JPH0733779A - Production of pyridineborane - Google Patents

Abstract

PURPOSE:To produce pyridineborane in high yield while suppressing an amount of pyridine used as a solvent to low value. CONSTITUTION:In producing pyridineborane from pyridine, sodium borohydride and a mineral acid, sulfuric acid having >=36wt.% concentration is used as a mineral acid and sodium borohydride and sulfuric acid are added to pyridine little by little and the reaction is carried out at -5 to 50 deg.C, preferably 0-40 deg.C. In the reaction, pyridine as a raw material also plays the role of a solvent in first half of the reaction and pyridineborane of the reactional product mainly plays the role of the solvent in the latter half of the reaction. As a result, pyridine as the solvent can be used in a smaller amount, compared with conventional technique and stirring is readily carried out and efficiency of the reaction can be raised. because the reactional system can be kept as a liquid phase state from the start to the end of the reaction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing pyridine borane. Pyridine borane is useful as a mild reducing agent used for reduction of oximes and as a reducing agent for electroless plating.

[0002]

2. Description of the Related Art Conventionally, as a method for producing pyridine borane which is a complex of pyridine and borane, (1) a method of reacting pyridine and diborane (J. Am. Chem. S.
oc. , 64, 328, 1942), (2) a method of reacting sodium borohydride with pyridine hydrochloride in the presence of pyridine as a solvent in a large excess (J.A.
m. Chem. Soc. , 77, 1506, 195
5 years), and (3) a method of mechanically kneading sodium borohydride and pyridine hydrochloride in a solid phase to cause a reaction (Soviet Patent 491640, 1975) and the like are known.

In the method (1), since diborane used as a raw material is a highly toxic gas, it is not easy to handle and the process control is troublesome. The method (2) requires the use of a large amount of pyridine because the starting materials, sodium borohydride and pyridine hydrochloride, are solid and have low solubility in pyridine as a solvent. Further, in order to obtain the target substance, it is necessary to separate pyridine and pyridineborane by a concentration operation, which is not efficient. The method (3) requires a special reaction apparatus because solid sodium borohydride and pyridine hydrochloride are reacted in the absence of a solvent. In the methods (2) and (3), it is necessary to produce pyridine hydrochloride from pyridine and hydrochloric acid in advance,
The process becomes complicated.

[0004]

SUMMARY OF THE INVENTION As described above, (1)-
The methods that have been used so far, such as (3), are all
It is hard to say that this method is industrially advantageous in terms of safety and economy. In view of the above situation, the present inventors do not need to use highly toxic diborane, do not use a special reaction apparatus, and an efficient method for producing pyridineborane with a small amount of solvent used. Diligently studied.

[0005]

As a result, the present inventors have found a method of reacting sodium borohydride and sulfuric acid by adding them to pyridine, and completed the present invention. The first gist of the present invention is to use sulfuric acid as a mineral acid and add this together with sodium borohydride into pyridine to complete the reaction in the same vessel to obtain pyridine borane.

The present invention will be described in detail below. In the present invention, pyridine is put in a container, and sodium borohydride and sulfuric acid are added thereto while stirring. The sulfuric acid concentration used is usually 36 to 100% by weight, preferably 50 to 98% by weight. The sulfuric acid concentration is
If it is less than 36% by weight, the hydrolysis reaction of sodium borohydride may occur, which is not preferable.

Usually, hydrochloric acid or sulfuric acid is used as the mineral acid. However, when a mineral acid having a concentration of less than 36% by weight is used, sodium borohydride may be hydrolyzed, which is not preferable. When hydrochloric acid is used, it cannot be used at a concentration of 36% by weight or more, and there is a problem of hydrolysis, so its use is unsuitable. When hydrogen chloride gas is used in place of hydrochloric acid having a concentration of 36% by weight or more, not only is the hydrogen chloride a high-pressure gas, it is expensive, and it is industrially used because it is highly corrosive to the equipment. It's not advantageous for you. Therefore, in the present invention, it is easy to obtain 36%.
Sulfuric acid that can achieve the above concentrations is used. Sulfuric acid having the above concentration or more is economically and industrially advantageous because it has less side reaction due to hydrolysis of sodium borohydride and less corrosiveness of the device.

The reaction temperature is usually in the range of -5 to 50 ° C, preferably 0 to 40 ° C. Temperatures exceeding 50 ° C are not preferable because the hydrolysis reaction of sodium borohydride is accelerated. On the other hand, if the temperature is lower than -5 ° C, the reaction rate becomes slow, which is not preferable.

The reaction time varies depending on the reaction temperature, and since it is necessary to remove the heat of reaction, it cannot be said unequivocally.
A range of 1 to 30 hours is usually suitable. Pyridine borane produced by the above reaction can be easily isolated and obtained by adding water to the reaction solution after the reaction, separating the solution, and concentrating the oil phase.

The second gist of the present invention is that, in the above pyridine borane synthesis reaction system, sodium borohydride and sulfuric acid are added little by little to pyridine for reaction, and the reaction is completed over a predetermined amount over time. It is in.

