Note: Descriptions are shown in the official language in which they were submitted.
2~98618
W097/03954 PCT~S96/11460
1 COMPOSITIONS CONTAINING PENTAERYTHRITOL
TETRAESTERS AND PROCESS FOR PROL)U~:llON TT~l~RF.OF
The present invention relates to novel
compositions containing tetraesters of
5 pentaerythritol, and to processes by which such
compositions can be produced. More specifically, the
present invention relates to the production of tetra
(3-alkylpropionate) esters of pentaerythritol by a
novel process which affords a number of process
10 advantages, which process also produces a novel
composition from which its major component, the
tetraester, can readily be recovered and purified.
Alkyl esters derived from alkylthioalkanoic
acids and the like are, in general, known to be useful
15 as stabilizers of organic materials such as polymer
resins and the like which are otherwise subject to
thermal and oxidative deterioration during processing,
extrusion or molding, as well as during use. Esters
having this general utility have in the past been
20 prepared by various procedures. Dexter, et al. U.S.
Patent No. 3,758,549, for example, basically teaches
transesterification procedures for the preparation of
these types of products. By such procedures, it is
often difficult to obtain a product that has a
25 tetraester content at or above 90% by weight,
particularly when the transesterification is carried
out on an industrial scale.
Stabilizers for enhancing the resistance of
polyolefins to deterioration can also be prepared by
30 reacting an alpha-olefin with a multi-functional ester
t of a mercaptocarboxylic acid. Stabilizers of this
W097/03954 PCT~S96/11460
219~fi~8
1 type and the process for their preparation are
disclosed in Kauder, et al. U.S. Patent No. 4,080,364.
Experience with this type of addition reaction
indicates the product thus formed has a tetraester s
5 content which typically does not meet or exceed 90~ by
weight.
Nakahara, et al. U.S. Patent No. 4,349,468
teaches the preparation of a pentaerythritol tetrakis
(3-laurylthiopropionate) stabilizer for polyolefins
10 which is produced by a process including heating an
alpha-olefin such a l-dodecene with a beta-
mercaptopropionic acid or ester in the presence of an
azonitrile or peroxide catalyst, followed by
esterifying the resultant alkylthiopropionic acid with
15 pentaerythritol. The resulting product is typically
inferior in that the alpha-olefin reaction produces an
unwanted isomer byproduct that, if not removed in a
separate purification step, lowers the quality of the
pentaerythritol ester.
Chisholm, et al. U.S. Patent No. 5,057,622
discloses production of a pentaerythritol tetraester
of 3-alkylthiopropionic acid by a process in which,
first, the corresponding alkyl mercaptan is reacted
with sodium acrylate under strongly basic conditions,
25 followed by acidification and a series of steps to
recover the free 3-alkylthiopropionic acid. Then, the
acid is esterified with pentaerythritol in the
presence of a strong acid catalyst. This overall
process scheme is relatively volume inefficient and
3o can present difficulties in the recovery of the
tetraester from its byproducts. f
2198618
W097/03954 PCT~S96/l1460
1 In addition, Chisholm, et al. U.S. Patent
Q No. 5,057,622 demonstrates that attempts to produce
pentaerythritol tetraesters o~ 3-dodecylthiopropionic
acid using the processes of the aforementioned Dexter,
5 et al. U.S. Patent No. 3,758,549, Kauder, et al. U.S.
Patent No. 4,080,364, and Nakahara, et al. U.S. Patent
No. 4,349,468 gave results that were unsatisfactory as
to reaction time, efficiency in catalyst use, yield,
presence o~ undesired byproducts, and/or ease of
10 recovery.
Thus, there remains a need for a process
that produces 3-alkylthiopropionate tetraesters of
pentaerythritol efficiently and that does so in a
manner that permits simple recovery of the tetraesters
in high yield.
The present invention is directed to a
process for producing a pentaerythritol tetrakis 3-
alkylthiopropionate tetraester wherein each alkyl
portion contains 4 to 20 carbon atoms, comprising
reacting pentaerythritol and lower alkyl (preferably
methyl) 3-alkylthiopropionate in the presence of an
organotin catalyst for said reaction under elevated
temperature conditions at which said tetraester forms.
More speci~ically, the pentaerythritol is reacted with
one or more lower alkyl 3-alkylthiopropionate esters,
wherein the lower alkyl portion contains 1 to 4 carbon
atoms and is unbranched, and the alkyl portion
contains 4 to 20 carbon atoms.
