UE.SCRIPTION Process for producing aqueous chlorous acid solution for use as disinfectant 5 TECI-INICAL FIELD [0001] The present invention relates to a process -for producing an aqueous chlorous acid solution used for disinfection/sterilization of food for pretreatment in food processing operations and related facilities. 10 BACKGROUND ART [0002] Conventionally, chlorine oxides (e.g., chlorine, hypochlorous acid, chlorous acid, and chlorine dioxide) are primarily used -for disinfection or sterilization of 'food for 15 pretreatment in food processing operations, such as fresh perishable food including vcgctablcs and 'fruits, and the facilities related to processing and production of processed Food, such as containers, preparation/cooking machincry, and plant equipment. Of these, chlorine and hypochlorous acid, when reacted with organic compounds., are known to produce trihalomethanes. which are carcinogenic compounds. This, along with recent 20 health-consciousness trend, has focused attention on acidified sodium chlorite (ASC) solution, which was developed in the United States of America and which possesses a high bactericidal effect and is less associated with trihalomethane-related adverse effects. Reference I : U.S.A. Patent No. 6,524.624 25 (0003] To produce the above-mentioned ASC solution, an aqueous chlorous acid solution is mixed with an acid known as "generally recognized as safe" (GRAS) and adjusted to pH 2.3 to 3.2. 30 (0004] However, the main active component of the above-mentioned ASC solution, chliorous acid, decomposes a short time after preparation due to its low stability, thereby reducing its bactericidal potential. The above-mentioned ASC solution, therefore, needs to be prepared 35 immediately before use. r0005] This preparation procedure is not only inconvenient but also associated with the c-ION01 102_Substituted 23 May 2013.rtf 01 |3L L |VO0 | disadvantages resulting from production of chlorine dioxide gas, which is highly likely to have toxic effects on individuals who inhal.c it and corrosive effects on food processing and cooking machinery and other related equipment. 5 DISCLOSURE OF INVENTION PROBLEM TO BE SOLVED Y INVENTION [0006] The prcscnt invention was mnade taking into account the above disadvantages The purpose of the present invention is to provide an easy-to-handle, long-acting, stable 10 aqueous chlorous acid solution. Another purpose of the present invention is to provide a disinfectant for use in pretreatment of food-processing operations that releases a reduced amount of chlorine dioxide, is safe to human health, and possesses a high bactericidal activity. 5 MEANS FOR SOLVING PROf4EMS [0007] In order to solve the aforementioned problems, a 'first feature of the process of the present invenLion is to employ a process for producing an aqueous chlorous acid solution for use as disinfectant, comprising; reacting an aqueous sodium chlorate D solution with a volume and concentration of sulfuric acid or aqueous solution thereof appropriate for maintaining pH of said aqueous solution at 2.3 to 3.4, thereby generating chloiic acid, and subsequently adding thereto at least an amount of hydrogen peroxide required for reducing said chloric acid to produce chlorous acid, 5 [0008] A second feature of the process of the present invention is to employ a process for producing an aqueous chlorous acid solution for use as disinfectant, comprising: reacting an aqueous sodium chlorate solution with a volume and concentration of sulfuric acid or aqueous solution thereof appropriate for maintaining pH of said aqueous solution at 2.3 to 3.4, thereby generating chloric acid, subsequently adding thereto at least an amount of hydrogen peroxide rcquircd for reducing said chloric acid to produce chlorous acid, and adding to the resulting aqueous solution at least one compound selected from the group consisting of inorganic acids and salts or a combination thereof, to adjust its pH in the range of 3.2 to 7A0 [0009] A third feature of the process of the present invention is to employ a process for producing an aqueous chlorous acid solution for use as disin-fectant, comprising: reacti g an aqucou's sodium clo to solutIo wd sulfuric acid Oraqe urn chJat souto withead ocnta lo solui acid 2or aqueous solution thereof appropriate for maintaining prt1i ofof Solution at 23 to 3.4, thrby genera ing chloric acid, Subsequeny adding thereto at least an amount of hydrogen peroxide rcqui -ed for reducing s equentl adi eto at oLls from, the adng to the results 'qeuss li coric acid to Produce chlorouIs hero, to a the ti g aqucous aOluton at least one Compound selected fh r o f, t h c o u 'S~ t fl 0 in r c a d O r g a n ic a c id s a n d s a lts o r a c o m b in a tio n therof t adust its PH1 in tile range of 1.2 to 7,0. (0010] 0 A forth feature of the proces; t 'forth~~~~ f t re o th pr es of the Present inventio n, s to e employ a Process for Producing an aqueous chloro s acid solu ftion is o empl o mpr s ngo g n quou sdim sf-or use a1S disinfectant, opiig reactig o an aqueous sodu loate solution with vOlu and concentration solution and 2c3nappropriatefo Sulfuic acid or aqueous solutio thereof appropriate for maintaining pH of said aqueous oluto at 2.3 to 3.4, thereby enrating chloric acid, subSequently adding threto at least an a ount of hydrogen per Xie required for reducing said c dloric acid to produce chlo -LI acid, adding to the resulting aqueous solution at last one Compo nd selected fro c tie group Consisting of inorganic a cids and salts or a combination thereof, and further adig at least one compound sekc cee iro or ah cobatoroeefadput a dis ad lealt oa comb iaion the -o to m th gup consisting of inorganic and organic acids and salts Or a combination on thelof ,to adjust thle pH in the range of 3.2 to 7.0. [0011] A fifth feature of the process o th present invention is to employ te process Producing an aqueous chlorous acid solutifor USs afdsnetn hri adi or aci acordin to nll of second or use asdsinfectant ..weei nadiorai a c i d a c c o d i n t o n y f s c o n I t o f o r t h f e a t u r e s o f t h e p r e s e n t P r o c e s s , i n c l u d e carbonic acid, Phosphoric acid, boric acid, or sulfuric acid. [0012] A sixth feature of the process of thc resent invention producing an aqueous chlorous acid solution for use as disinfectant wherein said inorganic salts according to any o f Second to fif-th features of tile esnpocsinld carbonates, hydroxides, phosphates, or borates. e sent process nclude 0013] A seventh feature of the process o tie Pesnt invention is to employ the rocesqs for' thle process fo rcs fth rsn ne 'roc ss or he roc ss -or Prodiling '-a aqueous ch oro ts acid Solution for us c as isinfectant, w herein said carbon q o u cg oro th e i d s u r o n ie p rou en im carbonate, potassiu t carbonat eature of the present roce s i clu e 5 djui ca bon t otasium car one, sodium bicarbonate, or 4 potassium bicarbonate. [0014] A eighth feature of the p ocess of the present invention is to employ the 5 process for the process for producing an aqueous chlorous acid solution for use as disinfectant, wherein said by iroxides according to the sixth or the seventh feature include sodium hydroxide or pot ssium hydroxide. [0015] 10 A ninth feature of the process of the present invention is to employ the process for producing an aqueous chloroas acid solution for use as disinfectant, wherein said phosphates according to any one of sixth to eight features include disodium hydrogenphosphate, sodium dih3 drogenphosphate, trisodium phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, or potassium dihydrogenphosphate, 15 [0016] A tenth feature of the process of the present invention is to employ the process for producing an aqueous chlorous acid solution for use as disinfectant, wherein said borates according to any one of sixth tc ninth features include sodium borate or potassium .0 borate, [0017] A clcvnth feature of the pro ess of the present invention is to employ the process for producing an aqueous olorous acid solution for use as disinfectant, wherein said 25 organic acids