GB2177396A

GB2177396A - Selective chlorination of phenolic compounds

Info

Publication number: GB2177396A
Application number: GB8615612A
Authority: GB
Inventors: Serge Ratton
Original assignee: Rhone Poulenc Specialites Chimiques
Current assignee: Rhone Poulenc Specialites Chimiques
Priority date: 1985-06-27
Filing date: 1986-06-26
Publication date: 1987-01-21
Also published as: FR2584068A1; BR8603221A; GB2177396B; FR2584068B1; GB8615612D0

Abstract

Phenolic compounds are selectively chlorinated with gaseous chlorine in the para position relative to the OH group in a molten medium and at a temperature equal to or below 120 DEG C, in the presence of at least 0.1% by weight of an organic sulphur compound, based on the phenolic compound.

Description

SPECIFICATION Process for selective chlorination of phenolic compounds The present invention relates to the chlorination of phenolic compounds using gaseous chlorine.

Chlorination of phenol and substituted phenols, especially the lower chlorophenols, has been known for a very long time.

However, one of the essential characteristics of this chlorination is the formation of several isomers in which the chlorine atoms are attached to the benzene ring at different points; this implies, on the one hand, a difficult subsequent separation of these various isomers and, on the other hand, the formation of proportions of isomers which do not necessarily correspond to what would be economically advantageous, bearing in mind the existing outlets for each of the isomers.

As a result, it is desirable that processes should be available for selective chlorination, especially for selective chlorination in an ortho position or the para position relative to the OH group of the phenolic compound.

U.S. Patent No. 3,920,757 describes the selective chlorination, by means of sulphuryl chloride, of phenolic compounds, in the para position relative to the OH group, in the presence of, on the one hand, certain metal halides or phenolates and, on the other hand, organic sulphur compounds. This process permits a considerable increase in the relative proportion of the chlorophenols having a chlorine atom para to the OH group, relative to the chlorophenols which have a chlorine atom, or atoms, in an ortho position. However, the presence of metal salts in the reaction medium reintroduces problems of separation when the chlorophenols obtained are isolated.

The present invention provides a process for selective chlorination, in the para position relative to the OH group, of phenolic compounds of formula (I):

in which Rl, R2, R3 and R4 are the same or different and each is hydrogen, chlorine, hydroxy, straight or branched alkyl of 1 to 4 carbon atoms, straight or branched alkoxy of 1 to 4 carbon atoms, or a -CHO group, provided that not more than three of Rl, R2, R3 and R4 simultaneously denote chlorine, not more than two of R, R2, Ra and R4 simultaneously denote alkyl or alkoxy, and not more than one of R1, R2, R3 and R4 denotes OH or -CHO, which process comprises contacting the said phenolic compound, in the molten state at a temperature equal to or below 1 20"C, with gaseous chlorine in the presence of at least 0.1% by weight of an organic sulphur compound, based on the said phenolic compound.

The organic sulphur compound used in the new process is liquid or solid under the conditions of the process and preferably belongs to one of the following three groups: A)-Organic sulphides of formula: Rs-S-R6 (oil) in which Rs and R6, which are identical or different, each denote:: phenyl; phenyl containing 1 to 3 substituents, which are identical or different, such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen atom, and hydroxyl; phenylalkyl in which the linear or branched aliphatic part contains 1 to 6 carbon atoms; phenylalkyl in which the linear or branched aliphatic part contains 1 to 6 carbon atoms and in which the cyclic part contains 1 to 3 substituents, which are identical or different, such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen, and hydroxyl; cyclopenty or cyclohexyl; cyclopentyl or cyclohexyl containing 1 to 3 identical or different substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen, and hydroxyl;; a phenylthiophenyl radical in which each ring is unsubstituted or substituted by 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; or linear or branched alkyl of 1 to 18 carbon atoms; or Rs and R6 together form a divalent, linear or branched aliphatic radical containing 4 to 8 carbon atoms, which is saturated or contains 1 or 2 ethylenic double bonds.

