Alkylthiopropionic pentaerythritol esters and solvent refining thereof

3-alkylthiopropionic acids which are esterified with pentaerythritol are provided. The esters are solvent refined with especially effective organic solvent blends. Tetraesters thus processed are especially useful as stabilizers for polymer resins and polymers.

DESCRIPTION 
BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention generally relates to a process for preparing esters 
of S-alkylthiopropionic acids and to the esters thus produced. More 
particularly, the invention relates to esters of 3-alkylthiopropionic 
acids with pentaerythritol or the like which are purified with a solvent 
blend and which are esters having an extremely high level of tetraester 
structure. 
Alkyl esters derived from alkylthioalkanoic acids and the like are, in 
general, known to be useful 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 
prepared by various procedures. Dexter et al U.S. Pat. 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 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 reacting an alpha-olefin with a multi-functional 
ester of a mercaptocarboxylic acid. Stabilizers of this type and the 
process for their preparation are disclosed in Kauder et al U.S. Pat. No. 
4,080,364. Experience with this type of addition reaction indicates the 
product thus formed has a tetraester content which typically does not meet 
or exceed 90% by weight. 
Nakahara et al U.S. Pat. No. 4,349,468 teaches the preparation of a 
pentaerythritol tetrakis (3-laurylthiopropionate) stabilizer for 
polyolefins which is produced by a process including heating an 
alpha-olefin such as 1-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 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. 
Alkylthiopropionic acids prepared by approaches such as these may be 
subjected to solvent refining according to the present invention. However, 
they do not typically directly produce, without special purification, an 
alkylthiopropionic acid which exhibits a high purity characteristic which 
will, when reacted with pentaerythritol or the like, form an ester product 
which has an extremely high tetraester content and a minimum of other 
components such as the triester. At times, a substantially high excess of 
the acid reagent is required, which is costly and inefficienct and can 
require removal of excess acid from the reaction product and purification 
at an intermediate stage. 
It has been determined that a 3-alkylthiopropionic acid having about 4 to 
about 20 carbon atoms in the alkyl group can be prepared by directly 
reacting an alkyl mercaptan having between about 4 and about 20 carbon 
atoms with an alkali metal acrylate, the reaction being carried out in the 
presence of a strong base catalyst, typically within an aqueous alkaline 
solution having a pH of at least about 11. Thereafter, the reaction 
solution is acidified to a pH which is at about 4 or below, and the 
3-alkylthiopropionic acid is then recovered from the water-insoluble phase 
of the acidified reaction solution. A tetraester product is then formed by 
esterification of the 3-alkylthiopropionic acid with pentaerythritol or 
the like. 
By the present invention, a tetraester prepared in this manner or in any 
other suitable manner is subjected to a purification procedure that has 
been found to be especially effective and efficient in removing unreacted 
acid and tris ester components from the tetraester product. The tetraester 
product is solvent refined with a blend of at least two organic solvents. 
Certain solvent blends are especially well suited for particular ester 
products. 
It is accordingly a general object of the present invention to provide an 
improved process for preparing an alkylthiopropionic acid ester. 
Another object of this invention is to provide an improved 
3-alkylthiopropionic acid ester of particularly high purity. 
Another object of the present invention is to provide an improved process 
for the work-up purification of a tetraester formed from a 
3-alkylthiopropionic acid and pentaerythritol. 
These and other objects, features and advantages of the present invention 
will be clearly understood through a consideration of the following 
detailed description. 
DESCRIPTION OF THE TICULAR EMBODIMENTS 
Reactant starting materials are 3-alkylthiopropionic acids having the 
formula RSCH.sub.2 CH.sub.2 COOH, wherein R has a carton chain length of 
between about 4 and about 20. These acids and tetraesters thereof with 
pentaerythritol may be prepared by any suitable procedure. 
The 3-alkylthiopropionic acids may be prepared by a direct addition 
reaction procedure which will minimize the recovery of anything other than 
the desired 3-alkylthiopropionic acid. The length of the carbon chain of 
the alkyl group within the 3-alkylthiopropionic acid is selected by the 
carbon chain length of the mercaptan which is charged into the reaction 
vessel. The selected mercaptan undergoes an addition reaction with an acid 
reactant or salt thereof to add the propionic acid component of the 
3-alkylthiopropionic acid. 
