Chemistry of inorganic compounds – Halogen or compound thereof – Chlorine dioxide
Reexamination Certificate
1999-03-04
2001-05-15
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Chlorine dioxide
C252S187210
Reexamination Certificate
active
06231830
ABSTRACT:
FIELD OF INVENTION
The invention relates to a broad field, being as broad as are the properties of chlorine dioxide. For example, in the field of dentistry alone, it can be used as a biofilm control to prevent the buildup of plaque which is responsible for tooth decay, as a whitener maintenance, as an oral/periodontal irrigant and as a breath freshener.
DESCRIPTION OF THE PRIOR ART
Chlorine dioxide (ClO
2
) has many beneficial properties. Chlorine dioxide is an efficient oxidant. Because it readily reacts with substances (phenolics and sulfides) known to cause taste and odor problems, chlorine dioxide is a widely used treatment for drinking water. Chlorine dioxide has other beneficial properties resulting from its ability to maintain its oxidizing power and antimicrobial properties over a wide pH range. For example, chlorine dioxide is effective against viruses, bacteria, and protozoan cysts. Chlorine dioxide has been shown to be effective in controlling cryptosporidium (Peters, J.; Mazas, E.; Masschelein, W.; 1989, “Effect of Disinfection of Drinking water with Ozone or Chlorine Dioxide on Survival of Cryptosporidium parvum Oocyst”. Appl. Environ. Microbiol., 55(6):1519-1522);(Korich, D.; Mead, J.; Madore, M.; Sinclair, N.; Sterling. C. 1990, “Effects of Ozone, Chlorine Dixoide, Chlorine and Monochloramine of Cryptosporidium parvum Oocyst Viability”. Appl. Environ. Microbiol., 56:1423-1428.);(Finch, G.; Liyanage, L.; Belosivic, M. 1995, “Effect of Chlorine Dioxide on Cryptosporidium and Giardia. In InProc. 3rd International Symposium on Chlorine Dioxide Use in Drinking Water, Wastewater and Industrial Applications. CMA, USEPA, and AWWARF.) which causes severe gastrointestinal problems (and even death) in AIDS and immunocompromised individuals. In contrast, chlorine is not effective in treating water sources containing cryptosporidium.
Other applications include its use as a bleaching agent, disinfectant, deodorant, and biofilm control. Even though it is not well understood, microbial cell walls and microbial membranes, being different from human cells, rupture when ClO
2
penetrates them at concentrations even below one part per million (PPM) whick is equivalent to one milligram per liter (mg/L). Alteration of electrolytic permeability, and metabolic processes quickly follow, destroying the microbes of which no immunity results.
Studies have been undertaken to determine if different oxychlorine species result in significant genetic or carcinogenic hazards to humans. Meier et al. studied the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite and sodium chlorate on the induction of chromosomal aberrations and spermhead abnormalities in mice (Environ. Sci. Technol., 28,592 (1994). Only the highly reactive hypochlorite ion (chlorine) resulted in a weak positive effect for mutagenic potential. The other compounds, including chlorine dioxide and sodium chlorite, failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Vilagines et al. attribute the relatively innocuous effect of chlorine dioxide to its inability to produce halomethanes, unlike hypochlorite and chlorine (Proc. AWWA Disinfect. Semin., 24 pp (1977); Chem. Abs. 93,173513f.). This observation has more recently been confirmed by Richardson et al in an extensive study of the reaction of chlorine dioxide with water borne organics by the EPA (Environ. Sci. Technol., 28, 592 (1994)).
Two subchronic 90-day animal toxicity studies have been reported (Chemical Manufacturers Association (CMA). 1992, “Study Report of a 90 Day Feeding Study for Sodium Chlorite in the Rat”. Arlington Va.);(Harrington, R.; Romano, R.; Gates, D.; Ridgeway, P. 1995, “Subchronic Toxicity of Sodium Chlorite in the Rat”. Jour. Amer. Coll. Toxicol., 14(1):21-33) for sodium chlorite. The general toxicological findings include: acute oral LD
50
=150 mg/kg, chronic no effect level=7.4 mg/kg, chronic mild effect level=19 mg/kg. Based on these data, a normal use pattern of a mouthrinse product (5,000 mg/L NaCLO
2
concentration, 3×per day, 90% expectoration) for a 150
1
b person maintains a >150 fold safety margin for acute toxicity effects. If the same person were to completely swallow the mouthrinse, a >20 fold safety margin is still maintained.
