GB2162516A - Process for the preparation of esters of acrylic and methacrylic acid - Google Patents

Abstract

A process for the preparation of an acrylic or methacrylic acid ester comprises transesterifying an acrylic or methacrylic acid ester of a C1-4 alcohol with a monohydric alcohol different from that esterified in the starting material in the presence of a catalyst system comprising a combination of compounds A and B wherein A represents the compound Lin Y, wherein Y represents halide or chlorate or carbonate or the salt of a carboxylic acid with 1 to 6 carbon atoms or an alkoxide with 1 to 4 carbon atoms, hydroxide or oxygen and n represents 1 or 2, depending on the valency of Y, and X represents the compound CaXq wherein X represents oxygen or chloride and q represents 1 or 2, depending on the valency of X, with the proviso that at least one of the two anionic components X and Y should contain oxygen.

Description

SPECIFICATION Process for the preparation esters of acrylic and methacrylic acid The invention relates to a process for the preparation of esters of acrylic and methacrylic acid.

More particularly it relates to a process for the production of esters of higher alcohols and of substituted alcohols, other than polyhydric alcohols, starting from the esters of acrylic or methacrylic acid with C14 alcohols, which are industrially available, by transesterification using metal compounds as catalysts.

In polymer technology, there is frequently a need to have acess to special esters of acrylic or methacrylic acids in addition to the (meth)acrylates such as methyl methacrylate which are produced on a large industrial scale. Such special esters may be used to vary the properties of a polymer, for example, or construct special polymer systems (cf. H.Rauch-Puntigam and Th.

Völker "Acrylund Methacrylverbindungen", Springer-Verlag, 1967). One problem is that such esters are quite difficult to prepare satisfactorily on an industrial scale.

The catalytic activity of (inorganic) bases in a number of transesterification reactions to prepare desired special compounds is known (e.g. Swiss Patent 239 750). This type of reaction is used with advantage to prepare higher (meth)acrylic acid esters or basic esters from methyl or ethyl (meth)acrylate (German Auslegeshrift 11 80 527, US Patent 2 138 763, G.D. Graves 8 M.B. Horn in "Acrylic Resins", Reinhold Publ. Corp., New York, 1 960). However, it is clear from the literature that the endeavours in the art thus far have been concentrated on providing particular catalysts to solve special problems. Thus, in J.Am.Chem.Soc. 77, 194 (1955), the transesterification of methyl methacrylate with tetraethylene glycol in benzene in the presence of sodium hydride is described. The methanol formed is distilled off as a benzene/methanol azeotrope.

The transesterification reaction of methyl acrylate or methyl methacrylate with dialkylaminoalkanol in the presence of calcium hydroxide or calcium oxide is known from Japanese Published Patent Application 75 142513 (cf. Chem.Abstr. 84, 1 36271f). The catalytic acceleration of the ester exchange of methyl methacrylate with, for example, 2-ethylhexanol by means of lithium compounds such as lithium hydride, alkyl lithium, phenyl lithium, lithium aluminium hydride, lithium borohydride or the alkoxides thereof, lithium salts of organic and inorganic acids, lithium acetyl acetonate, lithium oxide or lithium metal is also described in Japanese Published Patent Application 79 41 815 (cf. Chem.Abstr. 91, 40095v).Particular attention has been paid to the transesterification of lower esters of methacrylic and acrylic acid with glycidol to yield the glycidyl esters. The transesterification of methyl methacrylate with glycidol in the presence of alkali metal hydroxides (or alkali metal carbonates, sulphides, polysulphides or thiosulphates), lithium halides or sodium, potassium, rubidium or caesium iodides is the subject of Japanese Published Patent Application 80 94 378 (Chem.Abstr. 94, 121 290u).

The transesterification of methyl (meth)acrylate with glycidol in the presence of alkali metal halides, particularly lithium chloride to yield glycidyl methacrylate is described in Japanese Published Patent Application 80 105 676 (cf. Chem.Abstr. 94, 121 292w), whilst Japanese Published Patent Application 80 1 27 380 (Chem.Abstr. 95, 7026h) describes the transesterification of lower esters of other organic carboxylic acids with glycidol in the presence of alkali metal halides, particularly sodium bromide.

