PROCESS FOR THE PREPARATION OF TAUTOMERIC FORMS OF SUNSCREENS

Abstract

The compound of Formula 1

##STR00001##

is obtained efficiently and cheaply from the mixture of tautomeric forms by crystallisation from methanol.

Claims

1. A process for the preparation of the compound of formula 1 ##STR00005## comprising crystallizing from methanol a tautomer mixture obtained by reacting cyanuryl chloride with 2-ethylhexyl p-aminobenzoate.

2. Process according to claim 1 wherein the weight ratio of the tautomer mixture to methanol is 25% to 35%.

3. Process according to claim 1, wherein the crystallizing step is carried out by cooling to 15° C. the mixture solution heated to the boiling point of methanol.

4. Process according to claim 1 wherein the tautomer mixture is added to methanol in solid form.

5. Process according to claim 1 wherein the tautomer mixture is added to methanol in the molten state.

6. Product of formula 1 obtained by the process according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 shows the IR spectrum of the tautomer mixture of Formula I in molten state.

[0007] FIG. 2 shows the IR spectrum of the ground solid product of the tautomer mixture of Formula 1.

[0008] FIG. 3 shows the IR spectrum of crystallized and filtered compound Formula 1.

[0009] FIG. 4 shows the IR spectrum of crystallized and filtered compound of Formula 1.

DESCRIPTION OF THE INVENTION

[0010] It has now surprisingly been found that the compound of Formula 1 can be obtained by crystallising from methanol the tautomer mixture obtainable by reacting cyanuryl chloride with 2-ethylhexyl p-aminobenzoate.

[0011] Methanol is more convenient to use than ethanol for reasons of cost and legislative constraints, as ethanol is subject to specific tax controls which complicate its use for industrial purposes.

[0012] The object of the invention is therefore a process for the preparation of the compound of Formula 1

##STR00004##

comprising crystallisation from methanol of the tautomer mixture obtained by reacting cyanuryl chloride with 2-ethylhexyl p-aminobenzoate.

[0013] The tautomer mixture obtained by reacting cyanuryl chloride with 2-ethylhexyl p-aminobenzoate, the reaction typically being conducted in xylene at reflux, can be discharged from the reactor in the molten state at a temperature of 100-120° C. After cooling, the molten mixture can be added gradually to methanol, preferably at boiling point. Alternatively, the molten mixture can be cooled and ground to any particle size.

[0014] The weight ratio between the tautomer mixture and methanol preferably ranges between 25% and 35%, more preferably between 27% and 31%. The methanol solution can be filtered before cooling (to about 15° C.).

[0015] The invention is illustrated in greater detail in the examples below.

Example 1

[0016] 900 ml of xylol, 22.5 g of cyanuryl chloride and 94.2 g of p-aminobenzoic acid 2-ethylhexyl ester are loaded into a laboratory reactor. The mixture is heated at boiling point for about six hours, and the hydrochloric acid that develops is collected in a dilute soda solution. At the end of the reaction the xylol is distilled, but the reactor is maintained at a temperature of not less than 110/120° C., to obtain a tautomer mixture of Formula 1 in the molten state having the IR spectrum shown in FIG. 1.

Example 2

[0017] 500 ml of benzine with a boiling point higher than 140° C., 11 g of cyanuryl chloride and 50 g of p-aminobenzoic acid 2-ethylhexyl ester are loaded into a laboratory reactor. The mixture is heated to boiling point for about eight hours, and the hydrochloric acid that develops is collected in a dilute soda solution. At the end of the reaction the solvent is distilled, and the reactor is maintained at a temperature of not less than 110/120° C., to obtain a tautomer mixture of Formula 1 in the molten state. The molten mixture is discharged into a flat container and left to cool until solid. The resulting solid product is then ground. The IR spectrum is shown in FIG. 2.

Example 3

[0018] 600 ml of methyl alcohol is loaded into a laboratory reactor and heated to gentle boiling. The tautomer mixture prepared in Example 1 is then gradually dripped into the reactor. The mixture is then cooled to 20° C., and the crystallised product is filtered, to obtain 162 grams of the compound of Formula 1. The IR spectrum of the resulting product is shown in FIG. 3.

Example 4

[0019] 300 ml of methyl alcohol and the solid obtained in Example 2 are loaded into a laboratory reactor. The mixture is heated to boiling until completely dissolved. The mixture is then cooled to 20° C., and the crystallised product is filtered, to obtain 90 grams of the compound of Formula 1. The IR spectrum of the resulting product is shown in FIG. 4.