CA1043341A - Process for preparing pyrrolidone-5,5-diphosphonic acids - Google Patents

Abstract

A B S T R A C T

Pyrrolidone-5,5-diphosphonic acids having the formula wherein R is a member selected from the group consisting of hydrogen and alkyl having from 1 to 6 carbon atoms;
as well as their water-soluble salts. The pyrrolidone-5,5-aiphosphonic acids are excellent sequestering agents especially for alkaline earth metal ions. They are stabi-lizers for percompounds and are useful in the delaying of the setting times for gypsum.
This divisional application is particularly directed to the process of preparing said diphosphonic acids by (1) reacting a compound of the formulae and

Description

104;~
An object of the present invention is the obtaining of a pyrrolidone-5,5-diphosphonic acid derivative selected from the group consisting of (1) compounds of the formula O O
HO \ ~ ¦¦ ~ OH
HO~" C ~ OH

CH2 \ N-R

CH2 C=O

wherein R is a member selected from the group consisting of hydrogen and alkyl having from 1 to 6 carbon atoms, and

(2) water-soluble salts thereof.
Another object of the present invention is the development of a process for the production of the above pyrrolidone-5,5-diphosphonic acids or their water-soluble salts.
Another object of the present invention is the development of a process for the delaying or inhibiting of the precipitation of alkaline earth metal ions from solu-tion by the use of stoichiometric to substoichiometric amounts of the above pyrrolidone-5,5-diphosphonic acias or their water-soluble salts.
These and other objects of the invention will become more apparent as the description thereof proceeds.

~b/~' - 1 - ~

lV4;~341 me above ob~ecta hav~ been achleved by the de~elopment of new pyrrolidone-5,5-diphosphonic acid deri~atives selected from the group conQlstlng of (1) compound~ of the Formula I

O O
HO~ 11 ¦1 ~O}l HO~ \ / --OH
~C
i 2 N-R

C~2 C=O

wherein R is a member selected from the group consisting of hydrogen and alkyl haYin3 from 1 to 6 carbon atoms, pre-fera~ly al~yl having 1 to 4 carbon atoms, and (2) water-soluble salts thereof; as well as a process for the manufæc-ture o~ ~he new compounds and their appllcations.
me production of the new py~rolidone-5,5-diphos-phonic acide or thetr water-soluble salts can occur by the reactlon of a corresponding derivat~ve of succlnic acid with a phosphorus trihalide or phosphorous acid and a phos-pho~s trihalide and 6ubsequent alkaline hydrolys~s of the reaction product. In general, the reactions are conducted at temperatures between 50C and 120C. The ~uitable derlvati~e~ of succinic acld are succinlc acid dinitrlle and succ~nlc acid diamide. In addition, succlnic acid dla~ides ~ay be employed in which one hydrcgen atom in each amide group was replaced by an alkyl haYing from 1 to 6 - carbon atoms.

i~43;~41 ' m e reactlon can be carrled out, for example, in that the above-mentloned succlnic acid derlvatlves are melted with phosphorous acid, and then PC13 18 810wly added whlle stlrrlng. The reactlon product formed 18 subsequently sub~ected to alkaline hydrolysl~. Thls can be done by boil-lng with aqueous solutlons of strong bases, partlcularly ~lth sod~um hydroxide or potassium hydroxide solutlons.
m e above proces~ can also be conducted by ~tarting from succinic acid dinitrlle dissolved in an inert solvent such as dioxane or chlorinated hydrocarbons, and 6ubseq~ently mixed with phosphorus trihalide. m en phosphor-OU5 acid, preferably dissolved in an inert solvent, is added and the reaction product is hydrolyzed as abo~e. In the last mentioned method, the phosphorous acid can also be omitted, 1~ desired, and a correspondingly larger amount of phosphorus trihalide employed.
More particularly, the above' process for the pro-duction o~ the new pyrro~done-5,5-diphosphonic acid deriva-- ti~es Or Formula I consists es6entially o~ the steps of reacting a derivative of succinic acid of the formula X - CH2 - C~I2 - X
wherein X ~8 a member selected from the group con~isting o~ -CN, -CONH2 and -CONHR',where R'~is alkyl having 1 to 6 carbon ato~s, w~th at least the stoichiometric a~ount of a phosphorus reactant selected from the group consisting of a phosphorus trihalide and a mixture of a phosphorus trihalide and phosphorous acld, subJectlng the resultlng reactlon product to an alkalinc hydrolysis by the aetion o~ an aaueous s~rong mlneral base, and recovering said pyrrolldone-5,5-dlphosphon~c acid derlvatlve.

