CA1064691A - Unsymmetrical n,n'-di(sec-alkyl)p-phenylenediamines and n,n'-dialkyl-p-phenylenediamine mixtures - Google Patents

Abstract

ABSTRACT OF DISCLOSURE
Dialkyl-p-phenylenediamine compositions are described selected from the group consisting of N-isopropyl-N'-5-methyl-3-heptyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-1,4-dimethyl-pentyl-p-phenylenediamine and mixtures comprising first component of symmetrical N,N'-di(sec-hexyl)-p-henylene-diamine in less than 50% by weight of the total composition, second component of unsymmetrical N-(sec-hexyl)-N'-(sec-alkyl)-p-phenylenediamine having 7 or 8 carbon atoms in said sec-alkyl in amount greater than the first component and third component of symmetrical N,N'-di(sec-alkyl)-p-phenylenediamine having 7or 8 carbon atoms in each alkyl group which compositions are useful for preservation of organic materials.

Description

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This invention r~lates to dialkyl-~-phenylenediamines and mixtures thereof, to diene elastomers preserved therewith and to the preparation of such mixtures. More particularly, it relates to unsymmetrical di-secondary alkyl-~-phenylenediamines, to mixtures of symmetrical and unsymmetrical di-secondary alkyl ~-phenylenediamines, to processes for preparation ~hereof and to rubber compositions preserved therewith.
BACKGROUND OF THE INVENTION
Di(sec-alkyl)-p-phenylenediamines are powerful anti-oxidants and antiozonants for the preservation of diene rubber.
Higher members of 7 or 8 carbon alkyl groups having high anti-oxidant and antiozonan~ properties, acceptable low volatility and low skin burning ef~ect are produced from ketones of 7 or 8 carbon atoms and have become widely accepted in the rubber industry. ~he high antidegradant activity, availability and economy of the raw materials recommend lower alkyl groups.
However, the lower members of the series are volatile skin irritants with the result that not only are they rapidly lost from the rubber with resultant loss of preservative action but cause serious discomort to workmen. Unfortunately, ketones of 7 and 8 carbon atoms are limited in supply and expensivé. More~
i over, rubber preserved with 6 carbon atom alkyl compound, N,N'-di~l,4-dimethylbutyl)-~-phenylenediamine, from the more available, methyl i~obutyl ketone, gives evidence of being a skin sensitizer.
The ability of an agent to elicit a primary skin irritation is i ~
wholly different from that of producing skin sensitization.
Moreover, the product from methyl isobutyl ketone is a mixture o stereo i~omers which tend to form a semi-crystalline mass on standing.

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Certain unsymmetrical dialkyl-p-phenylenediamines are known. For example, certain unsymmetrical dialkyll~-phenylene~
diamines in which one alkyl is derived from an aldehyde and the other from a ketone are described in U.S. Patent No. 3,504,032 and test results described which indicate tha~ they possess antidegradant activi~y for diene elastomers comparable to that of the symmetrical N,N'-di(sec-alkyl)-~-phenylenediamines having 7 or 8 carbon atoms in each alkyl group which have become widely accepted in the rubber industry. However, reaction with aldehydes is difficult to control and leads to excessive by-product formation. Moreover, the requirements of low volatility and high degree of safety to workmen coming ` ~
., ,~.., in contact with ei~her the antidegradant or preserved rubber are severely limiting of practically usable antidegradants.
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SUMMARY OF THE INVENTION ;-~
It has been found that N-1,3-dimethylbutyl-N'-1,4-dimethylpentyl-~-phenylenediamine and N-isopropyl-N'-5-methyl~
... . .
3-heptyl-~-phenylenediamine are valuable, improved antidegrad-~ ants which present little or no hazard to workmen coming in .
;1~ 20 contact with rubber containing it. They irnpart unusally high ~ ~-~ resistance to degradation of diene elastomers by oæone under i both static and dynamia canditions. Waxes provide significant :; ~
protection from ozane under static conditions but antidegradants are required to supplement the static protection and to provide protection under conditions in which the elastomer i5 strained ;
or continually ~lexed.
In accordance with another embodiment of this invention, it has been found that dialkyl-p-phenylenediamine compositions obtainable from mixtures of 6 carbon atom ketones with 7 or 8 carbon atom ketones are characterized by an unexpectedly high ., . `~ . ".