B)-Dithiosphosphoric compounds of formula:

in which R7, R8 and Rg, which are identical or different, each denote: linear or branched alkyl of 1 to 18 carbon atoms; phenyl; phenyl containing 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; phenylalkyl in which the aliphatic part contains 1 to 6 carbon atoms; a phenylalkyl radical in which the aliphatic part contains 1 to 6 carbon atoms and in which the cyclic part contains 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl; cyclopentyl or cyclohexyl; or cyclopentyl or cyclohexyl containing 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; and r9 can also denote hydrogen; C)-Dithiophosphoric organometallic compounds of formula:

in which M denotes a divalent metal such as zinc, manganese, calcium, barium, magnesium, strontium, cadmium or mercury, and Rlo, Rill, R12 and R,3, which are identical or different, each denote:: linear or branched alkoxy of 1 to 18 carbon atoms; cyclohexyloxy or cyclopentyloxy; cyclohexyloxy or cyclopentyloxy containing 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl; phenylalkoxy in which the alkoxy part contains 1 to 6 carbon atoms; phenylalkoxy in which the alkoxy part contains 1 to 6 carbon atoms and the cyclic part contains 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; phenoxy; phenoxy containing 1 to 3 substituents such as alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl.

In the organic sulphide group (A) a distinction may be made between three subgroups: a) The compounds of formula (II), in which R5 and RG each denote phenyl, phenyl containing a substituent or substituents as indicated earlier, phenyalkyl, phenylalkyl containing a substituent or substituents as indicated earlier, phenylthiophenyl, or phenylthiophenyl containing a substituent or substituents as indicated earlier.

The compounds of this subgroup (A)(a) are particularly suitable for use in the present process.

Examples of these compounds are: diphenyl sulphide, phenyl 4-phenylthiophenyl sulphide, phenyl 4-chlorophenyl sulphide, di(4-chlorophenyl) sulphide, di(4-hydroxy-3,5-dimethylphenyl) sulphide, di(2-hydroxy-4, 6-ditert-butylphenyl) sulphide, and di(2-hydroxy-3,5-ditert-butylphenyl) sulphide.

b) The compounds of formula (II) in which: R5 denotes phenyl, phenyl containing a substituent or substituents as indicated earlier, phenylalkyl, phenylalkyl containing a substituent or substituents as indicated earlier, phenylthiophenyl, or phenylthiophenyl containing a substituent or substituents as indicated earlier; and R6 denotes linear or branched alkyl of 1 to 18 carbon atoms, cyclopentyl or cyclohexyl, or cyclopentyl or cyclohexyl containing a substituent or substituents as indicated earlier.

Examples of these compounds are: phenyl cyclohexyl sulphide, phenyl butyl sulphide, 4-chlorophenyl hexyl sulphide, 4-methylphenyl dodecyl sulphide, benzyl octyl sulphide, 4-methoxyphenyl ethyl sulphide, and phenyl stearyl sulphide.

The compounds of this subgroup (A)(b) are also highly suitable for use in the process of the invention.

c) The compounds of formula (Il) in which: R5 and R6 each denote a linear or branched alkyl of 1 to 18 carbon atoms, cyclopentyl or cyclohexyl, or cyclopentyl or cyclohexyl containing a substituent or substituents as indicated earlier; or R5 and R6 form a divalent, linear or branched aliphatic radical containing 4 to 8 carbon atoms, saturated or containing 1 or 2 ethylenic double bonds.

The alkyl radicals are chosen so that the organic sulphide is liquid or solid under the conditions in which the process is used.

Examples of these compounds are: ethyl cyclohexyl sulphide, dihexyl sulphide, ethyl hexyl sulphide, dioctyl sulphide, ethyl dodecyl sulphide, butyl stearyl sulphide, propyl 4-methylcyclohexyl sulphide, methyl 4-chlorocyclohexyl sulphide, thiophene, and tetrahydrothiophene.

