EP1071644A1

EP1071644A1 - Method for the selective hydrolysis of acetals or ketals in the presence of phthalides

Info

Publication number: EP1071644A1
Application number: EP99913162A
Authority: EP
Inventors: Andreas Weiper-Idelmann; Heinz Hannebaum; Hermann Pütter
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1998-02-27
Filing date: 1999-02-13
Publication date: 2001-01-31
Also published as: CA2321847A1; US6245945B1; DE19808296A1; WO1999043640A1; JP2002504533A; CN1165505C; CN1291969A

Abstract

The invention relates to a method for the selective hydrolysis of acetals in the presence of phthalides. According to said method a mixture (M) containing a) a phthalide of the formula (I) and b) an acetal or ketal of the formula (II) is reacted in the presence of between 1 and 10 mol water relative to the quantity of acetals or ketals of formula (II) at temperatures of between 10 and 200 DEG C, whereby the acetal or ketal of formula (II) is hydrolysed to the corresponding aldehyde or ketone. The substituents R<1>-R<8> have the meanings given in the description.

Description

Process for the selective hydrolysis of acetals or ketals in the presence of phthalides

description

The present invention relates to methods for the selective hydrolysis of acetals bςw. Ketals in the presence of phthalides, in which one contains a mixture (M)

a) a phthalide of the formula (I)

R ⁴ 0

Rl in which the substituents have the following meaning:

R ^ R ^ R ³ and R ⁴ : independently of one another hydrogen,

Cι ~ to C ₄ alkyl or halogen

and

b) an acetal or ketal of the formula (II)

OR ⁵

R ^β - OR ⁶ II

R7 in which the substituents have the following meaning:

R ⁵ and R ^5: independently Cι ~ C to _ß alkyl,

C ₆ ~ to Cχo-aryl or the radicals R ⁵ and R ⁶ together mean ethylene and

R ⁷ and R ⁸ : independently of one another C 1 to C 8 alkyl,

- A radical hydrogen and the other radical is a phenyl radical, in which 1 to 3 hydrogen atoms of the phenyl radical can be replaced by Cι ~ to Cg-alkyl radicals or Cχ ~ to C ₄ alkoxy radicals or - The radicals R ⁷ and R ⁸ together C ₃ - to C ₆ -alkanediyl, where a hydrogen atom can be substituted by a hydroxyl group

in the presence of 1 to 10 moles of water, based on the amount of _A cetalen or ketals of formula (II) are reacted with each other at temperatures of 10 to 200 ° C, wherein the acetal or ketal of formula (II) to the corresponding aldehyde or ketone hydrolyzed.

The invention further relates to an overall process for the preparation of purified phthalides and aldehydes or ketones, in which the selective hydrolysis is integrated and in which, starting from a compound (III) selected from the group comprising phthalic acid and phthalic acid derivatives of the general formula (III)

III

in which the substituents have the following meaning:

R ¹ , R ² , R ³ and R ⁴ : as in formula (I)

R9, Rio. _a ) independently of one another -COOH or COOX, where X is C 1 -C ₄ -alkyl,

b) one of the substituents R ⁹ or R ¹⁰ -COO Y ₄ and the other substituent

CO H ₂ , where Y is C 1 -C ₄ -alkyl or hydrogen,

c) R ⁹ and R ¹⁰ together -CO-O-CO-

and 0 to 20 parts by weight, based on the acetal or ketal of the formula (II), of a compound (IV) selected from the group comprising methylbenzene, core-substituted derivatives of methylbenzene in which 1 to 3 hydrogen atoms of the phenyl radical are represented by C 1 to 4 C _ß alkyl radicals or C ~ ~ to C ₄ alkoxy radicals can be replaced,

Cyclohexanone and 2-butanone in an unseparated electrolysis cell electrochemically converted to a mixture (M) containing phthalides of the formula (I) and aldehydes or ketones of the formula (II).