With more particular reference to the mercaptan, same has the formula RSH, 
wherein R has a carbon chain length of between about 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 other addition 
reactant are incorporated into the reaction vessel, although the acid 
component may be present at a concentration slightly in excess of the 
equimolar level. 
Concerning the other addition reactant, which may be characterized as the 
acid reactant, same can be charged to the reaction vessel as acrylic acid 
or as a derivative, typically an alkali metal salt thereof. Because the 
addition reaction is run under strongly basic conditions, the acid 
reactant is perhaps more properly characterized as an alkali metal 
acrylate, with the alkali metal being that of the base component which 
catalyzes the addition reaction. 
Any strong base can be utilized as the catalyst, provided an aqueous 
solution thereof will impart a pH of at least about 11 to the reaction 
composition. 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. 
Typical strong bases in this regard include aqueous potassium hydroxide, 
aqueous sodium hydroxide and the like. It is important that the reaction 
composition incorporate an adequate concentration of this strong base. The 
amount is to be adequate to convert any charged acrylic acid to its alkali 
salt, while still providing enough strong base to act as a catalyst for 
the addition reaction. For example, the reaction composition should 
typically include at least about 1.05 mole of strong base per mole of 
acrylic acid charged into the reaction vessel. 
The base catalyzed addition reaction is carried out with a sufficient 
quantity of solvent within the reaction composition. Preferably, the 
solvent is a mixture of organic solvent and water. Water alone may be 
suitable for acids made from mercaptans with short chain lengths such as 
C4, but using the solvent mixture is believed to be important in most 
cases. For example, the reaction is faster and less subject to foaming 
when the solvent is water combined with an organic solvent. Preferred 
organic solvents in this regard are oxygenated organic solvents, typically 
ones that are water-soluble oxygenated compounds exhibiting a ratio of 
from one to four carbon atoms for every oxygen atom. Exemplary solvents in 
this regard include 2-propanol, tetrahydrofuran, ethanol, methanol, 
2-ethoxyethanol, tert-butyl alcohol the like. An especially preferred 
solvent is a mixture of water and 2-propanol (isopropyl alcohol). A 
typical ratio of water to oxygenated organic solvent is between about 9 to 
1 and about 1 to 9. 
In a preferred aspect of this process, the mercaptan is added to the 
reactant composition after it already contains the alkali metal acrylate. 
It has been determined that, even when the reaction is carried out in the 
presence of oxygen, the incidence of undesirable disulfide formation is 
reduced significantly with this order of addition of reactants, when 
compared with the reverse order of addition, which can be characterized as 
the addition of acrylic acid to the reaction composition which already 
contains sodium mercaptide. When the reverse order of addition is desired, 
typically adequate control of disulfide formation can be attained by 
blanketing the reaction mixture with nitrogen, when this is feasible. 
After the addition reaction has progressed to the desired extent, the 
alkylthiopropionic acid is isolated from the reaction composition by 
proceeding first with acidification 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 alkylthiopropionic acid molten. After 
separation has been completed, the collected organic phase is preferably 
vacuum stripped in order to remove and recover the organic solvent and 
thereby provide the 3-alkylthiopropionic acid addition reaction product. 
Esterification of the 3-alkylthiopropionic acid, such as into its 
tetraester with pentaerythritol is typically carried out at an elevated 
temperature and under acid catalysis. Typically suitable catalysts in this 
regard are para-toluenesulfonic acid, xylenesulfonic acid, methanesulfonic 
acid, ethanesulfonic acid and the like. 
Irrespective of which esterification procedure is carried out, it is 
followed by an operation wherein the organic phase is solvent refined with 
an organic solvent. Preferably, the solvent refining medium is a blend of 
at least two organic solvents, which blend is particularly well suited for 
the specific alkylthiopropionic tetraester being prepared. One component 
of the solvent mixture is preferably 2-propanol. Other exemplary 
components of this type of solvent blend include other low molecular 
weight alcohols and low molecular weight esters, including materials such 
as methanol, ethanol, isopropyl alcohol, ethyl acetate, isopropyl acetate, 
and the like. It has been found that a suitable solvent blend will improve 
work-up purification procedures, when desired, in a manner that minimizes 
the expense thereof. These solvent blends minimize the need to solve the 
dilemma created by the fact that an especially high excess of the 
alkylthiopropionic acid will favor the formation of the tetraester over 
the less desirable triester, but such excess acid must be removed as an 
undesirable impurity from the tetraester. 
