CA1124743A - Process for preparing oxidation products of monoalkyl benzene compounds - Google Patents
Process for preparing oxidation products of monoalkyl benzene compoundsInfo
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- CA1124743A CA1124743A CA294,269A CA294269A CA1124743A CA 1124743 A CA1124743 A CA 1124743A CA 294269 A CA294269 A CA 294269A CA 1124743 A CA1124743 A CA 1124743A
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/10—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with ester groups or with a carbon-halogen bond
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Abstract
ABSTRACT OF THE DISCLOSURE
The invention relates to a process for preparing oxidation pro-ducts of monoalkyl benzene compounds by means of a gas containing molecular oxygen. This invention provides the possibility of processing the oxidation reaction mixture in a simple way into a number of desired products, such as, in particular, benzoic acid, benzaldehyde, and also benzyl benzoate and benzyl alcohol, in a pure state. According to the invention, oxidation products of monoalkyl benzene compounds are prepared by oxidizing a monoalkyl benzene com-pound by means of a gas containing molecular oxygen, after which the oxidation reaction mixture is subjected to a carboxylic acid esterification reaction.
The invention relates to a process for preparing oxidation pro-ducts of monoalkyl benzene compounds by means of a gas containing molecular oxygen. This invention provides the possibility of processing the oxidation reaction mixture in a simple way into a number of desired products, such as, in particular, benzoic acid, benzaldehyde, and also benzyl benzoate and benzyl alcohol, in a pure state. According to the invention, oxidation products of monoalkyl benzene compounds are prepared by oxidizing a monoalkyl benzene com-pound by means of a gas containing molecular oxygen, after which the oxidation reaction mixture is subjected to a carboxylic acid esterification reaction.
Description
1~2~L~7'~3 The invention relates to a process for preparing oxidation products of monoalkyl benzene compounds by means of a gas containing molecular oxygen.
It is commonly known to oxîdize monoalkyl benzene compounds by means of a gas containing molecular oxygen. The oxidation of toluene is used on a technical scale and, hence, the invention will be explained mainly with reference to the toluene oxidation. But the invention can also be used in the oxidation of other alkyl benzene compounds.
Some oxidation products formed in the oxidation of toluene are benzoic acid, benzaldehyde, benz~l alcohal and/or benzyl benzoate. The oxidation reaction may be effected either i~ the liquid phase with, e.g., a cobalt salt that is soluble in the reaction medium as a catalystJ or in the gaseous phase with, e.g., a catalyst based on vanadium ~Stanford Research Institute (~RI) Reports No. 7 C1965, 29; No. 7A (1968~, 241;
No. 7B ~197~), 53]. In most cases a very complex mixture of oxidation products is obtained, from ~hich the valuable components are difficult to recover. Especially the recovery of pure benzyl alcohol and benzyl benzoate is extremely difficult, as these compounds have boiling points that are only sllghtly different from some other undesired by-products of the oxidation reaction.
This invention provides the possibility of processing the oxidation reaction mixture in a ~imple way into a number of desired products, such as, in particular, benzoic acid, benzaldehyde~ and also benzyl benzoate and benzyl alcohol, in a pure state.
This invention relates to a proeess 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 separated from the resulting oxidatian reaction mixture, which contains compounds present in the oxidation reaction mixture of derivatives of such compounds, is subjected to a carboxylic acid esterification reaction.
d~ -:: .. .
1~247~3 In the esterificatian a carboxylic acid with, preferably, 1-18 carbon atoms, per molecule reacts to form an ester with alcohols contained in the reaction mixture, especially benzyl alcohol in the toluene oxidation, - 2a -112~7~3 and or to i'orm another ester with esters oi other acids than said carbox~liC acid that are contained in the reaction m~ ture, e~pecially benzyl esters oi volatile carboxylic acids with 1-6 carbon atoms per acid molecule, such as iormic acid, acetic acid, and propionic acid.
The carboxylic acid u~ed for the esteri~ication is pre~erably a benzene carboxylic acid, and notably the ~ame as ~ormed in the oxidation o~ the monoalkyl benzene compound in question, i.e. unsubstituted benzoic acid in the oxidation o$ toluene. According to another prei'erable embodiment oi' the process accord~ng to the invention, qaid carboxylic acid i9 acetic acid, propionic acid or butyric acid.
The esterii'ication and/or re-esteri~ication makes it possible considerably to raise the boiling point o$ the benzyl alcohol and/or the benzyl esters oi volatile carboxylic acids in the reaction mixture.
A number o~ more volatile components whose boiling points would be too close to that o~ said components to allow oi' e~i'ective separation can then be removed without any problem, e.g. by distillation. Moreover, the usei'ul product benzyl benzoate can be obtained in a pure state. Ii' acetic acid is used, the use~ul product benzyl acetate can be obtained. mese compounds are used in the manu~acture oi' scents and i'lavours.
In the esteriiication the alcohols and esters o~ volatile acids in the reaction mixture are pre~erably converted i'ully or almost iully into the esters o~ said carboxylic acid.
As the chemical properties oi' benzoic acid dii'~er considerably ~rom those o~ the esters obtained, the separation oi bsnzoic acid i'rom the reaction mixture, ii' necessary, presents no serious problem. ~enzoic acid, ii' any, can be extracted i'rom the reaction mixture by means o~, e.g., water, an aqueous solution o~ soda, diluted sod:Lum hydroxide solution, or another suitable extracting agent, or the reaction mixture can be separated by distillation.
~enzyl alcohol and benzyl esters og volatile acids originally present have been converted into benzyl esters oi said carboxylic acid in l~Z4743 the esterii'ication reaction. These benzyl esters can be recovered as such.
Another possibility is to subject the mixture containing benzyl ester to a hydrolysis Or ammonolysis, aiter the more volatila components have been removed. Thu9 benzyl benzoate, ~or instance, is converted into benzyl alcohol and benzoic acid or a salt thereoi', resp. 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 ~or the oxidation oi' toluene, 90 it can be used in an analogous way ior the oxidatlon oi' other monoalkyl benzene compounds with 1-4 carbon atoms in the alkyl group, which may also contain non interiering substituents at the benzene nucleus, e.g. halogen, nitro or sulphonic acid substituents.
~xamples are ethyl benzene, p-chlorotoluene, p-nitrotoluene, and p-toluene sulphonic acid.
me reaction conditions in the oxidation reaction do not deviate ~rom the well-known conditions. For the sake oi' brevity rei'erence 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 reactlon temperature ; 20 usually ranges between 100 and 200 C, the reaction pressure between 1 and 10 atm. The oatalyst is prei'erably a oompound o~ a transition metal, especially oobilt and~or manganese, that 19 soluble ln the reaction mixture~
~xamples oi suitable catalysts are the transition metal salts o~
oarboxylic acids, e.g. oobalt (II) acetate, manganese (II) propionate or oobalt (II) ootoate. Use may also be made o~ mlxtures o~ two or more transition metals, in particular, compounds oi cobalt and manganese. Ii' 90 desired, the oxldation may be carried out in the presence o~ a carboxylic acid as a promotor, in particular, acetic acid, and/or in the presence oi 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 -74;3 usually ranges between 200 and 600 C, the reaction pressure between 1 and 10 atm. The catalyst i9 preferably an oxide compound o~ a transition metal, in particular, vanadiu~, although compoundq oi, e.g., molybdenum, chromium, tungsten, and uranium may also be used. Suitable catalysts are, i'or instance, those based on the vanadates oi' silver, iron and/or one or more o~ the ~o-called rare-earth metals (atomic numbers 57 through 71, and also scandium and yttrium), e.g., scandium, yttrium, lan~hanum, cerium, or 'dldymium' ta mixture oi' praseodymium and neodymium). me catalyst is prei'erably put on a carrier, such as, e.g. aluminium oxide or ~ilicon oxide.
me gaseous mixture may contain steam and/or a vapour oi' a carboxylic acid~e.g. acetic acid, in addition to the monoalkyl benzene compound.
me esterii'ication may be carried out, e.g., at a temperature oi 100-300 C, the esteri~ication/re-esteri~ication without a catalyst prei'erably at a temperature oi' between 160 and 300 C.
