2,908,708 United States Patent Office Patented Oct. 13, 1959 1 2 reaction for same extent of conversion at a given tem perature. 2,908,708 The reaction product was cooled and weighed, then analyzed for P3+ and P5+, methane phosphoric acid, and PROCESS FOR PREPARING PHOSPHONATES total phosphorus content. ------Leland K. Beach, Westfield, N.J., assignor to Esso Re In general, the reaction products are clear, colorless search and Engineering Company, a corporation of liquids with densities above 1.0. On extended cooling at Delaware temperatures below 100° C., the products become solidi No Drawing. Application June 14, 1954 fied. On reheating the products are reliquefied. The Serial No. 436,731 0 products are water-soluble. The product obtained and described is useful as such, 6 Claims. (C. 260-461) without further purification. Other specific examples of the desired derivatives of This invention relates to a method for converting a 15 the methane phosphonic acids shown are the dimethyl phosphorous compound, e.g. phosphite or a phosphorous ester derivatives. acid, to a phosphonate, particularly methane phospho Improvements in yields of the desired methane phos nates, by reaction with an ester of a phosphoric acid, phonic acid derivatives obtained by using the process of particularly selected from the methyl esters. the present invention are shown in the following Table I. Methane phosphonic acid derivatives have been made 20 Table I by pyrolysis of dimethyl phosphite alone but not by re EFFECT OF METHYL PHOSPHATE UPON PYROLYSIS OF action of the phosphite ester or of phosphorous acid with METEY, POSFEITES AND PEIOSPEOROUSAC an ester of another oxy-acid, particularly such as a phos All samples heated slowly in pairs to reaction temperature, 270° C. MMEP=Monomethyl phosphite phoric acid. DMBP=Dimethylphosphite For the present invention, it was found that the 25 MPs Mixed mono- and di-methyl phosphates 3PO3=Phosphorous acid methane phosphonic acid derivatives can be obtained by Me3PO42-, Trimethylphosphate reaction of phosphorous acid or methyl phosphites with P3t=Phosphite phosphorus methyl esters of phosphoric acid, and the yields of de P5+. Elsired phosphate phosphorus of phosphate and phosphine sired product are better than in the absence of the methyl productS. phosphate esters. 30 Mole percent The desired methane phosphonic acid derivatives are Mole selectivity Yield percent per represented by the following general formula: Reactant mixture P3+. Un-Desired pass of O con- desired phos desired 2 verted P5+ phonate prod prod- prod- ucts CH-Féo-R, 35 ucts lucts A. MIMIIP--IPO3------37 4. 54 20 wherein R1 and R2 stand for hydrogen, methyl, or a B. MIMEIP--HPO-MePO4- 90 O 9. 82 phosphorus-containing radical. Specific examples of these C. Espos------41 100 0. O (derivatives are: D. Eisp O3-Me3PO4------37 0. 97 36 E. MMHP--H3PO3------39 40 60 23 40 F. MMHP--HPO-MP 42 9 91 38 2 o 2 o G. HaPO3-...------1. 100 - 0 0. CH-P-OH CH-P-0 CE H. BaPO-MP------9 9 62 5.6 N N OE OH Methane phosphonic Mono methylmethane The summarized data in Table I shows in the duplicate acid phosphonic acid experiments C and D that the presence of an equal 45 amount of trimethyl phosphate did not affect the per to 0 centage of HPOs decomposed but changed the course of CHA-P-O-P-CH2 2 this decomposition from 100% undesired products to OE YoE 97% desired products methane phosphonic acid de iPyro methane phosphonic acid 50 rivatives. ------In the pair of experiments G and H, mixed mono pH, and di-methyl phosphates caused HaPO3 to yield selec tively 62% of the desired methane phosphonic acid deriva tivesproducts. instead of giving 100% conversion to undesired 2 o on. The mixture of monomethyl phosphite and phosphorus (CH-P P-CH acid referred to in the Table I as Sample A and Sample O E contained by analysis of their aqueous solutions about 'Trimeric methane phosphonic acid anhydride 82 mole percent total phosphites including 52 mole per cent monomethyl phosphite, 30% HPO and 1% di EXAMPLES 60 methyl phosphite. These mixtures were obtained as bot The reactant phosphite or phosphorous compound was toms in the distillation of crude dimethyl phosphite "mixed in a Pyrex tube with about an equal volume of (DMHP). - the methyl phosphate reactant. Another portion of the In the absence of the added methyl phosphates or phosphite alone was also placed in a duplicate Pyrex tube. similarly reacting esters, there is a low yield of only 20% The liquid-containing tubes were heated side by side in 65 of the desired products per pass or per fresh batch. In -a metal bath at temperatures mainly in the range of 100' the duplicate experiment B, the added trimethyl phos to 300° C. A small amount of gas containing diethyl phate raised the conversion to 90% from 37% and tether was evolved and was removed. changed the yield to 82% of desired products per pass, The reaction proceeded satisfactorily and the heating which is a considerable advantage. Similarly, in the ex was stopped after a period of from 10 minutes to about 70 periments E and F the mixed added methyl phosphates 60 minutes. The trimethyl phosphate gave the quickest enhanced the yield of desired products although under 2,908,708 3 4 . these conditions they did not change the total phosphite - methyl phosphate. This concept is not to be construed conversion level very much. as limiting the invention. It has been found that dimethyl hydrogen phosphite The temperature required for the above-discussed (DMHP) when pyrolyzed initially forms no