As an example of suitable organic solvent blends, a blend of isopropanol 
and isopropyl acetate has been found to be an especially suitable refining 
solvent for recovering the crystalline tetraester of 
3-dodecylmercaptopropionic acid with pentaerythritol. A blend of methanol 
and isopropanol is generally preferred for the work-up purification of the 
liquid tetraester of 3-octylmercaptopropionic acid with pentaerythritol. 
It has been found that this solvent blend is non-miscible with this 
tetraester and 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 1 
and about 1 to 9. 
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 of 
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 has been observed to 
be generally equal in performance to similar ester stabilizers 
manufactured on a commercial scale by a process different from the 
procedure of the present invention and to not include the solvent refining 
techniques of this invention. 
Various tetraester stabilizers prepared 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 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 
thereinbetween, and they can exhibit good compatibility without excessive 
volatility. 
The following examples illustrate the present invention, as well as 
procedures previously used or taught for preparing acids and/or stabilizer 
esters having chemical structures generally along the lines of those 
prepared according to the present invention.

EXAMPLE 1 
To a stirred solution of 101.2 grams (0.50 mole) of 1-dodecylmercaptan in 
100 ml. of isopropanol under a nitrogen atmosphere at 25.degree. C., 46.2 
grams (0.58 mole) of 50% sodium hydroxide aqueous solution was added in 
one portion. The mixture exothermed to 70.degree. C., and a white 
precipitate formed. Isopropyl alcohol (50 ml.) was added to the slurry, 
which was cooled to 32.degree. C. with a water bath. 37.8 grams (0.525 
mole and 36 ml.) of acrylic acid was added dropwise over a 15 minute 
period. Additional isopropyl alcohol (50 ml. in two aliquots) was added, 
the exothermal reaction proceeded at 40.degree. C., and after 20 minutes 
of stirring, an additional 50 ml. of water was added. The solid components 
slowly dissolved in order to provide a homogeneous solution, which was 
refluxed for two hours. After standing overnight at 25.degree. C., the 
sample was analyzed to have 0.03% dodecylmercaptan. 
Acidification was carried out by heating the reaction composition to 
45.degree. C. and adding 58.3 grams of 50% aqueous sulfuric acid, after 
which same was poured into a separatory funnel, and the aqueous layer was 
drained. Washing was next carried out with three 100 ml. portions of 
water, with the third wash including a small amount of sodium sulfate. The 
washed organic layer was then vacuum stripped with a Roto-Vap rotary 
evaporator to give 128.6 grams of 3-dodecylthiopropionic acid product 
having a melting point of 59.degree.-62.degree. C. The yield by GLC was 
99.0% having an acid value of 204.2 (theory 204.4). 
EXAMPLE 2 
The procedure of Example 1 was substantially followed, except the 
1-dodecylmercaptan or 1-dodecanthiol was added dropwise over a 50-minute 
time span to the sodium acrylate solution, and the reaction then was 
continued as follows. The reaction mixture exhibited two phases, and no 
temperature change was noted. The reaction mixture was heated to reflux, 
and the resulting clear solution was refluxed for two hours and allowed to 
stand overnight at 25.degree. C. under nitrogen gas. It was then warmed to 
50.degree. C. to give a clear solution, and 58.3 grams of of 50% aqueous 
sulfuric acid was added. After pouring the composition into a separatory 
funnel, the aqueous layer was drained, and the organic layer was washed 
with three 100 milliliter aliquots of hot water containing a small amount 
of sodium sulfate. After vacuum stripping, 130.3 grams of 
3-dodecylthiopropionic acid product was collected, having a 
laurylmercaptan percentage of 0.02%, an acid value of 202.9 (204.4 
theoretical), and a derivatized GLC of 97.6% (derivatization being 
necessary because of an inadvertent cut-off of a portion of peak). 
