IL45990A - Process for producing n-phosphonomethyl glycine triesters - Google Patents

Description

Process for producing N-Phoaphonometliyl Glycine Trieaters o* -TOOK no T'S'^I 'nDi3isoiD-K TIS"1? v rtn PROCESS FOR PRODUCING N-PHOSPHONOMETHYL GLYCINE TRIESTERS Abstract of the Disclosure This disclosure relates to an electrolytic process for producing N-phosphonomethyl glycine esters "by the electrolysis of the tetra esters of N-phosphonomethylimino diacetic acid. In accordance with this disclosure, a solution of a tetra ester of N-phosphonomethylimino diacetic acid dissolved in a suitable solvent containing an electrolyte is subjected to an electromotive force or electric current in an electrolytic cell to be electrolytically oxidized to a triester of N-phosphonomethyl glycine. The triester of N-phosphonomethyl glycine produced can be hydrolyzed to the free acid and its salt derivatives which are useful as post-emergent herbicides.

PROCESS FOR PRODUCING N-PHOSPHONOMETHYL GLYCINE TRIESTER.fr This invention relates to a method of producing N-phosphonomethyl glycine triester "by the electrolytic oxidation of the tetra esters of N- (phosphonomethyl) im no-di-acetic acid. More particularly, this invention relates to the production of N-phosphonomethyl glycine triesters by the electrolysis of tetra esters of N- (phosphonomethyl ) imino-di-acetic acid in a suitable solvent medium containing a supporting electrolyte.

In accordance with the process of this invention, an organic solvent electrolytic solution of the tetra ester of N-phosphonomethylimino diacetic acid is charged into an electrolytic cell f tted with an anode and a cathode and an electromotive force or electric current impressed upon the cell whereby the tetra ester of N-phosphonomethylimino diacetic acid is electrolytically oxidized to yield the triester of N-phosphonomethyl glycine, as the principal product.

In a preferred method of conducting the process of this invention, a 5 to 20^ solution of tetra ester of N-phosphonomethylimino diacetic acid dissolved in acetonitrile containing a dissolved supporting electrolyte is charged into an electrolytic cell maintained at a temperature of from 0°C. or less to 100°C. or more and having noble metal, graphite or carbon electrodes. An electric current is then impressed on the cell by connecting the anode and cathode to a proper source of direct current with controls to maintain the current den- 600 sity at between .01 and ¾ΦΦ ma/cm2 for a time sufficient to oxidize the tetra ester of N-phosphonomethylimino 'diacetic acid to the triester of N-phosphonomethyl glycine.

The resultant reaction solution is then vacuum The triester residue is then dissolved in water, hydrolyzed and recovered as a N-phosphonometh l glycine by recrystalliza-tion upon the cooling of the water solution.

The concentration of the tetra ester of N-phosphono-methylimino diacetic acid employed in the process of this invention is not critical and is limited only by the solubility of the starting material in the particular solvent employed. Thus, for example, although concentrations as low as 0.01% by weight in the solvent can be employed, for reasons of efficiency and economy, it is preferred to employ concentrations of from about 5 to about 30 by weight, or even higher, of the tetra ester of N-phosphonomethylimino diacetic acid in the solvent containing supporting electrolyte.

The temperature at which the process of the instant invention is conducted is not narrowly critical and can range from as low as 0°C. to as high as 110°C. or even higher if a pressure cell is employed. The temperature employed is a function of the solvent boiling point, freezing point, pressure and solubility of reactants and reaction products. As is apparent to those skilled in the art, at lower temperatures a very dilute solution or a suspension must be employed since the solubility of the tetra ester of N-phosphonomethylimino diacetic acid starting material is lower at lower temperatures.

The process of the instant invention can be conducted at atmospheric pressure, super atmospheric pressures and subatmospheric pressures. For reasons of economy and ease of construction of the equipment employed in the process of this invention, it is preferred to conduct this process at approximately atmospheric pressure.

The type of electrolytic cell employed in the process glass container having one or more anodes and cathodes conne c-ed to a source of direct current, such as a battery and the like or a source of low alternating current. The cell can also consist of the two electrodes separated by an insulator such as a rubber or other non-conducting gasket.