Phthalides of the formula (I) and aldehydes or ketones of the formula (II) (compounds I and II) are valuable intermediates, in particular for the production of crop protection agents.

These compounds can be produced particularly economically electrochemically in coupled syntheses in an unseparated electrolytic cell from the compounds (III) and (IV), the compounds (I) and (II) then being obtained in the form of the mixture (M) (cf. DE-A-19618854 and the German application with the file number 197741423.0).

However, it is difficult to separate the resulting mixture (M) using technically simple, conventional separation processes such as distillation, since some of the acetals or ketals and phthalides form azeotropes.

The present task was therefore to develop a separation process which is not technically complex and as economical as possible and in which the loss of valuable product is as small as possible.

We have found that this object is achieved by the process described at the outset for separating the mixture (M) and the overall process for the preparation of the compounds (I) and (II).

It is surprising to the person skilled in the art that the problem can be solved with the method according to the invention. On the one hand, he could not have known that the aldehydes or ketones can be separated from the phthalides much more easily by distillation than the corresponding acetals or ketals. On the other hand, he would have expected that the hydrolysis of the acetals or ketals (II) in the presence of phthalides (I) could not be carried out economically.

The hydrolysis of acetals and ketals is described, for example, in J.Org.Chem. 1994, 59, 3098-3101. According to this teaching, the hydrolysis of acetals and ketals, in order to achieve useful space-time yields, is carried out in the presence of acids, acidic catalysts or auxiliaries, for example zeolites or ion exchangers, under sometimes drastic conditions, for example in supercritical water. On the basis of this teaching, the person skilled in the art would have assumed that the known processes for the hydrolysis of the acetals or ketals of the formula (II), if the reaction conditions are so mild that the acetal or ketal group is attacked practically exclusively and not the ester group of the phthalide , are not economically feasible because the response times are too long. On the other hand, he should have feared that by-products would form (hydrolysis of the phthalide) if the reaction conditions were chosen more drastically.

The selective hydrolysis can be carried out particularly efficiently in the case of mixtures (M) of this type using a phthalide of the formula (I) in which the radicals R 1, R ^3, R ³ and R ^{4 are} hydrogen.

The acetals or ketals of the formula (II) are preferably those in which the radicals R ⁷ and R ^{8 have} the following meaning:

one radical R ⁷ or R ^{8 is} hydrogen and the other radical is selected from the group consisting of p-methoxyphenyl, p-methylphenyl, pt.butylphenyl, o-methylphenyl and o-methoxyphenyl

the radicals R ⁷ and R ⁸ together 1-hydroxypentane-l, 5-diyl or

one R ⁷ or R ⁸ methyl and the other 1-hydroxyethyl.

P-tert is particularly preferred. -Butylbenzaldehyde dimethyl acetal.

The mixtures (M) usually contain 10 to 60, preferably 30 to 50% by weight of a phthalide of the formula (I) and 10 to 60, preferably 30 to 50 mol% of an acetal or ketal of the formula (II).

The mixtures (M) can furthermore comprise 0 to 20% by weight, based on the phthalide of the formula (I), of a compound (III) selected from the group comprising phthalic acid and phthalic acid derivatives of the general formula (III) III

in which the substituents have the following meaning:

R ¹ , R ² , R ³ and R ⁴ : as in formula (I)

R ⁹ , R ¹⁰ : a) independently of one another -COOH or COOX, where X is Ci to C ₄ alkyl,

b) one of the substituents R ⁹ or R ¹⁰ -COONY ₄ and the other substituent CONH ₂ , where Y is C 1 -C ₄ -alkyl or hydrogen,

c) R ⁹ and R ¹⁰ together -CO-O-CO-

and 0 to 20% by weight, based on the acetal or ketal of the formula (ii), of a compound (IV) selected from the group comprising and methylbenzene, core-substituted derivatives of methylbenzene in which 1 to 3 hydrogen atoms of the phenyl radical are formed by Cι ~ to Cβ-alkyl radicals or Cι ~ to C ₄ alkoxy radicals can be replaced, cyclohexanone and 2-butanone.