EXAMPLE 3 
The same basic ingredients and quantities thereof were reacted as specified 
in Example 1, except the initial reaction composition included 75 ml. of 
isopropanol and 50 ml. of water. The resulting clear solution was cooled 
to 60.degree. C., and the 1-dodecylmercaptan or laurylmercaptan was added 
during a 30-minute time period. No temperature change was noted, the 
composition was heated to reflux, and 25 ml. of water were added. Adding 
25 ml. of isopropyl alcohol resulted in a clear solution, which was 
refluxed for 3 hours, moderate foaming being observed. After cooling, 58.3 
grams of 50% aqueous sulfuric acid were added, and the composition was 
poured into a separatory funnel and washed with three 100 mililiter 
aliquots of hot water with sodium sulfate. Vacuum stripping yielded 134.5 
grams of 3-dodecylthiopropionic acid product having a melting point of 
60.degree.-62.5.degree. C., an acid value of 202.5 (204.4 theoretical), a 
laurylmercaptan percentage of 0.02%, and a yield of 98.2% by GLC. 
EXAMPLE 4 
To a stirred solution of 75.6 grams (1.05 mole, 72 ml.) of acrylic acid in 
200 ml. of isopropanol under nitrogen gas at 25.degree. C. a solution of 
46.2 grams (1.16 mole) of sodium hydroxide in 246 ml. of water was added. 
The temperature was then at 55.degree. C., and 202.4 grams (1.00 mole, 
239.6 ml.) of 1-dodecanethiol were added dropwise over 40 minutes, the 
temperature exotherming to 58.degree. C. A clear solution was visible at 
this point, and the reactant composition was heated to reflux for three 
hours, cooled to 60.degree. C., and 117 grams of 50% aqueous sulfuric acid 
were added, followed by stirring for 30 minutes. After separation and 
vacuum stripping at 100.degree. C. at 25 mmHg for 1 hour, the yield was 
270.7 grams of 3-dodecylthiopropionic acid product having a melting point 
of 58.5.degree.-62.degree. C., a laurylmercaptan content of 0.03%, an acid 
value of 204.05, and a yield by GLC in excess of 98.0%. 
EXAMPLE 5 
259.7 grams (0.946 mole) of 3-dodecylthiopropionic acid as prepared in 
accordance with Example 4, 30.67 grams (0.225 mole) of pentaerythritol, 
and 4.50 grams (0.024 mole) of hydrated para-toluenesulfonic acid were 
heated to 135.degree. C. with stirring. After the mixture had become 
molten, a vacuum of 20 mmHg was carefully applied, and stirring proceeded 
for 4 hours at 135.degree. C. The reaction composition was then poured 
into a separatory funnel containing 200 ml. of warm water and 6.647 grams 
(17.49 mmoles) of trisodium phosphate. An emulsion resulted, which was 
broken by adding sodium sulfate and placing the separatory funnel in an 
oven at 80.degree. C. After separation, washing proceeded with 200 ml. of 
warmed water containing a small amount of sodium sulfate, followed by 
vacuum stripping. The yield was 255.2 grams having a melting point of 
46.degree.-49.5.degree. C. and an acid value of 8.76. Analysis showed 
91.6% 3-dodecylthiopropionic tetraester of pentaerythritol and 8.4% of the 
triester. Several solvents were investigated for the refining of the crude 
3-dodecylthiopropionic acid ester of pentaerythritol product. 
The crude ester (initial melting point of 45.degree.-49.degree. C.) as 
heated with each test solvent, with stirring, using 1.5 volume of solvent 
per weight of crude ester, until a clear solution was obtained. The 
solution was allowed to cool to 26.degree. C. ambient temperature and 
crystallize for three hours. The crystals were collected, washed with a 
portion of the same solvent at 26.degree. C., dried in a vacuum 
desiccator, and weighed. The percent recovery and the melting point for 
esters recovered by each of the solvents are specified below, the 
acetate/alcohol runs illustrating the invention, with the others being 
provided for comparative purposes. 
______________________________________ 
Solvent % Recovery Melting Point 
______________________________________ 
isopropyl acetate/ 
85% 48-52.degree. C. 
isopropanol 1:1 
isopropyl acetate/ 
75% 48-51.degree. C. 
isopropanol 1:3 
isopropyl acetate/ 
86% 48-51.degree. C. 
isopropanol 1:4 
isopropyl acetate/ 
88% 48-51.degree. C. 
isopropanol 3:7 
isopropyl acetate/ 
85% 48-51.degree. C. 
isopropanol 1:6 
isopropyl acetate/ 
85% 48-52.degree. C. 
isopropanol 1:9 
ethyl acetate/ 67% 48-51.degree. C. 
isopropanol 1:1 
toluene/ 0% -- 
isopropanol 1:1 
methanol/ 76% 46-49.degree. C. 
