Tetrabasic acids

In case of a tetrabasic acid H4B the following protolysis equiUlaia are established  

The mathematical equations of the functions are given in the Appendix. The plotting of all species in the diagram can be made with the help of the line equations given in the Appendix. Following the procedures for the mono- to tribasic acids, this is stepwise made in Figs. 26, 27, 28, 29, 30, and 31. 

The line ofHsB has a slope of —2 forp Tas pH p Ta4 (HB is dominating). For pH p/sTa4 (B is dominating) the slope is —3. In some cases (e.g., example in Fig. 28) that line is already outside the range of the diagram. 

For the derivation of equations that allow an approximative calculation of pH values, it is again necessary to refer to the reactions of a monobasic acid HB in water  

The following quantities have to be considered chb Cjj o+ oh -Mathematics demand for the determination of n variables to have a system of n independent equations that do not contradict each other. Hence, four such equations are needed here. These are the already introduced Eq. (5) for the acidity constant, Eq. (9) for the ion product of water, Eq. (18) for the amount balance, and Eq. (49) for the charge balance  

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In the absence of metal coordination the compound would titrate as a typical tetrabasic acid having a stepwise titration curve as shown in Figure 6. 

In its unreacted form EDTA is a tetrabasic acid represented by... 

Being a tetrabasic acid, EDTA dissociates in solution to give four different ionic species, H3Y, H,Y2, Hy3-, Y4-, the relative amounts of which will depend upon the pH of the solution. The proportion of any species present is represented by its a value, an idea introduced in Chapter 3. 

When selenic acid and molybdic acid are heated together on a water-bath for several days a compound of composition Mo03.Se03 is formed, which is obtainable as a crystalline mass,4 and which with a little water yields a hydrate, having the formula Mo03.Se03.2H20 when dried at 110° C. This compound has the properties of a tetrabasic acid. 

The properties of he tetrabasic acid prepared from dibroiusuceinic ester by Perjcin differed from the acids obtained in other ways. Buchner repeated this work,however,and got only the jcnown acid. (Of.note on page HS. ) The 1,1,2,3 acid is also obtained by the action of barium hydroxide on dlcyancyclopropane 1,2,3 trlcarboxylate. ... 

According to A. Rosenheim and J. Pinsker, the f.p. of aq. soln. of hypophosphoric acid and its salts resemble those of pyrophosphoric acid and. its salts, and correspond with the formula H4P20a but it has been argued that this molecular weight really represents associated mols. (H2P03)2 and not the mol. H4P2Oa of a tetrabasic acid. 

The heats of neutralization of pyrophosphoric acid with sodium hydroxide show that the acid is probably tetrabasic, for H. Giran found that the first two displaceable hydrogen atoms have strongly marked acidic functions, and the other two have feeble acidic functions. The graphic formula (HO)2=PO.O.PO=(OH)2 is in agreement with the tetrabasicity of the acid, and with the work of W. A. Tilden and R. E. Barnett. 0. Favel also found pyrophosphoric acid behaved like a tetrabasic acid towards soluble blue indicator. The confident assumption that the phosphorus is quinquevalent precludes H. Wichelhaus formula (H0)2P.0.0.0.P(0H)2 but, before the formula (H0)2P0.0.P0(0H)2 can be definitely accepted, it must be shown that the formulae... 

The properties of silicomolybdic acid are like those of silicotungstic acid. Toward indicators having a pH of 5 to 6 it behaves as a tetrabasic acid. With phenolphthal-ein as the indicator it requires eight equivalents for titration in cold solution but twenty-four equivalents for titration at 100°C. With tertiary organic bases it is tetrabasic. 

Pyrophosphoric Acid (p. 171) may be titrated as a dibasic acid to pH =4-0 using methyl yellow, etc. as before also as a tetrabasic acid using phenolphthalein, thymolphthalein or thymol blue in the presence of barium salt. Electrometric titrations have also been performed.1... 

Stable complexes with EDTA and its related compounds are formed with most polyvalent metal ions, hence their wide use in chelation therapy. Pure EDTA is a white crystalline solid with a relative molar mass of 292.1. It is a weak, tetrabasic acid which is sparingly soluble in water. EDTA is not metabolized in the human body and is effectively non-biodegradable in the environment. 

H4P207 (Pyro or Dipolyphosphoric Acid) It is a tetrabasic acid but gives rise to only two series of salts e.g., Na2H2P207 and Na4P207. It also responds to ammonium molybdate test which is characteristic for ortho-phosphates. 

Being a tetrabasic acid, EDTA dissociates in solution to give four different ionic species, HsY", HY ", Y ", the relative amounts of which... 

Hrat 259 nm and pH 7-0. Freely sol in water- A % aq soln has a pH of about 2 and is stable at 0 for several hrs-ATP is a tetrabasic acid and after hydrolytic cleavage it is hexabasic. It is usually pptd as the dibarium salt with 4 or 6 mols of water of crystn which can be removed by prolonged drying at 100° over PjOj and in a vacuum. The anhydr salt is stable, but the hydrated salt slowly decomp forming 5 -adenylic acid and barium pyrophosphate, For use the hari-um salt is converted to the sodium or potassium salt by treatment with sodium or potassium sulfate in HCl soln. At pH 6,8 -7,4 the Na salt is stable hi aq soln provided ihe product is pure. Ba2+ catalyzes breakdown. Injectable solns of the disodium salt are marketed as Triftoffm, Adei phos Circttlen "Kyorin Atenen. 

Accordingly, the dihydrate should be a tetrabasic acid if the acidity were due to the hydrogen of the hydroxyl, but this is contrary to experimental facts. Similarly, osmium and ruthenium oxides might be expected to show a greater tendency to form acids than sulfur trioxide since they contain more oxygen atoms with double linking to combine with the water. It is evident, therefore, that a knowledge of the co-ordination number as well as of the atomic valence is necessary in order to determine the basicity of an acid. 

The last-mentioned cation behaves as a tetrabasic acid, whose four values were reported. Complexes of the biologically important purine bases adenosine and tetra-acetyl-adenosine have been synthesized... 

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