Method for producing monocyclic monoterpene diol

Abstract

To provide an efficient method for producing a monocyclic monoterpene diol.SOLUTION: A method for producing a monocyclic monoterpene diol according to the present invention, comprises a step of hydrolyzing a monocyclic monoterpene oxide represented by the following formula (II) under acidic conditions. [In the formula, a double line composed of a dotted line and a solid line indicates a carbon-carbon single bond or a carbon-carbon double bond, and R1 indicates a 2-propenyl group, etc.]SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for efficiently producing monocyclic monoterpene diols. [Background technology]

[0002] Engineering plastics are a general term for particularly high-performance plastics that are strong and heat-resistant. Among engineering plastics, polycarbonate has excellent transparency and impact resistance, so it is used not only as a lens material but also as a building material. However, since most engineering plastics are produced from petroleum and other raw materials, there are studies being conducted on producing polymers from biomass-derived raw materials.

[0003] For example, isosorbide, which is obtained by intramolecular dehydration of sorbitol, a sugar alcohol obtained by reducing glucose, has two hydroxyl groups and is therefore used as a raw material for polycarbonate (Patent Document 1, etc.). Polycarbonates containing isosorbide are also commercially available. It is also possible to produce polyurethane by reacting isosorbide with diisocyanate.

[0004] Furthermore, because the peels of mandarin oranges and lemons are inedible, tens of thousands of tons of them are discarded as waste annually, and effective utilization is desired. These waste materials contain cyclic monoterpenes such as limonene. Cyclic monoterpenes are inedible resources, and because they have a cyclic structure, polymers produced from cyclic monoterpenes have the advantage of having a higher glass transition temperature and superior thermal stability than linear polymers. Therefore, it is conceivable to use cyclic monoterpenes as raw materials for polymers.

[0005] One possible method for producing a polymer from a cyclic monoterpene is to oxidize limonene, which is a cyclic monoterpene having a double bond, to obtain limonene oxide, which is then hydrolyzed to form limonene diol, which is then reacted with diphenyl carbonate to produce polylimonene carbonate.

[0006] Non-Patent Documents 1 and 2 describe a method for producing limonenediol, in which an aqueous potassium hydroxide solution is added to a dimethyl sulfoxide solution of limonene oxide to hydrolyze it, the reaction solution is neutralized with concentrated hydrochloric acid, the target compound is extracted with an ether-dichloromethane mixed solvent, the extract is concentrated under reduced pressure, and the compound is recrystallized with aqueous methanol. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2004 / 111106 Pamphlet [Non-patent literature]

[0008] [Non-Patent Document 1] Fusao Kido et al., J.CHEM.SOC.PERKIN TRANS., 1, pp. 2989-2994 (1995) [Non-patent document 2] Fusao Kido et al., Tetrahedron, Vol. 51, No. 28, pp. 7697-7714 (1995) Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, there are known methods for producing limonenediol from limonene oxide, but these methods require neutralization of the reaction solution, extraction of the target compound with an organic solvent, concentration of the extract, and further recrystallization for purification, and are therefore not suitable for industrial mass production. Therefore, an object of the present invention is to provide a method for efficiently producing a monocyclic monoterpene diol. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result have found that by hydrolyzing a monocyclic monoterpene oxide under acidic conditions, crystals of the target compound, a monocyclic monoterpene diol, are precipitated from the reaction solution, and the target compound can be easily obtained by simply separating the precipitated crystals from the reaction solution, thereby completing the present invention. The present invention will now be described.

