WO1995014701A1

WO1995014701A1 - Ethylenically unsaturated compounds

Info

Publication number: WO1995014701A1
Application number: PCT/GB1994/002570
Authority: WO
Inventors: Michael John Driver; Stephen Harold Foster
Original assignee: Biocompatibles Limited
Priority date: 1993-11-23
Filing date: 1994-11-23
Publication date: 1995-06-01
Also published as: AU1073295A

Abstract

An improved process for producing ethylenically unsaturated zwitterionic phosphate ester compounds involves a two-step reaction, in the first of which an ethylenically unsaturated compound including a hydroxyl group is reacted with a halophospholane compound to form an intermediate which is subsequently ring opened in a second step using a trialkylamine to produce a zwitterionic product. The solvents used for the first and second steps are different to one another and the first solvent is removed from the product mixture of the first stage using a thin film evaporator with the intermediate being dissolved directly into the second solvent, thereby minimising side reactions. The product has improved purity compared to that made by known processes, which makes it particularly suitable for use in polymers, especially cross-linked hydrogel copolymers, used in ophthalmic applications.

Description

ETHYLENICALLY UNSATURATED COMPOUNDS The present invention relates to an improved process for producing ethylenically unsaturated phosphate ester compounds. The process is suitable as part of a process for producing polymerisable monomers for use in the production of polymers which mimic cell surfaces.In particular the process involves a two-stage reaction, the successive stages being conducted in the presence of different organic solvents. The present invention provides improved products which can be used to form clear polymer products, of particular use for ophthalmological applications, in the manufacture of contact lenses, for example.

The first published route (J.P. Appl. No. 60-21599, Kobunshi Runbunshu 1978, 35, 7, 423) to 2- (methacryloyloxyethyl) -2 '- (trimethylammoniumethyl) phosphate, inner salt (Hema-PC) is illustrated in Scheme I.

Scheme I

(1) (2)

26% H₂0, Et₃N

(4) (3)

28% Ag₂CO-_j

(5)

The bromoethyldichlorophosphate (1) , obtained from bromoethanol and phosphorus oxychloride, was treated with 2-hydroxyethylmethacrylate to give the phosphate diester chloride (2) . Hydrolysis gave the acid analogue (3) which, on reaction with trimethylamine in methanol, gave the phosphorylcholine derivative (4) . Conversion to the hydroxide salt (5) was effected using methanolic silver carbonate. The product (5) was isolated using column chro atography on silica-gel and the overall yield was under 5%.

In addition to the low overall yield, purification by column chromatography is inconvenient and expensive, particularly on a larger scale, and the product from this process was isolated in a hydrated form which may not be appropriate for some applications of the product or indeed, for the facile isolation of the product, a point subsequently accepted by the authors (Polymer Journal 1990, 22, 5, 355).

Synthetic processes for producing phosphoryl choline containing lipids, by a two step reaction, in the first step of which a hydroxyl substituted starting material is reacted with a halophospholane choline, followed by a ring opening reaction with a trialkylamine has been described by Chabrier and colleagues in FR-A-2,270,887 and Bui. Soc. Chim. de France (1974) 667-671. The first step is carried out in an organic solvent selected from benzene, ether and tetrahydrofuran. The second step is carried out in an aprotic solvent selected from acetone and acetonitrile. Dong & Butcher in Tetrahedron Letters (1991) 32, 5291-5294 also used the reaction of a hydroxyl group containing compound with a halophospholane, followed by ring opening using trimethylamine to make a synthetic sphingomyelin. The former step was carried out in benzene, with the latter step being carried out in a mixed solvent of benzene and acetonitrile.

An analogous two stage reaction has also been described for producing HEMA-PC, by Nakaya et al, as depicted in scheme 2. The process is described in JP-A-58- 154591, 1983 and Makromol. Chem. , Rapid Commun. , 1982, 3, 457) , and involves coupling of 2-hydroxyethylmethacrylate to the chlorophospholane (6) to give intermediate (7) which was trimethylaminated under pressure to give the diester (8).