Examples of dithiophosphoric compounds (B) of formula (III) are: di(O-isobutyl) S-hexyldithiophosphate, di(O-propyl) S-octyldithiophosphate, di(O-hexyl) S-ethyldithiophosphate, di(O-octyl) S-butyldithiophosphate, di(O-phenyl) S-phenyldithiophosphate, di(O-benzyl) S-isobutyldithiophosphate, O-phenyl O-hexyl S-ethyldithiophosphate, di(O-isobutyl) dithiophosphate, di(O-cyclohexyl) dithiophosphate, di(O-dodecyl) dithiophosphate, and di(O-4-dodecylphenyl) S-1 -phenylethyldithiophosphate.

Examples of dithiophosphoric organometallic compounds (C) of formula (IV) are the compounds described in U.S. Patents Nos. 2,680,123, 2,838,555 and 4,113,634.

The dithiophosphoric compounds of formulae (III) and (IV) may be prepared, in particular, by first reacting phosphorus pentasulphide with an alcohol, a phenol, a mixture of alcohols, a mixture of phenols, or a mixture of alcohols and phenols, so as to form di-O-esters of dithiophosphoric acid.

These di-O-esters of dithiophosphoric acid can then be: either used as such (i.e. as compounds of formula Ill in which R9 denotes a hydrogen atom), or S-esterified with an alcohol or a phenol to form the dithiophosphoric compounds of formula (III) in which R9 denotes a radical other than a hydrogen atom, or converted into salt form with a metal M oxide or hydroxide in order to form a compound of formula (IV).

U.S. Patents Nos. 2,680,123, 2,838,555 and 4,113,634 describe, in particular, processes for the preparation of compounds of formulae (III) and (IV).

The following may be mentioned specially among the phenolic compounds of formula (I) to which the process of the invention may be applied: phenol, 2-chlorophenol, 3-chlorophenol, 2,6-dichlorophenol, 2,3-dichlorophenol, 2,5-dichlorophenol, 2,3,5-trichlorophenol, 2,3,6-trichlorophenol, guaiacol, 2-ethoxyphenol, pyrocatechol, resorcinol, 3-methoxyphenol, 3-ethoxyphenol, ortho-cresol, meta-cresol, 2-ethylphenol, 3-ethylphenol, and 2-hydroxy-3-methoxybenzaldehyde.

The temperature at which the process of the invention is used is, in most cases, equal to or less than 100"C. In fact, as a general rule, the selectivity of the chlorination in the para position is proportionately better the lower the temperature. However, since the medium needs to be in the molten state, it is difficult to operate at excessively low temperatures. Consequently, the process is preferably carried out at a temperature of between 30 C and 80 C.

The molar ratio of chlorine to phenolic compound is usually less than or equal to 1.5 To avoid a more pronounced dichlorination of the phenolic compound, this ratio is preferably in the stoichiometric region, that is to say generally between 0.8 and 1.1.

The chlorine may be used by itself or may be diluted with an inert gas such as nitrogen, for example. The presence of an inert gas makes it possible to modify the gas flow rate, if desired, while maintaining the chlorine/phenolic compound ratio.

The process of the invention may be carried out non-continuously or continuously.

The following Examples illustrate the present invention.

EXAMPLE 1 and comparative test A The following are introduced into a 100-cm3 glass reactor fitted with a stirrer, a condenser, a dip tube permitting the delivery of gaseous chlorine, and a thermometer: 47.0 g of phenol (0.5 mole), 0.5 g of diphenyl sulphide (0.0027 mole).

The temperature is raised to 50 C, with stirring. While the test is maintained at this temperature, the reaction medium is supplied with gaseous chlorine through the dip tube.

The test is continued until the molar ratio of chlorine introduced to the phenol added reaches 0.8. Time at 50 C: 2 h 15 min.

The reaction mixture is then cooled to ambient temperature and its various constituents are estimated by gas phase chromatography.

The results obtained are collated in Table I below.

The same test is repeated without diphenyl sulphide (time at 50 C 2 h 15 min); the results of this comparative test are also collated in Table I.

The abbreviations used are as follows: DC =degree of conversion (of phenol), % CY =% yield based on the converted phenol PCP = para-chlorophenol OCP = ortho-chlorophenol 2,4-DCP = 2,4-dichlorophenol 2,6-DCP = 2,6-dichlorophenol.