Technological development has therefore taken the direction of solving any specific problems regarding the production of special esters of acrylic or methacrylic acid by providing specific transesterification catalysts. However, in the interests of maximum unity in technology, there is still a need for a process which is more generally applicable. Product quality and yield should also be improved, if possible. It follows that no deterioration can be allowed from an ecological or economical point of view. To make matters worse, there is a danger of polymerisation with the esters of polymerisable acids under the conditions of reaction and wiorking up and other side reactions. Additionally, there are also problems with transesterification with special alcohols.

We have now found that the transesterification of esters of radically polymerisable carboxylic acids such as acrylic or methacrylic acid with the special alcohols can be carried out using a particular catalyst system so that maximum possible transesterification is achieved, i.e. high yields with the highest possible selectivity.

None of the prior art known to us gives any indication that our catalyst system, formed from a variety of inherently inactive components, would show any synergistic effect in reactions of transesterification in accordance with the aims stated above.

According to the invention we thus provide a process for the preparation of an acrylic or methacrylic acid ester which comprises transesterifying an acrylic or methacrylic acid ester of a C14 alcohol with an alcohol different from that esterfied in the starting material and which with is other than a polyhydric alcohol, in the presence of a catalyst system comprising a combination of compounds A and B wherein A represents the compound Lin Y, wherein Y represents halide or chlorate or carbonate or the salt of a carboxylic acid with 1 to 6 carbon atoms or an alkoxide with 1 to 4 carbon atoms, hydroxide or oxygen and n represents 1 or 2, depending on the valency of Y, and B represents the compound CaXq wherein X represents oxygen or chloride and q represents 1 or 2, depending on the valency of X, with the proviso that at least one of the two anionic components X and Y should contain oxygen.

The transesterification reaction will conveniently be carried out with the esters of acrylic or methacrylic acid with C14 alcohols that are readily available industrially, particularly with C12 alcohols, i.e. particularly the ethyl and more particularly the methyl esters.

The alcohols used for the transesterification (which are different from those of the starting materials esters and are not polyhydric) can generally be represented by formula I R OH wherein R desirably represents (a) a linear alkyl group with 2 to 30 carbon atoms, (b) a branched alkyl group with 3 to 40 carbon atoms, (c) a cyclic alkyl group with 5 to 30 carbon atoms, (d) an aralkyl group with 7 to 1 8 carbon atoms.

(e) a heterocyclic group Z, (f) an alkyl group with 2 to 1 2 carbon atoms with one or more amine functions A in the molecule, (g) an alkyl group with 1 to 18 carbon atoms containing at least one functional group G which is different from the substitutions defined in (e) to (f).

The groups R according to (a) to (g) defined above may be substituted by one or more chemically inert substituents Q which are different from the substituents specified in definitions (e) to (g) above. The term "chemically inert substituents Q" as used herein refers to groups which are not radically polymerisable under the conditions of transesterification (apart from hydrocarbon residues), and particularly includes halogen atoms, such as fluorine, chlorine, bromine; or an ether group of formula -OR1, wherein R1 represents an alkyl group with 1 to 18 carbon atoms, preferably 1 to 6 carbon atoms, or a phenyl group, of a group

wherein R2 represents an alkyl group with 1 to 30 carbon atoms; or a group of formula ORí wherein R, has the same meanings as Rl or represents a group -NR3R4 wherein R3 and R4, independently of each other, represent hydrogen, phenyl or an alkyl group with 1 to 6 carbon atoms or wherein R3 and R4 together with the nitrogen atom to which they are both attached and optionally with other heteroatoms, form a five- or six-membered heterocyclic ring and wherein T represents oxygen or a group -NRs and n represents zero or one, whilst Rs represents hydrogen or an alkyl group with 1 to 6 carbon atoms.

The meanings given for R under (a) for formula (I) include linear, primary and secondary alcohols, particulary alcohols with upwards of 3 carbon atoms, more particularly alcohols with up to 24 carbon atoms.

Of the definitions for R under (b) for formula (I), particular mention should be made of primary and secondary branched alcohols, particularly those with 3 to 28 carbon atoms. Secondary alcohols according to (a) and (b) such as isopropanol and butan-2-ol- are particularly preferred.

