Patented Oct. 21, 1952 2,615,043

UNITED STATES PATENT OFFICE

METHOD OF PREPARING ETHYL DICHLOROPHOSPHINE Morris S. Kharasch, Chicago, 111., and Sidney Weinhouse, Chester, Pa., assignors to the United States of America as represented by the Score tary of War No Drawing. Application February 21, 1944, Serial No. 523,364 1 Claim. (Cl. 260-443) 1 2 The invention described herein may be manu the ?rst stage occurs; but when the reaction is factured and used by or for the Government for carried out above 80° 0., either in the presence governmental purposes without the payment to or absence of a high-boiling solvent, e. g. nitro us of any royalty thereon. benzene, both stages proceed simultaneously. This invention relates to a method for the The ethyl chloride formed in the second stage preparation of ethyldichloroarsine and related may be recovered quantitatively by chilling the organo-mineral-halides. evolved gases. Pure ethyldichloroarsine may be ,An object of this invention is to provide a obtained by distilling through an ef?cient c01 method for securing high yields of the desired lumn the product obtained in the reaction de product and which is Well suited for industrial 10 scribed. The density of the distillate is 1.6570 scale manufacture. for Ethyldichlcroarsine was introduced as a it chemical warfare agent by the Germans in 1918. The best known methods for preparing this com It boils at 825° C. under '25 mm. pressure. pound have been essentially the same as the Ger 15 As a speci?c example, the following directions man process. They are complicated and involve convenient for the preparation of ethyldichloro the following steps: (1) the conversion of ethyl arsine in batches of about 5 lbs. are given. The chloride into disodium ethyl arsenate; (2) the re reaction is carried out at above 90° C. and in the duction of disodium ethyl arsenate with sulfur absence of any solvent. Both stages of the re dioxide to form ethyl arsenious oxide; (3) the 20 action proceed simultaneously. treatment of ethyl arsenious oxide with hydrogen EXANIPLE 1 chloride to form ethyldichloroarsine. It has been con?rmed that this process gives an aver-' In a 5-liter, B-neck flask equipped with a drop age over-all yield of only about 27 to 36% at ping funnel having a gas inlet side arm, an e?i cient mechanical stirrer and a re?ux condenser the most. 25 It is evident that such prior methods are ill is placed 2,730 g. (15 moles) of arsenic trichlo suited for large scale operation. For this reason ride. Air is swept out of the flack by passing a new and radically different method has been dry nitrogen through a ?exible tube leading to developed. the glass inlet tube attached to the dropping In the new method of this invention, ethyldi funnel. The ?exible tube is then closed off with chloroarsine is prepared by a reaction of arsenic a screw clamp. The flask is placed in an oil trichloride with tetraethyl lead under suitable both heated to 100° C.; and after the arsenic conditions. trichloride has reached approximately that tem Theoretically, the over-all reaction is: perature, a few cc. of tetraethyl lead is added from the dropping funnel to the stirred arsenic trichloride. The start of the reaction, which oc~ However, it is important to note that the reaction ours in a few minutes, is indicated by clouding of evidently takes place in two stages. the liquid and separation of a white precipitate. ‘The’ ?rst stage of the reaction is represented A total of 1,620 g. (5 moles) of tetraethyl lead is by the equation: 40 then added through the dropping funnel at such a rate that the reaction mixture is kept gently boiling. During this addition of, the tetraethyl and proceeds spontaneously‘at room temperature lead and for one hour after the addition is com or at temperatures below 50° C. vAt these temper plete, stirring is continued, and the oil bath is held at a temperature of about lOO-ll0° C. atures-even an excess of arsenic trichloride fails 45 to detach a third ethyl radical from the lead About seven hours in all is required for these atom. operations. The second stage represented by: After the product has cooled to about room temperature, the ?ask is connected with a Claisen still-head. The product is distilled directly from 50 proceeds slowly at 80° C. and rapidly at tem the reaction mixture at 75 mm. pressure. The peratures above 90". C. receiver, a 3-liter, round-bottom ?ask, is con _The reactions may be carried out in the pres nected to a vacuum pump through a trap kept at ence of suitable ‘solvents, and the over-all reac —80° C. During the distillation the oil bath is tion may be carriedout in the absence of sol 5 01 maintained at 120° C.; the product distills at vents...'