CA1149408A - Co-oxidation of methyl benzenes and benzaldehyde - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The oxidation of methyl benzenes, such as toluene, with air or oxygen in the presence of acetic anhydride, or acetic acid and phosphorus pentoxide, and sulfuric acid catalyst to form a phenolic acetate and methylene diacetate may be carried out under mild conditions when small amounts of benzaldehyde are added to the reaction. The resulting acetates may then be pyrolyzed to yield phenolic compounds and formaldehyde, respectively.

Description

11~9408 BAC~GROUND OF THE INVENTION

Thls lnvention relates to novel processes for the oxidatlon of methyl benzenes. More particularly, this lnventlon relates to an lmproved procesæ ~or the oxldation of methyl benzenes wlth alr or oxygen in the presence of a strong acid c atalyst, benzaldehyde, and elther acetlc anhydride or the combination of acetic acld and phosphorus pentoxide. The products, in each case, are a phenollc acetate and, depending upon the reaction condltions, within methylene diacetate or formaldehyde (or paraformaldehyde). ~he phenolic acetate, and methylene diacetate, when obtained, may then be converted to the respective phenolic compounds and rormaldehyde or paraformaldehyde by pyrolysis or the like.

Earller work of ~rozhen et al, (Doklady Akad. Nau~, SSSR, 204, No. 4,872) established that acld catalyzed oxidatlon of toluene at high temperature and pressure ln acetlc anhydride followed by saponification of the reaction product gave phenol in modest yeild. More recent work has shown that phenyl acetate, methylene diacetate and acetic acid are the maJor products of the acid catalyzed air oxldation of toluene ln acetic anhydride. Despite recent improvements using catalysts initiators and promoters and acetic acid as a solvent this prior wor~ has necessltated high temperatures and pressures to achleve reasonable rates and yields.

SUMMARY OF THE INVENTI _ We have now discovered that the acid-catalyzed oxidation of methyl benzeneæ in acetlc anhydride, or ln acetic acid and phosphorus pentoxide to form a phenolic acetate, methylene dlacetate, and acetlc acid occurs at convenient rates and good yleld3 under mild conditions of temperature and presæure when the resction 18 carrled out in the presence of small

- 2 -amounts o~ benzaldehyde. The reaction proceeds readlly at temperatures as low as 80C and oxygen pressure o~ 1 atmos-phere. The resultlng acetates may then be converted to the respective phenollc compounds and ~ormaldehyde or paraformaldehyde by pyrolysis or the llke.

DESCRIPTION OF ~HE rNVENTION

The process wherein acetic anhydride ls employed may be depicted by the following equation, using toluene as an e~ample:

PhCH3+2AC20 + 2- C ~ C02H ~PhOAc + CH2(OAc)2 + HOAc PhCHO
Caro's Acid in which acetlc acid is being used so1ely as a solvent, together with Caro's acid, a promoter for the reaction.

The process wherein the combination acetic acid and pho8phorus pentoxide may be used in place of acetic acid may be deplcted a~ follows, using toluene:

rCH20 and/o~
PhC~3 + P205 + HOAc I 2 ~ ~4 , PhOAc + LCH2(0AC)2 PhCHO + ~P205 xH20 Caro t 8 Acid 1149~08 It wlll be understood, o~ cour8e, that these methods are equally appllcable to other methyl benzenes such as xylenes and tr~met ffl l benzenes, e.g., mesitylene and pseudocumene.

In general, these processes are carried out by oxidizing the desired methyl benzene with alr or oxysen in the liquid phase at pressures Or at least 1 atmosphere and at temperatures as low as ôOC to form equi~olar amounts of a phenollc acetate and methylene dlacetate, together ~ith acetic acid and lesser amounts o~ certain methyl-benzene-derived by-products. The phenolic acetate and methylene diacetate, following separation, may then be pyrolyzed to form the correspondlng phenolic compound and formaldehyde respectively, while the acetic acid ~ay be routinely converted to ~cetlc anhydrlde and recycled to the oxldation 6tep.

It will thus be seen that as contrasted with the prior art, thls invention is partlcularly characterized by the surprising discovery that the above-described oxldat~on can be carrled out under very mlld reactlon condltions by simply addlng small amounts Or benzaldehyde to the reactlon.