The pressure may range, e.g., between 1 and 10 atm. Ii so desired, use may be made oi any esteriiication/re-esteriiicatlon catalyst, e.g. a mineral acid, such as ~ulphuric acid or phosphoric acid or also borotriiluoride or zinc acetate.
me use oi an esterii'ication/re-esteriiicatlon catalyst may lead to contamination o~ the benzyl oster product. me esterii'ication/
re-esterii'icatlon may also proceed well in the absence oi' a catalyst.
me benzyl ester obtained oan be hydrolysed with a basic solution, in particular, an aqueous sodium hydroxide solution or a soda 901ution. Also potassium hydroxide or calcium hydroxide might be used.
But there is a need o~ sodium benzoate as a reaction product, so that benzyl benzoate is preierably hydrolysed with a basic sodium compound.
Ii' 90 desired, the benzoate salt thus obtained can be converted into a very pure ~ree benzene carboxylic acid, e.g., unsubstituted benzoic acid, by reaction with a strong acid, e.g. sulphuric acid or nitric acid.
~i~743 I~ ~o deRired, the hydroly~ls may also be e~fected by mean~
o~ an acid, instead oi' a basic, catalyst, e.g. a mineral acid, such as su:Lphuric acid or phosphoric acid. Oi course, i'ree carboxylic acid will then be ~ormed, which may be returned to the esteri~ication reactor.
me temperature in the hydrolysis reaction may range, ~or instance, bstween 30 and 200 C. The pressure is not critical and, i'or practical reasons, prei'erably ranges between 1 and 10 atm.
me benzyl ester obtained may also be a ~onolysed, i.e. be made to react with ammonia or a primary or secondary amine. Use is pre~ersbly made o~ ammonia, either in the gaseous state or as an aqueous solution, e.g. 50 ~ by weight oi' ammonia. I~ an amine is used, it is pre~erably an aliphatic amine with, pre~erably, 1-4 carbon atoms per hydrocarbon group attached to nitrogen. Preierence is given to primary aliphatic amines, e.g. monoethyl amine or isopropyl amine. Aniline or diethyl amine, i~or instance, may also be used.
The ammonolysis may be carried out, e.g., at a temperature oi 30-200 C at autogenous pressure or a higher pressure.
me invention will be elucidated with rei'erence to the reaction diagram annexed, indicated as iigure 1.
~- 20 Oxidation reactor 1 i9 i'ed with liquid toluene through conduit
It is commonly known to oxîdize monoalkyl benzene compounds by means of a gas containing molecular oxygen. The oxidation of toluene is used on a technical scale and, hence, the invention will be explained mainly with reference to the toluene oxidation. But the invention can also be used in the oxidation of other alkyl benzene compounds.
Some oxidation products formed in the oxidation of toluene are benzoic acid, benzaldehyde, benz~l alcohal and/or benzyl benzoate. The oxidation reaction may be effected either i~ the liquid phase with, e.g., a cobalt salt that is soluble in the reaction medium as a catalystJ or in the gaseous phase with, e.g., a catalyst based on vanadium ~Stanford Research Institute (~RI) Reports No. 7 C1965, 29; No. 7A (1968~, 241;
No. 7B ~197~), 53]. In most cases a very complex mixture of oxidation products is obtained, from ~hich the valuable components are difficult to recover. Especially the recovery of pure benzyl alcohol and benzyl benzoate is extremely difficult, as these compounds have boiling points that are only sllghtly different from some other undesired by-products of the oxidation reaction.
This invention provides the possibility of processing the oxidation reaction mixture in a ~imple way into a number of desired products, such as, in particular, benzoic acid, benzaldehyde~ and also benzyl benzoate and benzyl alcohol, in a pure state.
This invention relates to a proeess 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 separated from the resulting oxidatian reaction mixture, which contains compounds present in the oxidation reaction mixture of derivatives of such compounds, is subjected to a carboxylic acid esterification reaction.
d~ -:: .. .
1~247~3 In the esterificatian a carboxylic acid with, preferably, 1-18 carbon atoms, per molecule reacts to form an ester with alcohols contained in the reaction mixture, especially benzyl alcohol in the toluene oxidation, - 2a -112~7~3 and or to i'orm another ester with esters oi other acids than said carbox~liC acid that are contained in the reaction m~ ture, e~pecially benzyl esters oi volatile carboxylic acids with 1-6 carbon atoms per acid molecule, such as iormic acid, acetic acid, and propionic acid.
The carboxylic acid u~ed for the esteri~ication is pre~erably a benzene carboxylic acid, and notably the ~ame as ~ormed in the oxidation o~ the monoalkyl benzene compound in question, i.e. unsubstituted benzoic acid in the oxidation o$ toluene. According to another prei'erable embodiment oi' the process accord~ng to the invention, qaid carboxylic acid i9 acetic acid, propionic acid or butyric acid.
The esterii'ication and/or re-esteri~ication makes it possible considerably to raise the boiling point o$ the benzyl alcohol and/or the benzyl esters oi volatile carboxylic acids in the reaction mixture.
A number o~ more volatile components whose boiling points would be too close to that o~ said components to allow oi' e~i'ective separation can then be removed without any problem, e.g. by distillation. Moreover, the usei'ul product benzyl benzoate can be obtained in a pure state. Ii' acetic acid is used, the use~ul product benzyl acetate can be obtained. mese compounds are used in the manu~acture oi' scents and i'lavours.
In the esteriiication the alcohols and esters o~ volatile acids in the reaction mixture are pre~erably converted i'ully or almost iully into the esters o~ said carboxylic acid.
As the chemical properties oi' benzoic acid dii'~er considerably ~rom those o~ the esters obtained, the separation oi bsnzoic acid i'rom the reaction mixture, ii' necessary, presents no serious problem. ~enzoic acid, ii' any, can be extracted i'rom the reaction mixture by means o~, e.g., water, an aqueous solution o~ soda, diluted sod:Lum hydroxide solution, or another suitable extracting agent, or the reaction mixture can be separated by distillation.
~enzyl alcohol and benzyl esters og volatile acids originally present have been converted into benzyl esters oi said carboxylic acid in l~Z4743 the esterii'ication reaction. These benzyl esters can be recovered as such.
Another possibility is to subject the mixture containing benzyl ester to a hydrolysis Or ammonolysis, aiter the more volatila components have been removed. Thu9 benzyl benzoate, ~or instance, is converted into benzyl alcohol and benzoic acid or a salt thereoi', resp. 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 ~or the oxidation oi' toluene, 90 it can be used in an analogous way ior the oxidatlon oi' other monoalkyl benzene compounds with 1-4 carbon atoms in the alkyl group, which may also contain non interiering substituents at the benzene nucleus, e.g. halogen, nitro or sulphonic acid substituents.
~xamples are ethyl benzene, p-chlorotoluene, p-nitrotoluene, and p-toluene sulphonic acid.
me reaction conditions in the oxidation reaction do not deviate ~rom the well-known conditions. For the sake oi' brevity rei'erence 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 reactlon temperature ; 20 usually ranges between 100 and 200 C, the reaction pressure between 1 and 10 atm. The oatalyst is prei'erably a oompound o~ a transition metal, especially oobilt and~or manganese, that 19 soluble ln the reaction mixture~
~xamples oi suitable catalysts are the transition metal salts o~
oarboxylic acids, e.g. oobalt (II) acetate, manganese (II) propionate or oobalt (II) ootoate. Use may also be made o~ mlxtures o~ two or more transition metals, in particular, compounds oi cobalt and manganese. Ii' 90 desired, the oxldation may be carried out in the presence o~ a carboxylic acid as a promotor, in particular, acetic acid, and/or in the presence oi 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 -74;3 usually ranges between 200 and 600 C, the reaction pressure between 1 and 10 atm. The catalyst i9 preferably an oxide compound o~ a transition metal, in particular, vanadiu~, although compoundq oi, e.g., molybdenum, chromium, tungsten, and uranium may also be used. Suitable catalysts are, i'or instance, those based on the vanadates oi' silver, iron and/or one or more o~ the ~o-called rare-earth metals (atomic numbers 57 through 71, and also scandium and yttrium), e.g., scandium, yttrium, lan~hanum, cerium, or 'dldymium' ta mixture oi' praseodymium and neodymium). me catalyst is prei'erably put on a carrier, such as, e.g. aluminium oxide or ~ilicon oxide.
me gaseous mixture may contain steam and/or a vapour oi' a carboxylic acid~e.g. acetic acid, in addition to the monoalkyl benzene compound.
me esterii'ication may be carried out, e.g., at a temperature oi 100-300 C, the esteri~ication/re-esteri~ication without a catalyst prei'erably at a temperature oi' between 160 and 300 C.