according to any or e cf third to tenth features include succinic acid, citric acid, malic acid, acetic acid, or lactic a id. [0018] A twelfth feature of the pioc ss of the present invention is to employ the 30 process for producing an aq cois chlorous acid solution for use as disinfectant, wherein said organic salts accprd.ng to any one of third to eleventh features include sodium succinate, potassium sudciratc, sodium citrate, potassium citrate, sodium ma late., potassium palate, sodium acetat, potassium acetate, sodium lactate, potassium lactate, or calcium lactate '5 5 ADVANTAGIOUS EFFECT OF THE INVENTION [00191 According to the present invention, there can be provided an aqueous chliorous acid solution which is highly disinfecta t and stable. so that it will not need to be prepared 5 imnincdiately before being used and it is made possible to be preserved for future use. In addition, it prevents generation of e lorine dioxide so as to be harmless to human body and can be used without anxiety. [0020] 1o Moreover, the aqueous chlorous acid solution produced in accordance with the present invention can maintain prolonged stability and can be marketed as disinfectant commodities. BRIEF DESCRIPITON OF THE DR WINGS 5 [0021] Figure 1 shows the results of spectrophotomctric measurement of sample A conducted on the day of preparation. Figure 2 shows the results of spcctro. hotometric measurement of sample A conducted on day 10 of preparation. '0 Figure 3 shows the results of spectror hotometric measurement of sample A conducted on day 20 of preparation. Figure 4 shows the results of spectrophotometric measurement of sample A conducted on day 30 of preparation. Figure 5 shows the results of spectrophotometric measurement of sample B conducted on the 25 day of preparation. Figure 6 shows the results of spectrophotometric measurement of sample B conducted on day 10 of preparation. Figure 7 shows the results of spectrophotonetric rneasuremcnt of sample B conducted on day 20 of preparation. 0 Figure 8 shows the results of spectrop otomctric measurement of sample 13 conducted on day 30 of preparation. Figure 9 shows the results of spectrophotometric measurement of sample C conducted on the day of preparation. Figure 10 shows the results of spectrophotometric measurement of sample C conducted on 1 5 hour of preparation. Figure 11 shows the results of spectrophotometric measurement of sample C conducted on day I of preparation. .I ^kAI I -~ I I-- - I - - - -~ - VU I -JLL UIVV 6 Figure 12 shows the results of spectrophotometric mcas'urement of sample C conducted on clay 5 of preparation, uenn fsrpeCcnutdo Figure 13 shows the results of spectrophotometric measurcmcnt of sample D conducted on the day of preparation r s Figure 14 shows the results of spectrophotomctric measurement of sample D conducted on cl ay 10 of prepara ti oil Figure 15 shows thc results ofspcroplotonetric measurement of sample D conducted oi day 20 Of preparation. Figure 16 shows the results o' spectrophotometric measurement of sample A conducted on 0 day 30 of preparation, Figure 17 compares the time-course changes in pH values of the aqueous chlorous acid solutions of Examples 2, 3, and 4 and conventional ASC solution. BEST MODE FOR CARRING OUT THE INVENTION 5 [0022] Hereinafter, the preferred em odiments of thc present invention will be described with reference to accompanying figu es and tables. EXAMPLE I [0023] Example 1 of the present invention provides a process for producing an aqueous chlorous acid (HC0 2 ) solut on for use as disinfectant. According to this process, sulfuric acid (HzS0 4 ) or aqueous soluLion thereof is added to an aqueous sodium chlorate (NaC*103) solution to create acidic conditions, thereby generating chloric acid (-1C10 3 ), and the resulting ch oric acid undergoes a reduction reaction with an excess amount of hydrogen peroxide t> produce chlorous acid (-1C10 2 ). The essential hemica reactions of this production proce ss are presented by the folly wing equations A and B: [0024] [CHEMICAL FORMULA 1] 2NaC 103 142S04 2 H C 0 3+Na2SO4 (E uationA ) HC103 +1-202 I-C102+H20 +02- (EquationB ) [0025] Equation A indicates tha i chloric acid is generated by addition of an amount and concentration of sulfuric acid
