RADIOISOTOPES,52,57-64(2003)

Original

Reactivity of Benzenesulfonic Acids in the Hydrogen-Isotope Exchange Reaction

Dongyu ZHAO, Hiroshi IMAIZUMI* and Naoki KANO*

Graduate School of Science and Technology, Niigata University *Department of Chemistry and Chemical Engineering , Faculty of Engineering, Niigata University 8050 Ikarashi 2-Nocho, Niigata-shi, Niigata Pref. 950-2181, Japan

Received September 2, 2002

In order to reveal the reactivity of a functional group in an aromatic compound having two substituents

in the aromatic ring, the hydrogen-isotope exchange reaction (T for-H exchange reaction) between tritiated

water vapor (HTO vapor) and 3-amino-4-methoxybenzenesulfonic acid (and 2-aminotoluene-5-sulfonic

acid) was dynamically observed at 50•Ž (and 70•Ž) in a gas-solid system. Consequently, the specific

activity of the acid increased with time, and it showed that the T for-H exchange reaction occurred. Applying

the A•h-McKay plot method to the data observed, the rate constant of each functional group for the reaction

was obtained. After the additive property of the Hammett's rule was applied to this work; the new substituent

constants were obtained. From the above-mentioned, the following four items have been confirmed. (1) The

reactivity of the functional groups can be dynamically analyzed, and the A•h-McKay plot method is useful to

analyze the reactivity. (2) The additive property of the Hammett's rule is applicable to quantitative

comparison of the reactivity of the functional groups. (3) The reactivity of the functional groups can be

simultaneously analyzed by using the A•h-McKay plot method in the T-for-H exchange reaction. (4) The

method used in this work is also useful for analyzing the reactivity of a certain material having some kinds of

functional groups.

Key Words : trisubstituted aromatic compound, gas-solid reaction, T-for-H exchange reaction,

Hammett's rule, the A•h-McKay plot method, rate constant, benzenesulfonic acid

society, now it seems that the more the 1. Introduction number of nuclear power plants (the reprocess-

Recently, environmental pollution by ing plants for spent nuclear fuel, and advanced radioactive materials becomes a serious study of nuclear fusion) are, the more is the problem around the world. Tritium (3H or T) amount of T. The total radiation doses of contamination is one type of pollution. T is a tritium are relatively great among the radioisotope of hydrogen. Since the maximum radionuclides in atmospheric nuclear testy. So energy of the radiation (i.e., ƒÀ-ray) from T is the study of tritium-impact on environment very low (18.6 keV), the external exposure (and human being) turns more and more from T is not so important. However, if T is important. The exchange reaction between incorporated into human body, the following tritiated-water vapor and an aromatic problem must be considered since the half-life compound in gas-solid system had been studied of T is relatively long (12.3y) compared with for last twenty years. To determine the rate the human mean life. With development of constants (k) for the compound, the A•h-McKay

(3) 58 RADIOISOTOPES Vol.52, No.2 plot method was applied to the data obtained. scintillation counter. The specific activity was Some Hammett plots were made using both k corrected by calculation every three months values and the substituent constants, and the because the specific activity decreased with effect of the substituents on the reactivity was radioactive decay. revealed. With regard to monosubstituted 2)-5), The samples of 3-amino-4-methoxybenzene- disubstituted (except ortho-position) 6)-8), and sulfonic acid and 2-amino-5-sulfonic acid were

1, 3, 5-trisubstituted aromatic compounds9), purchased from Aldrich Chemical Company, the rate constants and the substituent Inc. and Wako Pure Chemical Industries, Ltd., constants were well fitted on the Hammett plot. respectively. The samples were sufficiently

As for trisubstituted aromatic compound powdered in an agate mortar, and then sieved having substituent (s) in ortho-position, the to obtain a grain size between 53 and 75 ƒÊm in applicability to the Hammett's rule has not diameter. Then the sieved samples were dried been so far clarified. So the compounds of 3- in a vacuum oven at 70•Ž till constant weight. amino-4-methoxybenzenesulfonic acid (and After that, the sample was preserved in a

2-aminotoluene-5-sulfonic acid) were selected desiccator containing silica gel. Each sample to employ the T-for-H exchange reaction with thus prepared was used for the gas-solid

HTO water in a gas-solid system. exchange reaction.