[0011] [1] A method for producing a monocyclic monoterpene diol, comprising: The monocyclic monoterpene diol is a monocyclic monoterpene diol represented by the following formula (I): [ka] [In the formula, A double line consisting of a dotted line and a solid line represents a carbon-carbon single bond or a carbon-carbon double bond; R 1 is R 1 When is connected to a six-membered ring through a carbon-carbon single bond, it represents 2-propenyl (-C(CH3)=CH2) or 2-propyl (-CH(CH3)2), and R 1 When is connected to a six-membered ring through a carbon-carbon double bond, it represents 2-propylidene (=C(CH3)2). A method comprising the step of hydrolyzing a monocyclic monoterpene oxide represented by the following formula (II) under acidic conditions: [ka] [In the formula, the double line consisting of a dotted line and a solid line, and R 1 has the same meaning as above] [2] The method according to [1] above, wherein the monocyclic monoterpene oxide represented by formula (II) is hydrolyzed at a pH of 5 or less. [3] The method according to [1] or [2], wherein the monocyclic monoterpene oxide represented by formula (II) is mixed in an amount of 15% by mass or less with respect to the acidic aqueous solution. [4] The method according to any one of [1] to [3] above, wherein the monocyclic monoterpene oxide represented by the formula (II) or a solution thereof is added dropwise to an acidic aqueous solution. [5] The method according to any one of [1] to [4], wherein the monocyclic monoterpene oxide represented by formula (II) is limonene oxide, and the monocyclic monoterpene diol represented by formula (I) is limonene diol. [6] The method according to any one of the above [1] to [5], wherein the monocyclic monoterpene oxide represented by the formula (II) is hydrolyzed in dilute sulfuric acid. [7] The method according to any one of [1] to [6] above, further comprising a step of recovering the precipitated crystals of the monocyclic monoterpenediol represented by formula (I). [Effects of the Invention]

[0012] According to the method of the present invention, monocyclic monoterpene diols can be produced extremely efficiently from monocyclic monoterpene oxides, the use of organic solvents can be omitted or reduced, and the energy required for distilling off the organic solvent and the labor of recrystallization are not required. Therefore, the present invention is industrially extremely advantageous as it can contribute to the technology of producing polymers from raw materials derived from plants rather than petroleum. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method of the present invention will be described below, but the present invention is not limited to the specific examples below. In the following, "a compound represented by formula (x)" will be abbreviated as "compound (x)".

[0014] 1. Manufacturing process of monocyclic monoterpene oxide In this step, monocyclic monoterpene oxide (II) is produced by oxidizing monocyclic monoterpene (III). In this disclosure, the carbon atoms of the six-membered ring of the monocyclic monoterpene are numbered as follows for convenience. This step is optional, and may not be performed if, for example, monocyclic monoterpene oxide (II) is commercially available.

[0015] [ka] [In the formula, the double line consisting of a dotted line and a solid line, and R 1 has the same meaning as above]

[0016] Examples of the monocyclic monoterpene (III) include the following: If a commercially available product of the monocyclic monoterpene (III) is available, it can be obtained and used, or it may be isolated from a plant material and used. [ka]

[0017] Limonene has two optical isomers, the R- and S-isomers. (R)-limonene is found in large amounts in citrus peels, and since most citrus peels are discarded, using (R)-limonene in the present invention will lead to more efficient use of resources. (S)-limonene is also found in peppermint oil. While the racemate is found in turpentine oil and the like, it is preferable to use either (R)-limonene or (S)-limonene in the present invention.

[0018] Alpha-terpinene is found in cardamom and marjoram, while gamma-terpinene and terpinolene are found in the essential oils of coriander, lemon, cumin, tea tree, etc. Terpinolene is also called delta-terpinene.

[0019] As described above, monocyclic monoterpene (III) can be extracted from plants and is therefore useful as a carbon-neutral raw material.

[0020] Monocyclic monoterpene oxide (II) can be synthesized by oxidizing monocyclic monoterpene (III) using standard methods. For example, adding an epoxidizing agent to a solution of monocyclic monoterpene (III) or adding hydrogen peroxide to a solution of monocyclic monoterpene (III) in the presence of a catalyst such as an osmium salt or tungstic acid is one example. Although double bonds other than the 1,2 carbon-carbon double bond may be epoxidized, the oxidation position can be adjusted using a catalyst. Furthermore, if an oxide other than the target compound is produced, the monocyclic monoterpene oxide (II) can simply be purified.

[0021] 2. Hydrolysis process In this step, monocyclic monoterpene oxide (II) is hydrolyzed under acidic conditions to obtain monocyclic monoterpene diol (I). In this step, the acidic conditions allow the hydrolysis reaction to proceed even at room temperature, and monocyclic monoterpene diol (I) with high optical purity can be efficiently obtained. Room temperature refers to a temperature at which neither heating nor cooling is performed, and generally refers to a temperature between 0°C and 35°C, but can also be 5°C or higher, 10°C or higher, or 15°C or higher, or 30°C or lower.