The present invention is also directed to
3o compositions of matter comprising at least about 90
wt.~, and more advantageously at least about 95 wt.%,
W097/039s4 PCT~S96/11460
2~98~ ~4~
1 of one or more tetrakis 3-alkylthiopropionate
tetraesters of pentaerythritol wherein each alkyl
portion contains 4 to 20 carbon atoms, together with
one or more tris(3-alkylthiopropionate) esters of
5 pentaerythritol and with lower (Cl to C4 ) alkyl 3-
alkylthiopropionate, i.e. methyl, ethyl, n-propyl or t
n-butyl 3-alkylthiopropionate, in each of which the
alkyl portion contains 4 to 20 carbon atoms.
The tetraesters produced in accordance with
the present invention are useful as stabilizers of,
for instance, polymeric resins against thermal
degradation and oxidative deterioration during
processing, extrusion or molding, as well as during
use of such polymeric materials.
The present invention uses lower alkyl 3-
alkylthiopropionate, wherein "lower alkyl" denotes an
alkyl chain, preferably not branched, which when
substituted with -OH is a relatively volatile alkanol.
Preferred lower alkyl groups are methyl, ethyl, n-
propyl and n-butyl. The most preferred lower alkyl
group is methyl. The 3-alkylthiopropionate used in
the process of the present invention can have been
formed by any of a number of techniques, the preferred
one of which is described hereinbelow.
The 3-alkylthiopropionate can be made by a
direct addition reaction procedure which is carried
out in order to minimize the recovery of anything
other than the desired 3-alkylthiopropionate. The
length of the carbon chain of the alkyl group within
the 3-alkylthiopropionate is selected by the carbon
chain length of the mercaptan which is charged into
2198618
W097/03954 PCT~S96/11460
~t ' ,~ ' .
~ ~ = r
l the reaction vessel. The selected mercaptan undergoes
an addition reaction with methyl acrylate to form the
3-alkylthiopropionate. The mercaptan has the formula
RSH, wherein R has a carbon chain length of between 4
and about 20 carbon atoms. Exemplary reactants in
this regard include n-butylmercaptan, n-
octylmercaptan, n-decylmercaptan, n-dodecylmercaptan
and the like. Generally equimolar charges of this
mercaptan and the ester addition reactant are
incorporated into the reaction vessel, although either
component may be present at a concentration slightly
in excess of the equimolar level.
The other addition reactant, which may be
characterized as the acrylate reactant, can be charged
to the reaction vessel as the corresponding lower
alkyl acrylate, wherein "lower alkyl" is as de~ined
above. The preferred reactant in this regard is
methyl acrylate. The addition reaction is run under
strongly basic conditions. Any strong base can be
utilized as the catalyst, provided an aqueous solution
thereof will impart a pH of at least about ll. The
strength of the base can be generally defined as one
wherein a 1% aqueous solution thereof has a pH of at
least about 13. Typically strong bases in this regard
include aqueous potassium hydroxide, and aqueous
sodium hydroxide. However, it is preferred to run
this reaction solvent-free, so solid pellets of
potassium hydroxide or other strong base are
preferably used rather than an aqueous solution. It
is important that the reaction composition incorporate
an adequate concentration of this strong base. The
W097/039S4 PCT~S96/l1460
2~9~8 -6- -
1 amount iB to be adequate to act ~s~a catalyst for the
addition reaction. For example, the reaction
composition should typically include at least about 1
to 2 mole percent of strong base per mole of acrylate
charged into the reaction vessel.
After the addition reaction has progressed
to the desired extent, the 3-alkylthiopropionate is
isolated from the reaction composition by proceeding
first with acidi~ication of the reaction mixture,
typically with a suitable aqueous mineral acid.
Aqueous and organic layers thereby defined are then
separated. If necessary, depending upon the carbon
chain length of the mercaptan reactant, the layers are
maintained at a temperature high enough to keep the
alkylthiopropionate molten. After separation has been
completed, the collected organic phase is preferably
vacuum stripped in order to remove (and optionally,
recover) unreacted components and thereby provide the
3-alkylthiopropionate addition reaction product.
The lower alkyl, and preferably methyl, 3-
alkylthiopropionate, however produced or obtained, is
reacted with pentaerythritol to produce the desired
tetraester. It has been discovered that this reaction
proceeds, at satisfactory rate and yield, when the 3-
alkylthiopropionate and the pentaerythritol are
reacted in the presence of an organotin catalyst for
the reaction, under elevated temperature conditions.