In this work, the following aims were chosen : (1) to quantitatively clarify the 2.2 The method of observation reactivity of NH2 and S03H groups in a Using the sample materials above-mentioned compound, (2) to clarify the effect of the and the vacuum line12), the hydrogen-isotope temperature (and the substituents) on the exchange reaction (i.e., T-for-H exchange reactivity of the functional group, (3) to reaction) was observed in a gas-solid system at ascertain whether the A•h-McKay plot method 50•Ž (and 70•Ž). The method of the is applicable to clarify the reactivity of the observation was roughly followings : (1) the groups, and (4) to ascertain whether the mass of each solid sample used was 12 mg per

Hammett's rulelo),11) is useful to analyze the run ; (2) after the reaction, distilled water was reactivity of aromatic compounds which have used to dissolve the solid materials used in the three kinds of functional groups (i.e., two sub- T-for-H exchange reaction ; (3) the activity of stituents and one functional group). the resulting solution was measured with a

liquid scintillation counter. The data observed 2. Experimental was analyzed with the A•h-McKay plot method,

2.1 Sample materials and k for each solid sample material used was

HTO water whose specific activity is 5•~10-3 obtained.

Ci g-1 was purchased from Japan Radioisotope Previously2), it was found that H atoms

Association, and was diluted to 1.6•~10-5 directly bonded to benzene ring could not

Ci g-1 (i.e., 6•~105 Bq g-1) with distilled water. exchange with T atoms in HTO vapor in the T-

The HTO water thus prepared was used in for-H exchange reaction. Accordingly, it was this work, whose specific activity was considered that only H atoms in the NH2 and

determined accurately with a liquid S03H groups of the solid sample material used

(4) Feb. 2003 Z. Dongyu et al.: Reactivity of benzenesulfonic acids in the hydrogen-isotope exchange reaction 59

in this work could exchange with T in HTO A; (b) the latter reaction continued, and the vapor. Prior to the observation, it was latter one was also attained equilibrium at confirmed (by calculation and experiment) that Point B; (c) the T-diffusion reaction into the three conditions3),8) for applying the A•h- inner phase of the sample occurred.

McKay plot method were satisfied. Consequently, the first part in Fig. 1 corresponds to Reactions (1) and (2) shown as 3. Results and Discussion follows, the second one corresponds to

3.1 The reactivity of amino and sulfonic Reaction (3), and the third corresponds to the

acid groups diffusion reaction.

In order to clarify the reactivity of NH2 and HO3S-C6H3(CH3)NH2+HTO•¬

SO3H groups in a trisubstituted aromatic TO3S-CsH3(CH3)NH2+H2O(1) compound, the T-for-H exchange reaction H03S-CsH3(CH3)NH2+HTO•¬ between 3-amino-4-methoxybenzene sulfonic HO3S-CsH3(CH3)NHT+H2O(2) acid (or 2-aminotoluene-5-sulfonic acid) and TO3S-C6H3(CH3)NH2+HTO•¬

HTO vapor was observed at 50•Ž (and 70•Ž). TO3SC6H3(CH3)NHT+ H2O(3)

The time-dependence of the exchange reaction In order to apply the A•h-McKay plot method at each temperature and each sample material to the data shown in Fig. 1, x•‡(F2) is initially was similar with each other. For the simplicity, calculated. Where, x•‡(F2) means the specific only the relation between the reaction time and activity of T in the NH2 group in the surface of specific activity of T in 2-aminotoluene-5- the sample when the exchange reaction sulfonic acid at 70•Ž was given in Fig.l. The between HTO vapor and the NH2 group figure showed that the reaction did occur attained equilibrium because the reactivity of because the activity of T in 2-aminotoluene-5- the SO3H group was much larger than that of sulfonic acid increased with time. Figure 1 consists of the following three parts : (a) the first part is the area from the origin to Point A; (b) the second one is the area from Point A to Point B; (c) the third is the area from Point B to the right end of the line. Previously13), it was found that the reactivity of the SO3H group was much larger than that of the NH2 group when the two groups existed in the same molecule. Accordingly, the three parts mentioned above correspond to the following three reactions, respectively: (a) two reactions (between HTO vapor and the SO3H group (and the NH2 one) at the surface of the solid sample) proceed at the same time, and the Fig.1 Specific activity vs. time for the reaction former reaction between HTO vapor and the between 2-aminotoluene-5-sulfonic acid and SO3H group was attained equilibrium at Point HTO vapor at 70•Ž.

