Diaryl-p-phenylenediamine disulfides

Details Diaryl-p-phenylenediamine disulfides Diaryl-p-phenylenediamine disulfides

2000-09-06

2003-09-30

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

Reexamination Certificate

active

06627686

ABSTRACT:

BACKGROUND OF THE INVENTION
Conventional N-aryl substituted diphenyldiamine antioxidants, such as Wingstay® 100 are widely used in the protection of rubber. Wingstay®100 is commercially available from The Goodyear Tire & Rubber Company and contains a mixture of di-o-tolyl-p-phenylenediamine, diphenyl-p-phenylenediamine and phenyl-o-tolyl-p-phenylenediamine.
While use of these conventional N-aryl substituted diphenyldiamine antioxidants provide excellent protection of rubber, improvements to the green strength of rubber is not observed. In order to obtain improvements to green strength, expensive crosslinkers are conventionally used. Unfortunately, use of such crosslinkers significantly increase the cost of production of such rubber compounds.
SUMMARY OF THE INVENTION
The present invention relates diaryl-p-phenylenediamine disulfides of the formula:
and mixtures thereof, wherein R
1
and R
2
are each independently selected from the group consisting of hydrogen and alkyls having 1 to 8 carbon atoms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention also relates to a rubber composition containing from 0.1 to 10 phr of diaryl-p-phenylenediamine disulfides of the formula:
and mixtures thereof, wherein R
1
and R
2
are each independently selected from the group consisting of hydrogen and alkyls having 1 to 8 carbon atoms.
In addition, there is disclosed a method for processing rubber comprising mixing with a rubber from 0.1 to 10 phr of a diaryl-p-phenylenediamine disulfides of the formula:
and mixtures thereof, wherein R
1
and R
2
are each independently selected from the group consisting of hydrogen and alkyls having 1 to 8 carbon atoms.
The disulfides used in the present invention may be present at various levels in the rubber compounds of the present invention. For example, the level may range from about 0.1 to 10.0 parts by weight per 100 parts by weight of rubber (also known as “phr”). Preferably, the level ranges from about 0.5 to about 5.0 phr.
The disulfides may be prepared by reacting a suitable substituted or unsubstituted diaryl-p-phenylenediamine with a sulfur compound. Representative of suitable diaryl-p-phenylenediamine disulfides compounds which may be used include those of the formula:
A N-aryl or N-alkaryl substituted diphenyldiamine of the above formula is used to prepare the disulfide compositions of the present invention. With respect to the above formula, each R
1
and R
2
may consist of hydrogen or an alkyl having a total of from about 1 to about 8 carbon atoms. R
1
and R
2
, however, may be different from the other substituent. Preferably, R
1
and R
2
are each hydrogen or an alkyl having 1 to 3 carbons. Representative of N-aryl substituted and N-alkaryl substituted diphenyldiamines which may be suitable for use in preparation of the compositions of the present invention include diphenyl-p-phenylenediamine, di-o-tolyl-p-phenylenediamine, phenyl-o-tolyl-p-phenylenediamine, di-o-xylyl-p-phenylenediamine, phenyl-o-xylyl-p-phenylenediamine, di-m-tolyl-p-phenylenediamine, phenyl-m-tolyl-p-phenylenediamine, di-m-xylyl-p-phenylenediamine, phenyl-m-xylyl-p-phenylenediamine, di-o-isopropylphenyl-p-phenylenediamine, phenyl-o-isopropylphenyl-p-phenylenediamine to name a few. The most preferred N-aryl substituted and N-alkaryl substituted diphenyldiamine is a mixture di-o-tolyl-p-phenylenediamine, diphenyl-p-phenylenediamine and phenyl-o-tolyl-p-phenylenediamine known in the industry as Wingstay® 100.
Representative examples of sulfur compounds which may be used include sulfur monochloride and sulfur dichloride. Preferably, the sulfur compound is sulfur monochloride.
The diaryl-p-phenylenediamine of formula IV is reacted with a sulfur compound under suitable conditions to form a disulfide of the formulas I, II and/or III. The diaryl-p-phenylenediamine may be reacted with sulfur in a variety of mole ratios. Generally, the mole ratio of the diaryl-p-phenylenediamine to the sulfur compound ranges from about 1.0:0.5 to about 1.0: 10.0 with a range of from about 1.0:6.0 to about 1.0:2.0 being preferred.
