GB1570858A

GB1570858A - Process for treatment of oxidation products formed by oxidizing a monoalkyl benzene compound or a derivative thereof

Info

Publication number: GB1570858A
Application number: GB53953/77A
Authority: GB
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1976-12-28
Filing date: 1977-12-28
Publication date: 1980-07-09
Also published as: FR2376121A1; IT1093094B; DE2758487A1; PT67457B; FR2376121B1; IN147882B; BE862394A; YU314777A; PT67457A; ES465462A1; JPS5382741A

Description

(4) PROCESS FOR TREATMENT OF OXIDATION PRODUCTS FORMED BY OXIDIZING A MONOALKYL BENZENE COMPOUND OR A DERIVATIVE THEREOF (71) We, STAMICARBON B.V., a Netherlands Limited Liability Company of P.O.

Box 10, Geleen, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for preparing oxidation products of monoalkyl benzene compounds by means of a gas containing molecular oxygen.

An example of such a process is the oxidation of toluene, to provide for example benzoic acid, benzaldehyde. benzyl alcohol and/or benzyl benzoate. The oxidation of toluene is used on an industrial scale. The invention may however also be applied to the oxidation of other alkyl benzene compounds.

The oxidation reaction may take place either in the liquid phase in the presence of an oxidation catalyst e.g. a cobalt salt that is soluble in the reaction medium, or in the gaseous phase in the presence of a catalvst based on vanadium or other transition metal (c.f.

Stanford Research Institute (SRI) Reports No. 7) 1965. 29; No. 7A (1968), 241; No. 7B (1976), 53. In most instances a complex mixture ot oxidation products is obtained from which the desired valuable components are difficult to recover. Thus the recovery of pure benzyl alcohol and benzyl benzoate is particularly difficult as these compounds have boiling points that are only slightly different from other and undesired products of the oxidation reaction.

Our patent application 53520/77 (Serial No. 1568440) relates to the treatment of tars containing benzyl benzoate.

The invention provides the possibility of processing the oxidation reaction mixture in a simple way into a number of desired products, in particular when oxidizing toluene, benzoic acid and benzaldehyde, and also benzyl benzoate and benzul alcohol, in a pure state.

According to the invention. oxidation products of monoalkyl benzene compounds are prepared by oxidizing a monoalkyl benzene compound by means of a gas containing molecular oxygen. characterised in that at least one stream which contains compounds present in the oxidation reaction mixture, or derivatives of such compounds, is subjected to an esterification reaction with a carboxylic acid.

The said carboxylic acid may be a carboxylic acid formed during the oxidation reaction, or present as a solvent during the oxidation reaction, or added to the oxidation reaction product after the oxidation has been completed.

In the esterification a carboxylic acid, preferably containing from 1 to 18 carbon atoms per molecule reacts to form an ester with alcohols contained in the reaction mixture, particularly benzyl alcohol in the toluene oxidation product, and/or to form another ester with esters of other acids than said carboxylic acid that are contained in the reaction mixture. especially benzyl esters of volatile carboxylic acids with 1-6 carbon atoms per acid molecule. such as formic acid. acetic acid, and propionic acid. The carboxylic acid used for the esterification is preferably a benzene carboxylic acid, and preferably is that formed in the oxidation of the monoalkyl benzene compound in question, i.e. unsubstituted benzoic acid in the oxidation of toluene. According to another preferable embodiment of the process according to the invention, in said carboxylic acid is acetic acid, propionic acid or butyric acid.

The esterification and/or re-esterification makes it possible to raise considerably the boiling point of the benzyl alcohol and/or the bcnzyl esters of volatile carboxylic acids in the reaction mixture. A number of more volatile components whose boiling points would be too close to that of said components to allow of effective separation can then be removed without any problem, e.g. by distillation. Moreover, the useful product benzyl benzoate can be obtained in a pure state. If acetic acid is used, the useful product benzyl acetate can be obtained. These compounds are used in the manufacture of scents and flavours.

In the esterification the alcohols and esters of volatile acids in the reaction mixture are preferably converted fully or almost fully into the esters of said carboxylic acid.

As the chemical properties ot benzoic acid differ considerably from those of the esters obtained, the separation of benzoic acid from the reaction mixture, if necessary, presents no serious problem. Bcnzoic acid, if any, can be extracted from the reaction mixture by means of, e.g. water, an aqueous solution of soda, diluted sodium hydroxide solution, or another suitable extracting agent, or the reaction mixture can be separated by distillation.