In the mixtures (M), the radicals R ¹ to R ⁴ in the compounds of the formulas (I) preferably have the same meaning as in the compounds of the formula (III).

The compounds of the formula (IV) are preferably those which serve as starting compounds for the electrochemical conversion to the corresponding compounds of the formula (I).

The selective hydrolysis is carried out in the presence of 1 to 10 ol of water, based on the molar amount of acetals or ketals of the formula (II). The reaction temperature is 10 to 200, preferably 80 to 140 ° C. The pressure at which the reaction is carried out is not critical and is generally from 0.5 to 10 bar. The selective hydrolysis can be carried out in the presence of catalytic amounts of a mineral acid, an organic acid or an acidic ion exchanger, but preferably no catalyst is added.

The selective hydrolysis can be carried out in the presence of an inert organic solvent, e.g. Acetone or in bulk.

The hydrolysis is preferably carried out according to one of the following variants:

Option A:

The mixture (M) and the water are preheated separately via heat exchangers and fed into the reactor. The mixing behavior can be influenced by internals or the optimization of the stirrer. At a pressure of 3-20 bar, temperatures of 80-180 ° C, dwell times of 10 seconds to 10 minutes are set. The reaction solution is let down in a flash vessel, the alcohol formed largely evaporating.

Variant B:

The variant B1 according to the invention represents continuous hydrolysis in a stirred reactor with a column attached under normal pressure:

Here, the mixture (M) and the water required for the hydrolysis (stoichiometric amount up to 10-fold molar excess) are fed separately to the kettle and reacted at temperatures from 100 to 140 ° C. and residence times from 1 to 60 min. Surprisingly enough water is still available in the reactor under these conditions in order to achieve complete hydrolysis of the starting material.

In a further embodiment (variant B2), the stream of the mixture (M) is fed via a column, so that intensive contact of the gaseous water rising from the boiler with the educt stream trickling down on the packing material of the column is ensured. In some cases, this enables a further reduction in the residence time in the stirred tank and / or a better conversion.

The mixtures (M) are obtained, for example, by combining a compound (III) with a compound (IV) in an organic solvent containing less than 50% by weight of water 7 includes, and electrochemically reacting in an undivided electrolysis cell by Getting Connected a compound (III) together with a _V (IV) in an organic solvent containing less than 50 wt .-% of water, and an undivided electrolysis cell is reacted electrochemically .

The preparation of the compounds of formula (I) and (II) onnectivity (III) of the _V and (IV) out in a combined production according to this _V is, for example, in DE-A-19618854 and 19741423 described.

In this process, commercially available electrodes made of graphite or carbon are used as electrode materials (both cathode and anode).

The electrolyte is usually a 2 to 40% by weight solution of a compound of the formula (III) in an organic solvent or a mixture of an organic solvent and water, the mixture generally being less than 50% by weight. %, preferably less than 25, particularly preferably less than 5% by weight of water.

Suitable organic solvents are, in particular, aliphatic C 1 -C ₄ -alcohols, in particular methanol or ethanol, or mixtures of such alcohols with a carboxylic acid amide such as dirnethylformamide or t-butylformamide.

As electrolyte salts, the electrolytes contain, for example, quarterly ammonium salts, such as tetra (C 1 -C ₄ -alkyl) on onium halides or tetrafluoroborates and preferably methyl triethylammonium or methyltriethylammonium methyl sulfate, usually in amounts of 0.4 to 10% by weight, based on the electrolyte.

In the production of aldehydes as co-products, the use of C ₁ -C ₆ -alkyl alcohols or ethylene glycol as a solvent is recommended, since the aldehydes are acetalized and protected against further oxidation.

As far as the other process parameters such as temperature and current density are concerned, they are not critical as long as they are within the normal range for the electrochemical conversion of organic compounds. For example, they are specified in DE-A-2510920.

