GB2054592A

GB2054592A - Production of an alcohol and a carboxylic compound

Info

Publication number: GB2054592A
Application number: GB8023774A
Authority: GB
Original assignee: University of Sheffield; Johnson Matthey PLC; BP Chemicals Ltd
Current assignee: University of Sheffield; Johnson Matthey PLC; BP Chemicals Ltd
Priority date: 1979-07-19
Filing date: 1980-07-21
Publication date: 1981-02-18

Abstract

An alcohol and a carboxylate group-containing compound are produced by contacting an aldehyde in neutral or alkaline aqueous medium with a catalyst comprising a complex of palladium, platinum, rhodium, ruthenium, osmium or iridium. Under neutral conditions the carboxylate-group containing compound is a carboxylic acid and under alkaline conditions a carboxylic acid salt. The molar ratio of alcohol to carboxylate group-containing compound in the product can be modified by addition to the catalyst of a ligand such as tertiary phosphine.

Description

SPECIFICATION Process for the production of an alcohol and a carboxylate group-containing compound The present invention relates to a process for the production of an alcohol and a carboxylate group-containing compound and in particular to a process for the production of ethanol and acetic acid.

Both ethanol and acetic acid are valuable industrial products which are produced on a large scale. Ethanol is generally manufactured either by fermentation of natural products e.g.

molasses or by hydration of ethylene in the present of an acid catalyst such as phosphoric acid supported on silica. Acetic acid is generally manufactured either by oxidation of paraffinic feestocks at elevated temperature and pressure or by reacting methanol with carbon monoxide in the presence of a rhodium catalyst promoted with a halogen compound. Alternative routes to ethanol and acetic acid, especially ones which utilise milder reaction conditions, are constantly under investigation.

In this context we have found that aldehydes can be converted in aqueous media to alcohols and either carboxylic acids or salts thereof, depending upon the pH of the aqueous medium, in the presence as catalyst of a noble transition metal complex under mild reaction conditions. In a neutral reaction medium the co-product is a carboxylic acid whereas in an alkaline reaction medium the co-product is a salt of a carboxylic acid. This result is surprising since in aqueous alkali only aldehydes not having hydrogen on the carbon atom alpha- to the aldehyde group are susceptible to the Cannizzaro reaction, which may be represented by the following

Under neutral conditions the reaction does not generally take place at all.

Aldehydes bearing alpha-CH groups undergo the base-catalysed aldol condensation in preference, for example acetaldehyde reacts as follows:

Accordingly the present invention provides a process for the production of both an alcohol and a compound containing a carboxylate grouping which process comprises contacting an aldehyde in neutral or alkaline aqueous medium with a catalyst comprising a complex of a noble transition metal as hereinafter defined.

The aldehyde reactant may be an aliphatic or an aromatic aldehyde. Furthermore hydrogen may be present or absent from the carbon atom alpha- to the aldehyde function. Suitable aldehydes which may be used in the process of the invention include acetaldehyde, formaldehyde, propionaldehyde and benzaldehyde, of which acetaldehyde is preferred. Unsaturated aldehydes and dialdehydes may also be used.