The pressure may range, e.g., between 1 and 10 atm. Ii so desired, use may be made oi any esteriiication/re-esteriiicatlon catalyst, e.g. a mineral acid, such as ~ulphuric acid or phosphoric acid or also borotriiluoride or zinc acetate.
me use oi an esterii'ication/re-esteriiicatlon catalyst may lead to contamination o~ the benzyl oster product. me esterii'ication/
re-esterii'icatlon may also proceed well in the absence oi' a catalyst.
me benzyl ester obtained oan be hydrolysed with a basic solution, in particular, an aqueous sodium hydroxide solution or a soda 901ution. Also potassium hydroxide or calcium hydroxide might be used.
But there is a need o~ sodium benzoate as a reaction product, so that benzyl benzoate is preierably hydrolysed with a basic sodium compound.
Ii' 90 desired, the benzoate salt thus obtained can be converted into a very pure ~ree benzene carboxylic acid, e.g., unsubstituted benzoic acid, by reaction with a strong acid, e.g. sulphuric acid or nitric acid.
~i~743 I~ ~o deRired, the hydroly~ls may also be e~fected by mean~
o~ an acid, instead oi' a basic, catalyst, e.g. a mineral acid, such as su:Lphuric acid or phosphoric acid. Oi course, i'ree carboxylic acid will then be ~ormed, which may be returned to the esteri~ication reactor.
me temperature in the hydrolysis reaction may range, ~or instance, bstween 30 and 200 C. The pressure is not critical and, i'or practical reasons, prei'erably ranges between 1 and 10 atm.
me benzyl ester obtained may also be a ~onolysed, i.e. be made to react with ammonia or a primary or secondary amine. Use is pre~ersbly made o~ ammonia, either in the gaseous state or as an aqueous solution, e.g. 50 ~ by weight oi' ammonia. I~ an amine is used, it is pre~erably an aliphatic amine with, pre~erably, 1-4 carbon atoms per hydrocarbon group attached to nitrogen. Preierence is given to primary aliphatic amines, e.g. monoethyl amine or isopropyl amine. Aniline or diethyl amine, i~or instance, may also be used.
The ammonolysis may be carried out, e.g., at a temperature oi 30-200 C at autogenous pressure or a higher pressure.
me invention will be elucidated with rei'erence to the reaction diagram annexed, indicated as iigure 1.
~- 20 Oxidation reactor 1 i9 i'ed with liquid toluene through conduit
2 and with air through conduit 3. me toluene contains 0.001 to 0.1 %
by weight o~ cobalt (II) acetate as a cataly~t in solution. In reaator 1, the toluene i9 oxidized in the liquid state at a temperature oi' 140 to 165 C and a pressure oi' 3 to 10 atm. me vent gas is passed i'rom the reactor through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6, the condensate is pas~ed 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 oxidation reactor 1 through conduit 10.
The liquid oxidation mixture ilows irom oxidation reactor 1 through conduit 11 to distillation column 12. In this column all components ~ qL743 with boilin~ ~in~ low~r thall that oi benzoic acid and, pre~erably, some bellzoic acid are distilled o~. Crude benzoic acid, which is puri~ied in the usual way, is recovered through conduit 13. me top product is passed through conduit 14 and ~ed to distillation column 15, in which the toluene and benzaldehyde, i$ any, are ~ully or partly distilled. me top product (conduit 16) may be returned to oxidation reactor 1, either as such or ailter benzaldehyde has been removed ~rom it by distillation.
me bottom product o~ column 15, which contains, i.a., benzyl alcohol, benzoic acid, benzyl iormiate, and benzyl acetate, i9 passed through conduit 1? to e~teri~ication reactor 18. Here the temperature is controlled at 200-250 C, the pressure is equal to atmospheric pressure.
In this reactor benzyl alcohol eqteri~ies with benzoic acid to benzyl benzoate and water, and the light benzyl esters, such as benzyl iormiate and benzyl acetate, re-esteriily with benzoic acid to ~orm benzyl benzoate and the iree light acids, such as iormic acid and ac*tic 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 al~o escape through this conduit. The reaction mixture passes through conduit 20 to distillation column 21, where the remainder oi these by-products i8 removed by distillation at a pressure oi 0.2 atm and is discharged as a vapour through conduit 22, and, ii 90 deslred, is returned to oxidation reactor 1 ~ilter condensation and removal oi the resultin~
; aqueous layer, while the liquid benzyl-beDzoate product leaves columns 21 through conduit 23. This product consists o~ crude benzyl benzoate which can be recovered through conduit 24 and ~rom which pure benzyl benzoate can be recovered by simple distillation.
me benzyl-benzoate product can be passed through conduit 25 to hydrolysis reactor 26, to which aqueous sodium hydroxide is ~ed 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. Ii the benzyl benzoate product supplied through conduit 25 still i~2~3 containQ ~ree benzoic acid, this is also converted into sodium benzoate in reactor 26.
The reaction mixture ~rom reactor 26 is ~ed 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 ei~ected. The aqueous layer con~ist~ o~ an aqueous sodium benzoate solution, which is discharged through conduit 31 and ~rom which solid sodium benzoate can be obtained by removal oi' water. me organic layer substantially consists oi' benzyl al¢ohol and toluene with some by-products with higher boiling points and is passed through conduit 32 to diQtillàtion column 33.
Thanks to the great dii'~erence between the boiling points oi toluene, benzyl alcohol, and the by-products, Reparation 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 15 through conduit 36. me toluene may be returned to extraction column 29 and the by-products may be returned to oxidation reactor 1.
- me ratio between the amounts oi' iree benzoic acid and sodium benzoate produced can be controlled to suit the requirements by controlling the amount oi benzoic acid that is distilled over in distillation column 12, also in dependence on the amount oi benzyl-benzoate produot discharged through conduit 24 Ii the need oi' benzyl alcohol is not great, the temperature ln distillation column 15 can be ad~usted to a higher value, 90 that alsa part o~ the benzyl alcohol present distils over and is returned to oxidation reactor 1 together with the toluene recycle flow.
Instead oi' distilling benzoic acid i'rom column 12 to have it available in esteriiication reactor 18, the required benzoic acid may, oi course, also be ied separately to reactor 18.
According to a ~urther embodiment oi' the inventian, the stream which is subjected to the carboxylic acid esterii'icatlon reaction is a tar containing benzylbenzoate or substituted benzylbenzoate. Such tars may be ~ormed in di~i'erent ways as i.a. described hereunder. me benzoic acid . .
~lZ~7~3 ~ay ~_ distilled completely or partly, together with all product~ with lower boiling points, ~rom the reaction mixture that contains benzoic acid, benzyl benzoate, other products with higher boiling points than benzoic acid and herein re~erred to as tar residue, unconverted toluene, and secundary products, such as benzyl alcohol and benzaldehyde, with lo~er boiling points than benzoic acid, and the distillate may be i'urther processed ~or pure benzoic acid, so that a tar containing benzyl benzoate and, possibly, some benzoic acid i9 obtainedas a residue. This residuemay be used as the starting material $or the process according to the invention.
A tar that contains benzyl benzoate and which may also be used as a starting material ~or the special embodiment o~ the process according to the invention may also ~orm i~ the above distillate i9 heated, whether or not in the presence o~ an esteri~ication or re-esterl~ication catalyst, e.g. sulphuric acid, phosphoric acid, boron tri~luoride, or zinc acetate, in order to esteri~y or re-esteriiy benzyl alcohol and/or light benzyl esters, such as benzyl i'ormiate and benzyl acetate, into benzyl benzoate, especially ii' the mixture still contains benzaldehyde during this esteri~ication reaction.
It is very di~icult to recover use~ul products ~rom such a tar containing benzyl benzoate. ~enzyl benzoate oan be distilled ~rom ; the tar residue, it is true, but a pure benzyl-benzoate product can hardly be obtained. Applicant has ~ound that the component ~luorenone ~- oi' the tar causes special problems in this connection. For, it has been i'ound that ~luorenon- can hardly be separated i'rom benzyl benzoate.