The electrolysis is generally carried out until the starting product of the formula (III) and / or the starting product of the formula (IV) is virtually completely phthalide of the formula (I) or to the formula (II) is implemented. The electrolysis is preferably carried out in such a way that when the conversion has progressed to such an extent that the molar ratio (E) formed from the proportion of phthalide and the sum of the proportion of phthalide and phthalic acid or the phthalic acid derivatives in the electrolyte is 0.8 : 1 to 0.995: 1, preferably 0.83: 1 to 0.99: 1 and particularly preferably 0.86: 1 to 0.95: 1, the electrolyte is discharged from the electrolysis cell.

One advantage of the latter variant is that the proportion of undesired by-products is particularly low and unreacted starting product, which can essentially only be separated off as a component of the mother liquor during the crystallization of the phthalide, can be added to the electrolyte again. The same applies to the coupled product or its starting compound, the anodic depolarizer. The process therefore works particularly economically.

The electrolysis can be carried out batchwise or continuously.

When the process is carried out continuously, the continuous discharge of the electrolyte and the continuous addition of the inert constituents of the electrolyte, such as the solvents and conductive salts, and the

Match the starting products for the electrochemical reaction to one another and to the reaction rate in such a way that the concentration of all constituents of the electrolyte remains largely constant. This applies in particular to the molar ratio (E), which is within the defined range.

In general, the discharged electrolyte is worked up by distillation before the selective hydrolysis. This is preferably done in the following way:

First the solvent is distilled off from the electrolyte and then a fraction containing mixture (M) is distilled off. The remaining distillation residue generally contains mainly the conducting salt.

The discharged electrolyte is generally distilled at a pressure of 1 to 100 mbar and a temperature of 100 to 220 ° C. For this purpose, a thin film evaporator is used, for example. The distillation residue, which mostly consists mainly of the conducting salt, can be returned to the electrolysis cell. W wOυ 9 ^y 9 ^y / 4 ^ 3o6o4 ⁱ 0υ PCT / EP99 / 00954

9

The electrolyte, which may have been pre-cleaned in this way, is the mixture (M) and is then subjected to the selective hydrolysis process.

Following the selective hydrolysis, the reaction mixture thus formed, which contains a phthalide of the formula (I) and the aldehyde or the ketone released from the acetal or ketal of the formula (II), is generally subjected to a fractional distillation.

The distillation is carried out according to customary methods. It is preferable to collect at least 2 separate fractions. One of the fractions contains essentially only the aldehyde or the ketone. Further impurities are generally only contained in amounts of up to 0.5% by weight.

Another fraction contains a phthalide of the formula (I) as the main constituent and, if appropriate, the compounds (III) and the aldehyde as further impurities. The further purification of this fraction can be carried out particularly easily by crystallization if the proportion of these impurities is not more than 20, preferably not more than 10% by weight, based on the phthalide of the formula (I).

A third separate fraction, which mainly contains low boilers, is also advantageously gained. These are by-products that have a lower boiling point than the valuable products.

The crystallization process used to purify the phthalide of the formula (I) obtained in this way, hereinafter referred to as "crude phthalide", is not subject to any restrictions. The crystallization can be carried out continuously or batchwise, in one stage or in multiple stages.

This is preferably carried out without the addition of an auxiliary, in particular without the addition of an organic solvent.

The crystallization is preferably carried out in one stage. In another preferred embodiment of the invention, the crystallization is carried out as fractional crystallization.

In the case of fractional crystallization, all stages which produce a crystallizate which is purer than the raw phthalide supplied are usually called cleaning stages and all other stages are called output stages. Expediently, more 10-stage process operated here according to the countercurrent principle, in which after crystallization the crystals are separated from the mother liquor in each stage and this crystals are fed to the respective stage with the next higher degree of purity, while the mother liquors are fed to the respective stage with the next lower degree of purity.

