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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rise in the pH of an unfrozen solution in ice due to the presence of NaCl and promotion of decomposition of gallic acids owing to a change in the pH
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Rise in the pH of an unfrozen solution in ice due to the presence of NaCl and promotion of decomposition of gallic acids owing to a change in the pH

机译：由于存在氯化钠，冰中未冻结溶液的pH升高，并且由于pH的变化而促进了没食子酸的分解

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Oxidative decomposition of gallic acid occurs in alkaline solutions but hardly arises in acidic solutions. We have found that the addition of sodium chloride promotes the decomposition of gallic acid caused by freezing even under neutral and acidic conditions. Even at pH 4.5, gallic acid was decomposed by freezing in the presence of NaCl; however, in the absence of NaCl, it was hardly decomposed by freezing at pH lower than 7. Chloride ions are more easily incorporated in ice than sodium ions when the NaCl solution is frozen. The unfrozen solution in ice becomes positively charged, and as a result, protons transfer from the unfrozen solution to the ice. We measured the pH in the unfrozen solution which coexists with single-crystal ice formed from a 5 mmol dm(-3) NaCl solution and determined the pH to be 8.6 at equilibrium with CO2 of 380 ppm or 11.3 in the absence of CO2 compared to pH 5.6 in the original solution. From the model calculation performed for gallic acid solution in the presence of 5 mmol dm(-3) NaCl, it can be estimated that the amount of OH- transferred from the ice to the solution corresponds to 1.26 x 10(-5) mol dm(-3). The amount of OH-transferred is concentrated into the unfrozen solution and affects the pH of the unfrozen solution. Therefore, the pH in an unfrozen gallic acid solution in ice becomes alkaline, and the decomposition of gallic acid proceeds. It is expected that other base-catalyzed reactions in weakly acidic solutions also proceed by freezing in the presence of NaCl without the need for any alkaline reagents.
机译：没食子酸的氧化分解在碱性溶液中发生，而在酸性溶液中几乎不发生。我们发现，即使在中性和酸性条件下，氯化钠的加入也会促进由冷冻引起的没食子酸的分解。即使在pH 4.5下，没食子酸也会在NaCl存在下冻结而分解。然而，在没有氯化钠的情况下，在低于7的pH值下冷冻几乎不会分解。冷冻氯化钠溶液时，氯离子比钠离子更容易掺入冰中。冰中的未冷冻溶液带正电，结果质子从未冷冻的溶液转移到冰中。我们测量了与5 mmol dm（-3）NaCl溶液形成的单晶冰共存的未冷冻溶液中的pH值，并确定在380 ppm的CO2平衡下pH为8.6或在无CO2的情况下与11.3相比。原始溶液的pH值为5.6。根据在5 mmol dm（-3）NaCl存在下对没食子酸溶液进行的模型计算，可以估计从冰转移到溶液中的OH-的量相当于1.26 x 10（-5）mol dm （-3）。转移的OH的量浓缩到未冷冻溶液中，并影响未冷冻溶液的pH值。因此，在冰中的未冷冻的没食子酸溶液中的pH变为碱性，并且没食子酸进行分解。可以预期，在弱酸性溶液中的其他碱催化反应也可以通过在NaCl存在下冷冻来进行，而无需任何碱性试剂。

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