NL7908008A - PROCESS FOR THE OXYDATION OF METHYLBENES. - Google Patents

Description

4 1 4 f.

Method for the oxidation of methylbenzenes.

This invention relates to a new process for the oxidation of methylbenzenes, and more particularly the oxidation of methylbenzenes with air or oxygen in the presence of a strongly acidic catalyst and in the presence of the acetic acid anhydride or the combination of acetic acid and phosphorus pentoxide.

In that case, as reaction products, depending on the circumstances, a phenyl acetate and methylenediacetate or formaldehyde (or paraformaldehyde) are formed. The phenyl acetate can, if desired, be converted into the phenol, and the methylene diacetate optionally formed in formaldehyde or paraformaldehyde (by pyrolysis or the like).

Grozhen et al. (Doklady Akad. Nauk, USSR, 204,

No. 4872) found that the acid catalyzed oxidation of toluene in acetic anhydride at high temperature and pressure followed by saponification of the reaction mixture in moderate yield gave phenol. More recent work has shown that phenylacetate, methylenediacetate and acetic acid are the main products of the acid-catalyzed oxidation of toluene in acetic anhydride with air. Despite improvements consisting of the use of catalysts and promoters, and acetic acid as a solvent, high temperatures and pressures are still required to achieve reasonable reaction rates and yields.

It has now been found that the acid-catalyzed oxidation of methylbenzenes in either acetic acid or the combination of acetic acid and phosphorus pentoxide to a phenyl acetate, methylenediacetate and acetic acid proceeds under mild conditions at decent rates and good yields when the reaction is conducted in the presence of a small amount of benz -aldehyde. The reaction proceeds smoothly at temperatures of no more than 790 80 08 2> 80 ° C and an oxygen pressure of only 1 atmosphere. The resulting acetates can, if desired, be converted into the phenol and formaldehyde or paraformaldehyde.

When using acetic anhydride, the 5 reaction equation is: 0CH_ + 2 Aco0 + 0-> 0 OAc + CH, (0Ac) „+ HOAc 3 22 acid 2 2

The strong acid used is sulfuric acid or monoper sulfuric acid H 2 SO 4 (CaroT acid).

When acetic acid and phosphorus pentoxide 10 are used, the reaction equation is: 0CHo + 3 HOAc + 2 Po0, + 0o> 0 OAc + CHo (0Ac) o + 4 HP0o 3 2 5 2 acid 2 2 3

Of course, this method is equally applicable to methylbenzenes other than toluene, including xylenes and trimethylbenzenes such as mesitylene and pseudocumene, etc.

In general, this process is carried out by oxidation of the selected methylbenzene with air or oxygen in liquid phase, at a pressure of at least 1 atmosphere and at temperatures of possibly only 80 ° C. Equimolecular amounts of phenylacetate and methylene diacetate are then formed, along with acetic acid and smaller amounts of certain by-products derived from methylbenzene. The phenyl acetate and the methylenediacetate, after being separated, can be pyrolyzed to the corresponding phenolic compound and formaldehyde, respectively, while the acetic acid can be recovered in a known manner and converted back into acetic anhydride, after which it is available again for the next step.

It is thus seen that, in contrast to the prior art, the oxidation can proceed under very mild conditions if only a small amount of benzaldehyde is added to the reaction mixture.

As already mentioned, the starting materials are a methylbenzene, such as toluene, xylene (o, m or p) trimethylbenzene (such as mesitylene or pseudocumene), acetic anhydride and oxygen or air, in the presence of a strongly acidic catalyst, preferably SO ^, and what's new, a little benzaldehyde. The weight ratio between methylbenzene and acetic anhydride should be 790 8 0 08 4 3 *, preferably between 50: 1 and 1:10, most preferably between 10: 1 and 2: 1, while the weight ratio between SO 2 and methylbenzene in general should be between 1: 2000 and 1:50, preferably between 1: 1000 and 1: 200. 0.01 to 1.0 g mol, preferably 0.05 to 0.10 g mol, of benzaldehyde are used per mole of methylbenzene. If one smells Se, 1 gmole per 1 to 20 gmole (preferably 2 to 5 gmole) of acetic acid is taken therefrom.

If desired, the reaction can proceed in excess of methylbenzene as a solvent, but also in a suitable organic solvent such as benzene or chlorobenzene.