AQ aforementioned, the reactants are methyl benzenes, 6uch a~ toluene, xylene (ortho, meta, or para) and trlmethyl-benzenes such as mesltylene and pseudocumene, together wlth acetlc anhydride and oxygen or a~r, in the presence of a strong acld catalyst, prererably ~ S04, and, as the novel reature Or this lnvention, benzaldehyde. The welght ratio o~
methyl benzene to acetlc ~nhydride should deslrably be in the range o~ ~rom about 50:1 to 1:10, and pre~erably 10:1 to 2:1, while the weight ratlo Or ~ S04 to ~ethyl benzene ~hould generally be ~rom about 5 x 10 4 to 1 x 10 , and pre~erably 1 x 10 3 to 5 x 10-3.

_ 4 -11~9~08 The amount Or benzaldehyde employed 18 about 0.01 to 1.0 moles, and preferably 0.05 to 0.10 moles, per mole of methyl benzene.

The amount of benzaldehyde employed is about 0.01 to 1.0 moles, and preferably 0.05 to 0.10 moles, per mole of methyl benzene.

When P205 18 employed, the amount i8 about 1:1 to 1:20 moles, and preferably 1:2 to 1:5 moles, per mole of acetic acid.
If deslred, the reaction may be run in excess methyl benzene reactant as a solvent, or in a suitable organic solvent such as benzene or chlorobenzene.

It has rurther been round that persulrate promoters such as sodium persulfate, potassium persulrate, persulruric acid or Dry Caro's acld are particularly effective promoters for this oxidation reaction. These promoters are deslrably used in amounts of from about 10-3 to 10 1 gm per gram of methyl benzene.

The reaction, which employs oxygen or equivalent ~mounts of air, can, and should, as aforestated, be carried out under relatively mild condltions, l.e., at temperatures of at least 80C, up to about 150C, and most desirably at about 90-120C, and at air or 2 pressures of at least 1 atmosphere, up to about 10 atmospheres, with the lower ranges of both pressure and temperatures being preferred.

The reaction product conta~ning the phenolic acetate and methylene diacetate, as well as acet'c Rcld, and lesser amounts of methyl benzene derlved by-products, and the like is then routinely treated to remove the acid catalyst, following which the t~o acetate product~ may be separated ~y distillation under vacuum. 5 11 ~9~08 ~ he recovered phenolie acetate ls then converted to phenol, cresol or the llke by pyrolysls. mi8 i8 conventlonally aehieved by heating the acetate at temperatures Or ~rom about 500 to 1000C, prererably at about 625C, and prererably in the presence o~ a catalyst such as triethyl phosphate and recovering the desired product by routine means.

In a llke manner, the pyrolysls Or methylene diacetate yields rormaldehyde and acetle anhydrlde. This pyrolysis ls conventlonally carried out ln one step ln a homogeneous gas phase reaetlon, at about 450-550C under reduced pressure.

Any acetic acid recovered ~rom the oxidation of the alkyl benzene may then be converted to acetlc anhydride ror recycling to the lnitlal oxldatlon step. Thls may readily be achieved e.g. by contactlng ketene with acetic acld at room temperature in the llquld phase.

In a rurther embodiment o~ this ln~entlon, lt has been found that when acetic anhydride is u~ed, as in the rirst o~ the above two reaction schemes~ qulte surprlsingly parafor-~aldehyde, together with a phenolic acetate, may be formed directly, and under mild condltlon~, by the oxidation of methyl benzenes in the presence o~ acetic anhydride, benzaldehyde, and an acid catalyst when (1) the ratio Or acetic anhydride to methyl benzene is controlled in such a fashlon as to induce the selectlve rormatlon o~ formaldehyde and the phenolic acetate, to the exclusion o~ methylene diacetate formation; and-(2) the flow rate of air or oxygen through the reaction ~edlum 18 suf~lcient to re20ve ~ormaldeyde as it i5 formed.

11~9~08 This process, uslng the oxidatlon Or toluene as an example, may be lllustrated by the rollowing equatlon:

PhCHO
PhCH + Ac20 + O ~ PhOAc + ~ O + HOAc Thls reactlon sche~e i8 ln contrast to the rlrst reactlon scheme mentioned above whlch reads as ~ollows:

PhCHO
PhCH3+ 2AC2 + 2 ~ PhOAc + C ~ (OAc)2 + HOAc m us lt wlll be seen that by reducing the amount Or acetlc anhydrlde ln the present case there i8 unexpectedly and selectlvely rormed ln addltlon to phenyl acetate, formaldehyde, to the substantial excluslon Or methylene diacetate. When this modif~catlon is accompanied by an adequate, continuous rlow Or alr or oxygen, formaldehyde vapor~ come out of solution where they are conden~ed and recovered from the reactlon medium, together wlth acetlc acid and lesser amounts of certain methyl benzene-derived by products. As aforestated, the phenyl acetate may then be pyrolyzed to rOrm phenol.

