JPS6055493B2 - Production method of α-branched aliphatic carboxylic acid anhydride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing α-branched aliphatic carboxylic acid anhydrides.

Specifically, the present invention relates to a method for producing an α-branched aliphatic carboxylic acid anhydride by oxidizing an α-branched aliphatic aldehyde in a liquid phase. Conventionally, methods for producing aliphatic carboxylic acid anhydrides include (1) reacting carboxylic acid with a dehydrating agent such as acetic anhydride or ketene, or (2)
) A method of oxidizing aldehydes with molecular oxygen is known.

The latter method is superior in that it can produce acid anhydride from aldehyde in one step, and is used to produce acetic anhydride from acetaldehyde. However, the conventional method uses a cobalt-copper compound as a catalyst, and if this method is directly applied to the oxidation of α-branched aliphatic aldehydes, side reactions such as oxidative cleavage occur frequently,
α-Branched aliphatic carboxylic acid anhydrides were obtained only in very low yields. In view of these circumstances, the present inventor conducted intensive research on the oxidation reaction of α-branched aliphatic carboxylic acids, and discovered a catalyst that can obtain α-branched aliphatic carboxylic acid anhydrides in good yield, thereby achieving the present invention. .

That is, the gist of the present invention is to produce an α-branched aliphatic carboxylic acid anhydride, which is characterized by oxidizing an α-branched aliphatic aldehyde with molecular oxygen in the presence of copper or a copper compound in a liquid phase. lies in the law. The present invention will be explained in detail below.

Examples of the α-branched aliphatic aldehyde to which the method of the present invention is applied include isobutyraldehyde, 2-ethylbutyraldehyde, 2-ethylhexylaldehyde, 2-methyloctylaldehyde, and cyclohexanecarbaldehyde.

So-called oxoaldehydes obtained by hydroformylation of olefins are suitable as raw materials for the process according to the invention. In the method of the present invention, the copper or copper compound used as a catalyst includes copper acetate, which is soluble in the reaction system;
Copper salts of carboxylic acids such as copper naphthenate and copper octylate, copper chloride, copper acetylacetone, etc., metal copper with extremely low solubility, cuprous oxide, copper iodide, etc. Copper compounds soluble in the system are preferred.

Of course, two or more types may be used in combination. When using a soluble copper compound in the reaction system as copper or a copper compound, the amount is usually 5 pp as a weight ratio of copper atoms to the reaction system.
The range is from m to 5%, more preferably from 50 ppm to 0.5%.

However, when using copper or a copper compound with low solubility, it may be used in excess of the above range. Examples of molecular oxygen used as the oxidizing gas include air, pure oxygen, or oxygen diluted with an inert gas.

The reaction temperature suitable for the oxidation is in the range of 10°C to 100°C, more preferably 30°C to 80'C.

The reaction pressure is not critical, but may be normal pressure or 10k91c.
The heating may be carried out under a slight pressure of about 1 ton. If the water produced by the reaction is continuously removed, the yield of α-monobranched aliphatic carboxylic acid anhydride can be improved.

The oxidation reaction can be carried out without a solvent, but it can also be carried out in the presence of a solvent.

Examples of preferred solvents include acetic acid esters such as ethyl acetate, acetone, benzene, and other substances that are relatively inert to oxidation reactions. There are no particular restrictions on the amount of solvent used. When carrying out the oxidation reaction in this manner, it is necessary that the amount of heavy metal atoms other than copper atoms present in the reaction system is small.

If the amount of heavy metal atoms is large, side reactions such as oxidative cleavage will actively occur, which is undesirable. In particular, low amounts of cobalt and manganese are required, usually 5% each.
ppm or less, preferably 1 ppm or less, chromium and vanadium each usually 20 ppm or less, preferably 5 ppm or less, and iron usually 100 ppm or less, preferably 20 ppm or less. (all ratios by weight) In addition, during this oxidation reaction, the α-monobranched aliphatic carboxylic acid anhydride and the corresponding α-monobranched aliphatic carboxylic acid are simultaneously produced, but the production ratio depends on the purpose of the reaction. It can be changed by changing the conditions.

After the oxidation reaction, well-known separation and purification methods such as gas-liquid separation,
By appropriately combining distillation and the like, the desired α-monobranched aliphatic carbonic acid anhydride can be obtained. According to the method of the present invention, a monobranched aliphatic carboxylic acid anhydride having the same carbon skeleton as the raw material alpha monobranched aliphatic aldehyde can be obtained.

Examples of such α-branched aliphatic carboxylic acid anhydrides include isobutyric anhydride, 2-ethylbutyric anhydride, and 2-ethylbutyric anhydride.
Examples include ethylhexanoic acid, 2-methyloctanoic anhydride, and cyclohexanecarboxylic anhydride. These α-monobranched aliphatic carboxylic acid anhydrides are useful as polymeric materials such as cellulose esters and dehydrating agents, and as raw materials for the synthesis of various chemicals such as acylating agents. According to the method of the present invention, these α-monobranched aliphatic carboxylic acid anhydrides can be produced with good yield, and there are few cleavage by-products.

In addition, in the case of an aldehyde such as acetaldehyde that has no branch at the α-1 position, the yield of acid anhydride is extremely low even if copper or a copper compound is used as a catalyst.

EXAMPLES The present invention will be described in more detail with reference to Examples below, but the present invention is not limited in any way by the Examples unless the gist of the invention is exceeded.

J Example 1 Isobutyraldehyde 6.3V (8
7.4 TrL, m01) and 35 ml of ethyl acetate were charged, and copper naphthenate was added as a catalyst to give a concentration of 50 ppm as copper atoms to the entire yarn.

In addition, the concentration of heavy metal impurities at this time is 1 weight P
It was below pm. 1. Warm the system to a temperature of 5,000 ml, and blow in air at a rate of 5 eIhr while stirring vigorously. The reaction was allowed to take place for some time.

Analysis of the product revealed that it was 17.5 mm of isobutyric anhydride.
1 (single yield 40.0%), isobutyric acid 25.17nm0
I (single yield 28.7%) was obtained, and small amounts of acetone, isopropyl formate, isopropyl alcohol, propylene, carbon monoxide, and carbon dioxide were also observed to be produced. For comparison, an oxidation reaction was carried out in the same manner except that copper naphthenate was not added, and almost no production of isobutyric anhydride was observed.

Example 2 2-ethylhexylaldehyde 12 in a glass flask
．． 2y (95.17TLm0 and benzene 30m1
and added 50 mg of anhydrous cupric chloride as a catalyst.
Oxidation was carried out in the same manner as in Example 1 at 60°C.

In addition, the concentration of heavy metal impurities at this time is 1 weight P
It was below pm. Analysis of the product revealed that anhydrous 2-
Ethylhexanoic acid 40.4mm01 (single yield 42.5
%), 2-ethylhexanoic acid 50.5m, m01 (53
．． 1%) was obtained. Example 3 2-methylhexylaldehyde 25% in a glass flask
．． 0y (219.2mm01) and copper powder 0 as catalyst
．． 1f was added thereto, and air was circulated at 70° C. for 3 hours to carry out oxidation.

Note that the concentration of metal impurities at this time is 1 weight Pp.
It was less than m. Analysis of the product revealed that it was 26.67 nm of methylhexanoic anhydride (yield 12.1%).
was found to be generated. Even in this case, no acid anhydride formation was observed unless copper powder was used.

Claims (1)

[Claims] 1. A method for producing an α-branched aliphatic carboxylic acid anhydride, which comprises oxidizing an α-branched aliphatic aldehyde with molecular oxygen in the presence of copper or a copper compound in a liquid phase.