Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-10-12
2001-06-12
Aulakh, C. S. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C546S157000, C546S153000, C546S255000
Reexamination Certificate
active
06245912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the preparation of N-alkyl sulfenimides. More particularly, the present invention relates to a novel process for converting N-alkyl sulfenamides to N-alkyl sulfenimides.
2. Description of Related Art
Sulfenimides have been used commercially as vulcanization accelerators and are said to be useful as pesticides. Sulfenimides have been made in the past by placing an N-alkyl sulfenamide in an organic solvent and converting the sulfenamide to the sulfenimide by the addition of anhydrous HCl gas. In this case, the amine hydrochloride salt is formed as a by-product. The amine hydrochloride salt is then removed by filtration or extraction and the product is isolated by crystallization and filtration. Alternatively, sulfenimides can be made from N-alkyl sulfenamides by placing the N-alkyl sulfenamide in an anhydrous organic solvent and adding an organic acid anhydride. This reaction produces the desired sulfenimide along with the free acid and the N-alkyl amide corresponding to the N-alkyl group of the starting sulfenamide and the acid anhydride used. Sulfenimides have also been made by the reaction of a sulfenyl chloride with an amine in an anhydrous solvent.
Reactions of sulfenamides with carbonyl compounds have been reported in the past. However, none of the these reactions has been found to produce a sulfenimide as the major product of the reaction.
U.S. Pat. No. 2,860,142 discloses a process for the conversion of sulfenamides to sulfenimides comprising treating an N-alkyl or N-cycloalkyl benzothiazolyl-2-sulfenamide with acetic anhydride or a homolog thereof, with or without the presence of a second solvent, at about 25 to about 75° C., for an appropriate period that can range from about 10 minutes to 24 hours. The resulting sulfenimide is isolated by crystallization, dilution, or by stripping off the solvent. The yields are very good.
U.S. Pat. No. 3,151,122 discloses a process for the preparation of N-alkyl- and N-cycloalkylbis(2-benzothiazolyl)sulfenimides comprising treating the corresponding 2-benzothiazolylsulfenamide under substantially anhydrous conditions with an acid having an ionization constant K
a
above 1×10
−3
at 25° C. The compounds are useful as accelerators in the vulcanization of any of the recognized sulfur-vulcanizable rubbers and show good resistance to scorch.
U.S. Pat. Nos. 5,079,305 and 5,189,174 disclose heterocyclic thiol sulfenimide compounds that are said to be useful as accelerators in the curing of natural and/or synthetic rubbers. The compounds can be represented by the formula:
Herein each of A
1
and A
2
, independently, is at least one heterocyclic ring containing one or more nitrogen atoms therein, or at least one heterocyclic ring containing one or more nitrogen atoms and (1) one or more hydrocarbyl substituents; or (2) one or more electron withdrawing groups; or (3) one or more electron releasing groups, wherein A
1
alternatively is thiazyl or a dithiocarbamoyl, and wherein R is: (a) a hydrogen atom, or (b) a hydrocarbyl radical having from 1 to 16 carbon atoms, or (c) the hydrocarbon radical of (b) wherein one or more of the carbon atoms is an oxygen atom, a nitrogen atom, or a substituted nitrogen atom wherein the substituted group is an alkyl and, in combination with the nitrogen atom, forms a heterocyclic ring having a total of one to seven carbon atoms, or (d) the hydrocarbyl radical of (b) containing a halogen, an amino, a cyano, an alkoxy, a hydroxy, or an alkoxycarbonyl. When the heterocyclic thiol sulfenimide compound is utilized as an accelerator for rubber, improved cure rates, longer scorch delay, and better reversion resistance are said to be obtained in comparison to conventional sulfenamides.
U.S. Pat. No. 5,204,481 discloses a process for producing N-alkyl or N-cycloalkyl-2-benzothiazolyl sulfenimides wherein aliphatic hydrocarbons are used as a reaction medium in converting N-alkyl or N-cycloalkyl-2-benzothiazolyl sulfenamides to the corresponding sulfenimides by reaction with an acid.
