The present invention relates to a process for the preparation of o-chloromethylbenzoyl chlorides of the general formula I

wherein R is identical or different substituents selected from the group consisting of hydrogen, Cι-C ₆ alkyl and halogen, and n = 0 to 4, preferably 0, by reacting a lactone of formula II

wherein R and n have the meanings stated for formula I, with a chlorinating agent in the presence of catalytic amounts of a phosphine and/or phosphine oxide.

Compounds of formula I are important intermediates for the preparation of pesticides.

The preparation of aromatic o-chloromethyl carbonyl chlorides using phosgene in the presence of an organic nitrogen compound as catalyst is disclosed in EP-583589. EP- 13264 proposes the preparation of chlorocarbonyl chlorides from aliphatic lactones with phosgene in the presence of phosphine oxide.

EP-583589 also discloses that aromatic o-chloromethyl carbonyl chlorides can be prepared from benzocondensated lactones with phosgene with the concomittant introduction of up to 100 mol % of hydrogen chloride, based on the lactone, or of such compounds which form

hydrogen chloride with phosgene, in the presence of an organic nitrogen compound as catalyst.

EP-413264 also discloses that aliphatic chlorocarbonyl chlorides can be prepared by reacting the corresponding aliphatic lactones with phosgene in the presence of a phosphine oxide as catalyst with the additional use of hydrogen chloride.

The disadvantages of this proposed process for a technical synthesis are the additional consumption of hydrogen chloride and the resulting undesirable stripping effects, corrosion damages and exhaust air pollution, as well as the low boiling points of the catalysts which, in particular at elevated reaction temperatures (>150°C), are highly volatile and can deposit on the condensers.

Accordingly, it is the object of this invention to avoid these disadvantages and to develop an environmentally safe method of obtaining aromatic o-chloromethylphenylalkanoyl chlorides and, in particular, o-chloromethylbenzoyl chlorides in high yields. An improved and cost-favourable process for the preparation of o-chloromethylbenzoyl chlorides has now been found which comprises carrying out the reaction of an aromatic lactone of formula II and, preferably, of phthalide (n = 0), with or without solvents, with a chlorinating agent in the temperature range from 80 to 240°C in the presence of a phosphine catalyst and/or phosphine oxide catalyst.

Another advantage is that the catalyst can be reused after being isolated from the reaction mixture.

catalyst

The process of this invention can be described as follows:

The phthalide or lactone of formula II and the arylphosphine catalyst or alkylphosphine catalyst can be placed in a reaction vessel with an inert solvent, but preferably without solvent, and can be reacted with a chlorinating agent in the temperature range from 100 to 240°C, preferably from 100 to 200°C, particularly preferably from 140 to 200°C, and at a pressure of 0.1 to 50 bar, preferably of 1 to 5 bar, particularly preferably at normal pressure. The process can be carried out batchwise or continuously.

The o-chloromethylbenzoyl chlorides are obtained in high yield and high purity.

The chlorinating agent is chloro, thionyi chioride, suifuryl chloride, phthaloyl chloride, PCI ₅ , PCI ₃ , phosphorus oxychloride or phosgene. Phosgene is particulariy preferred.

Suitable catalysts are arylphosphines or alkylphosphines or corresponding phosphine oxides or mixtures thereof. It is possible, for example, to use trialkylphosphines or trialkyl- phosphine oxides, whose unbranched or branched alkyl radicals contain 1 to 12, preferably 4 to 8, carbon atoms. Suitable compounds of this kind are typically trihexylphosphine, tributylphosphine oxide, trioctylphosphine and but-2-yldioctylphosphine oxide. However, it is preferred to use arylphosphines or arylphosphine oxides. Triphenylphosphine or triphenyl¬ phosphine oxide is particularly preferred. These examples are non-limiting. As can be proved, phosphine dichloride, which must be regarded as the actual reactant of lactone ring opening, is continuously formed in situ during the reaction and is then reconverted into phosphine or phosphine oxide and enters the reaction cycle again. The catalyst is preferably used in an amount of 0.1 to 10 mol %, preferably of 0.5 to 5 mol %, based on the amount of the phthalide or lactone of formula II.

The molar ratio of phosgene to the phthalide or lactone of formula II is from 0.8 : 1 to 10 : 1 , preferably from 1 :1 to 3 : 1, particularly preferably from 1 : 1 to 1.5 : 1. Slightly higher or lower or identical molar ratios correspondingly apply to the other above-mentioned chlorinating agents.

Inert solvents are suitably those solvents which do not react with the starting compounds and the reaction products under the reaction conditions. Typical examples are high-boiling hydrocarbons such as toluene, xylene and cumene, aromatic chlorine compounds, typically

chlorobenzene and dichlorobenzene as well as ethers, typically dioxane, and also nitriles such as benzonitrile and acetonitrile.

Where phthalide (m.p. 73°C) or another low-melting lactone of formula II is used, a solvent or diluent is usually not required.

Working Examples

Example 1

268.2 g of phthalide (2 mol) are placed in a sulfonation flask together with 5 mol % or 26.23 g of triphenylphosphine oxide and the mixture is then fused at c. 70°C and heated, with stirring, to 170°C. Subsequently, 2.4 mol (232.8 g) of phosgene are introduced under normal pressure over 4 to 5 hours. The reaction mixture is degassed with nitrogen and cooled, giving, in a rotation evaporator at 0.1 mbar and 120 to 140°C, the desired o-chloro¬ methylbenzoyl chloride in a yield of more than 94% of crude product and having a purity of at least 98%. A mixture of phosphine and phosphine oxide remains in the residue which can be reused.