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proportion of unsymmetrical dialkyll~-phenylenediamine and are valuable antidegradants, safe to use, having desirable physical properties. The compositions are antioxidants for diene elastomers, herein designated as "rubber," and other organic materials which deteriorate by absorption of oxygen from the atmosphere. They are also potent rubber antiozonants.
The preferred compositions are characterized by N,N'-di(sec-hexyl)-~-phenylenediamine content less than 50~ by weight of the total composition, unsymmetrical dialkyl-~-phenylenediamine in amount greater than N,N'-di(sec-hexyl)-~phenylenediamine and a proportion of symmetrical N,N'-di(sec-alkyl)-~-phenylenediamine of 7 or 8 carbon atoms in each alkyl group. Such compositions form directly from reductive alkylation of ~-nitroaniline or ~-phenylenediamine with a mixture of 6 - ;
-~ carbon atom ketone and at least one 7 or 8 carbon atom ketone.
It is believed that the undesirable properties of N,N'-di-.,, : .
(sec-hexyl)-~-phenylenediamine are suppressed in the mixtures ;
~nd that the high proportion of unsymmetrical dialkyl-p-phenylenediamine results from the influence o~ intermediate 20 monoalkylate which favors itsformation and from a favorable ~-r~activity relationship between the ketone reactants. The~-~
reactivity refers to total reactivity in the sequence of reaction~ involued in reductive alkylation. Thus, it will be appreciated that the ~ormation of product mixtures having -~
the compositions described is dependent upon unpredictable . ., total reactivities found to be conducive to formation of mixtures having a high proportion of unsymmetrical product.
Rubber compositions containing the mixtures exhibit little or no toxicity to human skin.
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The preferred 6 carbon atom ketone is methyl isobutyl ketone and the preferred 7 and 8 carbon atom ketones are methyl isoamyl ketone, 2-heptanone and 2-octanone. Other ketones having similar total reactivity ratios may be substitutedO
The lower ketone is usually within the range of 0.5-3.0 moles per mole of the higher ketone which may itself be a mixture of ketones with 1:1 mole ratio being particularly desirable for producing compositions containing less than 20% of the symmet-rical di-seconaary hexyl-~-phenylenediamine.
DESCRIPTION OF PREFERRED EMBODIMENTS
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To a hydrogenatox is charged in 90 parts by weight (0.5 molecular proportion) of N-isopropyl-p-nitroaniline, ~;~
250 parts by weigh~ ~1.9 molecular proportions) of 5-methyl-3-heptanone, 6 parts by weight o~ acidic carbon co-catalyst ~ ;~
(Summers U.S. Patent 3,414,616) and 10 parts by weight of 1% ~ -platinum on carbon catalyst. The charge is subjected to hydrogen for 30 minutes at 14~06-21.09 kg/sq cm hydrogen ;
pressure at a temperature of 25-100C. Hydrogen pressure is then raised to 28.1 kg/sq cm and temperature to 120C and the ;
reaction continued for 3 hours. The reaction mixture is : .:
cooled to 50C, removed from the hydrogenator, filtered, and volatile constituents removed by heating in vacuo to 185C at 3-4 mm mercury pressure. The residue is 23 parts by weight of , ... .
N-isopropyl-N'-5-methyl-3-heptyl-~-phenylenediamine, a dark viscous liquid.
N-1,3-dimethyl-N'-1,4-dimethylpentyl-~-phenylenediamine -~
ix obtainable by condensing methyl isoamyl ketone with p-nitro- `~
aniline to ~orm the anil intermediate, reducing the anil to N-1,4-dimethylpentyl~-nitroaniline and condensing it with methyl isobutyl ketone under conditions for reductive alkylation. To ... . .
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prepare the N-1,4-dimethylpentyl-~-nitroaniline intermediate, 138 parts by weight (1 molecular proportion) of ~-nitroaniline, 120 parts by weight (1.05 molecular proportions) of methyl isoamyl ketone, 7 parts by weight of acidic carbon black catalyst (Summers U.S. Patent No. 3,414,616) and about 175 parts by weiyht of xylsne are chaxged to a suitable reactor and the mixture heated at refluxing temperature (144-153C) for about ~ -~-1/2 hours during which time a portion of the xylene and a little water is removed. There is ~hen added 1 part by weight of salicylic acid and heating continued at refluxing temperatuxe ~153C) for about 8 hours while collecting 15 parts by weight of water. There is then added 100 parts by weight of methyl soamyl ketone and heating continued at 153C until a total of 18 parts by weight of water have been removed. The reaction mixture is strlpped of solvent, 240 parts by weight of alcohol added and the resulting solution added to a slurry of 28 parts by ;