In general, thl~ proce~s i8 carrled out as descrlbed abo~e by oxldizlng the deslred methyl benzene wlth air or oxygen ln the liquid phase at presRures of at least l atmosphere and at temperatures as low as 80C to rorm a phenolic acetate and paraformaldehyde, together with the aforementloned acetlc acld and methyl benzene-derlved by-products. Arter separatlon and recovery Or the phenyl acetate and para~ormaldehyde, the acetlc acld may be routinely converted to acetic anhydrlde and recycled to the oxldation step.

~1~9 ~08 In order to ~ully achie~e the obJects of thls invention and optimlze the formatlon of pararormaldehyde, lt ls essential that acetlc anhydride be metered lnto the reactlon mixture at a rate such that there is sur~icient acetlc anhydride present to selectively react with one of the toluene oxidation products, (phenol) to give phenyl acetate but not enough acetic anhydrlde to convert the other oxidation product (formsldehyde) to methylene dlacetate, under reaction conditions. This may eonveniently be accomplished by careful control of the amount o~ acetic anhydride introduced lnto the reaction as the oxidat~on process i8 monitored, e.~., by conventlonal chromatographlc techniques.

The amounts and flow rate of air or oxygen are not critical but should in any event be sufficient to both oxldize the methyl benzene and at the same time remove the formaldehyde as lt is rormed. Thus, it is only essentlal that the alr or oxygen be provided ln a continuous ~low. Generally, however, it ~ay be said that the amount Or said gas can vary from about 1 to 100 volumes o~ gas per volume Or llquid reaction mixture per unlt Or ~ me, and preferably should be about 10 volumes o~ gas per minute per volume Or reaction mlxture.

The reactlon i8 carrled out ln the presence of an acid catalyst, preferably H2S04, and benzaldehyde. The welght ratio of ~ S04 to methyl benzene should generally be ~rom about 5 x 10 to 1 x 10 2, and preferably 1 x 10 3 to 5 x 10 3, whlle the amount Or benzaldehyde employed should be about 0.01 to 1.0 moles, and preferably 0.05 to 0.10 moles, per mole o~
alkyl benzene.

ô -11`~9408 If desired, the reaction may be run in excess methyl benzene reactant as a solvent, or in a sultable org~nic solvent such as benzene, chlorobenzene, or acetic scid. m e latter is preferred inas~uch QS increased selectivitles are observed.
In order for rapid reactions in acetic acid, promoters such as Caro's Dry Acid should be present in amounts Or 10-100 wt. %
based on the amount of acetic anhydride used.

m e formaldehyde may be recovered either as a monomer or perferably as a solid polymer, pararormaldehyde, which solidlries on a cool surface downstream of the reactor.

The reaction mixture containing the phenollc acetate, as well as lesser amounts Or acetic acid, methyl benzene derived by-products, and the like is routinely treated to remove the acid catalyst, ~ollowing which the acetate may be recovered by distillation under vacuum.

The rollowing examples are provided solely for purposes of illustrating but not llmiting the novel processes of this inventlon. Examples 1 to 10 illustrate the process whereln acetic anhydride i8 employed; examples 11 to 13 illustrate the use Or acetic acld and phosphorus pentoxide; examples 14 and 15 illustrate the conversion Or phenyl acetate and methylene diacetste to phenol and formaldehyde respectively, and examples 16 to lô illustrate the direct recovery of ~ormaldehyde and paraformaldehyde when special reaction conditions are employed.

