JP7484189B2 - Method for producing triphenylmethane compound - Google Patents

Description

The present invention relates to a method for producing a triphenylmethane compound.

Patent Document 1 discloses a method for purifying a triphenylmethane compound by dissolving it in a good solvent and reprecipitation.

Patent Document 2 discloses a method for producing a triphenylmethane compound using an aryl acetal.

U.S. Pat. No. 9,529,286 U.S. Pat. No. 8,080,351

Conventionally, a method for producing a triphenylmethane compound has been known, which includes a synthesis step of reacting a compound represented by the following general formula (I) with a compound represented by the following general formula (II) in the presence of an acid in an amount less than 0.2 molar equivalent relative to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II) to synthesize a triphenylmethane compound represented by the following general formula (III): In this conventional method for producing a triphenylmethane compound, the yield of the obtained triphenylmethane compound represented by the general formula (III) was low.
Therefore, an object of the present invention is to provide a method for producing a triphenylmethane compound in a higher yield than when the reaction is carried out in the presence of an acid in an amount of less than 0.2 molar equivalents relative to the total number of moles of the amino groups.

Specific means for solving the above problems include the following aspects:

[1] A method for producing a triphenylmethane compound, comprising a synthesis step of reacting a compound represented by the following general formula (I) with a compound represented by the following general formula (II) in the presence of an acid in an amount of 1 molar equivalent to 1.5 molar equivalents relative to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II), to synthesize a triphenylmethane compound represented by the following general formula (III):
(In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group or an aralkyl group. R ¹⁰ and R ¹¹ may be linked to each other to form a ring. n represents 0 or 1. R ¹² represents an aldehyde group or -CH(OR _x ) ₂ , and the R _x represents an alkyl group.
In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group, an ω-hydroxyalkyl group or an aralkyl group. R ²⁰ and R ²¹ may be linked to each other to form a ring.

[2] The method for producing a triphenylmethane compound according to [1], wherein the acid has an acid dissociation constant (pKa) in water at 25° C. of less than −1.0.
[3] The method for producing a triphenylmethane compound according to [2], wherein the acid has an acid dissociation constant (pKa) in water at 25° C. of −3.0 or more and −2.0 or less.
[4] The method for producing a triphenylmethane compound according to any one of [1] to [3], further comprising a crystallization step of dissolving a crude product containing the triphenylmethane compound represented by the general formula (III) in a good solvent at 10° C. or higher and lower than 30° C. after the synthesis step, and then allowing the good solvent to stand at 10° C. or higher and lower than 50° C. to obtain a crystallization product containing the triphenylmethane compound represented by the general formula (III).
[5] The method for producing a triphenylmethane compound according to [4], wherein the good solvent contains an aliphatic alcohol.
[6] In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, and n represents 1. The method for producing a triphenylmethane compound according to any one of [1] to [5].
[7] In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms. The method for producing a triphenylmethane compound according to any one of [1] to [6].
[8] In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, and n represents 1;
In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms;
the amount of the acid is 1 molar equivalent or more and 1.2 molar equivalents or less with respect to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II);
The method for producing a triphenylmethane compound according to any one of [1] to [7].

The invention according to [1], [6], [7] or [8] provides a method for producing a triphenylmethane compound in a higher yield than when the reaction is carried out in the presence of an acid in an amount of less than 0.2 molar equivalents relative to the total number of moles of the amino groups.

The invention according to [2] provides a method for producing a triphenylmethane compound in a higher yield than when the acid dissociation constant (pKa) in water at 25°C of the acid is 2.46 or more.

According to the invention related to [3], there is provided a production method for producing a triphenylmethane compound in a higher yield than when the acid has an acid dissociation constant (pKa) in water at 25° C. of less than −3.0 or more than 2.5.
According to the invention related to [4], there is provided a production method for producing a triphenylmethane compound in a higher yield than when the method further includes a crystallization step of obtaining a crystal containing the triphenylmethane compound represented by the general formula (III) by a reprecipitation method in which a crude product containing the triphenylmethane compound represented by the general formula (III) is dissolved in a good solvent after the synthesis step, and the good solvent containing the crude product is added to a poor solvent to reprecipitate, thereby producing a triphenylmethane compound in a higher yield than when the method further includes a crystallization step of obtaining a crystal containing the triphenylmethane compound represented by the general formula (III).
According to the invention related to [5], there is provided a production method for producing a triphenylmethane compound in a higher yield than when the good solvent is n-hexane.