THF 1:1 
heptane 58% 48-51.degree. C. 
methylethyl ketone 
46% 48-51.degree. C. 
dibutyl ether 78% 44-47.degree. C. 
2-butoxyethanol 85% 50-51.degree. C. 
2-methoxyethanol 
none -- 
(oiled out) 
ethanol none 
(oiled out) 
-- 
acetonitrile none -- 
(oiled out) 
isopropanol none -- 
(oiled out) 
isopropanol acetate 
70% 48-51.degree. C. 
ethyl acetate 0% -- 
acetone 77% 48-51.degree. C. 
______________________________________ 
The melting point point improvements of some of the runs indicates that 
impurities (free acid and triester) are removed. The ester/alcohol 
mixtures according to the invention are safer than, for example acetone, 
because of higher boiling point and flash point, they gave better results 
than heptane, alcohols alone, or esters alone, and the respective boiling 
points of 2-butoxyethanol and of dibutyl ether are higher than desirable 
for production feasibility. 
EXAMPLE 6 
A charge of 146.3 grams (1.00 mole) of n-octylmercaptan, 200 ml. of 
isopropyl alcohol and 200 ml. of water were added to a round bottom flask. 
At room temperature, 46.4 grams (1.16 mole) of sodium hydroxide in 46.4 
ml. of water were added to the flask, and exotherm proceeded at 50.degree. 
to 60.degree. C. Over a 30-minute period, 75.1 grams (1.05 mole) of 
acrylic acid were added dropwise, and the temperature was then raised to 
85.degree. C. and the mixture was allowed to reflux for 2 hours. After 
cooling to 55.degree. C., 83 grams of 70% aqueous sulfuric acid (0.59 
mole) were added, with stirring for 30 minutes, followed by pouring into a 
separatory funnel. The aqueous layer was drained off and the organic layer 
was washed with an equal volume of water containing 2% sodium sulfate. 
After vacuum stripping at 60.degree. C., the reaction product was analyzed 
to contain 0.04 % octylmercaptan and a yield of 98.6% of 
3-octylthiopropionic acid product. 
EXAMPLE 7 
205 6 (0.441 mole) of the 3-octylthiopropionic acid prepared in Example 6, 
30.5 grams (0.224 mole) of pentaerythritol, and 2.24 grams (0.013 mole) of 
para-toluenesulfonic acid catalyst were added to a round bottom flask. A 
vacuum of approximately 20 mmHg was applied, and the temperature was 
raised to 135.degree. C. and held there for 5 hours, with stirring, in 
order to thereby remove water. The composition was allowed to cool to 
about 50.degree. C., after it was poured into a separatory funnel and 
washed with 50 ml. of water containing 11.9 grams of trisodium phosphate. 
After the aqueous layer was drained, the organic layer was washed with two 
aliquots of 125 ml. of 4% sodium sulfate and once with 200 ml. of a 4 to 1 
blend of methanol and isopropyl alcohol. Vacuum stripping and filtering 
yielded a reaction product having an acid value of 1.05 and analyzing at 
0.024% of n-octylmercaptan and a yield of at least 94% 
3-octylthiopropionic tetraester of pentaerythritol product. Chromatagram 
analysis indicated that the finished product contained 94.6% tetraester 
and 4.2% triester. 
EXAMPLE 8 
S-octylthiopropionic acid was synthesized by proceeding generally in 
accordance with Example 6, except the n-octylmercaptan was added to the 
acrylate salt. The result was a 99% yield of 3-octylthiopropionic acid 
product, having an acid value of 255.27 (256.9 theory) and an 
n-octylmercaptan analysis of 0.14%. 