It is preferred to employ an amount of the ester
representing a stoichiometric excess with respect to
3o the amount of pentaerythritol present. Generally the
amount of organotin catalyst can range up to about 5.0
W097/03954 21 9 8 6 ~ 8 PCT~S96/11460
--7--= =
l wt ~ based on the amount of pentaerythritol present,
although higher amounts of catalyst can be used to
advantage as well.
Preferred catalysts include organotin
5 compounds, in particular monoalkyltin hydroxide,
monoalkyltin chloride, monoalkyltin chlorohydroxide,
and/or mixtures thereo~, wherein the alkyl group
contains l to 8 carbon atoms. Mixtures of any of the
foregoing may also be used to advantage. Particularly
l0 preferred catalysts include monobutyltin chloride and
monobutyltin hydroxide, and a more preferred catalyst
comprises a 50:50 (by weight) mixture of monobutyltin
hydroxide and monobutyltin chloride, the total
combined amount of catalyst comprising about l.5 to
2.0 wt.~ based on the amount of pentaerythritol
present. Preferably, at least one organotin chloride
compound, and more preferably at least one alkyltin
chloride, compound is present in the catalyst
component.
Other useful catalysts include di(C1 to C8)
alkyl tin bis- (C8 to C12) carboxylate such as dimethyl
tin bis-neodecanoate, as well as mono (C1 to C8) alkyl
tin tris (3-alkylthiopropionate) and di (Cl to C8)
alkyl tin bis (3-alkylthiopropionate). Preferred
examples of the latter include dimethyl tin bis-3-
laurylthiopropionate and methyl tin tris-3-
laurylthiopropionate.
The reaction of the lower alkyl, e.g.
methyl, 3-alkylthiopropionate, pentaerythritol, and
3o catalyst should be carried out solvent-free. If
desired, a small but e~fective amount of solvent may
W097/03954 ,- PCT~S96/11460
~ ~9~6~8 -8-
l be employed, but it would have to be inert to the
reactants, have a very high boiling point, and be
relatively easily removed from the mixture formed by
the reaction.
The reaction is carried out at temperatures
effective to enable formation of the desired
tetraester. Effective reaction temperatures are
typically in the range of 150~C to 250~C, and more
typically in the range of about 175~C to 225~C. As
those experienced in this field will recognize, it may
be desirable to adjust the temperature during the
course of the reaction, for instance by raising the
temperature. The time required for satisfactory
conversion in the reaction can typically range from 2
to 20 hours.
The fact that such reaction temperature
conditions are able to achieve formation of the
desired tetraester product, particularly in
significant yields at acceptable rates, has been
confirmed and is all the more unexpected in view of
the teachings in the prior art, such as U.S. Patent
No. 5,057,622, suggesting that production of the
desired tetraester by transesterification would not be
successful. Indeed, the process of the present
invention accomplished formation of the desired
tetraester at yields above about 70% even before
isolation of the desired product.
It is also preferred to carry out this
reaction under relatively high vacuum, which thereby
3o provides shorter reaction times and more complete
reaction. While vacuum of about 15 mm Hg is useful,
W097/03954 2 ~ 9 8 6 1 8 . PCT~S96/l1460
_ g _
:
1 high vacuum on the order of about 2 mm Hg is
preferable.
Following completion of the
transesteri~ication reaction to form the desired
5 tetraester, the tetraester can be recovered from the
reaction mixture by subsequent recovery and
purification steps using procedures which are well
known in this field. For instance, the catalyst
should be filtered off and the product purified by one
10 or more recrystallization steps.
It is preferred that this
transesterification procedure be followed by an
operation wherein the organic phase is solvent refined
with an organic solvent. Preferably, the solvent
refining medium is one or more organic solvents which
are particularly well suited for the specific
alkylthiopropionic tetraester being prepared. A
preferred solvent is 2-propanol (isopropanol). Other
exemplary solvents include other low molecular weight
alcohols and low molecular weight esters, including
materials such as methanol, ethanol, ethyl acetate,
isopropyl acetate, and the like. It has been found
that a suitable solvent or blend will improve work-up
purification procedures, when desired, in a manner
that minimizes the expense thereof.
