Aminoalkyl (meth)acrylate stabilisation

Abstract

The present invention relates to the use of a stabilizing composition comprising at least one N-oxyl compound and at least one polymerization inhibitor other than an N-oxyl compound, for inhibiting transesterification catalyst degradation in a process for the synthesis of aminoalkyl (meth)acrylates. Preferably, the transesterification catalyst is a titanium organometallic compound and the stabilising composition comprises at least one N-oxyl derivative and at least one polymerization inhibitor chosen from phenolic compounds and phenothiazine compounds in a weight ratio of between 1 and 10, preferably between 4 and 10, limits inclusive.

Claims

1. A process for synthesizing aminoalkyl (meth)acrylates, comprising the step of transesterifying an alkyl (meth)acrylate of formula (II): ##STR00008## in which R is a hydrogen atom or a methyl group and R.sub.2 is a linear or branched alkyl group having from 1 to 4 carbon atoms, with an alcohol R1-OH of formula (III):
HO-A-N(R′1)(R′2)  (III) in which A is a linear or branched C.sub.1-C.sub.5 alkylene radical, R′1 and R′2, which are identical or different from one another, represent a hydrogen atom or a C.sub.1-C.sub.4 alkyl radical, in the presence of a transesterification catalyst selected from the group consisting of organometallic compounds of one of the following formulas: M(OR3).sub.4 in which R3 is a linear or branched C.sub.1-C.sub.5 alkyl radical and M is a group IV metal or, M{OC(CH3)═CH—C(CH3)═O}.sub.4 in which M is a group IV metal, whereby the transesterification is carried out in the presence of a stabilizing composition comprising at least one N-oxyl compound and at least one polymerization inhibitor selected from the group consisting of phenol compounds and phenothiazine compounds in a mass ratio of between 1 and 10, endpoints included.

2. The process as claimed in claim 1, wherein the aminoalkyl (meth)acrylate is dimethylaminoethyl acrylate.

3. The process as claimed in claim 1, in which the N-oxyl compound is selected from the group consisting of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), 4 -hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-OH-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine 1-oxyl (4-Oxo-TEMPO), and mixtures thereof.

4. The process as claimed in claim 1 in which the stabilizing composition comprises at least one polymerization inhibitor selected from the group consisting of phenothiazine, 4-methyl-2,6-tert -butylphenol, hydroquinone, and hydroquinone methyl ether.

5. The process as claimed in claim 1 in which the mass ratio of the N-oxyl compound to the one or more polymerization inhibitors is between 2 and 10, endpoints included.

6. The process as claimed in claim 1 in which the mass ratio of the N-oxyl compound to the one or more polymerization inhibitors is between 4 and 10, endpoints included.

7. The process as claimed in claim 1 in which the mass ratio of the N-oxyl compound to the one or more polymerization inhibitors is between 5 and 10, endpoints included.

8. The process as claimed in claim 1 in which the alcohol R1-OH is dimethylaminoethanol.

9. The process as claimed in claim 1 in which said group IV metal M is titanium.

10. The process as claimed in claim 1 in which said transesterification catalyst is selected from the group consisting of titanium alkoxides, tetraalkyl titanates, and Ti, Zr or Hf acetylacetonates.

Description

DETAILED ACCOUNT OF THE INVENTION

(1) The invention relates to the synthesis of aminoalkyl (meth)acrylates of formula (I):

(2) ##STR00006##
via transesterification reaction of an alkyl (meth)acrylate of formula (II):

(3) ##STR00007##
with an alcohol of formula: R.sub.1—OH,
in which R, R.sub.1 and R.sub.2 are as defined above.

(4) The term “(meth)acrylic” means acrylic or methacrylic; the term “(meth)acrylate” means acrylate or methacrylate.

(5) Possible examples of alcohol R.sub.1—OH include N,N-dimethylaminoethanol (DMAE), N,N-diethylaminoethanol, N,N-dimethylaminopropanol, 2-aminoethanol, and 2-methylaminoethanol.

(6) The alcohol R.sub.1OH is preferably a dialkylamino alcohol of formula (III):
HO-A-(R′.sub.1)(R′.sub.2)  (III)
in which: A is a linear or branched C.sub.1-C.sub.5 alkylene radical, R′.sub.1 and R′.sub.2, which are identical or different from one another, represent a hydrogen atom or a C.sub.1-C.sub.4 alkyl radical. With preference, R′.sub.1 and R′.sub.2 represent a C.sub.1-C.sub.4 alkyl radical,

(7) Preferably, the alcohol R.sub.1—OH is N,N-dimethylaminoethanol (DMAE), also hereinafter called dimethylaminoethanol.

(8) Preferably, the alkyl (meth)acrylate of formula (II) is methyl acrylate or ethyl acrylate, more preferentially ethyl acrylate.

(9) In one embodiment, the invention pertains to the synthesis of dimethylaminoethyl acrylate (DMAEA) by transesterification reaction of ethyl acrylate (EA) with dimethylaminoethanol.

(10) The transesterification catalyst is an organometallic complex, used generally in an amount that may range from 0.001 to 0.02 mol, preferably from 0.005 to 0.01 mol, per mole of alcohol R.sub.1—OH.

(11) The transesterification catalyst is preferably an organometallic complex based on titanium.

(12) The reaction temperature is generally between 80 and 150° C. and the pressure is generally maintained at between 0.5 and 1.1 bar. The reaction temperature is preferably between 90 and 130° C. and the pressure is of the order of 0.65 bar to atmospheric pressure.

