JPS6225134B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for isomerizing unsaturated esters. To explain in more detail, the general formula

[Formula] (In the formula, R ¹ represents hydrogen or a lower alkyl group, R ² and R ³ represent hydrogen or a saturated or unsaturated hydrocarbon group, and the hydrocarbon group contains at least one oxygen, sulfur It is recommended to use mercaptans and disulfides as catalysts in carrying out the isomerization reaction between the cis form and the trans form of β-γ unsaturated esters (which may have a heteroatom such as nitrogen). The present invention relates to a characteristic method for isomerizing β-γ unsaturated esters. Until now, methods for cis-trans isomerization of β-γ unsaturated alcohols include a method using an acidic catalyst (Japanese Patent Publication No. 38-8107) and a method using a transition metal catalyst (Japanese Patent Publication No. 51-29401). However, no examples of cis-trans isomerization of β-γ unsaturated esters have been found. Furthermore, when acidic, basic, or transition metal catalysts are used to isomerize β-γ unsaturated esters, double bonds shift, making it difficult to selectively perform cis-trans isomerization reactions. It was hot. The present inventors have carried out intensive research on the cis-trans isomerization reaction of β-γ unsaturated esters, and have found that by using specific mercaptans as a catalyst and heating in the open atmosphere, double bonds can be transferred. We have found that the isomerization reaction between the cis and trans forms proceeds extremely selectively without the presence of cis- and trans-forms.
Furthermore, when these specific mercaptans, other mercaptans, and disulfides are used as catalysts, the presence of a reaction initiator in an inert gas atmosphere allows the cis-type and trans-type isomerization reactions to occur independently of the specific mercaptans. It was found that the process proceeded with extremely high selectivity, similar to when used in Examples of mercaptans used in the present invention include unsubstituted and/or substituted aromatic thiols such as benzenethiol, omptoluenethiol, and chlorothiophenol, and alkyldithiols having 5 to 10 carbon atoms such as decyldithiol and octyldithiol. and other mercaptans such as thioglycolic acid and mercaptoethanol [the above are referred to as mercaptans]. In addition, mercaptans such as alkylthiols having 5 to 10 carbon atoms such as octylthiol, cyclic thiols having 5 to 10 carbon atoms such as cyclohexanethiol and cyclopentanethiol (these are referred to as mercaptans), diphenyl disulfur Diaromatic disulfides such as hydride, and disulfides having 5 to 10 carbon atoms such as dioctyl disulfide can be used. When using mercaptans or disulfides as catalysts, the reaction atmosphere and the presence of small amounts of additives are important. That is, it is important to use each of the mercaptan and disulfide catalysts in an inert gas atmosphere and with the addition of a reaction initiator. However, when using mercaptans as catalysts,
The reaction proceeds satisfactorily even in the absence of a reaction initiator in the open atmosphere. Examples of the inert gas include rare gases such as helium and argon, nitrogen, and hydrogen. In addition, as a reaction initiator, azobisisobutyronitrile [AIBN], benzoyl peroxide [BPO]
Examples of radical generators include: Specific examples of the unsaturated esters used in the present invention include the following esters obtained by dehydration condensation from alcohols and carboxylic acids. That is, [] alcohols include geraniol, nerol (3,7-dimethyl-2,6-octadien-1-ol), and farnesol (3,7,11-trimethyl-2,6-ol).
10-dodecatrien-1-ol), phytol (3,7,11,15-tetramethyl-2-hexadecen-1-ol), crotyl alcohol (2
-buten-1-ol). []
Examples of carboxylic acids include chain saturated or unsaturated fatty acids such as formic acid, acetic acid, propionic acid, caproic acid, butyric acid, acrylic acid, and pentenoic acid; aromatic carboxylic acids such as benzoic acid; may have at least one heteroatom such as oxygen, nitrogen, or sulfur in the hydrocarbon group. ] etc. can be exemplified. The catalyst used in the present invention has the characteristics that it can be easily and inexpensively obtained, selectively performs a cis-trans isomerization reaction, and that the catalyst can be separated and reused with a simple operation, Its industrial value is extremely high. Also, the amount used is based on the raw material unsaturated ester.
A range of 0.1 to 100 weight percent is preferred, particularly a range of 0.5 to 50 weight percent. 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 temperature is preferably in the range of 20°C to 250°C, particularly preferably in the range of 40°C to 200°C. Although the reaction proceeds highly selectively with or without a solvent, the selectivity can be further improved by using specific solvents. In this sense, particularly preferred examples of solvents include saturated alcohols such as hexanol, octanol, and decanol. After the isomerization reaction is completed, the catalyst is separated by simple distillation or a chemical separation operation using a dilute aqueous alkaline solution, and then, if necessary, the cis-type and trans-type can be separated and purified by precision distillation. The method of the present invention will be explained in detail with reference to Examples below. Example 1 1.5 g of thiophenol was added to 30 g of neryl acetate, and the mixture was stirred and reacted at 80° C. for 1.7 hours in the open atmosphere. The reaction solution was analyzed by gas chromatography, and the conversion of neryl acetate was 47%, and the selectivity to the produced trans-ester, ie, geranyl acetate, was 84%. Examples 2 to 5 In Example 1, the reaction atmosphere, addition of the reaction initiator azobisisobutyronitrile (AIBN), use of a solvent, and other reaction conditions were changed to those shown in Table 1, and the other conditions were the same as in Example 1. The reaction was carried out in the same manner as in 1, and Table 1
The results were obtained.

[Table] Example 6 In Example 1, the raw material was geranyl acetate,
The same procedure as in Example 1 was carried out except that n-octanol was used as the solvent twice the weight of the raw material and the reaction time was 2 hours. As a result, the conversion rate of geranyl acetate was 39
%, and the selectivity to the produced cis-ester, ie, neryl acetate, was 85%. Example 7 In Example 6, the same procedure as in Example 5 was carried out except that geranyl propionate was used as the raw material. As a result,
The conversion rate of geranyl propionate was 35%, and the selectivity to the produced cis-ester, ie, neryl propionate, was 91%. Example 8 The same procedure as in Example 6 was carried out except that geranyl caproate was used as the raw material in Example 6. As a result, the conversion rate of geranyl caproate was 38%, and the resulting cis-type ester, namely neryl caproate, was The selection rate was 86%.

Claims (1)

[Claims] 1 General formula [Formula] [In the formula, R ¹ represents hydrogen or a lower alkyl group, and R ² and R ³ represent hydrogen or a saturated or unsaturated hydrocarbon group. ] There is a cis-type and a trans-type β expressed by
-Mercaptans selected from aromatic thiols and alkyl dithiols having 5 to 10 carbon atoms are used as catalysts for the isomerization reaction between the cis form and the trans form of the γ-unsaturated ester, and the mixture is heated to 20 to 250°C. A method for isomerizing cis and trans forms of β-γ unsaturated esters. 2 General Formula [Formula] [In the formula, R ¹ represents hydrogen or a lower alkyl group, and R ² and R ³ represent hydrogen or a saturated or unsaturated hydrocarbon group. ] There is a cis-type and a trans-type β expressed by
- 5 to 5 carbon atoms as a catalyst for the isomerization reaction between the cis type and the trans type of a γ-unsaturated ester.
Using mercaptans selected from 10 alkylthiols and cyclic thiols having 5 to 10 carbon atoms and/or disulfides selected from diaromatic disulfides and dialkyl disulfides having 5 to 10 carbon atoms, in an inert gas atmosphere. 20 in the presence of a reaction initiator
A method for isomerizing cis and trans forms of β-γ unsaturated esters, characterized by heating to ~250°C.