The following describes embodiments of the present invention. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

In the numerical ranges described in this specification in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Also, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

In this specification, each component may contain multiple corresponding substances.
In this specification, when referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

-Method for producing triphenylmethane compounds-
The method for producing a triphenylmethane compound according to this embodiment includes a synthesis step of reacting a compound represented by the following general formula (I) with a compound represented by the following general formula (II) in the presence of an acid in an amount of 1 molar equivalent to 1.5 molar equivalents relative to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II), to synthesize a triphenylmethane compound represented by the following general formula (III).

In general formula (I) and general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group or an aralkyl group. R ¹⁰ and R ¹¹ may be linked to each other to form a ring. n represents 0 or 1. R ¹² represents an aldehyde group or -CH(OR _x ) ₂ , where R _x represents an alkyl group.
In general formula (II) and general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group, a ω-hydroxyalkyl group or an aralkyl group, and R ²⁰ and R ²¹ may be linked to each other to form a ring.

Conventionally, a method for producing a triphenylmethane compound represented by general formula (III) by reacting a compound represented by general formula (I) with a compound represented by general formula (II) in the presence of an acid catalyst is known. In the conventional production method, the acid (H ⁺ , proton) tends to protonate the oxygen atom of the aldehyde group in the compound represented by general formula (I). As a result, the carbon atom of the positively charged aldehyde group is likely to act electrophilically on the aromatic ring of the compound represented by general formula (II). As a result, an electrophilic substitution reaction proceeds, and the triphenylmethane compound represented by general formula (III) is thought to be formed.

Hereinafter, the compound represented by general formula (I) and the compound represented by general formula (II) will be collectively referred to simply as the "substrate." In addition, the triphenylmethane compound represented by general formula (III) will be hereinafter simply referred to as the "triphenylmethane compound."

However, the yield of the triphenylmethane compound represented by general formula (III) obtained in the conventional manufacturing method tends to be low. As a result of the inventors' investigation, the cause of this is presumed to be as follows.

When a substrate is reacted in the presence of an acid catalyst, the acid (H ⁺ , proton) may protonate a nitrogen atom of the substrate. When the acid catalyst is consumed for the protonation of the nitrogen atom of the substrate, the ratio of the acid catalyst applied to the reaction for forming a triphenylmethane compound is reduced. As a result, the reaction rate of the reaction for forming a triphenylmethane compound is reduced, which is considered to result in a decrease in the yield.

On the other hand, the method for producing a triphenylmethane compound according to this embodiment can produce a triphenylmethane compound in a high yield. The reason for this is not entirely clear, but is presumed to be as follows.

In the method for producing triphenylmethane according to this embodiment, a substrate is reacted in the presence of an acid in an amount of 1 molar equivalent to 1.5 molar equivalents relative to the total number of moles of amino groups contained in the substrate.
By reacting the substrate in the presence of 1 molar equivalent or more of acid relative to the total number of moles of the amino groups, that is, in a stoichiometric amount rather than a catalytic amount, even if a part of the acid is consumed for protonation of the amino groups, a decrease in the ratio of acid applied to the reaction forming the triphenylmethane compound tends to be suppressed. On the other hand, by reacting the substrate in the presence of 1.5 molar equivalents or less of acid relative to the total number of moles of the amino groups, the production of by-products due to decomposition of the triphenylmethane compound by the acid tends to be suppressed. As a result, it is considered that the method for producing a triphenylmethane compound according to this embodiment can produce a triphenylmethane compound in a high yield.

As described above, in conventional synthesis of triphenylmethane compounds, the amount of acid is set to a catalytic amount, and it is believed that the presence of a stoichiometric amount or more of acid promotes the decomposition of the reaction product. On the other hand, in the method for producing triphenylmethane compounds according to the present embodiment, it has been newly discovered that by making an acid present in a predetermined stoichiometric amount or more in the synthesis step, a decrease in the yield of triphenylmethane compounds can be suppressed even if protonation of the amino group of the substrate occurs.