But besides ~luorenone, other unidenti~ied compounds may play a part.
According to said embodiment o~ the invention a benzyl ester is prepared by subjecting a tar containing benzyl benzoate to acidoly~is with an acid with a low boiling point, 90 that the benzyl benzoate is converted lnto the benzyl ester o~ the acid with the low boiling point.
Acidolysis denotes a re-esterii'ication reaction in which an .
~llZ4743 ester o~ an acid A and an alcohol B reacts with an acid C, so that an ester o~ acid C and alcohol B is ~ormed in addition to (~ree) acid A. In the process according to the invention the ester o~ a benzoic acid and a benzyl alcohol react~, e.g., with acetic acid, 80 that a benzyl acetate is ~ormed in addition to (~ree) benzoic acid.
me term 'acid with a low boiling point' denotes an acid the benzyl ester o~ which has a lower bo~ling point than benzyl benzoate, which usually implles that the ~ree acld itseli also has a lower boiling point than benzoic acid.
By means o~ the acidolysis reaction according to said embodiment o~ the invention, the benzyl benzoate with a high boiling point, which is di ~icult to separate by distillation irom some tar components, is converted into benzoic acid and a benzyl ester with a considerably lower boiling point which considerably di~ers in chemical and physical properties ~rom the benzyl benzoate and the tar components. The benzyl ester with a low boiling point can be recovered in a pure ~orm ~rom the acidolysed mixture, e.g. by distillation. Such benzyl esters are us8~ul products, which are used, e.g.,in the scents and ~lavours industry. Hence, this embodiment makes it posqible to convert a waste product that was useless so ~ar into a uqe~ul substance.
The aoldolysis is prei'erably carried out with an aliphatic carboxyllc acid with }-6 carbon atoms, more in particular 2-4 carbon atoms, per molecule with a low boiling point. Use i~ prei'erably made o~ acetic acid, propionic acid, or butyric acid, although iormic acid, i'or instance, may also be used. As benzyl acetate is a valuable commercial product, special pre~erence is given to acetic acid. Benzyl acetate can very ~avourably be produced by the special embodiment oi' 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 oi' between 100 C
and 300 C, with or without a catalyst.
~12 ~ 74 3 The tar containing benzyl benzoate used as the starting material is pre~erably ~ree 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 oi distillation.
Any components in the starting product with lower boiling points than that o~ benzoic acid can be removed prior to the acidolysis treatment, e.g. in one o~ the ways described above.
As the chemicsl properties o~ benzoic acid are considerably di~erent ~rom those oi the resulting esters, the separation oi' benzoic acid ~rom the reaction mixture, ii' e~ected, does not constitute a ~erious problem. me benzoic acid can be extracted ~rom the reaction mixture, ior instance, by mean~ o~ water, an aqueous qoda solution, diluted sodium hydroxlde, or another suitable extracting agent, or the reaction mixture can be separated by distillation.
lS Benzyl benzoate in the starting material is converted into a benzyl ester with a lower boiling point in the acidolysis reaction. mis benzyl ester can be recovered as such. It is pos~ible to remove the benzyl ester with the low boiling point irom the reaction mixture by distlllation and then to subject it to a hydroly~is or ammonolysis treatment as described above. mus, benzyl acetate is converted lnto benzyl alcohol and acetio acid or a salt or amide thereo~. As benzyl alcohol 19 now the only more volatlle component in the reactlon mlxture in addition to the acetlc acid, it can readlly be removed by distlllation. me acetic acid may be returned to the acidolysis.
The invention will be ~urther explained with re~erence to the reaction diagram annexed, indicated as rigure 2.
Oxidation reactor 1 is ~ed with liquid toluene through conduit 2 and with air through conduit 3. The toluene contains 0.001 to 0.1 % by weight oi' cobalt (II) acetate as dissolved catalyst. In reactor 1 the toluene is oxidized in the liquid phase at a temperature oi' 140 to 165 C
and a pressure o~ 3 to 10 atm. The vent gas irom the reactor is passed ~Z~7~3 through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6 and the conden~ate is passed through conduit 7 to separator 8, where it is separated into an organic layer and an aqueous layer. me aqueous layer i~ removed through conduit 9; the organic layer is returned to oxidation reactor 1 through conduit 10.
The liquid oxidation mixture ilows irom oxidation reactor 1 through conduit 11 to distillation column 12, where all components with a lower boillng point than benzoic acid, plus, preierably, some benzoic acid, I are distilled oii and discharged through conduit 14. This top product substantially consists oi toluene and may be returned to oxidation reactor 1, either a~ a whole or aiter benzaldehyde has been recovered irom it by di3tillation. The bottom product ilows through conduit 13 to distillation j column 40, where all benzoic acid and components with a lower boiling point are distilled oii and discharged through conduit 41; this distlllate can be processed into pure benzoic acid in the usual way. me residue ilows through conduit 42 to distillation column 43. Column 43 may be a iilm evaporator.
The bottom product oi the distillation is discharged through conduit 44. m e resulting distillate, a mixture oi benzyl benzoate and tar, is passed through conduit 45 to acidolysis Peactor 46. me acidolysis reactor i9 ied with an acid with a low boiling point, acetic acid in thls ca~e, through oonduit 47, and with sulphuric acid as a catalyst through conduit 4~. The reaction mixture irom 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 acidolysi~ reactor 46 through conduits 51 and 47. A side $10w consisting oi benzyl acetate and some benzoic acid is withdrawn irom distillation column 50. This prevents benzyl acetate irom being returned into the process later on. mis side ilow 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 ~47~3 .
the washing device through conduit 56. me benzyl acetate product is recovered through conduit 57 and, ii 90 desired, may be iurther puri~ied, e.g. by ~ractional distillation. The bottom product ~rom column 50, which contains the major amount o~ 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 ~3 are omitted and the bottom product i'rom col D 12 is ied directly to acidolysis reactor 46.
men the bottom product ~rom column 50 is not returned to the process, but is discharged as tar.
The invention will be i'urther explained with rei'erence to the iollowing numerical examples/experiments.
Example I
In examples I to V re~erence is made to ~igure 1.
Toluene was oxidized in the liquid phase by means o~ air in oxidation reactor 1 at a temperature oi 160 C and a pressure oi 5 atmo~pheres and in the presence o~ 0.008 % by weight oi cobalt (in the i'orm oi acetate). In distillation column 12, the components with lower boiling points than benzoic acid and some benzoic acid were distilled ~rom the bottom ~low oi reactor 1 at atmospheric pressure. me product~ wlth lower bolllng points than benzyl alcohol are dlstilled irom the top product oi' distillation column 12 at atmospheric pressure in distillation column 15.
The composition, in % by weight, oi the bottom product discharged ~rom distillation column 15 through conduit 17 i9 given in Table I~ 'Other organic compounds' are, i.a., dibenzyl ether, acetophenone, methyl benzoate, 2-methyl diphenyl and 1,2-diphenyl ethane.
1~4~3 Table I
~low oi material conduit 17 conduit 19 conduit 20 benzyl alcohol 7.6 - 0.4 benzyl lormiate 9.9 - 0.9 benzyl acetate 14.3 - 8.9 benzyl benzoate - - 35.4 benzyl acid 51.7 - 31.4 other organic compounds 16.5 0,9 15.6 waterfiormlc acld/acetio acid - 4.1 2.1 Said bottom product is passed to esteri~ication reactor 18 that consists oi a l-litre glass llask to which a 40-cm long heating column is connected with a still head on top. me heating column is heated at 125-140 C to avoid condensation oi the volatile components iormed in the reaction 90 that they can be removed by way o~ the still head.
Another result is that the benzoic acid that has also evaporated condenses in the heating column, but does not solidi~y and, hence, $10ws back into the ilask. me residence time in reactor 18 amount~ to 30 minutes. An inert atmosphere (nitrogen) is maintained in the reactor. me ~lask is heated at the temperature speci~ied in Table II by means oi a metal bath.
me distillate and the residue are put together and the total is analysed. The results oi the analysis are also given ln Table II.