(H
2 S0 4 ) or aqueous solution thereof appropriate for maintaining the pH of the aqueous sodium chlorate (NaC10 3 ) solution at 2.3 to 3.4, while sodium ions arc eliminated concurrently, .,rrrn-s - -- U IIJLL IVUU I [0026] Then, equation B shows that chloric acid (HC103) undergoes a reduction reaction wt hydrogen peroxide (H22 Iod)udroe euto rec i wit hydion ot (11202) to produce chlorous acid (HC102). This reaction requires the s addition of at cast an ao t of hydrogen peroxide (or aqueous solution thereof) stoichioxeericaly required for the reduction reaction. Otherwise, the reaction will yield only chlorine dioxide. [0027] 0 [CHEMICAL FORMULA 2] HC 103+ H202 --> 2 C102+ H20 +02 T (Equationc) 2 C 102+1-1202 2 HC102+02 T ( Equation D) 2 C102+1-120 <=> HC02:HC103 ( Equation ) 2 H C10.2>H20 - C1203 ( Equatioii F) [0028] In cases where chlorine dioxide is generated, it will be convrtd to chlorous acid by a series of reactions shown by equations C to F. [0029] Chlorous acid (HC102) thus produced possesses the propensity to decompose quickly to chlorine dioxide gas or chlorine gas by interaction s among a plurality of chlorOu acid molecules or by the presence of chloride (CI) ions, hypochlorous acid 1-C1O), or other reductive agents. It is, therefore, necessary to provide a long-acting chorus acid (HC10 2 ) preparation effective for use as disinfectant [0030] Under these circumstances, it is necessary to provide a process for producing a stable, long tating aqueous chtorous acid (Nd 02) solution; and this is achieved by creating a transitional state to delay the progress of the decomposition reaction through the addition of at least one compound selected from the group consisting of inorganic and organic acids and salts or a combination thereof, to the aqueous chlorous acid (HC102) solution produced according to the process described in Example I above. This process is embodied in Examples 2,3, and 4. EXAMPLE 2 [0031] Specifically, according to Example 2, the aqueous chlorous acid (HC102) solution cl-tONO T Ino) . I.:. _ - V l )44 IVVV I 8 produced according to the process described in Example I is mixed with inorganic acid(s) or organic salt(s), or more specifically, at least one compound selected from the group consisting of carbonates and hydroxides or a combination thereof. 5 EXAMPLE 3 (0032] Also, according to Example 3, the aqueous Solution produced in Example 2 is mixed with at least onc compound selected 'from the group consisting of inorganic and organic acids and salts or a combination thereof 10 EXAMPLE 4 [00331 Moreover, according to Example 4, the aqueous solution produced in Example I is mixed with at least one compound selected from the group consisting of inorganic and 5 organic acids and salts or a combination thereof. [0034] As for the above, inorganic acids can be mentioned as well as carbonic acid, phosphoric acid, boric acid, and sulfuric acid. For the inorganic salts, carbonates and hydroxides - can be 0 mentioned as well as phosphates and borates. More specifically, the carbonates include sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate; the hydroxides include sodium hydroxide and potassium hydroxide; the phosphates include disodium hydrogenphosphate, sodium dihydrogenphosphate, trisodium phosphate, tripotassium phosphate, dipotassium hydrogenphosphate, and potassium .5 dihydrogenphosphate; and the borates include sodium borate and potassium borate. Moreover the above organic acids include succinic acid, citric acid, malic acid, acetic acid, and lactic acid; and appropriate examples of the organic salts include sodium succinatc, potassium succmate, sodium citrate, potassium citrate, sodium malate, potassium palate., sodium acetate, potassium acetate, sodium lactate, potassium lactate, and calcium lactate. 0 [0035] In Examples 2, 3, and 4, the following transitional states are temporarily created: + C10 2 ' Na-C102, K'+ C 102' K-C102, 5 H*'+ C ICOz#1-C102. These states contribute to delaying the progress of the conversion of chlorous acid
