1. Field of the Invention
The invention relates to a method of preparing polymerizable phosphonic acid diesters by reacting N-hydroxymethyl derivatives of (meth)acrylic acid amides with tertiary phosphites (i.e., phosphorous acid triesters).
2. Discussion of the Background
A number of different processes have been described previously for preparing compounds of general formula I: EQU H.sub.2 C.dbd.C(R.sub.1)--CO--N(R.sub.2)--CH.sub.2 --P(O)(OR.sub.3)(OR.sub.4) (I)
where
R.sub.1 is a hydrogen atom or a methyl group; PA0 R.sub.2 is a hydrogen atom or a C.sub.1 -C.sub.4 alkyl group, which can optionally be substituted, or a C.sub.3 -C.sub.4 alkenyl group; and PA0 R.sub.3 and R.sub.4 are identical or different groups such as phenyl, or C.sub.1-4 alkyl groups (possibly substituted), or alkylene groups which form 5- to 7-membered rings with the oxygen atoms and the phosphorus atom.
The known methods for preparing these compounds start from (meth)acrylic acid amide derivatives of formula II: EQU H.sub.2 C.dbd.C(R.sub.1)--CO--N(R.sub.2)--CH.sub.2 --X (II)
where R.sub.1 and R.sub.2 have the meanings given supra, and X is a dimethylamino group, a diethylamino group, an acetoxy group, a propanoyloxy group, a halogen atom, or a hydroxyl group. The compounds of formula II are then reacted with tertiary phosphites (phosphorus acid triesters), particularly aliphatic phosphorous acid triesters of formula III: EQU P(OR.sub.3)(OR.sub.4)(OR.sub.5) (III)
where R.sub.3, R.sub.4 and R.sub.5 are identical or different groups, such as phenyl or C.sub.1-4 alkyl groups, or R.sub.3 and R.sub.4 are alkylene groups which form 5- to 7-membered rings with the oxygen atoms and the phosphorus atom.
Thus, German OS No. 22 15 434 (which corresponds to U.S. Pat. No. 3,884,618) describes the reaction of phosphorous acid triesters with compounds of formula II where X is a OH group, at temperatures of about 100.degree.-200.degree. C. to produce a raw product. German OS No. 22 17 746 (which corresponds to U.S. Pat. No. 1,380,675) describes reactions of (meth)acrylamide derivatives of formula II (where X represents the various moieties indicated supra) with phosphorous acid triesters of formula III.
The polymerizable phosphonic acid esters of formula I are relatively high boiling substances. Thus, in German OS No. 22 17 746, 0,0-dimethyl N-methacrylamido-methylphosphonate is obtained as a liquid with a boiling point of 170.degree. to 180.degree. C. (at 1.2 to 1.5 Torr) in a yield of 76% of theoretical, from N-(acetoxymethyl)-methacrylamide. A corresponding undistilled raw product obtained from N-(hydroxymethyl)-methacrylamide should be comprised of this compound in amounts of up to 78% by wt. according to gc analysis.
Attempts to prepare (meth)acrylamidomethylphosphonates in high yields and high purities have been unsuccessful. Reactions carried out under the known reaction conditions produce relatively large amounts of methylenebisamides of (meth)acrylic acid from N-hydroxymethyl derivatives of (meth)acrylic acid amide, etc. If these bisamides are not removed by purification processes which are costly and lead to substantial losses of materials, they act as spurious crosslinking agents in the manufacture of polymers. References to the inadequate purity of the reaction products obtained can be found in German OS No. 25 38 282, where it is stated that the reaction products of reactions according to e.g., German OS No. 22 17 746, are mixtures of monomeric and oligomeric phosphonates.
As indicated in 1962 Makromolekulare Chem. 57:27, starting compounds (II) in which X is an acyloxy (e.g. acetoxy or propanoyloxy) group (as described in German OS No. 22 17 746) may be prepared by esterification of the corresponding methylol compounds by the appropriate carboxylic acid anhydrides. These anhydrides are however relatively costly materials, and the yields achieved, e.g., a 67% of theoretical yield of acetoxymethyl-methacrylamide, are relatively low.
These substances are required for the manufacture of industrially important polymers. There is therefore a strongly felt need for an improved method to obtain these polymerizable phosphonic acid esters and derivatives produced from these phosphonic acid esters in increased yield and purity (e.g. by substantial suppression of side reactions). Such a method should ideally produce raw products which can be used directly.