Table II
temperature (C) 200 210 230 250 benzyl alcohol (% by w.) 3.4 2.6 1.4 0.9 benzyl iormiate ' 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 benzolc acld ' 44.9 41.4 38.7 36.5 other organic compounds ' 16.5 16.5 16.5 16.5 water/iormic acid/acetic acid ' 1.4 2.8 3.5 4.3 112~7~3 The hi8her the temperature, the more products with lower boiling points, especially benzyl alcohol and benzyl 1'ormiate, but also benzyl acetate, are converted into benzyl benzoate with a hi~her boiling point.
Example II
S Example I i9 repeated, but now the bottom ilow (see conduit 17) oi' di~tillation column 15 with the composition according to Table 1 is heated in esteriiication reactor 18 $or 160 minute~. me temperature oi the metal bath is kept at 250 C. ~uring 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 iormiate and benzyl acetate, are converted into products with higher boiling points, especially benzyl benzoate.
Table III
time (minutes) boiling temperatures ( C) . ~ .
In T~ble I the compoaition oi' the starting ilow oi' materials (see condult 17), the composit10n oi the distillate (see conduit 19), and the composition oi the residue (see conduit 20) are given and expre3sed as % by weight calculated to the total oi the ilows in conduits 19 and 20.
The benzoic acid is distilled i'rom the bottom ilow oi' the esteriiication reactor 18 in distillation column 21 at a pre99ure oi 25 mm oi Hg. me composition oi' the top product (see conduit 22) and oi' the bottom product (see conduit 23, expressed in % by weight oi the total oi' the ilows in conduits 22 and 23, is given in Table IV, where the composition oi the ilow in conduit 20 is given ior comparison.
11~4~43 Table IV
~low oi material conduit 20 conduit 22 conduit 23 benzyl alcohol 0.4 0.4 benzyl ~ormiate 0.9 009 benzyl acetate 9.4 9.4 benzyl benzoate 37.3 0.2 37.1 other organic compound~ 16.4 11~1 S.3 benzoic acid 33.1 33.0 0.1 water/iormie acid acetic aoid 2.2 2.2 The bottom product o~ di~tillation column 21 i9 withdrawn through conduit 24. It iq distilled separately at a pressure oi 25 mm o~ Hg and a temperature o~ 210 C. In this way pure benzyl benzoate with a content o~ over 99.7 % by weight is obtained.
Example III
E~ample II is repeated. me crude benzyl benzoate in conduit 23 is now ied to hydrolysis reactor 26 through conduit 2S. Here it is madè to react with aqueous sodium hydroxide (12.5 % by weight o~ NaOH) that i9 supplied through conduit 27. The composition o~ the reaction mixture beiore hydrolysis is given in T~ble V.
In hydrolysis reactor 26 the reactlon mixture is stirred at 100 C
~or 30 minutes with re~lux oooling. The composition oi the oontents o~
reactor 26 aiter hydrolysis i9 also given in Table V.
7~3 Table V
~low o~ material be~ore hydrolysis a~ter hydrolysis (~ by weight) (% by weight) be~zyl benzoate 39.6 <0.01 benzoic acid 0.1 sodium hydroxide 7.9 0.3 water 46.7 46.7 benzyl alcohol - 20.2 sodlum benzoate - 27.1 other organlc compounds 5.7 5.7 me reaction mixture is extracted iour times with toluene in an amount o~ hal~ the weight o$ water, the toluene extracts are added together, and the toluene i9 iirst di3tilled oi'i with some water, and next the benzyl alcohol. me benzyl alcohol obtained appears to be pure i'or over 99.9 %
by weight.
The sodium ben7oate is recovered i'rom the aqueous phase by removal oi' water.
Exa~ple IV
Example I is repeated, but the benzoic acid is removed i'rom the bottom product oi' distlllation column 15 (see conduit 17) with the composition acoording to Table 1, by washing with an aqueous soda solution (10 % by weight oi! Na2C03), a~ter whlch acetic acld 19 added to the washed product.
The mixture obtained, the composition o1' which is given in Table VI
('beiore conversion'), i~ boiled in the esteri~ication reactor 18 until a bottom temperature o~ 155 C i8 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 result~ oi' analysis are also given in Table VI ('ai'ter conversion').
1~2-~7~3 Table VI
before conversionai'ter conversion (% by weight) (% by weight) benzyl alcohol 7.6 0.3 benzyl ~ormiate 9.9 8.7 benzyl acetate 14.3 2S.8 other organic compounds 16.5 16.6 acetic acid 51.7 47.1 ~ormic acid/water - 1.7 - 10 Example V
Example II is repeated, unless otherwise speci~ied. The crude benzyl benzoate in conduit 23, the compositlon oi which i9 given in Table IV, is now ied to an ammonolysis/hydrolysis reactor 26 through conduit 25. Here it i9 made to react with an aqueous ammonium-hydroxide 301ution (25.6 % by weight calculated as NH40H) that is supplied through ~conduit 2~. The composition o~ the reaction mixture be~ore ammonolysis/
hydrolysis is given in Table VII.
me reaction mixture is s~irred at 150 C and 15 atm i'or 4 hours - in ammonolysis/hydrolysis reactor 26, an autoclave with a stirring mechanism. Aiter cooling, the reaction mixture is given a pH of 6 by means oi 1 N aqueous sulphurlo acid and extracted three times with toluene in an amount oi hali' the welght oi water present. me toluene and the components with lower boiling points are evaporated irom the extract, the product obtained having a composition as mentioned in Table VII.
1~24~3 Table VII
be~ore ammonoly~is/a~ter ammonolysis/
hydrolysis hydrolysis benzyl benzoate 18.4 1.0 benzolc 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 recovsred by cry~tallization. The yield o~
benzamide can be raised at the C09t oi benzoic acid by carrying out the ammonolysis in the presence oi 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 i'ollowing example~ re~erence is made to iigure 2.
In oxidation reactor 1 toluene is oxidized in the liquid phase wlth air at a temperature oi 160 C and a pressure o~ 5 atmospheres and 2~ ln the pre~ence o~ 0.008 % by wei~ht oi oobalt ~as acetate). The deBree oi conversion oi the toluene is about 20 %. me components with a lower boiling point than benzoic acid and some benzoic acid are distilled i'rom the bottom i'low irom reactor 1 in di tillation column 12 at atmospheric pr2ssure. The bottom product ~rom distillation column 12 i9 distilled iurther at atmospheric pressure in distillation column 40, until virtually all benzoic acid and components with lower boiling points have been removed i'rom the reaction product. The residue is subjected to i'ilm evaporation in i'lash evaporator 43 at a temperature o~ 260 C and a pressure oi' 25 mm o~
Hg. Acetic acid and ~ulphuric acid are added to the distillate o~ the iilm evaporation, a mixture of benzyl benzoate and tar, in acidolysi~
reactor 46, consisting oi a glass ~lask with re$1ux condenser. me composition oi the mixture thus obtained is given in Table VIII (be~ore acidolysis). me tar residue consists o~, i.a., ~luorenone (about 40 %
by weight relative to the tar~, 1,2-diphenyl ethane and 2-, 3-,and 4-~ethyl diphenyls.
The mixture in the acidoly~is reactor is boiled for 2 hours at a temperature oi about 130 C. me composition oi' the reactor contents a~ter acidolysis is also given in Table VIII.
Table VIII
composition be~ore a~ter~low 51 ilow 52 i'low 53 % by w. acidolysi~ acidolysis benzoic acid 10.7 23.5 - l 52.0 àcetic acid 45.6 39.1 99 benzyl acetate - 16.0 1 99 benzyl benzoate 32.3 9.7 - - 21.7 tar residue 10.8 11.2 - - 25.0 sulphuric acid 0.60.6 - - 1.3 .
The reaction mixture i~ then separated into ~lows 51, 52, and 53 in distillation column ~0. The compositlon o~ these ilows is also glven ln Table VIII.
Experiments VII - X
me iollowing experiments show that the acldolysis reaction according to example VI can also be eiiected with other catalyst than sulphuric acid and also without the use o~ a catalyst.
Benzyl benzoate, acetic acid and the catalyst speciiied are mixed in the proportions stated. The reaction mixture is then boiled with re~lux ior the period indicated. A~ter the reaction the conversion o~ benzyl benzoate into benzyl acetate and benzoic acid is determined. The ~12~7~3 results ars given in Table IX.