[0022] When the double lines (dotted and solid) are all carbon-carbon single bonds, the monocyclic monoterpene oxide (II) has four optical isomers. For example, limonene exists as d-limonene and l-limonene, and limonene oxide, obtained by oxidation of limonene, has S- and R-isomers, each of which has trans- and cis-isomers depending on the position of the 2-propenyl and methyl groups.

[0023] If the double line consisting of a dotted line and a solid line is a carbon-carbon single bond, R 1 When (4R)-monocyclic monoterpene oxide (II) is used, in which the absolute structure at the 4-position carbon to which the group is attached is R, the reaction proceeds as shown in the following reaction formula: 1It is thought that the bulky group occupies the extial position, and under acidic conditions, a proton binds to the oxygen in the epoxy group, and the steric hindrance of the methyl group causes a water molecule to attack the second carbon from the opposite side of the epoxy group. The same is true for (4S)-monocyclic monoterpene oxide (II), in which the absolute configuration of the fourth carbon is S. As a result, each optical isomer of limonene oxide mainly produces the optically active isomer of the corresponding monocyclic monoterpene diol (I). (1R,2R,4R)-monocyclic monoterpene diol (I) 2 ) compared to (1S,2S,4R)-monocyclic monoterpene diol (I 1 ) is more likely to precipitate, and (1S,2S,4S)-monocyclic monoterpene diol (I 4 ) compared to (1R,2R,4S)-monocyclic monoterpene diol (I 3 Therefore, in the present invention, by separating the precipitated crystals, an optical isomer with high optical purity can be obtained.

[0024] [ka]

[0025] When all double lines consisting of dotted and solid lines are carbon-carbon single bonds, it is preferable to use a 4R or 4S isomer as the monocyclic monoterpene oxide (II) and a trans / cis mixture when the constituent carbon numbers of the six-membered ring are set as in formula (III). Optically active forms of monocyclic monoterpene (III) can be readily obtained as natural products, and monocyclic monoterpene oxides (II) optically active at the 4th position can be easily synthesized from optically active monocyclic monoterpene (III). Furthermore, monocyclic monoterpene oxides (II) synthesized by oxidation from optically pure monocyclic monoterpene (III) are generally inexpensive because they are racemic at the 1st position. Furthermore, according to the present invention, monocyclic monoterpene diols (I) with high optical purity can be obtained from such (4R)- or (4S)-monocyclic monoterpene oxides (II).

[0026] When either of the double lines, the dotted line and the solid line, is a carbon-carbon double bond, the 4th carbon is not an asymmetric carbon, but the mechanism of the epoxy ring opening is considered to be the same as that described above. For example, R 1 The reaction mechanism when the group is attached to the six-membered ring by a double bond is shown below. From each optically active monocyclic monoterpene oxide (II), (1S,2S)-monocyclic monoterpene diol (I 5 ) and (1R,2R)-monocyclic monoterpene diol (I 6 ) is produced. Monocyclic monoterpene diol (I 5 ) and monocyclic monoterpene diols (I 6 ) may be prone to precipitation from an acidic aqueous solution.

[0027] [ka]

[0028] In this step, the monocyclic monoterpene oxide (II) is hydrolyzed under acidic conditions. From the viewpoint of hydrolysis, an aqueous solvent is used as the solvent in this step, and the acidic aqueous solution is mixed with the monocyclic monoterpene oxide (II). The aqueous solvent refers to water or a mixed solvent of a water-miscible organic solvent and water. The water-miscible organic solvent refers to an organic solvent that is miscible with water without restrictions, and examples thereof include alcohol solvents such as methanol, ethanol, and 2-propanol; sulfoxide solvents such as dimethyl sulfoxide; and amide solvents such as dimethylformamide and dimethylacetamide. A water-miscible organic solvent is preferably used when the solubility of the monocyclic monoterpene oxide (II) in water is low. The amount of the water-miscible organic solvent used in the mixed solvent may be adjusted depending on the solubility of the monocyclic monoterpene oxide (II). For example, the proportion of the water-miscible organic solvent in the mixed solvent may be 50% by mass or less. If the ratio is 50% by mass or less, the target compound, monocyclic monoterpene diol (I), can be more reliably precipitated. The ratio is preferably 40% by mass or less, 30% by mass or less, or 20% by mass or less, and more preferably 10% by mass or less or 5% by mass or less. When a water-miscible organic solvent is used, the ratio is preferably 1% by mass or more or 2% by mass or more.