(13) According to the invention, the stabilizing composition comprising at least one N-oxyl derivative and at least one polymerization inhibitor other than an N-oxyl derivative enables the secondary reactions of radical polymerization during the synthesis to be prevented while avoiding the breakdown of the catalyst into insoluble salts.

(14) The stabilizing composition is generally introduced into the transesterification reactor in the form of a solution in the alkyl (meth)acrylate (II), in a proportion of 100 to 5000 ppm, preferably between 500 and 3000 ppm, relative to the initial charge of reactants.

(15) The N-oxyl compound is preferably in excess in the stabilizing composition; generally, the amount by mass of N-oxyl compound is more than 50%, preferably more than 80%, and may be from 80% to 95% relative to the stabilizing composition.

(16) The advantage endowed by the invention is that of using a more highly performing stabilizing composition than a polymerization inhibitor alone in the stabilization of (meth)acrylic monomers, with no adverse effect on the process by transesterification.

(17) The examples below illustrate the present invention without, however, limiting the scope thereof.

EXPERIMENTAL SECTION

(18) In the examples below, all of the concentrations are given in mass % and ppm by mass unless stated otherwise, and the abbreviations used are as follows:

(19) EA: Ethyl acrylate

(20) DMAE: Dimethylaminoethanol

(21) DMAEA: Dimethylaminoethyl acrylate

(22) PTZ: Phenothiazine

(23) 4-HT: 4-OH-TEMPO

(24) HQME: Hydroquinone methyl ether

(25) Ti(OEt).sub.4: Tetraethyl titanate

(26) TOF: Turn-over frequency

(27) MIS: Matter in suspension

(28) The protocol used for all of the inventive examples and comparative examples was as follows:

(29) A stirred 0.5 L reactor, heated by circulation of thermostated oil at 135° C. within a jacket, surmounted by a distillation column with Multiknit packing, with a condenser containing water-glycol mixture at the column top, a reflux head, a vacuum separator, receivers and traps, is fed continuously with the EA, the heavy alcohol (DMAE), and a transesterification catalyst (Ti(OEt).sub.4).

(30) The polymerization inhibitors (PTZ, 4-HT, EMHQ or a mixture of these compounds) are injected continuously as a mixture with the EA.

(31) Throughout the synthesis, air is sparged into the reaction mixture. The reaction is carried out at a temperature of 119-121° C. under a reduced pressure of 860 to 870 mm Hg.

(32) The ethanol formed during the reaction is removed at the rate it is formed, as an EA/ethanol azeotrope.

(33) The conversion rate is monitored by refractometric analysis of the azeotrope. The ethanol content is between 58% and 62%.

(34) The crude reaction mixture is withdrawn using an overflow and recovered in a receiver, for analysis after 120 h of operation.

(35) The bottom and distillate streams were analyzed by gas chromatography, to ascertain the yield of desired ester and the conversion of the heavy alcohol.

(36) The inhibitors were analyzed and quantified by liquid chromatography.

(37) The heavy impurities (catalyst+heavy byproducts formed) were quantified using a thermal balance.

(38) On the basis of these analyses, the catalytic activity after 120 h is also determined by the value of the TOF, calculated according to the formula below. The residence time Rt is determined according to the extraction flow rate at the bottom of the transesterification reactor.

(39) $\mathrm{TOF}=\frac{N_{\mathrm{DMAEA}}\left(\mathrm{moles}\right)}{N_{\mathrm{Catalyst}}\left(\mathrm{moles}\right)\times \mathrm{Rt}}$

(40) Tests in accordance with the invention were performed using a polymerization inhibitor in the form either of a mixture of 4-HT and PTZ with excess 4-HT (Examples 1 to 3) or a mixture of 4-HT and HQME with excess 4-HT (Example 4).

(41) For comparison, tests were carried out with 4-HT alone (Example 5), PTZ alone (Example 6), or a mixture of 4-HT and PTZ with excess PTZ (Example 7).

(42) For all of the tests in accordance with the invention (Examples 1 to 4), the reactor remained completely clear after 120 h of operation, with no observed reactor fouling.

(43) The comparative tests carried out with 4-HT alone (Ex 5) showed incidence of a white inorganic compound accumulating during the synthesis, with reactor fouling from 24 h of operation and loss of catalyst activity.

(44) The comparative tests carried out with PTZ alone (Ex 6) or a mixture of 4-HT and PTZ with excess PTZ (Ex 7) showed more substantial formation of soluble polymers (heavies >1.0%) in the transesterification reactor.

(45) The results of these tests are collated in Table 1 below.

(46) TABLE-US-00001 TABLE 1 Ex 5 Ex 6 Ex 7 Ex 1 Ex 2 Ex 3 Ex 4 comp. comp. comp. FEED EA (g/h) 61.8 62.2 62.2 61.5 62.0 59.9 59.9 DMAE (g/h) 34.3 34.5 34.5 34.2 34.4 33.3 33.3 Ti(OEt).sub.4 (g/h) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 STAB PTZ (g/h) 0.004 0.008 0.020 — — 0.05 0.05 HQME (g/h) — — — 0.008 — — — 4-HT (g/h) 0.039 0.041 0.040 0.040 0.040 — 0.012 RESULTS Conversion 83.0 83.7 83.2 79.9 83.5 83.1 83.0 (%) Yield (%) 84.1 84.2 84.3 83.0 81.6 82.8 82.9 TOF (h.sup.−1) 18.1 17.8 17.8 19.1 15.9 16.7 17.1 Heavies (%) 0.7 0.8 0.6 0.9 1.0 1.4 1.6 Fouling (h) >120 >120 >120 >120 24 >120 >120 Reactor clear clear clear clear MIS clear clear appearance