2- -ascorbic acid

Acetic acid is lipid soluble and able to rapidly diffuse through the plasma membrane, a factor that has a dramatic effect on the pH, of a cell (Greenacre et al., 2003). Intracellular acidification may, however, play a role in acids with short aliphatic chains (such as acetic acid), and much higher concentrations (20-80 mM) are needed for growth inhibition (Hazan, Levine, and Abeliovich, 2004). 

Ascorbic Acid [50-81-1] (1) is the name recognized by the lUPAC-IUB Commission on Biochemical Nomenclature for Vitamin C (1). Other names are L-ascorbic acid, L-xyloascorbic acid, and L-// fi (9-hex-2-enoic acid y-lactone. The name 

L-Ascorbic acid biosynthesis in plants and animals as well as the chemical synthesis starts from D-glucose. The vitamin and its main derivatives, sodium ascorbate, calcium ascorbate, and ascorbyl palmitate, are officially recognized by regulatory agencies and included in compendia such as the United S fates Pharmacopeia/National Formula (USP/NF) and the Food Chemicals Codex (FCC). 

The most significant chemical characteristic of L-ascorbic acid (1) is its oxidation to dehydro-L-ascorbic acid (L-// fi (9-2,3-hexodiulosonic acid y-lactone) (3) (Fig. 1). Vitamin C is a redox system containing at least three substances L-ascorbic acid, monodehydro-L-ascorbic acid, and dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid and the intermediate product of the oxidation, the monodehydro-L-ascorbic acid free radical (2), have antiscorbutic activity equal to L-ascorbic acid. 

The reversible oxidation of L-ascorbic acid to dehydro-L-ascorbic acid is the basis for its known physiological activities, stabiUties, and technical apphcations (2). The importance of vitamin C in nutrition and the maintenance of good health is well documented. Over 22,000 references relating only to L-ascorbic acid have appeared since 1966. 

It was treated as a venereal disease, with disastrous results. 

Ascorbic acid, known more familiarly as vitamin C, is used not only as on acidulant but also as a stabiliser within the soft drinks system, and its antioxidant properties serve to improve the shelf-fife stability of flavour components. Many of the ingredients used in flavourings are susceptible to oxidation, particularly aldehydes, ketones and keto-esters. Ascorbic acid shields these from attack by being preferentially oxidised and lost, leaving the flavour component unaffected. 

Another disadvantage of ascorbic acid is its effect on some colours in the presence of light. In the case of azo-colours, such as carmoisine, a fight-catalysed 

It is the flavour of a drink that provides not only a generic identity but also its unique character. This part of the sensory profile is responsible for pleasing and attracting the consumer. For example, having decided on a cola drink, the consumer will be able to differentiate between colas by virtue of the background flavouring components, which collectively provide a reference point to which the consumer can return, consciously or not, on future occasions whenever a particular1 brand of drink is selected. 

A flavouring consists of a mixture of aromatic substances carefully balanced to convey the right message to the sensory receptors of the consumer. The preparation of such a mixture is a serious matter the soft drinks flavourist, like the perfumer, must be well versed in the technique, be creative and be able to translate ideas into a practical solution. 

Depending on the desired profile, the flavourist may add to, or subtract from, a central theme until an acceptable blend is reached. 

Ascorbic acid (as-KOR-bik AS-id), or vitamin C, is one of the most important dietary vitamins for humans because it plays a crucial role in building collagen, the protein that serves as a support structure for the body. It is a water-soluble vitamin, which means that the body excretes any excess vitamin C in the urine and cannot store a surplus. For that reason, humans must consume vitamin C in their daily diets. Vitamin C is found in many fruits and vegetables and most kinds of fresh meat. Citrus fruits, such as oranges and lemons, are especially rich in the compound. 

Ascorbic acid. Red atoms are oxygen white atoms are hydrogen and black atoms are carbon. Gray sticks are double bonds, publishers 

Scurvy was common enough that many people searched for its cause and cure. Sailors were especially vulnerable to 

The vitamin C produced by plants and by synthetic methods are chemically identical and have identical effects in the human body. 