Benzyl alcohol and benzyl esters of volatile acids originally present are converted into benzyl esters of said carboxylic acid in the esterification reaction. These benzyl esters can be recovered as such. Another possibility is to subject the mixture containing benzyl esters to a hydrolysis or ammonolysis, after the more volatile components have been removed. Thus benzyl benzoate, for instance, is converted into benzyl alcohol and benzoic acid or a salt thereof, e.g. benzamide. As benzyl alcohol is now the only more volatile component in the reaction mixture. it can be separated in a simple way by distillation.

Just as the process according to the invention can be used for the oxidation of toluene, so it can be used in an analogous way for the oxidation of other monoalkyl benzene compounds with 1-4 carbon atoms in the alkyl group, which may also contain non interfering substituents at the benzene nucleus, e.g. halogen, nitro or sulphonic acid substituents. Examples are ethyl benzene, p-chlorotoluene, p-nitrotoluene, and p-toluene sulphonic acid.

The reaction conditions in the oxidation reaction do not deviate from the well-known conditions. For the sake of brevity reference is made to the known literature, especially the abovementioned SRI reports and the other literature mentioned there.

In the oxidation in the liquid state, the reaction temperature usually ranges between 100 and 2000C, the reaction pressure between 1 and 10 atm. The catalyst is preferably a compound of a transistion metal, especially cobalt and/or manganese, that is soluble in the reaction mixture. Examples of suitable catalysts are the transition metal salts of carboxylic acids e.g. cobalt (II) acetate, manganese (II) propionate or cobalt (II) octoate. Use may also be made of mixtures of two or more transition metals, in particular, compounds of cobalt and manganese. If so desired, the oxidation may be carried out in the presence of a carboxylic acid as a promotor, in particular, acetic acid, and/or in the presence of a halogen compound, especially hydrogen bromide or another bromide that is soluble in the reaction mixture.

In the oxidation in the gaseous state, the reaction temperature usually ranges between 200 and 600"C. the rection pressure between 1 and 10 atm. The catalyst is preferably an oxide compound of transistion metal, in particular, vanadium, although compounds of, e.g.. molybdenum. chromium, tungsten. and uranium may also be used. Suitable catalysts are. for instance. those based on the vanadates of silver, iron and/ore one or more of the so-called rare-earth metals (atomic numbers 57 through 71, and also scandium and yttrium). e.g., scandium, yttrium, lanthanum, cerium. or 'didymium' (a mixture of praseodymium and neodymium). The catalyst is preferably put on a carrier, such as, e.g.

aluminium oxide or silicon oxide.

The gaseous mixture may contain steam and/or a vapour of a carboxylic acid e.g. acetic acid, in addition to the monoalkyl benzene compound.

The esterification may be carried out, e.g., at a temperature of 100-300"C, the esterification/re-esterification without a catalyst preferably at a temperature of between 160 and 300"C. The pressure may range, e.g., between 1 and 10 atm. If so desired, use may be made of any esterification/re-esterification catalyst, e.g. a mineral acid, such as sulphuric acid or phosphoric acid or also borotrifluoride or zinc acetate.

The use of an esterification/re-esterification catalyst may lead to contamination of the benzyl ester product. The esterification/re-esterification may also proceed well in the absence of a catalyst.

The benzyl ester obtained can be hydrolysed with a basic solution, in particular, an aqueous sodium hydroxide solution or a soda solution. Also potassium hydroxide or calcium hydroxide might be used. But there is a need of sodium benzoate as a reaction product, so that benzyl benzoate is preferably hydrolysed with a basic sodium compound.

If so desired, the benzoate salt thus obtained can be converted into a very pure free benzene carboxylic acid, e.g., unsubstituted benzoic acid, by reaction with a strong acid, e.g. sulphuric acid or nitric acid If so desired, the hydrolysis may also be effected by means of an acid, instead of a basic, catalyst, e.g. a mineral acid, such as sulphuric acid or phosphoric acid. Of course, free carboxylic acid will then be formed, which may be returned to the esterification reactor.

The temperature in the hydrolysis reaction may range, for instance, between 30 and 200"C. The pressure is not critical and, for practical reasons, preferably ranges between 1 and 10 atm.

The benzyl ester obtained may also be ammonolysed, i.e. be made to react with ammonia or a primary or secondary amine. Use is preferably made of ammonia, either in the gaseous state or as an aqueous solution, e.g. 50% by weight of ammonia. If an amine is used, it is preferably an aliphatic amine with, preferably, 1-4 carbon atoms per hydrocarbon group attached to nitrogen. Preference is given to primary aliphatic amines, e.g. monoethyl amine or isopropyl amine. Aniline or diethyl amine, for instance, may also be used.

The ammonolysis may be carried out, e.g., at a temperature of 30-200"C at autogenous pressure or a higher pressure.

The invention will be elucidated with reference to the reaction diagram annexed, indicated as Figure 1.