109~34~
me new pyrrolidone-5,5-dlpho3phonlc ac~d deri~a-tlves of Formula I can also be produced by reactlng a succinlc acld monoamide or succlnlmide ln the above described manner ~ith phosphorus trihalides or phosphorous acld and phosphorus trlhalldes, and the reaction product iB subsequently hydro-~yzed. }n this case, it ls not necessary to use an alkallne hydrolysis. me hydrolysis can be effected by adding water ~ith sim~ltaneous heating.
~ ore particularly the above process for the pro-ductlon of the new pyrrolidone-5,5-diphosphonic acld deriva-tives of Formula I consists essentially of the steps of react ng a derivative of succinic acid selected from the group consisting of a compound of the formula O.
HOOC - CH2 - CH2 - C - ~

~nd a compound of the formula -- e . ~ C~
- ¦ N - R
, CH2 C
., O

whereln R i8 a member selected from the group consistlng of - hydrogen and alkyl havin~ 1 to 6 carbon atoms, with at least the ~toichio~etric amount of a phosphorus reactant selected from the gr~up consisting of a phosphorus trihalide and a mixture of a phosphorus trihalide and phosphorous acid, sub~ecting the resulting reaction product to an aqueous hydrolysls at an elevated temperature, and recoverlng sald pyrrolldone-5,5-dlphosphonic acid deri~ative.

1~ 4 ~ 3 ~1 In the above reactiona the phosphorus trlhalides ~hic~ can be u~ed are particularly phosphoru~ trichlorlde snd phosphorus tr~bro~ide. The latter was found to be partlcularly sui~able, if the nitriles are employed 8B the starting material.
The molar quantitatlve ratio of the succlnic acid derl~atives to the phosphorus reactant is 1:2 to 1:6. I~
succinic acld din~trile or succinlc acid dlamldes are used, a ratio of 1:4 is pre~erably utilized.
lG As far as the pyrrolidone-5,5-diphosphonlc acids are obtained after an alkaline hydrolysis, they are obtained in the form of the correspondlng alkall metal salts. They can be converted, if desired, açcordlng to known methods into the correspondlng free aci~s, for example, by means of cation-- e~chaneers. For the uses described below, however, the new pyrrolidone-5,5-dipho~phonic acid deri~atives can be also used in the form of their water-soluble salts, particularly the alkali metal salts, such as the potassium and sodium salts, and ammonium salts. Insofar as the pyrrolldone-5,5-diphosphonic acid derivatives are obtained directly in the ~orm of the acids, they can be easily con~erted into the water-so~uble salts, for example, by par'ial or complete neutralization with correspondin~ bases.
The salts correspond to the following Formula Ia O O
XO ~ 11 11 ~OX
X0 ~ \ / ~ OX (Ia~
C

C~2 cso 1S14~3~1 where X denotes hydrogen, NH4 or a metal cation, such as an alkali metal, but where at most three hydrogen atoms are present, R = hydrogen or alkyl with 1 to 6, preferably 1 to 4 carbon atoms.
Finally it was found that the pyrrolidone-5,5-di-phosphonic acid derivatives of the Formula I can also be produced by alkaline hydrolyzation of the phosphonic acids of the Formula II

R-N P-OH
l ¦ N~R
O=C \ / p ~ (II) (CH2)2 ~ OH

wherein R is hydrogen or alkyl having 1 to 6 carbon atoms.
By following this method the new pyrrolidone-5,5-diphosphonic acid derivatives of Formula I are obtained in particularly ~ood yields. The salts obtained can then be converted, if esired, in known manner into the corresponding acids, for -4xample, by means of cation-exchangers.
The production of the compounds of Formula II can be effected by reacting dicarboxylic acid derivatives of the formula X ~CH2)2 X

where X = CN, CONH2 or CONHR ~R - alkyl radical with 1 to 6 carbon atoms), with phosphorus trihalides and subsequent ~ydrolyzation of the reaction product, as described in our copending Canadian Patent Application Serial No. 207,800, filed August 26, 1974 jb~' - 6 -- lV43341 It ~as analytlcally determined that the products ~rom al~ the above-described production methods correspond to the cyclic Formula I and that possible products of the open-chalned structure o~ Formula II~