Of technological interest are the reactions wherein R represents linear, primary higher alcohols alcohols such as are obtained in large-scale industrial processes, with average carbon numbers of between 8 and 1 8. Mention may be made, for example, of the linear primary alcohols obtained by hydroformulation (of the DOBANOL type made by Shell Chemie), the alcohols with 4 to 20 carbon atoms produced by the Ziegler method by hydrolysis of aluminium alkoxides of the ALFOL type made by Messrs. Condea of Hamburg and the fatty alcohols and fractions of the LOROL type made by Henkel KG. Particular mention should be made of C10 24 alcohols, particularly C18 20 alcohols and, as specific examples, decyl, undecyl, lauryl, oleyl and octadecyl alcohols. Mention should also be made of alcohols bearing one or more substituents Q, such as fluorinated alcohols, chlorinated alcohols such as 2,3-dichloropropanol, etherified alcohols such as diethylene glycol 2-ethyl ether, n-butyldiglycol monomethyl ether, fi-methoxyethanol and p- ethoxyglycol, acylated alcohols such as fi-acetoxyethanol, ss-chloroacetoxyethanol, ethyl ss- hydroxypropionate or alcohols bearing amide groups, such as N-ethanol-N-methyl-fatty acid amides, e.g. the N-methyl ethanolamide of cocinic acid.

Of the definitions for R according to (c) for formula (I), useful alcohols include the technologically available alcohols such as cyclohexanol and cyclooctanol and also alkylated cyclic alcohols such as 3,3,5-trimethylcyclohexanol as well as terpenoid alcohols and derivatives such as isoborneol. The alicyclic group may bear any hydroxy group on an alkyl substituent.

As an example of the definition of R according to (d) for formula (I), aralkyl alcohols such as benzyl alcohol, phenylethanol and 3-phenyl-propanol-ol are of interest.

If R represents Z according to (e) for formula (I), heterocyclic alcohols which may carry the hydroxy group both on an alkyl substituent of the heterocyclic system and also on the heterocyclic system itself are of interest. The heterocyclic system refers, in particular, to three-, five- and six-membered heterocyclic groups, predominantly heterocyclic groups containing nitrogen and/or oxygen and/or sulphur, which may be substituted with C16 alkyl groups.

Mention may be made, for example, of imidazole derivatives such as 2-(imidazolyl)-ethanol, 2-(2 methyl-A2- 1 -imidazolinyl)-ethanol, alcohols of 2, 3-dihydro-4H-pyrane, 2, 2-dimethyl- 1, 3-dioxolan- 4-methanol, 2-N-morphoiinoethanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, and glycidine, hydroxymethyldioxolan and 2-ethyl-5-(ss-hydroxyethyl)-tetrahydropyrane.

In the definition of R under (f) for formula (I), reference is made particularly to alcohols of the formula HO-R'-NR3R4 wherein R' represents an optionally branched hydrocarbon chain with 2 to 30, preferably 2 to 1 2 carbon atoms, or an optionally substituted cyclic group with 5 to 20 carbon atoms and R3 and R4 have the same meanings as R3 and r4, particularly the dimethylamine- and diethylamine-substituted ethanols, propanols, butanols, pentanols and hexanols.

The definition of R according to (g) for formula (I) refers particulary to alcohols of the formula HO-R" wherein R" represents an optionally branched hydrocarbon group with 1 to 30, preferably 1 to 1 2 carbon atoms or an optionally alkyl- and/or halogen-substituted cyclic group with 5 to 20 carbon atoms, which contains as a functional group G one or more carbon, carbon double or triple bonds or a nitrile ureido, vinyl ether or vinyl carboxy function. Examples include allyl alcohol and vinyloxyethanol. On the other hand, results so far indicate that the catalyst system is unsuitable for the catalysis of the transesterification of tertiary alcohols or phenolic OH groups.

The catalyst system is conveniently used in catalytic amounts, generally from 0.01 to 10% by weight, preferably 0.2 to 5% by weight, based on the alcohol used. The proportion of component A in the catalyst system is conveniently 5 to 95% by weight, preferably 90 to 10% by weight the proportion of component B is conveniently 95 to 5% by weight, preferably 90 to 10% by weight; in particular, B may be present in an excess by weight compared with A, for example in twice the quantity.

A standard mixture might contain a quantity of 0.2 to 5% by weight, preferably 1 to 3% by weight, of component B together with 0.02 to 2, preferably 0.5 to 2% by weight, of component A, based on the quantity of alcohol used, more particularly it might contain A to B in a weight ratio of 1:2. Advantageously, the catalysts are used in finely divided form, e.g. in powder or fine crystalline form. Components A and B may be mixed together before use but they may also be added to the reaction mixtures as individual components.By way of example, preferred catalyst systems may be formed from lithium oxide and calcium oxide lithium hydroxide and calcium oxide lithium alkoxide and calcium oxide lithium carbonate and calcium oxide lithium acetate and calcium oxide lithium fluoride and calcium oxide lithium chloride and calcium oxide lithium bromide and calcium oxide lithium iodide and calcium oxide lithium chlorate and calcium oxide and lithium methoxide and calcium chloride (where a lithium alkoxide is referred to, the methoxides, ethoxides and tert.butoxides are preferred).