Furthermore, it has been found that persulfates, such as sodium persulfate, potassium persulfate, per sulfuric acid and permon sulfuric acid (Caro's acid) effectively accelerate this reaction. These promoters can be used in amounts from 1 to 100 mg per g of methylbenzene.

The reaction using oxygen or a corresponding amount of air can (as already mentioned) proceed under relatively mild conditions, ie at temperatures of at least 80 ° C and up to 150 ° C, preferably at temperatures between 90 ° and 120 ° C, and at air or oxygen pressures of at least 1 atmosphere, up to 10 atmospheres, preferably for both the lower temperatures and the lower pressures.

The reaction mixture containing the phenyl acetate, the methylene diacetate and the acetic acid, as well as smaller amounts of by-products, is then treated in the usual manner so that the acid catalyst is removed therefrom, after which the two acetates can be separated by vacuum distillation. The separated phenyl acetate is then converted by pyrolysis into phenol, cresol or the like. This is done in the usual manner by heating the acetate to temperatures between 500 ° and 1000 ° C (preferably around 625 ° C), preferably in the presence of a catalyst such as triethyl phosphate, after which the desired products are separated in the usual manner. Likewise, the pyrolysis of methylene diacetate leads to formaldehyde and acetic anhydride. This pyrolysis is carried out in a usual manner in one step in a homogeneous 790 8 Q 08 t 4 V gas phase, at 450 ° to 550 ° C and under reduced pressure. Any recovered acetic acid can be converted back into acetic anhydride so that it can be used in the next oxidation; this can easily be done, for example, by reacting it with liquid at room temperature in a liquid phase.

In a further elaboration of this invention, it has been found that when acetic anhydride is used, surprisingly paraformaldehyde can be formed directly next to the phenyl acetate, also under mild conditions, if (1) the ratio between acetic anhydride and methylbenzene is adjusted such that the selective formation of formaldehyde and phenylacetate is favored, and (2) the flow of air or oxygen through the reaction mixture is sufficient to remove the formaldehyde as it arises.

The course of events can then be represented by the following equation: 0CH3 + Ac20 + 02> 0OAc + CH20 + HOAc 2 4

Thus, it is seen that by limiting the amount of acetic anhydride, the reaction in this case is surprisingly directed to the selective formation of phenyl acetate and formaldehyde, essentially excluding methylene diacetate. When this modification is accompanied by a substantial and sustained flow of air or oxygen, formaldehyde vapors are released from the solution and condensed and separated along with the acetic acid and minor amounts of by-product. As already mentioned, the phenyl acetate can then be pyrolyzed to a phenol.

In general, this oxidation of methylbenzene continues. with air or oxygen in liquid phase, at a pressure of at least 1 atmosphere and at a temperature which only needs to be 80 ° C. After separating and recovering the phenyl acetate and the para-formaldehyde, the acetic acid can be recovered in a known manner and converted back into acetic anhydride. To take full advantage of this finding, it is necessary to add the acetic anhydride to the reaction mixture at such a rate that there is enough acetic anhydride to react with the one oxidation product of the toluene (the phenol) to phenyl acetate, but not enough to convert the other oxidation product (formaldehyde) into methylene diacetate under the reaction conditions. This can easily be done by moderating the supply of the acetic anhydride, for example using the results of chromatographic analysis as a guideline.

5 Amounts and supply rates of air or oxygen are not so important, but at least there must be enough to both oxidize the methylbenzene and to remove the resulting formaldehyde. So it is only essential that there is a sustained flow of oxygen or air. Generally, it can be said that the amount of gas can range from 1 to 100 parts by volume per volume of liquid reaction mixture per unit time, and preferably 10 parts by volume of gas per minute per volume part of reaction mixture.

The reaction takes place in the presence of an acid as a catalyst, preferably 2 SO 2, and benzaldehyde. The weight ratio between SO 2 and methylbenzene is generally between 1: 2000 and 1: 100, preferably between 1: 1000 and 1: 200, while the amount of benzaldehyde is between 0.01 and 1.0 µmol, preferably between 0 0.05 and 0.10 gmole per mole of alkylbenzene.

If desired, the reaction mixture can be carried out in excess of methylbenzene as a solvent, but also in a suitable organic solvent such as benzene, chlorobenzene or acetic acid.

The latter is preferable since better selectivity is observed. To obtain a rapid reaction in acetic acid, a promoter such as Caro's acid is used, and then in an amount of 10-100 wt% based on the amount of acetic anhydride.

