 |
Description  |
|
|
BACKGROUND OF THE INVENTION
The present invention relates to an oxidation process for the production of
S,S,S-tributylphosphorotrithioate.
S,S,S-tributylphosphorotrithioate is known to be useful as a defoliant.
This defoliant is typically produced by reacting phosphorus trichloride
with butyl mercaptan to form S,S,S-tributylphosphorotrithioite
(phosphite). The phosphite is then oxidized to form the corresponding
S,S,S-tributylphosphorotrithioate.
Processes for the production of phosphite are disclosed, for example, in
U.S. Pat. Nos. 2,682,554; 2,943,107; 3,885,002 and 5,183,916.
Processes for the oxidation of phosphite to form the corresponding
S,S,S-tributylphosphorotrithioate are disclosed in U.S. Pat. Nos.
2,943,107; 3,885,002 and 5,189,195. In the process disclosed in U.S. Pat.
No. 2,943,107, the oxidizing agent is selected from air, molecular oxygen,
peroxide, persulfates and chlorine water. The oxidizing agent for the
process of U.S. Pat. No. 3,885,002 is molecular oxygen itself or in the
form of air. In the process described in U.S. Pat. No. 5,189,195, peroxide
was used as the oxidizing agent.
The disadvantage of each of these known oxidizing agents is the need to
treat the crude oxidation product to improve the purity of the
S,S,S-tributylphosphorotrithioate. These known processes require at least
two (and often three) phase separation treatments to obtain a high purity
product. Multiple extractions result in lost product and decreased yield.
Such purification treatments also increase production time and expense.
Perborates and percarbonates are known materials. Sodium perborate is a
large scale industrial chemical which is used as a source of active oxygen
in detergents, as an alternative to various forms of chlorine for fiber
bleaching, and as a mild antiseptic and mouthwash. Sodium perborate has
also been investigated as a possible oxidizing agent for the production of
azo compounds from aniline as described in S. M. Mehta and M. V.
Vakilwala, J. Am. Chem. Soc., 74, 563 (1952) and L. Huestis, J. Chem. Ed.,
54, 327 (1977) and for alkenylboronic acids as described in D. S. Matteson
and R. J. Moody, J. Org. Chem., 45, 1091 (1980). To date, however,
perborates and percarbonates have not been used to oxidize materials such
as S,S,S-tributylphosphorotrithioite.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the
oxidation of S,S,S-tributylphosphorotrithioite which yields
S,S,S-tributylphosphorotrithioate of high purity in high yields.
It is another object of the present invention to provide a simple,
efficient process for the oxidation of S,S,S-tributylphosphorotrithioite
to S,S,S-tributylphosphorotrithioate.
It is also an object of the present invention to provide a process for
producing high quality S,S,S-tributylphosphorotrithioate in which high
purity product may be recovered after a single phase separation.
It is a further object of the present invention to provide a process for
oxidizing S,S,S-tributylphosphorotrithioite which may be carried out under
sufficiently mild conditions that no special equipment is required.
These and other objects which will be apparent to those skilled in the art
are accomplished by oxidizing S,S,S-tributylphosphorotrithioite with a
perborate or percarbonate at a pH of from about 6 to about 12 and at a
temperature of from about 40.degree. to about 65.degree. C. Alkali metal
perborates are preferred with sodium perborate being the most preferred
oxidizing agent.
DETAILED DESCRIPTION OF THE INVENTION
The S,S,S-tributylphosphorotrithioite (hereinafter referred to as
"phosphite") used as the starting material in the process of the present
invention may be made by any of the known processes. Such processes are
disclosed, for example, in U.S. Pat. No. 2,943,107; U.S. Pat. No.
2,682,554; U.S. Pat. No. 3,885,002; and U.S. Pat. No. 5,183,916.
The phosphite may be used with or without a solvent in the process of the
present invention. It is preferred, however, that it be used without a
solvent. Where the phosphite is used in solution, any of the known organic
solvents may generally be used. Toluene is an example of a suitable
solvent.
The oxidizing agents useful in the practice of the process of the present
invention are any of the known perborates and percarbonates. Examples of
these known oxidizing agents include: sodium perborate monohydrate, sodium
perborate tetrahydrate and sodium percarbonate. Perborates, particularly
alkali metal perborates are preferred. Sodium perborate in its various
hydrate forms is particularly preferred.
High concentrations of sodium percarbonate are not preferred because under
some conditions, carbon dioxide gas (indicated by foaming) is generated.
This carbon dioxide could cause problems when the oxidation reaction is
carried out on a large production scale.
The oxidizing agent is generally used in a quantity such that at least one
mole of oxidizing agent is present for every mole of phosphite. It is
preferred that from about 1.0 to about 1.4 moles of oxidizing agent be
present for every mole of phosphite to be oxidized.
The perborate or percarbonate is generally used in the form of a solid but
it may also be used as a solution in, for example, acetic acid and water.