[0029] The acid used to acidify the reaction solution in this step is not particularly limited, but examples thereof include inorganic acids such as sulfuric acid and nitric acid, and organic acids such as formic acid, acetic acid, propionic acid, oxalic acid, lactic acid, and citric acid.

[0030] The pH of the reaction solution may be adjusted appropriately within a range in which the hydrolysis of the monocyclic monoterpene oxide (II) proceeds satisfactorily and crystals of the monocyclic monoterpene diol (I) are precipitated, but for example, a pH of 5 or less is preferred. A pH of 5 or less allows for satisfactory hydrolysis of the monocyclic monoterpene oxide (II), and also allows for more reliable precipitation of crystals of the monocyclic monoterpene diol (I) with high optical purity. The lower limit of the pH is not particularly limited, but is preferably 0.1 or more from the viewpoint of safety. The pH is more preferably 0.5 or more, more preferably 0.8 or more, and more preferably 4 or less or 3 or less, and even more preferably 2 or less.

[0031] The concentration of the monocyclic monoterpene oxide (II) in the reaction solution may be adjusted appropriately from the viewpoint of the optical purity and yield of the precipitated monocyclic monoterpene diol (I) crystals, and can be adjusted, for example, to 2% by mass or more and 60% by mass or less. The higher the concentration, the higher the production efficiency, and the lower the concentration, the higher the optical purity of the obtained crystals tends to be. The concentration is preferably 3% by mass or more or 5% by mass or more, more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, 30% by mass or less, or 20% by mass or less, and even more preferably 15% by mass or less.

[0032] In this step, the monocyclic monoterpene oxide (II) may be added to the acidic aqueous solution, or the acidic aqueous solution may be added to the monocyclic monoterpene oxide (II) and then the acidic aqueous solution. However, from the viewpoint of reaction uniformity, it is preferable to add the monocyclic monoterpene oxide (II) to the acidic aqueous solution. Furthermore, from the viewpoint of the optical purity of the precipitated crystals of the monocyclic monoterpene diol (I), it is preferable to add the monocyclic monoterpene oxide (II) dropwise to the acidic aqueous solution. By adding the monocyclic monoterpene oxide (II) dropwise, it is possible to initially maintain the concentrations of the monocyclic monoterpene oxide (II) and the monocyclic monoterpene diol (I) in the reaction solution relatively low, and fine crystals of the optical isomers of the monocyclic monoterpene diol (I) that are more likely to precipitate are preferentially precipitated. The growth of the crystals of these optical isomers is thought to increase the optical purity of the monocyclic monoterpene diol (I). The dropwise addition rate of the monocyclic monoterpene diol (I) can be adjusted appropriately, for example, to 0.01 mg / sec or more and 200 mg / sec or less per 1 mL of the acidic aqueous solution. It is preferable to slow the dropwise addition rate because the heat dissipation efficiency of the reaction solution decreases as the scale of the reaction increases. For example, when the scale of the reaction is relatively small, such as when the reaction solution volume is 1 L or less, the dropwise addition rate can be adjusted to 50 mg / sec / mL or less. Furthermore, when the scale of the reaction is relatively large, such as when the reaction solution volume is 100 L or more, the dropwise addition rate can be adjusted to 20 mg / sec / mL or less. It is also preferable to dropwise add the monocyclic monoterpene oxide (II) to the acidic aqueous solution and adjust the final concentration of the monocyclic monoterpene oxide (II) in the reaction solution to fall within the above-mentioned range.

[0033] After mixing the acidic aqueous solution with the monocyclic monoterpene oxide (II), the reaction solution is preferably left standing or stirred to promote hydrolysis and precipitation of the monocyclic monoterpene diol (I). The conditions for leaving standing or stirring are not particularly limited, but for example, the reaction solution may be left standing or stirred at 0°C or higher and 35°C or lower for 5 minutes or longer and 50 hours or shorter. The temperature may be room temperature. The time is preferably 10 minutes or longer, more preferably 15 minutes or longer, and is preferably 30 hours or shorter, more preferably 20 hours or shorter.