HOOC - CH2 - CH2 - I - N~ - R (III) po ~ 2 ~here R denotes hydrogen or alkyl with 1 to 6 carbon atoms, appear only in insignificant amounts.
me new pyrrolidone-5,5-diphosphonic acid deriva-tives are excellent sequestering agents for poly~alent metal ~ons, partlcularly dl- and tri-valent metal lons. m ey are partlcularly suitable as sequestering agents for alkaline earth metal ion~, 80 that they can be used for many technical spplications, such as detergents and cleansers, a~ ~Jell as in water treatment. They can be employed in stoichiometric and ~ubstoichiometric amount~ as sequestering agents for alkallne earth metal ions. m ey al~o haYe a stab~lizing effect on percompounds.
They are also suitable a~ additiYes to delay the setting of gypsum and as ceramic 81ip liquefiers. For delay-ing the setting of gypsum, the potassium, sodium or ammoniumsalts, in addition to the-acids, can also ~e used. The corre~ponding lithium salts as well as zinc and magneQium aalts are li~cwi8e sultable.

433~1 Ihe followlng examples are lllu~tratlve of the ~rsctice of the in~ention wlthout belng limltati~e thereof ~n any respect.

Pyrrolidone~ diphosphonic acid O O
HO~ 11 Il, ON
HO ~ OH
~ C

CH2 C=0 (a) 24.4 gm of 2-hydroxy-2-oxo-3-amlno-3-pho~phonyl-6-oxo-l-aza-2-pho~phacyclohexane (see For~ula II) (0.12 mol) were heated with 400 ml of 2N sodium hydroxide solution to the boi}ing point for a period of time until no ~urther ammonia escapes with the steam. The solutlon was then con-centrated to 100 ml znd ~ixed with 300 ml of ethanol. me precipitation of the sodiu~ salt of the pyrrolldone-5,5-diphosphonic ac~d was completed with acetone and ethyl acetate. The oily substance was separated, dissolved ~ain ln H20 and pa~sed through a cation exchanger in the hydrogen cycle. The solutlon obtained was concentrated to 100 ml, and the pyrrolidone-5,5-dipho~phonic acld was precipitated w~th 300 ml of ethanol, 200 ml of acetone, snd 200 ml of ethyl acetate. Yield 14.3 gm = 63% of the theory.
(b) 58.5 gm of ~uccinic acid monoamide (0.5 mol) and 41 gm o~ H3P03 (0.5 mol) were melted at 70C and mixed 810wly wlth stirrin~ with 43.8 ml Or PC13 (0.5 mol). A~ter 3 hours at 70C the product was hydrolyzed with 200 ml of H20 and 49334~
bolled with actlvated carbon. me hot solution was filtered and the wrrolidone-5,5-dipho~phonic acld Wa8 preclpltated ~rom the filtrate wlth 400 ml Or ethanol and 400 ml of acetone. Crude yield 5.0 gm ~ 3.8% of the theory.
(c) 49.5 gm Or succinlmide (0.5 mol) and 41 gm of H3P03 (0.5 mol) were heated to 70C. To the homogeneous melt, 43.8 ml of PC13 (0.5 mol) were added slowly in drops. me reactlon product was held for 4 hour6 at 70C and then hydro-lyzed with 200 ml of H20 as (b) above. The pyrrolidone-5,5-diphosphonic acid was precipitated from the filtrate with300 ml of ~hanol and 300 ml of acetone. Crude yield 4.6 gm -

3.5% of the theory.
(d) 4 gm of succinic acid din~trile (0.5 mol) were dissolved in 400 ml of dioxane and 190 ml o~ PBr3 were added slowly in drop~. After stirring for another 4 hours at 70C
the viscous yellow mass was hydroly~ed with 300 ml o~ Nater.
A~ter filtration with activated carbon, the dloxane wss separated.
me aqueous phase was mixed with 500 ml of 6N NaOH
and heated until no further ammonla escaped. By adding an ethanol/acetone mixture, the sodium salt of pyrrolidone-5,5-dlphosphonic acid was precipitated.
- me free pyrrolidone-5,5-diphosphonic acid accordlne to (a) to (c) was obtained after drying at 50C as a mono-hydrate with a titrimetricslly determined molecular wel~ht of 265 (calc. 263.1). On drying at 80C in a vacuum oven, the anhydrous compound was obtained with a moleculsr weight o~ 247 (calc. 245.07).
Analy~ls:
Calculated: 19.60% C 3.70% H 5.71~ N 25.28~ P
Found: 19.34 3.61 5.66 25.24 1~ 4 ~ 3 ~1 In the IR-spectrum the compound showed a ~trong ~CO band at 1610 cm~l, M.P. 250C wlth decomposltion.

