Note: Descriptions are shown in the official language in which they were submitted.
~3~
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Case 3-13693/CGM 264/1+2/=
. . _
Continuous process for the preparation of alkyltin
thiocarboxylic acid esters
Alkyltin thiocarboxylic acid esters are known stabilisers for
homopolymers and numerous copolymers of vinyl chloride.
Their preparation is described e.g in Houben-Weyl,
Methoden der Organischen Chemie , Vol. XIII/6 (1978),
pp. 348-350. It is carried out by discontinuous reaction
of alkyltin oxides or alkyltin halides, in particular
alkyltin chlorides, with thiocarboxylicacid esters. The re~tion
with alkyltin chloride is preferably carried out in the
presence of a base as acld acceptor, under different
temperature, time and pH conditions.
The preparation of alkyltin thiocarboxylic acid esters from the
corresponding alkyltin halides is normally carried out in
the presence of an organic solvent, as described e.g. in
US patent 2 832 751. It is also known from the literature
to carry out the reaction without a solvent (q.v. US patent
3 716 568).
In the batchwise process~ using an organic solvent, it is
possible to carry out the reaction both at relatively low
and at more elevated temperature. In this reaction, the
aqueous phase is usually well and cleanly separated from
~he product p`hase.
The processes carried out without a solvent result in a
~ higher space/time yield~ Further, the step of
; regenerating the solvent is made redundant in these
processes.
The essential drawbacks of the process~s carried out with
an organic solvent are that the space/time yield is
dras~icaliy reduced and the solvent employed has to be
removed by distillation in the working up phase, resulting
in energy consumption and in spent air and wastewater
pollution. In addition, the flash point of the product
falls sharply on account of solvent residues, so that
greater safety measures are required in the plant.
On the other handJ the absence of a solvent in the
10 solvent-free processes is a disadvantage~ as usually a
very poor separation o the organic product phase from the
aqueous phase results. This means long standing times and
also product loss through the ~ormation of an intermediate
phase. In addL~on~ lengthy distill.ation times are requir~ed
15 for the residual water because of the difficulty of
separating it from the organic phase, with the consequence
that the product is subjected to prolonged exposure to heat.
Low temperatures are necessary for the batchwise
reaction of alkyltin halides with thiocarboxylic acid este~.The
20 reaction is so strongly exothermic that the addition of base
can only be made as quickly as the removal of heat through
the reactor jacket permits, thus resulting in lengthy
reaction times in large-scale production and, accordingly,in
a lower space/time yield. Moreover, at the start of the
25 addition of base the pH of the reaction mixture is ln the
strongly acid range (below pEI 1) and then gradually rises
to the neutral range. During the reaction in the acid range,
undesirable saponification reactions may occur7 e.g.
of the thiocarboxylates, which impair the quality of the
product. In addition, previous experience has shown that 7
in batchwise operation, the final pH value must be
adjusted exactly, so that uniform production is only ensured
~2 ~
by very careful monitoring. Exceeding the pH value results
in diminished product quality and in product loss.
The reaction of alkyl tin oxides with e.g. thio~rboxylic acid esters
necessitates the technically complicated intermediate
isolation and drying of the alkyltin oxides. The process
described in German Auslegeschrift 2 209 336 affords no
advantages, as the thin-film process requires complicated
reaction apparatus.
I~ is the object of the present invention to provide a
10 continuous process for the preparation of alkyltin thiocarboxylic
acid esters, which process makes it possihle to react
the reactanta in simple apparatus with short dwell times,
at constant pH and and in a wide temperature range, iE
desired without coollng or removing the heat of reaction
15 and neu~ralisation, thereby eliminating the pre~iously
descr~bed drawbacks of the known processes.
;
Accordingly, the present invention relates to a process
for the preparation of alkyltin thiocarboxylic acid es-ters from
alkyltin halides and thiocarboxy~c acid esters in the presence of
20 an acid acceptor~ which process comprises carrying out
the reaction continuously in a system consisting of 1 to 5
agitator vessels with an average dwell time of 1 to 60
minutes~ at a constant pH value in the range from 3 to 8,
~ ; and in a temperature range from 40 to 80C.
: ~ :
Surprisingly, it has been found that only in a continuous
operation~ as opposed to a discontinuous process, does no
loss of qualiSy occur, as the product is exposed to high
temperatures only for a short time and at a constant pH
value, preerabl~ in the neutral range. Accordingly~ it is
possible to obtain products in a continuous process, e.g.
~ 5~
at 75 C and pH 6.5, without loss of quality and in
substantially hi~her space/time yield. In addition, the
desired pH range can be easily adjusted during the entire
reactiOn. The process is carried ou~ in a continuously
operating reaction system consisting of 1 to 5 reaction
vessels, preferably of two reaction vessels.
If the reac~ion is carried out in a two-stage agitator
- vessel cascade~ the dwell time in the first vessel will be
from 1 to 60 minutes, preferably from 1 to 10 minutes, bu~
io most preferably from 1 to 5 minutes. The vessels of the
two-stage cascade may be of the same or different size.