Oxidation reactor 1 is fed with liquid toluene through conduit 2 and with air through conduit 3. The toluene contains 0.001 to 0.1 % by weight of cobalt (II) acetate as a catalyst in solution. In reactor 1, the toluene is oxidized in the liquid state at a temperature of 140 to 165 "C and a pressure of 3 to 10 atm. The vent gas is passed from the reactor through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6, the condensate is passed through conduit 7 to separator 8, where it separates into an organic layer and an aqueous layer. The aqueous layer is removed through conduit 9; the organic layer is returned to oxidiation reactor 1 through conduit 10.

The liquid oxidiation mixture flows from oxidation reactor 1 through conduit 11 to distillation column 12. In this column all components with boiling points lower than that of benzoic acid and, preferably, some benzoic acid are distilled off. Crude benzoic acid, which is purified in the usual way, is recovered through conduit 13. The top product is passed through conduit 14 and fed to distillation column 15, in which the toluene and benzaldehyde, if any, are fully or partly distilled. The top product (conduit 16) may be returned to oxidation reactor 1, either as such or after benzaldehyde has been removed from it by distillation.

The bottom product of column 15, which contains, i.a., benzyl alcohol, benzoic acid, benzyl formate, and benzyl acetate, is passed through conduit 17 to esterification reactor 18. Here the temperature is controlled at 200-2500C, the pressure is equal to atmospheric pressure. In this reactor benzyl alcohol esterifies with benzoic acid to benzyl benzoate and water, and the light benzyl esters, such as benzyl formate and benzyl acetate, re-esterify with benzoic acid to form benzyl benzoate and the free light acids, such as formic acid and acetic acid. The reaction water and the resulting light acids escape through conduit 19 as a vapour. Any by-products with boiling points up to about 250 "C also escape through this conduit. The reaction mixture passes through conduit 20 to distillation column 21, where the remainder of these by-products is removed by distillation at a pressure ot U.2 atm and is discharged as a vapour through conduit 22, and, if so desired, is returned to oxidation reactor 1 after condensation and removal of the resulting aqueous layer, while the liquid benzyl-benzoate product leaves columns 21 through conduit 23. This product consists of crude benzyl benzoate which can be recovered through conduit 24 and from which pure benzyl benzoate can be recovered by simple distillation.

The benzyl-benzoate product can be passed through conduit 25 to hydrolysis reactor 26, to which aqueous sodium hydroxide is fed through conduit 27. The temperature in the reactor 26 amounts to 90-110"C. In this reactor benzyl benzoate is hydrolysed to sodium benzoate and benzyl alcohol. If the benzyl benzoate product supplied through conduit 25 still contains free benzoic acid, this is also converted into sodium benzoate in reactor 26.

The reaction mixture from reactor 26 is fed through conduit 28 to extraction column 29, which is supplied with toluene through conduit 30 and in which a separation into an aqueous layer and an organic layer is effected. The aqueous layer consists of an aqueous sodium benzoate solution, which is discharged through conduit 31 and from which solid sodium benzoate can be obtained by removal of water. The organic layer substantially consists of benzyl alcohol and toluene with some by-products with higher boiling points and is passed through conduit 32 to distillation column 33. Thanks to the great difference between the boiling points of toluene, benzyl alcohol, and the by-products, separation by distillation presents no problems. Pure benzyl alcohol is recovered through conduit 34, while toluene is discharged through conduit 35 and the by-products are removed through conduit 36. l'he toluene may be returned to extraction column 29 and the by-products may be returned to oxidation reactor l.

The ratio between the amounts of free benzoic acid and sodium benzoate produced can be controlled to suit the requirements by controlling the amount of benzoic acid that is distilled over in distillation column 12, also in dependence on the amount of benzylbenzoate product discharged through conduit 24. If the need of benzyl alcohol is not great, the temperature in distillation column 15 can be adjusted to a higher value, so that part of the benzvl alcohol present also distils over and is returned to oxidation reactor 1 together with the toluene recycle flow.

Instead of distilling benzoic acid from column 12 to have it available in esterification reactor 18 the required benzoic acid may, of course. also be fed separately to reactor l8.

According to a further embodiment of the invention, the stream which is subjected to the carboxylic acid esterification reaction is a tar fumed in the oxidation of a monoalklyl benzene compound and containing benzvlbenzoate or substituted beazylbeazoate. Such tars mav be formed from the product of oxidation of an alkyl benzene as herein before described in different ways as described for example hereinafter. The benzoic acid may be distilled completely or partly, together with all products with lower boiling points, from the reaction mixture that contains benzoic acid, benzyl benzoate, other products with higher boiling points than benzoic acid and herein referred to as tar residue, unconverted toluene and secondarv products. such as benzvl alcohol and benzaldehyde, with lower boiling points than benzoic acid, and the distillate may be further processed for pure benzoic acid, so that a tar containing benzyl benzoate and, possibly. some benzoic acid is obtained as a residue.

