Patented Jan. 24, 1950 2,495,220 UNITED STATES PATENT OFFICE - 2495,220 METHOD OF PREPARNG PEOSPATs ESTERS Alan Bell, Kingsport, Tean, assignor to Eastman Kodak Company, Rochester, N. Y., a corpora tion of New Jersey No Drawing. Application December 26, 1946, Serial No. 718,612. Claims. (C. 260-461) 2 This invention relates to compounds useful for phosphate, or tri-2-ethyl hexyl phosphate or, in insecticidal purposes prepared by reacting tri other words, any of the trialkyl phosphates, the alkyl or triaryl phosphates or thiophosphates alkyl groups of which have not more than eight with sulfur acid halides. carbon atoms. If desired, trialkyl phosphates in Insecticides ordinarily divide themselves up in which the alkyl groups have substituents there to those of the contact type, the most commonly on, such as chlorine or alkoxy groups, or com known members of which are nicotine sulfate pounds in which the halogen is linked directly and pyrethrum and those which poison by inges to the P may be employed to prepare materials tion thereof. In recent years new materials of having effective toxic properties by the process the contact insecticidal type have been developed, described herein. the most commonly known of these new mate O The lower aryl phosphates, such as triphenyl rials being "DDT" and "Bladan,' the latter a or tricresyl phosphate, the mixed alkyl phos German development. As for insecticides of the phates, such as ethyl propyl, or ethyl butyl phos ingested type, the most commonly known at the phates, the alkyl aryl phosphates, such as ethyl present time are the arsenic compounds, such as phenyl phosphate, or the thiophosphates of any lead arsenate, which leave poisonous residues 5 of the alkyl or aryl groups listed herein may be upon the material to which they are applied. employed if desired. One object of my invention is to provide a The compounds which may be reacted with the new type of phosphorus compounds which have alkyl or aryl phosphates or thiophosphates to greatly improved properties as contact insecti produce toxic materials in accordance with my cides. Another object of my invention is to pro 20 invention are the sulfur acid halides, particu vide a new type of phosphorus Compounds which larly thionyl chloride, sulfuryl chloride, sulfur not only are useful as contact insecticides but monochloride, thionyl bromide, or sulfury bro also are toxic when ingested but which do not mide. leave a poisonous residue upon the material to The reaction of triethyl phosphate with thionyl which they have been applied. A further ob chloride is as follows: ject of my invention is to provide a process for making phosphorus compounds which are useful for killing insects, rodents, etc., by reacting or a (CHO)-P ganic phosphates with sulfur acid halides. 30 N I have found that the residues resulting from O -- SO -- 2CHC the reaction of organic phosphates with sulfur (CHO)-P acid chlorides are useful, both as contact insec a ticides and as stomach poisons, the toxicity as O a contact insecticide being much greater than 35 As the triethyl phosphate is used in a double that of the contact insecticides now employed molar amount to the sulfur acid chloride, it is and also which may be employed without leaving preferred that it be employed in that proportion a Substantial poisonous residue after a short to prepare the tetraethyl pyrophosphate having time upon the materials to which they are toxic properties produced in accordance with my applied. 40 invention. The reaction is promoted by the ap The organic phosphates which may be em plication of heat, it being usually desirable to ployed as the starting materials in processes in heat the mixture of the reactants to at least an accordance with my invention are any of the 80 C. temperature to make the reaction go. If lower alkyl or aryl phosphates or thiophosphates. the reaction proceeds vigorously, cooling may be The phosphates of the lower alcohols, such as 45 desirable to retard the reaction. The reaction triethyl phosphate, have been found to be par may be carried out by maintaining the tempera ticularly useful for this purpose. A triethyl ture at 80° C. or the temperature may be allowed phosphate useful as the starting material in the to proceed upwards to a temperature, such as preparation of insecticides in accordance with 140 C., 160° C. or even more, although greatly my invention is that prepared by the process de 50 elevated temperatures are unnecessary and often scribed and claimed in U. S. Patent No. 2,407,279, require enclosed conditions, such as an autoclave. dated September 10, 1946, of Hull and Snodgrass. The use of a higher temperature does shorten the Other compounds which may be employed as the reaction time, but it also increases the chances starting material are tripropyl phosphate, tri of decomposition of the product prepared. As butyl phosphate, triamyl phosphate, trimethyl 55 may be seen from the above equation, alkylhalide 2,495,220 3 4 and SO2 are formed during the course of the re essentially of di (diethylphospho) sulfate which action. As the reaction is carried out at an ele