_ g _ Into a manometric gas-recirculation oxidation apparatus were charged following reactants:

Toluene 21.4 ml Acetic Anhydride 4.0 ml Sulfuric Acid 1 drop (cao.o3g) Air in the reaction flask was replaced with nitrogen and the reaction mixture was heated to 101-3C. When the temperature reached the desired level nitrogen was replaced by pure oxygen and the gas recirculating pump was started, charging oxygen through the liquid at 300-400 ml/min. The gas uptake was measured in the mercury filled buret by a/
displacement method. Liquid samples were withdrawn from the reaction vessel and analyzed by standard gas chromatographic techniques. No measurable oxyg~n uptake occurred under these conditions and no oxidation product(s) were found in the reaction mixture. After 2 hours and 25 minutes on stream 0.49g of benzoyl peroxide, a free radical initiator, was added to the reaction mixture and the reaction was continued for additional 2 hours and 35 minutes. A slow oxygen uptake, a total of 185 ml was recorded as a function of time.
At the end of this period, toluene oxidation products were analyzed by gas chromatography. The wt.% values given are normalized on the basis of the following compounds:
Methylene diacetate (MDA), benzaldehyde (BAL), phenyl acetate (PA), benzyl acetate (BAC), phenyl hemiformal acetate (PHF), and other, unidentified products appearing within the same GC scanning range.

~i .

11~9408 Although benzaldehyde is an added reagent it is conveniently included in the product analysis since it appears within the GC scanning range of toluene oxidation products.
The reaction mixture contained, calculated on the basis of the normalized product scans less than 1% of methylene diacetate (MDA) and ~3% phenyl acetate (P~). The bulk of the oxidized product was benzyl acetate (BAC), 28%, and benzylidine diacetate (BDA) 26%, together with a number of unidentified products.

Into the reactor was charged:

Tdluene 21.4 ml Acetic Anhydride 4.0 ml Sulfuric Acid 1 drop (0.03g) The reaction was carried out in the same manner as in Example 1 for 1 hour. There was no oxygen absorption over this time period, at the end of which 1.0 ml. benzaldehyde and 3 drops of sulfuric acid were added. The oxygen absorp-tion commenced after a few minutes; at the end of the reaction after total of 3 hours, 50 minutes 636 ml oxygen had been absorbed. Analysis of the liquid oxidation product carried out as described in Example 1 showed 10% MDA and 11% PA were present, together with 20% BAC and 12% phenylhemiformal acetate (PHF), a precursor of both PA and MDA.

Into the reactor was charged:

Toluene 21.4 ml Acetic Anhydride 4.0 ml Sulfuric Acid 1 drop (0.03g) !~

11~9408 The reaction was carried out initially as in Example 1 for 4 hours and 16 minutes with only negligible oxygen uptake recorded over this time period. At the end of this period 1.0 ml. of benzaldehyde and 0.56g. of potassium persulfate were added to the reaction mixture. The oxygen uptake commenced after a few minutes and a total of 712 ml oxygen were absorbed by the end of 7 hours and 33 minutes.
The toluene conversion, based on oxygen absorbed was ca 10%.
The liquid product analysis as determined in Example 1, showed 10% MDA, 12% PA, 16~ BAC and 10% PHF among the oxidation products of toluene.

Into the reactor was charged:

Toluene 21.4 ml Acetic Anhydride4.0 ml Acetic Acid12.0 ml Benzaldehyde2.0 ml Dry Caro's Acid0.25 g Sulfuric Acid3 drops (~0.lg) Reaction was carried out initially as in Example 1 with all the ingredients added at the start and after 2 hours and 20 minutes a liquid product sample was analyzed; 12% MDA, 11% PA and 9.5% of PHF were present in the product. The reaction was continued for a total of 6 hours and 55 minutes.
At 3 hours and 34 minutes 2.0 ml of acetic anhydride and at 6 hours and 4 minutes 0.25g of Dry Caro's acid were added.

The final liquid oxidation product, analyzed as in Example 1, contained 20% MDA, 19% PA, 13~ BAC and 4% PHF. The total oxygen uptake was 490 ml with 1.6 m mole CO2 produced in the reaction.

Into the reactor was charged:

Toluene 21.4 ml Acetic Anhydride4.0 ml Acetic Acid12.0 ml Benzaldehyde1.0 ml Co-stearate 7.4 mg The oxidation reaction was carried out initially as in Example 1. At the end of 3 hours and 15 minutes 514 ml oxygen had been absorbed. The product, analyzed as in Example 1, contained 16% MDA, 5~ PA and 7% PHF.

Into the reactor was charged:

Toluene 21.4 ml Acetic Anhydride8.0 ml Acetic Acid12.0 ml Benzaldehyde1.0 ml Sodium Perborate1.54 g.
Tetrahydrate Sulfuric Acid3 drops (~ 0.1 g.) Reaction was carried out as in Example 1. After

3 hours and 22 minutes 780 ml oxygen had been absorbed.