Scheme 2

V -o„ . 0,o -o_cι _Et±-,N→ Λ.,-^ _ΛSo.

o °

(6) (7)

Me,N MeCN

(8) HEMA-PC For the first stage of the reaction the authors describe the use of etheral solvents such as diethylether and tetrahydrofuran. Triethylamine hydrochloride, a byproduct of the reaction, precipitated from these solvents and was removed by filtration to give a solution of the phospholane (7) . The solvent was then removed by distillation and the residual material dissolved in acetonitrile and heated with trimethylamine to give the product (8) after concentration. Precipitation of chloroform solution of (8) from acetone was the described means of purification. The basic chemical process is used in our earlier publication WO-A-92-07885.

We have now found that the product (8) , prepared and purified in this way, may not be of the desired purity for certain applications, such as the production of co-polymers intended for fabricating or coating medical devices, for example. In particular, it may not be suitable for use in ophthalmological applications, in the manufacture of contact lenses, for example. The presence of residual reagents or byproducts may have adverse toxicological implications, for example, and the presence of insoluble impurities may have adverse effects on the properties of ophthalmic devices, for example, their light transmission or expansion properties. We have discovered that side- products are formed during the preparation and isolation of the Hema-phospholane derivative (7) as a result of the labile nature of the compound itself and because of the presence of impurities in the chlorophospholane (6) which are not easily discerned. We have also found that the process sometimes fails to give any appreciable amount of product (8) during scaled-up experiments. Furthermore in the process described, in the final step of the reaction a 5-fold excess of trimethylamine is used, hence requiring the use of a pressurised reactor system. It would be desirable to avoid the necessity for the use of such a system. We have now devised a new process to overcome these problems. A new process according to the present invention comprises: i) a first stage in which an ethylenically unsaturated compound of the formula I

Y-B-OH I wherein B is a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain,

Y is an ethylenically unsaturated polymerisable group selected from

wherein: R is hydrogen or a 0,-0₄ alkyl group;

A is -0- or -NR - wherein R is hydrogen or a 0,-0₄ alkyl group or R¹ is a -B-OH where B is as defined above.

K is a group -(CH₂)_p0C(0C)-, -(CH₂)_pC(0)0-, -(CH₂) 00(0)0-, -(CH₂) NR²-, -(CH₂) NRC(0)-, -(CH₂)_pC(0)NR²-, (CH₂)_pNR²C(0))-, -(CH₂)_pOC(0)NR²-, -(CH₂)_pNR²C(0)NR²- (in which the groups R² are the same or different), -(CH₂)_pO-, -(CH₂)_pS0₃-, or a valence bond, and p is from 1 to 12 and R 2 i.s hydrogen or a 0,-0₄ ^alkyl group is reacted with a phospholane reagent II

(R³)₂C-O > (R 4)₂CI-0/^P Hal, in which each R is the same or different and is H or C 1-4 alkyl, each R 4 i1s the same or di.fferent and is H or C 1-4 alkyl,

Hal is halogen atom, to form a diester product compound of the formula III and hydrogen halide by-product

in which Y, B R 3 and R4 are as defi.ned previously, the reaction being carried out in the presence of a first solvent in which the ethylenically unsaturated reagent and the phospholane reagent are soluble, the hydrogen halide by-product is removed from the product mixture and at least a portion of the first solvent is then removed from diester product III, and ii) a second stage in which the diester compound III is reacted in the presence of a second solvent which is different to the first solvent, characterised in that the first solvent is removed from the diester in a thin film evaporator in which the solvent is evaporated and the diester maintained and collected as a liquid which is diluted immediately upon collection in said second solvent. Preferred ethylenically unsaturated compounds are those of general formula IA or IB. CH₂=

where R, A, B and K are as defined with reference to formula (I) . Compounds IA are preferred.

Preferably R is hydrogen, methyl, or ethyl, more preferably methyl, so that the monomer of formula IA is an acrylic acid, methacrylic acid or ethacrylic acid derivative.