TABLE I

diphenyl DC of CY of CY of CY of CY of para/ortho Tests sulphide T C phenol PCP OCP 2,4-DCP 2,6-DCP selectivity in g % % % % % I ~~~~~ I ~~~~ I ~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I I I I I I I I I I I I I Example 1 0.5 50 C 72.7 66.5 21.7 11.3 0.55 3.04 Compara tive test 0 50 C 75.2 54.5 34.3 10.65 0.55 1.59 A para-chlorophenol/ortho-chlorophenol molar ratio.

EXAMPLE 2 and comparative test B The apparatus used is the same as in Example 1. The following are introduced: 47.0 g of phenol (0.5 mole) 0.5 g of diphenyl sulphide (0.0027 mole).

Temperature: 50 C.

The chlorine introduced is diluted with nitrogen (gases premixed): rate of supply of chlorine: 5 litres/hour; rate of supply of nitrogen: 45 litres/hour.

The test is continued until the molar ratio of chlorine introduced to phenol added is 0.8. Time at 50 C: 2 h 15 min.

The results obtained are collated in Table II below.

The same test is repeated, but with the further addition of 0.5 g of aluminium chloride (time at 50 C: 2 h 15 min); the results of this comparative test are also collated in Table II.

TABLE II

diphenyl Al DC of CY of CY of CY of CY of para/ortho Tests sulphide chloride T C phenol PCP OCP 2,4-DCP 2,6-DCP selectivity in g % % % % % 1 I ~~~~ I ~~~~~ I ~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~~~ | Example 2 0.5 0 50 C 81.4 77.65 20.15 2.25 0.035 1.85 | ~~~~~ I 1 I ~~~~~ I ~~~~ I ~~~~ I~~~~ | ~~~~ I~~~~ I ~~~~ I ~~~~~~ I | | | | | | | | | | I Cc-Oars- I I I I I I I I I I tive test 0.5 0.5 50 C 76.2 76.8 19.7 3.1 0.18 3.09 B EXAMPLES 3 to 6 The same apparatus and the same procedure as in Example 1 are used.

The differences between the tests relate to: the temperature at which the chlorination is carried out, and the sulphur compound used: diphenyl sulphide (DPS) methyl phenyl sulphide (MPS).

The main parameters of these tests and the results obtained are collated in Table III below; Example 1 has been recorded in this table by way of comparison.

TABLE III

Examples Sulphur T C DC of CY of CY of CY of CY of para/ortho compound (time) phenol PCP OCP 2,4-DCP 2,6-DCP selectivity in g % % % % % DPS 50 C Example 1 0.5 (2 h 15) 72.7 66.5 21.7 11.3 0.55 3.06 MPS 50 C Example 3 0.5 (2 h 15) 74.3 62.8 25.8 10.6 0.55 2.43 DPS 80 C Example 4 0.5 (2 h 15) 68.6 60.0 25.8 13.6 0.60 2.32 DPS 100 C Example 5 0.5 (2 h 15) 72.6 57.2 29.9 12.3 0.60 1.91 MPS 100 C Example 6 0.5 (2 h 15) 74.0 60.9 29.7 8.7 0.40 2.05 EXAMPLES 7 and 8 The same apparatus as in Example 1 and the same procedure as in Example 2 are used, that is to say the chlorine gas is diluted with nitrogen (same flow rates as in Example 2).

Example 7 is performed with di(4-chlorophenyl) sulphide (DCPS).

Example 8 is performed with di(2-hydroxy-3,5-di-tert-butylphenyl) sulphide (HTPS).

The results obtained in both examples are collated in Table IV below, together with those of Example 2, for comparison.

TABLE IV

Examples Sulphur T C DC of CY of CY of CY of CY of para/ortho compound (time) phenol PCP OCP 2,4-DCP 2,6-DCP selectivity in g % % % % % | ~~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ ~~~~~~ DPS 50 C Example 2 0.5 (2 h 15) 81.4 77.65 20.15 2.25 0.035 3.85 I ~~~~~~~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~ I ~~~~~~~~~~~~~~~~ I ~~~~~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~ I ~~~~~~~~~~~~~~~~~~ I ~~~~~~~~~~~~~~~~~~ I ~~~~~~~~~~~~~~~~~~ I I I I I | I I I I I I DCPS 50 C Example 7 0.5 (2 h 15) 80.0 74.2 22.8 2.95 0.065 3.25 I ~~~~~ I ~~~~ I ~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~ I ~~~~~ | ~~~~~~~ I MTPS 50 C Example 8 0.5 (2 h 15) 79.7 73.3 24.2 2.35 0.15 3.03 EXAMPLES 9 and 10 The same apparatus and the same procedure as in Example 1 are used.