This residue may be used as the starting material for the process according to the invention.

A tar that contains beuzyl benzoate and which may also be used as a starting material for the special embodiment of the process according to the invention may also form if the above distillate is heated. whether or not in the presence of an esterification or re-esterification catalyst. e.g. sulphuric acid, phosphoric acid, boron trifluoride, or zinc acetate, in order to esterify or re-esterify benzyl alcohol andxor light benzyl esters, such as benzyl formate and beazyl acetate, into beazyl benzoate, especially if the mixture still contains benzaldehyde during this esterification reaction.

It is very difficult to recover useful products from such a tar containing benzyl benzoate.

Benzyl beiizoate can be distilled from the tar residue, it is true, but a pure benzyl-benzoate product can only be obtained with difficultv. It has been found that the componet tluorenone of the tar causes special problems in this connection. For, it has been found that fluorenone can hardly be separated from benzyl benzoate. But besides fluorenone, other unidentified compounds may play a part.

According to this embodiment of the invention a benzyl ester is prepared by subjecting a tar containing benzyl benzoate to acidolysis with an acid with a low boiling point, so that the benzvl benzoate is converted into the benzyl ester of the acid with the low boiling point.

Acidolvsis denotes a re-esterification reaction in which an ester of an acid A and an alcohol B reacts with an acid C, so that an ester of acid C and alcohol B is formed in addition to (free) acid A. In the process according to the invention the ester of a benzoic acid and a benzvl alcohol reacts, e.g., with acetic acid, so that a benzyl acetate is formed in addition to (free) benzoic acid.

The term acid with a low boiling point' denotes an acid the benzyl ester of which has a lower boiling point than benzyl benzoate. which usually implies that the free acid itself also has a lower boiling point than benzoic acid.

Bv means of the acidolysis reaction according to this embodiment of the invention, the benzyl benzoate with a high boiling point, which is difficult to separate by distillation from some tar components, is converted into benzoic acid and a benzyl ester with a considerably lower boiling point which considerablv differs in chemical and physical properties from the benzyl benzoate and the tar components. The benzyl ester with a low boiling point can be recovered in a pure form from the acidolysed mixture, e.g. by distillation. Such benzyl esters are useful products, which are used, e.g.. in the scents and flavours industry. Hence, this embodiment makes it possible to convert a waste product that was useless so far into a useful substance.

The acidolysis is preferably carried out with an aliphatic carboxylic acid with 1-6 carbon atoms, more in particular 2-4 carbon atoms, per molecule with a low boiling point. Use is preferably made of acetic acid, propionic acid, or butyric acid, although formic acid, for instance, may also be used. As benzyl acetate is a valuable commerical product, special preference is given to acetic acid. Benzyl acetate can very favourably be produced by the special emboidment of the process according to the invention.

The acidolysis reaction may be carried out under the same conditions as described above, i.e. at a temperature of between 1000C and 300"C, with or without a catalyst.

The tar containing benzyl benzoate used as the starting material is preferably free of impurities with lower boiling points than benzoic acid. It will then be possible to recover the benzyl ester with a low boiling point in a pure state in a simple way by means of distillation.

Any components in the starting material having lower boiling points than that of benzoic acid can be removed prior to the acidolysis treatment, e.g. in one of the ways described above.

As the chemical properties of benzoic acid are considerably different from those of the resulting esters, the separation of benzoic acid from the reaction mixture, if effected, does not constitute a serious problem. The benzoic acid can be extracted from the reaction mixture, for instance, by means of water, an aqueous soda solution, diluted sodium hydroxide, or another suitable extracting agent, or the reaction mixture can be separated by distillation.

Benzyl benzoate in the starting material is converted into a benzyl ester with a lower boiling point in the acidolysis reaction. This benzyl ester can be recovered as such. It is possible to remove the benzyl ester with the low boiling point from the reaction mixture by distillation and then to subject it to a hydrolysis or ammonolysis treatment as described above. Thus, benzyl acetate is converted into benzyl alcohol and acetic acid or a salt or amide thereof. As benzyl alcohol is now the only more volatile component in the reaction mixture in addition to the acetic acid, it can readily be removed by distillation. The acetic acid may be returned ot the acidolysis.

The invention will be further explained with reference to the reaction diagram annexed, indicated as Figure 2.