In the compounds of formula IB K may be a valence bond and B a group, K may be a group and B a valence bond, both K and B may be groups or K and B may together be a valence bond. Preferably B is a group where K is a valence bond. Where K is a group then preferably p is from 1 to 6, more preferably 1, 2 or 3 and most preferably p is 1. When K is a group -(CH₂)pNR²-, -(CH₂)pNR²C(0)-, -(CH₂)pC(0)NR²-, -(CH₂)pNRC(0)0-, -(CH₂)pOCNR²-, or -(CH₂)pNR²C(0)NR²- then R² is preferably hydrogen, methyl or ethyl, more preferably hydrogen.

Preferably B is: an alkylene group of formula -(C ₂)a-, wherein the groups -(CR₂)- are the same or different, and in each group -(CR₂)- the groups R are the same or different and each group R is hydrogen or C,._A alkyl, preferably hydrogen, and a is from 1 to 12, preferably 1 to 6; an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably -CH₂0(CH₂)₄-; an oligo-oxaalkylene group of formula -[ (cr⁴ ₂)bO]c(CR ₂)b- where the groups -(CR*₂)- are the same or different and i .n each group -(CR4₂)- the groups R4 are the same or di .fferent and each group R4 i.s hydrogen or C,^ alkyl, preferably hydrogen, and b is 2 or 3 and c is from 2 to 11, preferably 2 to 5; or a valence bond but only if Y contains a terminal carbon atom.

Preferred groups B include a valence bond and alkylene, oxaalkylene and oligo-oxaalkylene groups of up to 12 carbon atoms.

In the process of the present invention the hydrogen halide by-product of the first stage is preferably removed by reaction with an organic base, usually a trialkylamine, to form a hydrogen halide salt of the base which precipitates out of the product mixture as it is formed. The hydrogen halide salt may be removed, for instance, by filtration.

In the process the first solvent is an ether, a nitrile or an ester. Preferably it is an ester, for instance a lower alkyl ester of a C,.₆-carboxylic acid, preferably lower alkyl acetate, most preferably ethyl acetate.

In the process of the present invention it is preferred for at least 80% of the first solvent to be removed in the thin film evaporator. It may be unnecessary to remove all trace of the first solvent, although preferably at least 90% of the solvent is removed, more preferably at least 95%. In general it is preferred for a high proportion of the solvent to be removed, since it may well interfere with, for instance slow down, the second stage of the reaction.

In the present process the solvent used in the second stage, that is the said second solvent, is preferably a nitrile derivative of a C,.₆-carboxylic acid. The most readily available solvent is acetonitrile.

In the process of the present invention the use of the ester solvent in the first stage provides improvements over the prior art utilising the ethereal solvents for that stage for a number of reasons. Firstly, diethyl ether and tetrahydrofuran, two examples of ethereal solvents described in the prior art, are known to form peroxides which, in addition to being potentially explosive, may also promote the hydroperoxidation of the diester intermediate or of the final product. Both those materials may become unstable (for instance may prematurely polymerise) and/or may increase the rate of reaction during copolymerisations, for instance by acting as initiators. Furthermore the esters tend to be less hazardous to use and cheaper than the ethereal solvents. Peroxide formation in ethyl acetate, does not take place, so that the intermediate diester is relatively stable. In the process of the present invention, in the phospholane reagent II, R and R are preferably each hydrogen. Preferably the halogen atom in compound II is chlorine although other halides may be used. Where the hydrogen halide by-product is removed by reaction with a trialkylamine, that compound is preferably triethylamine.

The preferred phospholane starting material is a commercially available compound. We have discovered that the purity of the compound is of great significance to the process as a whole. If impure phospholane is used, the intermediate diester compound may be unstable, and may prematurely polymerise or, in some instances, may be coloured and thus unsuitable for ophthalmological end uses, or may result in an end product having an unpredictable rate of polymerisation. We believe that impurities in the phospholane starting material which may adversely affect the reaction may be due to contact of the compound with moisture, for instance during storage. The inventors have found that the P nuclear magnetic resonance spectrophotometry is the most appropriate method of analysis for this material, since this can identify polyphosphate species which may result from moisture contact. In the course of their investigations, the present inventors have found that the intermediate product of the formula III reacts rapidly (in less than 10 minutes) with water at room temperature to form a number of products. Where the group Y B is the residue of a 2-hydroxyethyl methacrylate compound, the by-products of this side reaction include 2-hydroxyethyl methacrylate and the ring opened hydroxyethyl phosphate diester. This compound, it is believed, may result in unwanted polymerisation being initiated, for instance via the phospholane ring of the compound of the formula III.