(:HC]O
2 ) to chlorine dioxide (C10 2 ), which enables the fonnation of an aqueous V | JLL IVVV I 9 chlorous acid solution that is capable of sustaining chlorous acid (HClO 2 ) for an extended time and releases a reduced amount of chlorine dioxide (C102). [0036] 5 Now, the lower the p-i value (the :tronger the acidity) of a chlorine oxide, the stronger its bactericidal potential is known to be. The tables below show the results of experiments on the relationship between pH values and bactericidal powers. in these experiments, a pathogenic Eschcrichia coil strain (0157:1-17) was used as the Lest microbc. Sodium chlorite (Wako ]urc Chemical Industrics, Ltd., Osaka, Japan, 80%) was 10 used as the test chlorine oxide. Ci ric acid (Wako, 98%), lactic acid (Wako, 85% to 92%), and acetic acid (Wako, 99.7%) were used as an activator. Thirty-mL aliquots of an aqueous sodium chlorite solution (0.5 g/L, pH 9.8) were adjusted to pH 2.0, 3.0. 4.0, 5.0, 6.0, 7.0, and 8.0 by addition of citric acid, lactic acid, or acetic acid. Phenol index measurement procedure was employed for assessment of the bactericidal effect. Ten-mL aliquots of the 15 test solutions diluted as appropriate were transferred to test tubes, allowed to warm for at least 5 minutes in a thermostatic water bath set at 20 0 C 1 PC. Then, I-mL aliquots of the test microbe preparation, prc-warmed in a similar manner, were added to the test tubes, and sampling was performed by use of a platinum loop at 2.5, 5, 10, and 15 minutes after the addition. The sampled microbial mixtures were inoculated into a 20 normal bouillon medium and incubated at 37 0 C for 48 hours, Bacterial growth was visually observed; positive growth was designated as '+' and negative growth as [0037) [TABLE 1] 25 Bactericidal potential for sodium chlorite solution: Activator Citric acid pH 3.0 4,0 5.0 6.0 7.0 8.0 tiG(in.) _ 2.5 + + + + 5 - - + + + 10 - - - + + + 15 - - + + 30 cHONO 1 102 Substmel n Me 2f 'e 10 {0038] [TABLE 2] Bactericidal potential for sodium chlorite solution : Activator Lactic acid pi 3,0 4.0 5. 0 6.0 7.0 8.0 timehmin.) 2.5 + + + 4 5 - - + + + + 10 - + + + 15 - - - + 5 [0039] [TABLE 3] Bactericidal potential for sodium chl rite solution: Activator Acetic acid 10 pH 3.0 4.0 5.0 6.0 7.0 8.0 time(min.) 2. 5 - - + + + + 5' - - + + + + 10 - - - + + + 15 - - - - +.~ + [0040] 15 As shown in the tables above, anueous sodium chloritc solutions having pH 7.0 or higher fell short of completely eradicating the test E. coli strain in 15 minutes. However, complete eradication was achieved i 2.5 minutes when the p-X was adjusted to 4.0 or lower, in 10 minutes when the pH was adjusted to 5.0, and in 15 minutes when the pH was adjusted to 6.0. These findings de onstrate a higher bactericidal potential for sodium 20 chloride solution having a more acidic pH value. These findings also demonstrate that the difference in the type of activator poses no significant difference in the bactericidal power of sodium chlorite solution, cHONOI 102_Substituted 23 May 2013.rtf 11 [0041] Thus. chloritc solution exhibits a stronger bactericidal effect when it is more acidic. However, when its pH is strongly acidic, for example, at a value in the order of 2.0, its applicable areas 5 in food industry are limited because of its negative effects such as denaturation of protein components of the sterilized food items. [0042] [CHEMICAL FORMULA 3] 10 5 C 1 02-± 4H" -> 4C 1 02 + 5C1+ 2 1420 (a) (5Na C 1 02+ 4CI3COOH --- > 4C 102+ 4 CH 3 COONa + N a C I +2H20) 3C 10f 2C103 C 1- (b) (3Na C 1 02 2 N a C 1 03 Na C 1) Autodecomposition is C102 C1 -1- 2 0 (c) [0043] The above Chemical Formula 3 represents the decomposition of chlorite compounds in an acidic solution. When the solution has a lower (more acidic) pH 20 value, the decomposition of chlorite compounds is enhanced, that is, the absolute kinetic rates of the reactions