The temperature of the solution or melt during the crystallization is advantageously between -10 and 75 ° C., in particular between 20 and 70 ° C. The solids content in the crystallizer is usually between 0 and 70 g, preferably between 30 and 60 g per 100 g of use.

In a further advantageous embodiment of the invention, the crystallization takes place in apparatuses in which the crystals are in the

Crystallizer grow on cooled surfaces, i.e. fixed in the apparatus (e.g. layer crystallization method from Sulzer Chemtech (Switzerland) or static crystallization method from BEFS PROKEM (France).

Furthermore, the crystallization can be carried out by cooling apparatus walls or by evaporating a solution of the crude phthalide in vacuo. 5 to 30% by weight are particularly suitable for this. -% solutions of the crude phthalide in methanol.

In the case of crystallization by cooling, the heat is dissipated via scratch coolers which are connected to a stirred tank or a container without a stirrer. The circulation of the crystal suspension is guaranteed by a pump. In addition, there is also the option of dissipating the heat through the wall of a stirred tank with a wall-mounted stirrer. Another preferred embodiment in cooling crystallization is the use of cooling disk crystallizers, such as those manufactured by Gouda (Holland). In a further suitable variant for crystallization by cooling, the heat is removed via conventional heat exchangers (preferably tube bundle or plate heat exchangers). In contrast to scratch coolers, stirred tanks with wall-mounted stirrers or cooling crystal disks, these devices have no device for avoiding crystal layers on the heat-transferring surfaces. If a state is reached during operation in which the thermal resistance takes on too high a value due to the formation of a crystal layer, the switchover to a second apparatus takes place. The first apparatus is regenerated during the operating time of the second apparatus (preferably by melting the crystal layer or flushing the apparatus with unsaturated solution). If the heat resistance in the second set is too high, you switch again 11 to the first set, etc. This variant can also be operated alternately with more than two sets. In addition, the crystallization can be carried out by conventional evaporation of the solution in vacuo.

All known solid-liquid separation processes are suitable for separating the mother liquor from the crystallized phthalide. In a preferred embodiment of the invention, the crystals are separated from the mother liquor by filtration and / or centrifugation. The filtering or centrifuging is advantageously preceded by a pre-thickening of the suspension, for example by hydrocyclone (s). All known centrifuges that work discontinuously or continuously are suitable for centrifugation. Thrust centrifuges that can be operated in one or more stages are most advantageously used. In addition, screw screen centrifuges or screw discharge centrifuges (decanters) are also suitable. Filtration is advantageously carried out by means of suction filters, which are operated batchwise or continuously, with or without an agitator, or by means of a belt filter. In general, the filtering can be carried out under pressure or in vacuo.

During and / or after the solid-liquid separation, further process steps can be provided to increase the purity of the crystals or the crystal cake. In a particularly advantageous embodiment of the invention, after the crystals have been separated from the mother liquor, the crystals or the crystal cake are washed and / or sweated in one or more stages.

When washing, the amount of washing liquid is suitably between 0 and 500 g of washing liquid / 100 g of crystals, preferably between 30 and 200 g of washing liquid / 100 g of crystals.

Suitable washing liquids are, for example

a) the solvent, if crystallization is from a solvent,

b) liquid pure product or

c) liquid feed product.

Washing can be carried out in the usual apparatus for this. Advantageously, washing columns in which the mother liquor is separated off and washed in one apparatus are centrifuged 12 f gen, which can be operated in one or more stages, or

Filter groove or band filter used. Washing can be on

Centrifuges or belt filters can be carried out in one or more stages. Here, the washing liquid can be passed in countercurrent to the crystal cake.

Sweating is a local melting of contaminated areas. The amount of sweat is advantageously 0.1 to 90 g of melted crystals / 100 g of crystals before sweating, preferably 5 to 35 g of melted crystals / 100 g of crystals. Sweating on centrifuges or belt filters is particularly preferred. Carrying out a combination of washing and sweating in one apparatus can also be suitable.