~i weight of sodium borohydride (NaBH4) in about 240 parts by , weight of ethyl alcohol at 50C. A solution forms which is -~
stirred for about 3 hours at 30-50C, filtered and the solvent removed from the iltrate by distilla~ion. Xylene is added and the xylene solution washed with water and moat of the xylene removed in vacuo.
- To conduct the next step, 3 molecular proportions ``
(300 parts by weight) of methyl isobutyl ketone, 1 molecular proportion of N-1,4-dimethylpentyl-p-nitroaniline in xylene prepared a~ described above, 8 parts by weight of 1~ platinum on carbon and 8 parts by weight of acidic carbon co-catalyst are chaxged to a suitable reactor. Reduction of the nitro group is effected at 110C, 14.06 kg/sq cm hydrogen pres~ure (200 lb~/sq in). The temperature is then increased to about ., .

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140C and the hydrogen pres~ure to 28.284 kg/sq cm. After about 2 hours, the pressure is released and the reaction mixtuxe cooled, filtered, water removed from the filtrate by distillation and the residue fractionated in vacuo collecting an amber liquid, b.p. 200-205C at 2-3 mm Hg pressure.
In another and preferred embodiment, N-1,3-dimethyl-butyl-~-nitroaniline is prepared by condensing p-nitrochloro-benzene with 2-amino-5-methylhexane. Into an autoclave is charged 117 parts by weight (0.75 molecular proportion) of p-nitrochlorobenzene, 258 parts by weight (2.25 molecular ~;
proportions) of 2-amino-5-methylhexane and 40 parts by weight ~2.25 molecular proportions) of water. The charge is heated ;
at 158-172C for about 15 hours at a pressure of 6.79-7.03 kg/s~ cm until the E~nitrochlorobenzene has essentially disappeared. The xesulting N-1,3-dimethylbutyl-~nitroaniline -is then alkylated as follows:
A hydrogenator is charged with 116 parts by welght (0.5 molecular proportion) of N-lr 3-dimethylbutyl-~-nitro-aniline, 200 parts by weight t~.0 molecular proportions) of methyl isobutyl ketone, 10 parts by weight of 1% platinum on carbon catalyst (50% wet) and 0.2parts by weight of acetic acid.
~he charge is heated at 100C under 28.12 kg/sq cm hydrogen ~`~
pressure for 4 hours, filtered and the filtrate stripped of volatiles by heating to 180C/5 mm Hg pressure. The residue ;
is distilled collecting N-1,3-dimethylbutyl-N'-1,4-dimethyl-pentyl-~-phenylenediamine, b.p~ 175C/l mm Hg pressure.
Mixtures of diallcyl-~-phenylenediamines of the invention preferablyare prepared by reductive alkylation of p-nitro~
aniline (PNA) with a mixture of ketone~. Reductive alkylation refers to the well-known process of reacting an amine or nitro 1~646~.