American chemist Linus Pauling (1901-1994) believed that very large doses of vitamin C could prevent and cure the common cold and 

L-Ascorbic acid (vitamin C, ASA) is produced on a scale of 80 kt a-1 worldwide it is used in food supplements, pharmaceutical preparations, cosmetics, as an antioxidant in food processing and a farm animals feed supplement [145]. It is synthesized in vivo by plants and many animals, but not by primates, including Man, or microbes. 

The industrial production of ASA has been dominated by the Reichstein-Grussner process (Fig. 8.29) [146] since the mid 1930s. Although the intermedi- 

The final oxidation step of the primary alcohol at C-l in L-Srb requires acetone protection, which is carried out in a standard textbook way in the presence of an excess of sulfuric acid. The oxidation at C-l has been accomplished in a number of ways [147] it seems that nowadays aerobic oxidation in the presence of palladium or platinum is preferred. Deprotection, requiring additional sulfuric acid, affords 2KLG, which is transformed into ASA via esterification and lac-tonization. Alternatively, the diacetone derivative of 2KLG can be converted directly into ASA by treatment with HC1 in an organic solvent. 

Obvious shortcomings of the Reichstein procedure are the modest yield (50— 60% from L-sorbose is often mentioned) and the acetone protection-deprotection sequence. Overall, 1 ton of sodium sulfate is produced per ton of ASA (acetone is recycled). It should be noted, on the other hand, that the catalytic hydrogenation and microbial oxidation steps are in all respects highly efficient, even by today s standards [153] and impeccably green [154]. 

Grafting a microbial oxidation of L-Srb into 2KLG on the Reichstein process, which is an obvious improvement to the latter, results in a two-stage fermentative process (Fig. 8.30a). China was the first country to develop [155] and universally adopt such a process [156]. Its production costs are said to be 30% lower that those of the traditional process [157]. Cerestar has claimed an 89% yield (100 g I.1 STY 78 g IT1 d ) of 2KLG from L-Srb in a mixed culture of G. oxy-dans and Bacillus thuringiensis [151]. Such processes have now been introduced in Europe, for example by KGS (Krefeld, Germany) and DSM (Dairy, Scotland). 

BP Ascorbic acid JP Ascorbic acid PhEur Acidum ascorbicum USP Ascorbic acid 

C-97 cevitamic acid 2,3-didehydro-L-t reo-hexono-l,4-lactone E300 3-oxo-L-gulofuranolactone, enol form vitamin C. 

Ascorbic acid is used as an antioxidant in aqueous pharmaceutical formulations at a concentration of 0.01-0.1% w/v. Ascorbic acid has been used to adjust the pH of solutions for injection, and as an adjunct for oral liquids. It is also widely used in foods as an antioxidant. Ascorbic acid has also proven useful as a stabilizing agent in mixed micelles containing 

Ascorbic acid occurs as a white to light-yellow-colored, nonhygroscopic, odorless, crystalline powder or colorless crystals with a sharp, acidic taste. It gradually darkens in color upon exposure to light. 

Acidity/alkalinity pH = 2.1-2.6 (5% w/v aqueous solution) Density (bulk)  

CHEMICAL NAME = ascorbic acid CAS NUMBER = 50-81-7 MOLECULAR FORMULA = C6H806 MOLAR MASS =176.1 g/mol COMPOSITION = C(40.92°/o) H(4.58%) 0(54.50%) 

MELTING POINT = 192°C BOILING POINT = decomposes DENSITY = 1.95 g/cm3 

Until the 20th century, it was thought that scurvy was confined to humans. Most plants and animals have the ability to synthesize ascorbic acid, but it was discovered that a limited number of animals, including primates, guinea pigs, the Indian fruit bat, and trout, also lack the ability to produce ascorbic acid. In vertebrates, ascorbic acid is made in the fiver from glucose in a four-step process. Each step requires a specific enzyme and humans lack the enzyme required for the last step, gulonolactone oxidase. 