represented by above equations (a), (b), and (c) become elevated. Practically, with a decreased pH value, the dominance of the reaction products of equation (a) is reduced. However, with a decrease in pH, the total decomposition percentage shifts to a larger value, resulting in an increased amount of C102 25 (chlorine dioxide) generated. Therefore, the lower the pH value of the aqueous solution becomes, the more likely it makes the disinfectant harmful to human health and disinfection operation awkward due to the release of toxic and irritating C10 2 gas, although it improves the bactericidal and bleaching potentials. Also, a lower p-I solution renders chlorous acid more unstable, and thereby enhances the conversion of chlorous acid to 30 chlorine dioxide. As a result, the duration of the bactericidal activity is reduced. [0044] Therefore, when an aqueous chlorous acid (HC1 02) solution is mixed with any of the above mentioned inorganic acids, inorganic salts, organic acids, or organic salts, the solution should 35 be adjusted to pH 3.2 to 7.0, from the viewpoint of suppressing chlorine dioxide release and maintaining the bactericidal activity. The pH-I values should reach as high as allowed by the requirements on the bactericidal activity conditions within the above range. This contributes to producing an aqueous chlorous acid solution emitting a reduced amount of c-TONO I 102 Substituted 23 Ma) 2013,rtP 12 chlorine dioxide (C102) by slowing the conversion of chlorous acid to sodium chlorite (NaC10 2 ) while maintaining chlorous acid (HC10 2 ) for an extended time, (0045] 5 As described below, to confirm the effects of the present invention, the following samples were prepared and subjected to measurement. First, a chlorous acid solution prepared according to Example I was mixed with I mol/L sodium carbonate to pH 5.7. The solution (corresponding to an aqueous chlorous acid solution prepared according to Example 2) was added to a 0.05 mol/L sodium 10 borate/succinate buffer (pH 5.7) to give a 3% chlorous acid content. To sum up, this solution (corresponding to an aqueous chlorous acid solution prepared according to Example 3) was prepared by adding to an aqueous chlorous acid solution an inorganic salt compound, followed by addition of a combination of an inorganic salt and an organic salt as buffer, This solution was termed sample A. 15 [0046] Second, the chlorous acid solution prepared according to Example I was mixed with I mol/L sodium carbonate to pH 5.7. Subsequently, this solution was mixed with deionized water to give a 3% chlorous acid content. In other words, this solution (corresponding to an aqueous z0 chliorous acid solution prepared according to Examplc 2) was prepared by adding to an aqueous chlorous acid solution an inorganic salt compound. This solution was tanned sample B. [0047] 25 Moreover, an aqueous solution containing 25.0 % chlorous acid (Wako, 80%) was mixed with I mol/L solution of citric acid (Wako, 98%) to p1-I 2.6. The resulting solution was mixed with deionized water to give a 3% chlorous acid content. This process corresponds to a conventional technique for preparing above-mentioned ASC solution. This solution was termed sample C. 30 [0048] Furthermore, the chlorous acid solution prepared according to Example 1 was added to 0.05 mol/L sodium boratc/succinate buffer (pH 6.8) to give a final pH of 5.7 and a chlorous acid content of 3%. In other words, this solution (corresponding to an aqueous chliorous acid 35 solution prepared according to Example 4) was prepared by adding to an aqueous chlorous acid solution a combination of an inorganic salt and an organic salt as buffer. This solution was termed sample D. cHONOI 102_Substitutcd 23 May 2013.rtf 13 [0049] The time-course stability of chlorous acid (HC10 2 ) in each sample was compared by measurement of UV spectra and molecular content. The measurement samples all 5 contained 3% chlorous acid (HC102). UV spectrum measurement was conducted on a spectrophotometer adjusted to provide an absorbance of approximately 