appreciable methylations ranges between an upper limit of about 350 amount of phosphates. As the pyrolysis reaction pro C. and a lower limit determined by that resulting from ceeds, substantial amounts of material which analyzes in spontaneous reaction of the cold reagents. It is believed aqueous solutions as monomethyl phosphite (MMHP) that 100° C. to 275 C. is a preferred operating range. and H3PO3 form. Consequently as the pyrolysis is con The amounts of methylating agents used is of course in tinued these are converted into more undesired products, fluenced by many considerations including the feed com phosphates and phosphines. Accordingly, it is beneficial O position, catalyst, temperature and the economics of the to add methyl phosphate esters at some stage of the particular reaction. Excess trimethyl phosphate of course pyrolysis for conversion of phosphites to the desired phos would give the maximum yield and fastest reaction ac phonate derivatives. cording to the present interpretation of the data. In the examples given in the Table I, extraneous phos Phosphates are desirable agents since present processes phate esters were added to the phosphite pyrolysis feeds 5 for phosphite pyrolysis include systems for handling these to ascertain the specific affects of the phosphate esters. pyrolytic products. Borates are attractive because of In an improved embodiment, the present invention con the possibility that they might be regenerable with meth templates the production of dimethyl phosphate along anol treat to give volatile trimethyl borate. with dimethyl phosphite by judicious addition of POCl3 In special cases other methyl esters might be more to the PCls feed to methanol to form such a mixture. 20 desirable. Another embodiment of this invention involves the It is envisioned that mixtures of methyl esters might addition of trimethyl phosphate or similar ester to the re be especially interesting. Methyl chloride in methyl action mixture in the pyrolysis of dimethyl hydrogen phosphate or borate is suggested. - phosphite at the proper time for obtaining maximum yield. Products of this invention may be employed in pre In the staged recirculating pyrolysis of DMHP this 25 paring fuel, lubricating oil, and grease additives, deter invention envisions the addition of the methyl ester to a gents, fire retardants, insecticides, and plasticizers. The point near the end of the pyrolysis. For example in an methane phosphonic acids undergo reaction with alcohols, apparatus containing two circulating units the ester is esters, salts, bases, as well as with halogens and non added to the effluent before or during addition of the metallic halides. effluent to a final pyrolysis state. 30 In addition to the preceding ideas many others will The use of methyl esters such as trimethyl phosphate now be obvious to those skilled in the art. - does not exclude the use of BF or other such catalysts. The invention described is claimed as follows: In fact where trimethyl or dimethyl phosphate is added 1. Process for preparing a methane phosphonate which to DMHP in a pyrolysis reaction, BF may also have comprises reacting a phosphorous compound selected from been added. One attractive process involves the use of 35 the group consisting of phosphorous acid and methyl BF3 to catalyze the desired reactions at the beginning esters thereof with a methyl ester of a phosphoric acid. and the addition of methyl phosphates to give better 2. Process for preparing a methane phosphonate by re yields during the last half of the reaction when large acting a phosphorous acid and a methyl ester thereof with amounts of unconverted phosphites such as monomethyl a methyl ester of a phosphoric acid. phosphite and HPOs are present. 40 3. Process for preparing a methane phosphonic acid In staged pyrolysis such as that above it is advantageous and methyl esters thereof which comprises reacting a to use methyl phosphates in the higher temperature, sec phosphite with a methyl ester of a phosphoric acid. ond stage. BF is especially beneficial at lower temper 4. Process for preparing a methane phosphonic acid ature early stages. and a methyl ester thereof which comprises reacting a Study of the action of tri- or dimethyl phosphate on 45 phosphorous acid with a methyl ester of a phosphoric phosphorous acid indicates that ester interchange may acid. occur. This concept does not limit the invention, how 5. Process for preparing methane phosphonic acid and ever, and is not meant to indicate that mono- or dimethyl a methyl ester thereof which comprises heating a mix phosphite is essential to the production of methane phos ture containing phosphorous acid and mono-methyl phos phonic acid derivatives. 50 phite with a mixture containing mono- and dimethyl While trimethyl phosphate is a more desirable methylat phosphate to temperatures in the range of 100 to 350° C. ing agent, it costs more than di- or monomethyl phos 6. Process for preparing a methane phosphonic acid phate. On the basis of equal methyl content it may be and methyl esters thereof which comprises heating a mix no more desirable. One view holds that the last methyl, ture containing phosphorous acid and mono-methyl phos i.e., the one visualized as held by the weakly acid POH, 55 phite with trimethyl phosphate to temperatures in the is the reactive one. On this basis the trimethyl phos range of 100° to 350° C. phate has two methyls in reserve but the active methyl is the same as or similar in activity to that in mono No references cited.