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Fig. 2 A•h-McKay plot of NH2 group for Fig. 3 A•h-McKay plot of SO3H group for

2-aminotoluene-5-sulfonic acid at 70•Ž. 2-aminotoluene-5-sulfonic acid at 70•Ž.

the NH2 one. Using the values from point A to figures for the rest reactions were analyzed, point B in Fig. 1, the A•h-McKay plot for the and k values were obtained. The results are

NH2 group has been made (Fig. 2). To obtain tabulated in Table 1. the straight line, the correlation coefficient has From Table 1, the ratio of k value for the been calculated by applying the method of the S03H group to k value for the NH2 one in 2- least squares. In Fig. 2, the dashed line shows aminotoluene-5-sulfonic acid molecule is shown the extrapolation from point A to the origin. as follows :

The gradient of the straight line in Fig. 2 can 50•Ž(-S03H):(-NH2)=10:1 (4) satisfy the condition of significance at the 1% 70•Ž(-S03H):(-NH2)=7.6:1 (5) level, and it is equal to k for the NH2 group in The ratios of k values for the same kind of the sample material. Then each value between group at different temperature are the next : point A and the origin in Fig. 1 was subtracted S03H group (70•Ž):(50•Ž)=1.4:1 from the value corresponding to the dashed (6) line in Fig. 2. Using the each data subtracted, NH2 group (70•Ž):(50•Ž)=1.8:1 the A•h-McKay plot of the S03H group has been (7) made (Fig. 3). In Fig. 3, x•‡(F1) means the From the above comparison, the following specific activity of T in the sample when the characteristics are obtained : a) the reactivity reaction between HTO vapor and the S03H of the S03H group is 8-10 times greater than group attained equilibrium. In other words, that of the NH2 one ; b) both the reactivity of x•‡(Fl) is the specific activity of T in the S03H the S03H group and that of the NH2 one group at the surface of the sample in Reaction increase with temperature.

(1). The gradient of the straight line in Fig. 3 From Table 1, k values for the S03H and can also satisfy the condition of significance at NH2 groups in 3-amino-4-methoxybenzene- the 1% level, and it equals k for the S03H sulfonic acid can be compared with each other group in the reaction. In the same manner, the at 50•Ž (and 70•Ž):

(6) Feb. 2003 Z. Dongyu et al.: Reactivity of benzenesulfonic acids in the hydrogen-isotope exchange reaction 61

Table 1 Rate constants for the NH2 and S03H groups obtained in this work and previously obtained

50•Ž (-S03H):(-NH2)=9.5:1 (8) decreasing temperature. (2) k values for the

70•Ž (-S03H):(-NH2)=7.9:1 (9) NH2 group also decreased. The ratios of k values for the same kind of As to 2-aminotoluene-5-sulfonic acid and p- group at different temperature are given as aminobenzenesulfonic acid, methyl group is follows : bonded with benzene ring in meta-position in

S03H group (70•Ž):(50•Ž)=1.3:1 the former. Comparing the data of the above

(10) two compounds in Table 1, the following item

NH2 group (70•Ž):(50•Ž)=1.6:1 was obtained regarding the effect of the

(11) methyl group on k for the NH2 one (and the

From the comparison, it is found that the S03H one) : the ratio of k values for the NH2 results are similar to the results obtained in 2- group increased with temperature compared aminotoluene-5-sulfonic acid. to the ratio of k values for the S03H one. It is generally known that the electronic 3.2 The effect of methoxy (or methyl) effects (I-effect and R-effect) can be seen in group in ortho position on the rate substituted benzoic acids, and that these constants of sulfonic acid group (and effects can be classified into following four amino one) in a trisubstituted aromatic types according to the species of substituent2). compound (A) I-effect goes to an electron-attractive effect 3-Amino-4-methoxybenzenesulfonic acid has (abbreviated below as (+)) ; R-effect goes to a methoxy group in para position as a an electron-donative one (abbreviated below as substituent, whereas m-aminobenzenesulfonic (-)). (B) I-effect goes to (+) ;R-effect goes to acid has not such a substituent. Comparing the (+). (C) I-effect goes to (-) ; R-effect goes to data of the above-mentioned compounds in (-). (D) I-effect goes to (-) ; R-effect goes to Table 1, the following two items were obtained (+). As for methoxy group as a substituent, regarding the effect of the methoxy group on k methoxy group corresponds to Case (A) for the NH2 group (and the S03H one). (1) k since the oxygen atom possesses large values for the S03H group decreased with electronegativity and has lone-pair electrons