1 at the wavelength of maximunr absorption when used to measure sample solutions diluted with an appropriate volume of ion exchanged water. Measurement of chlorous acid content was performed by the iodometric titration method described hereafter. Samples were l0 aerated in an airtight container to eliminate chlorine dioxide dissolved in the samples. Then, approximately 10 g of each sample was measured accurately, and water was added to make the volume precisely 100 mL. These solutions were designated as test solutions. A volume of each of the test solutions containing approximately 0.06 g of chlorous acid (HC102) was accurately measured, placed in an iodine flask, mixed with 12 mL of 15 sulfuric acid (3-+100), and water was added to make the volume approximately 55 nL. Immediately after adding 4 g of potassium iodide to the solution, the flask was stoppered and kept in a dark place for 15 minutes, Titration was performed by using 0.1 mol/L sodium thiosulfate and a starch indicator, and the amount of chlorous acid in the solution was determined by the formula; 1. mL of 0.1 mol/L sodium thiosulfate solution= 20 0.001711 g of HC102. Separately, blank tests were conducted for correction. The test solutions were stored in a dark place for preservation tests. Aliquots of the test solutions were subjected to measurements of chlorous acid content, UV absorption, and pH values immediately after preparation and at 1, 2, 3, 24, 48, 72, 96, 120, 240, 480, and 720 hours after preparation. 25 [0050] Consequently, the spectrometric measurement results identified two absorption peaks in the wavelength range of 248 to 420 ni immediately after preparation of samples A, B, C, and D: one absorption peak in the vicinity of 260 nm corresponding to acidic chlorite ions (H4* + 30 C102) and the other absorption peak near 350 nm corresponding to chlorine dioxide (C102). These results demonstrate the presence of chlorous acid (HC102) (Figs. 1, 5, 9, and 13), because they indicate the concurrently ongoing chain of reactions shown in Chemical Formula 4 involving chlorous acid (HC10 2 ), chlorine dioxide (C102), and acidic chlorite ion (C102-). 35 c-ION01 102_Substiuted 23 May 2013.rtf 14 [0051] [CHEMICAL FORMULA 4] Chain of reactions of chlorous acid, chlorine dioxide, and acidic chlorite ion H+ C 102- <=> HC102 e. 0102 -- C102 5 [0052] For sample C, although the presence of two peaks was clearly recognizable at 1 hour (Fig. 10), the two peaks became less visible at 24 hours (Fig, 11), and thereafter the measurement results presented a single peak near 350 nm (Fig. 12). These changes 10 indicate the progress of conversion of chlorous acid to chlorine dioxide. [0053] Meanwhile, samples A, B, and D showed two peaks near 260 and 350 nm after 30 days (Fig. 4, 8, and 16). It follows that the aqueous chlorous acid solution of the present invention 15 provides more stable chlorous acid solutions than conventional disinfectants. [0054] Of these, sample B, as shown in Figs. 5, 6, 7, and 8, which illustrate the time course of 20 changes in UV absorption, demonstrates marked changes in the shape of the two peaks as the period extends to 10, 20, and 30 days. On the contrary, samples A and D maintained on day 30 the two peaks observed on day 0 (Figs. 1, 2, 3, 4, 13, 14, 15, and 16). These results suggest little change over time for samples A and D in the composition of chlorous acid, chlorite ions, chlorine dioxide, and other chlorine oxide 25 compounds. it is apparent, therefore, that Example 2 (involving addition of inorganic salt), Example 3 (involving addition of inorganic salt followed by addition of inorganic acid and salt), and Example 4 (involving addition of organic acid and salt) preserve the initial composition of the solution better than conventional disinfectants. 