GB2153819A

GB2153819A - Selective halogenation of benzene di- and tri-methanol compounds; novel halomethyl-benzene methanols

Info

Publication number: GB2153819A
Application number: GB08500671A
Authority: GB
Inventors: Alan Thomas Costello; David John Milner
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1984-02-10
Filing date: 1985-01-11
Publication date: 1985-08-29
Also published as: DE3585632D1; EP0152174A3; HU198664B; NZ210864A; GB8403548D0; EP0152174A2; GB2153819B; EP0152174B1; GB8500671D0; ATE73751T1; JPH0453853B2; AU3774385A; CA1269400A; JPS60184035A; AU568903B2; HUT39695A; US4590308A

Abstract

Benzene di- and tri-methanol compounds are selectively halogenated by reaction in aqueous solution at 70 to below 100 DEG C with HCl or HBr in the presence of a water immiscible solvent eg. toluene. The process is particularly suitable for the preparation of 4-bromo- and 4-chloromethyl-2,3,5,6-tetrafluorobenzene methanols which are believed to be novel compounds and useful in the synthesis of pesticidal compounds.

Description

1 GB 2 153 819 A 1

SPECIFICATION

Selective halogenation of benzene di- and tri-methanol compounds This invention relates to a process for the selective halogenation of benzene di- and tri-methanol compounds. The compounds obtained by the process are useful as chemical intermediates in, for exampl'e, the synthesis of pesticidal products. The invention includes certain of the compounds, themselves, which are novel.

According to the present invention there is provided a process for the monohalogenation of a compound le; of the formula (I):

0-(C1-1,0H (I) R 15 in which R is any substituent other than a substituent that has a significant water solubilising effect on compound (11), as hereinafter defined, or that is halogenated under the conditions of the process, m is zero or an integer of from 1 to 4 and n is 2 or 3, to form a compound of the formula (II):

CH2X 20 (CH 011 25 2)n-1 in which X is bromine or chlorine and R, m and n have the meanings already given, which process comprises reacting an aqueous solution of compound (1) with hydrochloric or hydrobromic acid in the presence of a 30 water immiscible organic solvent which is inert to the reactants, the partition coefficient of compound (1) in the aqueous/organic phases being greater, with respect to the aqueous phase, than the partition coeff icient of compound (11).

By "partition coefficient" is meant the ratio of the equilibrium concentrations of a substance dissolved in two immiscible solvents. In this case, the partition coefficients of compounds (1) and (11) are the ratios of their equilibrium concentrations in the aqueous phase to their equilibrium concentration in the organic phase.

The water immiscible organic solvent is selected so that sufficient of compound (1) resides in the aqueous phase to undergo halogenation, and compound (11) has a substantially higher preference for the organic phase than compound (1) to avoid over-halogenation. In principle, compound (1) could reside largely in the organic phase provided the partitions of compounds (1) and (11) between the two phases are sufficiently different, Ideally, compound (1) is soluble in the aqueous but not the organic phase and compound (11), vice versa.

The substituent R will also have an effect on the partition coefficients of compounds (1) and (11) and substituents, such as sulphonic acid groups, which will significantly increase the solubility of compound (11) 4.5 in the aqueous phase should be avoided. Substituents which R may be include alkyl, especially C1-4 alkyl, 45 alkoxy, especially C1-4 alkoxy, formyl, alkylcarbonyl, especially C1-4 alkylcarbonyl, nitro and halogen.

The process of the invention is of particular interest forthe monohalogenation of compounds (1) in which n is 2, especially when the hydroxymethyl groups are in positionspara to each other, and more especially when R,, is C14 or F4. In particular, the process may be used for the preparation of 4-ch I oro rn ethyl -2,3,5,6 tetrafluorobenzene methanol and 4-bromo methyl-2,3,5,6-tetraf I uo ro benzene methanol which are novel compounds and form another aspect of the present invention.

The process may be conveniently carried out by mixing together an aqueous solution of compound(l), hydrochloric or hydrobromic acid and the water immiscible solvent and heating them with stirring to a temperature of 70'C or above, but below 1 OOOC. If preferred, compound (1) may be dissolved in aqueous acid rather than separately in water, and then mixed with the solvent. The mixture is stirred and maintained at the 55 desired temperature until reaction is judged complete, for example, by sampling the aqueous layer at intervals to determine the amount of unreacted compound (1) remaining. The aqueous and organic layers may then be separated, the organic layer dried and the solvent removed by evaporation to obtain the compound (11). Alternatively, a counter-current extraction process may be used, in which compound (11) is continuously extracted as it is formed by solvent passed through the aqueous medium. Such extraction techniques are known and descibed in, for example, OPP[ Briefs, 15(1-2), 63-70 [19831; Org.Synth.Coll,Vol., 3,446-8 [19551 and JACS, 72, 5137-8 [1950].

The strength of the aqueous solution of compound (1) is not critical; typically there is about 10% by weight of compound (1) in the total aqueous phase.

2 GB 2 153 819 A 2 The amount of acid used should be in excess of 1 mol and is preferably from 4 to 5 mols of acid per mol of compound (1).