- -methyi-p-yrrolidone-5,5-dlphosphonlc acid O O
HO~II 11 O~I
HO ~ \ / ~ OH
C~
1 2 1_CH3 CH2 C=O

(a) 64.4 gm o~ 1-methyl-2-hydroxy-2-oxo-3-methylamino-3-phosphonyl-6-oxo-1-aza-2-phospha-cyclohe~ane (0.237 mol) were heated with 800 ml of a 2N KOH æolution to the boiling point for a period of time untll no further methylamine passss over with steam. After filtration, the potassium salt of N-methyl-pyrrolidone-5,5-diphoæphonic acid was separated from the alkaline solution by preclpitation with ethanol and acetone. The potassium salt was again dlssolved in H20 and passed through a cation exchanger ln the hydrogen cycle.
The N-methyi-pyrrolidone-5,5-diphosphonic acid was isolated from the concentrated solution with ethanol and acetone.
Yleld 16.4 gm (27~ of the theory) (b) 28.5 ~m of succlnic acld monomethylamide (0.216 mol) were melted with 35.4 gm of H3P03 (0.432 mol) at 70C and then 610wly mlxed with 37.8 ml of PC13 (0.432 mol). After an addltional 5 hours at 70C, the product was hydrolyzed with 300 ml of H20. Flltratlon with actlvated carbon at the bolling point yielded a clear solution fro~ whlch the N-methyl-pyrrolidone-5,5-dlphosphonlc acid was precipitated with ethanol and acetone. Crude yield 4.2 ~m ~7% of the theory).

_ 10 --4733~
The N-methyl-pyrrolldone-5,5-diphosphonlc acld was obtainea after drylng at 50C as a monohydrate with a molecular weight of 279 (calc. 277.1). A M er drylng at ~0C ln the vacuum oven, the anhydrous compound wa~ obtalned with a molecular welght of 259 (calc. 259.1).
Analysis:
Calculated: 23.18~ C 4.28% H 5.41~ N 23.91% P
Found: 22.90 4.16 5.45 23.12 m e compound shows in the IR-spectrum a strong ~ CO
band at 1650 cm~l, M.P. above 270C with decompositlon.

N-ethyl-pyrrolidone-5,5-diphosDhonic acid O O
HO ll tl ~OH
HO~ \ / ~ OH
C

- C~I2 C=O

(a) 88.5 gm of 1-ethyl-2-hydroxy-2-oxo-3-ethylamino-3-pho~phonyi-6-oxo-1-aza-2-phospha-cyclohexane (0.295 mol) ~ere boiled with 147.5 gm of a 40% NaOH solution (1.475 mol) ~or a length of ti~e untll no further ethylamine escaped.
Then the product was ~lltered with activated carbon and the sodium ~alt of N-ethyl-pyrrolidone-5~5-diphosphonic acid was precipitated with ethanol and acetone. The oily ~ubstance was again dlssolved ln H20 and passed through 8 cation ex-~hanger in the hydrogen cycle, and the N-ethyl-pyrrolidone-5,5-dlphosphonic acld w~8 lsolated fro~ the extract with - ethanol and scetone. Yield 7~ gm (90~ o~ the theory).

