Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for the
preparation of 2-benzothiazolyl sulphenic acid morpholide
(hereinafter referred to ~s MBS) in which the MBS is
separated in the solvent-free state from an aqueous
reaction mixture and obtained in a high degree of
purity and stability in storage.
The aqueous reaction mixture i9 obtained when MBS
is synthesized from 2-benzothiazolyl di~ulphide,
mercaptobenzothiazole or its sodium salt and a multiple
molar excess of morpholine by the action of an oxidizing
agent such as NaOCl, C12 or ~ 2 The term "MBS" is used
in this invention to denote not only 2-benzothi~zolyl
sulphenic acid morpholide but also the corresponding
compounds which are alkyl-substituted in the morpholine
moiety, such as the product obtained from the re~ction
with 2,6-dimethylmorpholine. MBS is an important
vulcanization accelerator from the class o~ sulphenamides.
It is known that the synthesis of benzothiazolyl
sulphenamides can be carried out in an organic solvent.
The desired end product is obtained as a solution in
the organic solvent and is either precipitated by the
addition of water or obtained as a solvent-free melt by
evaporation of the solvent (US Patent No. 2,782,202).
It is also known (US Patent No. 3,178,~28) that
MBS can be prepared in an aqueous mixture in which the
sulphenamide is insoluble. A sufficiently high tem-
perature may be employed in this method so that the MBS
can be directly obtained in the molten state. In that
case, however, the molar quantity of morpholine used
3o must not exceed 1.5 times the molar quantity of benzo-
thiazole derivatives present, so as to ensure that the
MBS will not decompose prematurely, i.e. while the
reaction is taking place. Since morpholine is used in
such a small e~cess of only 50 mol /0, a reaction time
of several hours is required.
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If a short reaction time is required~ it i9
generally necessary to carry out the reaction in an
aqueous mixture with a molar excess o~ morpholine of
200% or more. In order to prevent decomposition of
MBS during its preparation when such a large excess of
morpholine i9 used, the reaction temperature must be
kept well below the melting point of MBS (about 82 to
85C). The reaction i9 therefore generally carried out
in the range of from 30 to 60C.
It is well known that there are considerable
disadvantages in converting MBS, which has been
obtained from a reaction mixture with a large excess of
morpholine, into the solvent-free liquid state and keeping
it in such state, sirlce MBS is a relatively unstable
substance which rapidly decomposes at elevated temper-
atures. It is also known that sulphenamides decompose
all the more rapidly the higher the concentration of
~ree amine.
Aqueous reaction mixtures obtained ~rom the prepa-
ration of MBS using a large molar excess of morpholinehave therefore hitherto o~ necessity been worked up as
suspensio~s at room temperature, for example by filtering
the crystalline insoluble MBS from the reaction mixture,
freeing it from mother liquor by vigorous washing with
large quantities of water, and then drying. These
operations, however, as also the recovery of morpholine
from the wash waters~ are time consuming and expensive.
The preparation of MBS with a large excess of
morpholine results in a suspension of solid MBS in a
3o mixture of water and morpholine which still contains, in
solution7 organic by-products and sometimes also inorganic
salts formed in the reaction. Such a suspension contains
more than 0.5 mol of morpholine, generally from 1.5 to
2 mols per mol of MBS.
It has now been ~ound that MBS can be obtained in the
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form of a solvent-free liquid of high quality and stability from
a suspension if the suspension is heated to melt the crystalline
MBS, the resulting molten phase is rapidly separated from the
aqueous phase, and the molten phase is then freed from any
volatile constituellts still presen-t, such as wa~e~ and morphol~ne.
These operations are carried out in immediate succession o~er a
total period of not more than 15 minutes.
This invention thus provides a process for isolating a
2-benzothiazolyl sulphenic acid morpholide from an aqueous
suspension thereof, which comprises
ta) heating the suspension to melt the morpholide,
(b) rapidly separating the molten phase from the
aqueous phase, and
(c) removing volatile constituents still present in the
molten phase,
the sum of residence times from beginning to end of the three
stages (a) to (c) amounting to not more than 15 minutes.
It is suprisingly found that in spite of the large excess
of morpholine originally present, thi~ method results in an MBS
melt which is stable in storage and does not undergo the rapid
decomposition normally found in MBS.
The process according to the in~ention is equally
applicable to the preparation and separation of the various
analogues, in particular 2-benzothiazolyl sulphenic acid 2,6-
dimethylmorpholide.