<Structure of substrate and triphenylmethane compound>
In general formula (I) and general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group or an aralkyl group. R ¹⁰ and R ¹¹ may be linked to each other to form a ring. n represents 0 or 1. R ¹² represents an aldehyde group or -CH(OR _x ) ₂ , and R _x represents an alkyl group.

In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group, a ω-hydroxyalkyl group or an aralkyl group. R ²⁰ and R ²¹ may be linked to each other to form a ring.

In general formula (I) and general formula (III), examples of the alkyl group represented by R ¹⁰ and R ¹¹ include a linear alkyl group having 1 to 10 carbon atoms and a branched alkyl group having 3 to 10 carbon atoms.
Examples of the linear alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group.
Examples of the branched alkyl group having 3 to 10 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group.
Among the above, the alkyl group represented by R ¹⁰ and R ¹¹ in general formula (I) and general formula (III) is preferably a lower alkyl group having 1 to 8 carbon atoms, such as a methyl group, an ethyl group, a propyl group, a pentyl group, a butyl group, an isopropyl group, an isobutyl group, a sec-butyl group, or a tert-butyl group.

In general formula (I) and general formula (III), examples of the aralkyl group represented by R ¹⁰ and R ¹¹ include aralkyl groups having 7 to 30 carbon atoms.
Examples of the aralkyl group having 7 to 30 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a 4-phenylbutyl group, a phenylpentyl group, a phenylhexyl group, a phenylheptyl group, a phenyloctyl group, a phenylnonyl group, a naphthylmethyl group, a naphthylethyl group, an anthrathylmethyl group, and a phenyl-cyclopentylmethyl group.
Among the above, the aralkyl group represented by R ¹⁰ and R ¹¹ in general formula (I) and general formula (III) is preferably an aralkyl group having 7 to 15 carbon atoms, such as a benzyl group, a phenylethyl group, a phenylpropyl group, or a 4-phenylbutyl group.

In general formula (I) and general formula (III), R ¹⁰ and R ¹¹ may be bonded to each other to form a ring. Examples of the ring structure formed by bonding R ¹⁰ and R ¹¹ to each other include heterocyclic amines having 2 to 10 carbon atoms (e.g., an aziridine group, a pyrrolidino group, a piperidino group), and the like.

In general formula (I) and general formula (III), n represents 0 or 1, and preferably n represents 1.

In general formula (I), R ¹² represents an aldehyde group or -CH(OR _x ) ₂ , and R _x represents an alkyl group. In general formula (I), examples of the alkyl group represented by R _x in -CH(OR _x ) ₂ include the same as those exemplified as the alkyl groups in R ¹⁰ and R ¹¹ described above.

In general formula (II) and general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group, an ω-hydroxyalkyl group or an aralkyl group. Preferred embodiments of the alkyl group and aralkyl group in R ²⁰ , R ²¹ and R ²³ include the alkyl group and aralkyl group exemplified above for R ¹⁰ and R ¹¹ .

In general formula (II) and general formula (III), examples of the alkyl chain in the ω-hydroxyalkyl group represented by R ²⁰ , R ²¹ , and R ²³ include a linear alkyl chain having from 1 to 10 carbon atoms, and a branched alkyl chain having from 3 to 10 carbon atoms. Examples of the linear alkyl chain having from 1 to 10 carbon atoms and the branched alkyl chain having from 3 to 10 carbon atoms include the same as those exemplified for the alkyl groups in R ¹⁰ and R ¹¹ described above.

In general formula (II) and general formula (III), ^R20 and ^R21 may be bonded to each other to form a ring. Preferred embodiments of the ring formed by ^R20 and ^R21 bonded to each other include the same as those exemplified above for the ring formed by ^R10 and ^R11 bonded to each other.

In one aspect of this embodiment, the triphenylmethane compound is
In general formula (I) and general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, and n may be a structure representing 1.
In general formula (I) and general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 5 carbon atoms, and n may be a structure representing 1.

In one aspect of this embodiment, the triphenylmethane compound is
In general formula (II) and general formula (III), R ²⁰ , R ²¹ and R ²³ may each independently be a structure representing an alkyl group having 1 to 8 carbon atoms;
In general formula (II) and general formula (III), R ²⁰ , R ²¹ and R ²³ may each independently have a structure representing an alkyl group having 1 to 5 carbon atoms.