1~,334~
(b) 43 gm Or succlnic acld bl~ethylamide (0.25 mol) were melted with 82 gm Or H3P03 (1.0 mol) at 70C. To the ~lt, 88 ml of PC13 (1.0 mol) were 810wly added in drop~ and the mixture was leît standing for 5 hours at 70C. Then the mixture was hydrolyzed with 250 ml of H20 and filtered with activated carbon. The riltrate was mixed with 0.5 liter o~ 6N NaO}I solution and heated so long until no further ethylamine passed over. The sodium salt oi N-ethyl-pyrrolidone-5,5-diphosphonic acid was preclpitated with ethanol/acetone, 10 dlQsolved again ln H20 and passed through a cation exchanger in the hydrogen cycle. The N-ethyl-pyrrolidone-5,5-diphos-phonic acid was precipltated from the extract with ethanol and acetone. Yield 16.5 gm (22,~ of the theory). After drying at 50C, the substance was obtained as a monohydrate with a molecular weight of 292 (calc. 291.1).
Analysis:
Calculated: 24.75~ C 5.19% H 21.28% P
F~und: 24.79 5.o6 21.08 After drying in the vacuum oven at 80C, the anhy-20 drous compound was obtained with a molecular weight of 276 (calc. 273.1).
In the IR-spectrum the substance sho-~s a strong ~) C~) band at 1640 cm~l, M.P. 250C.

1'~4~34~

N-butyl-pyrrolldone-5,5-dlphosphonlc ac~d - O O
HO~ 11 ~ OH
HO~ \ / ~ OH
C~
1 2 N-C4Hg CH2 C=O

40 gm of 1-butyl-2-hydroxy-2-oxo-3-butylamino-3-phosphonyl-6-oxo-l-aza-2-pho6pha-cyclohexane (0.112 mol) were boiled with 400 ml of 2N NaOH solutlon for a length of tlme until no further butylamine escaped. Then the mixture was flltered with activated carbon and the sodium 6alt of N-butyl-pyrrolidone-5,5-diphosphonic acld was lsolated with ethanol/
acetone. The oily substa~ce was dissolved ln water and passed through a cation exchanger in the hydrogen cycle.
The N-butyl-pyrrolidone-5,5-diphosphonic acid was isolated rrom the concentrated extract with ethanol and acetone.
Yleld 23 gm (58$ of the theory).
A~ter drying at 50C, the compound was obtained as a monohydrate.
The molecular weight was determined titrimetrically as 321 (calc. 319.2).
Analysis:
Calculated: 30.10~ C 6.oo% H 4.39% N 19.41% P
Found: 30.02 5.66 4.27 18.64 A~ter drying at 80C ln a vacuum oven, the anhydrous compound was obtained with a molecular wei~ht o~ 303 (cQlc.
301.2) The co~pound shbws ln the IR-spectrum a strong J CO
band at 1660 cm~l, M.P. over 240C with decompo~ition.

`` 1~4~339t1 - ' PreDaration of Salts (a) 25.9 gm o~ N-methyl-pyrrolldone-5,5-diphosphon~c acid were dissolved ln 100 ml of water and mixed with 100 ml of a 4N llthium hydroxide solutlon. On addition o~ 300 ml o~ ethanol, the tetra-lithium salt oi N-methyl-pyrrolidone-5,5-diphosphonic acid was precipitated.
(b) 27.31 gm of N-ethyl-pyrrolidone-5,5-dipho~phonic acid were dissol~ed in 100 ml of water and mixed w~th 100 ml o~ a 2N NH40H solution. On addition of 300 ml of ethanol, the di-ammonium salt of N-ethyl-pyrrolidone-5,5-diphosphonic acid was precipitated.
(c) 24.5 gm of pyrrolidone-5,5-diphosphonic acid (p.l mol) were dissolved in 100 ml of water. To this solution, a solution of 13.6 gm of ZnC12 (0.1 mol) dissol~ed in 50 ml o~ water was added. The precipitation of the zinc salt of pyrrolldone-5,5-diphosphonic acld was completed by the addi-tlon of 300 ml of ethanol.
(d) The magnesium salt of pyrrolidone-5,5-diphosphonic acid was obtained by replacing the ZnC12 by 9.4 gm of MgC12 (0.1 mol) using the same procedure as described under (c) Sequestration of calcium In the ln~estigation of the sequestration o~ calcium, a modlfled Hampshire test was employed and worked as follows:
1 gm of the se~uestering agent was disæolved in 50 ml o~ H20, ad~usted with NaOH to a pH of 11. ~0 ml of a Ca++ ~olutlon (1470 mg o~ CaC12 2H20/1! were mixed wlth 100 ml o~ a sodium carbonate solution (7.15 gm NaC03 10H20/1).
men the solution o~ the sequester~n~ a~ent was added ln drop~