As an example of suitable organic solvent
blends, a blend of methanol and isopropanol is
generally preferred for the work-up purification of
the liquid tetraester of 3-octylmercaptopropionic acid
3o with pentaerythritol. It has been found that this
solvent blend is non-miscible with this tetraester and
W097/03954 - PCT~S96/11460
2~986i8 -10-
l performs well as an extracting solvent for any
triester impurity and unreacted octylmercaptopropionic '
acid. A typical two-component solvent blend would be
at a ratio of between about 9 to l and about l to 9.
In this manner, a product can be obtained
which contains 90 wt.~ or more, preferably 95 wt.~ or
more, of the desired tetra (3-alkylthiopropionate)
ester of pentaerythritol. The composition of matter
will also contain minor amounts of the triester, that
is, a tri (3-alkylthiopropionate) ester of
pentaerythritol, as well as a minor amount of
unreacted lower alkyl, e.g. methyl, 3-
alkylthiopropionate ester. Generally, the amounts of
the triester byproduct and of the unreacted ester can
comprise up to about O.l wt.~ or even up to about l
wt.~, although of course lesser or higher amounts may
be present depending on the degree of completion of
the reaction.
Esters of the type discussed herein are
typically suitable for use as stabilizers for
polymers. The tetraesters with pentaerythritol have
been found to be especially useful as stabilizers for
a class of proprietary polymers and polymer blends
having a terephthalate ester component and a rubbery
type of component. Articles extruded from these types
o~ proprietary polymers have superior impact
resistance properties and can be suitable for use as
automobile bumpers and the like. The 3-
dodecylthiopropionate tetraester of pentaerythritol
3o has been observed to be generally equal in performance
to similar ester stabilizers manufactured on a
W097/03954 21 9 8 61 8 PCT~S96/11460
--11- i.,; .
1 commercial scale by a process believed to be more
complicated than the procedure of the present
invention.
Various tetraester stabilizers prepared
5 according to this invention have different physical
properties which may be particularly advantageous for
different proprietary polymers. For example, esters
made from dodecylmercaptan are solid at room
temperature and less likely to exhibit a noticeable
10 odor when in use as a stabilizer. Esters made from
octylmercaptan are basically liquid at room
temperature, are less waxy than esters having a
greater molecular weight, and can be more compatible,
particularly with polymer resins that tend to be
liquid at room temperature. Esters prepared from
decylmercaptan typically have properties the-
reinbetween, and they can exhibit good compatibility
without excessive volatility.
The invention is described further in the
following Examples, which are present for purposes of
illustration and are not intended to limit the scope
of that which is regarded as the invention.
3o
WOs7/03954 PCT~S96/11460
219~18 -12-
1 EXAMPLE 1. ~5
A. Production of Methyl 3-laurY~thiopro~ionate:
In a one-liter 3 neck flask was placed 380 g
lauryl mercaptan (LM). After fitting the flask with a
5 condenser and nitrogen purge, 2.0 g KOH pellets were
added. An addition funnel with 160 g methyl acrylate
(MA) was placed on the flask. The contents of the
flask were heated to 55~C. The MA was then slowly
added over 90 minutes to maintain the temperature
l0 between 50~C and 65~C. After an additional 30 minutes
of mixing, the contents were analyzed. An additional
6 g MA was added and mixed for 45 minutes. After
analyzing, the product was washed by adding 2.0 g
concentrated H~SO4, 200 g water and mixing. After
settling, the aqueous layer was decanted and the
product was transferred to a side-arm flask. The
product was dried and the residual MA was steam
stripped off under vacuum at 93~C.
B. Production of Pentaerythritol Tetrakis (3-
Laurylthiopropionate)
In a one-liter sidearm flask were placed
491.4 g of the product of Step A., 46.38 g mono-
pentaerythritol, 0.34 g monobutyl tin hydroxide and
0.34 g monobutyltin chloride. The mixture was heated
under vacuum to 175~C for l hour, then the temperature
was increased to 200~C for 3 hours. The product was
analyzed and then filtered using Whatman #40 filter
paper and Celite filter aid to remove a small amount
3~ of solids. To a 2 liter beaker 477.0 g filtered
product and 477.0 g isopropyl alcohol (IPA) were
W097/03954 2 1 9 8 6 1 8 PCT~S96/l1460
-13-
l added. The mixture was heated to 50~C and with
-I stirring allowed to cool and crystallize. The mixture
was cooled to 27~C and the crystals were collected and
washed with 20 ml IPA. The crystals and mother liquor
5 were analyzed. To a clean 2 liter beaker 342 g "wet"
crystals and 313 g IPA were added. This mixture was
heated to 57~C. With stirring it was allowed to cool
and crystallize. After cooling to 27~C the crystals
were collected and washed with 20 ml IPA. The
lO crystals and mother liquor were analyzed.