Any solvent having a boiling point above the reaction temperature may be used, provided that it is inertto the reactants and satisfies the requirements with regard to partition coefficients of compounds (1) and (11) as discussed earlier. Toluene is ideal but it is envisaged that other solvents may be used such as xylene, higher 5 boiling petroleum fractions and chlorinated hydrocarbons. When a continuous extraction process is used, the solvent is preferably lighter than water.

The amount of solvent is not critical. Conveniently sufficient is used to obtain about a 10% solution of compound (11) and hence the aqueous and solvent phases will usually be of approximately equal volume.

1() The starting material, compounciffl, maybe obtained by reduction of the halide of the corresponding di- or 10 tri-carboxylic acid. A process for preparing 2,3,5,6-tetrafluorobenzene-1,4-dimethanol is described in UK Patent Specification No. 2127013. The corresponding tetrachloro compound may be obtained by reduction of tetrachloroterephthaloyl chloride which is commercially available. When reduction of the acid halide is carried out in a water miscible solvent, e.g. when using NaBH4 in diglyme, the reduction mixture may be used directly in the process of the invention without isolation of the benzene di- ortri-methanol compound.is The compounds (11), obtained by the process of the invention, are useful as chemical intermediates for the synthesis of various products. For example, 4-bromo- and 4-chloromethy]-2,3,5,6-tetrafluorobenzene methanols are precursors of 4-methyl-2,3,5,6-tetraf 1 u o ro benzene methanol which is useful in the preparation of pesticidal compounds. In this case, reduction of the 4-bromo- and 4-ch lo ro methyltetraf 1 u o ro benzene methanols to the corresponding 4-methyl compound may proceed using the solvent solutions without prior 20 isolation of the 4-bromo- and 4- chloromethyl compounds.

The invention is illustrated by the following two Examples in which percentages are by weight.

EXAMPLE 1

Preparation of 4-chloromethyl-2,3,5,6-tetrafluorobenzene methanol 2,3,5,6-Tetrafluoro-1,4-benzene dimethanol (lg; 4.8m. mol) was added to hydrochloric acid 360Tw (10 mi, 115m.mol) at 20'C,followed bytoluene (10 m[). The mixturewasthen stirred and warmed to 90'C and maintained at this temperature for 7 hoursto completethe reaction.

The mixture was then cooled and the stirring stopped. After being allowed to settle, the lower aqueous layer was runoff. The toluene layer was dried over magnesium sulphate and the solvent removed under 30 reduced pressure to give a pale coloured solid (0.65g; 60% yield).

The aqueous layer was extracted with ether (2 x 10 m]), the extracts combined and the ether removed under reduced pressure to give 0.2g of starting material.

The yield of product in terms of diol consumed was 75%.

EXAMPLE 2

Preparation of 4-bromomethyl-2,3,5,6tetrafluorobenzene methanol 2,3,5,6-Tetrafluoro-1,4-benzene dimethanol (19; 4.8m.mol) was added to water (5mi). Hydrobromic acid 48% (5m1; 47 m.mol) was then added followed bytoluene (10mi). The mixture was stirred and warmed to 85 to 90'C and maintained at this temperature for 4 hours. The mixture was then cooled, the agitation stopped 40 and the toluene layer separated.

The toluene was dried over magnesium sulphate and removed under reduced pressure to give a cream coloured solid (0.7g; yield 54%).

The aqueous layer was extracted with ether (2 x 10mi) and the ether removed under reduced pressure to give 0.5g of starting material. The yield of product in terms of material consumed was 100%.

Claims

1. A process for the monohal.ogenation of a compound of the formula ffl:

50 "0- (CH20H) n (I) R, 55 in which R is any substituent other than a substituent that has a significant water solubilising effect on compound (11), or that is halogenated under the conditions of the process, m is zero or an integer of from 1 to 3 4 and n is 2 or 3, to form a compound of the formula (1l):

CH2X RM GB 2 153 819 A 3 61 -- (CH20F.1)n-1 (11) in which X is bromine or chlorine and R, m and n have the meanings already given, which process comprises reacting an aqueous solution of compound (1) with hydrochloric or hydrobromic acid in the presence of a water immiscible organic solvent which is inert to the reactants, the partition coefficient of compound (1) in the aqueous/organic phases being greater, with respect to the aqueous phase, than the partition coefficient 15 of compound (11).

2. A process according to claim 1 in which R is selected from the group comprising alkyl, alkoxy, formyl, alkylcarbonyl, nitro and halogen.

3. A process according to claim 1 in which Rn is C14 or F4 and n is 2.

4. A process according to claim 3 in which the hydroxymethyl groups are in positions para to each other. 20

5. A process according to anyone of the preceding claims in which the water immiscible organic solvent is toluene.

6. A process according to anyone of the preceding claims in which the reaction is carried out at a temperature of from 70'Cto below 100T.

7. A process substantially as herein described with reference to Example 1 or 2.

8. 4-Ch I oro m ethyl -2,3,5,6-tetrafl uo ro benzene methanol.

9. 4-Bromomethyl-2,3,5,6-tetrafluorobenzene methanol.

Printed in the UK for HMSO, D8818935, 7185, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A IlAY, from which copies may be obtained.