also has insecticidal value. wated temperature, the ethyl halide and SO2 are Eacample 4-60 parts of thionyl chloride were substantially completely driven off during the mixed with 148 parts of trimethyl phosphate. course of the reaction so that there remains a The reaction began without heating and methyl res due essentially consisting of tetra alkyl pyro chloride and SO2 were evolved in substantially phosphate or tetra alkyl pyro thiophosphate theoretical amounts. The mass was finally heated which is useful directly as an insecticidal mate to 130-135 C. for A hour. 150 parts of a light rial. It is preferred that the residue be employed colored liquid essentially comprised of tetra as it is obtained as refining of this residue may O result in a decrease of insecticidal properties, methyl pyrophosphate were obtained. particularly if the material is distilled at ele Eacample 5-64.5 parts of tri-isopropyl phos wated temperatures. However, distillation under phate were mixed with 17.9 parts of thionyl chlo reduced pressure may be employed in order to ride, and the mass was heated for one hour at minimize decomposition or other change in the s 125-130° C. Isopropyl chloride and sulfur dioxide insecticide. By such distillation diluents may be formed and distilled off during the reaction. 53 removed and a more concentrated product ob parts of a brown oil essentially comprised of tetra tained. In carrying out the reaction the tem isopropyl pyrophosphate were obtained. perature to be employed is a matter of selection Ecample 6-38 parts of diethyl propyl phos by the individual operator, depending upon 20 phate were mixed with 12 parts of thionyl chlo whether Speed of reaction or low decomposition ride and the maSS was heated to 100-110° C. for of product is desired. The temperatures speci 2 hour at the end of which time all of the ethyl fied in the examples have been found to be quite chloride, little or no propyl chloride, and SO2 suitable, and it is preferred to operate the reac which had formed were evolved. 30 parts of a tion ordinarily within these temperatures, 25 brown oil essentially consisting of a tetra alkyl ti The following examples illustrate my inven pyrophosphate, the alkyl of which was ethyl and O propyl, were obtained. Eacample 1.-80 parts (approximately 7 mols.) Eacample 7-20 parts of triethyl thiophosphate of thionyl chloride were mixed with 255 parts were heated for A hour at 110-115° C. with 6 (approximately 1.4 mols.) of triethyl phosphate 30. parts of thionyl chloride. A dark-colored liquid and the mass was heated. The reaction began essentially consisting of tetraethyl pyro thiophos at about 80 C., and the temperature was slowly phate was obtained. raised to 140-145 C. where it was maintained for Eacample 8-58 parts of the tetraethyl pyro about 2 hour. During the reaction substantially phosphate product prepared in Example 1 Were theoretical amounts of ethyl chloride and sulfur 35 mixed with 12 parts of thionyl chloride, and the dioxide were evolved. 221 parts of a liquid which mass was heated at 110-15 C. for A hour. The appeared to consist essentially of tetra ethyl pyro oretical amounts of ethyl chloride and Sulfur di phosphate were obtained. The liquid was soluble oxide were evolved, 53 parts of a brown oil were in water and most organic solvents. When puri obtained, principally consisting of the product ob fied, the product exhibited the following prop 40. tained by combining two molecules of the tetra erties: ethyl pyrophosphate to give hexaethyl tetra poly phosphate. The hexaethyl tetra polyphosphate dis1.4-1.175 so prepared showed itself to be much more toxic m=1.414-1.418 than the corresponding compound prepared from Phosphorus 19-21% 5. triethyl phosphate and phosphorus pentoxide. Sulfur 0% The compounds prepared in accordance with Chlorine 0% my invention are very potent insecticides as Com Eacample 2-60 parts (approximately 5 mol.) m pared with the insecticides now available. For of thionyl chloride were mixed with 280 parts example, the liquid obtained by the process of Ex (approximately 1.0 mol.) of tributyl phosphate 50 ample 7, when tested against German roaches in and the mass was heated. The temperature was a. A percent concentration, gave a 100 percent kill maintained at 110-120° C. for about two hours in 1A2 hours, whereas the reaction product of tri and Sulfur dioxide was evolved during the re ethyl thiophosphate and POCl3 which was em action. The butyl chloride which had formed ployed as a check had no effect under the Same and was not evolved was removed by heat 55 conditions upon the roaches in a period of 24 ing under a slightly reduced pressure. 