[0034] 3. Recovery process In this step, crystals of the monocyclic monoterpene diol (I) precipitated in the hydrolysis step 2 are recovered. The recovery conditions are not particularly limited, but for example, the precipitated monocyclic monoterpene oxide (II) may be separated from the liquid by filtration or centrifugation, washed with a poor solvent such as water, and then dried.

[0035] The monocyclic monoterpene diol (I) produced by the method of the present invention has high optical purity. 1 The fraction calculated by the following formula from the integral values ​​of peaks with different chemical shift values ​​(δ) for optical isomers analyzed by H NMR is preferably 95% or more, more preferably 96% or more or 98% or more, and even more preferably 99% or more, 99.5% or more, or 99.8% or more. The upper limit of the fraction is not particularly limited, but 100% is preferred. Major optical isomer fraction (%) = [peak integral value of major optical isomer / sum of peak integral values ​​of monocyclic monoterpene diol (I)] × 100

[0036] Since monocyclic monoterpene diol (I) has two hydroxyl groups, it can be used as a polymer monomer. For example, by reacting it with phosgene or diphenyl carbonate, it can be used as a raw material for polycarbonate containing the following structural unit. Furthermore, by reacting it with diisocyanate, it can be used as a raw material for polyurethane containing the following structural unit.

[0037] [ka] [In the formula, the double line consisting of a dotted line and a solid line, and R 1 has the same meaning as above, and R 2 represents a divalent organic group such as 2,6-tolylene, 2,4-tolylene, methylenebis(4,1-phenylene), naphthalenediyl, xylylenediyl, cyclohexanediyl, hexyl, or methylenebis(4,1-cyclohexylene). [Example]

[0038] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the invention by making appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention.

[0039] Examples 1 to 5 While stirring ion-exchanged water (200 mL) at room temperature, 98% sulfuric acid was added dropwise to adjust the pH as shown in Table 1. Next, while stirring the pH-adjusted acidic aqueous solution (20 mL), (R)-limonene oxide (cis / trans isomer mixture, Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise in an amount such that the final concentration (amount of limonene oxide / (amount of acidic aqueous solution + amount of limonene oxide)] × 100 was 3% by mass. After the dropwise addition, the mixture was stirred overnight at room temperature. Next, the precipitated crystals were filtered, washed with water, and vacuum-dried overnight. The yield of the produced limonene diol relative to the starting limonene oxide was calculated. Note that the yield was calculated using the following formula, since no starting (R)-limonene oxide remained in the reaction solution. Yield (%) = [moles of isolated limonene diol / moles of raw limonene oxide] x 100 The obtained crystals 1The proportion of the major isomer, (1S,2S,4R)-(+)-limonene-1,2-diol, was determined by H NMR analysis. The results are shown in Table 1. In the table, "LO" indicates limonene oxide. The 2-position proton peak of the major isomer is in the range of 3.67 to 3.62, and the 2-position proton peak of the minor isomer is in the range of 3.61 to 3.55. Therefore, the major isomer fraction was calculated from the integral values ​​of these peaks.

[0040] [Table 1]

[0041] As shown in Table 1, it was demonstrated that limonene-1,2-diol with high optical purity can be obtained by hydrolyzing (R)-limonene oxide in an acidic solution.

[0042] Examples 6 to 15 The yield of limonene-1,2-diol and the proportion of the major isomer, (1S,2S,4R)-(+)-limonene-1,2-diol, were determined in the same manner, except that the pH was adjusted as shown in Table 2 and the final concentration of (R)-limonene oxide was changed from 3% by mass to 5% by mass. The results are shown in Table 2.

[0043] [Table 2]

[0044] As shown in the results in Table 2, by increasing the concentration of the raw material compound (R)-limonene oxide in the reaction solution, it was observed that the yield could be improved while maintaining the fraction of the main optical isomer at 100%.