The current densities employed in the process of this invention can range from as low as 1 milliampere per square centimeter (ma/cm2) to 6oo or more ma/cm2. In general, it is preferred to employ current densities of from about 1 to about 10 for best yields of the desired triester of N-phosphono-methyl glycine. At higher current densities, the electrolytic efficiency of the cell is decreased. At the higher current densities there are also undesirable side reactions, such as electrolysis of the solvent and decomposition of the desired product into undesirable by-products.

The electrodes, i.e., the anode and cathode, employed in the- process of this invention can be constructed of a wide variety of materials and combinations of materials. Thus, for example, the anodes may be constructed of any conductive sub- stance, such as lead, graphite, lead oxide, lead sulfate, carbon in various forms, platinum, various metal oxides such as manganese dioxide, copper oxide, nickel oxide and the like, and can be in mny different forms such as gauze, solids, porous, etc. Other electrode materials are less preferred since they corrode rapidly and their ions contaminate the electrolyte, thereby rendering the isolation of the product more expensive and difficult.

The cathodes can also be of any conductive substance such as copper, lead, platinum, palladium, lead oxide, graphite, carbon and the like. It is preferred to employ a employed in the process of this invention. ^ The supporting electrolytes which can be employed to render the solvent medium conducting include the metal per-chlorates, fluoroborates, acetates, hexafluoro phosphate and the like. The only limitation on the enabling electrolyte being employed is that it dissolves in the solvent, that it ionizes in the solvent and that it is not oxidized at the potential of the oxidation of the tetra ester of N-phosphono-methylimino diacetic acid in the specific solvent being employed. Specific examples of such enabling electrolytes are salts such as ammonium hexafluoro phosphate, ammonium fluoroborate and the alkali or alkaline earth metal salts such as sodium, potassium or rubidium hexafluoro phosphate, sodium fluoroborate, tetramethylammonium fluoroborate, tetraethylammonium fluoroborate, tetramethylammonium ethylsulfate, tetraethylammonium ethylsulfate, trimethylammonium luoroborate, tri-meth lammonium hexafluorophosphate , tetramethylammonium toluenesulfonate, tetraethylammonium toluenesulfonate dimethylammoniurn fluoroborate, dieth lammonium perchlorate, tetrapropylammonium perchlorate, lithium perchlorate, tetraethylammonium acetate and the like.

In the process of this invention, a solvent is essential. The solvent must be one in which the tetra ester of N-phosphonomethylimino diacetic acid is soluble and also in which the supporting electrolyte is soluble so that the solution is conductive.

Illustrative of the solvents that can be employed in the process of this invention are nitriles such as aceto-nitrile, propionitrile, benzonitrile, etc.; nitro compounds such as nitromethane, nitroethane, etc; halogenated hydro * , methyl ether and mixtures of the above solvents with each other and with aliphatic alcohols, etc. ^ It is, of course, apparent to those skilled in tlft art that the time of reaction is variable and is determined by variables such as current density, electrode area, concentration and volume of the reaction solution. i The triesters of N-phosphonomethyl glycine product of the process of the present invention are recovered from the reaction solution by conventional techniques known to those skilled in the art, such as by extraction and recrystallization, centrifugation, ' concentration and the like. The triesters can be hydrolyzed with an acid such as dilute hydrochloric acid to yield N-phosphonomethyl glycine vjhich is useful as a herbicide.

I f the es ter groups attached to the di aceti c aci d moiety are di fferent , a mi xture of tri es ters of N- phosphonomethyl glycine are obtai ned, before hydrolys i s . " L_ _ The hydrolysis reaction solution can be vacuum evaporated to eliminate the water, acid, and alcohol by-product.

The solid which remains can be dissolved in water and then cooled to precipitate the N-phosphonomethyl glycine, which is recovered by filtration.

The tetra e:;ters of N-phosphonomethylimino diacetic acid useful in tho process of this invention are those havin the .general formula wherein R, R', R' ' and ' ' are each independently monovalent hydrocarbon radicals containing from 1 to 12 carbon atoms, interconnecting the hydrocarbon moieties.

