3,463,840 United States Patent Office Patented Aug. 26, 1969 1. 2 phonates in small yields. When at least three moles of mer 3,463,840 captan are employed, the alkylthioalkyldithiophospho PROCESS FOR PRODUCING ALKYLTHOALKYL nates are obtained in good yields. PHOSPHONODTHOC ESTERS Alkylthioalkyldithiophosphonates are known com Marion F. Botts, Independence, Mo., and Erik K. Regel, Mission, Kans, assignors to Chemagro Corporation, pounds and are useful as defoliants, Regal patent 3,193,- New York, N.Y., a corporation of New York 372. The procedure for preparing such compounds in the No Drawing. Original application June 24, 1966, Ser. No. Regal patent, namely reacting PCls with a hydrocarbon 560,097. Divided and this application Jan. 3, 1968, Ser. and a disulfide in the presence of a Friedel-Crafts catalyst, No. 708,745 however, is relatively expensive considering the overall Int, Cl, C07f 9/40, A01n 9/36 O yields and reaction conditions employed. U.S. C. 260-972 8 Claims Accordingly, it is an object of the present invention to develop a novel method for making alkylthioalkyldithio phosphonates. ABSTRACT OF THE DISCLOSURE Another object is to develop a novel method for Compounds are prepared having the formula 5 making analogues of alkylthioalkyldithiophosphonates wherein the alkyl thio group is replaced by haloalkylthio. O SR3 A further object is to develop a method of preparing RSCIP N dithiophosphonates which cannot be synthesized by other R SR4 routes. where R, Ra, and R4 are alkyl or monohaloalkyl and R2 20 An additional object is to develop a novel method for is hydrogen, alkyl, monohaloalkyl, aryl, haloaryl or al killing nematodes. Still further objects and the entire scope of applica kylthioalkyl by (1) reacting 1 mole of phosphorus tri bility of the present invention will become apparent from chloride with one mole of an aldehyde having the formu the detailed description given hereinafter; it should be la RCHO at a temperature below 0° C., and (2) re 25 understood, however, that the detailed description and acting this product with 3 moles of a mercaptain or mixture specific examples, while indicating preferred embodi of mercaptains having the formula RSH, RSH and RASH ments of the invention, are given by way of illustration at a temperature below 0°C. The compounds are useful only, since various changes and modifications within the as nematocides. spirit and scope of the invention will become apparent 30 to those skilled in the art from this detailed description. This application is a division of our copending appli It has now been found that these objects can be at cation, Ser. No. 560,097, filed June 24, 1966. tained by preparing compounds having the following for The present invention relates to the preparation of alkyl mula: thioalkylphosphonodithioates and the use of Such com 3 5 pounds as nematocides. Risch (SR. The reaction of aldehydes whith phosphorus trichloride N has been investigated by several authors, e.g., Fossek, R SR4 II Monatshefte vol. 5, page 121 (1884), Kabashnik et al., where R1, R3 and R4 are alkyl (including cycloalkyl) and Chem. Abst. vol. 44, page 7257 (1950), and Conant et al., 40 haloalkyl and R2 is hydrogen, alkyl, monohaloalkyl, aryl, Jour. Amer. Chem. Soc., vol. 42, page 2337, vol. 43, pages haloaryl, and alkylthioalkyl. Preferably R1, Ra and R4 do 1928 and 10191, vol. 44, page 2530 and vol. 46, page 192. not have over six carbon atoms. Phosphorus trichloride adds on to aldehydes in an eXo Examples of compounds suitable as nematocides with thermic reaction at temperatures below 0° C., e.g., -50 in the invention are C. to -70° C. The products obtained are thermally un 45 S.S.-diethyl ethylthiomethane dithiophosphonate, stable and are in equilibrium with phosphorus trichloride S.S.-dimethyl 1-methylthio ethane dithiophosphonate, and aldehydes. The products have the formula: S.S.-diethyl 1-ethylthioethane dithiophosphonate, S.S.-dipropyl 1-propylthioethane dithiophosphonate, RCH-P Clah -- Cl N / S.S.-dibutyl 1-butylthioethane dithiophosphonate, O 50 S.S.-dicyclohexyl 1-cyclohexylthioethane dithiophos I phonate, where R is the residue of the aldehyde beyond the first S.S.-dimethyl 1-methylthiopropane dithiophosphonate, carbonation. S.S.-diethyl 1-ethylthiopropane dithiophosphonate, This addition product, however, easily reacts with mer S.S.-dipropyl 1-propylthio propane dithiophosphonate, captans. There are various possible competing reactions, 55 SS-dimethyl 1-methylthiobutane dithiophosphonate, including the following: S.S.-diethyl 1-ethylthiobutane dithiophosphonate, S.S.-dihexyl 1-hexylthiobutane dithiophosphonate, (a) mercaptal formation; S.S.-dimethyl 1-methylthio 2-ethylhexane dithiophos (b) trithiophosphite formation; phonate, (c) reaction of the mercaptain with the addition product. 