The difference between the tests relates to the quantity of the diphenyl sulphide added (and hence the diphenyl sulphide/phenol weight ratio).

The results obtained in these two examples are collated in Table V below, together with those of Example 1, for comparison.

TABLE V

Sulphur Examples compound T C DC of CY of CY of CY of CY of para/ortho in g (time) phenol PCP OCP 2,4-DCP 2,6-DCP selectivity % % % % % | 1 1 I I I I I 1 50 C Example 9 0.1 (2 h 15) 72.2 63.8 26.2 9.5 0.45 2.44 50 C Example 1 0.5 (2 h 15) 72.7 66.5 21.7 11.3 0.55 3.06 | | I I I I I I I 50 C Example 10 2.5 (2 h 15) 69.1 66.7 21.3 11.6 0.55 3.13 EXAMPLES 11 to 13 The same apparatus as in Example 1 and the same procedure as in Example 2 are used, that is to say the chlorine gas is diluted with nitrogen (same flow rates as in Example 2).

Example 12 is performed with:

Example 13 is performed with:

The results obtained are collated in Table VI below. TABLE VI

Sulphur DC of CY of CY of CY of CY of para/ortho Examples T C compound phenol PCP OCP 2,4-DCP 2,6-DCP selectivity (time) in g % % % % % I ~~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ I ~~~~ I 1 I ~~~~ I ~~~~~~ I I I I I I I I I I I 50 C | I I I I I I Example 11 0.5 (2 h 15) 81.1 65.3 30.5 3.9 0.30 2.14 50 C Example 12 0.5 (2 h 15) 78.1 67.95 27.1 4.6 0.30 2.50 | I I I I I I I I I I I 50 C I I I I I I I Example 13 0.5 (2 h 15) 73.15 64.55 28.1 6.7 0.50 2.30

Claims

1. A process for the selective chlorination, in the para position relative to the OH group, of a phenolic compound of the formula:

in which R1, R2, Ra and R, are the same or different and each is hydrogen, chlorine, hydroxy, straight or branched alkyl of 1 to 4 carbon atoms, straight or branched alkoxy of 1 to 4 carbon atoms, or a -CHO group, provided that not more than three of R1, R2, Ra and R4 simultaneously denote chlorine, not more than two of Rl, R,, Ra and R4 simultaneously denote alkyl or alkoxy, and not more than one of Rl, R::, Ra and R4 denotes OH or -CHO, which process comprises contacting the said phenolic compound, in the molten state at a temperature equal to or below 120 C with gaseous chlorine in the presence of at least 0.1% by weight of an organic sulphur compound, based on the said phenolic compound.

2. Process according to claim 1, in which the said organic sulphur compound is an organic sulphide which is liquid or solid under the conditions of the process, and has the formula: R5-S-R6 (II) in which: R and Rx, which are identical or different, each denote:: phenyl; phenyl containing 1 to 3 substituents, which are identical or different, chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen atom, and hydroxyl; phenylalkyl in which the linear or branched aliphatic part contains 1 to 6 carbon atoms; phenylalkyl in which the linear or branched aliphatic part contains 1 to 6 carbon atoms and in which the cyclic part contains 1 to 3 substituents, which are identical or different, chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen, and hydroxyl; cyclopenyl or cyclohexyl; cyclopentyl or cyclohexyl containing 1 to 3 identical or different substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen, and hydroxyl;; a phenylthiophenyl radical in which each ring is unsubstituted or substituted by 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; or linear or branched alkyl of 1 to 18 carbon atoms; or R, and R6 together form a divalent, linear or branched aliphatic radical containing 4 to 8 carbon atoms, which is saturated or contains 1 to 2 ethylenic double bonds.