30 [0055] Table 4 depicts the changes over time in chlorous acid content. The results show that sample C (ASC) lost half of the initial chlorous acid content within 2 hours after preparation, and lost it almost completely on day 4. On the other hand, samples A, B, and D retained much of the initial chlorous acid content even on day 30. Therefore, the aqueous chlorous acid cHONO I 102_Substituted 23 May 2013.rtf 15 solutions of the present invention are superior to conventional disinfectants, because they maintain chlorous acid content for an extended time. [0056] 5 Of these, samples A and D maintained the initial chlorous acid content (prepared on day 0) for 30 days. This indicates that the aqueous chlorous acid solutions prepared according to Examples 3 and 4 possess the highest capacities of maintaining the stability of chlorous acid over time. 10 (0057] [TABLE 4] Comparison of maintenance of chlorous acid (HC10 2 ) in solutions (HC102 content 3%) r Ohr lhr 2hr 3hr 24hr 49hr 72hr 96hr 120hr 240hr 430hr 720hr *. + + +I + + + + + + + + 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3,0 3.0 2.9 2.8 2.7 4. *14~ - +. +I +F + +~ SamploB 3.2 3.2 3.2 3.2 3.1 3.0 .,0 2.9 2.9 2.6 2.3 2.1 SampliC 3.0 1.9 1.6 1.4 1.0 0.9 0.9 ND ND ND ND ND +. + 4 .I 4. + + +. -4- 1. -4. SampIeD 3,0 3.0 3.0 3.0 2.9 2.9 2.9 3.0 3.0 2.9 2.9 27 15 Lower figures in each cell represent HC102 content (%), and upper signs designate UV measurement results: +, presence of two absorption peaks identified at 260 and 350 nm; -, presence of a maximum absorption peak identified only in the vicinity of 350 nm. 20 [0058] Fig. 17 shows the time course of changes in pH values for samples A, 13, C, and D. The pH value of sample B, which was initially set at 5.7, temporarily elevated to the order of 6, and gradually decreased thereafter. On the other hand, sample A, which had an initial pH value of 25 5.8, retained the pH level after 30 days, indicating the effectiveness of the buffering action. Likewise, sample .D, which had an initial pH value of 5.7, maintained the pH level after 30 cHONOI102_SubstuLted 23 May 2013.rtf 16 days, indicating the effectiveness of the buffering action. These results indicate that pH can be stabilized either by directly adding a buffer agent to the aqueous solution or by adding a buffer agent after pH adjustment with sodium carbonate. 5 [0059] As can be seen from the above, the aqueous solution obtained by acidifying an aqueous sodium chloride solution, as in the process for producing ASC, rapidly loses the chlorous acid (HC 102) content by a highly accelerated conversion of the acid to chlorine dioxide (C102). The aqueous solutions obtained according to the present invention, however, adjust the 10 shortage or excess of hydrogen ions resulting from oxidation-reduction reactions of chlorine oxides while buffering the pH within a narrow range. Consequently, stabilization of pH contributes to preserving the transitional state of chlorous acid (HC10 2 ): H* + C-10 2 " HC10 2 , and this allows for maintaining the chlorous acid content by sustaining the stochiometric balance of molecules and ions in the aqueous 15 chlorous acid solution. These observations argue that the process of the present invention exhibits superiority in providing an aqueous solution that has a high bactericidal activity and an extended stability of chlorous acid (HC102). 2o [0060] The present invention achieves a long-term stabilization of chlorous acid, which has a high bactericidal potential. It will, therefore, enable commercial distribution of aqueous chlorous acid solutions on the market that have not been successfully circulated as sales products. It will contribute to widespread social adoption of chlorous acid, which is useful as 25 disinfectant. [0061] So 'far, the present invention has been explained based on embodiments with reference figures and tables. However, the present invention is not restricted to these 30 implementations, and can be practiced in various modes within the scope of the accompanying claims, INDUSTRIAL APPLICABILITY [0062] 35 The aqueous chlorous acid solution obtained according to the present invention can be applied for bleaching, removal of bloodstains, and other similar uses, in addition to bactericidal purposes. cHON01 102_Substituted 23 May 2013.rtf