Note: Descriptions are shown in the official language in which they were submitted.
~ 168246
It is kncwn that 2-chlorobenzthiazoles and 2-chlorokenzoxa-
zoles can be prepared from the corresponding 2-mercaptobenzazoles by
direct chlorination (German Offenlegungsschrift 1,670,453, and J.
Org. Chem. 23, 1,500 (1958)). In this pro oe ss, the reaction is car-
ried out, in the case of the thiazole, at elevated bemperatures and
in the presen oe of catalytically active quantities of N-substituted
carboxylic acid amides, such as, for example, dimethylformamide, and
2-chlorobenzthiazole is obtained in a yield of pu,re m~terial of 87%
of theory.
The oxazole is also prepared by carrying out the reaction
in an inert solvent, but at a 1GW temFeratu~e and without the addi-
tion of a catalyst; the yield of 2-chlorobenzoxazole is 82% of
theory. If it is ncw desired to synthesize 2,6-dichlorobenzthiazole
and 2,6-dichlorobenzoxazole, which are valuable intermediate pro-
duct~, for example for the manufact~re of active oowpcurds for plant
prokection (German Offenlegungsschrift 2,640,730), in the same man-
ner, but using 6-chloro-2-mercaptobenzthiazole and 6-chloro-2-
-mercaptobenzoxazole as the starting materials, it has to be stated
that, in this case, it is only possible to achieve oonsiderably
lcwer yields and that a large quantity of
1 ~68~4
mdistillable residues is formed.
The present invention is therefore based on the
object of improving the yields in the preparation of
2,6-dichlorobenzthiazole and 2,6-dichlorobenzoxazole and
of reducing the formation of by-products which cannot be
utilized further.
It has been found that this is possible if the
potassium or sodium salts of 6-chloro-2-mercaptobenzthi-
azole are chlorinated instead of the free compound and
if these salts are suspended, for this reaction, in
special ine~t solvents.
m e invention relates, therefore, to a process
for the manufacture of 2,6-dichlorobenzthiazole and
2,6-dichlorobenzoxazole of the formula
Cl ~ X ~ ~l
- which comprises subjecting the potassium or sodium salts
of 6-chloro-2-mercaptobenzoxazole or 6-chloro-2-~ercapto-
benzthiazole to chlorination in the presence of a halo-
genated aliphatic or aromatic hydrocarbon, as a suspend-
ing agent.
Yields of 90% or more of the desired process pro-
ducts are obtained by the procedure according to the
invention The quantities of residue are correspond-
ingly low.
From many points of view it could not be foreseen
that the reaction would proceed smoothly. Thus, it is
1 1682
4 --
surprising that the reaction takes place at all, since
the al~ali metal salts of the free mercapto compounds are
virtually insoluble in the halogenated hydrocarbons used.
Secondly, it was known that only the disulfides are
formed if benzthiazole and benzoxazole mercaptides are
ch~orinated in solution (German Offenlegungsschrift
2,800,462).
m e process according to the invention also
makes it possible to use, as starting materials, without
having to accept an appreciable reduction in yield there-
by, crude alkali metal 2-mercaptides of 6-chlorobenzthi-
azole or 6-chlorobenzoxazole, which are available as
intermediate products.
~he chlorination is carried out in the tempera-
ture range betwe~n -20 and ~150C. Somewhat higher
temperatures are required for the chlorination of the
thiazole (~ 20C, preferably 80 - 100) than for the
- chlorination of the oxazole, which is carried out at the
temperature which is set up spontaneously, namely between
-lO and 100C, preferably between 20 and 60C. In the
chlorination of the thiazole it is advantageous to fol-
low a procedure in which part of the quantity of chlorine
required is passed in at temperatures from 20 to 8~C,
until the sulfenyl chloride has been formed, after which
the temperatures are increased and chlorination is con-
tinued. It is also possible to pass in all the
chlorine at the higher temperature. ~n the case of
the oxazole, the chlorination of the sulfenyl chloride
which is formed as an intermediate does not require
l 1~8246
-- 5
elevated temperatures.
~ he quantity of chlorine required is approx.
2.3 to 3 moles per mole of alkali metal mercaptide emp-
loyed, if the chlorine is passed into the reaction
5 mixture at atmospheric pressure. If the reaction is
carried out in a closed system, that is to say excluding
chlorine losses as far as possible, it is possible to
reduce the quantity of chlorine to 2 to approx. 2.3 moles.
The solven-ts used àre halogenated hydrocarbons,
such as, for example, carbon tetrachloride, tetrachloro-
e*hane or chlorinated benzenes, but chiefly chlorobenzene
and o-dichlorobenzene and particularly the last of these.
In general, the quantities of solvent are such that the
suspension formed can still be stirred. However, it
is also possible to use less solvent and then to pass
chlorine into the suspension under pressure in a closed
system.
If desired, catalytic quantities of an
N-substituted carboxylic acid amide, for example dimethyl-
formamide, can be added in order to accelerate thereaction.
When the reaction is complete, the sulfur
dichloride formed in the reaction is removed by distil-
lation, if appropriate also as a mixture with the solvent,
it being possible to re-use the latter.
m e alkali metal chloride produced in the chlor-
ination can be removed by filtration or, in the case of
the chlorination of thiazole, extracted with water after
previously removing the sulfur dichloride.