1~4~334~
~rom a burette until the calclum carbonate preclpitate was redlssol~ed. The values formed have been reported ln Table I.
For the sake Or simpllclty, only the value for the varlous substltuents for R accordlng to Formu~a I are indlcated ln the leit column o~ the Table.
T A B ~ E

O O
HO ~ 11 11 ~OH
HO~ \ / ~OH
C

CH? C=O

R ~ H or alkyl having 1 to 6 carbon atoms.
.
Consumption of Compound Se~uestering mg caco~ sequ~s-Agent Solution tered p~r gm of R (ml) Compound .
H 2.9 8~5 CH3 2.6 960 C ~ 5 2.5 lO00 C4Hg 2.9 865 Practlcally ldentical results were obtained if, lnstead Or the acids, the corresponding sodium, potasslum or ammonium sa;ts were employed.

1~4334~

Threshold Effect me prevention of the prec1pitatlon Or poorly ~oluble calclum compounds by ~ubstolchlometric amounts of a sequesterlng agent was determined with the HQmpshlre test at room temperature. m e procedure was as follows:
50 mg of the sequeQtering ~gent were dlssolved ln 10 ~1 of X20 (standardized wlth NaOH to pH 11) and mixed wlth 100 ml of a sodium carbonate solution (14.3 gm of NaC03 lOH20/1). Then sufficlent o~ a calclum solution (36.8 gm of CaCl~ 2H20/1) was added in drops from a burette untll a permanent cloudiness was ~ust formed. Table II reports the results of these tests. For an explanatlon of the data in the left-hand column of the Table, see Example 6.

T A B ~ E I I

Consumptlon mg CaCo3 Substance of Ca Sequestered Solution per gm of R (ml) Mg CaCo3 Compound H 2.1 52.5 1050 CH3 2.8 70.0 1400 C2X5 3-3 82.5 1650 C4~9 2.2 55.0 lloo Practically ldentlcal results are obtalned lf, ~nstead of the aclds, the correspondlng sodlum, potas~ium or ammonium ~alts were employed.

~ ~ ~43341 E~AMPLE ~
Delay of settlng of Gyp~um ~ ypsum materials ln the form of plaster, pla~ter of Paris, or in ~ixture wlth aggrPgates, llke limRstone, sand, perllte or celluloe, set relati~ely fast, so that rapid proce~sing must take place. A delay o~ the ~ettlng time can -be achieved w~th the additlon of the aboYe-descrlbed phos-phonic aclds, and the processing o~ the gypsùm materials can thus be considerably facilitated.
In the following tests, each of the ~arious phosphon-ic acids o~ the invention was added to the water before the gypsum was mlxed. Howe~er, water-soluble salts of the phosphonic acids, partlcularly the lithlum, sodlum, potassium ana ammonium salts can also be mixed lnstead with the gypsum or added shortly after the m~xing of the gypsum material together with the water. Specifically the following 6etting ~alues were found and reported in Table II~, uslng ln each test 20.0 gm of gypsum and 9 ml Or H20. me setting time ls - the time interYal in which the gypsum was spreadable and easy to handle.
For the explanation of the data ~n the left colu~n of Table III, see Example 6.

1~4339~1 T A B L E I I I
. ~ _ Substance AmountSettlng Time R (mg) (mln.) . _ - 15 C4H9 45 llo Comparable results are obtained by using the corresponding magnesium and zinc salts.
, me preceding specific embodiments are lllustrative o~ the pract$ce of the inventlon. It is to be understood, houever, that other expedlents ~nown to those skilled in the art or d$scussed herein ma7 be employed uithout departing from the spirit of the inYention or the scope of the appended clal~s.
This application is a division of copending Canadian application Serial No. 207,803, filed August 26, 1974.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of a pyrrolidone-5,5-diphosphonic acid derivative selected from the group consisting of compounds of the formula wherein R is a member selected from the group consisting of hydrogen and alkyl having from 1 to 6 carbon atoms, and (2) water-soluble salts thereof, which consists essentially of the steps of reacting a derivative of succinic acid selected from the group consisting of compounds of the formulae and wherein R is as defined above,with at least the stoichiometric amount of a phosphorus reactant selected from the group consisting of a phosphorus trihalide and a mixture of a phos-phorus trihalide and phosphorous acid, subjecting the resulting reaction product to an agueous hydrolysis at an elevated temp-erature, and recovering said pyrrolidone-5,5-diphosphonic acid derivative.