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(and methyl group is also an electron-donative constant for meta-substituted benzenesulfonic group). acid. K is the equilibrium constant for the When methoxy group is in para-position, the former material ; and K0 is the equilibrium extent of R-effect is larger than that of I-effect, constant for the latter one ; ƒÏ is the reaction and finally the methoxy group in para-position constant, ƒÐ is the substituent constant. is an electron-donative one. This matter leads Accordingly, it seems that a quantitative to increasing electron density on oxygen atom relation exists between k and a when the in the SO3H group13). Accordingly, k value for Hammett's rule can be applied to the reaction. the SO3H group is decreased. In the previous As for multi-substituted aromatic compound, work4), p-methoxy group can decrease k value if there is no substituent in ortho-position for for NH2 group in aniline. As for methyl group functional group (in this work, the functional as a substituent, it corresponds to Case (C). group is SO3H group), the additive property of

Since electron-donative effect of methyl group the Hammett's rule can be adopted to obtain is weak, the effect of the methyl group on k the total substituent constant (i.e., new ƒÐ) in the value for the SO3H group is also weak. multi-substituted aromatic compoundl4)

Ortho substituted benzenesulfonic acid log10(k/ko)=ƒÏƒ°ƒÐ(14) usually has a peculiarity (ortho effect). Since In Eq. (14), the new substituent constant methoxy and methyl groups are huge groups, (al) of the total substituents (i.e., NH2 and the result of the steric hindrance effect resists OCH3 groups) in 3-amino-4-methoxybenzene- the T-for-H exchange reaction, and decreases k sulfonic acid and the new substituent constant values for the NH2 group. (ƒÐ2) of that (i.e., NH2 and CH3 groups) in 2-

aminotoluene-5-sulfonic acid can be calculated :

3.3 Applicability of the Hammett's rule ƒÐl=ƒÐm(-NH2)+ƒÐp(-OCH3)=

-0 In general, the effect of the substituent of .16+(-0.268)=-0.428 (15) each aromatic compound on the reactivity of ƒÐ2=ap(-NH2)+ƒÐm(-CH3)=

-0 the compound can be quantitatively expressed .66+(-0.069)=-0.729 (16) with the Hammett's rule11). The rule is shown The calculated results are tabulated in Table in the following equation : 2. Using k and a in Table 2, the Hammett plots

log10(k/ko)=ƒÏƒÐ(12) are made (Fig.4). In each plot, there are four

log10(K/Ko)=ƒÏƒÐ(13) dots. Two dots (Points 1 and 2) belong to the

where k is a rate constant for a meta (or trisubstituted compounds above obtained, and para)-substituted aromatic compound, k0 is the the others (Points 3 and 4 ) belong to the

rate constant for the unsubstituted aromatic disubstituted ones. Each number in Fig. 4

compound, K is the equilibrium constant for a corresponds to the same (material) number in

meta (or para)-substituted aromatic compound. Table 2. Since the correlation coefficient of

K0 is the equilibrium constant for the each straight line in Fig. 4 can satisfy the

unsubstituted aromatic compound, ƒÏ is the condition of significance at the 1% level, it is

reaction constant, a is the substituent constant. confirmed the reactivity of the compounds

As for this work, k is a rate constant for a used in this work follows the Hammett's rule.

substituted benzenesulfonic acid ; k0 is the rate Accordingly, the gradient of each straight line

(8) Feb. 2003 Z. Dongyu et al.: Reactivity of benzenesulfonic acids in the hydrogen-isotope exchange reaction 63

Table 2 Rate constants for SO3H group and substituent constants for substituted benzenesulfonic acid calculated in this work and obtained by McDaniel (and Brown)

Fig.4 Each plot of the logarithm of the is equal to the reaction constant (ƒÏ) and it is relative rate constant for substituted 0.37 at 50•Ž, or 0.37 at 70•Ž. benzenesulfonic acid and substituent