1 16~2~
The alkali metal mercaptides of 6-chloro-2-mercapto-
benzoxazole and 6-chloro-2-mercaptobenzthiazole required as
starting materials are accessible, for example, by reacting 5-
chloro-2-aminophenol with alkali metal xanthates.
The process according to the invention is carried out,
for example, by suspending the mercaptide (particularly the
potassium salt, in the case of 6-chloro-2-mercaptobenzoxazole) in
the solvent and passing in l.0 to 1.05 moles of chlorine per mole
of mercaptide, initially at room temperature, if appropriate with
cooling and, if appropriate, in the presence of catalytically
active quantities of dimethylformamide (0.1 to 5~ by weight,
relative to the mercaptide). The mixture is then heated, in the
case of the thiazole, to 80 to 100C and a further 1.3 to 2.0 moles
of chlorine are passed in at this temperature; in the case of the
oxazole, the further chlorine iB also added at room temperature.
The sulfur dichloride which has been formed is then distilled off,
the alkali metal chlorides are removed by filtration or by
extraction with water and, finally, the volatile constituents
(solvents) are removed by distillation under normal pressure. The
2,6-dichlorobenzazoles are then obtained in a very pure condition
by distillation in vacuo. It is possible to dispense with further
purification of the reaction products.
The following examples are intended to illustrate
the invention in greater detail.
-6
~ ~82~
Example 1
240 g (1 mole) of potassium 2-~ercapto-6-chlorokenzthia-
zole are suspended in 800 ml of tetrachloroethane and 3.5 g of
dimethylformamide are added. 1.0 mole of chlorine is passed in at
room temperature and 1.4 moles of chlorine are passed in at 85 to
90 C. The sulfur dichloride is then distilled off, together with a
little tetrachlor oe thane, and the potassium chloride is filtered off
and rinsed with 200 ml of tetrachloroethane. ~fter the tetrachloro-
ethane has been removed by distillation under normal pressure,
192.1 g of 2,6~dichlorobenzthiazole (99.6~ pure according to gas
chromatography), corresponding to a yield of pure material of 93.8%
of theory, are obtained by vacuum distillation (under 1.3 mbars).
Melting point 96C.
Example 2
The reaction is carried out as described in Example 1.
Hcwever, 3.0 moles of chlorine are passed in. The solvent 1l~Pd is
chlorobenzene.
Yield: 191.1 g of 2,6-dichlorcbenzthiazole (99.9% pure
according to gas chrcmatography), corresponding to a yield of pure
material of 93.7~ of theory. ~elting point 96 & .
Example 3
240 g (1 mole) of 98% strength potassium 2-mercapto-6-
-chlorobenzthiazole are suspended in 800 ml of chlorobenzene. 3.5 g
of d~methylformamide are added and 1 mole of chlorine is passed in
initially at room temperature, follcwed by a further 2 moles of
chlorine
~r~
.
1 1~824~
at 85 to 90C. m e sulfur dichloride which has been
formcd is tllen clistilled off, together with some chloro-
benzene (150.9 g), and 200 ml of water are added at
approx. 60C. The aqueous phase is drained off,
after which the solvent is distilled off from the organic
phase under normal pressure. The residue is distilled
in vacuo, under 1.3 mbars, 187.4 g of 2,6-dichlorobenz-
thiazole (9~% pure according to gas chromatography) being
produced, corresponding to a yield of pure material of
92.0% of theory. Melting point 95C.
Example 4
The reaction is carried out as in Example 1, but
without the addition of dimethylformamide, and 190.6 g
(93 4~ of theory) of 2,6-dichlorobenzthiazole are
obtained.
Example 5
223 5 g (1 mole) of potassium 6~chloro-2-mer-
captobenzoxazole are suspended in 500 ml of chlorobenz-
ene and 180 g (2.5 moles) of chlorine gas are added in
the course of 3 hours at a temperature of approx. 25C.
Stirring is con~inued for 12 hours at room temperature
and excess chlorine is blown out of the mixture by means
of nitrogen. The precipitated potassium chloride is
filtered off and rinsed with approx. 200 ml of chloro-
benzene. The filtrate is then distilled. Whenthe sulfur dichloride and chlorobenzene have been dis-
tilled off, 171 g (91% of theory) oX 2,6-dichlorobenz-
oxazole are obtained, having a melting point of
49 - 51C and a boiling point of 124 - 12~.5C under
116824~
_ g _
approA. 25 mbars.
EXam~le 6 (_onlpaIison)
202 g (1 mole)of 6-chloro-2-mercaptobenzthiazole
and 3 5 g of dimethylformamide are suspended in 1,000 ml
of tetrachloroethane, and 1.05 moles of chlorine are
i.nitially passed in at room temperature, followed by 1.4
moles of chlorine at 85C. m e sulfur dichloride and
the tetrachloroethane are distilled off under normal
pressure and 167.6 g of 2,6-dichlorobenzthiazole, cor-
responding to 82.1,' of theory, are then obtained by
~acuum distillation under a pressure of 1.3 mbars at a
delivery temperature of approx. 123C.