Ignatov et al.,
Zhurnal Obshchei Khimii
, 47(5):1096-1103 (1977) studied the reactions of 2-benzothiazolylsulfeneamide and N-cyclohexyl-2-benzothiazolylsulfenamide with acetic acid, acetyl chloride, acetic anhydride, benzoyl chloride, picryl chloride, butyl acetate, maleic anhydride, phthalic anhydride, hydrochloric acid, trichloroacetic acid, thioacetic acid, and hydrogen sulfide. This enabled the authors to determine the optimum conditions for the synthesis of bis-2-benzothiazolylsulfenimide and N-cyclohexyl bis(2-benzothiazolyl)sulfenimide, which compounds are said to have valuable properties as general purpose rubber vulcanization accelerators.
The disclosures of the foregoing are incorporated herein by reference in their entirety.
SUMMARY OF THE INVENTION
In the process of the present invention, a sulfenamide is converted to a sulfenimide by a reaction with an aldehyde. The process is carried out by placing an N-alkyl sulfenamide in an appropriate organic solvent, then adding a stoichiometric excess of an aldehyde, heating the mixture to boiling and removing the water formed in the reaction until the reaction is complete. The product thus formed can be isolated by filtration from the reaction mixture or by evaporation of the reaction solvent, followed by crystallization of the crude reaction product, and filtration from a suitable solvent.
More particularly, the present invention is directed to a process for the preparation of sulfenimides comprising:
mixing, in a hydrocarbon solvent, a sulfenamide of the formula
with an aldehyde of the formula
R
4
CHO
where X is a sulfur atom, a —C═N— group, or a —C═C— group, R
1
and R
2
are independently selected from the group consisting of hydrogen, alkyl, and aryl or may be joined to form a saturated or unsaturated ring or aromatic ring, R
3
is alkyl or cycloalkyl, and R
4
is a hydrocarbon radical wherein the carbon bearing the aldehyde function is bonded only to other carbon atoms, a substituted or unsubstituted aryl ring, or a heteroaromatic ring; and heating the mixture at a temperature and for a period of time sufficient to convert the sulfenamide to the sulfenimide.
The reaction can be represented by the equation:
In a particularly preferred embodiment, the reaction can be represented by the equation:
In light of the reported reaction of N-cyclohexyl 2-benzothiazolylsulfenamide with acetone, and the reaction of 2-benzothiazolylsulfenamide with cyclohexanone, the reaction of N-cyclohexyl 2-benzothiazolylsulfenamide with an aldehyde to form N-cyclohexyl bis(2-benzothiazolyl)sulfenimide in high yield is surprising and unexpected.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As disclosed above, the present invention is directed to a process for preparing a sulfenimide by reacting a sulfenamide of the structure:
with an aldehyde of the structure R
4
CHO.
In the formula for the sulfenamide, X is a sulfur atom, a —C═N— group, or a —C═C— group. Thus, the ring shown in the formula will be of one of the following structures:
R
1
and R
2
in the formula can be the same or different and can be hydrogen, alkyl, or aryl, or can be joined to form a saturated or unsaturated ring or an aromatic ring. Where they can be straight or branched chain alkyl, which term is intended to include cycloalkyl, they are preferably of 1 to 12 carbon atoms, e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, cyclopentyl, cyclohexyl, cycloheptyl, isomers of the foregoing, and the like. It is preferred that, where R
1
and/or R
2
are alkyl, they are alkyl of one to eight carbon atoms, and more preferred that they are of one to four carbon atoms. Those skilled in the art will realize that where R
1
and/or R
2
are cycloalkyl, the cycloalkyl ring may be substituted, typically with one or more alkyl groups, generally lower alkyl groups, such as methyl, ethyl, propyl, butyl, isomers thereof, and the like.
Where R
1
and/or R
2
are aryl, they are p
Barrows Franklin H.
Stieber Joseph F.
Aulakh C. S.
Grandinetti Paul
Thompson Raymond D.
Uniroyal Chemical Company, Inc.
LandOfFree
Process for making N-alkyl bis(2-pyridyl) sulfenimides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for making N-alkyl bis(2-pyridyl) sulfenimides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for making N-alkyl bis(2-pyridyl) sulfenimides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546830