In the process the side reactions such as those described above are minimised by utilising as a starting material a phospholane reagent of the formula II having a purity by ¹P NMR of at least 90%, more preferably at least

95%, for instance at least 99%. By this we mean that the

P NMR trace consists primarily of a single peak, and has only low or insignificant amounts of material with peaks at higher and lower ppm values. In order to minimise the possibility of moisture contact with the phospholane reagent of the formula II or the diester intermediate of the formula III, the moisture content of the two solvents must be kept to minimum. The water content of the first solvent, for instance should preferably be less than 0.1% by weight, more preferably less than 0.05% by weight, and most preferably less than 0.01% by weight. Likewise the water content of the second solvent should be within the same ranges.

The present inventors have further determined that the diester intermediate of the formula III is thermally unstable. Using the conventional process of recovering the intermediate III from the first solvent, that is by rotary evaporator, the intermediate sometimes undergoes a "run away" reaction leading to complete gelation (by polymerisation of the ethylenically unsaturated groups) and total loss of the final product. This is a particular problem when the reaction is scaled from laboratory to pilot plant scale. Even partial gelation results in insoluble impurities, which are difficult to remove and which contaminate the product leading to non-homogeneous products. These of a thin film evaporator minimises or avoids these problems altogether, since the time that the intermediate diester III is a concentrated form and is exposed to heat is minimised.

The temperature during the thin film evaporator step is preferably around 20-50°C, more preferably in the range 35-45°C. The typical time for a sample of the product mixture of the first stage in the thin film evaporator chamber is less than 1 minute, preferably less than 30 seconds for instance in the range 10-15 seconds. Preferably the diluent second solvent into which the intermediate III is collected is cooled, for instance to below 20°C, preferably to around 0°C.

The process of the present invention is of particular value where the second stage of the process comprises the ring opening amination reaction in which the compound of the formula III is reacted with a trialkylamine in the said solvent to form a compound of the formula IV

O R³ R⁴ Y-B-O-P II-O-CI- CI-N(R ), IV

0 I_ R ι₃ u ⁺ in which each group R is a C,.₂₄ alkyl group and Y, B, R

4 , and R are each as defined above. The groups R may be the same or different and may be ^cι-₂₄~' Preferably C,.,₂-alkyl, more preferably at least two of the groups R being methyl.

The compound IV is a polymerisable compound, that is the ethylenically unsaturated group is capable of undergoing radical initiated addition polymerisation, usually in the presence of ethylenically unsaturated copolymerisable comonomers.

In the second stage of the process, the trialkylamine, which is preferably trimethylamine, is generally used in an excess. It is unnecessary to use an excess of greater than 3 or 2-fold and, where the amine is gaseous, lower amounts are preferred to avoid the necessity of employing pressurised reactor systems. Approximately 1.5-fold excess, that is 1.5 times the stoichiometric amount for reaction with the actual or theoretical amount of compound III is found to be convenient.

The zwitterionic product of the formula IV is generally recovered from the final product mixture as a solid. The present inventors have discovered that the second stage of the reaction tends to take a place at a rate such that the crystals of the zwitterionic products which are formed are very small. This leads to difficulties in separating them from the product mixture, in particular where the separation involves a filtration step. During a filtration step it is difficult for the filter cake of product to be protected from contact with air and moisture, which could otherwise become absorbed into the product to contaminate it and, possibly, to cause side reactions. The inventors have discovered that these difficulties may be minimised by subjecting the product mixture of the second stage to a special recovery procedure.