It is advantageous to use an excess of the acrylic or methacrylic acid ester beyond the quantities required stoichiometrically for transesterification. In general, an excess of 1.5 to 10, preferably 1.5 to 3 and particularly 2.5, times the stoichiometrically calculated quantity is used.

Accordingly, when the batch sizes are increased beyond the laboratory scale it is advisable to reduce the excess of (meth)acrylic acid ester used as starting material.

It is not generally necessary to use a solvent. However, if desired, inert (non-radical forming) solvents may be used, e.g. hydrocarbons such as toluene, cyclohexane, n-hexane or heptane. It is advisable to use a stabiliser (radical binding agent) in order to inhibit polymerisation of the (meth)acrylates present. The stabilisers used may be conventional stabilisers, e.g. hydroquinone compounds, thio compounds or amines in the usual quantities (50 to 5000 ppm). [Cf. H.

Rauch-Puntigam, Th.VGlker "Acryl- und Methacrylverbindungen" ' Springer-Verlag, p. 1 65, (1967)].

The reaction is preferably carried out at above ambient temperature, preferably in the range from 60 to 1 20 C. In general, the total reaction times range from 5 to 20, preferably from 6 to 1 2 hours. As a guide to the duration of the actual alcoholysis, this will be 3 + 1 hour in many cases, whilst the remainder of the reaction may take a further 2 to 3 hours to complete, although the batch size will play a part. If the particularly preferred methyl methacrylate or acrylate is used, the methanol formed during transesterification may appropriately be drawn off in an azeotropic mixture with the methacrylic acid ester (at 65 to 75"C).

The reaction may in general be carried out as follows: The alcohol is introduced into a suitable reaction vessel with the excess (meth)acrylic acid ester and the stabiliser. The catalyst may be added during the reaction or it may be present from the start, whilst components A and B of the catalyst system may be added separately or in admixture. Thus, for example, lithium alkoxide may be used in a suitable solvent (e.g. lithium methoxide in methanol). Otherwixse, it is advisable to add the catalyst in finely divided form, preferably as a powder or granules. However, the initial distribution of the catalyst does not appear to be inherently critical.

The reaction mixture is brought to the reaction temperature with stirring. If, for example, methyl methacrylate is used, it may be heated to boiling point and the methanol formed is advantageously removed in azeotropic mixture with the ester up to a temperature of 70"C at the head of the distallation column. At a head temperature of up to about 98"C, remaining methanol is drawn off together with any unreacted ester; advantageously, the remaining methyl ester is finally distilled off under reduced pressure at a maximum sump temperature of 1 50 C.

Working up may be effected in a manner known per se; for example, it has proved useful to mix the crude ester with Fuller's earth or activated charcoal and, after stirring for a short time, filter it through flotation filters or pressure filters.

The yields of the required transesterification product are high in the process according to the invention, generally of the order of above 90%. The extremely small amounts of compounds of addition to the vinyl double bond and other by-products formed are considerably advantageous features of the process.

The following Examples serve to illustrate the process according to the invention.

Examples Apparatus used 2 litre round flask with mushroom-shaped heating cover, sabre stirrer, thermometer, air inlet tube, metallised column filling, glass Raschig rings measuring 4 X 4 mm, automatic gas phase separator, cooler, adaptor, receiver.

Method: The alcohol ROH and methyl methacrylate are placed in the flask in a molar ratio of 1:2.5 with 200 ppm of hydroquinone monomethyl ether and with powered LiCI/CaO in a weight ratio of 1:2. The reaction mixture is heated to boiling, with stirring and with air being introduced. The methanol formed during alcoholysis is drawn off until the formation of methanol has ceased.

Then, without limiting the temperature at the head, the excess methyl methacrylate is distilled over up to a sump temperature of 1 35 C. Then the product is degassd at 11 0,C and 10 mbar.