Within the context of this specification the noble transition metals are defined as palladium, platinum, rhodium, ruthenium, osmium and iridium. The preferred noble transition metals are rhodium and ruthenium. The noble transition metal complex is preferably soluble in the aqueous medium under the conditions of the reaction. Suitable noble transition metal complexes include [Rh2(C5Me5)2(0 H)3]Cl.4H20, [Rh2(C5Mes)2 Cl4],[Ru2(C6Me6)2(OH)3]Cl.4H20, [Rh2(C5Me5)2(H)(0C0R)2+Z- wherein R = alkyl or aryl and Z- is a non-coordinating anion, [Ru2(C6Me6)2(OCOR)3]+Z- wherein R = alkyl or aryl and Z- is a non-co-ordinating anion, as well as other catalysts of the general type [Rh2(arene)2X4] wherein X is halogen and arene is benzene, p-cymene, etc. The complexes may be prepared by methods well-known in the art.Thus the complex [Rh2(C5Mes)2(0H)3]CI.4H20 which is a stable, crystalline orange solid may be prepared by reacting [Rh2(C5Me5)2CI4] with aqueous sodium hydroxide. The preparation of this and the complex (Rh2(C5Me5)2CI4 is described in detail in Accts Chem Res, 1 978 11, 301 (P M Maitlis); J Amer Chem Soc, 1969, 91 5970 (J W Kang, K Moseley and P M Maitlis) and J Organometallic Chem 1971, 26, 393. The complex [Ru2(C6Me6)2(0H33CI.4H20 may be prepared by reacting the complex [Ru2(C6Me6)2CIJ which has been described in JCS Chem Comm, 1978, 582 (M A Bennett, T-N Huang, A K Smith and T W Turney) with aqueous sodium carbonate.

The use of rhodium complex catalysts may lead to a product in which the molar ratio of alcohol to the compound containing a carboxylate group is approximately 1:1. The use of ruthenium complexes may substantially increase the molar ratio of the compound containing a carboxylate group to the alcohol in the product. The molar ratio may also be adjusted by the addition to the catalyst of suitable ligands. Suitable ligands include tertiary phosphines, in particular phosphines having the formula R3P and tertiary amines of formula RsN, wherein R is a hydrocarbyl group. Suitably the phosphine is triphenylphosphine which effects a significant increase in the amount of ethanol and a small decrease in the amount of the carboxylate groupcontaining compound in the product.Suitably the molar ratio of the ligand to the noble metal complex may be in the range 0.1 to 100, preferably 1 to 3.

The molar ratio of aldehyde to catalyst in the reaction mixture may suitably be in the range 1 to 5000, preferably 50 to 500. The amount of aqueous medium in the reaction mixture is not critical provided sufficient is present to perform the reaction. On the other hand an excessive amount is not desirable because it unnecessarily burdens product separation and recovery.

The process may suitably be carried out at atmospheric pressure, though pressures above and below atmospheric may be employed. The reaction temperature may be in the range O to 300"C, preferably 5 to 200C.

In neutral aqueous medium an alcohol and a carboxylic acid are produced by the process of the invention. At elevated temperatures in particular some product interaction may occur resulting in the formation of esters. In alkaline medium the carboxylic acid is converted to the salt of the metal species of the alkaline compound employed to adjust the pH. Thus in a neutral aqueous medium the use of acetaldehyde as the feed material produces acetic acid and ethanol.

The same reaction in aqueous medium made alkaline by the addition of, for example sodium hydroxide, produces ethanol and sodium acetate. Suitably the pH of the alkaline aqueous medium may be in the range 8 to 1 2. The reaction may also be carried out in aqueous organic solvents such as acetone and tetrahydrofuran.

The process may be carried out batchwise or in a continuous manner; it may also be carried out heterogeneously using the metal complex on an inert support. The products formed in the process may be recovered from the reaction medium and separated in known manner.

The invention will now be illustrated by reference to the following Examples.

Example 1 0.04 m moles l0Rh2(C5Me5)2(0H)3]Ci.4H20 was dissolved in aqueous 10% v/v acetaldehyde (3.6 m moles) solution and held at 22"C for a period of 5 hours. The reaction was directly monitored by 'H NMR R spectroscopy and by gas chromatography (PEG-400/100'C or Pora- pak-Q/200C) using standard samples of ethanol and acetic acid for comparison.

Details of the reaction conditions and the products obtained are given in the Table.

Example 2 The procedure of Example 1 was repeated except that the reaction time was increased to 23 hours.

Example 3 The procedure of Example 1 was repeated except that the temperature was increased to 50"C.

Example 4 The procedure of Example 1 was repeated except that the temperature was increased to 50"C and the reaction time to 23 hours.