225 parts hours. A large number of German roaches was of colorless liquid essentially comprised of tetra dusted with dust containing A2 percent of a resi butyl pyrophosphate were formed, which liquid due prepared in accordance with Example 1. A was insoluble in water but was soluble in the com 100 percent kill was obtained in one-half hour. non Solvents. O Like results were obtained using a residue ob Eacample 3-104 parts (approximately .77 mol.) tained in accordance with the process of Example of sulfuryl chloride were mixed with 307 parts 3. When German roaches were subjected to a (approximately 1.7 mols.) of triethyl phosphate, Spray of the material as obtained by the process and the mixture was slowly heated to 140-150° C. of Example 1 in 1 percent concentration in propyl where it was maintained until gas evolution had 5 alcohol-kerosene (4:1), a kill of 80 percent was practically ceased. By this time the ethyl chlo obtained in 10 minutes. Field tests were con ride and a Substantial part of the Sulfur in the ducted with the same residue on beans against form of oxides of Sulfur had been evolved from the Mexican bean beetle with aqueous sprays the maSS. 285 parts of a liquid believed to be com (containing a wetting agent) of 1 to 1000 and 1 to prised essentially of tetraethyl pyrophosphate 70 2000. Both sprays killed the larvae which could were formed, which liquid was soluble in water be seen strewn on the ground 30 minutes after and most organic Solvents. If this reaction is Spraying. There was no foliage injury to the carried out at 90-100° C., ethylchloride is evolved, beans. At these concentrations these materials but the reaction product containing Sulfur is for show themselves to be about ten times as toxic. the most part stable and the product is comprised 75 as DDT. 2,495,220 5 Products in accordance with my invention also ever, as also referred to in the preceding de show the characteristic of being stomach poisons scription, compounds suitable as insecticides may and, hence, are useful against many types of be prepared by reacting alkyl phosphates or animal life. For instance, in a test upon grass other phosphates with other sulfur-containing hoppers using a residue in accordance with that chlorides as illustrated by the following ex prepared by the process of Example 1 on wheat amples. bran in A percent strength, a kill of 100 percent Eacample 9. In this example the reaction was was obtained in two hours. Products prepared carried out between sulfur monochloride and tri in accordance with my invention have proved to ethylphosphate. In this reaction between sulfur be effective against plant lice, aphids, Spiders, monochloride (1 mole) and triethyl phosphate flies, bean beetles, Harlequin bugs, etc., in con (2 moles) it is preferred that a higher tempera centrations as low as 1 part to 2000 parts of water. ture be used than with the other sulfur chlorides. However, for maximum efficiency this solution The reaction begins at about 160° C. with evolu must be used within a few hours after its prep tion of ethyl chloride and deposition of sulfur. aration. Solutions, however, in which a non 5 73 parts of triethyl phosphate and 27 parts of polar solvent or a combination of non-polar sulfur monochloride were heated at 160-170° C. solvents is employed as the dissolving material for about two hours until no more ethyl chloride enable the insecticide to retain its toxicity almost was evolved. If the temperature is raised much indefinitely. Some of the solvents which are beyond this point, the mixture tends to blacken useful in this connection are the lower alcohols, 20 and polymerize. The reaction product is filtered such as methyl, propyl or ethyl, acetone, petro from the deposited sulfur and excess triethyl leum distillates, such as kerosene, benzine, Stod phosphate removed by vacuum distillation. The dard solvent or the like, chlorinated hydrocar yield of crude product is 50 parts. It is a water, bons, such as carbon tetrachloride or ethylene alcohol and acetone soluble, dark amber-colored chloride or aromatic hydrocarbons, such as liquid. benzene, toluene, xylene, or mixtures of any of Eacample 10.-In accordance with this example these solvents. rather than employing a trialkyl phosphate a An advantage of these insecticides, when used substituted phosphate was employed. That is, 21 as stomach poisons, is that they do not have a parts of diethyl chlorophosphate was reacted permanent residual toxicity, the poisonous effect 3) with 7% parts of thionyl chloride. The reaction being dissipated after a time. For instance, when materials were heated together at about 90° C. a material Such as that prepared in accordance to 100° C. for approximately one hour. As in the with Example 1 is sprayed upon fruits or vege previously described reactions the ethyl chloride tables, the toxicity of the material has substan and oxides of sulfur were distilled off. In this tially disappeared at the end of 24 hours, thus 35 particular reaction it is preferred to hold the ten being markedly advantageous over stomach perature below 100° C. to minimize polymeriza poisons which are employed at the present time tion. The resultant product which was useful as in this respect. an insecticide is believed to be comprised of a The residues prepared in accordance with my dichlor diethylpyrophosphate, invention are useful as rodenticides, and here 40 The use of these various compounds as stomach again have the advantage that the materials be insecticides on grasshoppers is disclosed in my come non-poisonous to humans or other animals