The formaldehyde can be collected either as a monomer or (and preferably) as a solid polymer; the paraformaldehyde deposits as a solid on a cold surface downstream of the reactor.

The reaction mixture containing the phenyl acetate and smaller amounts of acetic acid, by-products derived from methylbenzene and the like is then treated in a known manner such that the acid catalyst is removed therefrom and the acetate can be recovered by vacuum distillation.

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The invention is now further illustrated by the accompanying, non-limiting examples, Examples I and X illustrating the use of acetic anhydride and Examples XI through XIII using the combination of acetic acid and phosphorus pentoxide; Examples XIV and XV illustrate the conversion of phenyl acetate and methylene diacetate into phenol and formaldehyde, respectively, and Examples XVI and XVIII relate to the direct formation of formaldehyde and paraformaldehyde under certain reaction conditions.

Example I

Into a manometric oxidation apparatus with gas recirculation were added: toluene 21.4 ml acetic anhydride 4.0 ml sulfuric acid 1 drop (approx. 30 mg).

The air from the device was expelled by nitrogen and the reaction mixture was brought to a temperature of 101-3 ° C. When the temperature reached the desired value, the nitrogen was replaced with pure oxygen and the recirculation pump was started, which was 300-400 ml / min. blew oxygen into the liquid. Gas uptake was measured in a burette filled with mercury using a displacement method. Liquid samples were occasionally taken and these were analyzed by gas chromatography in a standard manner. Under these conditions, there was no measurable oxygen uptake and no oxidation products. After 2 hours and 25 minutes, 0.49 g of benzoyl peroxide, a free radical initiator, was added, and the reaction mixture continued for 2 hours. and watched for 35 minutes. There was now a slow oxygen uptake, a total of 185 ml. This reaction mixture was then also examined by gas chromatography.

In this analysis, as well as in the following examples, the weight percentages given are normalized based on the following compounds: methylene diacetate (MDA.), Benzaldehyde (BAL), phenyl acetate (FA), benzyl acetate (BA), phenoxymethyl acetate (FOMA ) and other unidentified 790 8 0 08 f 7% * products appearing in a gas chromatogram nearby. Although benzaldehyde is an additive, it is conveniently included in the products as well, since it always appears in the gas chromatograms in the vicinity of the toluene oxidation products.

The reaction mixture of this first example contained, on this normalized basis, less than 1% methylene diacetate (MDA) and less than 3% phenyl acetate (FA). The main products were 28% benzyl acetate, 26% benzylidene diacetate (BDA) 10 and a number of other unidentified products.

Example II

The following were introduced into the reactor:

Toluene 21.4 ml

Acetic anhydride 4.0 ml 15 Sulfuric acid 1 drop (approx. 30 mg)

The reaction was carried out in the same manner as in Example 1 for 1 hour. There was no oxygen uptake, and after one hour 1.0 ml of benzaldehyde and 3 drops of sulfuric acid were added. The oxygen uptake now started after a few minutes, and after 20 a total of 3 hours and 50 minutes 636 ml of oxygen had been taken up. Analysis of the liquid reaction mixture showed 10% MDA and 11 Z FA along with 20% BA and 12% FOMA (a precursor to both FA and MDA).

Example III

25 The following were introduced into the reactor:

Toluene 21.4 ml

Acetic anhydride 4.0 ml

Sulfuric acid 1 drop (30 mg).

The reaction was initially run as in Example 30I, and in 4 hours and 16 minutes there was only negligible oxygen uptake. 1.0 ml of benzaldehyde and 0.56 g of potassium persulfate were now added. The oxygen uptake now started after a few minutes and after 7 hours and 33 minutes a total of 712 ml of oxygen had been absorbed. Based on the acid to consumption, about 10% of the toluene had been converted. Analysis of the liquid reaction mixture showed 10% MDA, 12% FA, 16% BAC and 10% FOMA.

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F

tr 8

Example IV

The following were introduced into the reactor:

Toluene 21.4 ml

Acetic anhydride 4.0 ml 5 Acetic acid 12.0 ml

Benzaldehyde 2.0 ml

Dry Caro's acid 0.25 g

Sulfuric acid 3 drops (approx. 100 mg)

The reaction was initially run as in Example 10 and a liquid sample was taken after 2 hours and 20 minutes; it was found to have formed 12% MDA, 11% FA and 9.5% FOMA. In total, the reaction was continued for 6 hours and 55 minutes. After 3 hours and 34 minutes another 2.0 ml of acetic anhydride was added, and after 6 hours and 4 minutes 0.25 g of dry Caro's acid.