Analysis of the liquid oxidation product, as in Example 1, showed 14~ MDA ~2% PA, 37% benzaldehyde and 34% other products.

Into the reactor was charged:

Toluene 42.8 ml Acetic Anhydride 8.0 ml Sulfuric Acid 2 drops (0.07g) Reaction was carried out initially as in Example 1.
The following reactants were added in the course of the oxida-tion reaction at given time intervals: cyclohexanone, 0.6 ml at 35 min. over a 40 min. period; azobisisobutyronitrile (AIBN), 66 mg. at 186 min.; potassium persulfate, 0.20 g. at 300 min. The reaction was carried out for a total of 10 hours and 27 minutes whereby a total oxygen uptake was 790 ml.
Only traces of the desired products PA and MDA were found among the oxidation products.

Into the reactor was charged:

p-Xylene 24.1 ml Acetic Anhydride 4.0 ml Benzaldehyde 1.0 ml Dry Caro's Acid 0.5 g Sulfuric Acid 3 drops (v^0.1g) Chlorobenzene 1.0 ml (as internal standard) The reaction was carried out initially as in Example l; the reaction temperature was 104-7 and after 4 hours the total oxygen uptake was 582 ml. Analysis of the oxidized product showed the presence of ~-cresyl acetate 28%, and methylene diacetate 16%, 7.5 m mole of carbon dioxide was also formèd.

-Into a 300 ml rocker bomb was charged:

Toluene 43.0 ml Acetic Anhydride 8.0 ml Benzaldehyde 2.0 ml Dry Caro's Acid 1.0 g Sulfuric Acid 0.11 g 1149~08 The bomb was pressurized with 120 psi oxygen and 170 psi nitrogen, i.e. total 290 psi at room temperature and was heated to 120 over a 30 minute period. The reactor was heated at 115-120 for 3 hours, 35 minutes, resulting in the pressure drop of 65 psi. Analysis of the oxidation product, as in Example 1, showed 17% PA, 24% MDA and 8% PHF.

Into a 300 ml rocker bomb was charged:

Toluene 50 ml Acetic Anhydride 11.4 ml Sulfuric Acid 0.11 g The bomb was pressurized with 30 psi oxygen and 145 psi nitrogen, i.e. total of 175 psi at room temperat~re.
The reactor was heated at 130 for an 8 hour period; no pressure drop was observed and no oxadation products were detected in the reaction mixture at the end of the reaction.

Into a manometric gas-recirculating oxidation apparatus was charged, under nitrogen Toluene 21.4 ml.
Acetic Acid 12.0 ml.
Benzaldehyde 1.0 ml.
Phosphorous Pentoxide 2.5 g.
Dry Caro's Acid 0.5 g.

f` .....

The reaction mixture was heated to 102, nitrogen was replaced by pure oxygen and the gas recirculating pump was turned on, sparging oxygen below the surface of the liquid at a rate of 350 ml./min. The oxygen uptake was measured in the mercury filled buret by displacemcnt. Liquid samples were withdrawn from the reaction flask, and analyzed by standard gas chromatographic techniques.

. .

:1149408 After 1 hr. ~nd 15 mln. 197 ~1. o~ oxygen had been ab60rbed. The toluene oxldatlon products were analyzed by GC.
The ~t.~ value~ glven are normalized on the basls of the rollowing co~pounds: Methylene diacetate (MDA), benzaldehyde (BAL), phenyl acetate (PA), benzyl acetate (BAC.), phenyl heml-formal acetate (PHF), and other, unldent~fied product~ appear-ing wlthin the same GC scanning range. Although benzaldehyde 1~ an added reagent it i3 conveniently included in the product analysls since lt a~pears wlthln the GC scanning range Or toluene oxidation product3. The react~on mlxture cont~lned, calculated on the basls of the normalized product ~can~:
(MDA) 8%, (BAL) 30~, (PA) 23%, (~AC) 5%, other unidentiried products within the same scannlng range 34%. The reactlon was contlnued for 5 hrs. at the end o~ this perlod the reactlon product analy7-ed:MDA 14%, BAL, 30~, PA 20~, BAC 3%, others 33%.