Oxidation reactor 1 is fed with liquid toluene through conduit 2 and with air through conduit 3. The toluene contains 0.001 to 0.1 % by weight of cobalt (II) acetate as dissolved catalyst. In reactor 1 the toluene is oxidized in the liquid phase at a temperature of 140 to 1650C and a pressure of 3 to 10 atm. The vent gas from the reactor is passed through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6 and the condensate is passed through conduit 7 to separator 8, where it is separated into an organic layer and an aqueous layer. The aqueous layer is removed through conduit 9; the organic layer is returned to oxidation reactor 1 through conduit 10.

The liquid oxidation mixture flows from oxidation reactor 1 through conduit 11 to distillation column 12, where all components with a lower boiling point than benzoic acid, plus, preferably, some benzoic acid, are distilled off and discharged through conduit 14.

This top product substantially consists of toluene and may be returned to oxidation reactor 1. either as a whole or after benzaldehyde has been recovered from it by distillation. The bottomXproduct flows through conduit 13 to distillation column 40, where all benzoic acid and components with a lower boiling point are distilled off and discharged through conduit 41; this distillate can be processed into pure benzoic acid in the usual way. The residue flows through conduit 42 to distillation column 43. Column 43 may be a film evaporator.

The bottom product of the distillation is discharged through conduit 44. The resulting distillate. a mixture of benzyl benzoate and tar, is passed through conduit 45 to acidolysis reactor 46. The acidolysis reactor is fed with an acid with a low boiling point, acetic acid in this case, through conduit 47, and with sulphuric acid as a catalyst through conduit 48. The reaction mixture from the acidolysis reactor passes through conduit 49 to distillation column 50. in which unconverted acetic acid is distilled and removed as the top product.

The acetic acid is returned to acidolysis reactor 46 through conduits 51 and 47. A side flow consisting of benzyl acetate and some benzoic acid is withdrawn from distillation column 50. This prevents benzyl acetate from being returned into the process later on. This side flow is passed through conduit 52 to washing device 54, where it is washed with aqueous sodium hydroxide solution supplied through conduit 55. The aqueous phase leaves the washing device through conduit 56. The benzyl acetate product is recovered through conduit 57 and, if so desired, may be further purified, e.g. by fractional distillation. The bottom product from column 50, which contains the major amount of benzoic acid, unconverted benzyl benzoate, sulphuric acid and the tarry impurities, is returned to distillation column 40 through conduits 53 and 13.

In a variant embodiment the columns 40 and 43 are omitted and the bottom product from column 12 is fed directly to acidolysis reactor 46. Then the bottom product from column 50 is not returned to the process, but is discharged as tar.

The invention will be further explained with reference to the following numerical Examples/experiments .

Example 1 In Example 1 to V reference is made to Figure 1.

Toluene was oxidized in the liquid phase by means of air in oxidation reactor 1 at a temperature of 160 "C and a pressure of 5 atmospheres and in the presence of 0.008 % by weight of cobalt (in the form of acetate). In distillation column 12, the components with lower boiling points than benzoic acid and some benzoic acid were distilled from the bottom flow of reactor 1 at atmospheric pressure. The products with lower boiling points than benzyl alcohol are distilled from the top product of distillation column 12 at atmospheric pressure in distillation column 15.

The composition, in % by weight, of the bottom product discharged from distillation column 15 through conduit 17 is given in Table I. 'Other organic compounds' are, i.a., dibenzyl ether, acetophenone, methyl benzoate, 2-methyl diphenyl and 1,2-diphenyl ethane.

TABLE 1 Flow of material conduit 17 conduit 19 conduit 20 benzyl alcohol 7.6 - 0.4 benzyl formate 9.9 - 0.9 benzyl acetate 14.3 - 8.9 benzyl benzoate - - 35.4 benzoic acid 51.7 - 31.4 other organic compounds 16.5 0.9 15.6 water/formic acid/acetic acid - 4.1 2.1 Said bottom product is passed to esterification reactor 18 that consists of a 1-litre glass flask to which a 40-cm long heating column is connected with a still head on top. The heating column is heated at 125-140 "C to avoid condensation of the volatile components formed in the reaction so that they can be removed by way of the still head. Another result is that the benzoic acid that has also evaporated condenses in the heating column, but does not solidify and, hence, flows back into the flask. The residence time in reactor 18 amounts to 30 minutes. An inert atmosphere (nitrogen) is maintained in the reactor. The flask is heated at the temperature specified in Table II by means of a metal bath.

The distillate and the residue are put together and the total is analysed. The results of the analysis are also given in Table II.