The final reaction mixture was found to contain 20% MDA, 19% FA, 13% BA and 4% FOMA upon analysis. Total oxygen uptake was 490 ml to form 1.6 mg mol CO2.

Example V

Into the reactor were charged: 20 Toluene 21.4 ml

Acetic anhydride 4.0 ml

Acetic acid 12.0 ml

Benzaldehyde 1.0 ml

Co-stearate 7.4 mg. The reaction was carried out as in Example I.

After 3 hours and 15 minutes, 514 ml of oxygen was taken up. The reaction mixture was found to contain 16% MDA, 5% FA and 7% FOMA.

Example VI

Into the reactor were charged: Toluene 21.4 ml

Acetic anhydride 8.0 ml

Acetic acid 12.0 ml

Benzaldehyde 1.0 ml

NaB03.4H2 O 1.54 g 35 Sulfuric acid 3 drops (M00 mg). The reaction was carried out as in Example 1. After 3 790 80 08 9 hours and 22 minutes, 780 ml of oxygen had been taken up. The analysis of the liquid reaction product showed 14% MDA, less than 2% FA, 37% benzaldehyde and 34% other products.

Example VII

5 The following were introduced into the reactor:

Toluene 42.8 ml

Acetic anhydride 8.0 ml

Sulfuric acid 2 drops (approx. 70 mg)

The reaction was carried out as in Example 1. In the course of the oxidation, 0.6 ml of cyclohexanone over 40 minutes (from 35 min. To 75 min.), 66 mg of azobis-isobutyronitrile after 186 minutes, 200 were added. mg of potassium persulfate after 300 minutes. The reaction was continued for a total of 10 hours and 27 minutes, taking in a total of 790 ml of oxygen. Only traces of the desired products FA and MDA were found in the reaction mixture.

Example VIII

Into the reactor were charged: p-Xylene 24.1 ml 20 Acetic anhydride 4.0 ml

Benzaldehyde 1.0 ml

Dry Caro's acid. 0.5 g

Sulfuric acid 3 drops (M00 mg)

Chlorobenzene 1.0 ml 25 (as internal standard)

The reaction was carried out as in example I; the reaction temperature was 104-7 ° C and after 4 hours the total oxygen uptake was 582 ml. Analysis of the reaction mixture showed 28% p-cresyl acetate and 16% methylene diacetate; 7.5 mg-30 moles of CO2 had also been generated.

Example IX

Into a 300 ml shaking autoclave were placed: 35 790 80 08, 10

P

\

Toluene 43.0 ml

Acetic anhydride 8.0 ml

Benzaldehyde 2.0 ml

Dry Caro's Acid 1.0 g 5 Sulfuric Acid 0.11 g

In the autoclave, bee. room temperature pressed 8.4 ata oxygen and 11.9 ata nitrogen, so a total of 20.3 ata, and the autoclave was heated to 120 ° C over 30 minutes. The mixture was kept at 115-120 ° C for 3 hours and 35 minutes, causing a pressure drop of 4.5 ata in total. Analysis of the oxidation product showed 17% FA, 24% MDA and 8% FOMA.

Example X.

Into a 300 ml shaking autoclave: 15 Toluene 50 ml

Acetic anhydride 11.4 ml

Sulfuric acid 0.11 g

In the autoclave, 2.1 ata oxygen and 10.2 ata nitrogen were pressed at room temperature, so a total of 12.3 20 ata. The reactor was kept at 130 ° C for 8 hours with no pressure drop occurring and no oxidation products were found afterwards.

Example XI

In a manometric oxidation apparatus with gas recirculation were placed under nitrogen:

Toluene 21.4 ml

Acetic acid 12.0 ml

Benzaldehyde 1.0 ml

Phosphorus pentoxide 2.5 g 30 Dry Caros acid 0.5 g

The reaction mixture was warmed to 102 ° C, the nitrogen was replaced with pure oxygen, and the gas recirculation pump was turned on, giving 350 ml / min. oxygen was blown below the liquid surface. Oxygen uptake was measured by displacement in a mercury-filled burette. Liquid samples were occasionally taken and analyzed by gas chromatography in a known 790 8 0 08 * π manner.