EXA~T.h' 12 Into a 300-ml. rocking bomb was charged:

Toluene 43.0 ml.
Acetlc Anhydrlde 2.0 ml.
Acetic Acid 16.0 ~1.
Benzaldehyde 2.0 ml.
Dry Caro~s Acld 1.0 g.
Phosphorus Pentoxide 5.0 g.
Sulfuric Acid 0.11 g.

The bomb was pressurized with 120 p~i of oxygen and 170 psl nitrogen and was heated to 120C over a 30 min. perlod, then held at 120C for 1 hr. 25 ~in. The pressure drop after coollng to room temperature was 32 ~sl. The reaction ~lxture was anslyzed for the toluene oxidation products a~ ln Example 1.
MDA 21f, 8AL 18~, PA 21~, BAC 5%, phenylhemi~ormal acetate (PHF) 8%, others 26~.

Into the manometric reclrculating resctor wa~
charged:
Toluene 21.4 ml.
Acetlc Acid 12.0 ml.
Benzaldehyde 1.0 ml.
Dry Caro's Acid 0.5 g.
Anh. Magnesium Sul~ate3.0 g.

The reaction was carried out as in Example 1 at 103C for 2 hrs. and 30 min. At the end o~ this period no detectable oxidation products were shown by the gas chromato-graphy.
EXAMPI,E li Pyrolysis Or methylene diacetate to pararormal-dehyde and acetic anhydride can be accompli~hed thermally at about 500C ln a ~nown manner.

Alternatively, the catalytic pyrolysis of methylene diacetate may be carried out at about 300C in the presence of a catalyst composed of 5~ sodium chloride mixed with silica gel, dried and calcined. The methylene diacetate, dissolved in n-hexane, is passed through a passified tubular reactor packed with the catalyst at a space velocity of 900 hr 1 and a temperature of 300C. Paraformaldehyde and acetic anhydride condense downstream and are separated routinely. Selectivities exceed 93% for acetic anhydride and 95% for methylene diacetate.

Pyrolysis of phenyl acetate to phenol and ketene is accomplished thermally at 625C by passing it through a well-conditioned tubular reactor. The effuent is condensed to give 84% yièld of phenol and 89% yield of ketene.

The reaction may be carried out at a somewhat lower temperature in the presence of triethyl phosphate catalyst at space velocities of between 900 and 1000 hr 1. Yields in excess of 90% are obtained.

Cresyl acetate may be converted in a like manner to cresol.

The results of the foregoing Examples can better be appreciated in light of the following discussion:

Example 1 shows that essentially no oxidation of toluene occurs in the presence of acetic anhydride and sulfuric at ~he pressures and temperatures given. It further shows that upon addition of a free radical chain initiator such as 1149~08 benzoyl peroxide, a slow oxidation reaction takes place but the predominant products are not the desired phenyl acetate (PA) and methylene diacetate (MDA) which are both present in amounts less than 3%.

Example 2 shows that addition of benzaldehyde to toluene plus acetic anhydride plus sulfuric acid causes a reasonably rapid reaction to occur, wherebyv~10% MDA, 11% PA
and 12% PHF, a precursor of MDA and PA, are formed.

Example 4 shows that the oxidation of toluene in the presence of acetic anhydride, and acetic acid, benzalde-hyde, dry Caro's acid, and sulfuric acid gives a superior selectivity to PA and MDA. The key factor here would appear to be the addition of Caro's acid plus acetic acid to other previou~ly used reactants.

Example 5 shows that addition of a conventional toluene oxidation catalyst i.e. a cobalt salt, does not promote a selective reaction since only 5% of PA was found together with 11% BAC.

Example 6 shows that another strong, non-heavy metal oxidant such as sodim perborate does not promote the formation of PA since less than 2% of the latter was present.

Example 7 shows that use of another carbonyl-containing promoter, cyclohexanone, instead of benzaldehyde does not result in the formation of the desired products, PA and MDA.

1149~08 Example 8 shows that benzaldehyde can promote the oxidation of higher homologs of toluene e.g., xylenes, In the case of p-xylene, p-cresyl acetate is formed.

Example 9 shows that when co-oxidation of toluene and benzaldehyde is carried out at 120 i.e. at low tempera-ture and somewhat elevated pressure of oxygen (120 psi), substantial quantities of both PA and MDA are obtained.

Example 10 shows that no oxidation occurs at 130 in the absence of benzaldehyde.