body, carbonyl compound, in this instance a ketone, and hydrogen in the presence of hydrogenation catalyst. The following example is illustrative:
To an autoclave equipped with a turbine of other suit-able agitator, coil for heating or cooling, thermowell, vents, rupture discs, appropriate sampling device and stainless steel filter is charged 138 parts by weight (1.0 mole) of PNA, 120 parts by weight tl.2 mole) of methyl isobutyl ketone (MIBX), 137 parts by weight (1.2 mole) of methyl isoamyl ketone (MIAK), ;
6.0 parts by weight of 1% platinum on carbon and 6 parts by weight of acidic carbon co-catalyst (Summers U.S. Patent 3,414,616). The autoclava reactor system is purged twice with nitrogen and twice with hydrogen, the agitator started (600 rpm) ~ -and the reactor contents heated to 95-100C. Hydrogen is fed - `
to the system (7.031 kg/sq cm) and the reactor contents held at ~-~
; 100-125C by cooling. After about 20 minutes, the temperature is raised to 145-150C and the pressure raised to about 29.8 kg/sq cm. A sample is withdrawn after 30 minutes and analyzed. ~;
~ A sample is taken every 30 minutes thereafter and mono-N-alkyl-~-phenylenediamine content is plo~ted against time on semilog paper and the plot extrapolated or interpolated to the time required to reach 2~ mono-N-alkyl-p-phenylenediamine such time being regarded as the end point of the reaction. The completed ;~
i batch is cooled and the autoclave vented, the hydrogen pressure being u~ed to discharge the contents through the filter.
Analysi~ of the product obtained gives as an average of t~o runs 18.6% N,N'-di(1,3-dimethylbutyl)-~-phenylenediamine, ~` -30.6% N,N'-di(1,4-dimethylpentyl)-~-phenylenediamine, and 50.2% N-~1,3-dim2thylbutyl)-N'-(1,4-dimethylpentyl)-~-phenylene-diamine.

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Typical results of reacting different MIBK/MIAK ratios by the aforesaid procedure are summarized in the Table below.
The charge of ketones is based on a charge of 138 parts by weight (1 mole) of PNA. Ca~alyst dosage is 6-7 parts by weight of 1% platinum on carbon and the same amount of acidi~ carbon black. The hydrogenations are generally effected at 60-120C
and 7.14 kg/sq cm (nitro reduction), after which the temperature is increased to 145-180C and the hydrogen pressure to about 28 kg/sq cm to complete the alkylation. End point of the ~-reaction is determined by the disappearance of monoalkylated product. In the Table "DiC-6" indicates N,N'-ditl,3-dimethyl- -~-butyl)-~-phenylenediamine, "Di C-7" indicates symmetrical . ~:; ., N,N'-di~sec~alkyl)-~-phenylenediamine having 7 carbon atoms `~
; in each alkyl group, namely N,N'-di~1,4-dimethylpentyl)-~
phenylenediamine ~from MIAK), N,N'-di(2-heptyl)-~-phenylene-dia~ine ~from 2-heptanonel and N~N'-di(2-octyl)-p-phenylene-diamine (from 2-octanone) and "mixed" :indicates the u~symmetrical N,N'-dialkyl-p-phenylenediamine having 1,3-dimethylbutyl as one -~
alkyl and a 7 or 8 carbon group depending upon the particular 20 hlgher ketone reactant a~ the other alkyl. -. , ;. ,, . ~ .
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TAsLE I