Illustrative of the monovalent hydrocarbon radicals represented by R, R' , R ' 1 and R ' ' ' are alkyl groups of the^ formula CaH2a + χ such as methyl, ethylpropyl, butylhexyl, octyl, decyl, dodecyl and; their isomers, etc; alkenyl groups of the formula CaH2& wherein a is as previously defined,, such as ethenyl, propenyl, butenyl, octenyl, dodecenyl and; their isomers, etc; aryl groups containing 6 through 10 carbon atoms such as phenyl, tolyl, xylyl, ethylphenyl, diethylphenyl and the like; aralkyl groups such as benzyl, phenylethyl, phenyl-propyl, dimethylphenylpropyl, dimethylphenylbutyl and the like; and the halogenated derivatives thereof containing up to > halogen atoms.

By the term halogen as employed herein is meant_. fluorine, chlorine, bromine and iodine.

Illustrative of the hydrecarbonoxy hydrocarbon groups represented by R, R', R'' and R''' are those of the formula R^- (R2-0)m-R3 wherein R3 is alkylene or alkoxy alkylene of not more than 8 carbon atoms; R2 is all:ylene of not more than four carbon atoms; R1 is selected from he group consisting of alkyl and alkenyl of not more than 6 car' cn atoms ; and m is an integer from 0 to 2. Illustrative of the groups represented by R'O / 2Q7m - R3 - ere alkoxyalk; 1, alkenoxyalkyl, alkoxy- alkoxyalkyl, alkenoxye Γ,-.oxyalkyl, 'ialkoxyalk l', alkenoxy(al- 2,4-diethoxybutyl, 2-methoxy-4-allyl-oxybutyl, l-ethoxy-2-propenoxyethyl, 4- (2-allyloxyethox )-2-methoxybutyl, 2- (4-methoxybutoxy)ethyl, 2- (2-methoxyethox )butyl and the like.

The following example serves to further illustrate the process of this: invention. In the example, all parts are by weight unless otherwise specifically set forth.

EXAMPLE 1 This example was conducted in a glass frit divided electrolytic cell. The anolyte consisted of l.l8g. of the tetraethylester of N-phosphonomethylimino diacetic acid dissolved in fifty milliliters of acetonitrile containing o.2m. ammonium hexafluorophosphate. The catholyte was 0.2m. ~Θ Θ NH4 PF in acetonitrile. The anode was platinum foil, the cathode platinum, and a saturated calomel reference electrode was in the anode compartment.

The electrolysis was conducted at +1.6v vs. saturated calomel electrode. The initial current was 30ma and after 5 hours had dropped to less than 3ma and 0.002 Faradays of electricity had been passed. The anolyte was concentrated °n a rotary evaporator. A portion of the residue was hydrolyzed in 20 hydrochloric acid by refluxing for 1 hour. Nuclear magnetic spectral analysis indicated that the residue was a 2 to 1 mixture of N-phosphonomethylimino diacetic acid and N-phosphonomethyl glycine indicating that a 33 conversion of the tetra ester to triester had been accomplished.

Claims (5)

1. 45990/2 WHAT IS CLAIMED IS: 1 , A process for producing a triester of N-phosphonomethyl glycine which comprises subjecting a solvent solution of a tetra ester of N-phosphonomethylimino d1 acetic add containing a supporting electrolyte to a di rect electric current «hereby said tetra ester is oxidized to the triester, said solvent being one 1n which the tetra ester and the supporting electrolyte is soluble, and wherein said tetra ester has the general formula: wherein R, R' , R" and R' " are each independently monovalent hydrocarbon radicals containing from 1 to 12 carbon atoms, halogenated monovalent hydrocarbon radicals and hydrocarbon oxyhydrocarbon groups containing from 1 to 4 oxygen atoms interconnecting the hydrocarbon moieties . 45990/2

2. A process as claimed 1n Claim 1 wherein the tetra ester is a tetra al kyl ester.

3. A process of Claim 2 wherein the sol vent is acetoni tri le.

4. A process of Cl aim 3 wherein the supporting electrolyte is ammonium hexafl uorophosphate.

5. A process of Claim 3 wherein the tetra ester is tetra ethyl -N-phosphonomethyl imi no di acetate Attorneys for App cant