Sodium, potassium, and calcium salts of ascorbic acids are called ascorbates and are used as food preservatives. These salts are also used as vitamin supplements. Ascorbic acid is water-soluble and sensitive to light, heat, and air. It passes out of the body readily. To make ascorbic acid fat-soluble, it can be esterified. Esters of ascorbic acid and acids, such as palmitic acid to form ascorbyl palmitate and stearic acid to form ascorbic stearate, are used as antioxidants in food, pharmaceuticals, and cosmetics. 

As noted, vitamin C is needed for the production of collagen in the body, but it is also essential in the production of certain hormones such as dopamine and adrenaline. Ascorbic acid is also essential in the metabolism of some amino acids. It helps protect cells from free radical damage, helps iron absorption, and is essential for many metabolic processes. The dietary need of vitamin C is not clearly established, but the U.S. National Academy of Science has established a recommended dietary allowance (RDA) of 60 mg per day. Some groups and individuals, notably Linus Pauling in the 1980s, recommend dosages as high as 

Reduction of chromic acid by ascorbic acid proceeds in a two- 

Catalytic oxidation of ascorbic acid has been reported to occur in the cobalt(11)-glycylclycine-dioxygen system at pH 7. 5 - 9.0, together with the formation of a cobalt(III) complex [1]. 

Detailed kinetic studies on the oxidative dehydrogenation of ascorbic acid (H A) to dehydroascorbic acid (DHA) by molecular oxygen 

Remarkably, the kinetic behavior differs in these two background electrolytes. 

In KNO solution the rate law given by Equation (6) has been found 

The reaction of dichromate with ascorbic acid monitored by ESR spectroscopy results in the detection of Cr(V) species, but at higher pH values generation of 

The reactions of both trisoxalato ferrate(III) and trisoxalatocobaltate-(III) with ascorbic acid have been examined. Evidence is presented in the reaction with Fe(III) for the formation of an intermediate prior to a relatively slow inner-sphere electron transfer reaction, which is independent of pH, ascorbic acid concentration, and ionic strength. For the cobalt complex, the pH (8-10) of the reaction medium leads to reaction with the doubly deprotonated ascorbate ion for which the rate constant is 20 s at 25 °C. Complexation of Fe(III) by 

The reaction between the ferrocenium cation and ascorbic acid was used as a comparative reaction in the study of copper(II) oxidation of ascorbic acid in acetonitrile/water mixtures. Small quantities of acetonitrile do not affect the ferrocenium reaction but do increase the redox potential for the redox couple, 

Ascorbic acid has been used as a sacrificial reductant in the [Ru(bpy)3] photosensitizer Ti02/Pt reduction of H2O to molecular hydrogen.The reaction proceeds according to the scheme in equations (58)-(63), where ecB stands for an 

The anti-cancer drug ds,cis,traw5-[Pt(IV)(NH2Pr )2Cl2(OH2)2] has been postulated to react through the reduced Pt(II) species. The rate of reduction by ascorbic acid has been measured and equilibrium kinetics observed with kf = 0.103 and kb = 0.78 X 10 Ms at 25 °C. From the data, a two-electron redox process has been proposed.  

The anaerobic oxidations (to dehydroascorbic acid, A) by several chelate complexes of Fe(III) have a stoichiometry 

The chelates employed were diethylenetriaminepentaacetic acid (DTPA), 1,2- 

The rate sequence is determined by the entropy term and correlates with the oxidation potential of the chelate complex, indicating an outer-sphere electron transfer. 

The anaerobic V(IV) oxidation of ascorbic acid (H2A) in the pH range 1.75-2.85 follows a rate law 

A two-equivalent process is proposed, yielding V(II). In the presence of oxygen 

Other reports have discussed the reactions of L-ascorbic acid with fatty acids in strong sulphuric acid, 4-toluidine, and various oxidizing agents.  

