AU632937B2 - Process for the preparation of methanolic methyltri-n- alkylphosphonium iodide solution - Google Patents

Description

"ci~Y~ 632931.o COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: SComplete Specification Lodged: Accepted: Published: Priority Related Art ame of Applicant 4 Address of Applicant ,Actual Inventor Address for Service HOECHST AKTIENGESELLSCHAFT D-6230 Frankfurt/Main 80, Federal Republic of Germany HEINZ ERPENBACH, REINHARD GRADL, ERHARD JAGERS, ANDREAS SEIDEL and NORBERT WEFERLING WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA i" Complete Specification for the invention entitled: PROCESS FOR THE PREPARATION OF METHANOLIC METHYLTRI-N-ALKYLPHOSPHONIUM IODIDE SOLUTION The following statement is a full description of this invention, including the best method of performing it known to L HOE 90/H 015 The invention relates to a process for the preparation of methanolic methyltri-n-alkylphosphonium iodide solution having 3 to 8 carbon atoms in the carbon chain and prepared from tri-n-alkylphosphine and methyl iodide in a diluent.

Quaternary phosphonium salts are effective promoters in carbonylation reactions for preparing acetic acid and acetic anhydride where noble metal compounds, in particular rhodium compounds, are used as the catalyst.

eeooo 6 10 Suitable :preparation methods are described in DE-A-2,450,965.

Recently, in particular the rhodiumcarbonyl complexes

[CH

3

P(C

4

H,)

3 ]Rh(CO)I, or [CH 3

P(C

4

H,)

3 ]Rh(CO 2

,I

2 are described for effective catalyst systems (EP-B-0,240,703).

The quaternary phosphonium halides are prepared according to the reaction scheme R3P Hal-R' [R3"-R']Hale *t When methyl iodide is reacted with tertiary phosphines, a very vigorous reaction occurs, making necessary the use 20 of diluents, such as ether or benzene (HOUBEN-WEYL: "Methoden der Orqanischen Chemie" [Methods of Organic 0 0* Chemistry], 1963, volume 12.1, page 79).

In industry, hexane is nowadays used as the diluent. The disadvantage of all previously utilized diluents is that the quaternary phosphonium halide precipitates as a salt and has to be separated off from the diluent before further use as a promoter in carbonylation reactions.

Surprisingly, it has no% oeen found that the reaction o' tri-n-alkylphosphine having 3 to 8 carbon atoms in thu carbon chain with methyl iodide takes place in a homogeneous phase if methanol is used as the diluent. The formation of the desired phosphonium salts by this method takes place quantitatively, relative to the component I I ~SYIZ~iP~cP~-'i"Wi -64 used in less than an equivalent amount.

The process of the invention can furthermore preferably and alternatively comprise a) carrying out the reaction with the exclusion of air, b) using tri-n-alkylphosphine and methyl iodide in a molar ratio of 1 to (1.1 to 0.95), c) adjusting the molar ratio of methyltri-n-alkylphosphonium iodide to methanol to 1 to (1 to 20), in particular to 1 to (4 to 00 10 The process of the invention makes it unnecessary to Scompletely separate off a foreign diluent and to redissolve the methyltri-n-alkylphosphonium iodide in the reaction mixture of the carbonylation; furthermore, the carbonylation products are not contaminated with a *15 foreign diluent and the purification or disposal of the foreign diluent which is contaminated after multiple use is omitted.

*oo Example 1 0. A mixture of 168 g (1.05 mol) of tri-n-propylphosphine 20 and 320 g of methanol is initially introduced into a 1 1 multi-neck flask, equipped with stirrer, internal thermometer, reflux condenser, dropping funnel and nitrogen introduction line, which has been rendered inert with nitrogen. 150 g (1.06 mol) of methyl iodide are aided dropwise to this mixture at room temperature over a period of 2 hours with vigorous stirring. After the dropwise addition is completed and the exothermic reaction has subsided, the reaction mixture is kept under reflux conditions for another hour.

The 31P NMR spectrum of the clear, colorless solution no longer showed any signal of the starting compound tri-npropylphosphine (-33 ppm). 99% of the 1 P NMF signal intensity for methyltripropylphosphonium iodide was found

L

at +31 ppm.

Example 2 202 g (1 mol) of tributylphosphine and 160 g (5 mol) of methanol are initially introduced into a 0.5 1 multi-neck flask, equipped with stirrer, internal thermometer, dropping funnel, reflux condenser and nitrogen introduction line, which has been rendered inert. Under an inert gas atmosphere, the mixture is heated to 60°C, and 157 g (1.1 mol) of methyl iodide are added dropwise over a 9***oo period of 40 minutes. The enthalpy of the reaction which is liberated keeps the mixture boiling without any S. additional heat input. After the addition of methyl S. iodide, the clear, colorless reaction mixture is kept at 65 0 C for another 45 minutes.

Analysis of the 31 P NMR spectrum of the product showed that the tributylphosphine had been converted quantitatively to methyltributylphosphonium iodide (+32 ppm).

Example 3 As described in Example 2, 70 g (0.5 mol) of methyl 20 iodide are added dropwise to 190 g (0.52 mol) of tri-noctylphosphine in 275 g of methanol. The reaction is allowed to continue at 65 0 C for another 2 hours.

As expected, in addition to traces of oxide and residual unconverted tri-n-octylphosphine -32.5 ppm), only 25 methyltrioctylphosphonium iodide (+31 ppm) was found in the 31 P NMR spectrum of the product.

Claims (6)

1. A process for the preparation of a methanolic solution of methyltri-n- alkylphosphonium iodide having 3 to 8 carbon atoms in the carbon chain, which comprises reacting tri-n-alkylphosphine having 3 to 8 carbon atoms in the carbon chain with methyl iodide in a homogenous phase by using methanol as the diluent.

2. The process as claimed in claim 1, wherein the reaction is carried out with the exclusion of air.

3. The process as claimed in one of claims 1 or 2, wherein tri-n- S alkylphospine and methyl iodide are used in a molar ratio of 1 to (1.i to 0.95).

4. The process as claimed in one of claims 1 to 3, wherein the molar ratio of methyltri-n-alkylphosphonium iodide to methanol is adjusted to 1 to (1 to 20), in particular to 1 to (4 to

5. A process for preparing a methanolic solution of methyltri-n- alkylphosphonium iodide as described in Examples 1 to 3.

6. A methanolic methyltri-n-alkylphosphonium iodide solution obtained by the process as claimed in at least one of claims 1 to DATED this 27th day of October, 1992. HOECHST AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA DBM:KJS:JL VAX doc 023 AU7623191.WPC