Preparation of alkylphosphonothioic dihalides
United States Patent 11 1 Hinkamp et al.  
 [ 4] PREPARATION OF ALKYLPHOSPHONOTHIOIC DIHALIDES [75] Inventors: James B. Hinkamp, Birmingham;  
 Vincent F. llnizda, Huntington Woods, both of Mich.  
 [73] Assignee: Ethyl Corporation, Richmond, Va.  
 [22] Filed: Sept. 8, 1967 [2]] Appl. No.: 666,507  
 [52] U.S. Cl. 260/543 P [51] Int. Cl. C07i 9/42 [58] Field of Search 260/543 P [56] References Cited UNITED STATES PATENTS 2,591,782 4/1952 Cook 23/l4 3,l49,l37 9/1964&#39; Huffman.... 260/448 3,518,303 6/1970 Maier 260/543 OTHER PUBLICATIONS Oknobystin et 211., Academy of Sciences, USSR I958) Apr. 22, 1975 p. 977-979 (Eng. Translation).  
  Karavanov et al., Chemical Abstract, Vol. 63 (8-1- Primary E.\&#39;aminerLorraine A. Weinberger Assistant Examiner-Paul .l. Killos Attorney, Agent, or FirmDonald L. Johnson; Robert A. Linn [57] ABSTRACT Alkylphosphonothioic dihalides are prepared in improved yields by reacting a trialkyl aluminum with a thiophosphoryl halide in the absence of a hydrocarbon solvent. The reaction need not be carried out with pure thiophosphoryl halide. Instead, the thiophosphoryl halide can be in the mixture produced by reacting phosphorus trihalide and sulfur with an aluminum trihalide catalyst.  
 5 Claims, No Drawings PREPARATION OF ALKYLPI-IOSPHONOTI-IIOIC DII-IALIDES BACKGROUND OF THE INVENTION The preparation of alkylphosphonothioic dihalides in low yield has been described in German Patent No. 1,235,911. A need exists for an improved method which affords higher yields of product. This invention satisfies that need.  
  Thiophosphoryl halides used as starting materials are also old compounds and they have been described with methods for their preparation. In this regard. reference is made to US Pat. Nos. 2.591.782. 2.715.561. 2.802.717. 2.850.353. 2.850.354. 2.911.281. and 2.915.361. The aforementioned Cook patent. US. Pat. No. 2.591.782. discloses a preparation of thiophosphoryl chloride from sulfur. phosphorus trichloride and an aluminum halide catalyst.  
  The alkylphosphonothioic dihalides produced by the process of this invention are useful as chemical intermediates. One method of use has been described in US. Pat. No. 3.024.278.  
 SUMMARY OF THE INVENTION In essence. this invention comprises the discovery that high yields of alkylphosphonothioic dihalides are obtained when a thiophosphoryl halide is reacted with a trialkyl aluminum in the substantial absence ofa hydrocarbon solvent. The thiophosphoryl halide used can be present in the reaction mixture produced by making it from phosphorus trihalide and sulfur using an aluminum halide catalyst.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of this invention comprises a process for the preparation ofa compound having the formula RPSX said process comprising the reaction of a. a thiophosphoryl halide selected from PSCL, and  
  PSBr with b. an alkyl aluminum having the formula R Al. R being an alkyl radical having up to 6 carbon atoms; said reaction being conducted in the substantial absence of a hydrocarbon solvent. Because of their availability. use of triethyl or trimethyl aluminum is preferred.  
  The preparation of alkylphosphonothioic dihalides by the process of this invention is readily carried out by simply admixing the reactants. To achieve good yields in a reasonable time. reaction temperatures within the range of from about to about 150C. are used. Preferably. temperatures of from 60 to 100C. are employed. The reaction pressure is not critical. Subatmospheric or elevated pressures can be used if desired.  
 The reaction is conveniently carried out under ambient pressure. Preferably. the process is conducted under nitrogen. or in the presence of a similar inert atmosphere.  
  The reaction time is not a truly independent variable but is dependent at least to some extent on the inherent reactivity of reactants and the reaction temperature. In general, higher temperatures usually result in shortened reaction times. As a rule. the reaction of a thiophosphoryl trichloride and alkyl aluminum (according to the process of this invention) is complete within a period of about 15 minutes to 18 hours. In many instances. reaction times of about one to six hours are sufficient.  
  As stated above. the process of this invention is carried out in the substantial absence of a hydrocarbon solvent. By this. it is meant that the reaction is carried out by reacting the thiophosphoryl halide and the alkyl aluminum without adding any common hydrocarbon solvent to the reaction zone. Any minor amount of hydrocarbon solvent present as an impurity in the starting materials is not overly deleterious. In other words. it is not necessary to carefully purify the starting materials to remove any traces of hydrocarbon solvent. Thus. it is possible to use readily available forms of the reactants.  
  The stoichiometry of the reaction is not critical. In general. best results are achieved if a stoichiometric amount or a slight excess of the alkyl aluminum is employed. Thus. it is preferred that from about 1.0 to about 1.2 theories of alkyl aluminum be employed per each mole of thiophosphoryl halide. A theory&#34; is the amount (on a mole basis) of alkyl aluminum theoretically required to react with one mole of PSX to produce an alkylphosphonothioic dihalide.  