However, while some reports (Schwartz and Parks, 1974) indicate a correlation between the oxidation of ascorbic acid and the development of an oxidized lipid flavor, Smith and Dunkley (1962c) concluded that the oxidation of ascorbic acid alone cannot be used as an index of lipid oxidation. They reported that although ascorbic acid oxidation curves for homogenized and pasteurized milk were similar, the homogenized samples had a significantly lower tendency to develop oxidized flavor. 

Several workers have shown that a high concentration of ascorbic acid added to liquid milk inhibits oxidation. Chilson (1935) suggested that added ascorbic acid acts as a reducing agent, which is oxidized more readily than milk fat. Bell et al. (1962) suggested that addition of L-ascorbic acid to cream produced a medium less conducive to oxidation by lowering the oxidation-reduction potential. Addition of an adequate level of surface-active ascorbyl palmitate to milk products may retard lipid oxidation by orientation at the lipid-aqueous interface where it intercepts free radicals (Badings and Neeter, 1980). 

The effect of P-carotene on human serum albumin oxidation by 2,2 -azobis (2-amidinopropane) dihydrochloride under 15,150, and 760 torr of O2 to form carbonyls was related to O2 tension, antioxidant concentrations and interaction between mixtures of antioxidants (Zhang and Omaye 2000). High concentration of P-carotene produced more protein oxidation in the presence of high O2 tension by a prooxidant mechanism. Mixtures of P-carotene, a-tocopherol and ascorbic acid provided better protective effects on protein oxidation than any single compound. 

The staurosporine (200 nM)-induced apoptotic damage in chick embryonic nemones was reduced by 1 nM-lO M retinoic acid in a concentration-dependent manner by depressing the production of reactive oxygen species (Ahlemeyer and Krieglstein 1998). 

Inhibition by a-tocopherol of protein kinase C has been reviewed in Azzi et al. (1992, 1995, 1996) and Newton (1995). Such an inhibition is not caused by a direct binding of a-tocopherol to the enzyme but by preventing its activation via phosphorylation (Tasinato et al. 1995). a-Tocopherol exerts its action independently of its free-radical scavenging capacity and most probably by interacting with a yet not characterised receptor molecule in smooth muscle cells (Boscoboinik et al. 1991, 1994, 1995). a-Tocopherol prevents uniquely protein kinase C-o phosphorylation and its functional activation. 

Influences of ATP, ADP, and Cyclic Nucleotides on the Formation of Reactive Oxygen Intermediates 

Ascorbic acid is the major water-soluble antioxidant present in cells and plasma. It will quench reactive oxygen species as 02 (Nishikimi 1975), HO (Bielski et aL 1975), and O2 (Bodannes and Chan 1979). On the other hand, it reduces Fe to Fe and thus will stimulate Fenton catalysis of H2O2 — HO. Hydroperoxide-dependent lipid peroxidation in rat liver microsomes was enhanced by ascorbic acid (Laudicina and Marnett 1990). Ascorbic acid protected cardiac microsomes against lipid peroxidation and oxidative damage (Mukhopadhyay et al. 1993). It diminished both luminol- and lucigenin-amplified H2O2 derived chemiluminescence in concentrations 10 (Klinger et al. 1996). 

Vitamins are organic molecules that mainly function as catalysts for reactions in the body. A catalyst is a substance that allows a chemical reaction to occur using less energy and less time than it would take under normal conditions. 

Vitamin C is also important as it helps protect the fat-soluble vitamins A and E, as well as fetty acids from oxidation. It is therefore a reducing agent and scavenger of radicals (sink of radicals). Radicals, molecules with unpaired electrons, are very harmful to the body as a result of their high reactivity, which may induce mutations and possibly cancer. Vitamin C, being an excellent source of electrons, can therefore donate electrons to free radicals such as hydroxyl and superoxide and quench their reactivity. 