The purity of the phthalide obtained is preferably 97 to 99.9% by weight, in particular 98.5 to 99.5% by weight.

The mother liquor and washing solution can be returned to the electrolysis cell without further work-up, especially if crystallization has been carried out without the addition of an auxiliary and the anodic coupling product has been separated, since it essentially consists of a mixture of phthalide and the corresponding starting compound.

The same also applies in the event that the crystallization was carried out with the aid of solvents which are also used in the electrolyte.

If the crude phthalide has crystallized from a solution or has been washed with a solution which is not part of the electrolyte, the solvent is distilled off and the distillation residue can then be returned to the electrolysis cell.

As already mentioned in the introductory part of the description, the selective hydrolysis is an important process step in the context of an overall process in order to produce a highly pure phthalide of the formula (I) together with the acetals in an electrochemical coupling production in a particularly economical manner. Experimental part

example 1

The starting materials 5642 g pt. Butyltoluene (TBT) and 8681g dimethyl phthalate were in an electrolysis analogous to Example 6 of DE-A-19618854 but without cosolvent and with N-methyl-N, N, N-tri-butylammonium methyl sulfate 1.2 wt .-% implemented as a conductive salt in 30 kg of MeOH.

After the reaction had ended (after taking up a charge of 4.5 F based on TBT), the discharge was freed from the solvent by distillation, and then the conductive salt and high boilers were separated off using a short-path evaporator. The raw material thus obtained (12185 g) was hydrolyzed in a continuously operated stirred tank.

The raw material of the electrochemical coupling synthesis had contents of 33% p-tert-butylbenzaldehyde dimethyl acetal and 35% phthalide.

A portion of the raw material (1000 g) was placed in a stirred kettle with a column attached and, after adding 62 g of water, heated to 106 ° C. The methanol formed and the excess water distilled off via the column. Then the continuous feed of raw goods and water into the stirred tank was started, a total of another 10936 g of raw goods were converted. The level in the stirred tank was kept over an overflow so that a residence time of 30 min. was guaranteed. The temperature was 102 to 110 ° C. The acetal conversion was> 99.5%, the crude aldehyde obtained (10949 g) had a content of 36%.

3744 g of pure p-tert-butylbenzaldehyde was obtained from the hydrolysis discharge by rectification in vacuo as the main fraction. This corresponds to a yield of 61% p-t-butylbenzaldehyde over the entire process. If the recycling of the starting materials and intermediates is taken into account, the selectivity is 83%.

The distillation sump 4780 g with a phthalide content of 71% was freed of high boilers via a short path evaporator and subjected to crystallization, as described in Example 1 of DE-A-19741423. 3224 g of pure phthalide with a content> 99% were obtained. This corresponds to a yield of 54% phthalide over the entire process. If the recycling of the starting materials and intermediates is taken into account, the selectivity is 85%.

Claims

y 'J04υ. PCT / EP99 / 00954 patent claims

1. Process for the selective hydrolysis of acetals in the presence of phthalides, whereby a mixture (M) containing

a) a phthalide of the formula (I)

R ⁴ 0

in which the substituents have the following meaning:

R ^ R ^ R ³ and R ⁴ : independently of one another hydrogen,

Cι ~ to C ₄ alkyl or halogen

and

b) an acetal or ketal of the formula (II)

OR ⁵

_R 8- OR ⁶ II

R ⁷ in which the substituents have the following meaning:

R ⁵ and R ⁶ : independently of one another C ₁ -C ₆ -alkyl,

C ₆ - to Cio-aryl or the radicals R ⁵ and R ⁶ together mean ethylene and

R ⁷ and R ⁸ : independently of one another C 1 to Ce alkyl,

- A radical hydrogen and the other radical is a phenyl radical in which 1 to 3 hydrogen atoms of the phenyl radical can be replaced by Ci to C ₆ alkyl radicals or -C ~ to C ₄ alkoxy radicals or

- The radicals R ⁷ and R ⁸ together C ₃ - to Cβ-alkanediyl, and a hydrogen atom can be substituted by a hydroxyl group 15 in the presence of 1 to 10 mol of water, based on the amount of acetals or ketals of the formula (II), reacted with one another at temperatures of 10 to 200 ° C., the acetal or

Ketal of formula (II) hydrolyzed to the corresponding aldehyde or ketone.