Table IX
expleriment VII VIII ¦ IX ¦ X
eatalyst none phosphoric aeid p-toluene jsulphonic acid ~sulphuricacid % by w. o~ catalyst - 20 , 1 I 1 relative to benzyl 1.
benzoate moles o~ aeetie acid 2 2 8 8 relative to benzyl benzoate reaction tima (hours) 26 7 6 4 conversion o~ benzyl 4 40 14 70 benzoate (%) ,
by weight o~ cobalt (II) acetate as a cataly~t in solution. In reaator 1, the toluene i9 oxidized in the liquid state at a temperature oi' 140 to 165 C and a pressure oi' 3 to 10 atm. me vent gas is passed i'rom the reactor through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6, the condensate is pas~ed 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 oxidation reactor 1 through conduit 10.
The liquid oxidation mixture ilows irom oxidation reactor 1 through conduit 11 to distillation column 12. In this column all components ~ qL743 with boilin~ ~in~ low~r thall that oi benzoic acid and, pre~erably, some bellzoic acid are distilled o~. Crude benzoic acid, which is puri~ied in the usual way, is recovered through conduit 13. me top product is passed through conduit 14 and ~ed to distillation column 15, in which the toluene and benzaldehyde, i$ any, are ~ully or partly distilled. me top product (conduit 16) may be returned to oxidation reactor 1, either as such or ailter benzaldehyde has been removed ~rom it by distillation.
me bottom product o~ column 15, which contains, i.a., benzyl alcohol, benzoic acid, benzyl iormiate, and benzyl acetate, i9 passed through conduit 1? to e~teri~ication reactor 18. Here the temperature is controlled at 200-250 C, the pressure is equal to atmospheric pressure.
In this reactor benzyl alcohol eqteri~ies with benzoic acid to benzyl benzoate and water, and the light benzyl esters, such as benzyl iormiate and benzyl acetate, re-esteriily with benzoic acid to ~orm benzyl benzoate and the iree light acids, such as iormic acid and ac*tic 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 al~o escape through this conduit. The reaction mixture passes through conduit 20 to distillation column 21, where the remainder oi these by-products i8 removed by distillation at a pressure oi 0.2 atm and is discharged as a vapour through conduit 22, and, ii 90 deslred, is returned to oxidation reactor 1 ~ilter condensation and removal oi the resultin~
; aqueous layer, while the liquid benzyl-beDzoate product leaves columns 21 through conduit 23. This product consists o~ crude benzyl benzoate which can be recovered through conduit 24 and ~rom which pure benzyl benzoate can be recovered by simple distillation.
me benzyl-benzoate product can be passed through conduit 25 to hydrolysis reactor 26, to which aqueous sodium hydroxide is ~ed 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. Ii the benzyl benzoate product supplied through conduit 25 still i~2~3 containQ ~ree benzoic acid, this is also converted into sodium benzoate in reactor 26.
The reaction mixture ~rom reactor 26 is ~ed 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 ei~ected. The aqueous layer con~ist~ o~ an aqueous sodium benzoate solution, which is discharged through conduit 31 and ~rom which solid sodium benzoate can be obtained by removal oi' water. me organic layer substantially consists oi' benzyl al¢ohol and toluene with some by-products with higher boiling points and is passed through conduit 32 to diQtillàtion column 33.
Thanks to the great dii'~erence between the boiling points oi toluene, benzyl alcohol, and the by-products, Reparation 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 15 through conduit 36. me toluene may be returned to extraction column 29 and the by-products may be returned to oxidation reactor 1.
- me ratio between the amounts oi' iree benzoic acid and sodium benzoate produced can be controlled to suit the requirements by controlling the amount oi benzoic acid that is distilled over in distillation column 12, also in dependence on the amount oi benzyl-benzoate produot discharged through conduit 24 Ii the need oi' benzyl alcohol is not great, the temperature ln distillation column 15 can be ad~usted to a higher value, 90 that alsa part o~ the benzyl alcohol present distils over and is returned to oxidation reactor 1 together with the toluene recycle flow.
Instead oi' distilling benzoic acid i'rom column 12 to have it available in esteriiication reactor 18, the required benzoic acid may, oi course, also be ied separately to reactor 18.
According to a ~urther embodiment oi' the inventian, the stream which is subjected to the carboxylic acid esterii'icatlon reaction is a tar containing benzylbenzoate or substituted benzylbenzoate. Such tars may be ~ormed in di~i'erent ways as i.a. described hereunder. me benzoic acid . .
~lZ~7~3 ~ay ~_ distilled completely or partly, together with all product~ with lower boiling points, ~rom the reaction mixture that contains benzoic acid, benzyl benzoate, other products with higher boiling points than benzoic acid and herein re~erred to as tar residue, unconverted toluene, and secundary products, such as benzyl alcohol and benzaldehyde, with lo~er boiling points than benzoic acid, and the distillate may be i'urther processed ~or pure benzoic acid, so that a tar containing benzyl benzoate and, possibly, some benzoic acid i9 obtainedas a residue. This residuemay be used as the starting material $or the process according to the invention.
A tar that contains benzyl benzoate and which may also be used as a starting material ~or the special embodiment o~ the process according to the invention may also ~orm i~ the above distillate i9 heated, whether or not in the presence o~ an esteri~ication or re-esterl~ication catalyst, e.g. sulphuric acid, phosphoric acid, boron tri~luoride, or zinc acetate, in order to esteri~y or re-esteriiy benzyl alcohol and/or light benzyl esters, such as benzyl i'ormiate and benzyl acetate, into benzyl benzoate, especially ii' the mixture still contains benzaldehyde during this esteri~ication reaction.
It is very di~icult to recover use~ul products ~rom such a tar containing benzyl benzoate. ~enzyl benzoate oan be distilled ~rom ; the tar residue, it is true, but a pure benzyl-benzoate product can hardly be obtained. Applicant has ~ound that the component ~luorenone ~- oi' the tar causes special problems in this connection. For, it has been i'ound that ~luorenon- can hardly be separated i'rom benzyl benzoate.
But besides ~luorenone, other unidenti~ied compounds may play a part.
According to said embodiment o~ the invention a benzyl ester is prepared by subjecting a tar containing benzyl benzoate to acidoly~is with an acid with a low boiling point, 90 that the benzyl benzoate is converted lnto the benzyl ester o~ the acid with the low boiling point.
Acidolysis denotes a re-esterii'ication reaction in which an .
~llZ4743 ester o~ an acid A and an alcohol B reacts with an acid C, so that an ester o~ acid C and alcohol B is ~ormed in addition to (~ree) acid A. In the process according to the invention the ester o~ a benzoic acid and a benzyl alcohol react~, e.g., with acetic acid, 80 that a benzyl acetate is ~ormed in addition to (~ree) benzoic acid.
me term 'acid with a low boiling point' denotes an acid the benzyl ester o~ which has a lower bo~ling point than benzyl benzoate, which usually implles that the ~ree acld itseli also has a lower boiling point than benzoic acid.
By means o~ the acidolysis reaction according to said embodiment o~ the invention, the benzyl benzoate with a high boiling point, which is di ~icult to separate by distillation irom some tar components, is converted into benzoic acid and a benzyl ester with a considerably lower boiling point which considerably di~ers in chemical and physical properties ~rom the benzyl benzoate and the tar components. The benzyl ester with a low boiling point can be recovered in a pure ~orm ~rom the acidolysed mixture, e.g. by distillation. Such benzyl esters are us8~ul products, which are used, e.g.,in the scents and ~lavours industry. Hence, this embodiment makes it posqible to convert a waste product that was useless so ~ar into a uqe~ul substance.
The aoldolysis is prei'erably carried out with an aliphatic carboxyllc acid with }-6 carbon atoms, more in particular 2-4 carbon atoms, per molecule with a low boiling point. Use i~ prei'erably made o~ acetic acid, propionic acid, or butyric acid, although iormic acid, i'or instance, may also be used. As benzyl acetate is a valuable commercial product, special pre~erence is given to acetic acid. Benzyl acetate can very ~avourably be produced by the special embodiment oi' 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 oi' between 100 C
and 300 C, with or without a catalyst.