Into a manometric gas-recirculation oxidation apparatus was charged:

Toluene 42.8 ml Acetic Anhydride1.0 ml Benzaldehyde 1.0 ml Sulfuric Acid2 drops (~ 0.06g) Air in the reaction flask was replaced by nitrogen and the reaction mixture was heated to ~100C. When the temperature reached 100C nitrogen was replaced by pure oxygen and the gas recirculating pump was started, sparging oxygen through the liquid at 300-400 ml/min. The gas uptake was recorded with time by measuring the displacement in a mer-cury filled gas buret assembly. L~~quid samples were withdrawn from the reaction flask and analyzed by standard gas chromato-graphic techniques. Acetic anhydride was added, incrementally, to the reaction mixture from a motor driven syringe pump between 49-108 min., 0.72 ml and 172-220 min. 0.20 ml. At the end of this time period (3 hours, 40 min.) the oxygen . .~. ., ~ , - 21 -, . .

1149'~(~8 Uptake was 349 ml and the oxidized product contained phenyl acetate (PA) 26%, methylene diacetate (MDA) 7%, phenyl hemiformal acetate (PHF) 2%, benzyl acetate tBAC) 14~. A
substantial quantity of a white solid covered the cold sur-faces of the reactor and condenser. Analysis showed this material to be a solid polymer of formaldehyde, i.e., paraformaldehyde.

In accordance with foregoing procedure, but sub-stituting xylene for toluene, there is obtained cresyl acetate and paraformaldehyde, together with acetic acid and related by-products.

Into the reactor was charged:

Toluene 42.8 ml Acetic Anhydride 1.0 ml Benzaldehyde 1.0 ml Potassium Persulfate 0.54 g Sulfuric Acid 2 drop t~ 0.06 g) The reaction was carried out as in Example 1, at 100C with incremental addition of acetic anhydride between 33-73 min., 0.82 ml and 100-160 min., 0.62 ml. After 2 hrs.
40 min. the reaction was stopped, with a total oxygen uptake of 280 ml. The oxidation product contained PA-17%, MDA-trace, BAC 8~. The cold walls of the reactor and condensor were covered with a white solid which was shown to be solid paraformaldehyde by infrared analysis.

Into the reactor was charged:

Toluene 42.8 ml Acetic Anhydride 16.0 ml Benzaldehyde 1.0 ml Potassium Persulfate 0.43 g Sulfuric Acid 2 drops (~ 0.06 g) 11~9408 The reaction was carried out as in Example 1, except that all the reactants were present initially and no incre-mental addition was carried out. At the end of 5 hr. reaction had stopped with total of 240 ml oxygen absorbed.

Only 3% PA and MDA were found among the oxidation products which also contained 19% BAC. No solid paraformal-dehyde was detected.

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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the oxidation of methyl benzenes to form a phenolic acetate and formaldehyde or paraformaldehyde which comprises reacting said methyl benzene with air or oxygen and acetic anhydride in the presence of an acid catalyst and benzaldehyde, wherein the amount of acetic anhydride present is insufficient to form methylene diacetate, thereby selectively forming said phenolic acetate, together with free formaldehyde or paraformaldehyde, and wherein the flow rate of air or oxygen is sufficient to provide the continuous removal of said formaldehyde or paraformaldehyde as it is formed.

2. The process of Claim 1 wherein the reaction is carried out at temperatures of at least about 80°C and pressures Or at least about 1 atmosphere.

3. The process of Claim 1 wherein the acid catalyst is H2SO4.

4. The process of Claim 1 wherein the temperature is from about 80° to 150°C.

5. The process of Claim 1 wherein the pressure is from about 1 to 10 atmospheres.

6. The process of Claim 1 wherein a suitable organic solvent is employed.

7. The process of Claim 6 wherein the solvent is acetic acid and a promoter for said acid is present.

8. The process of Claim 1 wherein the reaction is carried out in the presence of a persulfate promoter.

9. The process of Claim 8 wherein the promoter is Dry Caro's acid.

10. The process of Claim 1 wherein the benzaldehyde is present in amounts of 0.01-1.0 moles based on the methyl benzene.

11. The process of Claim 1 wherein the methyl benzene is toluene and the products are phenyl acetate and formaldehyde and/or paraformaldehyde.

12. The process of Claim 1 wherein the methyl benzene is xylene and the products are cresyl acetate and formaldehyde and/or paraformaldehyde.