60 S.S.-diethyl 1-ethylthio 3-chlorobutane dithiophosphonate, It has now been found that at temperatures well be S,S-diethyl 1-ethylthio 2-ethylthiobutane dithiophos low 0° C., e.g., -70 to -50 C., reaction (c) is the phonate, predominant reaction. S.S.-dimethyl 1-methylthio phenylmethane dithiophos When mercaptains are reacted with a compound of phonate, Formula I in a 1:1 mole ratio, the expected ox-chloroalkyl 65 S.S.-diethyl 1-ethylthiophenylmethane dithiophos chloridophosphonothioates could not be isolated. phonate, In similar fashion, when two moles of mercaptain Were S.S.-dibutyl 1-butylthio phenylmethane dithiophosphonate, reacted with a compound of Formula I, the expected ov S,S-diethyl 1-ethylthiop-chlorophenylmethane dithio alkylthioalkylchloridophosphonothioates could not be iso phosphonate, lated. 70 S.S.-diethyl propylthio methane dithiophosphonate, Instead, whether one mole or two moles of mercaptain S.S.-diethylbutylthiomethane dithiophosphonate, were used, there was isolated only alkylthioalkyldithiophos S.S.-dibutyl ethylthiomethane dithiophosphonate, 3,463,840 3 4. S.S.-dibutylbutylthiomethane dithiophosphonate, formed the mercaptal instead under the described reac S.S.-di (3-chloropropyl) 1-(3' chloropropylthio)ethane tion conditions. dithiophosphonate, The present invention is suitable for preparing dithio S.S.-diethyl 1-ethylthio 3-chloropropane dithiophos phosphonates which cannot be synthesized by other phonate, routes or which can be synthesized only with difficulty by S.S.-dimethyl 3-ethylthio propane dithiophosphonate, other methods. S.S.-dimethyl-1-methylthio-m-bromophenylmethane The reaction of the aldehyde with mercaptain can be dithiophosphonate, carried out in the presence of a solvent, e.g. benzene, S.S.-diamyl 1-amylthio o-chlorophenylmethane dithio toluene, carbon tetrachloride, chloroform or the like al phosphonate, though this is not essential. S.S.-diisopropyl -isopropylthiop-tolylmethane dithio O The general procedure employed to prepare the alkyl phosphonate, thioalkyl dithiophosphonates was as follows: S.S.-diethyl 1-ethylthio 2-methylpropane dithiophos phonate, GENERAL PROCEDURE S.S.-dimethyl 1-methylthio 2,6'-dichlorophenylmethane 5 Phosphorus trichloride was placed in a three necked dithiophosphonate, flask equipped with a thermometer, stirrer, condenser and S.S.-dimethyl-1,3-di(ethylthio) propane dithiophos dropping funnel. External cooling was provided by an phonate. acetone-Dry Ice bath. At -70° C. the aldehyde was added As aldehydes for the reaction, there can be used slowly while agitating the phosphorus trichloride. The formaldehyde (including trioxane and paraformalde 20 temperature was kept at -70° C. by adjusting the addi hyde), tion rate of the aldehyde. After addition of the aldehyde acetaldehyde, was completed the reaction mixture was agitated for 1 propionaldehyde, hour at -70° C. butyraldehyde, Then the mercaptain was added dropwise at -70° C. isobutyraldehyde, 25 to -60 C. The reaction mixture was then allowed to valeraldehyde, Warm up to -40° C. where hydrogen chloride began to hexaldehyde, evolve, and the reaction mixture was agitated for 1 hour 3-methylthio propionaldehyde, after the addition was completed. 2-ethylhexanal, Finally the reaction mixture was slowly brought up to 2-chlorobutyraldehyde, 30 room temperature and without agitation allowed to stand 3-chlorobutyraldehyde, for several hours. The crude product was then washed 2-ethylthiobutyraldehyde, with water until neutral, dried and distilled in a high benzaldehyde, WaC. 2-butylthioacetaldehyde, In order to separate small amounts of mercaptals from p-chlorobenzaldehyde, 35 the desired dithiophosphonate, the crude product is pref o-chlorobenzaldehyde, erably redistilled or fractionated over a small Vigreaux m-bromobenzaldehyde, column. 2,6-dichlorobenzaldehyde, Example 1 3-ethylthiopropionaldehyde, Using the General Procedure 1 mole (137.39 grams) 3-chloropropionaldehyde, 40 of phosphorus trichloride was reacted with 30 grams of p-tolualdehyde, paraformaldehyde (equivalent to 1 mole of formalde o-tolualdehyde, hyde). There was then added dropwise 3 moles (186 2,4,6-trichlorobenzaldehyde, grams) of ethyl mercaptan. The product was S.S.-diethyl 3-ethylthiopropionaldehyde. ethylthiomethane dithiophosphonate B.P., 120° C., n25 As mercaptains there can be used methyl mercaptain, 45 1.5652, Code No. 6480, yield 19%. ethyl mercaptan, propyl mercaptan, butyl mercaptain, Example 2 amyl mercaptan, cyclohexyl mercaptan, 3-chloropropyl The same product as that of Example 1 was prepared mercaptain, isobutyl mercaptan, secondary butyl mercap by an alternate procedure, namely, reacting 1 mole of tan, octyl mercaptan, 2-chlorobutyl mercaptan, 3-bromo 50 Sodium ethyl mercaptide with 1 mole of