The compound represented by general formula (I) and the compound represented by general formula (II) may each be used alone or in combination of two or more kinds.

The following are examples of compounds represented by general formula (I), but the present embodiment is not limited to these.

The following are examples of compounds represented by general formula (II), but the present embodiment is not limited to these.

Below, examples of triphenylmethane compounds represented by general formula (III) are shown, but the present embodiment is not limited thereto.

The method for producing a triphenylmethane compound according to the present embodiment may contain other reactants other than the acid, such as a reaction promoter, and the solvent.
Examples of the reaction accelerator include orthoester compounds such as triethoxymethane. When an orthoester compound is included, it is preferable that R ¹² in the compound represented by general formula (I) is an aldehyde group, from the viewpoint of more efficiently proceeding with the reaction with R ¹² being an acetal group.

<Synthesis process>
In the synthesis step, a compound represented by general formula (I) and a compound represented by general formula (II) are reacted in the presence of an acid in an amount of 1 molar equivalent to 1.5 molar equivalents relative to the total number of moles of amino groups contained in the compound represented by general formula (I) and the compound represented by general formula (II), to synthesize a triphenylmethane compound represented by general formula (III).

The acid may be either an inorganic acid or an organic acid. The acid may be used alone or in combination of two or more kinds.
Examples of inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid.
Examples of the organic acid include toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, and methanesulfonic acid.
Among the above, from the viewpoint of further improving the yield of the triphenylmethane compound, the acid preferably contains at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, and methanesulfonic acid, more preferably contains at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, and toluenesulfonic acid, and even more preferably contains toluenesulfonic acid.

From the viewpoint of further improving the yield of the triphenylmethane compound, the acid preferably contains an acid whose acid dissociation constant (pKa) in water at 25°C is less than -1.0, and more preferably contains an acid whose pKa is -3.0 or more and -2.0 or less.

When the acid used has a plurality of acid dissociation constants (pKa), the acid dissociation constant (pKa) specified above means the first acid dissociation constant (pKa1).
When a plurality of acids are used, the acid dissociation constant (pKa) defined above means the first acid dissociation constant (pKa1) of the acid having a lower value among the plurality of acids.

The amount of acid is 1 molar equivalent or more and 1.5 molar equivalents or less relative to the total number of moles of amino groups contained in the compound represented by general formula (I) and the compound represented by general formula (II). From the viewpoint of further improving the yield of the triphenylmethane compound, the amount is preferably 1 molar equivalent or more and 1.3 molar equivalents or less, and more preferably 1 molar equivalent or more and 1.2 molar equivalents or less.

In particular, from the viewpoint of producing a triphenylmethane compound in which, in general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, n represents 1, and R ²⁰ , R ²¹ , and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms in a higher yield, it is preferable that the amount of the acid is 1 molar equivalent or more and 1.2 molar equivalents or less with respect to the total number of moles of amino groups contained in the compound represented by general formula (I) and the compound represented by general formula (II).

The molar blending ratio of the compound represented by general formula (I) to the compound represented by general formula (II) (compound represented by general formula (I)/compound represented by general formula (II)) is, for example, preferably 1/3 or more and 1/2 or less, more preferably 1/2.7 or more and 1/2 or less, and even more preferably 1/2.5 or more and 1/2 or less, from the viewpoint of further improving the yield of the triphenylmethane compound.

In the synthesis step, as long as the compound represented by the general formula (I) and the compound represented by the general formula (II) can be reacted in the presence of an acid, a solvent may be used or the reaction may be carried out under neat conditions without using a solvent. In the case of the reaction under neat conditions, the acid is preferably an inorganic acid.
As the solvent, known solvents such as 1-butanol (n-butanol), 2-butanol, t-butyl alcohol, 1,4-dioxane, toluene, methyl ethyl ketone, etc. Among the above, 1-butanol (n-butanol) is preferable as the solvent.

The reaction temperature can be set appropriately depending on the solvent used, but may be, for example, from 50°C to 150°C, or from 80°C to 130°C.

