CS257100B1 - Process for preparing 3-chlorobenzaldehyde acetals - Google Patents

Abstract

The method for producing 3-chlorobenzaldehyde acetals of the general formula I, where X represents an alkyl group with 1 to 5 carbon atoms, or both X together represent an oligomethylene group - (CH2)n_< where n is an integer 2 or 3, by reacting 3-chlorobenzaldehyde with an alcohol of the general formula H -/CH|- (CH2)n - CH2, \OH/p OH, where n represents 1 or 2 and p = 0 to 2, consists in the reaction taking place in the presence of 0.1 to 5.0 g of catalyst per 1 mol of aldehyde, the active component of which is acid salts or salts of a strong acid and a weak base, optionally in the presence of an inert solvent, while the resulting water is removed azeotropically.

Description

The invention relates to the preparation of acyclic and cyclic acetals of 3-chlorobenzaldehyde of the general formula I

OX

Cl

CH 'ΟΧ (I) wherein each X is either an alkyl group having 1 to 5 carbon atoms, or both X together are an oligomethylene group - (CH ₂ ) _n -, wherein n is an integer of 2 or 3.

Said compounds of formula (I) are useful intermediates of the chemical industry, for example the preparation of certain insecticidal compositions (see, for example, K. Naumann Chemie der Synthetic Pyrethroid Insectizide, Springer-Verlag Berlin 1981).

The process for the preparation of acetals of formula I has not been described. However, the preparation of several certain acetals has been described by reacting 3-chlorobenzaldehyde with the corresponding orthoformate or the corresponding alcohol, in the presence of a strong acid (see e.g.

J. Amer. Chem. Soc. 101, 4672 (1979); Ger. Off. 2,951,496). A disadvantage of the present processes is the fact that the acid must be removed very carefully before further processing, often by shaking it with alkali, since its further presence leads to decomposition products. While some polymeric acids (ion exchangers) can be separated relatively simply, for example by filtration, these acids are destroyed when reused and their disadvantage in industrial production is their relatively high cost. A disadvantage is also the high price of orthoformates.

These shortcomings of the current processes are solved by a novel process for the preparation of acetals of formula I by reacting 3-chlorobenzaldehyde with an alcohol of formula II

H - / CHI - (CH 2) - CH 2 (II (II, 1 OH / p OH) where n = 0, 1 and p = 0 to 2, the essence of the invention being that the reaction proceeds in the presence of a catalyst whose the active ingredient are acidic or strong acid and weak base salts, such as potassium hydrogen sulphate KHSO4, such as ammonium chloride NH4Cl, FeSO4, copper sulfate CuSO4. however, an amount of 0.1 to 5.0 g / mol of aldehyde is preferred.

The reaction is preferably carried out at the boiling point of the reaction mixture, optionally in the presence of an inert solvent, the resulting water being gradually removed by azeotropic distillation. For example, 1,2-dichloroethane, benzene and toluene are preferably used as the inert solvent.

After distilling off the solvent and any excess alcohol of formula II, the product of formula I formed can be distilled directly from the reaction vessel without removing the catalyst. The yields of the method exceeded 90%. Optionally, a new batch can be added to the residue in the reaction vessel and the reaction process repeated without adding catalyst.

The examples below illustrate the method of the invention without limiting its scope in any way.

Example 1

A mixture of 14.0 g (0.1 mol) of 3-chlorobenzaldehyde, 6.5 g (0.105 mol) of ethylene glycol, 75 mg of potassium hydrogen sulfate and 50 ml of dichloroethane was refluxed with stirring using azeotropic water separator. When no more water was separated, the solvent was distilled off and the product was fractionated in vacuo. Virtually all of the product boiled at 129-132 ° C / 1.3 kP. Yield 17.9 (97%) of 2- (3-chlorophenyl) -1,3-dioxolane (I; XX = -CH ₂ CH ₂ -), purity 96% (by gas chromatography).

The reaction was carried out as described in Example 1, except that mg of ferrous sulfate was used. 16.8 g (91%) of Compound I was obtained; X = X = -CH ₂ CH ₂ at 96% purity.

Example 2

Example 3

The reaction was carried out as in Example 1 except 75 mg of ammonium chloride was used. Yield 16.2 g (88%) of product X; X = X = -CH ₂ CH ₂ ; purity 96%.

Example 4

A mixture of 10.0 g of 3-chlorobenzaldehyde, 70 ml of absolute ethanol, 50 ml of benzene and 70 mg of potassium hydrogen sulfate was heated to boiling with slow azeotrope collection (8 h). The residue was distilled under vacuum at 102 ° C / 0.4 mm Hg, yield 13.8 g (90%) of 3-chlorobenzaldehyde diethyl acetate (I; X = C 1 H 4); containing 7% starting aldehyde.

Example 5

From a mixture of 10 g of 3-chlorobenzaldehyde, 50 ml of n-butanol and 70 mg of potassium hydrogen sulfate, n-butanol was distilled off along with the reaction water over a period of 5 hours. Then the product was distilled at 122-124 ° C / 0.3 mm Hg. 17.4 (90%) of 3-chlorobenzaldehyde di-n-butyl acetate of 94% purity was obtained.

Claims (5)

OBJECT OF THE INVENTION A process for the preparation of 3-chlorobenzaldehyde acetals of the formula I wherein X represents an alkyl group having 1 to 5 carbon atoms, or both X together represent an oligomethylene group - (CH ₂ ) _n -, wherein n is an integer of 2 or 3, by reaction of 3- of chlorobenzaldehyde with an alcohol of formula II Η -I CH (CH ₂ ) _n - CH ₂ (II) OH OH where n = 0 or 1 and p = 0 to 2, characterized in that the reaction is carried out in the presence of 0.1 to 5.0 g of catalyst per mole of aldehyde, the active ingredient of which are acid or strong acid salts and weak bases, optionally in the presence of an inert solvent, whereby the water formed is removed azeotropically. 2. A process according to claim 1, wherein the salt is an alkali metal bisulfate. 3. A process according to claim 1, wherein the salt is copper (II) or iron (II) sulfate. 4. A process according to claim 1 wherein the salt is ammonium chloride. 5. A process as claimed in claim 1, wherein 1,2-dichloroethane, benzene or toluene is used as the inert solvent.