Richter, according to U.S. Pat. No. 5,738,840 uses hypochlorite to produce chlorine dioxide by using a molar ratio of metal hypochlorite salt to chlorite salt of up to 10:1. But, the stoichiometry of the reation of sodium chlorite with sodium hypochlorite to produce chlorine dioxide predicts that 2 moles of chlorite ion are required to react with 1 mole of hypochlorite ion to generate 2 moles of chlorine dioxide:
2NaCLO
2
+NaOCL+H
2
O→2CLO
2
+2NaOH+NaCL
This means that under ideal conditions without the possibility of side reactions, a 2:1 molar ratio of sodium chlorite to sodium hypochlorite will produce 2 moles of chlorine dioxide. However, solutions of sodium hypochlorite can decompose over time (Adam, L; Bubnis, B.; Gordon, G. “Minimizing Chlorate Ion Formation in Drinking Water When Hypochlorite Ion Is the Chlorinating Agent”, American Water Works Association—Research Foundation (AWWA-RF ISBN 0-89867-781-5) Denver Colo., 1994,195pp.). Thus, one purpose for maintaining an excess hypochlorite ion concentration is to ensure that the concentration of hypochlorite ion exceeds the minimum stoichiometric required after 9 months storage. A drawback to this embodiment is that when the hypochlorite ion concentration is in large excess, the resulting solution after mixing can have as much as 2,000 times more hypochlorite ion (chlorine) than chlorine dioxide (details are in next paragraph). It is well documented that chlorine disinfection is potentially accompanied by unwanted side reactions leading to the formation of trihalomethanes and possible long-term health risk. Decomposition of hypochlorite ion can also result in a build-up of chlorate ion, an unwanted by-product.
3OCl—→ClO
3
—+2Cl—
So, the reason for Richter's higher molar ratio is because the half-life of NaOCl is approximately 30 days. In order to have a product on a retail shelf for a period of 6-9 months, with its separate activator vial, this higher molar ratio is necessary. This excess hypochlorite ion means that initially, when the hypochlorite ion is fresh, there is more hypochlorite ion than generated chlorine dioxide. Using a 0.2% (2000 mg/L) solution of sodium chlorite with 10 times as much sodium hypochlorite or 2% (20,000 mg/L), and generating approximately 10 mg/L of chlorine dioxide, one will have 2,000 times more hypochlorite ion than chlorine dioxide. This makes Richter's product a chlorinator, rather than an oxygenator (if his product is used soon after its formulation), with resulting trihalomethanes, mentioned above as a suspect health risk. Another disadvantage of the Richter patent, is that after the 9th month, when sodium hypochlorite levels are in the 5-40 mg/L range it infringes the Oikawa et al., patent. A further disadvantage, is that after 12 months when hypochlorite ion levels are nil to non-existent, no activation occurs at all.
Oikawa et al., U.S. Pat. No. 5,165,910 uses hypochlorite ion to produce chlorine dioxide. They discovered that much less hypochlorite ion than a molar ratio of 1:2 of hypochlorite to sodium chlorite is all that is necessary to produce from 15-30 mg/L from sodium chlorite concentrations up to 20,000 mg/L. They state, as well noted among those skilled in the art, that chlorine dioxide can be a deodorizer. This would include using ClO
2
on substrates from refrigerators to oral cavities, which raises genuine concerns about the validity of the Richter patent, which is used in oral cavities.
Ratcliff, U.S. patents e.g. U.S. Pat. Nos. 4,689,215; 4,696,811; 4,837,009, and McNicholas et al., U.S. Pat. No. 3,271,242 use a deodorizing oral rinse of approximately 1.25-<2.0 mg/L ClO
2
. Theses patents, although they generate some ClO
2
, would c
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