TABLE II Temperature ("C) 200 210 230 250 benzvl alcohol (% by w.) 3.4 2.6 1.4 0.9 benzyl formiate ' 7.5 6.8 5.7 4.2 benzyl acetate ' 14.3 12.0 11.6 11.2 benzyl benzoate ' 11.9 17.9 22.6 26.4 benzoic acid ' 44.9 41.4 38.7 36.5 other organic compounds ' 16.5 16.5 16.5 16.5 water/formic acid/acetic acid ' 1,4 2.8 3.5 4.3 The higher the temperature, the more products with lower boiling points, especially benzyl alcohol and benzyl formate, but also benzyl acetate, are converted into benzyl benzoate with a higher boiling point.

Example II Example I is repeated, but now the bottom flow (see conduit 17) of distillation column 15 with the composition according to Table 1 is heated in esterification reactor 18 for 160 minutes. The temperature of the metal bath is kept at 2500C. During heating the boiling temperature in reactor 18 is observed (see Table III). The boiling temperature rises as components with lower boiling points, such as benzyl alcohol, benzyl formiate and benzyl acetate, are converted into products with higher boiling points, especially benzyl benzoate.

TABLE III Time (minutes) Boiling temperatures ("C) 0 206 10 221 20 224 40 233 80 238 160 224 In Table I the composition of the starting flow of materials (see conduit 17), the compositions of the distillate (see conduit 19), and the composition of the residue (see conduit 20) are given and expressed as % by weight calculated to the total of the flows in conduits 19 and 20.

The benzoic acid is distilled from the bottom flow of the esterification reactor 18 in distillation column 21 at a pressure of 25 mm of Hg. The composition of the top product (see conduit 22) and of the bottom product (see conduit 23, expressed in % by weight of the total of the flows in conduits 22 and 23, is given in Table IV, whe

Example IV Example I is repeated, but the benzoic acid is removed from the bottom product of distillation column 15 (see conduit 17 with the composition according to Table 1, by washing with an aqueous soda solution (10 % by weight of Na2CO3), after which acetic acid is added to the washed product. The mixture obtained, the composition of which is given in Table VI ('before conversion'), is boiled in the esterification reactor 18 until a bottom temperature of 155"C is reached, which takes about 8 hours. The column on the reactor is not heated. The distillate (see conduit 19) and the residue (see conduit 20) are analysed together.

The results of analysis are also given in Table VI ('after conversion').

TABLE VI Before conversion After conversion (% by weight) (% by weight) benzyl alcohol 7.6 0.3 benzyl formate 9.9 8.7 benzyl acetate 14.3 25.8 other organic compounds 16.5 16.6 acetic acid 51.7 47.1 formic acid/water - 1.7 Example V Example II is repeated, unless otherwise specified. The crude benzyl benzoate in conduit 23, the composition of which is given in table IV, is now fed to an ammonolysis/hydrolysis reactor 26 through conduit 25. Here it is made to react with an aqueous ammoniumhydroxide solution (25.6 % by weight calculated as NH40H) that is supplied through conduit 27. The composition of the reaction mixture before ammonolysis/hydrolysis is given in Table VII.

The reaction mixture is stirred at 150 OC and 15 atm for 4 hours in ammonolysis/hydrolysis reactor 26, an autoclave with a stirring mechanism. After cooling, the reaction mixture is given a pH of 6 by means of 1 N aqueous sulphuric acid and extracted three times with toluene m an amount of half the weight of water present. The toluene and the components with lower boiling points are evaporated from the extract, the product obtained having a composition as mentioned in Table VII.

TABLE VII Before ammonolysis/ After ammonolysis/ hydrolysis hydrolysis benzyl benzoate 18.4 1.0 benzoic acid 0.03 37.7 ammonium hydroxide 20.2 water 58.7 benzyl alcohol - 42.6 benzamide - 6.4 other organic compounds 2.6 12.2 The benzamide can be recovered by crystallisation. The yield of benzamide can be raised at the cost of benzoic acid by carrying out the ammonlysis in the presence of less water or no water at all.

The benzyl alcohol and the benzoic acid can be recovered by distillation.

Example VI In this and the following Examples reference is made to Figure 2.

In oxidation reactor 1 toluene is oxidized in the liquid phase with air at a temperature of 160 "C and a pressure of 5 atmospheres and in the presence of 0.008 % by weight of cobalt (as acetate). The degree of conversion of the toluene is about 20 %. The components with a lower boiling point than benzoic acid and some benzoic acid are distilled from the bottom flow from reactor 1 in distillation column 12 at atmospheric pressure. The bottom product from distillation column 12 is distilled further at atmospheric pressure in distillation column 40. until virtuallv all benzoic acid and components with lower boiling points have been removed from the reaction product. The residue is subjected to film evaporation in flash evaporator 43 at a temperature of 260 "C and a pressure of 25 mm of Hg. Acetic acid and sulphuric acid are added to the distillate of the film evaporation, a mixture of benzyl benzoate and tar, in acidolysis reactor 46, consisting of a glass flask with reflux condenser.