.When.low-boiling solvents are used, only 82-83° C. About 80% of the product distills over 2,616,048 ' 3 4 in four to ?ve hours; the distillation of the re Reactions similar to the one used in the prepa mainder is slower because of the large amount ration of ethyldichloroarsine may be used for the of lead chloride in the ?ask. The process may be preparation of a number of related organo-min hastened by gradually reducing the pressure. eral-halides, in general, represented by the for About ten: hoursis required to‘ distill over. an mula amount equivalent to a 95% yield. ' The density of the crude water-white product varied in four runs from 1.6735 to 1.6799 as com wherein Rn represents organic radicals, such as pared to 1.6570 for the very pure. materialdis alkyl, aryl, alkaryl or aralkyl radicals; M repre tilled through a column. Hence the distillate. sents'ametal, non-metal or semi-metal, such as obtained as described is 95.5 to 97% pure. The arsenic, phosphorus or antimony; and K121. stands impurity is arsenic trichloride, the boiling point. forhalogen groups, generally chloride or bromide of which is 20% below that of 'ethyldichloroar groups; the subscripts n and m being whole num sine. Fractionation through a column readilyv berslwhich add upto the valence of the con separates the two substances, and the arsenic 15 stituent which is three for the trivalent min trichloride may be recovered. Thea-percentages. eral. atom... thus obtained check well with the composition. Preparations here described are those of (1) calculated from the density of the crude mate diethylchloroarsine (C2H5)2ASC1; (2) ethyldi rial. chlorophosphine C2H5PC12 and (3) ethyldichloro The described method?» with slight modi?ca 20 stibine C2H5SbCl2. tions which are apparent can be applied on: a commercial scale‘.v On an industrial scale- the. EXAMPLE" 2' crude~~reaction product may: be separated; from Diethylchloroarsine: prepaTaz'ion-.—-At? high theprecipitated lead- chloride by ?ltration. This temperatures, excess tetraethyl lead reacts with type of. separation hasbeen- successfully. carried ‘ . ethyldichloroarsine. to. form diethylchloroarsine. out. No di?iculties were experienced in carrying Ethyldichloroarsine, 5215’ g. (0.3‘mole) was heated out the method describedv with proper precau to 120° C., and 48.5 g. (0.15mole) of ‘tetraethyl tions in handling the materials and in remov lead was slowly added.v The‘ separation of a lng‘ fumes. white precipitate indicated: that ‘reaction had oc ‘ For the purpose of comparison, arsenic. tri.~ .' .. curred: After themixture had' been kept at 120°" chloride was treated with tetraethyl lead in-av C. for two hours, the producttwasi distilled'di manner similar to that described except in using rectly'from‘ therreaction?ask. A‘ yield of 393 g. carbon tetrachloride asa solvent in the reaction of diethylch'loroarsinewas obtained. This prod mixture and treating‘the mixture for‘about twelve‘ uctboi'led. at .74‘~78° C. under-"74 mm’. pressure. hours atapproximately the boiling point of the ‘ solvent. The yield of .ethyldichloroarsine by‘ this‘ D22. 1.215 low-temperature preparation was only 69% if the Anal. Calcd. for EtzASCl: CI, 21.1. Found: Cl, ?rst stage reaction is usedas a basis‘ of calcula 18.0. tion, and is only 46% if the over-all reaction is’ The product is. therefore, mainly diethyl- used. Similar results were obtained’wh'en ben .zchloroarsine with a small amount‘ of triethyl- zene (boiling point ofz178~° C'.). orligroin were used arsine. as solvents and. the reaction carried out at tem The white residue from the'reaction was peratures below 80° C. washed with benzene; it weighed" 49‘ g. The‘ In. another investigation. the proportion. of’ theoretical'yield was 50.5%‘. arsenic trichloride to tetraethyl lead. Was- in-. Anal. Calcd. for (C2H5)2PbCl2: Cl‘, 212. creased tofour moles to,one.. Benzene was used " Found: (:1, 21.9; as a solvent, and the reaction was carriedout 'at' below 80° C. The recoveredqarsenio.trichloride. EXAMPLE 3? amounted to 1.3 mole equivalent; the ethyldii Ethylolichlorophosphine preparation-Phos chloroarsine obtained was equivalent totwomoles ’ phorus trichloride, 69 g". (0.5 mole) was‘placed in of arsenic trichloride. These'resultsv show. that a three-necked ?askv ?tted with a‘ dropping fun at atemperature. below 80° C., a large ,excess- of. nel, mechanical stirrer and‘ a're?ux condenser.‘ arsenic trichloride was capable of removing only ‘While a slow stream of nitrogenwas passed‘ into two ethyl groupsfrom the tetraethyl lead the ?ask;v 54 g. (0.167‘ mole) of’ tetraethyl lead In all reactions conductedv at temperatures .55 vwas added.