It is preferred that the perborate or percarbonate be in the form of a
coarse powder. The particle size of the powder is not an essential feature
of the invention.
The oxidation is carried out at a pH of from about 6 to about 12,
preferably from about 6 to about 7.
The reaction is conducted at a temperature of from about 40.degree. to
about 65.degree. C., preferably from about 60.degree. to about 65.degree.
C. When shorter reaction times are desired, the reaction temperature is
preferably maintained at from about 60.degree. to about 65.degree. C.
The process of the present invention generally produces yields of about 99%
of theoretical in reaction times of from about 2 to about 6 hours.
Commercially available equipment may be used in the conduct of the process
of the present invention. Due to the relatively mild reaction conditions
employed in the process of the present invention, expensive equipment
designed specifically for use in this process is not required.
The process of the present invention is particularly advantageous in that
high purity S,S,S-tributylphosphorotrithioate may be easily recovered. The
product may, for example, be recovered by simple phase separation of the
aqueous and organic phases. Only one phase separation is necessary to
recover high purity product in high yield. Although more than one phase
separation may be performed to recover the product of the present
invention, such multiple separations are not usually desirable because
product yield is reduced after each separation.
Having thus described our invention, the following examples are given as
being illustrative thereof. All parts and percentages given in these
examples are parts by weight and percentages by weight, unless otherwise
indicated.
EXAMPLES
Example 1
A 3000 ml 4-necked round-bottomed flask was equipped with an overhead
stirrer, thermometer, pH probe and a 1000 ml addition funnel, a heating
mantle and an ice bath. 892.5 grams (3.0 moles) of phosphite were charged
to the flask and agitation of the flask was begun. The flask was heated to
60.degree. C. and 15 grams of the total amount of perborate to be added
(329.4 grams (3 moles+10% excess) of sodium perborate monohydrate) were
added to the flask. Dilute hydrochloric acid was added dropwise at a rate
of 3 drops per second. The exotherm of the reaction was allowed to
increase the flask temperature to no greater than 65.degree. C. The
perborate was added in 15 gram increments every 3 minutes while dilute
hydrochloric acid was being simultaneously added for a period of
approximately 60 minutes. The addition of dilute hydrochloric acid was
continued until a pH of 4 was reached. The contents of the flask were then
heated for 30 minutes at 60.degree. C. and analyzed for completeness of
the reaction by gas chromatography. After the reaction had been completed
(2-3 hours), the pH was adjusted to 10.5 with a 50% aqueous sodium
hydroxide solution. The contents of the flask were then heated at
60.degree. C. for 1 hour. 600 grams of water were then added to the flask
and the flask contents were agitated for 15 minutes at 60.degree. C. The
aqueous and organic phases were separated. The aqueous phase contained
less than 0.1% S,S,S-tributylphosphorotrithioate. The organic phase was
steam stripped, dried and filtered. The yield of
S,S,S-tributylphosphorotrithioate was 98.25% (Active Ingredient: 98.65%)
Example 2
A 500 ml 4-necked round-bottomed flask was equipped with a stirrer,
thermometer, addition funnel and heating mantle. 148.7 grams (0.5 moles)
phosphite and 184.7 grams (0.5 moles) sodium percarbonate trihydrate were
added to the flask and heated to 60.degree. C. with stirring. A 15%
solution of hydrochloric acid was added over a 1 hour period while the
temperature was maintained at 60.degree. C. and the pH was kept at 4. 160
ml of 15% hydrochloric acid was added. The pH of the contents was
subsequently determined to be 8.4. The yield of
S,S,S-tributylphosphorotrithioate was 98%.
Example 3
The effect of reaction time and temperature was studied by repeating the
procedure of Example 1 with the exception that the temperature and
reaction times were varied. The results are reported in Table 1.
TABLE 1
______________________________________
REACTION % ACTIVE
TEMP. pH REACTION TIME INGREDIENT
______________________________________
40-45.degree. C.
6-7 6 hrs. 99.0%
50-55.degree. C.
6-7 4 hrs. 98.7%
60-65.degree. C.
6-7 2 hrs. 98.8%
______________________________________
Example 4
The effect of pH on the oxidation of the present invention was studied by
repeating the procedure described in Example 1 with the exception that the
pH of the reaction mixture was varied. The results of this study are
reported in Table 2.
TABLE 2
______________________________________
REACTION REACTION % ACTIVE %
TEMP. pH TIME INGREDIENT
YIELD
______________________________________
60-65.degree. C.
6-7 2 hrs. 98.8% 99.1%
60-65.degree. C.
8-9 3 hrs. 98.8% 99.0%
60-65.degree. C.
11-12 4 hrs. 98.2% 98.4%
______________________________________
Although the invention has been described in detail in the foregoing for
the purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of the
invention except as it may be limited by the claims.
* * * * *
|
|
 |
|
 |
Description |
|