3. Process according to claim 1, in which the said organic sulphur compound is a dithiophosphoric compound which is liquid or solid under the conditions of the process, and has the formula:

in which R7, R8 and R9, which are identical or different, each denote: linear or branched alkyl of 1 to 18 carbon atoms; phenyl; phenyl containing 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; phenylalkyl in which the aliphatic part contains 1 to 6 carbon atoms; a phenylalkyl radical in which the aliphatic part contains 1 to 6 carbon atoms and in which the cyclic part contains 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl; cyclopentyl or cyclohexyl; or cyclopentyl or cyclohexyl containing 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; and R. can also denote hydrogen.

4. Process according to claim 1, in which the said organic sulphur compound is a dithiophosphoric organometallic compound, which is liquid or solid under the conditions of the process, and has the formula:

in which M denotes a divalent metal; and R,l,, R", R,? and Ria, which are identical or different, each denote: linear or branched alkoxy of 1 to 18 carbon atoms; cyclohexyloxy or cyclopentyloxy; cyclohexyloxy or cyclopentyloxy containing 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl; phenylalkoxy in which the alkoxy part contains 1 to 6 carbon atoms; phenylalkoxy in which the alkoxy part contains 1 to 6 carbon atoms and the cyclic part contains 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or hydroxyl; phenoxy; phenoxy containing 1 to 3 substituents chosen from alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen and hydroxyl.

5. Process according to claim 2, in which the organic sulphur compound used is an organic sulphide of formula II which is liquid or solid under the conditions of the process, and in which R and R6 each denote phenyl, substituted phenyl as defined in claim 2, phenylalkyl, substituted phenylalkyl as defined in claim 2, phenylthiophenyl, or substituted phenylthiophenyl as defined in claim 2.

6. Process according to claim 2, in which the organic sulphur compound used is an organic sulphide of formula Il which is liquid or solid under the conditions of the process, and in which: Rs denotes phenyl, substituted phenyl as defined in claim 2, phenylalkyl, substituted phenylalkyl as defined in claim 2, phenylthiophenyl, or substituted phenylthiophenyl as defined in claim 2, and R6 denotes: a linear or branched alkyl of 1 to 18 carbon atoms, cyclopentyl or cyclohexyl, or substituted cyclopentyl or cyclohexyl as defined in claim 2.

7. Process according to claim 1, in which the organic sulphur compound used is: diphenyl sulphide, phenyl 4-phenylthiophenyl sulphide, phenyl 4-chlorophenyl sulphide, di(4-chlorophenyl) sulphide, di(4-hydroxy-3,5-dimethylphenyl) sulphide, di(2-hydroxy-4,6-ditert-butylphenyl) sulphide, or di(2-hydroxy-3,5-ditert-butylphenyl) sulphide.

8. Process according to any one of claims 1 to 7, in which the chlorination is carried out at a temperature equal to or less than 100"C.

9. Process according to claim 8 in which the chlorination is effected at 30"C to 80"C.

10. Process according to any one of claims 1 to 9, in which from 0.1 to 10% by weight of the organic sulphur compound is used, based on the phenolic compound of formula (I).

11. Process according to claim 10 in which 0.5 to 296 by weight of the said organic sulphur compound is used based on the phenolic compound of formula (I).

12. Process according to any one of claims 1 to 11, in which the phenolic compound of formula (I) which is chlorinated is phenol, s-chlorophenol, 3-chlorophenol, 2,6-dichlorophenol, 2,3-dichlorophenol, 2,5-dichlorophenol, 2,3,5-trichlorophenol, 2,3,6-trichlorophenol, guaiacol, 2-ethoxyphenol, pyrocatechol, resorcinol, 3-methoxyphenol, 3-ethoxyphenol, ortho-cresol, meta-cresol, 2-ethylphenol, 3-ethylphenol, or 2-hydroxy-3-methoxybenzaldehyde.

13. Process according to claim 1 substantially as described in any one of the foregoing Examples.

14. A para-chlorinated phenolic compound when produced by the process of any of the preceding claims.