JPS6230971B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing aldehydes from unsaturated alcohols. To explain in more detail, the general formula

A general formula characterized by reacting an unsaturated alcohol represented by the formula with an aromatic mercaptan as a catalyst in an inert gas by adding a reaction initiator.

Method for producing an aldehyde represented by the formula [wherein R ¹ represents hydrogen or a lower alkyl group, and R ² represents a saturated or unsaturated hydrocarbon group]. ]. Conventionally, methods for producing aldehydes from unsaturated alcohols include: (1) isomerization using solid catalysts such as Cu-Zn, Cu-Cr, and ZnO; (2) A method of isomerization using an alumina catalyst. (3) Isomerization method using Pt, Pd, Rh/SiO ₂ catalyst. etc. can be mentioned. However, although there are cases in which these methods can obtain the target product with high selectivity, in general, in gas phase reactions using solid catalysts, the reaction results are greatly influenced by the fine structure of the surface layer of the catalyst. This is difficult to avoid and requires special care and skill in the preparation of the catalyst. In order to overcome these conventional drawbacks, the present inventors investigated a method for producing aldehydes from unsaturated alcohols using a liquid phase method. The present invention was completed based on the discovery that aldehydes can be obtained with extremely high selectivity by using a reaction initiator in an atmosphere. Mercaptans used in the present invention include benzenethiol, O,m,p-toluenethiol,
These are unsubstituted and/or substituted aromatic mercaptans such as chlorothiophenol. Here, alkyl mercaptans such as octyl mercaptan and tesyl mercaptan, alkyl dithiols such as dithioglycol and decyl dithiol, other thioglycolic acids,
When mercaptans such as mercaptoethanol are used, the conversion rate is low and the yield is low. The aromatic mercaptans that can be used in the present invention are catalysts that can be easily and inexpensively obtained, and the catalyst can be separated and reused after the reaction with a simple operation, and has extremely high industrial value. . Specific examples of such unsaturated alcohols used in the present invention include geraniol and nerol (3,7-
dimethyl-2,6-octadien-1-ol), falnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol),
Phytol (3,7,11,15-tetramethyl-2
-hexadecen-1-ol). Examples of aldehydes obtainable in the present invention include citronellal, 3,7,11-trimethyl-6,10-dodecadien-1-al, and 3,7,11,15-tetramethyl-hexadecane-1-al. All aldehydes are important substances in the fragrance industry and are used as fragrances or as intermediate raw materials for fragrance synthesis. In addition, these aldehydes are compounds useful as intermediate materials for the synthesis of medicines and agricultural chemicals; for example, citronellal and the like are useful as intermediates for the synthesis of juvenile hormone-like active substances. The amount of the catalyst used in the present invention is preferably in the range of 0.5 to 100% by weight, particularly preferably in the range of 1 to 50% by weight, based on the raw material unsaturated alcohol. If the amount of catalyst used is more than 50% by weight, it is not preferable from an economical point of view, and if it is less than 0.5% by weight, the progress of the reaction will be slowed down, which is undesirable. The reaction atmosphere is an inert gas atmosphere using a reaction initiator, and the inert gas is:
It is a gas that does not participate in reactions such as rare gases such as helium and argon, and nitrogen. In addition, the reaction initiator is an additive that initiates a radical reaction such as azobisisobutyronitrile [AIBN], benzoyl peroxide [BPO], etc., and the amount added is 0.05 to 10% relative to the unsaturated alcohol. It is preferably 0.5 to 5% by weight, particularly 0.5 to 5% by weight. This reaction provides aldehydes with high selectivity without using a solvent. Although the reaction rate is often reduced when a solvent is used, the selectivity of the aldehyde can be further improved by using a specific solvent. Examples of solvents that have the effect of improving aldehyde selectivity include N,N-dimethylformamide (DMF);
N,N-diethylformamide (DEF), N,N
-Acid amides such as dimethylacetamide (DMAA), sulfur-containing compounds such as dimethylsulfoxide (DMSO) and tetramethylsulfone (sulfolane), urea compounds such as tetramethylurea, phosphoric acid amides such as hexamethylphosphoramide, etc. It is a typical polar aprotic solvent with a high dielectric constant. In addition, pyridine and pyridine derivatives are also effective. The reaction temperature is preferably in the range of 20°C to 200°C, particularly preferably in the range of 50°C to 150°C. After the reaction is complete, the catalyst is separated by simple distillation or chemical separation using a dilute alkaline aqueous solution, etc.
Distillation can separate the product and unreacted raw materials. The method of the present invention will be explained in detail with reference to Examples below. Example 1 3 g of thiophenol and 0.9 g of azobisisobutyronitrile (AIBN) were added to a mixed solution of 20 g of geraniol and 10 g of nerol, and the mixture was heated to 100 g in a nitrogen atmosphere.
The mixture was allowed to stir at ℃ for 1 hour. Analysis of the reaction solution by gas chromatography revealed that the conversion rate of the geraniol/nerol mixture was 50%, and the selectivity of the produced citronellal was 89%. Example 2 In Example 1, thiophenol was changed to 6 g, and 80
The same procedure as in Example 1 was carried out except that the mixture was stirred at ℃ for 4 hours and 25 minutes. As a result, the conversion rate of the geraniol/nerol mixture was 80%, and the selectivity of the produced citronellal was 86%. Examples 3 to 5 The reaction was carried out in the same manner as in Example 1, except that the solvent was used and other conditions were changed as shown in Table 1, and the results shown in Table 1 were obtained.

[Table] Example 6 The same procedure as in Example 1 was carried out except that the raw material was nerol and the reaction time was 45 minutes. As a result, the conversion of nerol was 76%, and the selectivity of geraniol produced was 49%. , the selectivity for citronellal produced was 45%. That is, the unsaturated alcohol conversion rate was 40%, and the selectivity from consumed unsaturated alcohol to citronellal was 87%. Example 7 Example 6 was carried out in the same manner as in Example 6, except that the raw material was geraniol and the reaction time was 30 minutes. As a result, the conversion of geraniol was 71%, the selectivity of nerol produced was 25%, and the selection of citronellal produced was The rate was 60%. That is, the unsaturated alcohol conversion rate was 53%, and the selectivity from consumed unsaturated alcohol to citronellal was 81%. Comparative Example 1 The same procedure as in Example 3 was carried out except that the reaction atmosphere was an air atmosphere and stirring was performed for 3 hours without adding AIBN. As a result, the conversion rate of the geraniol/nerol mixture was 31%. The citronellal selectivity was 51% and the citral selectivity was 43%.

Claims (1)

[Claims] 1. General formula The method is characterized in that an unsaturated alcohol represented by the following formula is reacted with an aromatic mercaptan as a catalyst in an inert gas by adding a reaction initiator. general formula A method for producing an aldehyde represented by [In the formula, R ¹ represents hydrogen or a lower alkyl group, and R ² represents a saturated or unsaturated hydrocarbon group. ]