Note: Descriptions are shown in the official language in which they were submitted.
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me present invention relates to 2-(3-methyl-
piperidinothio)-benzothiazole and 2-(4-methylpiperidinothio)
-benzothiazole and to a process for their preparation in
water. More particularly this invention relates to the
order of addition of the reactants when the reaction is
carried out in water in the absence of organic solvents.
These sulfenamides are known to be good vulcani-
zation accelerators for the curing of natural and synthetic
rubber. mese materials do not exhibit early vulcanization,
known as scorch, and accomplish vulcanization quickly once
the vulcanization temperature has been reached.
Aqueous preparations of these sulfenamides have
been reported in Canadian Patent No. 890,433 which discusses
the merits of these compounds as accelerators and describes
their preparation from sodium mercaptobenzothiazole in
water, and from other benzothiazole-containing precursors
in organic solvents. Preparation of these materials from
benzothiazolyl disulfide in water is not described. Other
examples of aqueous preparations of sulfenamides can be
found in U.S. Patents 2~045,888; 3,178,428 and 3,144,652.
Attempts to prepare these materials using the usual prior
art order of addition of oxidation of an aqueous benzothia-
solyl disulfide-amine mixture, where the amine is 3-methyl-
piperidine or 4-methylpiperidine~ yielded a product of poor
form and poor purity.
It is therefore an ob~ect of the present invention
to provide an improved process for the production of 2-(3-
methylpiperidinothio)-benzothiazole and 2-(4-methylpiperi-
dinothio)-benzothiazole in a completely aqueous medium.
Other ob~ects will become apparent to those skilled in this
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art as the description proceeds.
It has now unexpectedly been discovered that
changing the order of addition of reactants according to the
present invention allows preparation of 2-(3-methylpiperi-
dinothio)-benzothiazole and 2-(4-methylpiperidinothio)-
benzothiazole of good form, purity and yield. me sulfen-
amides are prepared in an aqueous reaction medium by adding
the amine to an aqueous benzothiazolyl disulfide and bleach
mixture as contrasted to the prior art procedure of adding
bleach to a mixture of amine and benzothiazolyl disulfide.
Ihe invention comprises
(a) placing the benzothiazolyl disulfide in water
to form a slurry,
(b) adding bleach to the slurry,
(c) adding an amine selected from the group
consisting of 3-methylpiperidine and 4-methylpiperidine, and
(d) allowing the mixture to react to obtain the
sulfenamide.
me term "bleach" as used throughout the specifi-
cation and claims is intended to denote oxidizing agentswhich permit the reaction to occur. The most preferred
oxidizing agent is sodium hypochlorite, commonly referred
to as bleach.
The invention as described uses a methylpiperidine
pr~cursor. These methylpiperidines may be obtained by the
catalytic reduction of the corresponding picolinium salts
in aqueous acidic medium. Aqueous solutions of these methyl-
piperidinium salts derived from such catalytic hydrogena-
tions are adaptable for use in the present invention without
neutralization, isolation or purification of the amine.
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When utilizing these salts, the method of the present
invention comprises
(a) placing benzothiazolyl disulfide in water to
form a slurry,
(b) adding bleach to the slurry,
(c) adding a suitable base such as aqueous sodium
hydroxide,
(d) adding a salt solution selected from the group
consisting of sulfate, acetate and chloride salts of 3-
methylpiperidine and 4-methylpiperidine,such as 4-methyl-
piperidinium acetate and 3-methylpiperidinium sulfate, and
(e) allowing the mixture to react.
The amine salts are thus neutralized in situ during the
reaction. When desired, the amine salt solution can be
preneutralized using a basic material to give a crude
aqueous amine which can be used in the process in place of
pure amine.
Representative examples of amine salts useful in
the present invention are 3-methylpiperidinium sulfate, 4-
methylpiperidinium acetate, 4-methylpiperidinium chloride
and 3-methylpiperidinium phosphate.
Representative examples of suitable bases useful
in the practice of the present invention are aqueous sodium
hydroxide, aqueous potassium hydroxide, aqueous sodium car-
bonate, aqueous potassium carbonate and aqueous sodium bi-
carbonate.
The process of the present invention is effective
when the bleach~ benzothiazolyl disulfide, an amine or amine
salt and sodium hydroxide are present in stoichiometric
amounts. Excess amounts of bleach from 0 to 45 percent and
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of amine from 0 to 35 percent can be used. While higher
amounts of excess amine show slightly improved purity, the
improvement is negligible at amine excesses above 45 percent.
Preferred proportions of reactants based on benzothiazolyl
disulfide are from 25 to 35 percent molar excess of bleach
and from 15 to 25 percent molar excess of amine or amine
salt and sodium hydroxide. Such excesses of reactants pro-
duce 2-(3-methylpiperidinothio)-benzothiazole and 2-(4-
methylpiperidinothio)-benzothiazole of excellent purity and
in higher yields than if stoichiometric amounts of reactants
are used~
me process is generally carried out by adding
bleach to an aqueous slurry of benzothiazolyl disulfide in
a reaction chamber equipped with good agitation. me amine
or amine salt and sodium hydroxide is then added at a moder-
ate rate. me temperature is preferably maintained in a
range of about 20 C. to about 45 C. during the addition,
although temperatures from about 15 C. to about 90 C. can
be used. The mixture is stirred briefly and cooled if
necessaryO The product solidifies in the aqueous mixture
when the aqueous mlxture is below the melting point of the
solid. me product is then separated~ water washed and
dried to complete the process.
me invention and its improvements over the art
are more completely described with reference to the examples
belcw in which all parts and percentages are by weight
unless otherwise specified.