After 1 hour and 15 minutes, 197 ml of oxygen was taken up, and the reaction mixture then contained 8% MDA, 30%

BAL, 23% FA, 5% BA and 34% unidentified products. The reaction was continued for a total of 5 hours, and then the reaction product contained 14% MDA, 30% BAL, 20% FA, 3% BA, and 33% others. Example XII

Into a 300 ml shaking autoclave were placed: 10 Toluene 43.0 ml

Acetic anhydride 2.0 ml

Acetic acid 16.0 ml

Benzaldehyde 2.0 ml

Dry Caro's Acid 1.0 g 15 Phosphorus Pentoxide 5.0 g

Sulfuric acid 0.11 g

In the autoclave, 8.4 ata of oxygen and

Pressed 11.9 ata of nitrogen, the autoclave was heated to 120 ° C in 30 minutes

heated and held for 1 hour and 25 minutes. In it, a pressure drop of 2.2 ata occurred. The reaction mixture was analyzed according to the previous examples and found to contain 21% MDA, 18% BAL, 21% FA, 5% BA, 8% FOMA and 26% others.

Example XIII

25 Into the manometric reactor with gas recirculation were introduced:

Toluene 21.4 ml

Acetic acid 12.0 ml

Benzaldehyde 1.0 ml 30 Dry Caro's Acid 0.5 g

MgSO4 3.0 g

The reaction was carried out in accordance with Example I at 103 ° C. By gas chromatography, no oxidation products were then detectable in the reaction mixture.

35 Example HV

Pyrolysis of methylene diacetate to para 790 8 0 08 12 formaldehyde and acetic anhydride can be carried out in known manner at 500 ° C. On the other hand, the pyrolysis of methylene diacetate can also take place at about 300 ° C under the influence of 5% NaCl on silica gel as a catalyst. The methylenediacetate, dissolved in 5 n-hexane, is passed at a space count of 900 per hour through a passive steel tube filled with the dried and calcined catalyst. Downstream of the reactor, paraformaldehyde and acetic anhydride are collected in known manner. The selectivity is above 93% for acetic anhydride and above 95% for paraformaldehyde.

Example XV

Pyrolysis of phenylacetate to phenol and ketene is done by heating at 625 ° C in a well-conditioned tube reactor. The effluent is condensed to a liquid containing 84% phenol, and the yield of ketene is 89%.

The reaction can also take place at a slightly lower temperature in the presence of triethyl phosphate as a catalyst with space velocities of 900 to 1000 per hour. Then one also gets yields above 90%.

Similarly, cresyl acetate can be converted to cresol.

The following can be said about the previous examples:

Example I shows that in the presence of acetic anhydride and sulfuric acid, toluene is essentially not oxidized at the given pressure and temperature, and that with the addition of a free radical initiator (benzoyl peroxide), a slow oxidation occurs, but both of the desired phenyl acetate and less than 3% of the methylene diacetate is produced.

Example 2 shows that addition of benzaldehyde leads to a fairly fast reaction, resulting in about 10% MDA, 11% FA and 12% FOMA. From example IV, it can be seen that the oxidation of toluene in the presence of acetic acid, acetic anhydride, sulfuric acid and dry Caro's acid leads to better selectivity for FA and MDA; the better effect is probably due to the addition of Caro's acid and acetic acid.

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Example V shows that the addition of a conventional oxidation catalyst for toluene, namely a cobalt salt, does not lead to a selective reaction since only 5% FA was found in addition to 11% BA. Example VI shows that another strong oxidizing agent (other than a heavy metal salt, namely sodium perborate) also does not promote the formation of phenyl acetate, since only 2% of it was found. Example VII shows that the use of another promoter with a carbonyl group, namely cyclohexanone instead of benzaldehyde, also does not lead to the formation of the desired products, FA and MDA.

Example VIII shows that benzaldehyde can also promote the oxidation of homologues of toluene, namely xylene. In this case the p-cresyl acetate is formed from p-xylene. Example IX shows that the joint oxidation of toluene and benzaldehyde at 120 ° C and somewhat higher pressures (8.4 ata oxygen) produces significant amounts of both FA and MDA.

From example X it can be seen that in the absence of benzaldehyde no oxidation occurs even at 130 ° C.