Since the sulfur compound is halogenated, such as sulfur monochloride, it is preferred to conduct the reaction between the sulfur compound and the diaryl-p-phenylenediamine in the presence of a scavenger or “neutralizer” which does not interfere with the disulfide formation. Representative examples include triethylamine, pyridines such as methyl pyridine and the like.
An organic solvent may be used to dissolve the diaryl-p-phenylenediamine compound. The solvent is preferably inert to the reaction between the diaryl-p-phenylenediamine and the sulfur compound. Illustrative of solvents suitable for use in the practice of this invention include: saturated and aromatic hydrocarbons, e.g., hexane, octane, dodecane, naphtha, decalin, tetrahydronaphthalene, kerosene, mineral oil, cyclohexane, cycloheptane, alkyl cycloalkane, benzene, toluene, xylene, alkyl-naphthalene, and the like; acetone; ethers such as tetrahydrofuran, tetrahydropyran, diethylether, 1,2-dimethoxybenzene, 1,2-diethoxybenzene, the dialkylethers of ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, oxyethyleneoxypropylene glycol, and the like; fluorinated hydrocarbons that are inert under the reaction conditions such as perfluoroethane, monofluorobenzene, and the like. Another class of solvents are sulfones such as dimethylsulfone, diethylsulfone, diphenolsulfone, sulfolane, and the like. Mixtures of the aforementioned solvents may be employed so long as they are compatible with each other under the conditions of the reaction and will adequately dissolve the diaryl-p-phenylenediamine compound and not interfere with the reaction.
The reaction between the diaryl-p-phenylenediamine and the sulfur compound to form the diaryl-p-phenylenediamine disulfides is exothermic and may be conducted over a wide temperature range. The temperature may range from moderate to an elevated temperature. In general, the reaction may be conducted at a temperature of between about 0° C. to 150° C. The preferred temperature range is from about 50° C. to 120° C., while the most preferred temperature range is from about 80° C. to 100° C.
The reaction pressure to form the diaryl-p-phenylenediamine disulfide is not deemed to be critical. Pressures ranging from about 0 kPa to 689 kPa may be used.
The reaction is preferably conducted in a nitrogen atmosphere.
The process for the preparation of the diaryl-p-phenylenediamine disulfide may be carried out in a batch, semi-continuous or continuous manner. The reaction may be conducted in a single reaction zone or in a plurality or reaction zones, in series or in parallel. The reaction may be conducted intermittently or continuously in an elongated tubular zone or in a series of such zones. The material of construction of the equipment should be such as to be inert during the reaction. The equipment should also be able to withstand the reaction temperatures and pressures. The reaction zone can be fitted with internal and/or external heat exchangers to control temperature fluctuations. Preferably, an agitation means is available to ensure the uniform reaction. Mixing induced by vibration, shaker, stirrer, rotating, oscillation, etc. are all illustrative of the types of agitation means which are contemplated for use in preparing the composition of the present invention. Such agitation means are available and well known to those skilled in the art.
The diaryl-p-phenylenediamine disulfides may be used in “elastomers or rubbers.” The term “elastomer or rubber” as used herein embraces both vulcanized forms of natural and all its various raw and reclaim forms as well as various synthetic rubbers. The synthetic elastomers include conjugated diene homopolymers and copolymers and copolymers of at least one conjugated diene and aromatic vinyl compound. Representative synthetic polymers include the homopolymerization products of butadiene and its homologues and derivatives, as for example, methyl-butadiene, dimethylbutadiene and pentadiene as we

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