The reaction time can be set appropriately, but may be, for example, until the substrate (i.e., raw material) is consumed, and may be from 1 hour to 48 hours, or from 3 hours to 30 hours.

<Crystallization process>
The method for producing a triphenylmethane compound according to this embodiment preferably includes a crystallization step.

In the crystallization step, there is no particular limitation as long as it is a method for crystallizing the triphenylmethane compound represented by the general formula (III) from the crude product after the synthesis step, and it may be any of a two-liquid crystallization method using a poor solvent and a good solvent, a reprecipitation method, a one-liquid crystallization method using only a good solvent, etc.

From the viewpoint of obtaining the triphenylmethane compound in a higher yield, the crystallization step is preferably a step of obtaining a crystal containing the triphenylmethane compound represented by the general formula (III) by dissolving the crude product containing the triphenylmethane compound represented by the general formula (III) in a good solvent at 10°C or higher and lower than 30°C after the synthesis step, and then allowing the good solvent to stand at 10°C or higher and lower than 50°C to obtain a crystal containing the triphenylmethane compound represented by the general formula (III).

The type of the good solvent is not particularly limited, and any solvent that dissolves the triphenylmethane compound can be used. The good solvent may be used alone or in combination of two or more. The term "dissolved" refers to a state in which no remaining dissolved material is visually observed.
The good solvent preferably contains an aliphatic alcohol, for example, from the viewpoint of obtaining a triphenylmethane compound in a higher yield. Examples of the aliphatic alcohol include lower aliphatic alcohols having 1 to 10 carbon atoms, ethylene glycol, etc. Among the above, the aliphatic alcohol preferably contains a lower aliphatic alcohol having 1 to 10 carbon atoms, and more preferably contains a lower aliphatic alcohol having 1 to 5 carbon atoms.

The concentration of the triphenylmethane compound dissolved in the good solvent is not particularly limited as long as it is possible to crystallize a crystal containing the triphenylmethane compound, but for example, it is preferably 30% by mass or less relative to the total amount of the good solvent, and more preferably 1% by mass or more and 20% by mass or less.

The temperature of the good solvent in which the crude product is dissolved may be 10° C. or higher and lower than 30° C., may be 15° C. or higher and 28° C. or lower, or may be room temperature (22° C.±4° C.).
The temperature at which the good solvent is allowed to stand may be 10° C. or higher and lower than 50° C., may be 15° C. or higher and 28° C. or lower, or may be room temperature (22° C.±4° C.).

<Other processes>
The method for producing a triphenylmethane compound according to this embodiment may include other steps (hereinafter simply referred to as "other steps") in addition to the synthesis step and the crystallization step.

As other steps, for example, the following steps may be independently included after the synthesis step.
(1) A neutralization step of neutralizing the reaction solution.
(2) A liquid separation step of mixing at least one of an aqueous ammonium chloride solution, water, and saline with the reaction solution, and then separating the mixture into an organic layer and an aqueous layer.
(3) A drying step in which the solvent or water is dried from the reaction solution by vacuum drying or the like.
(4) An adsorption step in which the reaction solution is treated with an adsorbent such as silica gel, alumina, activated carbon, etc.

<Application>
The use of the triphenylmethane compound according to the present embodiment is not particularly limited, and the compound can be used as an antioxidant in an electrophotographic photoreceptor housed in an image forming apparatus; a hole trapping agent; a charge transporting agent, etc. For example, the triphenylmethane compound according to the present embodiment is particularly excellent as an antioxidant contained in at least one layer, such as a surface protective layer or a charge transporting layer, in an electrophotographic photoreceptor housed in an image forming apparatus.

The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of this disclosure. Note that "parts" means "parts by mass" unless otherwise specified.

-Production of triphenylmethane compounds-
[Examples 1 to 3, 5 to 11, Comparative Examples 1 and 2]
In a flask, the amount and type of substrate shown in Table 1 and 3 equivalents of n-butanol as a solvent were added, and the flask was placed under a nitrogen atmosphere. Then, the amount and type of acid shown in Table 1 were added, and the reaction was carried out at 110°C for 24 hours. After the reaction was completed, the reaction solution was neutralized with an aqueous sodium hydroxide solution, and the organic layer and the aqueous layer were separated. Then, the solvent in the organic layer was distilled off to obtain a crude product. To the obtained crude product, the amount and type of solvent shown in Table 1 as a good solvent was added, and the solution in which the crude product was dissolved was stirred for 120 minutes at room temperature (23°C). Then, the crystals crystallized in the solution were filtered and dried to obtain the target product: a compound represented by general formula (III). The yield is shown in Table 1.