Example 1 shows the preparation of sulfenamide
using the prior art bleach addition method. Example 2
demonstrates the process of the present invention. Example
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3 illustrates the use of an amine salt solution in the
process of the present invention. All examples used tech-
nical grade (98.6%) benzothiazolyl disulfide.
,ExamPle 1
A 250 milliliter round-bottom flask was charged
with 17.2 grams (.05 mole) of benzothiazolyl disulfide, 80
milliliters of water and 11.9 grams (.12 mole) of 3-methyl-
piperidine. me mixture was stirred for 10 minutes at room
temperature. A slimy, greenish emulsion resulted. To the
emulsion was added 28.5 milliliters (.065 mole) of 2.28M
bleach dropwise over a 5 minute period. During the addition
the temperature rose from 21 C. to 38.50 C. The emulsion
was stirred for about 10 minutes between 380 C. and 34 C.,
during which time the product solidified in irregular
greenish-brown chunks. After cooling to 240 C. the mixture
was filtered. The product was water washed and dried at
40 C. me product was obtained in 97.3 percent yield and
had a melting point between 55.50 c. and 590 c. Purity by
reduction with hydrogen sulfide followed by titration of
the amine with dilute acid was 90.2 percent.
ExamPle 2
A 250 milliliter round-bottom flask was charged
with 17.2 grams (.05 mole) of benzothiazolyl disulfide, 80
milliliters of water~ and 28.5 milliliters (.065 mole) of
2.28M bleach. The mixture was stirred, forming a cream
colored slurry after approximately 10 minutes. To this
slurry was added 11.9 grams (.12 mole) 3-methylpiperidine
dropwise over a 5 minute period. During the addition the
temperature rose to 35 C. The emulsion was allowed to stir
for about 10 minutes at a temperature between 380 C. and
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35 C. The mixture was cooled to 240 C. solidifying the
product as small, light tan granules of uniform size. The
solids were filtered, washed with water and dried at ~oo C.
The product was obtained in 98.4 percent yield, having a
melting point between 57.5O C. and 61 C. A purity of 96.9
percent was obtained using the method described in Example 1.
Exam~le ~
A 250 milliliter round-bottom flask was charged
with 8.6 grams (.025 mole) of benzothiazolyl disulfide, 40
milliliters of water and 13.6 milliliters (.0325 mole) of
2.39M bleach. A solution of 2.4 grams (.o6 mole) of sodium
hydroxide in 10 milliliters of water was added. me mixture
was cooled slightly to maintain the temperature at about
250 C. To this mixture was added 20.4 grams (.06 mole) of
an aqueous solution of 4-methylpiperidinium sulfate (29.2
percent theoretical amine content) dropwise over a 2 minute
period while the mixture was agitating. ~uring addition the
temperature rose from 21 C. to 29.50 C. me mixture was
stirred for approximately 15 minutes at 280 C. to 29 C.
during which time the product solidified as tan granules.
The granules were water washed and dried at 40 C. me
product was obtained in 96.6 percent yield and had a melting
point between 48.5 and 50 C. Using the method described in
Example 1~ a purity of 94.5 percent was obtained.
me results of Examples 1-3 are s D arized in
Table I. me column titled "Method of Addition" refers to
the material added last to a mixture of benzothiazolyl di-
sulfide and other reactants. Thus~ Example 1 is seen to be
an illustration of prior art procedures and Examples 2 and
3 are illustrations of the present invention.
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Table I
Method of Amine Yield Melting Purity
Ex. Addition Source (%) Point C. (%) Form
1 bleach amine 97.3 55-59 90.2greenish
chunks
2 amine amine 98.4 57.5-61 96.9 tan
granules
3 amine salt amine salt 96.6 48.5-50 94.5 tan
granules
Examples 1 and 2 demonstrate the contrast between
the prior art and the methods of the present invention.
When the process of the prior art is used in aqueous solu-
tion, a preliminary reaction between the disulfide and amine
occurs in the water giving a curd-like mixture thought to be
sulfenamide and amine-mercaptobenzothiazole salts. Subse-
quent bleach oxidation of this mixture as described in
Example 1 results in a sulfenamide of lower purity and poor
form. me process of the present invention avoids the pre-
reaction. A clean oxidation to the sulfenamide results
when the amine is added to the disulfide in the presence of
aqueous bleach as described and exemplified in Example 2.
The amine salt solution addition described in
Example 3 may also be run using preneutralized amine salt
solution. me preneutralization gives a crude solution of
aqueous amine which can then be used in the process exem-
plified in Example 2 in place of pure amine. The reaction
is now the same as the process using pure amine, except
water is present in the reagent amine.
While certain representative embodiments and
details have been shown for the purpose of illustrating the
invention, it will be apparent to those skilled in this art
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that various changes and modifications may be made therein
without departing from the spirit or scope of the invention.
