Process for the manufacture of thiophosphoryl chloride

Details Process for the manufacture of thiophosphoryl chloride Process for the manufacture of thiophosphoryl chloride

1999-06-21

2001-06-26

Dunn, Tom (Department: 1754)

Chemistry of inorganic compounds

Phosphorus or compound thereof

Sulfur containing

C423S300000

Reexamination Certificate

active

06251350

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of thiophosphoryl chloride which is useful as an intermediate for the synthesis of insecticidally active compounds. The improvement comprises the presence of a catalytic amount of a nitroxide free radical in the reaction mixture.
BACKGROUND OF THE INVENTION
A process for the preparation of thiophosphoryl chloride is known in the art. British Patent 694,380 discloses the preparation of thiophosphoryl chloride (PSCl
3
) by refluxing phosphorous trichloride (PCl
3
) and excess sulfur at atmospheric pressure, in the presence of carbon (activated with K
2
S) and about 40 mole percent of thiophosphoryl chloride for about three hours. German Patent 1,145,589 discloses that thiophosphoryl chloride is obtained by treating phosphorous trichloride and sulfur in liquid phase at atmospheric pressure, using aluminum or alloys thereof, preferably aluminum wastes, as a catalyst. Thiophosphoryl chloride is preferably used as the reaction medium and moderator. Further, U.S. Pat. No. 5,464,600 discloses that thiophosphoryl chloride is obtained by reacting phosphorous trichloride and sulfur in the presence of a catalytic amount of a tertiary amine.
SUMMARY OF THE INVENTION
The present invention provides an improved process for preparing thiophosphoryl chloride by reacting phosphorous trichloride with sulfur in the presence of a catalytic amount of a tertiary amine, and in the presence of a catalytic amount of a nitroxide free radical of the following general
wherein R
1
, R
2
, R
3
and R
4
represent an alkyl group.
The improvement comprises the presence of a catalytic amount of the nitroxide free radical.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved process for preparing thiophosphoryl chloride by reacting phosphorous trichloride with sulfur in the presence of a catalytic amount of a tertiary amine, and in the presence of a nitroxide free radical. The improvement comprises the addition of a catalytic amount of the nitroxide free radical in the reaction mixture. The nitroxide free radical is of the following general formula:
wherein R
1
, R
2
, R
3
and R
4
represent an alkyl group.
In a preferred embodiment, the nitroxide free radical is 2,2,6,6-tetramethyl-1-piperidinyloxy (“TEMPO”). TEMPO is a standard nitroxide free radical which may be commercially obtained from Lancaster [CAS # 2564-83-2]. Further, in this embodiment, the tertiary amine may be selected from a group of pyridines which are preferably substituted pyridines such as 5-ethyl-2-methylpyridine, 2-methylpyridine, 2,4-dimethylpyridine, 2,6-dimethylpyridine, 2,4,6-trimethylpyridine, trialkylamines (e.g., tripropylamine and tributylamine), tris-[2-(2-methoxyethoxy)ethyl]amine and 1,8-diazabicyclo[5.4.0]undec-7-ene.
In the process of the invention, the sulfur and phosphorous trichloride can be employed in a ratio of sulfur to phosphorous trichloride that is in the range of about 1.0:1.0 to about 1.5:1.0, and preferably about 1.4:1.0. The nitroxide free radical may be present in a ratio of nitroxide free radical to phosphorous trichloride that is in the range of about 0.002:1.0 to about 0.004:1.0, and preferably about 0.00314:1.0. The tertiary amine can be used in a ratio of tertiary amine to phosphorous trichloride that is in the range of about 0.15:1.0 to about 0.20:1.0, and preferably about 0.16:1.0.
The reaction can be conducted at initial temperatures of about 110° C. to about 140° C., and preferably from about 115° C. to about 120° C.
The reaction product containing thiophosphoryl chloride is typically distilled to remove the thiophosphoryl chloride. Following isolation of the thiophosphoryl chloride and phosphorous oxychloride by-product, the distillation heel which contains the tertiary amine and the nitroxide free radical, can be recycled for use in another reaction of phosphorous trichloride and sulfur.
In accordance with the invention, the process is well suited to either a batch or continuous reaction. In the continuous reaction, the distillation heel is recycled continuously to a primary reactor stage, where the sulfur and phosphorous trichloride are reacted.
The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.


REFERENCES:
patent: 5464600 (1995-11-01), Newallis et al.
patent: 1145589 (1963-03-01), None
patent: 694380 (1953-07-01), None

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