Example XVI

20 Into a manometric oxidation apparatus with gas recirculation:

Toluene. 42.8 ml

Acetic anhydride 1.0 ml

Benzaldehyde 1.0 ml 25 Sulfuric acid 2 drops (^ 70 mg)

The air in the reaction flask was displaced by nitrogen and the mixture was heated to about 100 ° G. When it reached 100 ° C, the nitrogen was replaced with pure oxygen and the gas recirculation pump was turned on, blowing 300-30 400 ml of oxygen into the liquid per minute. The course of the gas uptake with time was monitored in a mercury-filled burette.

Samples were taken from the liquid and analyzed by gas chromatography. Using a syringe pump, 0.72 ml of acetic anhydride was added between 49 and 108 minutes and 0.20 ml of anhydride between 172 and 220 minutes. At the end of 3 hours 40 minutes, the oxygen uptake was a total of 349 ml, and the oxidation product contained 26% FA, 7% MDA, 2% FOMA and 14% BA. A significant amount of white solid was deposited on the cold surfaces of the reactor and its condenser; this was found to be paraformaldehyde on analysis.

Correspondingly, cresyl acetate and paraformaldehyde were obtained from toluene instead of xylene, together with acetic acid and related by-products.

Example XVII

Into the reactor were charged: 10 Toluene 42.8 ml

Acetic anhydride 1.0 ml

Benzaldehyde 1.0 ml

Potassium persulfate 0.54 g

Sulfuric acid 2 drops (1 mg) The reaction was again carried out at 100 ° C with the addition of acetic anhydride between 33 and 73 min (0.82 ml) and 100-160 min (0.62 ml). The reaction was stopped after 2 hours and 40 minutes; the total oxygen uptake was now 280 ml.

The oxidation product contained 17% FA, a trace of MDA and 8% BA. A white matter was deposited on the cold walls of the reactor and condenser, which was found to be paraformaldehyde by infrared analysis. Example XVIII

The following were introduced into the reactor:

Toluene 42.8 ml 25 Acetic anhydride 16.0 ml

Benzaldehyde 1.0 ml

Potassium persulfate 0.43 g

Sulfuric acid 2 drops (WO mg)

The reaction was carried out as in Example 1, except that nothing was added in the meantime. The reaction product contained only 3% FA and MDA, and further 19% BA. Solid paraformaldehyde was not observed.

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Claims (15)

Process for the oxidation of methylbenzenes to phenyl acetates and methylene diacetate, whereby the methylbenzene is oxidized in acetic anhydride or in a combination of acetic acid and phosphorus pentoxide under the influence of a strong acid as a catalyst with air or oxygen, characterized in that it oxidation takes place in the presence of benzaldehyde, at a temperature of at least 80 ° C and a pressure of at least 1 atmosphere. 2. Process according to claim 1, characterized in that the catalyst is sulfuric acid. Process according to claim 1 or 2, characterized in that the reaction temperature is between 80 ° and 150 ° C. 4. A method according to any one of the preceding claims, characterized in that the pressure is between 1 and 10 atmospheres. A method according to any one of the preceding claims, characterized in that a suitable organic solvent is used. Process according to claim 5, characterized in that the solvent is acetic acid and a promoter for that acid. 7. Process according to any one of the preceding claims, characterized in that the reaction takes place in the presence of a persulfate as a promoter. A method according to claim 7, characterized in that the promoter is Caro's acid. 9. Process according to any one of the preceding claims, characterized in that 0.01 to 1.0 g mol of benzaldehyde is used per mole of methylbenzene. Process according to any one of Claims 1 to 9, characterized in that toluene is oxidized to phenyl acetate and methylenediacetate. 11. Process according to any one of claims 1 to 9, characterized in that a xylene is oxidized to a cresyl acetate and methylene diacetate. 790 80 08 t, '16 f Process according to any one of the preceding claims, characterized in that the phenyl acetate and the methylene diacetate are separated and pyrolysed to form a phenol and formaldehyde, respectively. Process according to any one of the preceding claims, characterized in that the oxidation is carried out in the presence of an amount of acetic anhydride insufficient to convert the resulting formaldehyde to methylene diacetate, and that sufficient air or oxygen is blown through to form the resulting form aldehyde. from the liquid reaction mixture. 14. Methods mainly according to description and / or examples. 15 790 8 0 08