The dwell times in the individual reaction vessels will
there~ore correspondingly dif~er. The reaction temperature
is in the range from 40 to 80C, preferably Erom 50 to
15 60C. By appropriate choice of temperature when charging
the reaction vessels with the starting materials~ it is
also possible to carry oùt the reaction adiabatically
This is done by adding the starting materials continuously
at low temperature, preferably in the range from 20 to 30C.
20 The heat o reaction and neutralisation need not be removed,
so that cooling energy can be saved.
In the continuous operation of this invention, the pH range
is kept between 3 and 8, preferably at a constant value
between 5 and 7, during the entire reaction. The pM can be
25 adjusted in simple manner, e.g. by a pH meter~ with a base.
Suitable bases are: alkali metal hydroxldes and alkaline
earth metal hydroxides such as sodium~ potassium or
calcium hydroxide; alkaline earth oxides such as calcium
oxide; and also ammonia or alkali me~al carbonates such
30 as sodium carbonate or potassium carbonate. They are
preferably used in the form of 10 to 50 % solutions.
Particularly advantageous is e.g. 18 to 20 % sodium
~ 3
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hydroxide solution. However, tertiary amines such as
triethylamine or pyridine may also be used, if desired,
It i9 preferred to carry out the reaction of this invention
without an organlc solvent However, the reaction may also be
carried out in the presence of an inert organic solvent.
Examples of suitable solvents are aliphatic and aromatic
hydrocarbons, ethers, esters and ketones, such as he~ane,
petroleum ether, toluene, xyLenes, methyl isobutyl ketone
or methyl acetate.
10 Various alkyltin thiocarboxylic acid esters may be prepared by the
process of this invention. Particularly interesting compounds
are those of the formula
Rxsn[s(cH2)ncooR ]4-x
wherein x and n are l or 2, R is methyl, butyl, octyl~
15 Lauryl or the -CH~C~2C00-n-C4Hg group, and R' is a
-cl6alkYl group
R às butyl may be n-butyl, isobutyl or tert-butyL, with
n-butyl being preferred. R as octyl may be n-octyl or
2-ethylhexyL, with n-octyl being preferred.
20 R' may be e.gO straight chain or branched octyl, decyl,
~` - dodecyl, tetradecyL and hexadecyL, as well as the
commercially a~ailable mixtures of alcohols known as
alfols, which contain substantially alkyl groups having
the same number of carbon atoms and are mainly branched.
~;; 25 The alkyl groups are here known as "aLfyls"
The starting materials employed for ~he proces~ are alkyltin
haLides and thiocarboxylic acid esters. The alkyltin haLides
~ 5
-- 6 --
employed are chlorides, bromides or iodides, preferably
alkyltin chlorides or bromides in an amount of 85 to
115 mole %, based on the thiocarboxylic acid esters. The thio-
carboxylic acid esters are known compounds. Thioglycolic and
thiopropionic acid esters are especial]y preferred.
The initiation of the continuous reaction is conveniently
effec~ed batchwise, beginning first with the addition of
the reagents, then adding the a~ueous solution of ~he base
for adjusting the desired pH range, and finally adding
10 both reaction omponents and the solution of the base
continuously.
The starting alkyltin halides and thiocarboxyLic acid esters may be
added to the reactor at 20-30C either as a previously
prepared mixture or added separately at different
15 temperatures
The process of the invention may be carried out e.g. in the
following system:
To initiate the reaction, the appropriate alkyltin chlori~e
or chlorides and the corresponding thiocarboxylic acid ester
20 are pumped in the required molar ratio into the reactor
until this latter is about half full, With stirring, an
aqueous solution of the base is then added until the desired
pH value is reached, after wh~l the continuous addition
of the sodium hydroxide solutiona the alkyltin chloride(s)
25 and the thiocarboxylic ~d ester is commenced with. When the
controlled volume has been reached, the reaction mixture
is pumped into the second reactor such that the controlled
volume in the second ag~ator vessel is maintained.
~: :
After an average dweLl time o~ 1 to 60 minutes, pre~erably
30 of 1 to 10 minutes and, most preferably, of 1 to 5 minutes,
~238C3
-- 7 --
the reaction mixture is discharged con~inuously from ~he
reactor in order to separate the organic phase from the
aqueous phase, The separa~ion of the water from the reac~ion
mixture drawn off from the reactor is preferably effected
by a continuously operating liquid-liquid extractor or
else also by suitable separating columns.
Liquid-liquid extractors are conventional separators used
in chemical engineering. Particulars on the individual
extraction methods are to be found in Ullmann,
10 Enzyklop-adie der technischen Chemie, Vol. 2, 4th
edition (1972)~ on page 553, and a description of ~he
individual apparatus and extractors will be found on
pp. 560-564. The continuously operating liquid-liquid
centrifugal extractor is particularly advantageous for
15 separating water from the reackion mixture drawn of from
the reactor 9 preferably at 4~-50C.
The so isolated product phase may conveniently also be
dried continuously, e.g. by continuous spray drying or al50
with ~he aid of a thin-film or falling film
20 evaporator.
