated to a temperature of 140.degree. C. under an atmosphere of nitrogen to give a liquid melt. Isobutylene was then passed through the melt at a rate of 200 milliliters per minute until absorption of isobutylene ceased, after a period of 5 hours. After cooling, the reaction mixture was taken up in 100 parts of toluene and washed with aqueous sodium hydroxide and then with water to neutrality. Removal of toluene solvent under vacuum furnished 12.8 parts of a pink oil which slowly solidified. Recrystallization of this solid from ethanol yielded 2,2'-di-isopropyl-4,4'-di-t-butyldiphenylamine as white needles having a melting point of 65.degree. to 66.degree. C. and the following elemental analysis:

Found Calculated (for C.sub.26 H.sub.39 N) carbon 84.63 85.38 hydrogen 10.94 10.75 nitrogen 3.94 3.82

EXAMPLES 12, 13 and 14

0.15 percent (weight/volume) solutions of 2:4:4'-tri-t-butyldiphenylamine and 2:2'-di-ethyl-4:4'-di-t-butyldiphenylamine respectively in acetone were made up. To each of these solutions were added 40 parts by weight of unstabilized polypropylene powder. A further 60 parts by volume of acetone were added to each mixture to form slurries which were hand mixed to ensure homogeneity. The solvent was then removed from each slurry by evaporation.

Samples of the respective dry powders were then placed in a mould (6.0 inches .times. 6.0 inches .times. 0.015 inch). The mould was then heated in a press under constant pressure for 5 minutes. A pressure of 20 tons/square inch was applied for 1 minute, cooling was commenced and pressure increased so that when the temperature reached 150.degree. C., the pressure was 80 tons/square inch. Cooling was continued to 50.degree. C., when the mould was removed from the press.

An oven aging test was carried out using strips from the pressings (the strips being 6.0 .times. 1.0 inch) in an air circulating oven maintained at 150.degree. C. The time taken for the test strip to fail by cracking on flexing the sample through 180.degree. C. was noted.

The results achieved, including a control experiment, are set out below: ##SPC4##

EXAMPLES 15-17

The following synthetic rubber formulation was made up:

styrene/butadiene copolymer rubber 100 parts zinc oxide 5 parts stearic acid 2 parts clay filler 50 parts sulphur 2 parts dibenzothiazolyl disulphide 1.5 part accelerators tetramethylthiuram disulphide 0.25 part antioxidant under test 1 part

The formulations were prepared on a two-roll mill according to the following sequential procedure:

1. Mastication of the rubber for 2 to 3 minutes.

2. Addition of zinc oxide, stearic acid and antioxidant.

3. Addition of part of the clay after 5 minutes.

4. Addition of remainder of the clay after 15 minutes.

5. Addition of accelerators after 20 minutes.

6. Addition of sulphur, cutting and rolling after 25 minutes.

7. Grinding, six passes through a tight nip.

The optimum cure times for the various samples were then determined using the R.A.P.R.A. (Rubber and Plastics Research Association) Curometer. The samples were then vulcanized at 153.degree. C. for a period of the respective optimum cure time plus 2 minutes.

Various physical properties of both the aged and unaged rubber compositions were determined, the details of the evaluations being set out in the following Table IV. References to the test methods used are shown at the foot of the table. For the purpose of comparison, Table IV also contains details relating to a control experiment. ##SPC5##

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