The IPA was then stripped f rom the two
mother liquors by heating under vacuum to 95~C. The
two mother liquors were combined and analyzed
To a 500 ml side arm flask were added 174.8
l~ g mother liquors and 6.89 g pentaerythritol. No
catalyst was added because the mother liquors
contained catalyst. The mixture was heated to 2000C
under vacuum and cooked for 2 hours. A dark gray
product formed which was analyzed and filtered using
Whatman #40 filter paper and Celite filter aid. The
filtered product was light yellow.
To a beaker was added 146.9 g filtered
product and 146.9 g IPA and those contents were heated
to 46~C. The solution was cooled with stirring to
27~C. Crystals formed and were filtered off and
washed with 20 ml IPA. Crystals and mother liquor
were analyzed.
To a beaker 91.9 g "wet" crystals and 92.3 g
IPA were added. The mixture was heated to 54~C and
3o then was cooled to 27~C with stirring. The crystals
were filtered off and washed twice with 20 ml IPA.
W097/03954 . PCT~S96/11460
2~9~6~ -14-
l The extra wash was given because of the larger
percentage of catalyst present. The crystals and
mother liquor were analyzed.
Analyses of the various reaction products
5 and fractions for methyl 3-laurylthiopropionate
("ML"), pentaerythritol tris (3-laurylthiopropionate)
("Tris"), and the desired tetraester, in wt.~, are
shown in the following Table 1:
Table 1
HPLC
%ML ~Tris
%Tetraester
After Cook 18.00 9.74 72.26
1st Crystals 2.92 1.86 95.22
15 1st Mother liquor61.28 32.62 6.10
2nd Crystals 0.57 0.73 98.69
2nd Mother Liquor47.10 44.15 8.75
Mother Liquor Rework
20 After Cook 16.59 8.58 74.83
1st Crystals 2.25 1.34 96.41
1st Mother Liquor53.12 34.69 22.19
2nd Crystals c.l c.l >99.8
2nd Mother Liquor43.42 29.17 27.41
The yield based on 2nd crystals and mother
liquor crystals was 84.4~.
The yield based on pentaerythritol was 96.6
(including rework crystals and known losses).
EXAMPLE 2
3~The transesteri~ication reaction to produce
pentaerythritol tetrakis (3-laurylthiopropiona~e) was
W097/03954 219 8 6 18 PCT~S96/11460
-15- ~
l carried out with varying amounts of two different
cataly~ts to assess desirable catalyst amounts. The
reactions were run for 6 hours at 205~C with mild
vacuum being applied for the last two hours The mole
5 ratio of methyl ester to pentaerythritol was 5:l. The
crude reaction mixture was filtered to remove a small
amount o~ black solids and re-crystallized twice from
equal weights of IPA. It is clear from the results
shown in Table 2 that catalyst type and concentration
are both important factors in determining the yield.
TABLE 2
CatalystConcentration
Yield
15 Monobutyltin hydroxide540 ppm 31.84
Monobutyltin hydroxide1080 ppm 50.96
Monobutyltin hydroxide1620 ppm 59 81
Monobutyltin chloro hydroxide 540 ppm 31.98
Monobutyltin chloro hydroxide 1620 ppm 68.09
Thus, the catalyst concentration is
preferably at least lO00 ppm (based on the total
reaction mass) and more pre~erably at least 1500 ppm.
The process of the present invention affords
a number o~ advantages which distinguish it further
from past practices. The reaction to form the
tetraester can be run solvent-free, thus avoiding the
expense, the additional materials handling burden, and
the solvent removal burden that are imposed by the use
of solvents. Indeed, even the water requirements are
minimal, so contamination of product by water is
3~ likewise minimized. Removal of recrystallization
solvent is easier The tetraester has a lower acid
W097/03954 p~8~8 16- PCT~S96/11460
1 value. The mother liquors (process streams) employed
in the process can be recycled with mihimal
requirements for purification and without requiring
further reactions of the byproducts~present.
