DRAMATIC EFFECT OF THE SPECIFIC SOLVATION ON THE REACTIVITY OF QUATERNARY AMMONIUM FLUORIDES AND POLY(HYDROGEN FLUORIDES), (HF)-NORMAL.F-, IN MEDIA OF LOW POLARITY
DRAMATIC EFFECT OF THE SPECIFIC SOLVATION ON THE REACTIVITY OF QUATERNARY AMMONIUM FLUORIDES AND POLY(HYDROGEN FLUORIDES), (HF)-NORMAL.F-, IN MEDIA OF LOW POLARITY
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DOI：
10.1021/jo00263a013
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发表时间：
1989-01-20
影响因子：
3.6
通讯作者：
RAMPOLDI, A
中科院分区：
文献类型：
--
作者：
LANDINI, D;MAIA, A;RAMPOLDI, A
定量研究了在低极性溶剂中，有限数量的水分子的特定溶剂化作用对己基4 N + F ~-的氟阴离子的本征反应性（亲核性和碱性）的影响。通过将阴离子的特定水合n从8.5降低到0，亲核性增强外推到约3个数量级。这种增强比在相同条件下通过使其他卤化物脱水获得的增强高得多（~ 100倍）。所发现的无水阴离子的亲核性标度，F-> CT> Br-> T，反映了偶极非质子溶剂和气相中众所周知的那些。在相同水合范围内的比较表明，氟阴离子的碱性比其亲核性更受特定溶剂化作用的影响。将该研究扩展到季铵聚（氟化氢）Q+（HF）nF-，其中n= 1，2，提供了以下反应性标度：F-> HF 2-> H2 F3-。通过与氟化氢以顺序F·HF 2 '<H2 F3'的相互作用，F”阴离子的稳定性增加，解释了在聚（氟化氢）的情况下观察到的相对于假设的无水氟化物的反应性低得多的反应性（F '：HF 2'：H2 F3”= 8.5 X 101 2345：1.2 X 102：1）。这也解释了这些阴离子对特定水合的不同敏感性，其以相同的顺序降低：F“> HF 2”> H2 F3“。离子氟化物作为有机氟衍生物合成中的氟源、1作为碱辅助反应中的质子提取物2以及作为有机甲硅烷基化合物反应的促进剂3的重要性是有据可查的。特别是，亲脂性的季鎓氟化物被发现是在非质子有机溶剂中进行反应的首选试剂，即使是低极性的。1 '3在这些介质中，庞大的季盐产生松散的离子对，其中阴离子未溶剂化，因此具有高度反应性。第4、5项
A quantitative study of how the intrinsic reactivity (nucleophilicity and basicity) of the fluoride anion of hexyl4N+ F" is affected in solvents of low polarity bythe specific solvation of a limited number of water molecules has been performed. The nucleophilicity enhancement is extrapolated to be about 3 orders of magnitude by reducing the specific hydration n of the anion from 8.5 to 0. Such enhancement is much higher (~ 100 times) than that obtained, under the same conditions, by dehydrating the other halides. The nucleophilicity scale of anhydrous anions found, F"» CT> Br"> T, reflects those well-known in dipolar aprotic solvents and in the gas phase. Comparison in the same hydration range shows that the basicity of the fluoride anion is much more affected by specific solvation than is its nucleophilicity. Extension of this study to quaternary ammonium poly (hydrogen fluorides) Q+(HF) nF~, where n= 1, 2, provides the following reactivity scale: F"» HF2"> H2F3". The increasing stabilization of F" anion, byinteraction with hydrogen fluoride in the sequence F «HF2'< H2F3~, accounts for the much lower reactivity observed in the case of poly (hydrogen fluorides) with respect to that of the hypothetical anhydrous fluoride (F': HF2': H2F3"= 8.5 X 101 2345: 1.2 X 102: 1). This also explains the different sensitivity of these anions to the specific hydration which decreases in the same order: F'» HF2"> H2F3'.The importance of ionic fluorides as sources of fluorine in the synthesis of organofluorine derivatives, 1 as proton abstractors in base-assisted reactions, 2 and as promotors of organosilyl compound reactions3 is well documented. In particular, lipophilic quartemary onium fluorides are found to be reagents of choice for carrying outreactions in aprotic organic solvents even of low polarity. 1'3 In these media, bulky quaternary onium salts give rise to loose ion pairs in which the anions are unsolvated andhence highly re-active. 4, 5