Proton condition phosphoric acid

Protonation of pyrrole, furan and thiophene derivatives generates reactive electrophilic intermediates which participate in polymerization, rearrangement and ring-opening reactions. Pyrrole itself gives a mixture of polymers (pyrrole red) on treatment with mineral acid and a trimer (146) under carefully controlled conditions. Trimer formation involves attack on the neutral pyrrole molecule by the less thermodynamically favored, but more reactive, (3-protonated pyrrole (145). The trimer (147) formed on treatment of thiophene with phosphoric acid also involves the generation of an a-protonated species. 

Stereoselective l.4-reduction oi the 1.3-butadiene system to olefin 57 lakes place tinder the conditions of the Birch reduction. Intramolecular protonation of the intermediate carbanion at the 18-position to give 57 occurs with high selectivity syn to the hydroxymethy-iene group Conversion into phosphoric acid derivative 58 and cleavage of the phosphoric acid amide group under (he conditions of the Bcnkeser reduction provides compound 5921 Fluonde ion causes the release of free p-amyrin (1) in a final step I Li, NH3(iyTllF (1/1.75), -78 C 93%. 

Strong acids have low pK values weak acids have high pK values. For example, formic acid is moderately strong pfC = 3.75. The pK values for other adds and proton-donating compoimds are phosphoric acid (H3PO4), 2.14 acetic acid (CH3COOH), 4.76 carbonic acid (H2CO3), 3.8 ammonium ion (NH ), 9.25 and bicarbonate ion (HCOj), 10.2. The values for K and pK refer to reactions that are reversible in aqueous solution and have attained a condition of equilibrium. 

The base-neutralizing capacity of the phosphoric acid system with reference to the equivalence point, / = 2 (solution of Na2HP04 with the proton condition 2[H3P04] -h [H2P04 ] -h [H ] = [POj ] -h [OH" ]), is given by... 

Many anionic species appearing in the solubility products may also be involved in protonation equilibria in solution, such as those of phosphoric acid H2P04 H+ + HPO42 HPO42 P04 -I- H + etc. When the prospects for the formation of a solid phase under certain solution conditions are investigated, the activity, or concentration, of the particular anionic species specified in the solubility product must be known, not only total phosphate or total calcium, etc. The data in Table 3.3 show that, at pH > 5, the most stable (i.e., insoluble) solid calcium phosphate is hydroxyapatite. 

State the proton condition for a solution of phosphoric acid, H3PO4, in pure water. 

To devise polymeric systems that can conduct protons with little or no water, in addition to possessing good chemical and electrochemical stability above 100 °C, is very challenging and has been the focus of intensive research over the last decade. One of the most successful strategies has been to replace the water with less volatile compounds. For example, strong 0x0 acids, e.g. phosphoric acid or sulfuric acid, have been complexed with basic polymers such as polybenzimidazole (PBI). PEMs based on PBIs doped with phosphoric acid have been used successfully at temperatures well above 100 °C under very dry conditions. However, there is still a risk that the acid will be partly leached out, especially at low temperature and high humidity. 

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