In the recovery procedure, it is preferred for the product mixture to be heated to (or maintained at) a temperature at which all of the product zwitterionic compounds of the formula IV is in solution in the second solvent, and then to cool, preferably in a sealed vessel, or in a vessel which has been purged with inert gas, for a period of at least one hour, and preferably 2-16 hours, to reach ambient temperature and subsequently cooled further to a temperature in the range -20 to -5°C, preferably around -5°C, at which it is stored for a period of at least 1 hour, for instance in the range 1-24 hours, for instance around 16 hours. The rate of cooling from the temperature at which the zwitterionic product is fully dissolved, which is for instance above 60°C, for instance 70-80°C, to the final low temperature, is preferably on average at least 10°C per hour, more preferably at least 15°C per hour. Subsequently the solid is recovered from the product suspension by filtration, preferably after the mixture is allowed to warm to ambient temperature.

It is preferred for the filtration of the final product to be conducted in an inert atmosphere. That is, after all the liquid has passed through the filter cake of product, any gas which passes through the filter cake comprises an inert atmosphere. Preferably the gas has a moisture content of less than 100 ppm, more preferably less than 10 ppm, for instance less than 1 ppm.

The filter cake is preferably subsequently washed using a dry non-solvent liquid. For instance cold acetonitrile and/or ethyl acetate, each having moisture content of less than 0.1%, more preferably less than 0.01%, may be used to wash the solid.

The solid may subsequently be purified by further recrystallisations, for instance from dry acetonitrile (or other solvent used as the second stage solvent) under similar conditions to the initial recovery of zwitterionic product from the product mixture. Preferably the solution of zwitterionic product in the solvent of the product mixture or of the solution from which the product is to be recrystallised, is subjected to a filtration stage whilst hot, to remove insoluble impurities or by-products from the product. By using the cooling procedure described for the process larger size crystals of product are produced and this eases the filtration step and minimises the exposure of the solid to potentially moisture containing gas.

Where the present invention uses 2-hydroxyethyl methacrylate as the ethylenically unsaturated starting material I, suitable reaction conditions are as follows.

2-Hydroxyethyl methacrylate is mixed with a suitable non-nucleophilic organic base such as a trialkylamine, preferably triethylamine, in dry ethyl acetate and cooled to a temperature between -70°C and 0°, preferably -10°—5°C under an inert atmosphere, dry nitrogen for example, and then treated with a solution of the compound II, preferably 2-chloro-2-oxo-l,3,2-dioxaphospholane, in dry ethyl acetate, drop-wise at a rate such that the temperature of the reaction does not rise above -5°C-0°C. The reaction mixture is allowed to warm to 0-25°C, preferably 10-15°C, after the addition and stir for 0.2-3 hours, preferably 1 hour. The precipitate of triethylamine hydrochloride is removed by filtration under an inert atmosphere, for example, by pumping the solution containing the intermediate III from the reaction vessel using a peristaltic pump and a filter stick to leave behind the precipitate. The ethyl acetate solution containing III is passed through a thin-film evaporator under vacuum with warming to 20-50°C, preferably 35-45°C. The solvent is removed from the phospholane intermediate III during the passage through the evaporation chamber (typical time) of a sample in this chamber is 10-15 seconds) and the concentrate sample of III then drips into a cooled collection vessel containing dry acetonitrile.

At the end of the solvent removal phase this dilute acetonitrile solution of III is ready for the preferred second stage trimethylamination reaction. During this process the cyclic phospholane III is not exposed to the atmosphere, thereby preventing hydrolysis, and it is kept as a dilute, chilled solution prior to the reaction with trimethylamine. After purging with an inert gas, the solution is heated to 50°C for 5-24 hours, preferably 12-16 hours, with a mixture of trimethylamine (1-5 equivalents, preferably 1-2 equivalents) in dry acetonitrile. The ratio of acetonitrile to III at this stage is preferably 6-3:1 volume/weight, although other suitable ratios may be used.

At the end of this period any excess trimethylamine is then removed by applying a low vacuum and the solution then treated with activated charcoal or other suitable decolourising material, and warmed with stirring for 0.2-2 hours, preferably 0.2-0.5 hours at a temperature of 20- 80°C, preferably 70-80°C. The mixture is then filtered through a filtering aid such as Celite® or pumped into a crystallising vessel using a peristaltic pump and filter stick, using an in-line filter if desired. The filtrate is then allowed to cool to ambient temperature in a sealed vessel for 1-24 hours, preferably 3 hours and subsequently stored at -20°- -5°C, preferably -5°C for 1-24 hours, preferably 16 hours.