[Example 4]
After the reaction was completed under the same conditions as in Example 1, the reaction solution was neutralized with an aqueous sodium hydroxide solution, and the organic layer and the aqueous layer were separated. Thereafter, the solvent in the organic layer was distilled off to obtain a crude product.
A 20/3 mixture of ethanol and deionized water was prepared and preheated to 53° C. Next, a crude solution containing the crude product obtained above, which was obtained by dissolving the crude product in ethyl methyl ketone at room temperature (23° C.), was added to the mixture over 20 minutes. After that, the mixture mixed with the crude solution was mixed for an additional 15 minutes and then allowed to cool to room temperature (23° C.) to obtain crystals.
The precipitated crystals were then filtered and dried to obtain the target product: the compound represented by general formula (III). The yield is shown in Table 1.

[Comparative Example 3]
Except for not adding acid, a triphenylmethane compound was produced in the same manner as in Example 1. The results are shown in Table 1.

In Table 1, *1 indicates the molar equivalent of the acid relative to the total number of moles of amino groups contained in the compound represented by general formula (I) and the compound represented by general formula (II). In Table 1, *2 indicates that in the crystallization step, crystals containing a triphenylmethane compound were obtained by the reprecipitation method as shown in Example 4.

As shown in Table 1, it was found that the production of the triphenylmethane compound in the Example can produce the triphenylmethane compound in a higher yield than the production of the triphenylmethane compound in the Comparative Example.

Claims (8)

A method for producing a triphenylmethane compound, comprising: a synthesis step of reacting a compound represented by the following general formula (I) with a compound represented by the following general formula (II) in the presence of an acid in an amount of 1 molar equivalent to 1.5 molar equivalents relative to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II), to synthesize a triphenylmethane compound represented by the following general formula (III), wherein the acid has an acid dissociation constant (pKa) in water at 25° C. of −3.0 or more and −2.0 or less.
(In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group or an aralkyl group. R ¹⁰ and R ¹¹ may be linked to each other to form a ring. n represents 0 or 1. R ¹² represents an aldehyde group or -CH(OR _x ) ₂ , and the R _x represents an alkyl group.
In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group, an ω-hydroxyalkyl group or an aralkyl group. R ²⁰ and R ²¹ may be linked to each other to form a ring.

The method for producing a triphenylmethane compound according to claim 1, wherein the acid includes at least one selected from the group consisting of toluenesulfonic acid and benzenesulfonic acid. The method for producing a triphenylmethane compound according to claim 1 , wherein the acid comprises toluenesulfonic acid. The method for producing a triphenylmethane compound according to any one of claims 1 to 3 further comprises a crystallization step in which, after the synthesis step, a crude product containing the triphenylmethane compound represented by the general formula (III) is dissolved in a good solvent at 10°C or higher and lower than 30°C, and the good solvent is allowed to stand at 10°C or higher and lower than 50°C to obtain a crystal containing the triphenylmethane compound represented by the general formula (III). The method for producing a triphenylmethane compound according to claim 4, wherein the good solvent includes an aliphatic alcohol. In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, and n represents 1. The method for producing a triphenylmethane compound according to any one of claims 1 to 5. The method for producing a triphenylmethane compound according to any one of claims 1 to 6, wherein in the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms. In the general formula (I) and the general formula (III), R ¹⁰ and R ¹¹ each independently represent an alkyl group having 1 to 8 carbon atoms, and n represents 1.
In the general formula (II) and the general formula (III), R ²⁰ , R ²¹ and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms;
the amount of the acid is 1 molar equivalent or more and 1.2 molar equivalents or less with respect to the total number of moles of amino groups contained in the compound represented by the general formula (I) and the compound represented by the general formula (II);
The method for producing a triphenylmethane compound according to any one of claims 1 to 7.