From the above-mentioned, it was found that constant(ƒÐ). (1) the Hammett's rule could be applied to Symbol k is a rate constant for each substituted benzenesulfonic acid, and ko clarify the reactivity of aromatic compounds in is the rate constant for m-amino- the T-for-H exchange reaction, (2) the reactivity benzenesulfonic acid. of trisubstituted aromatic compound could be

analyzed by applying the additive property of 7) Imaizumi, H., Nishiwaki, K. and Kano, N.: the Hammett's rule even if the compound had Radiochim. Acta, 76, 201-204 (1997) an ortho-substituent. 8) Imaizumi, H., Sakai, H. and Kano, N.: J. Radioanal. Nucl. Chem., 241(3),(3)451-455(1999) References 9) Imaizumi, H., Sakai, H. and Kano, N.: Radioisotopes, 49, 285-291(2000) 1) Fry, R., Deslevins, and Wanecke, E.:IAEA 10) Hammett, L. P.: J. Am. Chem. Soc., 59, 96-103 Bulletin, 40(4), 32(1998) 2) Imaizumi, H., Kobayashi, K. and Okada, M.: (1937) Radiochim. Acta, 42,151-154(1987) 11) Mcdaniel, D. H. and Brown, H. C.: J. Org. Chem, 23, 420-427 (1958) 3) Imaizumi, H., Uchida, K., and Okada, M.,: Nippon 12) Okada, M. and Imaizumi, H.: Radiochim. Acta, 37, Kagaku Kaishi,1988, 853-857 161-164(1984) 4) Imaizumi, H., Sasaki, T. and Okada, M.: Radiochim. 13) Imaizumi, H., Koyanagi, T. and Zhao, D.: J. Acta, 49, 53-55 (1990) 5) Imaizumi, H. and Muramatsu, K.: Radiochim. Radioanal. Nucl. Chem., 252(3), 467-472(2002) Acta, 65,53-57(1994) 14) Inamoto, N.:•gHammett Rule•h, pp. 22-26, Maruzen 6) Imaizumi, H. and Yumoto, Y.: Radiochim. Acta, 68, Co. Ltd. (1983) 141-144(1995)

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要 旨

水素 同位体交換反応 におけるベンゼンスル ホン酸 の反応性

趙 東宇,今 泉 洋*,狩 野直樹*

新 潟 大 学 大 学 院 自然 科 学 研 究 科 *新 潟 大 学 工 学 部化 学 シス テ ム 工 学 科

950-2181新 潟 県 新 潟 市 五 十 嵐 二 の 町8050

一 つ の 分 子 中 に二 つ の置 換 基 を持 つ芳 香 族 化 合 物 の官 能 基 の 反 応 性 を 明 らか に す る た め に ,3-ア ミノー4-メ トキ シーベ ンゼ ンス ル ホ ン酸(ま た は2-ア ミ ノ トル エ ンー5-ス ル ホ ン酸)と トリ チ ウ ム 水 蒸 気(HTO蒸 気)と の 間 で起 こ る水 素 同位 体 交換 反 応(T-for-Hexchangereaction)を,固 気 系 にお い て 速 度 論 的 に観 測 した(50,70℃)。 そ の結 果,こ の酸 の比 放 射 能 は時 間 と と も増 加 し,T- for-H交 換 反 応 が起 こ っ た こ とが わ か っ た 。観 測 され た デ ー タ にA”-McKayプ ロ ッ ト法 を適 用 して こ の反 応 お け る各 官 能 基 の速 度 定数 が得 られ た 。 さ らに,本 研 究 にHammett則 の 加 成 性 を 適 用 し, 新 た な置 換 基 定 数 を算 出 した。 以 上 の結 果 か ら,次 の 四 つ が 明 らか に な っ た 。(1)官 能 基 の 反 応 性 を速 度 論 的 に解 析 す る こ とが で き,そ の 解 析 に はA”-McKayプ ロ ッ ト法 が 有 効 で あ る。(2)こ れ ら官 能 基 の 反 応 性 の定 量 比 較 に,Hammett則 の加 成性 が 適 用 で き る。(3)こ れ らの 官 能 基 の 反 応 性 はT-for-H交 換 反応 に お い て,A”-McKayプ ロ ッ ト法 を適 用 す る こ とで,同 時 に 解析 す る こ とが で き る。(4)本 研 究 で使 っ た手 法 は 多種 の官 能基 を持 つ化 合物 の 反 応性 を解 析 す るの に有 効 で あ る。

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