~12 ~ 74 3 The tar containing benzyl benzoate used as the starting material is pre~erably ~ree 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 oi distillation.
Any components in the starting product with lower boiling points than that o~ benzoic acid can be removed prior to the acidolysis treatment, e.g. in one o~ the ways described above.
As the chemicsl properties o~ benzoic acid are considerably di~erent ~rom those oi the resulting esters, the separation oi' benzoic acid ~rom the reaction mixture, ii' e~ected, does not constitute a ~erious problem. me benzoic acid can be extracted ~rom the reaction mixture, ior instance, by mean~ o~ water, an aqueous qoda solution, diluted sodium hydroxlde, or another suitable extracting agent, or the reaction mixture can be separated by distillation.
lS Benzyl benzoate in the starting material is converted into a benzyl ester with a lower boiling point in the acidolysis reaction. mis benzyl ester can be recovered as such. It is pos~ible to remove the benzyl ester with the low boiling point irom the reaction mixture by distlllation and then to subject it to a hydroly~is or ammonolysis treatment as described above. mus, benzyl acetate is converted lnto benzyl alcohol and acetio acid or a salt or amide thereo~. As benzyl alcohol 19 now the only more volatlle component in the reactlon mlxture in addition to the acetlc acid, it can readlly be removed by distlllation. me acetic acid may be returned to the acidolysis.
The invention will be ~urther explained with re~erence to the reaction diagram annexed, indicated as rigure 2.
Oxidation reactor 1 is ~ed with liquid toluene through conduit 2 and with air through conduit 3. The toluene contains 0.001 to 0.1 % by weight oi' cobalt (II) acetate as dissolved catalyst. In reactor 1 the toluene is oxidized in the liquid phase at a temperature oi' 140 to 165 C
and a pressure o~ 3 to 10 atm. The vent gas irom the reactor is passed ~Z~7~3 through conduit 4 to condenser 5. The non-condensable gases escape through conduit 6 and the conden~ate is passed through conduit 7 to separator 8, where it is separated into an organic layer and an aqueous layer. me aqueous layer i~ removed through conduit 9; the organic layer is returned to oxidation reactor 1 through conduit 10.
The liquid oxidation mixture ilows irom oxidation reactor 1 through conduit 11 to distillation column 12, where all components with a lower boillng point than benzoic acid, plus, preierably, some benzoic acid, I are distilled oii and discharged through conduit 14. This top product substantially consists oi toluene and may be returned to oxidation reactor 1, either a~ a whole or aiter benzaldehyde has been recovered irom it by di3tillation. The bottom product ilows through conduit 13 to distillation j column 40, where all benzoic acid and components with a lower boiling point are distilled oii and discharged through conduit 41; this distlllate can be processed into pure benzoic acid in the usual way. me residue ilows through conduit 42 to distillation column 43. Column 43 may be a iilm evaporator.
The bottom product oi the distillation is discharged through conduit 44. m e resulting distillate, a mixture oi benzyl benzoate and tar, is passed through conduit 45 to acidolysis Peactor 46. me acidolysis reactor i9 ied with an acid with a low boiling point, acetic acid in thls ca~e, through oonduit 47, and with sulphuric acid as a catalyst through conduit 4~. The reaction mixture irom 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 acidolysi~ reactor 46 through conduits 51 and 47. A side $10w consisting oi benzyl acetate and some benzoic acid is withdrawn irom distillation column 50. This prevents benzyl acetate irom being returned into the process later on. mis side ilow 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 ~47~3 .
the washing device through conduit 56. me benzyl acetate product is recovered through conduit 57 and, ii 90 desired, may be iurther puri~ied, e.g. by ~ractional distillation. The bottom product ~rom column 50, which contains the major amount o~ 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 ~3 are omitted and the bottom product i'rom col D 12 is ied directly to acidolysis reactor 46.
men the bottom product ~rom column 50 is not returned to the process, but is discharged as tar.
The invention will be i'urther explained with rei'erence to the iollowing numerical examples/experiments.
Example I
In examples I to V re~erence is made to ~igure 1.
Toluene was oxidized in the liquid phase by means o~ air in oxidation reactor 1 at a temperature oi 160 C and a pressure oi 5 atmo~pheres and in the presence o~ 0.008 % by weight oi cobalt (in the i'orm oi acetate). In distillation column 12, the components with lower boiling points than benzoic acid and some benzoic acid were distilled ~rom the bottom ~low oi reactor 1 at atmospheric pressure. me product~ wlth lower bolllng points than benzyl alcohol are dlstilled irom the top product oi' distillation column 12 at atmospheric pressure in distillation column 15.
The composition, in % by weight, oi the bottom product discharged ~rom distillation column 15 through conduit 17 i9 given in Table I~ 'Other organic compounds' are, i.a., dibenzyl ether, acetophenone, methyl benzoate, 2-methyl diphenyl and 1,2-diphenyl ethane.
1~4~3 Table I
~low oi material conduit 17 conduit 19 conduit 20 benzyl alcohol 7.6 - 0.4 benzyl lormiate 9.9 - 0.9 benzyl acetate 14.3 - 8.9 benzyl benzoate - - 35.4 benzyl acid 51.7 - 31.4 other organic compounds 16.5 0,9 15.6 waterfiormlc acld/acetio acid - 4.1 2.1 Said bottom product is passed to esteri~ication reactor 18 that consists oi a l-litre glass llask to which a 40-cm long heating column is connected with a still head on top. me heating column is heated at 125-140 C to avoid condensation oi the volatile components iormed in the reaction 90 that they can be removed by way o~ the still head.
Another result is that the benzoic acid that has also evaporated condenses in the heating column, but does not solidi~y and, hence, $10ws back into the ilask. me residence time in reactor 18 amount~ to 30 minutes. An inert atmosphere (nitrogen) is maintained in the reactor. me ~lask is heated at the temperature speci~ied in Table II by means oi a metal bath.
me distillate and the residue are put together and the total is analysed. The results oi the analysis are also given ln Table II.
Table II
temperature (C) 200 210 230 250 benzyl alcohol (% by w.) 3.4 2.6 1.4 0.9 benzyl iormiate ' 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 benzolc acld ' 44.9 41.4 38.7 36.5 other organic compounds ' 16.5 16.5 16.5 16.5 water/iormic acid/acetic acid ' 1.4 2.8 3.5 4.3 112~7~3 The hi8her the temperature, the more products with lower boiling points, especially benzyl alcohol and benzyl 1'ormiate, but also benzyl acetate, are converted into benzyl benzoate with a hi~her boiling point.
Example II
S Example I i9 repeated, but now the bottom ilow (see conduit 17) oi' di~tillation column 15 with the composition according to Table 1 is heated in esteriiication reactor 18 $or 160 minute~. me temperature oi the metal bath is kept at 250 C. ~uring 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 iormiate and benzyl acetate, are converted into products with higher boiling points, especially benzyl benzoate.
Table III
time (minutes) boiling temperatures ( C) . ~ .
In T~ble I the compoaition oi' the starting ilow oi' materials (see condult 17), the composit10n oi the distillate (see conduit 19), and the composition oi the residue (see conduit 20) are given and expre3sed as % by weight calculated to the total oi the ilows in conduits 19 and 20.
The benzoic acid is distilled i'rom the bottom ilow oi' the esteriiication reactor 18 in distillation column 21 at a pre99ure oi 25 mm oi Hg. me composition oi' the top product (see conduit 22) and oi' the bottom product (see conduit 23, expressed in % by weight oi the total oi' the ilows in conduits 22 and 23, is given in Table IV, where the composition oi the ilow in conduit 20 is given ior comparison.
11~4~43 Table IV
~low oi material conduit 20 conduit 22 conduit 23 benzyl alcohol 0.4 0.4 benzyl ~ormiate 0.9 009 benzyl acetate 9.4 9.4 benzyl benzoate 37.3 0.2 37.1 other organic compound~ 16.4 11~1 S.3 benzoic acid 33.1 33.0 0.1 water/iormie acid acetic aoid 2.2 2.2 The bottom product o~ di~tillation column 21 i9 withdrawn through conduit 24. It iq distilled separately at a pressure oi 25 mm o~ Hg and a temperature o~ 210 C. In this way pure benzyl benzoate with a content o~ over 99.7 % by weight is obtained.
