Production of ethylenically unsaturated acids or esters thereof

1. A production process for the manufacture of ethylenically unsaturated acids or esters thereof, by reaction of an alkanoic acid, or ester of an alkanoic acid, of the formula R 3 —CH 2 —COOR 4 where R 3 and R 4 are each independently hydrogen or an alkyl group, in the presence of a catalyst system to produce said ethylenically unsaturated acid or ester product characterised in that the acid or ester product is subsequently contacted with a dienophile to thereby remove discolouration therefrom; wherein the dienophile is different from said ethylenically unsaturated ester or acid product.

2. A production process according to claim 1 , wherein the dienophile is a compound of formula I

wherein Z is selected from the group consisting of —C(O)Y, —CN, —NO 2 or halo, wherein Y is selected from the group consisting of hydrogen, alkyl, hetero, —OR, halo or aryl, wherein R, R 1 and R 2 independently represent hydrogen, alkyl or aryl and hetero represents N, S or O which hetero atoms may be unsubstituted or substituted with one or more of the groups consisting of hydrogen, alkyl, —OR, aryl, aralkyl or alkaryl, wherein R is as defined for Y above; Z′ may be any one of the groups selected for Z above or may additionally be hydrogen, alkyl, aryl or hetero; or Z and Z′ may together be —C(O)Y(O)C— so that the dienophile forms a cyclic group of formula Ia

wherein R 1 and R 2 are as defined above, Y is hetero as defined above or Y represents an alkylene group of formula —(CH 2 ) S — wherein S is 1, 2 or 3.

3. A production process according to claim 1 , wherein the ethylenically unsaturated acids or esters are selected from a C 0-8 alk acrylic acid or alkyl (C 0-8 alk)acrylate.

4. A production process according to claim 1 , wherein the reaction is that of an alkanoic acid or ester thereof with a methylene or ethylene source such as a source of formaldehyde in the presence of the catalyst system.

5. A production process according to claim 2 , wherein R 1 and R 2 are independently selected from hydrogen or alkyl.

6. A production process according to claim 2 wherein when one of R 1 or R 2 is alkyl, the other is hydrogen.

7. A production process according to claim 2 , wherein both R 1 and R 2 are hydrogen.

8. A production process according to claim 1 , wherein DETA treatment of the acid or ester product also takes place in a separate step than contact with a dienophile.

9. A production process according to claim 8 , wherein the dienophile concentration and, if present, the DETA concentration is selected so that a suitable excess is present for their respective uses.

10. A production process according to claim 1 , wherein the dienophile is present in the range 10 to 50,000 ppm by weight in the crude product to be treated.

11. A production process according to claim 1 , wherein the dienophile is selected from the list consisting of:—

maleic anhydride, maleimide, thiophen-2,5-dione, acrylic acid, acrolein, alkyl acrylates, acrylonitrile, maleic acid, dialkyl maleate and vinyl halides.

12. An ethylenically unsaturated acid or ester crude product purification process characterised in that the acid or ester crude product is contacted with a dienophile to remove at least one colour forming impurity therefrom.

13. A process for preparing and purifying an ethylenically unsaturated acid or ester of the following formula:—

R 3 —C(═(CH 2 ) m )—COOR 4

wherein R 3 and R 4 are defined in the same way as for the alkanoic acid or ester above; and m is 1 or 2;

the process comprising the steps of—

a) contacting an alkanoic acid or ester of the formula R 3 —CH 2 —COOR 4 , wherein R 3 and R 4 are as already defined above, with a methylene or ethylene source of formula I,

where R 5 and R 6 are independently selected from C 1 -C 12 hydrocarbons, preferably, C 1 -C 12 alkyl, alkenyl or aryl as defined herein, or H, more preferably, C 1 -C 10 alkyl, or H, most preferably, C 1 -C 6 alkyl or H, especially, methyl or H;

X is either O or S, preferably, O;

n is an integer from 1 to 100, preferably, 1 to 10, more preferably 1 to 5, especially, 1-3;

and m is 1 or 2, preferably 1;

in the presence of a suitable catalyst and optionally in the presence of an alcohol to produce an impure ethylenically unsaturated acid or ester of the formula:—

R 3 —C(═(CH 2 ) m )COOR 4 ;

b) subsequently contacting the impure ethylenically unsaturated acid or ester of step (a) with a dienophile to thereby remove discolouration therefrom; wherein the dienophile is different said ethylenically unsaturated ester or acid product.