CO J has been utilized to generate a disulfide radical anion in a synthetically altered human a-haemoglobin chain. The electron of the disulfide radical anion then transfers to the protein heme group at a nominal distance of approximately 12 A with an intramolecular rate constant of 188 23 s at room temperature and pH 7. Similarly, CO J reduces the [Fe(CN)6] modified [ferricytochrome C551 Ru(III)] with a rate constant of 1.9 x 10 s to give the stable Fe Ru and 

The rhodium(II) radical [Rh(dmgH)2PPh3], formed by laser photolysis of the corresponding dimer, is oxidized by a range of cobalt(II) complexes which have coordinated halides. Electron transfer is believed to occur through a ligand-mediated pathway and the reaction rate is dependent upon the choice of halide. In an examination of the Ti(III)-induced cyclization of epoxyolefins, a mechanism has been invoked which involves a metal-centered radical.  

The nickel(IV) oxime, bis(6-amino-3-methyl-4-azahexa-3-ene-2-one oxime)nickel(IV), and the nickel(III) oxime, (15-amino-3-methyl-4,7,10,13-tetraazapentadeca-3-ene-2-one oxime)nickel(III), complexes react with hydro-quinone. Proton-related equilibria for both the nickel complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the Ni(III) complex there is evidence of an inner-sphere process. The [NiL(TCCat)] complex (TCCatH2 = tetrachlorocatechol L = 2,4,4-trimethyl-1,5,9-triazacyclododec-l-ene) forms a 1 1 adduct with tetrachloro-1,2-benzoquinone. Spectroscopic evidence suggests that this compound can be described formally as a quinone adduct of a Ni(I)-semiquinone moiety arising from inner-sphere ligand oxidation. The crystallographically determined structure (11) is shown below. Several copper complexes of a vareity of semiquinones also exist in solution in equilibrium with the corresponding catechol complexes.  

With the Ru dimers, [ Ru(bpy)2 2(M-L)], ESR data indicate that these binuclear semiquinone complexes are near the borderline between anion radical complexes and metal-centered mixed-valence species/ The thermal reaction between [W(CO)6] and tetrachloro-l,2-benzoquinone in toluene produces the tris(quinone) tungsten complex/ Features of the molecule indicate that the quinones are coordinated as catecholate ligands and the tungsten ions are in a formal +6 oxidation state. Quinones trapped within a polymeric electrode film can act as electron sinks and/or sources. IJ/I and [FeCCN) ] have been utilized as charge-release mediators. 

Np(VI) reduction by Kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone) has been studied. The rate constant and activation parameters, at /u. = 1.0 M and T = 25X, are k = 1.63 0.08 s AH = 82.7 3.4 kJ moP and AS = 34 12 J K mol L A mechanistic scheme was proposed to account for these data. A variety of oscillations has been observed in the Co, Br -catalyzed O2 oxidation of cyclohexanone. A kinetic model based on the formation of Co is proposed. Benzophenone ketyl has been employed as an electron transfer initiator in the selective catalytic ligation of [ /i-(CF3)2C2 Co2(CO)6L]. Rapid incorporation of labeled CO may be observed. 

74UW VO 2 73KT 

HO OH 1 1 HOCH2CHCHCH2OH C,H 0, meso-Butane-1,2,3,4-tetraol (meso-4 10 4 -erythritol) L 

Other references 41S,57RL,60AT,63NF,66IR,70C 

Other references 57RL,63NF,66IR,67CBa,70C 

Hirsch, P. Kovdfi, and V. KovdCik, J. Carbohydrates, Nucleosides, Nucleotides, 1974,1,431. T. Kitahara, T. Ogawa, T. Naganuma, and M. Matsui, Agric. and Biol. Chem. (Japan), 1974, 38, 2189. 

Evidence has been presented to show that dehydro-L-ascorbic acid (obtained by oxidation of L-ascorbic acid) exists mainly as a bicyclic hydrated species (304) i.e. 3,6-anhydro-L-Ary/(7-hexulono-l,4-lactone hydrate) in aqueous solution.  

Brimacombe s group has described an attempt to prepare relatives of leucodrin (305) and conocarpin (306) by intramolecular Michael cyclization of the enolate anion obtained by demethylation of 2-0-(jE)-cinnamoyl-5,6-0-isopropylidene-3-0-methyl-L-ascorbic acid (307). However, treatment of (307) with lithium iodide in DMSO furnished the isomeric 2-C-methyl derivative (308) by remethyla-tion of the enolate anion by the liberated methyl iodide. 