Example III
E~ample II is repeated. me crude benzyl benzoate in conduit 23 is now ied to hydrolysis reactor 26 through conduit 2S. Here it is madè to react with aqueous sodium hydroxide (12.5 % by weight o~ NaOH) that i9 supplied through conduit 27. The composition o~ the reaction mixture beiore hydrolysis is given in T~ble V.
In hydrolysis reactor 26 the reactlon mixture is stirred at 100 C
~or 30 minutes with re~lux oooling. The composition oi the oontents o~
reactor 26 aiter hydrolysis i9 also given in Table V.
7~3 Table V
~low o~ material be~ore hydrolysis a~ter hydrolysis (~ by weight) (% by weight) be~zyl benzoate 39.6 <0.01 benzoic acid 0.1 sodium hydroxide 7.9 0.3 water 46.7 46.7 benzyl alcohol - 20.2 sodlum benzoate - 27.1 other organlc compounds 5.7 5.7 me reaction mixture is extracted iour times with toluene in an amount o~ hal~ the weight o$ water, the toluene extracts are added together, and the toluene i9 iirst di3tilled oi'i with some water, and next the benzyl alcohol. me benzyl alcohol obtained appears to be pure i'or over 99.9 %
by weight.
The sodium ben7oate is recovered i'rom the aqueous phase by removal oi' water.
Exa~ple IV
Example I is repeated, but the benzoic acid is removed i'rom the bottom product oi' distlllation column 15 (see conduit 17) with the composition acoording to Table 1, by washing with an aqueous soda solution (10 % by weight oi! Na2C03), a~ter whlch acetic acld 19 added to the washed product.
The mixture obtained, the composition o1' which is given in Table VI
('beiore conversion'), i~ boiled in the esteri~ication reactor 18 until a bottom temperature o~ 155 C i8 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 result~ oi' analysis are also given in Table VI ('ai'ter conversion').
1~2-~7~3 Table VI
before conversionai'ter conversion (% by weight) (% by weight) benzyl alcohol 7.6 0.3 benzyl ~ormiate 9.9 8.7 benzyl acetate 14.3 2S.8 other organic compounds 16.5 16.6 acetic acid 51.7 47.1 ~ormic acid/water - 1.7 - 10 Example V
Example II is repeated, unless otherwise speci~ied. The crude benzyl benzoate in conduit 23, the compositlon oi which i9 given in Table IV, is now ied to an ammonolysis/hydrolysis reactor 26 through conduit 25. Here it i9 made to react with an aqueous ammonium-hydroxide 301ution (25.6 % by weight calculated as NH40H) that is supplied through ~conduit 2~. The composition o~ the reaction mixture be~ore ammonolysis/
hydrolysis is given in Table VII.
me reaction mixture is s~irred at 150 C and 15 atm i'or 4 hours - in ammonolysis/hydrolysis reactor 26, an autoclave with a stirring mechanism. Aiter cooling, the reaction mixture is given a pH of 6 by means oi 1 N aqueous sulphurlo acid and extracted three times with toluene in an amount oi hali' the welght oi water present. me toluene and the components with lower boiling points are evaporated irom the extract, the product obtained having a composition as mentioned in Table VII.
1~24~3 Table VII
be~ore ammonoly~is/a~ter ammonolysis/
hydrolysis hydrolysis benzyl benzoate 18.4 1.0 benzolc 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 recovsred by cry~tallization. The yield o~
benzamide can be raised at the C09t oi benzoic acid by carrying out the ammonolysis in the presence oi 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 i'ollowing example~ re~erence is made to iigure 2.
In oxidation reactor 1 toluene is oxidized in the liquid phase wlth air at a temperature oi 160 C and a pressure o~ 5 atmospheres and 2~ ln the pre~ence o~ 0.008 % by wei~ht oi oobalt ~as acetate). The deBree oi conversion oi the toluene is about 20 %. me components with a lower boiling point than benzoic acid and some benzoic acid are distilled i'rom the bottom i'low irom reactor 1 in di tillation column 12 at atmospheric pr2ssure. The bottom product ~rom distillation column 12 i9 distilled iurther at atmospheric pressure in distillation column 40, until virtually all benzoic acid and components with lower boiling points have been removed i'rom the reaction product. The residue is subjected to i'ilm evaporation in i'lash evaporator 43 at a temperature o~ 260 C and a pressure oi' 25 mm o~
Hg. Acetic acid and ~ulphuric acid are added to the distillate o~ the iilm evaporation, a mixture of benzyl benzoate and tar, in acidolysi~
reactor 46, consisting oi a glass ~lask with re$1ux condenser. me composition oi the mixture thus obtained is given in Table VIII (be~ore acidolysis). me tar residue consists o~, i.a., ~luorenone (about 40 %
by weight relative to the tar~, 1,2-diphenyl ethane and 2-, 3-,and 4-~ethyl diphenyls.
The mixture in the acidoly~is reactor is boiled for 2 hours at a temperature oi about 130 C. me composition oi' the reactor contents a~ter acidolysis is also given in Table VIII.
Table VIII
composition be~ore a~ter~low 51 ilow 52 i'low 53 % by w. acidolysi~ acidolysis benzoic acid 10.7 23.5 - l 52.0 àcetic acid 45.6 39.1 99 benzyl acetate - 16.0 1 99 benzyl benzoate 32.3 9.7 - - 21.7 tar residue 10.8 11.2 - - 25.0 sulphuric acid 0.60.6 - - 1.3 .
The reaction mixture i~ then separated into ~lows 51, 52, and 53 in distillation column ~0. The compositlon o~ these ilows is also glven ln Table VIII.
Experiments VII - X
me iollowing experiments show that the acldolysis reaction according to example VI can also be eiiected with other catalyst than sulphuric acid and also without the use o~ a catalyst.
Benzyl benzoate, acetic acid and the catalyst speciiied are mixed in the proportions stated. The reaction mixture is then boiled with re~lux ior the period indicated. A~ter the reaction the conversion o~ benzyl benzoate into benzyl acetate and benzoic acid is determined. The ~12~7~3 results ars given in Table IX.
Table IX
expleriment VII VIII ¦ IX ¦ X
eatalyst none phosphoric aeid p-toluene jsulphonic acid ~sulphuricacid % by w. o~ catalyst - 20 , 1 I 1 relative to benzyl 1.
benzoate moles o~ aeetie acid 2 2 8 8 relative to benzyl benzoate reaction tima (hours) 26 7 6 4 conversion o~ benzyl 4 40 14 70 benzoate (%) ,
Claims (26)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
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 separated from the resulting oxidation reaction mixture, which contains compounds present in the oxidation reaction mixture of derivatives of such compounds, is subjected to a carboxylic acid esterification reaction.
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 acids that are volatile under the reaction conditions present in the reaction mixture are re-esterified into esters of said carboxylic acid.
3. Process according to claim 1, characterized in that the carboxylic acid contains at most 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 relative 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 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 claim 1, characterized in that a 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 according to claim 1, characterized in that a tar containing benzyl benzoate is subjected to an acidolysis reaction with an acid with a low boiling point, 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 accoding to claim 14, 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 claim 14, characterized in that the tar containing benzyl benzoate is obtained by oxidizing a mono-alkyl benzene compound with a gas containing molecular 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 20 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 claim 14, 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 claim 1, 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 a substituted or unsubstituted benzyl alcohol is recovered from the organic layer.
26. Process according to claim 25, characterized in that sodium benzoate is recovered.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7711922 | 1977-10-31 | ||
| NL7711922A NL7711922A (en) | 1977-10-31 | 1977-10-31 | Oxidn. of mono:alkyl-benzene cpds. esp. toluene - with prod. subjected to esterification to facilitate recovery of benzyl alcohol etc. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1124743A true CA1124743A (en) | 1982-06-01 |
Family
ID=19829437
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA294,269A Expired CA1124743A (en) | 1977-10-31 | 1978-01-03 | Process for preparing oxidation products of monoalkyl benzene compounds |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1124743A (en) |
| NL (1) | NL7711922A (en) |
-
1977
- 1977-10-31 NL NL7711922A patent/NL7711922A/en not_active Application Discontinuation
-
1978
- 1978-01-03 CA CA294,269A patent/CA1124743A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL7711922A (en) | 1979-05-02 |
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