EXAMPLE 9 
The procedure generally in accordance with Example 7 was followed, using 
200.1 grams (0.916 mole) of the 3-octylthiopropionic acid product of 
Example 8, together with 29.7 grams (0.218 mole) of pentaerythritol, and 
2.26 grams (0.013 mole) of para-toluenesulfonic acid. The resulting 
product, after solvent refining with a 4:1 blend of methanol and 
isopropanol, analyzed at 0.01% of n-octylmercaptan and had an acid value 
of 0.04. Chromatagram analysis showed a product tetraester peak at 5.48 
minutes, indicating 97.9% of the pentaerythritol tetraester of 
3-octylpropionic acid product, and a triester impurity peak at 4.12 
minutes, amounting to 1.3% of the product. 
EXAMPLE 10 
To a stirred slurry of 607.2 grams (3.00 moles) of laurylmercaptan in 1200 
ml. of 1:1 water/isopropanol at 25.degree. C. under nitrogen atmosphere 
was added 276.8 grams (3.46 moles) of a 50% aqueous sodium hydroxide 
solution. The reaction composition exothermed to 46.degree. C. Then, 226.8 
grams (3.15 moles) of acrylic acid were added dropwise over 35 minutes, 
and the reaction composition exothermed to 68.degree. C. The reaction 
composition was then refluxed for 3 hours. After cooling slightly, 248.6 
grams (1.77 moles) of 70% aqueous sulfuric acid was added, and additional 
acid was added as needed until the pH reached 3. The composition was then 
poured into a separatory funnel, and the aqueous layer was drained. The 
organic layer was washed three times with 800 ml. of hot 3% aqueous sodium 
sulfate. Residual isopropanol and water were vacuum stripped at 
60.degree.-70.degree. C. and 70 mmHg until nothing further distilled. The 
temperature was raised to 100.degree. C. and the pressure was reduced to 
25 mmHg to remove any residual acrylic acid. The yield of 
3-dodecylthiopropionic acid product was 813.5 grams, with a melting point 
of 60.degree.-62.degree. C., an acid value of 203.8 (theory 204.4), and a 
percent laurylmercaptan of 0 046%. The percent yield was 98.8%. 
EXAMPLE 11 
Approximately 100 ml. water and 14.4 grams (0.2 mole) of acrylic acid were 
added to a flask and stirred. Then, 16 grams (0.2 mole) of a 50% solution 
of sodium hydroxide were added, followed by 18 grams (0.2 mole) of 
n-butylmercaptan from a dropping funnel. At the start of the addition, the 
sodium acrylate solution was at 40.degree. C. as a result of the 
neutralization exotherm. After adding approximately one-half of the butyl 
mercaptan, a second liquid phase had formed. Addition was interrupted, and 
the flask was heated to 87.degree. C. The remaining mercaptan was then 
added in two portions at 30 minute intervals, and within 3 hours of the 
beginning of the process, a single clear solution was obtained. 
This solution was cooled, extracted with two portions of benzene, the 
benzene was discarded, and the solution was then acidified with dilute 
sulfuric acid. Two phases formed, and these were separated. The aqueous 
phase was extracted with benzene, which was added to the organic phase. 
The organic phase became milky and was cleared by addition of diethyl 
ether. Next, the solution was drained over sodium sulfate and stripped on 
a rotary evaporator to provide 22.2 grams of 3-butylthiopropionic acid 
product, and the yield was thus 68.5% of theoretical. The acrylic acid had 
a purity estimated at 97%, indicating that the 0.2 mole of sodium 
hydroxide was more than adequate to convert all of the acrylic acid 
actually used to sodium acrylate and leave about 0.006 mole of sodium 
hydroxide to act as the addition reaction base catalyst in accordance with 
the present invention. 
COMATIVE EXAMPLE A 
The pentaerythritol tetraester of 3-dodecylthiopropionic acid was prepared 
by transesterification of pentaerythritol with methyl 
3-dodecylthiopropionate in accordance with the transesterification process 
of Dexter et al U.S. Pat. No. 3,758,549. 