Example 5 The procedure of Example 1 was repeated except that the amount acetaldehyde was increased to 1 7.8 m moles, the temperature was increased to 50 C and the reaction time was increased to 1 6 hours.

Example 6 The procedure of Example 5 was repeated except that the reaction time was increased to 112 hours.

Example 7 The procedure of Example 1 was repeated except that the amount of [Rh2(C5Me5)2(OH)3]- Cl.4H20 was increased to 0.08 m mole and the temperature was increased to 50 C.

Example 8 The procedure of Example 7 was repeated except that the reaction time was increased to 23 hours.

Example 9 0.04 m moles [Rh2(C5Me5)2Cl4J was dissolved in aqueous 10% v/v acetaldehyde (1 7.8 m moles) solution and held at 50 C for a period of 1 6 hours. The reaction was monitored in an identical manner to that described in Example 1.

Example 10 The procedure of Example 9 was repeated except that the reaction time was increased to 40 hours.

Example 11 The procedure of Example 9 was repeated except that the reaction time was increased to 1 36 hours.

Example 12 0.04 m mole [Ru2(C6Me6)2(OH)3iCl.xH2O dissolved in aqueous 10% v/v acetaldehyde (5.3 m moles) solution and held at 22"C for a period of 91 hours. The reaction was monitored in an identical manner to that described in Example 1.

Example 13 The procedure of Example 1 2 was repeated except that the amount of acetaldehyde was increased to 10.6 m mole.

Example 14 The procedure of Example 1 2 was repeated except that the amount of acetaldehyde was increased to 10.6 m mole, the reaction temperature was increased to 50"C and the reaction time reduced to 1 8 hours.

Example 15 The procedure of Example 14 was repeated except that 0.04 m mole triphenylphosphine was incorporated in the reaction mixture.

Example 16 Example 1 5 was repeated except that the amount of triphenylphosphine was increased to 0.12 m moles.

Example 17 0.04 m mole of [Ru2(p-cymene)2Cl4] was dissolved in aqueous 10% v/v acetaldehyde (10.6 m moles) held at 50"C for 20 hours. The reaction was monitored in an identical manner to that described in Example 1.

Example 18 0.04 m moles (Rh2(C5Me5)2(0H)3JCI 4H20 was dissolved in aqueous 2% v/v propionaldehyde (6.0 ml, 1.67 m moles) and held at 50"C for a period of 72 hours. The solution was directly analysed by gas chromatography (Porapak Q/200C) and was shown to contain 0.6 moles of propan-1-ol and 0.6 m moles of propionic acid.

Example 19 The procedure of Example 1 8 was repeated except that the catalyst used was 0.04 m mole [Rh2(C5Me5)2CIJ. GC analysis of the product solution showed the presence of 0.4 m mole propan-1-ol and 0.4 m mole propionic acid.

Example 20 The procedure of Example 1 8 was repeated except that the catalyst used was 0.04 m mole [Ru2(C6Me6)2(0H)3]CI 4H20. GC analysis of the product solution showed the presence of 0.3 m moles of propan-1-ol and 0.8 m moles of propionic acid.

Example 21 The procedure of Example 1 8 was repeated except that the catalyst used was 0.04 m mole [Ru2(cymene)2Cl4]. GC analysis of the product solution showed the presence of 0.3 m mole of propan-1-ol and 0.9 m moles of propionic acid.