The crude ester is investigated by gas chromatography. The results are shown in the following Table: TABLE Percentage by weight LiCl/CaO Conversion Yield of esterified Example (based on (based on product based on No. Alcohol ROH alcohol ROH) alcohol ROH) alcohol conversion 1 Butan-2-ol 1.1 / 2.2 56.5 % 100 % 2 Cyclohexanol 0.9 / 1.8 99.2 % 100 % 3 Benzyl alcohol 0.8 / 1.7 100 % 92.7 % 4 2-Ethyl-hexanol 0.7 / 1.5 100 % 92.1 % 5 ALFOL 10 0.65 / 1.3 100 % 93.4 % 6 DOBANOL fatty alcohol mixture1) 0.55 / 1.1 100 % 83.3 % 7 Tetrahydrofurfuryl alcohol 0.85 / 1.7 100 % 83.8 % 8 Allyl alcohol 1.3 / 2.6 97.7 % 95 % 9 Glycidol 1.1 / 2.2 98.8 % 30.9 % 10 2-Dimethylaminoethanol 1.0 / 2.0 99.1 % 88.5 % 11 tert. Butanol 1.1 / 2.2 no reaction 12 Phenol 0.9 / 1.8 no reaction 1) Mixed alcohol consisting of 77% by weight DOBANOL 25 L (Shell) and 23 % by weight fatty alcohol (Henkel) with average carbon number 14.2 Instead of lithium chloride and calcium oxide it is also possible to use catalyst systems consisting of calcium oxide and lithium oxide calcium oxide and lithium hydroxide calcium oxide and lithium methoxide calcium oxide and lithium tert.butoxide calcium oxide and lithium acetate calcium oxide and lithium bromide calcium oxide and lithium iodide calcium oxide and lithium chlorate and calcium chloride and lithium methoxide Comparable results are obtained.

Claims (14)

1. A process for the preparation of an acrylic or methacrylic acid ester which comprises transesterifying an acrylic or methacrylic acid ester of a C,~4 alcohol with an alcohol different from that esterified in the starting material and which with is other than polyhydric alcohol, in the presence of a catalyst system comprising of a combination of compounds A and B wherein A represents the compound Lin Y, wherein Y represents halide or chlorate or carbonate or the salt or a carboxylic acid with 1 to 6 carbon atoms or an alkoxide with 1 to 4 carbon atoms, hydroxide or oxygen and n represents 1 or 2, depending on the valency of Y, and B represents the compound CaXq wherein X represents oxygen or chloride and q represents 1 or 2, depending on the valency of X, with the proviso that at least one of the two anionic components X and Y should contain oxygen.

2. A process as claimed in claim 1, wherein the catalyst system is used in an amount of from 0.01 to 10% by weight, based on the alcohol used.

3. A process as claimed in either of Claim 1 and claim 2, wherein the compound A in the catalyst system is used in an amount of from 5 to 95% by weight whilst compound B is used in an amount of from 95 to 5% by weight, based on the alcohol used

4. A process as claimed in any one of claims 1 to 3, wherein the catalyst system comprises one or more of the combinations calcium oxide and lithium oxide, calcium oxide and lithium hydroxide, calcium oxide and lithium methoxide calcium oxide and lithium tert.butoxide, calcium oxide and lithium acetate, calcium oxide and lithium chloride, calcium oxide and lithium bromide, calcium oxide and lithium iodide, calcium oxide and lithium chlorate, and calcium chloride and lithium methoxide.

5. A process as claimed in any one of claims 1 to 4, wherein the reaction time is 5-20 hours.

6. A process as claimed in claim 5 wherein the reaction time is 6-1 2 hours.

7. A process as claimed in any one of claims 1 to 6, wherein the acrylic or methacrylic acid ester of the C14 alcohol is used in an excess relative to the alcohol used for transesterification.

8. A process as claimed in claim 7, wherein the acrylic or methacrylic acid ester is used in a 1.5 to lO-fold excess over the alcohol used.

9. A process as claimed in claim 8 wherein the acrylic or methacrylic acid ester is used in a 2.5 fold excess.

10. A process as claimed in any one of claims 1 to 9, wherein transesterification is carried out at a temperature of between 60 and 1 20 C.

11. A process as claimed in any one of claims 1 to 10, wherein the methacrylic acid ester is methyl methacrylate.

1 2. A process as claimed in claim 10, wherein the methanol formed is drawn off azeotropically together with methyl methacrylate in the course of transesterification.

1 3. A process as claimed in any one of claims 1 to 12, wherein the crude transesterification product is obtained in yields of more than 90%, based on the alcohol used.

14. A process as claimed in claim 1 substantially as herein described.

1 5. A process substantially as herein described with reference to the Examples.