AU610952B2 - Process for the preparation of alpha-alkylacroleins - Google Patents

Description

or S.1l of C010panY and S Ignatures of Its 0Olitetrs as Prescrl~ed W~ Its Articles of Asssest 'n.

D. B. Mischlewski .Regtste0r'ed' "P'dt'dt...~ih 2 5 j j C- e dwid. Waitt'5 sons" Ti-E COMMISSIONER ori PATENTS.

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P COMMONWEALTH OF AUSTRALIA~ PATENTS ACT 1952-69 COMPLETE SPECIFICATION (OR IGINAL) Class I t. Class Application Number: Lodged: eomplete Specification Lodged: Accepted: 4. Published: PPriority: I ellated Art: 41 Name of Applicant: Address of Applicant: Actual Inventor: 4 Address for Service: HOECHST AKTIENGESELLSCHAFT 45 Bruningstrasse, D-6230 Frankfurt/Main Republic of Germany 8O, Federal GERHARD DIEKHAUS, Walsurermarkstrasse 89, Oberhausen 11, and HARALD KAPPESSER, Waidmannsweg 24, Oberhausen 11, Federal Republic of Germany EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: PROCESS FOR THE PREPARATION OF ALPHA-ALKYLACROLEINS The following statement is a full description of this invention, including the best method of performing it known to -usw 2- Process for the preparation of alpha-alkylacroleins The present invention relates to an improved process for the preparation of alpha-alkylacroleins by the reaction of aldehydes with the general formula R.CH 2 CHO and formaldehyde.

Numerous processes for the preparation of methacrolein are known.

Of these processes, the ones which proceed from propionaldehyde S have gained in significance in recent years as the starting materials are readily accessible.

CC C C C For example, a yield of approximately 46% of methacrolein is 0 0 6 Sooobtained by condensation of the starting aldehydes on catalysts 0 0 0 00 containing sodium hydroxide and silicic acid (cf. C.A. volume 56 o o [1962 columns 2321 and 2322).

0 o 00o0 0 0 0 0,o The DE-C1 875 194 describes the preparation of methacrolein by 00 "2 the addition of piperidine dropwise to a mixture of aqueous formaldehyde solution, propionaldehyder sodium chloride and butyric acid at boiling temperature over 2 to 3 hours. After Al another 3 hours after-reaction a 95% yield of methacrolein should be obtained. Apart from the fact that long reaction times are necessary, it was nowhere near possible to obtain the high yield when the instructions were followed.

According to the teachings of the DE-B2 28 55 504 in order to prepare methacrolein, propionaldehyde is reacted with formalde- 1_ 3hyde in the presence of a catalyst system consisting of a secondary amine and a carboxylic acid having up to 5 carbon atoms and left to react at temperatures of 70 to 120 0 C and pressures of 2 to 10 bar. The process gives 80 to 82% yields of methacrolein.

The DE-Al-30 25 350 describes the general elaboration of the I above-described process to cover the preparation of 2-methylene ct a Cte C C 4 aldehydes.

C r r, The subject of the DE-Al 31 06 557 is a process for the preparation of alpha-alkylacroleins by the reaction of alkanals with formaldehyde and secondary amine in the presence of acid. The o reaction takes place in an acidic to neutral environment at pH 0 00 values of 2.5 to 7. According to the examples, high yields of 0 o a 0 0 methacrolein of 90 and more are obtained but the process 0 0o requires extremely high amounts of amine of 0.5 to 1 equivalents 0 00 per mole of alkanal.

0a0 The DE-Al 32 13 681 also relates to a process for the preparation of alpha-alkylacroleins from alkanals and formaldehyde in the presence of secondary amines and, optionally, of acids. It is characterised in that the reaction is conducted at overpressure and at a temperature of more than 150 0 C and with a reaction time of max. 25 minutes. This process also provides methacrolein in high yields but requires the employment of comparatively high temperatures and pressures.

-4 Therefore the task consisted in developing a procedure which supplies alpha-alkylacroleins in high yields under as mild reaction conditions as possible.

This task is solved by a process for the preparation of alphaalkylacroleins from aldehydes with the general formula R.CH 2 .CHOr R being a straight-chain or branched alkyl group having 1 to 0 O °:a00 carbon atoms, and formaldehyde in the presence of 0.02 to 0.05 o, I• moles of a secondary amine and 0.02 to 0.065 moles of a carboxy- 0 o00 s lic acid having up to 5 carbon atoms per mole of the aldehyde o 0 0 0 0 0 R.CH2.CHO. at 70 to 120 0 C and 0.2 to MPa, characterised in that the molar ratio of amine to carboxylic acid is 1 0.8 to 1 1.3 O 0 and the reaction is performed in two stages, the aldehyde 0°0 0 R.CH2.CHO and formaldehyde being reacted in the first stage in "0000" the presence of the secondary amine and 25 to 75 mole of the "0"0 carboxylic acid and the reaction being completed in the second .0 stage after the remaining carboxylic acid has been added.