The composition of the mixture thus obtained is given in Table VIII (before acidolysis The tar residue consists of, i.a., fluorenone (about 40 % by weight realtive to the tar), 1.2-diphenyl ethane and 2-, 3-, and 4-methyl diphenyls.

The mixture in the acidolysis reactor is boiled for 2 hours at a temperature of about 130 "C. The composition of the reactor contents after acidolysis is also given in Table VIII.

TABLE VIII Composition Before After flow 51 flow 52 flow 53 '. by w. acidolysis acidolysis benzoic acid 10.7 23.5 - 1 52.0 acetic acid 45.6 39.1 99 - beazyl acetate - 16.0 1 99 beazyl benzoate 32.3 9.7 - - 21.7 tar residue 10.8 11.2 - - 25.0 sulphuric acid 0.6 0.6 - - 1.3 The reaction mixture is then separated into flows 51, 52 and 53 in distillation column 50.

The composition of these flows is also given in Table VIII.

Expeninetits VII - X The following experiments show that the acidolysis reaction according to Example VI can also be effected with other catalyst than sulphuric acid and also without the use of a catalyst.

Benzyl benzoate. acetic acid and the catalyst specified are mixed in the proportions stated. The reaction mixture is then boiled with reflux for the period indicated. After the reaction the conversion of benzyl benzoate into benzyl acetate and benzoic acid is determined. The results are given in Table IX.

TABLE IX Experiment VII VIII IX X catalyst none phosphoric acid p-toluene sulphonic acid sulphuric acid Xs by w. of catalyst - 20 1 1 relative to benzvl benzoate moles of acetic acid 2 2 8 8 relative to benzyl benzoate reaction time (hours) 26 7 6 4 conversion of benzyl 4 40 14 70 benzoate (sic) WHAT WE CLAIM IS: 1. Process for preparing oxidation products of monoalkyl benzene compounds by oxidizing a monoalkyl benzene compound by means of a gas containing molecular oxygen, characterized in that at least one stream, which contains compounds present in the oxidation reaction mixture, or derivatives of such compounds, is subjected to an esterification reaction with a carboxylic acid.

2. Process according to claim 1, characterized in that, in the esterification reaction, both the alcohols present in the oxidation mixture are esterified into esters of said carboxylic acid and the esters of carboxylic acid that are volatile under the reaction conditions present in the reaction mixture are re-esterified into esters of said carboxylic acid.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. removed from the reaction product. The residue is subjected to film evaporation in flash evaporator 43 at a temperature of 260 "C and a pressure of 25 mm of Hg. Acetic acid and sulphuric acid are added to the distillate of the film evaporation, a mixture of benzyl benzoate and tar, in acidolysis reactor 46, consisting of a glass flask with reflux condenser. The composition of the mixture thus obtained is given in Table VIII (before acidolysis The tar residue consists of, i.a., fluorenone (about 40 % by weight realtive to the tar), 1.2-diphenyl ethane and 2-, 3-, and 4-methyl diphenyls. The mixture in the acidolysis reactor is boiled for 2 hours at a temperature of about 130 "C. The composition of the reactor contents after acidolysis is also given in Table VIII. TABLE VIII Composition Before After flow 51 flow 52 flow 53 '. by w. acidolysis acidolysis benzoic acid 10.7 23.5 - 1 52.0 acetic acid 45.6 39.1 99 - beazyl acetate - 16.0 1 99 beazyl benzoate 32.3 9.7 - - 21.7 tar residue 10.8 11.2 - - 25.0 sulphuric acid 0.6 0.6 - - 1.3 The reaction mixture is then separated into flows 51, 52 and 53 in distillation column 50. The composition of these flows is also given in Table VIII. Expeninetits VII - X The following experiments show that the acidolysis reaction according to Example VI can also be effected with other catalyst than sulphuric acid and also without the use of a catalyst. Benzyl benzoate. acetic acid and the catalyst specified are mixed in the proportions stated. The reaction mixture is then boiled with reflux for the period indicated. After the reaction the conversion of benzyl benzoate into benzyl acetate and benzoic acid is determined. The results are given in Table IX. TABLE IX Experiment VII VIII IX X catalyst none phosphoric acid p-toluene sulphonic acid sulphuric acid Xs by w. of catalyst - 20 1 1 relative to benzvl benzoate moles of acetic acid 2 2 8 8 relative to benzyl benzoate reaction time (hours) 26 7 6 4 conversion of benzyl 4 40 14 70 benzoate (sic) WHAT WE CLAIM IS:

1. Process for preparing oxidation products of monoalkyl benzene compounds by oxidizing a monoalkyl benzene compound by means of a gas containing molecular oxygen, characterized in that at least one stream, which contains compounds present in the oxidation reaction mixture, or derivatives of such compounds, is subjected to an esterification reaction with a carboxylic acid.