2. The method according to claim 1, wherein the radicals R ⁷ or R ^{8 have the} following meaning:

- A radical R ⁷ or R ^{8 is} hydrogen and the other radical is selected from the group consisting of p-methoxyphenyl, p-methylphenyl, pt. butylphenyl, o-methylphenyl and o-methoxyphenyl- the radicals R ⁷ and R ⁸ together 1-hydroxypentane-l, 5-diyl or one radical R ⁷ or R ⁸ methyl and the other radical 1-hydroxyethyl.

3. The method according to claim 1 or 2, wherein the radicals R ^! , R ² , R ³ and R ⁴ in formula (I) are hydrogen.

4. The method according to claim 3, wherein the phthalide of the formula (I) is a compound in which the radicals R ^ R ^ R ³ and R ^{4 are} hydrogen and the acetal of the formula (II) is p-tert-butylbenzaldehyde dimethyl acetal.

5. The method according to claims 1 to 4, wherein the mixture (M) 0 to 20 wt .-%, based on the phthalide of formula (I), a compound (III) selected from the group containing phthalic acid and phthalic acid derivatives of the general Formula (III)

III

in which the substituents have the following meaning:

R ¹ , R ² , R ³ and R ⁴ : as in formula (I) 16

R9 _t crack; a) independently of one another -COOH or

COOX, where X is C 1 -C ₄ -alkyl,

b) one of the substituents R ⁹ or R ¹⁰

-COO Y ₄ and the other substituent CONH ₂ , where Y is C _x - to C ₄ ~ alkyl or hydrogen,

c) R ⁹ and R ^x0 together -CO-O-CO-

and 0 to 20% by weight, based on the acetal or ketal of the formula (II), of a compound (IV) selected from the group comprising and methylbenzene, core-substituted derivatives of methylbenzene in which 1 to 3 hydrogen atoms of the phenyl the rest can be replaced by Cχ ~ to C ₆ ~ alkyl radicals or Cι ~ to C ₄ alkoxy, contains cyclohexanone and 2-butanone.

6. The method according to claims 1 to 5, wherein the reaction is carried out in the presence of catalytic amounts of a mineral acid, an organic acid or an acidic ion exchanger.

7. The method according to claims 1 to 6, wherein the reaction mixture is subjected to a fractional distillation following the selective hydrolysis.

8. The method according to claims 1 to 7, wherein the mixture

(M) containing the phthalides of the formula (I) and the acetals or ketals of the formula (II) by electrolysis by preparing a compound (III) together with a compound (IV) in an organic solvent which is less than Contains 50 wt .-% water, electrochemically converted in an undivided electrolysis cell.

9. The method according to claim 8, wherein when the conversion in the electrolysis has progressed to such an extent that the molar ratio (E) formed from the proportion of phthalide and the sum of the proportion of phthalide of the formula (I) and the compound (III) in the electrolyte is 0.8: 1 to 0.995: 1, discharges the electrolyte from the electrolysis cell, subjects it to the selective hydrolysis process and, after the fractional distillation of the reaction mixture from the fractions in which the phthalide of the formula (I) is present, the phthalide crystallizes and optionally separated from the mother liquor. 17

10. The method according to claim 8 or 9, wherein the electrolyte discharged is worked up by distillation prior to the selective hydrolysis after the electrolysis.

11. The method according to claim 10, wherein the distillative workup of the electrolyte is carried out by removing the organic solvent and then a fraction in which the phthalides of the formula (I) and the acetals or ketals of the formula (II) are present distilled off the electrolyte.