The formation of dicarboxylic acids from L-ascorbic acid is noted in Chapter 2. 

Utsumi, Y. Kirino, and T. Kwan, Chem. Pharm. Bull. Japan), 1975, 23, 1516, 1632. 

Reagents i, MejCtOMela-H- - ii, Ac20-py iii, H+ iv, BzCl(l mole)-py v, CrOj-py vi, NaBH4 vii, MeONa-MeOH 

L-ascorbic acid 2-[ S]suIphate having a high specific activity has been obtained by sulphation of 5,6-O-isopropylidene-L-ascorbic acid with [ S]sulphur trioxide in DMF the presence of pyridine promoted considerable side-reactions, perhaps initiated by hydrolysis of the 5,6-0-isopropylidene group.  

Dehydro-L-ascorbic acid afforded the l,2-bis(phenylhydrazone) of the tricarbonyl compound (325), in addition to 3-hydroxy-2-pyrone, on heating with phenylhydrazine hydrochloride. Similar treatment of L-t/ireo-pentosulose (L-xylosone) gave the same bis(phenylhydrazone), but it was established that L-xylosone is not the main precursor of (325) in the oxidative degradation of dehydro-L-ascorbic acid.  

The crystal structure of the C-benzyl derivative (326) of a keto-iorm of L-ascorbic acid has been determined.  

The kinetics of autoxidation of L-ascorbic acid catalysed by Cu+ ions have been determined. Important features of the autoxidation, including the formation of hydrogen peroxide as a stable intermediate and of a ternary complex containing oxygen, copper(i), and ascorbate, were discussed. Reagents that complexed Cu+ ions were shown to inhibit the autoxidation. Cu+ apparently remains formally univalent throughout the entire reaction cycle and acts as an electron carrier between two substrate molecules. Other workers have shown that the metal-ion-catalysed oxidation of L-ascorbic acid at alkaline pH values is inhibited by superoxide dismutase. The kinetics and mechanism of the oxida- 

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M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

Sorbitol is manufactured by the reduction of glucose in aqueous solution using hydrogen with a nickel catalyst. It is used in the manufacture of ascorbic acid (vitamin C), various surface active agents, foodstuffs, pharmaceuticals, cosmetics, dentifrices, adhesives, polyurethane foams, etc. 

Akkermans R P, Wu M, Bain C D, Fidel-Suerez M and Compton R G 1998 Electroanalysis of ascorbic acid a comparative study of laser ablation voltammetry and sonovoltammetry E/eofroana/ys/s 10 613... 

METHOD 4 [110, 111] - guaiacol and cupric perchlorate (Cu(CI04)2)-ascorbic acid (that s vitamin C, bubba ) are mixed in an appropriate solvent under oxygen atmosphere in a flask to give about 30% catechol. 

Formate is an excellent hydride source for the hydrogenolysis of aryl halides[682]. Ammonium or triethylammonium formate[683] and sodium formate are mostly used[684,685]. Dechlorination of the chloroarene 806 is carried out with ammonium formate using Pd charcoal as a catalyst[686]. By the treatment of 2,4,6-trichloroamline with formate, the chlorine atom at the /iiara-position is preferentially removed[687]. The dehalogenation of 2,4-diha-loestrogene is achieved with formic acid, KI, and ascorbic acid[688]. 

Since allylation with allylic carbonates proceeds under mild neutral conditions, neutral allylation has a wide application to alkylation of labile compounds which are sensitive to acids or bases. As a typical example, successful C-allylation of the rather sensitive molecule of ascorbic acid (225) to give 226 is possible only with allyl carbonate[l 37]. Similarly, Meldrum s acid is allylated smoothly[138]. Pd-catalyzed reaction of carbon nucleophiles with isopropyl 2-methylene-3,5-dioxahexylcarbomite (227)[I39] followed by hydrolysis is a good method for acetonylation of carbon nucleophiles. 