3. Process according to claim 1 or 2, characterized in that the carboxylic acid contains

not more than 18 carbon atoms per molecule.

4. Process according to claim 3, characterized in that the carboxylic acid is a benzene carboxylic acid.

5. Process according to claim 4, characterized in that the benzene carboxylic acid used in the esterification is the same acid as that formed in the oxidation of the monoalkyl benzene compound.

6. Process according to claim 5, characterized in that toluene is oxidized and unsubstituted benzoic acid is used as the benzene carboxylic acid in the esterification.

7. Process according to claim 5 or 6, characterized in that the benzene carboxylic acid is allowed to form in the oxidation reaction and at least part of it is left in the oxidation reaction mixture for use in the esterification.

8. Process according to claim 7, characterized in that part of the benzene carboxylic acid is distilled from the oxidation reaction mixture together with the more volatile components, the distillation residue is recovered as crude benzene carboxylic acid, and the distillate is fed to the esterification reactor.

9. Process according to claim 3, characterized in that the carboxylic acid is an aliphatic carboxylic acid with 2-4 carbon atoms per molecule.

10. Process according to claim 9, characterized in that the carboxylic acid is acetic acid.

11. Process according to any one of the claims 1-10, characterized in that the substituted or unsubstituted benzyl ester of said carboxylic ester is recovered from the reaction product of the esterification.

12. Process according to claim 11, characterized in that benzyl benzoate is recovered.

13. Process according to claim 11, characterized in that benzyl acetate is recovered.

14. Process acccording to claim 1, characterized in that a tar formed in the reaction mixture formed by oxidizing a monoalkyl benzene compound and containing benzyl benzoate is subjected to an acidolysis reaction with an acid the benzyl ester of which has a lower boiling point, than benzyl benzoate, so that the benzyl benzoate is converted into the benzyl ester of the acid with the low boiling point.

15. Process according to claim 14, characterized in that the acid is an aliphatic carboxylic acid with 1-6 carbon atoms per molecule.

16. Process according to claim 15, characterized in that the acid is an aliphatic carboxylic acid with 2-4 carbon atoms per molecule.

17. Process according to claim 16, characterized in that the acid is acetic acid.

18. Process according to any one of the claims 14-17, characterized in that before the acidolysis reaction the tar is freed of components with lower boiling points than benzoic acid.

19. Process according to claim 18, characterized in that the tar containing benzyl benzoate is obtained as the distillation residue when a mono-alkyl benzene compound is oxidized with a gas containing molecular oxygen and the benzoic acid is distilled off completely or partly, together with all products with lower boiling points.

20. Process according to claim 19, characterized in that the tar containing benzyl benzoate is obtained as a distillate by evaporation of said distillation residue.

21. Process according to any one of the claims 14-18, characterized in that the tar containing benzyl benzoate is obtained by oxidizing a mono-alkyl benzene compound with a gas containing molecule oxygen, distilling off the benzoic acid completely or partly, together with all products with lower boiling points, and heating the distillate to esterify or to re-esterify any benzyl alcohol and/or light benzyl esters present to benzyl benzoate.

22. Process according to claim 10 or 21, characterized in that the residue of the product mixture from the acidolysis reaction, from which the resulting benzyl ester with a low boiling point has been distilled off, is returned to the separation by distillation preceding the acidolysis reaction.

23. Process according to any one of the claims 14-22, characterized in that the resulting benzyl ester of an acid with a low boiling point is distilled off together with some benzoic acid from the product mixture of the acidolysis reaction.

24. Process according to any one of the claims 1-23, characterized in that the reaction product of the esterification is subjected to a hydrolysis.

25. Process according to claim 24, characterized in that the hydrolysis is effected with an aqueous solution of an alkali metal hydroxide and/or an alkali metal carbonate, the resulting aqueous solution of an alkali metal salt of said carboxylic acid is separated from the organic layer obtained, said alkali metal salt is recovered from the alkali metal salt solution, and the substituted or unsubstituted benzyl alcohol is recovered from the organic layer.

26. Process according to claim 25, characterized in that the sodium benzoate is recovered.

27. Process according to claim 1, as substantially indicated in the specification and/or the Examples.

28. Oxidation product of a monoalkyl benzene compound prepared with the use of the process according to any one of the claims 1-26.