-. Reaction; wasextrem'ely slow; there above 80° C., with or Without solvent, wherethree was. no precipitation. of lead until the mixture had.v moles of arsenic trichloride to one mole of tetra» been‘ refluxed‘ for two. hours. The. ?ask. was ethyl lead were used, the yield of ethyldichloro~ heated in an oil bath at 110-“ C. untilthe mixture arsine approached the theoretical. For ex. ceased to re?ux (36 hours). The volatile mate ample, in a preparation in which nosolvent was. rial was then distilled directly from the reaction employed, the yield was 96.5%. vessel. The~58.5 gof'colorless, evil-smelling dis The liquid collected by condensing gas evolved.’ tillate (B. P. 94-97“ C. at 760mm.) represents-a. during the reaction had. a molecular weight cor yieldlof89 per cent. ' responding to that of ethyl chloride, and-boiled-l Anal. Calcd. for. C2H5PC12; . CI, 54.2..- Found; at 12° C. The solid residue .was almost purelead 65 " Cl;,56.2, 56.1. chloride. Anal. Calcd. for PbCh: C1,. 25.5. Found: 01, EXAMPLE 4 25.8.v Ethyldichlorostibine preparation.—In the .ap~ When .an equimolecular. mixture of diethyl—. paratusfor ' preparing ethyldibhloroarsine, 68.4 g. lead‘ dichloride and arsenic- trichloridei. was.v 70.. (0.3 mole) of dried and pulverized‘antimony'tri heated to 125°. 0., there'was a vigorousreaction. chloride was suspended in. 160: cc: of solvent. and,.ethyl chloride w-assevolved. The reaction. Tetraethyl lead' (323g, 0.1.mole) wasthen added mixture wasv distilled at..75 mm.v The product. ; slowly. Themixture was heated underre?ux for 2 obtained, was ethyldichloroarsine in. a. yield. of. eight hours .and then cooled. After the solvent; 15-: hadbeen removed by; distillation,.theiresiduewask 2,615,043 5 6 distilled under reduced pressure. The product the organo groups may be methyl or phenyl radi which boiled be-tween‘l13“ and 120° C. at 25 mm. cals for greater effectiveness. In the event the was redistilled. A total of 48.6 g. of a colorless organo-metal halides lack the desired viscosity liquid was obtained (B. P. 62-83“ C. at 1 mm., or persistency, they may be used together with D 2.182) . suitable thickening agents. For example, ethyl Anal. Calcd. for EtSbCh: Cl, 31.95. Found: dichloroarsine may be blended with cellulose 31.40. acetatebutyrate. A 5% solution of this type is In these preparations a halide of a trivalent comparable in consistency to glycerine and is mineral constituent is treated with an organo quite stable. In addition to increasing the vis lead compound under conditions that are proper 10 cosity of the agent, a thickening additive may ly controlledto bring about replacement of the aid in lowering the volatility. The organo-min desired number of halogen constituents in the eral-halides may also be used in mixtures with halide by organic radicals. To obtain proper other toxic agents. control of the reactions, it is advantageous to It is to be understood that modi?cations may heat the halide under re?ux and to control the 15 be made which come within the spirit and scope rate of reaction by the rate of addition of the or of the invention. gano-lead compound. The control is important We claim: -for allowing the reaction to be brought up to the A method of preparing ethyldichlorophosphine proper high temperature level. It has been which comprises reacting phosphorus trichloride shown that desired products are not obtained in 20 with tetraethyl lead at a temperature above satisfactory yields unless the reaction iscarried 90° C. ‘ out at a proper temperature level. MORRIS S. KHARASCH. At a sufficiently high reaction temperature SIDNEY WEINHOUSE. level, which may vary with the reactants and is in a number of instances of the order of 90° C. REFERENCES CITED and higher, the organo-lead compound, repre The following references are of record in the sented by PbRd or R2PbX2, R being a, hydrocar ?le of this patent: bon radical and X a halide radical, tends to be Raiziss et 2.1.: “Organic Arsenical Compounds,” reduced to PbX2, the dihalide. Thus, likewise, pp. 42‘ and 43 (1923). at a suf?ciently elevated reaction temperature, 30 Textbook of Inorganic Chemistry, by Friend, a PbR4 compound, such as tetraethyl lead, is vol. XI, part III (1936) , pp. 31, 32, 210 and 211. made to lose more than 2 R. (hydrocarbon) radi Gilman et al.: Jour. Organic Chem., vol. 4 cals from a molecule. (1939), pp. 162 to 168. The organo-mineral-halides, and particularly Cengio Giom: Chim. Ind. I, 68-75 (1919). the organo-mineral-dihalides in which the min Matsumiya: “Mem. C01. 301. Kyoto Imp. Univ.,” eral constituent is trivalent, have important uses vol. 8, pp. 391 to 396 (1925). as chemical warfare agents. In some instances