Catechinone hair dyestuff was produced chemically from (+)-catechin by the oxidation with O2 in basic water/alcohol mixed solution. The effects of reaction conditions such as basicity, sorts of added base, temperature, alcohol molar fraction of solvent and sorts of added alcohols on the catechinone formation were studied in order to increase the efficiency of the dyestuff production. The amount of obtained catechinone increases with increasing basicity of the reaction solution. The dyestuff is obtained by adding monoethanol amine, diethanol amine, triethanol amine, l-arginine, Na2CO3, K2CO3, Na3PO4 or NaOH into the solution as a base and the most preferable base is monoethanol amine. The optimum temperature for the production in water/ethanol solution is 30°C. It was found that water-soluble alcohols such as methanol, ethanol, 2-propanol, 1-propanol and tert-butyl alcohol are available for preparing the dyestuff. The optimum alcohol molar fraction of the mixed solvent used for the dye formation is 0.45 for methanol, 0.25 for ethanol and 0.20 for 2-propanol, 0.15 for 1-propanol and 0.10 for tert-butyl alcohol. The amount of the obtained dyestuff reaches a maximum at 1) 0.35 and 0.59, 2) 0.35 or 3) 0.35 mol·kg¨1 of the concentration of (+)-catechin for the 1) water/methanol, 2) water/ethanol or 3) water/1-propanol system, respectively.
A great number of people dye their hair in the world today. Above all, human hair dyeing by using oxidation dyes is most frequently employed. The advantages of the permanent hair colouring technique using the oxida- tion dye are the higher dyeability for darker hair and higher colour fastness to washing [
Under such the situation, the authors invented catechinone (4-(3,4-dihydro-3α,5,7-trihydroxy-2H-1-benzo- pyran-2α-yl) 1,2-benzoquinone) as a safer hair dyestuff and it is prepared by oxidising (+)-catechin [
Nevertheless, the yield of catechinone is not high in one batch of the reaction solution because of the low solubility of (+)-catechin in an aqueous solution, and then it should be improved for practical use. The solubility of (+)-catechin in ethanol is over 30 times higher than that in water. Then, the chemical dyestuff preparation was attempted by adding ethanol into the reaction solution and increasing the concentration of (+)-catechin to in- crease the dye production efficiency in the previous study [
In this study, the relationships between the amount of the formed catechinone and the dye preparation condi- tions such as basicity, sorts of added base, temperature, alcohol molar fraction of solvent and sorts of added al- cohols were studied for the oxidation reaction of (+)-catechin in water/alcohol solution.
(+)-Catechin and other reagents described below were purchased from Sigma and Nacalai tesque, respectively. (+)-Catechin hydrate, ethanol (EtOH, 99.5%), methanol (MeOH, 99.8%), 1-propanol (1-PrOH, 99.5%), 2-pro- panol (2-PrOH, 99.7%) and tert-butyl alcohol (t-BuOH, 99.0%) were used without further purification. Monoe- thanol amine (MEA), diethanol amine (DEA), triethanol amine (TEA), l-arginine (Arg), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), sodium phosphate (Na3PO4) and sodium hydroxide (NaOH) were used as base without further purification.
Chemical structure of catechinone
(+)-Catechin and a base were dissolved in 100 g of distilled water/alcohol mixed solvent. Oxygen gas (≥99.5 vol%) was introduced continuously into the reaction solution through porous glass ball filter (pore size: 40 - 50 μm) at 100 ml∙min−1 of flow rate, and the solution was stirred for prescribed time at 20˚C - 50˚C.
The reaction solution was sampled at several time intervals and diluted by distilled water with a dilution ratio (f). The ultraviolet-visible absorption spectra of the sampled solution were measured by a Hitachi U-3900H spec- trophotometer at 25˚C. The dye formation behaviour was monitored by using the absorbance at 430 nm (A430) at each reaction time (t). The obtained f·A430 values correspond to the concentration of the formed dye [
The apparent basicity of the reaction mixed solution (pH*) was determined through the measurement by a TOA-DKK MM-60R multi water quality meter with a TOA-DKK ELP-031 glass combination electrode at 25˚C.