  Although not bound by any theory. it is believed that the preparation of alkylphosphonothioic dihalides according to this invention proceeds according to the following equation:  
 The complexed alkylphosphonothioic dihalide is freed by various methods. One of these methods involves pouring the reaction mixture over ice. A preferred method comprises treating the reaction mixture with dioxane or an alkali metal halide such as sodium chloride. This treatment form uncomplexed alkylphosphonothioic chloride and an alkali metal aluminum tetrahalide such as NaAlCl In general. an approximately stoichiometric quantity of alkali metal halide is used: 1.0 to 1.5 moles per mole of phosphonothioic halide complex being preferred. After the reaction mixture has been so treated. the product can be separated from the reaction mixture by distillation. Preferably. the distillation is carried out under reduced pressure. say 18 to 50 mm. Hg.  
  The following examples serve to illustrate the process of this invention but do not limit it. All parts are by weight.  
 EXAMPLE I One and one-half moles (206 g) of PCl and 0.15 moles (19.5 g) of AlCl catalyst were charged to a nitrogen-flushed. 500 ml, stirred flask. The charge was heated to 60. Then 1.5 moles (48.0 g) of sulfur were added incrementally in 15 minutes. converting the PCl to PSCl The reaction initiated immediately. Air cooling on the flask maintained the temperature between 58 and 67C. during the addition.  
  Triethyl aluminum addition to the charge was begun at a mass temperature of 61C. to ethylate PSCL, and thus form EtP(S)Cl Again. the reaction initiated immediately. Sixty grams (1.05 theories) were fed to the charge dropwise in 37 minutes. Air cooling maintained the temperature at -86C. during the feed. Ground NaCl (37.8 g) was added to the charge to break the EtP(S)Cl .AlCl complex by forming NaAlCL.  
  The product. EtP(S)Cl. was recovered by a simple distillation from the reactor over a 48 minute period.  
 The distillation was terminated at a maximum pot temperature of 150C. and a minimum pressure of 6 mm Hg. The colorless distillate (228.1 g 93.271 yield) analyzed 99.0 per cent pure by VPC. 1R confirmed the structure of the product.  
  Similar results are obtained when the reaction of ethyl aluminum and PSCl is carried out at 65 and 85C.  
  Similar results are obtained when the phosphorus trichloride and sulfur are reacted at and 75C.  
  Similar results are obtained when the product is recovered by distillation at 18 and C. and at a temperature of 145 to 190C.  
 EXAMPLE ll The procedure of Example I was essentially repeated in a nitrogent-purged reaction vessel. The reaction of triethyl aluminum with PSCL, was conducted at 8090C. The maximum liquid temperature when distilling the product was 190C. The distillation pressure was 50 mm Hg.  
  The yield of product. C H PSCl was 92 per cent. It analyzed 94.5 per cent pure.  
  Similar results are obtained when 1.0 and 1.5 theories of sodium chloride are used to disrupt the C- ,H PSCl- AlCl complex. Similar results are also obtained when the triethyl aluminum to PCL, ratio was, on a molar basis. 1.2 to 1 and 1.0 to 1.0.  
 EXAMPLE 111 Alkylating Agents Product (CH; ),-,Al CH PSCI (b) (nC,H..) -.Al n-C.,H,,PSC1. (c) (n-C.;H 1.1 MAI n-C H PsCl Experiments d. e. f and g are all conducted by reacting the alkylating agent listed below with the PSBr in the reaction mixture produced by reacting PBR and S Alkylating Agent Product (d) (CH;,)Al CH;,PSBr (e) iso-C;,H7 l Al iso&#39;C;,H;PSBr (f) (secC..H,.);,Al sec-C H,,PSBr g (lSO-Ca m );.A] iso-C -H PSBr:  
  In each instance above. yields are reduced if the reaction between the trialkyl aluminum and thiophosphoryl halide is conducted in the presence of added hydrocarbon solvent such as hexane, heptane. pentane, ligroin, and the like.  
 We claim:  
  &#39;1. A process for the preparation of a compound selected from the class consisting of CH PSCI and C H PSCl said process comprising a. preparing thiophosphoryl trichloride by reacting sulfur with phosphorus trichloride in the presence of a catalytic quantity of aluminum chloride at a temperature within the range of from about 20 to about C., and  
 b. reaction said thiophosphoryl trichloride in the thereby produced reaction mixture with an alkylating agent selected from trimethyl aluminum and triethyl aluminum at a reaction temperature of from about 60 to about C.. said process being conducted in the absence of added hydrocarbon solvent and with from about 1.0 to about 1.2 theories of said alkylating agent.  
  2. The process of claim 1 wherein Step (a) comprises the addition of said phosphorus trichloride to a mixture of said sulfur and aluminum chloride catalyst.  
  3. The process of claim 2 wherein said alkylating agent is trimethyl aluminum.  
  4. The process of claim 3 wherein said alkylating agent is triethyl aluminum.  
  5. The process of claim 4 being further characterized by the recovery of the ethyl phosphonothioic dichloride reaction product from the resultant reaction mixture by (i) treating said resultant reaction mixture with sodium chloride and (ii) thereafter distilling the resultant mass at a reduced pressure of from about 18 to about 25 mm Hg. and at a temperature of from about to about C.