Ketone Composition of Product Record No. Parts by Wei~t Mole ~ Percent b~ Weight of Product MIBK MIAK of MIBK Di C-6 Di C-7 Mixed 6~035 86 196 33 4~2 54.0 41.8 71127 80 171 34 4.6 50.6 42.5 71125 115 121 50 16.7 28.5 52.6 71514 120 154(1) 50 21.6 27.2 51.1 68034 130 148 50 15.8 31.3 52.9 10 71135 130 148(2) 50 12.0 32.8 53.8 71134(3) 150 171 50 14.6 29.6 56.1 71170 138 116 57.5 25.0 23.8 51.2 71128 150 :91 65 35.9 11.0 49.3 68037 170 105 65 34.6 14.2 49.4 .: , ~ : -~ 71171 ~168 . 82 70 44 10.0 45.9~

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~ )2-~ctanone (2? 2-heptanone (3)Catalyst charge 7.6 parts by weight and co-catalyst charge ~, 6 parts by weight It will be appreciated that the components of the reaction products do not necessarily total 100% due to . experimental error in the analysis. Products No. 71125, 71127 :~ ~ :
. .
and 71128 ahow that incxeasing the mole percent of MIBK rom : 34 to 50 to 65~ in a total of 2.3 moles of ketone increases the Di C-6 component only to about 36%. Products No. 68035, .
68034 and 68037 show that similax increase of the mole percent o~ MI~K in a total o about 2.6 moles of ketone increases the Di C-6 component only to about 35~. Pxoducts No. 71170 and 30 71171 shaw that increasing the mole percent of MIBK ~rom 57.5 ~.
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to 70 in a to'cal of about 2.4 moles of ketone produces a product containing less than 50% Di C-6. Products No. 71514 from 2.4 moles total ketone and No. 71135 from 2.6 moles total ketone show that the composition of products from 2-octanone and 2 heptanone are similar to those from MIAK. In every case, more than 40% of the mixed isomer is present and its proportion exceeds that of the Di C-6 component. Preferred are ratios of the ketones which produce no more than about 25% of the Di C-6 ~ ~-component.
Rubber ozone resistance data for the products o this ~ -invention are illustrated by a method published by Decker and Wise, The Stress ~elaxation Method for Measuring Ozone Cracking, Rubber World, April 1962, page 66. The equipment ; ~ ~-comprises an oven serving as an ozone cabinet filled with ozone generating equipment and racks for both static and d~namic `~
testing. Static racks handle stocks at strains of 5, 10, 20, 30 and 40%. The dynamic rack is a reciprocal mechanism which -l imparts a 25% strain to the rubber test piece on movement of a top~plate which moves vertically with respect to a stationary bottom plate. The mechanism is driven at a rate of 90 cycles per minute by a gear mounted on the outside of the cabinet.

, The test pieces are 2-inch long T-50 ~ASTM D599-55) specimens died from standard ~tress strain test sheets (ASTM D15-57T).
They are mounted by placing the ends in radial slots milled into the edge3 of circular plates o the racks. The tab ends .
ik into circumferential grooves machined into the outer surface~ of the plates.
., :
The stress relaxation method is based on the principle that the effective cross-sectional area of a small test piece of rubber is reduced by ozone cracking. The extent of cracking ;, -11-~646~ ~

in a test piece i~ determined by measuring the forces re~uired to extend the test piece 100% before and after exposure to ozone. The ozone concentration for the test is 25 parts ozone/100 million parts air. As the strip begins to crack, the number of stress supporting rubber chains decreases and the force required to extend the strip 100% is reduced. The ratio of this force to ~he original force is calculated at ~ ~ -approximately 16-hour interval of exposure to ozone. The graph of force vs. time is essentially a s~raight line and the time required for obtaining a predetermined percent of the original force is determined from the graph. The ability of the rubber to resist ozone attack is evaluated by comparison of these times to times for suitable controls to reach corresponding percent of the original force. The percents of original moduli of the rubber test pieces are listed as percent retention in the Table infra and the times i to reach those retentions are recorded. Longer times indicate , ~ .
better ozone resistance of the rubber stock. The intermittent test comprises 2-hour cycles during which the specimens are exposed dynamically 15% of the time and during the remainder of the time are exposed tatically at 25% strain. ;`;
The test stocks comprise typical formulations for components of pneumatic tires. On the basis of 100 parts rubber, all parts are by weight and "oil extended SBR" ~`
; indicates styrene butadiene copolymer rubber having about 25% oil presenk.
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Oil extended SBR 137.5 Furnace carbon black (ISAF) 65 Zinc oxide 3 Stearic acid Aromatic type oil 1.5 ;
Sulfur 2 .1 tert-butyl-2-benzothiazole- 1.2 ~ :.
.l sulfenamide , .~ . ~ .
Anti~egradant (where present) 2.0 Stock 1 is a control stock containing no antidegradant. '.,',~
Stock 2 contains as antidegradant N,N'-di(5-methyl-3-heptyl)~
~-phenylcnediamine and Stock 3 contains as the antidegradant N-isopropyl-N'-5-methyl-3 heptyl-~-phenylenediamine. The stocks -are: cured in a press and determinations are made on the cured : .
unaged.samples and on cured samples aged in an oven for 24 hours .::
at 100C. ~ ... . -.~ TABLE II
,-:
Stock