The mixture is allowed to warm to ambient temperature and is filtered under an inert atmosphere. The solid is washed with dry acetonitrile and dry ethyl acetate. The product is then dried in vacuo to give a white, free flowing solid.

These steps allow the isolation of high purity monomer which may, if desired, be further purified by subsequent recrystallisations from dry acetonitrile under similar conditions to those described above.

Analysis of this material using standard techniques including thin layer chromatography (TLC) , high performance liquid chromatography (HPLC) , nuclear magnetic resonance (NMR) and elemental microanalysis indicates a high level of purity. Solubility evaluation and colour analysis indicates that the isolated material is particularly suitable for use in ophthalmic applications. For instance the monomer may be reacted, eg polymerised, and used in the processes described in our earlier publications WO-A- 9305081, WO-A-9207885 and WO-A-9301221, the disclosures of which are herein incorporated by references. The invention will be illustrated by the following example. Example 1

Preparation of 2-(methacryloyloxyethyl)-2' ftrimethyl ammonium ethyl) phosphate, inner salt

A solution of 2-hydroxyethylmethacrylate (1.13 kg, 8.7 mol) and triethylamine (0.93 kg, 9.2 mol) in dry ethyl acetate (61) under a dry nitrogen atmosphere was cooled to -10°C when a solution of 2-chloro-2-oxo-l,3,2- dioxaphospholane (1.25 kg, 8.7 mol) having a purity by P nmr of greater than 95% in dry ethyl acetate (0.751) was added at a rate such that the temperature of the reaction mixture did not rise above -5°C. The mixture was stirred for a further 2 hours during which time the temperature was allowed to rise to 15°C. The precipitate of triethylamine hydrochloride was removed by filtration and the solvent removed from the filtrate by passage down a thin-film evaporator in vacuo . The intermediate cyclic phospholane was collected as a dilute solution in dry acetonitrile. This solution, under a nitrogen atmosphere, was treated with a solution of trimethylamine (0.78kg, 13.2mol) in dry acetonitrile and the mixture warmed to 50°C for 16 hours. Excess trimethylamine was removed in vacuo and activated charcoal (50 g) was added. The mixture was stirred at 80°C and then filtered. The filtrate was allowed to cool to room temperature over 3 hours. The mixture was stored at - 5°C overnight, allowed to warm to 20°C and was filtered under a dry nitrogen atmosphere. The product was washed with dry acetonitrile (0.51), then dry ethyl acetate (3 x 0.51) and dried in vacuo at 25°C.

¹H-NMR (200MHZ) (D₂0) : -56.19 (1H, s) , 5.76 (1H, m) , 4.40 (2H, m) , 4.30 (2H, m) , 4.17 (2H, m) , 3.66 (2H, m) , 3.22 (9H, S) , 1.95 (3H, s) .

Claims

1. A process comprising the following stages: i) a first stage in which an ethylenically unsaturated compound of the formula I Y-B-OH I wherein B is a straight or branched alkylene, oxaalkylene or oligo-oxaalkylene chain,

Y is an ethylenically unsaturated poly erisable group selected from

wherein:

R is hydrogen or a 0,-0₄ ^alkyl group;

A is -O- or -NR - wherein R is hydrogen or a ^-C^ alkyl group or R is a group -B-OH;

K is a valence bond or a group -(CH₂)_pOC(OC)-, - (CH₂)_pC(0)0-,

-(CH₂)_pOC(0)0-, -(CH₂)_pNR²-, -(CH₂)_pNR²C(O)-,

-(CH₂) C(0)NR²-, (CH₂) NR²C(0))-, -(CH₂) OC(0)NR²-,

-(CH₂) NR2C(0)NR2- (i.n whi.ch the groups R2 are the same or different), -(CH₂)_pO-, -(CH₂)_pS0₃-, p is from 1 to 12 and R² is hydrogen or a 0,-0₄ ^alkyl group is reacted with a phospholane reagent II

in which eac R s the same or different and is H or C,.₄ alkyl, each R 4 is the same or di.fferent and i.s H or C,.₄ alkyl.

in which Y, B R 3 and R are as defi.ned previously, the reaction being carried out in the presence of a first solvent in which the ethylenically unsaturated reagent and the phospholane reagent are soluble, the hydrogen halide by-product is removed from the product mixture, and ii) a second stage in which the diester compound III is reacted in the presence of a second solvent which is different to the first solvent characterised in that the first solvent is removed from the diester III in a thin film evaporator in which the solvent is evaporated and the diester maintained and collected as a liquid which is diluted immediately upon collection in said second solvent.