000 0 00 0 0 0 0 Surprisingly, the claimed measures lead to high yields of alphaalkylacroleins within a short time although the reaction is performed at moderate temperatures and only slightly elevated pressure.

The group R in the general formula of the aldehydes used as starting materials stands for an alkyl group with 1 to 10 carbon atoms. This group can be straight-chain or branched. Examples of i aldehydes which can be brought to react according to the claimed 1 i ~I III 1-L-1 tll-. I-lli IP iOi -tl procedure are propanal, n-butanal, 3-methylbutanal, n-pentanal, n-hexanal, 3-methylhexanal, 4-methylhexanal, n-heptanal. The process has proved particularly successful for the reaction of propanal, n-butanal, 3-methylbutanal.

Formaldehyde is generally employed as an aqueous solution. How- S ever, it can also be reacted in polymerised form as paraformalde- S hyde.

Aldehyde R.CH2.CHO and formaldehyde can be brought to react in o I C stoichiometric ratio. However, it is also possible to use one of the two aldehydes in excess. It has proved useful to use 0.9 to 0 00 0 00 .o 1.5 moles of formaldehyde per mole of aldehyde R.CH 2

CHO.

S The use of a solvent, apart from water, in which the formaldehyde 0 S can be contained is not necessary but is expedient when a poly- 0o0o meric form of the formaldehyde is used. Suitable solvents are hydrocarbons and aliphatic alcohols, e.g. isodecane, toluene and 2-ethylhexanol.

An important feature of the claimed process is the use of secondary amines and carboxylic acids, both act together as catalysts, in certain ratios to each other and to the aldehyde. 0.02 to 0.05, preferably 0.025 to 0.035 of a secondary amine and 0.02 to 0.065 moles, preferably 0.025 to 0.040 of a carboxylic acid with up to 5 carbon atoms are used per mole of aldehyde.Furthermore, it is characteristic for the new process that the molar ratio of i PSU~.LI 6 amine to carboxylic acid is 1 0.8 to 1.3. Amine and carboxylic acid are preferably added in a molar ratio of 1 1 and in particular in a molar ratio of 1 1.1 to 1.3.

Both low and higher-molecular aliphatic compounds can be used as secondary amines. The alkyl groups can be the same or different.

SExamples of suitable secondary amines are dipropylamine, methylbutylamine, ethylbutylamine or di-n-octylamine. Di-n-butylamine has proved particularly successful. The secondary amines do not need to be used as a homogeneous substance, mixtures of the isomers of the same amine or mixtures of different amines have proved well suited for the performance of the reaction.

The carboxylic acids with up to 5 carbon atoms can contain one or Smore carboxyl groups. Formic acid, acetic acid and in particular

C

Spropionic acid, butyric acid or valeric acid which are used as such or in mixtures have proved useful.

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Another very important feature of the procedure according to the invention is the performance of the reaction in two stages. The aldehyde and formaldehyde are first reacted with some of the carboxylic acid in the presence of all the secondary amine. Then the remaining carboxylic acid is added. 25 to 75, preferably to 65 mole of the carboxylic acid is added to the reaction mixture in the first stage, the rest in the second stage. It is expedient to perform both stages of the reaction in the same reactor. It was not to be foreseen that the graduated addition of Lii ;i i ~iii i _ili-i I-r 7 acid, which means that the reaction takes place in different pH ranges, would lead to an appreciable increase in yield.

Normally the reaction takes place in the liquid phase with the reaction pressure being maintained between 0.2 and 1 MPa, preferably 0.2 to 0.4 MPa. powever, it is also possible to perform the I, i reaction in the gaseous phase. The reaction temperature is bet- I tC r ween 70 and 120 0 C, temperatures of 95 to 110'C are preferred.

S When the reactants are reacted in the liquid phase, a pressure vessel is employed in which the aldehyde and formaldehyde are placed under nitrogen atmosphere and, optionally, the amount of 0 o: the carboxylic acid which is used in the first stage. Then it is expedient to add the secondary amine with intensive stirring. It S°0 is also possible to add amine and carboxylic acid to the original o a 000 01 0 aldehyde mixture. If necessary, the reaction mixture must be 0 00 o cooled to maintain it within the range of the reaction tempera- 0 oo ture. However, by adding the reactants in portions, it can be ensured that the reaction temperature is not exceeded. After all the amine has been added, the mixture is left to react for 20 to minutes and the remaining carboxylic acid is then added, also with intensive mixing. In some cases it may be necessary to heat the reaction mixture to attain the reaction temperature. After i another 20 to 60 minutes the reaction is completed. The reaction mixture is left to cool, whereupon it separates into an organic and an aqueous phase. The new procedure can be performed both discontinuously and continuously, i.e. in a two-stage stirred -I'i cascade. The alpha-alkylacrolein is recovered from the raw product in more than 99% purity by fractionated distillation. Additional cleaning is not necessary for most applications.