companion copending application S. N. 718,613, after a short time which is not characteristic fled December 26, 1946. of many rodenticides which are used. Therefore, it is apparent from the foregoing In the materials prepared by my invention, I S that my invention is susceptible of certain vari have found that the tetra alkyl pyrophosphate ations. Hence, I do not wish to be restricted ex residues in which methyl or ethyl constitute the cept insofar as is necessitated by the prior art and major portion of the alkyl hydrolyze at a faster the spirit of the appended claims. rate, and therefore lose their toxicity more rapidly claim: when subjected to hydrolyzing conditions, than 1. A method of preparing phosphate com those in which higher alkyl groups, such as pounds having - useful insecticidal properties propyl or butyl, are employed. The latter mate which comprises heating to a temperature be rials, however, are more slowly effective for in tween 80° C. and 160° C. a reaction mixture con secticidal purposes than the tetraethyl pyrophos sisting essentially of two moles of lower trialkyl phates prepared in accordance with my invention. 5 phosphate and one mol of thionyl chloride, said Therefore, it is often desirable for insecticidal heating being sufficient to cause the liberation of purposes to employ a mixture of the lower tetra approximately one mol of SO2 and two mols of alkyl pyrophosphates and the higher tetra alkyl alkyl chloride. pyrophosphates, the lower compounds giving a 2. The process in accordance with claim 1 in quick kill and the higher compounds giving the () which at least one of the alkyl radicals of the mixture a residual effect. For instance, suitable lower trialkyl phosphate is from the group con mixtures which might be employed are mixtures sisting of propyl and butyl. of either ethyl or methyl compounds with the 3. A method of preparing a tetraalkyl pyrophos propyl or butyl pyrophosphates. Also useful in phate which comprises heating to a temperature this connection are the tetra alkyl pyrophos between 80° and 160° C. a reaction mixture con phates in which part of the aikyl radicals are sisting essentially of two mols of triethyl phos ethyl and other groups in the compound are phate and one mol of thionyl chloride, Said heat propyl or butyl, All of the residues obtained ing being sufficient to cause the liberation of ap in accordance with the processes described here proximately one mol of SO2 and two mols of alkyl in, and particularly in the examples, give ma O chloride. terials having insecticidal properties. 4. A method for preparing tetraethyl pyrophos In the above description I have set forth in phate which comprises mixing together thinoyl particular compounds illustrating my preferred chloride and triethyl phosphate to form a liquid embodiment, namely, the reaction product of reaction mixture consisting essentially of ap alkyl phosphates with thionyl chloride. How- is proximately two mois of the triethyl phosphate 2495,220 7 8 to one mol of the thionyl chloride, and heating a major part of all of the sulfur and halogen con said liquid reaction mixture sufficiently to cause tained in said sulfur acid halide. the liberation of approximately all of the Sulfur 7. A process in accordance with claim 6 in and chlorine of said thionyl chloride as sulfur which the phosphate is triethyl phosphate and dioxide and ethyl chloride. the acid halide is thionyl chloride. 5. A method of preparing phosphate compounds having useful insecticidal properties which com ALAN BELL. prises heating to a temperature between 80 and 160° C. a reaction mixture consisting essentially REFERENCES C TED of two mols of lower trialkyl phosphate and one O The following references are of record in the mol of a sulfur acid halide from the group con file of this patent: sisting of thionyl chloride, sulfuryl chloride, thionyl bromide and sulfuryl bromide, said UNITED STATES PATENTS heating being sufficient to cause the liberation from the recation of approximately all of the Number Name Date sulfur and halogen contained in said sulfur acid 2,242,260 Prutton ------May 20, 1941 halide, 2,370,786 Fox ------Mar. 6, 1945 6. A process for preparing a reaction product having useful insecticidal properties which com OTHER REFERENCES prises heating a reaction mixture consisting es Adler et al., Chemical Industries, vol. 51, Octo Sentially of a phosphate from the group consisting ber 1942, pages 516, 517. of the lower alkyl phosphates and the lower alkyl Chemical and Engineering News, vol. 23, Sep thiophosphates, and at least one Sulfur acid halide tember 10, 1945, pages 1520-1521. from the group consisting of thionyl chloride, sul Balarew, "Zeit, anorg. Chem.' vol. 99, (1917), furyl chloride, thionyl bromide and Sulfuryl bro 25 page 190. mide, said phosphate being present in Said reac Mellor, "Modern Inorganic Chemistry" (1939 tion mixture in a greater molar amount than said ed.), page 480. acid halide, and said heating being sufficient to Hall et al., Ind. and Eng. Chem., vol. 40, No. 4, cause reaction and to liberate from the reaction pages 694-699, April 1948.