The colour of reaction solution turns orange and reddish brown with reaction time showing the formation of catechinone dyestuff. Catechinone is hardly obtained in acidic and neutral reaction solution without base. The rate of catechinone formation increases with increasing the basicity of aqueous reaction solution [
The pH* dependence of the (f·A430)200min for the catechinone produced in water/ethanol solution (xA = 0.28) with MEA at 30˚C
. The reaction condition and the resulting rate and amount of catechinone dye. The reactions are started in water/ethanol solution (xA = 0.28) at mS = 0.172 mol∙kg−1 at 30˚C
Base | pKbb | mB/mol∙kg−1 | pH*c | v/s−1 | (f·A430)200min | |
---|---|---|---|---|---|---|
1 | None | - | - | 4.84 | ~ 0 | 2.50 |
2 | MEA | 4.49 | 0.010 | 8.76 | 6.23 × 10−3 | 47.5 |
3 | MEA | 4.49 | 0.050 | 9.26 | 2.76 × 10−2 | 248 |
4 a | MEA | 4.49 | 0.10 | 9.56 | 6.97 × 10−2 | 507 |
5 | MEA | 4.49 | 0.50 | 10.13 | 1.35 × 10−1 | 1148 |
6 a | DEA | 5.12 | 0.10 | 9.21 | 1.79 × 10−2 | 133 |
7 a | TEA | 6.24 | 0.10 | 8.65 | 2.72 × 10−3 | 29.0 |
8 | Arg | 4.91 | 0.10 | 9.34 | 2.54 × 10−2 | 92.3d |
9 | Na2CO3 | 3.68 | 0.10 | 9.76 | 1.41 × 10−1 | 660 |
10 | K2CO3 | 3.68 | 0.10 | 10.15 | 1.62 × 10−1 | 670 |
11 | Na3PO4 | 1.68 | 0.0068 | 8.87 | 2.91 × 10−3 | 23.5 |
12 | NaOH | - | 0.10 | 10.06 | 1.70 × 10−1 | 546 |
aPrevious work [
promoted by higher basicity of the reaction solution. This relationship is similar to that between pH and the rate of catechinone formation in aqueous solution [
Furthermore, the preparation of the dyestuff was made in the mixed solution with basic amino acid l-arginine or inorganic bases such as Na2CO3, K2CO3, Na3PO4 or NaOH (as listed in
The rate of oxidation reactions are generally influenced by temperature. It is instructive to study the effect of re- action temperature on catechinone formation for obtaining better condition to produce the dyestuff efficiently.
Relationship between reaction temperature (T) and (f·A430)140min for catechin preparation in wa- ter/ethanol mixed solution with MEA at xA = 0.28
Next, the dependence of the maximal amount of formed dye on the concentration of (+)-catechin in the reac- tion solution with the alcohols was investigated to elucidate the optimum condition for producing the dyestuff. MeOH, EtOH and 1-PrOH are convenient linear alcohols and they were employed in the experiments as at each xA = 0.45, 0.25 or 0.15, respectively for obtaining maximum.
Relationship between alcohol molar fraction (xA) of the water/ethanol mixed solvent and the amount of the catechinone at 140 min ((f·A430)140min)
Relationship between xA and (f·A430)140min for the dye production at 140 min with O2 gas introduced at 30˚C in the water/methanol (¢), water/ethanol (), water/1-propanol (r), water/2-propanol (s) or water/tert-butyl alcohol (¯) solution with MEA
Relationship between maximum of f·A430 ((f·A430)max) and the concentration of (+)-catechin (mS) for the dye forma- tion in water/alcohol mixed solution with MEA at 30˚C. The xA is 0.45 (¢), 0.25 () or 0.15 (r) for the methanol, ethanol or 1-propanol added system, respectively
kinds of water/alcohol systems. The maximum value of f·A430 is ca. 1600 in all the reaction systems. The mS value to give the maximum f·A430 for water/EtOH and water/1-PrOH systems is 0.35 mol∙kg−1 and the values for water/MeOH system are 0.35 and 0.59 mol∙kg−1.
The results show that the amount of formed catechinone depends on the sort of alcohols, the alcohol molar fraction and the concentration of (+)-catechin, and there are optimum xA and mS values to obtain the dyestuff ef- ficiently. It can be said that the EtOH is most preferable as the solvent added for the production of the dyestuff, because its safety is highest, its handling is easiest during and after the production and it is most economical.
The relationships between the amount of the formed catechinone and the dye preparation conditions such as ba- sicity, sorts of added base, temperature, alcohol molar fraction of solvent and sorts of added alcohols were stud- ied for the oxidation reaction of (+)-catechin in water/alcohol solution. The amount of catechinone obtained in- creases with increasing basicity and the dyestuff is obtained by adding MEA, DEA, TEA, l-arginine, Na2CO3, K2CO3, Na3PO4 or NaOH. The optimum temperature for the production in water/ethanol solution is 30˚C. The optimum alcohol molar fraction of the mixed solvent for the dye formation is 0.45, 0.25, 0.20, 0.15 or 0.10, with the methanol, ethanol, 2-propanol, 1-propanol or tert-butyl alcohol system, respectively. The amount of the ob- tained dyestuff reaches maximum at 1) 0.35 and 0.59, 2) 0.35 or 3) 0.35 mol∙kg−1 of the fed concentration of (+)-catechin for the 1) water/MeOH, 2) water/EtOH or 3) water/1-PrOH system, respectively.
This study was financially supported partly by the Japan Society for the Promotion of Science Research Founda- tion Grant (No. 21500732) and partly by Japan Science and Technology Agency as Adaptable & Seamless Technology Transfer Program through Target-driven R & D (No. AS2211611E). Japanese patent application number: 2012-219084 (12 November 2012).