First, methyl 3-dodecylthiopropionate was prepared by adding dropwise with 
stirring 90.5 grams (1.05 mole) of methyl acrylate to 202.4 grams (1.0 
mole) of lauryl mercaptan containing 0.5 gram of sodium methoxide. After 
15 minutes, half of the methyl acrylate had been added, and the pot 
temperature was 75.degree. C. The addition was complete in 30 minutes, and 
the pot temperature was 80.degree. C. The reaction was allowed to stand 
for 1 hour and was shown by GLC to contain 1.2% of several compounds from 
the lauryl mercaptan. The mixture was washed with 250 ml. of 5% aqueous 
hydrochloric acid and twice washed with water. The product was then 
stripped on a rotary evaporator to remove water and excess methyl 
acrylate. After filtration, the yield was 281.7 grams of colorless methyl 
3-dodecylthiopropionate, which by GLC contained 98.1% product, 0.7% of an 
isomer, and 1.3% of lauryl mercaptan impurities. 
A mixture of 144.1 grams (0.50 mole) of methyl 3-dodecylthiopropionate, 
13.62 grams (0.10 mole) of pentaerythritol, and catalyst as shown below 
was heated with various means to remove methanol byproduct. A 
toluene-methanol azeotrope, vacuum, and nitrogen purge were used to remove 
methanol. 
______________________________________ 
Method of Sodium Product 
Removing Methoxide Composition 
Methanol Scale Catalyst Tetra:Tris 
______________________________________ 
Toluene 0.50 mole ester 
0.50 g @ 0 time 
9 hr 49:51 
azeotrope 
0.10 mole PE 
0.50 g @ 6.5 hr 
12 hr 63:37 
(no column) 0.50 g @ 13.5 hr 
20 hr 84:16 
Aspirator 
0.25 mole ester 
0.50 g @ 0 time 
2 hr 58:42 
(11 mm) 0.05 mole PE 
0.50 g @ 22 hr 
6 hr 57:43 
22 hr 73:27 
26 hr 72:28 
29 hr 79:21 
Vacuum 0.25 mole ester 
0.50 g @ 0 time 
6 hr 69:31 
(18 mm) 0.05 mole PE 
0.50 g @ 2 hr 
24 hr 74:26 
0.50 g @ 4 hr 
29 hr 75:25 
0.50 g @ 6 hr 
0.50 g @ 24 hr 
N.sub.2 stream 
0.25 mole ester 
0.50 g @ 0 time 
6 hr 51:49 
1/2" into 
0.05 mole PE 
0.50 g @ 4 hr 
24 hr 77:23 
mixture 0.50 g @ 25 hr 
29 hr 91:9 
N.sub.2 stream to 
0.25 mole ester 
1.0 g @ 0 time 
4 hr 40:60 
bottom of 
0.05 mole PE 20 hr 82:18 
mixture 28 hr 86:14 
Toluene 0.25 mole ester 
0.25 g @ 0 time 
6 hr 52:48 
azeotrope 
0.05 mole PE 
0.25 g @ 25 hr 
24 hr 74:26 
ten-plate 30 hr 83:17 
Oldershaw 
column 
Toluene 0.25 mole ester 
0.25 g 0 time 
4 hr 50:50 
azeotrope 
0.05 mole PE 
1.22 g (0.01 6 hr 63:37 
ten-plate mole) of 4-DMAP 
Oldershaw as co-catalyst 
column 
Toluene 0.25 mole ester 
0.25 g @ 0 time 
2 hr 42:58 
azeotrope 
0.05 mole PE 4 hr 46:54 
ten-plate 6 hr 58:42 
Oldershaw 8 hr 62:38 
column 24 hr 80:20 
Vacuum 0.40 mole ester 
0.50 g @ 0 time 
6 hr 58:42 
(17 mm) 0.05 mole of PE 8 hr 58:42 
24 hr 65:35 
Vacuum 0.40 mole ester 
0.50 g @ 0 time 
2 hr 41:59 
(17 mm) 0.05 mole PE 
0.50 g @ 6 hr 
4 hr 40:60 
6 hr 37:63 
8 hr 77:23 
24 hr 81:19 
Toluene 0.25 mole ester 
0.50 g of 2 hr 93.2:6.8 
azeotrope 
0.05 mole PE 
LiOCH.sub.3 @ 0 time 
4 hr 96.2:3.8 
ten-plate 6 hr 94.5:5.5 
Oldershaw 
column 
______________________________________ 
None of the reactions using sodium methoxide as catalyst was satisfactory, 
requiring long reaction times and often repeated additions of catalyst. In 
the reactions using the toluene-methanol azeotrope and a ten-plate 
Oldershaw column (to improve efficiency), the odor of methyl acrylate was 
evident. This would indicate a reversal of the reaction is occurring. 