The process according to the invention permits the preparation of alpha-alkylacroleins at low temperatures and under conditions which do not require special apparatus. The high yield of unsato a 00 urated aldehyde which i obtained despite simple reaction control 000ao o go is remarkable.

o eq 0 00 00 0 o 00 0 00 The process according to the invention is described int more detail in the following examples. Naturally it is not intended to a0 0 Q 00 S limit the invention to the special embodiments.

0 00 000000 Example 0000003 0 In a pressure vessel with a volume of 0.6 m equipped with stiroooo° rer, aldehyde R.CH 2 .CHO and formaldehyde (in the form of a 00 0 o oo aqueous solution) and part of the carboxylic acid in the amounts listed in the table are mixed under a nitrogen atmosphere. All the di-n-butylamine is added within 30 minutes. The reaction mixture is heated within another 30 minutes to 95 to 100 0 C. After the remaining carboxylic acid has been added, the mixture is left to after-react for 30 minutes, optionally with stirring. '.he reaction mixture is cooled, the aqueous phase separated. The composition of the organic phase is determined by gas chromatography.

Table 1: Preparation of 2-methylacrolein

C

Ce I C

C

0 46' 00 0 0 00 0 40 00 9 0 64 0 606040 044060 0 0 O 00 00 0 604 0 *4 6 0 00 0 propionaldehyde (kmol) formaldehyde (kmol) di-n-butylamile (kmol) kmol amine/kmol propionaldehyde propionic acid (kmol) 1st stage 2nd stage kmol acid/kmol propionaldehyde kmol acid/kmol amine GC analysis of the organic phase 2-methylacrolein aldol after-runnings yield of the theoretical value) Example 1 (comparison) 1.8 1.98 0.045 0.025 0.027 0 .027 0 .015 0.6 92.7 5.6 81.7 Example 2 2.16 2.38 0.054 0.025 0.054 0.032 0.022 0.025 92.25 89.0 0 000 0 0 0 0 0 0 0 00 0 0 00 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 *a CoO 00 0 00 0 Table 2: Preiparation of 2-ethylacrolein Example 3 Example 4 (comparison) (comparison) Example 5 Example 6 n-butyraldehyde (kmol) formaldehyde Ckmol) di-n-butylamine Ckmol) kmol amine/kmol butyraldehyde n-butyric acid Ckmol) 1st stage 2nd stage kmol acid/kmol butyraldehyde kmol acid/kmol amine GC-analysis of org. phase 2-ethylacrolein Aldol af ter-runnings yield of theor.) 1.75 1.75 0.0446 0 .026 0.014 0 .014 0.008 0.3 91.6 3.9 4.5 84.5 2.11 2.11 0.0549 0.026 0.055 0.055 0.026 1.0 1.75 1.75 0.0446 0.025 0.055 0.018 0.037 0.03 1.2 92.6 1.4 0.4 97.4 1.75 1.75 0.0446 0 .025 0.055 0.0275 0.0275 0.03 1.2 84.9 5.5 3.2 76.7 90.4 0.2 98.4

Claims (4)

1. 3. A process according to claim 1 or 2, characterised in that 0.025 to 0.04 moles of a carboxylic acid having up to 5 carbon atoms are added per mole of aldehyde.
2. 4. A process according to one or more of the claims 1 to 3, characterised in that the molar ratio of amine to carboxylic acid is 1 1 and in particular 1 1.1 to 1.3. s acid having up to 5 carbon atoms per mole of aldehyde R.CH2.CHO at 70 to 120 0 C and 0.2 to 1 MPa, characterised in that the molar ratio of amine to carboxylic acid is 1 0.8 to 1 1.3 and the reaction is performed in two stages, the /2 M IMI" -~11 91 I C CC Cr C, Cr C( C C c C, o at 0CC 0 0 o 00 A process according to one or more of claims 1 to 4, charac- terised in that 30 to 65 mole of carboxylic acid is added to the reaction mixture in the first stage.
3. 6. A process according to one or more of the claims 1 to characterised in that di-n-butylamine is used as the secon- dary amine.
4. 7. A process according to one or more of the claims 1 to 6, characterised in that propionic acid, butyric acid or valeric acid is used as carboxylic acid. DATED this 24th day of November 1988. HOECHST AKTIENGESELLSCHAFT EDWD. WATERS. SONS PATENT ATTORNEYS QUEEN STREET MELBOURNE. VIC. 3000. i- i- L j