[0045] Example 16 and Comparative Examples 1 to 3: Study of pH adjusters The yield of limonene-1,2-diol and the proportion of the major isomer, (1S,2S,4R)-(+)-limonene-1,2-diol, were determined in the same manner as in Examples 6 to 15, except that no pH adjuster was used or the pH adjuster was changed to one shown in Table 3 and the pH was adjusted as shown in Table 3. The results are shown in Table 3. In Table 3, "-" indicates that no crystals were precipitated and therefore the fraction of the optical isomer could not be calculated.

[0046] [Table 3]

[0047] As shown in the results in Table 3, even when the reaction solution was adjusted to an acidic state with acetic acid, an organic acid, the main optical isomer with high optical purity could be produced. On the other hand, when the pH of the reaction solution was not adjusted or when the reaction solution was adjusted to an alkaline pH with sodium hydroxide, almost no crystals were precipitated. When the reaction solution was adjusted to an alkaline pH, the hydrolysis of limonene oxide probably took an extremely long time or required heating compared to when the reaction solution was adjusted to an acidic pH, and therefore it is considered that this method is not industrially useful.

[0048] Examples 17 to 20: Examination of raw material compound concentrations The yield of limonene-1,2-diol and the proportion of the major isomer, (1S,2S,4R)-(+)-limonene-1,2-diol, were determined in the same manner as in Examples 6 to 15, except that the pH of the reaction solution was adjusted to 0.94 and the final concentration of the raw material compound, (R)-limonene oxide, in the reaction solution was adjusted as shown in Table 4. The results are shown in Table 4.

[0049] [Table 4]

[0050] As shown in Table 4, the yield tended to increase as the concentration of the raw material limonene oxide in the reaction solution increased, but when the concentration was excessively high, the yield decreased slightly. Furthermore, the optical purity of the obtained crystals was 94% or higher, which is sufficiently high compared to that of conventional asymmetric synthesis. However, when the concentration of the raw material limonene oxide in the reaction solution was high, the optical purity tended to decrease slightly. However, using a reaction solution with a higher concentration tends to increase the yield, and therefore can be said to be effective for efficient production.

[0051] Example 21 The yield of limonene-1,2-diol and the proportion of the major isomer, (1R,2R,4S)-(-)-limonene-1,2-diol, were determined in the same manner as in Examples 6 to 15, except that (S)-limonene oxide (cis / trans isomer mixture, Sigma-Aldrich) was used as the raw material and the pH of the reaction solution was adjusted to 1.60. The results are shown in Table 5.

[0052] [Table 5]

[0053] As shown in Table 5, according to the method of the present invention, the main optical isomer of limonene-1,2-diol was obtained with high purity even when (S)-limonene oxide was used as the raw material compound.

Claims

1. 1. A process for producing a monocyclic monoterpene diol, comprising: The monocyclic monoterpene diol is a monocyclic monoterpene diol represented by the following formula (I): 【Chemistry 1】 [In the formula, A double line consisting of a dotted line and a solid line represents a carbon-carbon single bond or a carbon-carbon double bond; R 1 is R 1 is bonded to the six-membered ring through a carbon-carbon single bond, it represents 2-propenyl or 2-propyl, and R 1 is bonded to the six-membered ring via a carbon-carbon double bond, it represents 2-propylidene. A method comprising the step of hydrolyzing a monocyclic monoterpene oxide represented by the following formula (II) under acidic conditions: 【Chemistry 2】 [wherein the double line consisting of a dotted line and a solid line, and R 1 has the same meaning as above]

2. The method according to claim 1, wherein the monocyclic monoterpene oxide represented by formula (II) is hydrolyzed at a pH of 5 or less.

3. The method according to claim 1, wherein the monocyclic monoterpene oxide represented by formula (II) is mixed in an amount of 15 mass % or less with respect to the acidic aqueous solution.

4. The method according to claim 1, wherein the monocyclic monoterpene oxide represented by formula (II) or a solution thereof is added dropwise to an acidic aqueous solution.

5. The method according to claim 1, wherein the monocyclic monoterpene oxide represented by formula (II) is limonene oxide and the monocyclic monoterpene diol represented by formula (I) is limonene diol.

6. The method according to claim 1, wherein the monocyclic monoterpene oxide represented by formula (II) is hydrolyzed in dilute sulfuric acid.

7. The method according to claim 1, further comprising a step of recovering the precipitated crystals of the monocyclic monoterpene diol represented by formula (I).

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