The various stages of the process according to the
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invention may be carried out by known methods. For
example, heating of the suspension and its conversion
into a mixture o~ aqueous phase and melt phase may be
- carried out by direct supply of energy or indirectly,
8 . g. in a heat exchanger. The subsequent isolation Or
the melt phase may be achleved by the action Or centri-
fugal force, e.g. in a ~eparator, or by gravity~ e.g.
in a ~eparating flask. Subsequent freeing of the melt
phase from volatile constituents, such as water and
morpholine, is ad~antageously carried out by rapid
evaporation, preferably under vacuumJ e.g. in a thin
layer evaporator.
When carrying out the stage of evaporation of the
melt phase, it has been found to be an additional
advantage to carry a stream of gas, e.g. nitrogen, air
and/or steam, in countercurrent to the film of mel-k.
The procedure described above obviates the time-
consuming stages of f:iltration7 washing and drying of
the MBS produced in suspension in the presence of a
large excess of morpholine as well as the costl7
procedure of recovering the morpholine from the wash
waters.
The melt of MBS which is obtained after stage
(c) may be converted into the solid crystalline state
25 by cooling in known manner so that the MBS may be
obtained in a usual commercial form.
The invention is illustrated in the following
Examples. The percentages given are percentages by
weight.
30 Example 1
150 kg of a reaction mixture obtained from the
synthesis of MBS and consisting of 20% Of MBS~ 20%
of morpholine, 10h of sodium chloride, 49/0 of water,
and lh of by-product and having ~ temp~rature o~ about 30C
35 are pumped through a steam-heated tubular heat exchanger.
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The re~idence time during heating up is 1.6 minutes.
The mixture, which i 3 obtained from the heat exchanger
at u temperature of about B5C, i8 fed into the iront
end of a separating flask which i9 inclined at an angle
of 3. While the aqueous phase flows lnto a reaeiver
~rom the highest point at the rear end of the ~eparating
flask, the dropY of melt sink to the bottom and flow a~
a layer to the lowest point in the flask, from where
they are continuously removed through a discharge
valve so that a residence time of 4 minutes is not
exceeded~
A short inclined piece of pipe is attached to the
bottom discharge valve of the separating flask and opens
into the inlet of a commercial thin layer evaporator
having a heating surface o~ 0.2 m2. The evaporator is
operated at 30 Torr and 120C. Steam is injected at
its lower end at the same temperature at the rate of
about 2 kg/hour. The residence time in the thin layer
evaporato~r is less than 1 minute. A melt of MBS, which
20 has excellent stability in storage and in which the
residual morpholine content is about 0.2~o by weight, is
removed from the sump of the thin layer evaporator at
the rate of about 30 kg/hour. The melt can be converted
into the usual commercial form of scales by cooling on
a scraping roller.
Example 2
A reaction mixture obtained from the synthesis of
MBS and consisting Of 21.7% of MBS, 21.7% of morpholine,
1.1~ of organic by-products and 55.5% of water is passed
through a heat-insulated tube at the rate of 138 kg/hour.
Steam is added to the reaction mixture at the rate of
12 kg/hour just behind the tube inlet. The mixture
leaves the tube at about 85C; its residence time in the
tube is about 10 seconds. It then flows into a centri-
fugal separator 1 litre in capacity, where it is separated
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into a melt phase and an aqueous phase. The residence
time of the melt in the separator is less than 60
seconds. The melt flows through a 0.5 litre storage
vessel to a thin layer evaporator which has a heatlng
surface of 0.2 m2 and which is operated at 120C ~nd
30 Torr, Nitrogen at the same temperature is in,jected
into the lower end of the evaporator at a rate of about
?.5 Nm3/h. An MBS melt which contains a residue of
about 0.2% by weight of morpholine and i9 very stable
in storage is discharged from the sump of the thin layer
evaporator at about 30 kg/hour.
E~ample 3
138 kg/hour of a reaction mixture consisting of
20% by weight of 2-benzothiazolyl sulphe~ic acid 2,S-
dimethylmorpholide, 20% of 2~ 6-dimethylmorpholine,
7.5% of sodium chloride, 51% of water and 1.5% Of by-
products are treated in the same way as described in
Example 2 . 27 . 5 kg of a melt of 2-benzothiazolyl
sulphenic acid 2,6-dimethylmorpholide which has very
good stability in storage are obtained. This product
can be converted into a commercial form by cooling on a
scraping roller.
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