Spray drying, thin-film or falling film evaporators are
also known drying or evaporating systems. Such equipment
is described e.g in Ullmann, Enzyklopadie der technischen
Chemie. Vol. 2, 4th Edition (197Z) on pp, 712-713
25 (spray driers) and on pp. 655-656 (thin-film and fal~ing
film evaporators).
The following Examples describe the invention in more
detail
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Example 1: 100 parts by weight of a mixture of 30 mole %
of mono-n-octyltin trichloride and 70 mole % of
di-n-octy~in dichloride together with 104 parts by weight
of 2-ethylhexyl thioglycolate are pumped continuously
at a temperature of 60C into a reactor system comprising
a cascade of two reactors each equippecl with stirrer, level
meter,pH meter and thermome~er. With efficient stirring~
aqueous sodium hydroxide solution is simultaneously added
to the reaction mass such that a pH of 6.5-7.0 is
lQ maintained in the first reactor. The addition of sodium
hydroxide is controlled by the pH meter in the first
reactor. The reaction mixture is pumped into the second
reactor, the volume being controlled by the level meter.
Feed and discharge of the reaction mixture are controlled
15 such that the dwell time of the reaction mass in the first
reactor is 5 minutes. The heat of reaction liberated
during the reaction is removed such that a constant
temperature of 60C is kept in the fir~t and in the second
reactor.
20 Aqueous sodium hydroxide(very little~ is also introduced
into the second reactor in order to maintain a constant pH
of 6.9 (control of addition by pH meter). The reaction mass
is then pumped from the second reactor into a liquid-liquid
extractor, in which the salt-containing aqueous phase is
25 separated continuously from the product. The product is
then spray dried and clarified by filtration, ~o give
a viscous liquid consisting of a mixture of 30 mole % of
2-ethylhexyl mono-n-octyltin tristhioglycolate
and 70 mole % oE 2-ethylhexyl di-n-octyltin bisthioglycolate.
30 The yield is 98 % of theory, based on the two starting mono
and dioctyltin chlorides.
Analysis: Sn (theory) : 15.5 %; S: 9.0 %
Sn (found) : 15.2 %; S: 8.9 %.
~38~5
Example 2: 100 parts by weight of mono-n-butyltin
trichlori.de and 307 parts by weight of tetradecyl
thioglycolate are pumped continuously a.t a temperature of
30C into a reactor system comprising a cascade of two
reactors each equipped with stirrer, l.evel meter~
pH meter and thermometer Aqueous sodium hydroxide is
introduced in~o the first reactor (control of addition by
pH meter) such that a p~ of about 5 is kept therein. The
reaction mass is then pumped into the second reactor, the
10 volume being controlled by the level meter Feed and
discharge are so controlled that the dwell time of ~he
reaction mass in the first reactor is 2 minutes. The heat
: of reaction is removed so that the temperature in the first
and second reactor does not exceed 50 C.
15 Aqueous sodium hydroxide is also introduced into the second
reactor in order to obtain a constant pH of 5
(control of addition by pH meter). The reaction mass is
pumped from the second reactor into a continuously operating
liquid-liquid extractor which separa~es the aqueous
20 phase from the product phase. The produc~ phase is then
spray dried and clarified by filtration, affording a
viscous liquid of the formula n-C4HgSn(SCH2COOC14H29)3.
The yield is 96 % of theory, based on the starting
mono-n-butyltin tri~hloride.
25 Analysis: Sn (theory) : 11.4 %; S: 9 3 %
Sn (found) : 11.2 %; S: 901 %,
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E~ A previously prepared mixture of 100 parts by
weight of di-n-octyltin dichloride and 98 parts by weight of
2-ethylhexyl thioglycolate is pumped con~inuously at room
temperature into a reactor system comprising a cascade
of two reactors each equipped with stirrer, level meter,
pH meter and thermometer. Simultaneously, aqueous sodium
hydroxide solution is added, with efficient stirring, to
the reaction mass such that 2 pH of 6.5 to 7.0 is maintained
in the first reactor. The addition of sodium hydroxide is
10 controlled by the pH meter in the first reactor. The heat
of reaction liberated during the reaction is not removed.
The reaction temperature is 65C. (The temperature is
determined by the adiabatic mode of operation and is
dependent on the temperature of the starting mixture of
15 dioctyltin dichloride and 2-ethylhexyl thioglycolate).
The reaction mass is then pumped into the second reactor
(volume control by the level meter), Feed and discharge
of the reaction mixture are so controlled that the dwell
time of the reaction mass in the first reactor is 5
20 minutes.
Aqueous sodium hydroxide solution (very little) is also
introduced into the second reactor in order to maintain a
constant pH of 6.9 (control of addition by pH meter). The
reaction mass is then pumped from the second reactor into a
25 liquid-liquid extractor, in which the salt containing
aqueous phase is separated continuously from ~he product.
The product is subsequen~ly spray dried and clarified by
filtration, affording a v~cous liquid consisting of
2-ethylhexyl di-n-octyltin bi~oglycolate The yield is
30 97 % of theory~ based on the starting di-n~octyltin
dichloride.
Analysis : Sn (theory) : 15,8 %; S: 8.5 %
Sn (found) : 15~7 %; S: 8.3 %.