TABLE Example Catalyst CH3CHO Reaction Temp EtOH produced HOAC produced No (m moles) (m moles) Time ( C) (hours) m moles T/N* m moles T/N* 1) ( 3.6 5 22 0.15 4 0.2 5 2) ( 3.6 23 22 0.35 9 0.35 9 3) [Rh2(C5Me5)2(OH3)]Cl.4H2O ( 3.6 5 50 0.55 14 0.6 15 4) (0.04) ( 3.6 23 50 0.95 24 1.0 25 5) (17.8 16 50 2.5 61 2.5 61 6) (17.8) 112 50 5.9 148 6.5 163 7) [Rh2(C5Me5)2(OH)3]Cl.4H2O ( 3.6 5 50 0.7 9 0.9 11 8) (0.08) ( 3.6) 23 50 1.1 14 1.2 15 9) [Rh2(C5Me5)2Cl4] (17.8 16 50 1.7 43 1.6 40 10) (17.8 40 50 2.2 55 2.6 62 11) (0.04) (17.8 136 50 4.0 100 4.2 105 12) [Ru2(C6Me6)2(OH)3]Cl.xH2O ( 5.3 91 22 0.3 7 1.9 47 13) (0.04) (10.6 91 22 0.7 18 3.3 82 14) [Ru2(C6Me6)2(OH)3]Cl.xH2O 10.6 18 50 1.4 35 5.0 125 (0.04) 15) [Ru2(C6Me6)2(OH)3]Cl.xH2O 10.6 18 50 2.2 55 4.3 108 (0.04) + 0.04 m mole PPh3 16) [Ru2(C6Me6)2(OH)3]Cl.xH2O 10.6 18 50 2.4 60 4.0 100 (0.04) + 0.12 m mole PPh3 17) [Ru2(p-cymene)2Cl4] 10.6 20 50 1.7 43 3.3 83 (0.04) *T/N=turnover: mmoles of alcohol or acetic acid per m mole of catalyst

Claims

1. A process for the production of both an alcohol and a compound containing a carboxylate grouping which process comprises contacting an aldehyde in neutral or alkaline aqueous medium with a catalyst comprising a complex of a noble transition metal as hereinbefore defined.

2. A process according to claim 1 wherein the aldehyde is acetaldehyde.

3. A process according to either one of the preceding claims wherein the noble transition metal is rhodium or ruthenium.

4. A process according to any one of the preceding claims wherein the complex of the noble transition metal is soluble in the aqueous medium.

5. A process according to any one of the preceding claims wherein the complex is Rh2 (C5Me5)2 (0H)3JCl.4H20.

6. A process according to any one of claims 1 to 4 wherein the complex is [Rh2(C5Me5)2Cl4.

7. A process according to any one of claims 1 to 4 wherein the complex is [Ru2(C6Me6)2 (OH)3]Cl.4H2O.

8. A process according to any one of claims 1 to 4 wherein the complex is [Rh2(C5Me5)2 (H)(OC0R)2J+Z- wherein R is alkyl or aryl and Z is a non-coordinating anion.

9. A process according to any one of claims 1 to 4 wherein the complex is [Rh2(arene)2X4] wherein X is halogen and arene is benzene or p-cymene.

10. A process according to any one of the preceding claims wherein there is added to the catalyst a ligand which is either a tertiary phosphine of formula R3P or a tertiary amine of formula R3N, wherein R is a hydrocarbyl group.

11. A process according to claim 10 wherein the ligand is triphenylphosphine.

1 2. A process according to either one of claims 10 and 11 wherein the molar ratio of the ligand to the noble metal complex is in the range 1 to 3.

1 3. A process according to any one of the preceding claims wherein the molar ratio of aldehyde to catalyst in the reaction mixture is in the range 50 to 500.

1 4. A process according to any one of the preceding claims wherein the aldehyde is contacted with the catalyst at a temperature in the range 5 to 200"C.

1 5. A process according to any one of the preceding claims wherein the aldehyde is acetaldehyde, the aqueous medium is neutral and the products are acetic acid and ethanol.

1 6. A process according to any one of claims 1 to 14 wherein the aldehyde is acetaldehyde, the aqueous medium is alkaline and the products are ethanol and sodium acetate.

1 7. A process according to claim 1 substantially as hereinbefore described with reference to Examples 1 to 21.

1 8. Alcohols and compounds containing carboxylate groupings whenever produced by the process as claimed in any one of claims 1 to 1 7.