Uronic acids are biosynthetic intermediates m various metabolic processes ascorbic acid (vitamin C) for example is biosynthesized by way of glucuronic acid Many metabolic waste products are excreted m the urine as their glucuronate salts... 

Probably the most extensively applied masking agent is cyanide ion. In alkaline solution, cyanide forms strong cyano complexes with the following ions and masks their action toward EDTA Ag, Cd, Co(ll), Cu(ll), Fe(ll), Hg(ll), Ni, Pd(ll), Pt(ll), Tl(lll), and Zn. The alkaline earths, Mn(ll), Pb, and the rare earths are virtually unaffected hence, these latter ions may be titrated with EDTA with the former ions masked by cyanide. Iron(lll) is also masked by cyanide. However, as the hexacy-anoferrate(lll) ion oxidizes many indicators, ascorbic acid is added to form hexacyanoferrate(ll) ion. Moreover, since the addition of cyanide to an acidic solution results in the formation of deadly... 

Masking by oxidation or reduction of a metal ion to a state which does not react with EDTA is occasionally of value. For example, Fe(III) (log K- y 24.23) in acidic media may be reduced to Fe(II) (log K-yyy = 14.33) by ascorbic acid in this state iron does not interfere in the titration of some trivalent and tetravalent ions in strong acidic medium (pH 0 to 2). Similarly, Hg(II) can be reduced to the metal. In favorable conditions, Cr(III) may be oxidized by alkaline peroxide to chromate which does not complex with EDTA. 

Br , citrate, CE, 2,3-dimercaptopropanol, dithizone, EDTA, E, OH , NagP30io, SCN , tartrate, thiosulfate, thiourea, triethanolamine BE4, citrate, V,V-dihydroxyethylglycine, EDTA, E , polyphosphates, tartrate Citrate, CN , 2,3-dimercaptopropanol, dimercaptosuccinic acid, dithizone, EDTA, glycine, E, malonate, NH3, 1,10-phenanthroline, SCN , 820 , tartrate Citrate, V,V-dihydroxyethylglycine, EDTA, E , PO , reducing agents (ascorbic acid), tartrate, tiron... 

Acetate, (reduction with) ascorbic acid + KI, citrate, V,V-dihydroxyethylglycine, EDTA, F , formate, NaOH + H2O2, oxidation to CrOJ , NagP30io, sulfosalicylate, tartrate, triethylam-ine, tiron... 

Ascorbic acid + KI, citrate, CN , diethyldithiocarbamate, 2,3-dimercaptopropanol, ethyl-enediamine, EDTA, glycine, hexacyanocobaIt(III)(3—), hydrazine, E, NaH2P02,... 

Acetylacetone, ascorbic acid, citrate, C20j, EDTA, F , H2O2, hydrazine, mannitol, NagP30io, NH2OH HCI, oxidation to molybdate, 8CN , tartrate, tiron, triphosphate... 

Ti Ascorbic acid, citrate, F , gluconate, H2O2, mannitol, NagP30io, OH , SOJ , sulfosalicylic... 

Chromate(VI) Reduction with arsenate(III), ascorbic acid, hydrazine, hydroxylamine, sulfite, or thiosul-... 

Ibrahim and co-workers developed a new method for the quantitative analysis of hypoxanthine, a natural compound of some nucleic acids. " As part of their study they evaluated the method s selectivity for hypoxanthine in the presence of several possible interferents, including ascorbic acid. 

If the weak acid is monoprotic, then the FW must be 58.78 g/mol, eliminating ascorbic acid as a possibility. If the weak acid is diprotic, then the FW may be either 58.78 g/mol or 117.6 g/mol, depending on whether the titration was to the first or second equivalence point. Succinic acid, with a formula weight of 118.1 g/mol is a possibility, but malonic acid is not. If the analyte is a triprotic weak acid, then its FW must be 58.78 g/mol, 117.6 g/mol, or 176.3 g/mol. None of these values is close to the formula weight for citric acid, eliminating it as a possibility. Only succinic acid provides a possible match. 

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