JPH0115486B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for producing aldehydes, and in particular to a method for producing the corresponding aldehydes by catalytic reduction of carboxylic acids with Grignard reagents using Cp ₂ TiCl ₂ as a catalyst. In recent years, attempts have been made to utilize various reactions that occur when Grignard reagents are used in the presence of catalytic amounts of transition metal compounds in syntheses. However, most of these attempts have focused on systems in which the reaction does not occur without a catalyst, or even if it does occur, the reaction rate is slow. ,
Not much research has been done so far. In the process of researching the effects of transition metal compounds on the Grignard reaction, the present inventors surprisingly found that the reaction between a Grignard reagent and a carboxylic acid, which proceeds easily without a catalyst, has a catalytic amount of Cp. ₂ TiCl ₂ [Cp represents a cyclopentadienyl group and its derivatives. ] Due to the existence of
Taking a completely different route than in the case of no catalyst,
We also found that this catalytic reduction reaction is useful as a method for synthesizing aldehydes. The method for producing an aldehyde by catalytic reduction of a carboxylic acid using a Grignard reagent of the present invention includes a Grignard reagent of the general formula RMgX [R represents a linear or branched alkyl group, a cycloalkyl group, and an aralkyl group, X represents Cl, Br or I. ] and a carboxylic acid with the general formula R ¹ COOH [R ¹ is a straight or branched alkyl group,
Represents a cycloalkyl group, an aralkyl group, and a heterocycle. A heterocycle is a 5- or 6-membered ring in which 1, 2 or 3 of the atoms constituting the ring are composed of one or more selected from S, N and O. It cannot contain α,β-unsaturated alkenyl groups, but may have substituents as long as they are inert to the reactants and products. ] and a catalytic amount of Cp ₂ TiCl ₂ [Cp represents a cyclopentadienyl group or a derivative thereof. ] to obtain an aldehyde of the general formula R ₁ CHO. ^{2 RMg}
The fact is that it gives alcohol. This reaction is used as one of the methods for synthesizing carbinol. The above-mentioned catalytic reduction discovered by the present inventors was completely unexpected from such conventional knowledge. The present invention therefore provides an alternative method for producing the corresponding aldehydes from carboxylic acids. However, the contact action of Cp ₂ TiCl ₂ is not observed for carboxylic acids containing an α,β-unsaturated alkyl group. When attempting to obtain the corresponding aldehyde from a carboxylic acid, reduction with a metal hydride is effective for derivatives such as esters, amides, and acid anhydrides. However, to produce aldehydes directly from the free acid, a special reducing agent such as HAl(NR ₂ ) ₂ must be used, and the reaction requires twice the stoichiometric amount of reducing agent. Requires. In comparison, the use of Grignard reagents allows reduction at a much lower cost. Cp ₂ TiCl ₂ used as a catalyst in the present invention is regenerated when obtaining the product, and its recovery is extremely easy, so the impact on cost is not a problem. Although the reaction of the present invention proceeds easily, except when targeting aromatic carboxylic acids,
The aldehyde produced is not further reduced to alcohol. Experiments have shown that the reason for this is that RCH(OMgX) ₂ , an intermediate in the catalytic reduction reaction, is stable under the reaction conditions, and aldehydes are produced only through hydrolysis. This means that the desired aldehyde can be easily isolated and obtained from the reaction mixture by distillation. Example 1 63 ml of a 1.0 M ether solution of i-C ₄ H ₉ MgBr (63
mmol), Cp ₂ TiCl ₂ 75 mg (0.30 m
mol) and stirred for 5 minutes, then n-
3.9 g (30 mmol) of C ₆ H ₁₃ COOH was added. The mixture was reacted by stirring at room temperature for 4 hours to carry out hydrolysis, followed by post-treatment according to a conventional method and the aldehyde was separated by distillation. As a result of comparison with a standard product by NMR and GLC, it was confirmed that it was n-heptanal. Yield is 74%. Catalytic reduction of other carboxylic acids was attempted in the same manner, and the corresponding aldehydes were obtained. The above results are summarized in the table.

[Table] Example 2 The following Grignard reagent was used,
Catalytic reduction of various carboxylic acids was carried out. catalyst
The amount of Cp ₂ TiCl ₂ was 1 mol % in each case, and the other reaction conditions were the same as in Example 1. The yields of the Grignard reagent used, the raw material carboxylic acid, and the aldehyde are shown together.

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Claims (1)

[Claims] 1. Grignard reagent of the general formula RMgX [R represents a linear or branched alkyl group, cycloalkyl group, or aralkyl group, and X represents Cl, Br or I. ] and a carboxylic acid with the general formula R ¹ COOH [R ¹ is a straight or branched alkyl group,
Represents a cycloalkyl group, an aralkyl group, and a heterocycle. A heterocycle is a 5- or 6-membered ring in which 1, 2 or 3 of the atoms constituting the ring are composed of one or more selected from S, N and O. It cannot contain α,β-unsaturated alkenyl groups, but may have substituents as long as they are inert to the reactants and products. ] and a catalytic amount of Cp ₂ TiCl ₂ [Cp represents a cyclopentadienyl group or a derivative thereof. ], characterized in that the reaction is carried out in the presence of the general formula R ¹ CHO
A method of producing aldehydes. 2. The method for producing an aldehyde according to claim 1, wherein the carboxylic acid group R ¹ is an alkyl group or a cycloalkyl group, and the generated aldehyde is separated and obtained by distillation.