2. A process according to claim 1 in which the first solvent is an ether, a nitrile or an ester, preferably a lower alkyl ester of a C,.₆-carboxylic acid, preferably lower alkyl acetate, most preferably ethyl acetate.

3. A process according to claim 1 or 2 in which the second solvent is a nitrile derivative of a C,.₆-carboxylic acid, preferably acetonitrile. 4. A process according to any preceding claim in which the ethylenically unsaturated compound I is selected from those of general formula IA

R CH₂=

in which R is hydrogen, methyl, or ethyl, more preferably methyl, A is -0-, and B is: an alkylene group of formula -(C ₂)_a-, wherein the groups -(CR₂)- are the same or different, and in each group

-(CR₂)- the groups R are the same or different and each group R is hydrogen or C,.₄ alkyl, preferably hydrogen, and a is from 1 to 12, preferably 1 to 6; an oxaalkylene group such as alkoxyalkyl having 1 to 6 carbon atoms in each alkyl moiety, more preferably -CH₂0(CH₂)₄-; an oligo-oxaalkylene group of formula -[CH ₂)_bO]_c(CR ₂)_b- where the groups -(CR₂)- are the same or different and in

4 , each group -(CR₂)- the groups R are the same or different and each group R is hydrogen or C,.₄ alkyl, preferably hydrogen, and b is 2 or 3 and c is from 2 to 11, preferably 2 to 5; B preferably being -(CH₂)₈, in which a' is 2 to 4.

5. A process according to any preceding claim in which in the phospholane reagent II, R 3 and R4 are preferably each hydrogen.

6. A process according to any preceding claim in which there is used as a starting material a phospholane reagent of the formula II having a purity by ³¹P NMR of at least 90%, more preferably at least 95%, for instance at least 99%.

7. A process according to any preceding claim in which the water content of the first solvent and of the second solvent is less than 0.1% by weight, preferably less than 0.01% by weight.

8. A process according to any preceding claim in which the second stage of the process comprises the ring opening amination reaction in which the compound of the formula III is reacted with a trialkylamine reagent (N(R )₃) to form a compound of the formula IV

O R³ R⁴ Y-B-O-P II-O-CI- CI-N(R₅), IV

I l₃ l₄ +

0_ R⁵ R* in which each group R is the same or different and is a C,.₂₄-alkyl, preferably C,.,₂ alkyl, more preferably lower alkyl group and Y, B, R 3 and R4 are each as defi.ned in claims 1, 4 or 5 above.

9. A process according to claim 8 in which the trialkylamine reagent is present in the reaction mixture for the second step in an amount in the range 1 to 2 times the stoichiometric amount for reaction with the diester compound III.

10. A process according to claim 8 or 9 in which the product mixture containing IV is heated to (or maintained at) a temperature at which all of the product zwitterionic compound of the formula IV is in solution in the solvent, and then allowed to cool, preferably in a sealed vessel, or in a vessel which has been purged with inert gas, for a period of at least one hour, and preferably 2-16 hours, to reach ambient temperature and subsequently cooled further to a temperature in the range -20 to -5°C, preferably around -5°C, at which it is stored for a period of at least 1 hour, for instance in the range 1-24 hours, for instance around 16 hours.

11. A process according to any of claims 8 to 10 in which the solid product IV is removed from the product suspension by filtration.

12. A process according to claim 11 in which the filtration is conducted in an inert atmosphere, preferably such that any gas which passes through the filter cake has a moisture content of less than 100 ppm preferably less than 1 ppm.