Also, the repeated addition of catalyst needed would indicate catalyst is 
being consumed by the reverse reaction. Although lithium amide 
(LiNH.sub.2) was an excellent transesterification catalyst, after four 
hours the reaction had become yellow and the odor of methyl acrylate was 
noticeable, so that the result was unsatisfactory. 
COMATIVE EXAMPLE B 
Acid catalyzed and metal salt catalyzed transesterifications were also 
tried. Substantially the same conditions were used as in the reactions of 
Comparative Example A, with the following unsatisfactory results: 
______________________________________ 
Product 
Method of Composition 
Removing Methyl Ester: 
Methanol Scale Catalyst Tris:Tetra 
______________________________________ 
Toluene 0.25 mole ester 
0.5 ml 6.5 hr 
azeotrope 
0.05 mole PE methane- (no reaction) 
ten-plate sulfonic 
Oldershaw acid 
column 
Vacuum 0.25 mole ester 
1.00 g 5 hr 68:15:17 
(18 mm) 0.05 mole PE Fascat 4101 
23 hr 20:9:71 
organotin 
catalyst 
______________________________________ 
COMATIVE EXAMPLE C 
The procedure essentially as described in Kauder et al U.S. Pat. No. 
4,080,364 was followed for preparation of a 3-octylthiopropionate 
pentaerythritol tetraester by the addition reaction of 1-octene with the 
pentaerythritol tetraester of 3-mercaptopropionic acid. 100.0 grams (0.205 
mole) of the pentaerythritol tetraester of 3-mercaptopropionic acid were 
placed into a round bottom flask. An azo initiator (0.25 gram of Vazo-64) 
was dissolved in 105.8 grams (0.943 mole) of 1-octene. This mixture was 
then poured into a funnel. The contents of the flask were heated to 
85.degree.-90.degree. C., and an additional 0.25 gram of Vazo-64 was 
added. The contents of the funnel were added slowly so as to maintain the 
temperature at about 100.degree.-110.degree. C. After addition was 
complete, the reaction composition was stirred at 90.degree. C. for one 
hour, and at this time an additional 15 grams of 1-octene were added, and 
the mixture was stirred for an additional hour. Then, 20 ml. of water 
were added, and the free 1-octene was steam distilled out at 115.degree. 
C. for 30 minutes. After cooling, filtering and washing with water, the 
organic material was extracted and stripped in a rotary evaporator. 
Analysis of the reactant product showed a product peak indicating 
pentaerythritol tetraester of 3-octylthiopropionic acid at 5.32 minutes 
amounting to 85.9%, but with a shoulder indicating an incompletely 
resolved impurity, along with 14% of a well resolved impurity, presumably 
a triester. The acid value of the product was 0.094. 
COMATIVE EXAMPLE D 
The process as specified in Synthetic Example 7 of Nakahara et al U.S. Pat. 
No. 4,349,468 was followed. 168.3 grams (1.0 mole) of 1-dodecene were 
combined with 0.5 gram of Vazo-64 (an azo compound catalyst), and 120.2 
grams (1.13 mole) of 3-mercapto propionic acid were added dropwise. An 
exotherm occurred, the temperature reaching 85.degree. C. The reaction 
composition was stirred for an additional three hours at 80.degree. C., 
poured into water, and the solid precipitate was collected by filtration. 
Recrystallization from acetone yielded 240.2 grams of product. The 
recrystallized crude product gave an assay of 98.8% and a melting point of 
60.5.degree.-62.degree. C. The crude product collected after filtration 
analyzed by GLC as 95.6% product (3-dodecylthiopropionic acid), 4.4% 
isomer, and 1.3% unknown. 
Esterification of product made according to this process in order to form 
the pentaerythritol tetraester of 3-dodecylthiopropionic acid results in a 
soft, waxy tetraester product found to be inferior to other tetraester 
products, such as when formed by way of the synthetic sequence starting 
with methyl acrylate, as specified in Comparative Example A hereinabove. 
It will be understood that the embodiments of the present invention which 
have been described are illustrative of some of the applications of the 
principles of the present invention. Numerous modifications may be made by 
those skilled in the art without departing from the true spirit and scope 
of the invention.