2 3 ~ ~.

20 :; Unaged dynamic ozono resistance~

: 80%~retention, hours 17 59 57 Unaged:stati~ ozone~resistance~

00% retention, hours ~ 14 69 >192 ~ Unaged Intermittent ozone resiutance:

r ~ 80% retention,~hours 6 48 64 i~

Aged dynamic ozone resistance: .

; 80% retention, hours 22 32 27 ;
. .. .
Aged static ozone resistanceg -:~

80% retention, hours 18 26 23 :.:; :::m :
: ` :
Aged intermittent ozone re~istance:

: 80% retention, hour~ 22 30 26 .. : .
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The improvement in unaged static ozone resistance of Stock 3 over Stock 2 i9 especially significant because the dialkyl-~-phenylenediamine antidegradants are used primarily for short term static protection. They migrate to the rubber surface more ~uickly than the N-alkyl-N'-aryl-~-phenylene-diamine antidegradants and provide excellent early protection to the rubber.
Another test stock comprises:

- Styrene-butadiene copolymer rubber 100 (SBR 1500) ; Carbon black (HAF) 50 Zinc oxide 4 , Stearic acid 2 ~ydrocarbon oil processing aid10 ;`-Sulfur 1.75 ~, ..
Morpholinothiobenzothiazole Antidegradant ~where pxe ent) 2 ;~
Stock 4 i~ a control stock containing no antidegradant. Stock 5 contains symmetrical N,N'-di(lr3-dimethylbutyl)-p-phenylene-diamine. Stock 6 contains the new N-1,3-dimethylbutyl-N'-1,4-dimethylpentyl-~-phenylenediamine. Stock 7 contains 1 part each of N,N'-di(1,3-dimethylbutyl)-~-phenylenediamine and N,N'-di(l,4-dimethylpentyl)- r phenylenediamine. Stock 8 contains -~
symmetrical N,N'-di(1,4-dimethylpentyl)-~-phenylenediamine.
Static ozone tests of only a few of the stocks fa11 to a 90%
level so that the Ytocks cannot be compared by the aforedes-cribed method. :

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TABLE III
_ _ Stock Dynamic ozone resistance~
90% retention, hours 5 33 36 . 32 32 :
; 80% retention, hours 10 47 49 47 44 ; 70~ retention, hours 16 58 60 58 55 Static ozone resistance~
90~ retention, hours 3 >208 >208 >208 208 .`-Intermittent ozone xesistance~
90% retention, hours 2 29 33 31 28 ~ :
80% retention, hours 7 42 . 46 44 41 70% retention, hours 11 54 57 56 52 : Commerclal use is generally in conjunction with a wax.
Thus, a typiaal foxmulation for the sidewall of pneumatic tires ~;;:
: comprises~
cis-4-Polybutadiene rubber 30 Oil extended SBR ~ 96 : General purpose furnace black 50 20~ Zinc oxide 3 Stearic acid~
: Wax 5 ,~
Sulfur ~ 2.2 ;~ ::;
N~tert-buty1-2-benzothiazole-1.2 :;~
enamide :: Antidegradant ~where present) 2.0 ~:

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Stock 9 is a control stock containiny no antidegradant.
Stock 10 is another control stock and contains antidegradant N,N'-di(1,4-dimethylpentyl)-~-phenylenediamine. Stock 11 contains Product No. 68034 and Stock 12 contains Product No.
68035. The stocks are cured in a press and determinations ~ -are made on the cured unaged samples and on cured samples aged in an oven for 24 hours at 100C.
TABLE IV
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Stock 9 10 11 12 ` ~

Unaged dynamic ozone resistance: ~ ;

90% retention, hours 3 26 17 26 ; 80% retention, hours 5 34 33 37 70~ retention, hours 8 42 45 50 ~i Unaged static ozone resistance: -~

~ 90% retention, hours 29 176~208 >208 ~
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Unaged intermlttent ozone resistance:

90% retention, hours 6 67 69 ~69 80% retention, houxs 12 96 90 99 ., ~ .
~ 2070~ retention, hours 18 109 108 110 ~
. :
Aged dynamic ozone resistance: ; -90~ retention, hours 3 10 11 11 ,. . : ~ :
80% retention, hours 8 19 21 21 70% retention, hours 11 27 28 29 Aged static ozone resistance:

90% retention, hour~ 120 168 166 179 Aged intermittent ozone resistance:

90% retention, hours 19 23 29 48 80% retention, hours 29 67 61 71 3070~ retention, hours 40 93 86 96 ~ ' ~

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The marked improvement in unaged static ozone resistance exhibited by Stocks 11 and 12 is especially significant because ~ '-' the N,N'-dialkyl-~-phenylenediamines are used primarily for short term static ozone protection. They reach the rubber ,~
surface more quickly than N-alkyl-N'-phenyl-~-phenylenediamine antidegradants and complement the effect of wax. Wax provides a physical barrier to ozone which gives considerable sta*ic protection but the degree of protection is regarded as inade~
quate in the absence of a chemical antiozonant. Moreover, wax ' ~' alone is generally detrimental to dynamic,protection.
Skin tests on typical rubber compositions of the `~ invention show that they are comparable to control compositions -~
preserved with ~-phenylenediamine antiozonants known from long ' commercial experience to be safe to use. Illustrative of the properties of the new compositions of this invention is the ',~
safety to human skin observed from dermatitic tests on human volunteer subjects with rubber preserved with antidegradant ~ ;
compositions of the invention according to a modified repeated insult patch test method designed to correlate with results conforming to commercial experience. Human subjects not pre~
viously exposed to the test materials are subjected to squares ' -'-of the appropriate test material. After 24 hours the square is removed and sites examined for reaction. After a 24 hour ,~
rest period, the test materials are reapplied. After fifteen such applications, a two-week rest period is allowed after which final challenge application is made to the same sites. ' ~ , The test composition comprises, all parts being by weight: ~