The present invention will be described in detail below. In the present invention, sodium borohydride and sulfuric acid are added to pyridine in the container. In this case, a method in which a required amount of sodium borohydride is previously added to pyridine and then sulfuric acid is gradually added, and a required amount of sulfuric acid is previously added to pyridine, and then sodium borohydride is gradually added Either of the method and the method of adding sodium borohydride and sulfuric acid little by little to pyridine can be adopted. Among them, the method of adding sodium borohydride and sulfuric acid little by little to pyridine is preferable because the stirring is easy, the reaction proceeds rapidly, and the heat of reaction is easily removed.

As a method of adding sodium borohydride and sulfuric acid little by little to pyridine, the amount to be added is divided into several parts and added stepwise, continuously added little by little, or There is a method of alternately adding small amounts, but any method may be used. When sodium borohydride and sulfuric acid are added all at once, the slurry concentration becomes high, which makes stirring difficult and also makes it difficult to control the heat of reaction.

In the method of the present invention, when sodium borohydride and sulfuric acid are added to pyridine, sulfuric acid reacts with pyridine and instantly becomes pyridine sulfate. The pyridine sulphate then reacts with the added sodium borohydride to pyridine borane and sodium sulphate.

Under the reaction conditions of the present invention, the reaction product sodium sulfate is a solid and pyridine borane is present as a liquid.

Therefore, in the first half of the reaction, pyridine as a raw material and in the latter half of the reaction, pyridine borane as a product mainly serve as a solvent. Therefore,
By using the above-described method of the present invention in which the additive material is reacted little by little over time, the amount of pyridine used as a solvent can be suppressed to an extremely small amount as compared with the prior art.

Further, since the reaction system is in a state in which the liquid phase exists from the start to the end, stirring is facilitated and the reaction efficiency can be increased.

In the present invention, the amount of pyridine used is
For sodium borohydride, usually 0.9-4.
The molar ratio is 0 times, preferably 1.0 to 2.0 times. When the amount of pyridine used is less than 0.9 times by mole, sodium borohydride remains unreacted, which is not preferable.
On the other hand, when it is used in excess of 4.0 times, it takes time to recover unreacted pyridine, which is not efficient.

The amount of sulfuric acid used is usually in the range of 0.4 to 0.7 times mol, preferably 0.5 to 0.6 times mol, with respect to sodium borohydride. When the amount of sulfuric acid used is less than 0.4 times by mole, sodium borohydride remains unreacted, while when it is used in excess of 0.7 times by mole, pyridineborane may be partially decomposed. Not preferable.

Further, in the method for producing pyridine borane of the present invention, the reaction is completed in the same container (one-pot reaction).
This is also an advantage as an industrial production method.

[0020]

EXAMPLES The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited thereto.

Example 1 A 1-liter five-necked flask equipped with a stirrer, a thermometer, and a condenser was charged with 79.3 g (1.0 mol) of pyridine under a nitrogen atmosphere. Then, at 10 ° C. with stirring, 37.8 g (1.0
70 g of 70% by weight sulfuric acid using a dropping funnel.
(0.5 mol) was alternately added into pyridine over 4 hours, and then the reaction was carried out at the same temperature for about 1 hour. After the reaction was completed, 210 g of water was added to about 35 ° C. The temperature was raised and the liquid was separated into an oil phase and an aqueous phase. The oil phase was concentrated under reduced pressure to obtain 84.5 g of pyridine borane (purity 98.0%: by high performance liquid chromatography). The yield based on sodium borohydride was 90.9%.

Example 2 Pyridine borane was obtained by performing the same reaction as in Example 1 except that sodium borohydride and sulfuric acid were continuously added. The yield based on sodium borohydride was 91.
It was 5%.

Examples 3 to 8 Experiments were conducted in the same manner as in Example 1 except that the reaction conditions (temperature, time), the concentration of sulfuric acid, and the molar ratio of sulfuric acid and pyridine to sodium borohydride were changed as shown in Table 1. Then, pyridine borane was obtained. The results are shown in Table 1.

Comparative Example 1 Pyridine borane was obtained by the same reaction as in Example 5 except that 30% by weight sulfuric acid was used instead of 50% by weight sulfuric acid. The results are shown in Table 1.

Comparative Example 2 Pyridine borane was obtained by the same reaction as in Example 5 except that 35% by weight hydrochloric acid was used instead of 50% by weight sulfuric acid. The results are shown in Table 1.

[0026]

[Table 1]

[0027]

EFFECTS OF THE INVENTION By the method of the present invention, it has become possible to produce pyridine borane in a high yield and with a low amount of pyridine used as a solvent. In addition, the method of the present invention is a one-pot reaction, so the number of steps is small,
Excellent from an industrial point of view.

Claims (5)

[Claims] 1. A method for producing pyridine borane, which comprises using sulfuric acid as a mineral acid when producing pyridine borane from pyridine, sodium borohydride and a mineral acid. 2. A method for producing pyridine borane, which comprises adding sodium borohydride and sulfuric acid to pyridine. 3. A method of adding sodium borohydride and sulfuric acid into pyridine is divided into several amounts to be added and added stepwise, continuously added little by little, or Alternate little by little,
3. The manufacturing method according to claim 2, which is based on any one of the above and. 4. The production method according to claim 1, wherein the sulfuric acid concentration is 36% by weight or more. 5. The production method according to claim 1, 2 or 3, wherein the reaction temperature is −5 to 50 ° C.