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~06~69~ -Natural rubber 50 ci~-4-Polybutadiene rubber 30 Oil extended SBR (about 27% oil) 27.5 High abrasion furnace black 45 Processing oil 5 . ::
Zinc oxide 5 Stearic acid Wax 2 ~ : :
Sulfur N-cyclohexyl-2-benzothiazole- 1 sul~enamide ~ Antidegradant (where present) 3 ; ~ Appropriate controls without antidegradant and with known p-phenylenediamine antidegradants of establishsd safe~ty are run at the same time. Re.sults with N-isopropyl-N'-5-methyl-3- :.:
,,: :
heptyl-~-phenylenedlamine, N-1,3-dimethylbutyl-N'1,4-di=e~hyl- ;
pentyl-p-phenylenediamine,: Produc~ No. 68034 and Product No.
: -~68035~are comparable to the ~-phenylenediamine controls.
In general, the antidegradants of this invention are : .
; 20 valuable for the preservation of sulfur-vulcanizable diene~
rubbers. Those~containing moxe than~50%~ diene hydrocarbon ~
. are preferred. The group of rubbers includes natural rubbers,- ~ :
~ tyrene-~utàd1ene;aopolymer~r bber and;the vaxious stereo~
r ~ speci~ic polymerized dienes, for examplei cis-polybutadiene~
and ais-polyisoprene. The compositions are alBo ~useful in~
diene rubbers of low unsaturation such a :butyl rubber and -~
ethylene-propylene-diene terp~lymer rubber (EPDM). The amount t~ use will vary depending upon the paxticular formulation and ,,: - ~ . : ,. ~
~r : the purpose of the compounder but, in~general, the amounts will 30~` ~all vithin ~he rang~ of 0.1 to 5~ of th~ rubb~r content. :~ ~ .

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: :,:. -~1~6~6~1 Stereospecific rubbers are normally obtained as cements and it is important to add antidegradant to the organic solvent composition immediately after polymerization has been completed ~`
because these rubbers deteriorate rapidly unless adequately protected immediately af~er polymerization. The new anti- ;
degradants are also suited for addition to latex, for ~example, to protect the rubber phase of SBR rubber. ~-` Aithough the invention has been illustrated~by ~
typical examples, it is not limited thereto. Changes and ~-~ 10 modifications of the examples of the'invention herein chosen ; for purposes of disclosure can be made which do not constitute 1 depar~ure from the spirit and scope of the invention.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Dialkyl-p-phenylenediamine composition comprising first component of symmetrical N,N'-di(sec-hexyl)-p-phenylene-diamine in less than 50% by weight of the total composition, second component of unsymmetrical N-(sec-hexyl)-N'-(sec-alkyl)-p-phenylenediamine having 7 or 8 carbon atoms in said sec-alkyl in amount greater than the first component and third component of symmetrical N,N'-di(sec-alkyl)-p-phenylenediamine having 7 or 8 carbon atoms in each alkyl group.

2. Composition of claim 1 in which hexyl is 1,3-dimethyl-butyl and alkyl, both occurrences, is 1,4-dimethylpentyl.

3. Composition of claim 1 or 2 in which the first compo-nent is less than 30% by weight of the composition and the second component is greater than 40% by weight of the composi-tion.

4. Process of making a composition of symmetrical and unsymmetrical dialkyl-p-phenylenediamines which comprises reduc-tively alkylating p-nitroaniline or p-phenylenediamine with a mixture of methyl isobutyl ketone and a ketone selected from the group consisting of methyl isoamyl ketone, 2-heptanone and 2-octanone, said mixture having methyl isobutyl ketone content within the range of about 30-65 percent.

5. Vulcanizable diene rubber having incorporated there-in a stabilizing amount of dialkyl-p-phenylenediamine composi-tion comprising first component of symmetrical N,N'-di(sec-hexyl)-p-phenylenediamine in less than 50% by weight of the total composition, second component of unsymmetrical N-(sec-hexyl)-N'-(sec alkyl)-p-phenylenediamine having 7 or 8 carbon atoms in said sec-alkyl in amount greater than the first com-ponent and third component of symmetrical N,N'-di(sec-alkyl)-p-phenylenediamine having 7 or 8 carbon atoms in each alkyl group.

6. Vulcanized diene rubber having incorporated therein a stabilizing amount of dialkyl-p-phenylenediamine composition comprising first component of N,N' di(1,3-dimethylbutyl)-p-phenylenediamine in less than 30% by weight of the total composition, second component of N-(1,3-dimethylbutyl)N'-(1,4-dimethylpentyl)-p-phenylenediamine in amount greater than 40%
by weight of the total composition and third component of N,N'-di(1,4-dimethylpentyl)-p-phenylenediamine.

7. The composition of claim 6 wherein the rubber is styrene butadiene copolymer rubber.