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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Neptunium(iv)-hydroxamate complexes: their speciation, and kinetics and mechanism of hydrolysis
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Neptunium(iv)-hydroxamate complexes: their speciation, and kinetics and mechanism of hydrolysis

机译：Neptunium（IV） - 羟肟酸盐复合物：它们的形象，和水解动力学和机制

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Simple hydroxamic acids such as acteohydroxamic acid (AHA) have been identified as suitable reagents for the control of Pu and Np in advanced separation processes for nuclear fuel reprocessing such as the Advanced PUREX or UREX based recycle processes, due to their ability to strip the tetravalent form of Pu and Np from tri-butyl phosphate into nitric acid. However, both free and metal bound hydroxamates are known to undergo acid catalysed hydrolysis at low pH, the kinetics of which must be characterised before implementation of PUREX/UREX based reprocessing flowsheets. In support of this implementation, a comprehensive thermodynamic and kinetic model that describes both the complex speciation and hydrolysis of AHA in the presence of Np(iv) has been developed. The model has two unique features: (i) in the case of the hydrolysis reaction kinetics, the model includes the hydrolysis of not only free AHA but also both the mono- and bishydroxamato-Np(iv) complexes; (ii) for the associated speciation calculations, the model explicitly includes the ionic strength dependence of not only the mono- and bishydroxamato-Np(iv) complexes but also the mono- and bisnitrato neptunium(iv) and monohydroxoneptunium(iv) complexes. For the latter three species, respective SIT coefficients of epsilon(1,NO3) = -0.13 +/- 0.03 kg mol(-1), , epsilon(2,NO3) = -0.37 +/- 0.13 kg mol(-1), epsilon(1,OH) = -0.36 kg mol(-1) and log(10)K01,OH = -1.23 were also determined. Using experimental data from a series of kinetic studies on the Np(iv)-AHA system, this model has been used to determine the rate constants for hydrolysis of mono- and bis-acetohydroxamatoneptunium(iv) at 25 degrees C for the first time. These were found to be 3.5 x 10(-5) +/- 2.5 x 10(-5) dm(3) mol(-1) s(-1) and 1.9 x 10(-3) +/- 1.3 x 10(-3) dm(3) mol(-1) s(-1), respectively. Comparison of these values with the rate constants for hydrolysis of free AHA indicates that complexation of AHA with Np(iv) increases the rate of hydroxamate hydrolysis - an observation that we attribute to the electron withdrawing effect of the metal centre within the Np(iv)-AHA complex increasing the susceptibility of the AHA carbonyl carbon to nucleophilic attack, the accepted first step in its mechanism of hydrolysis.
机译：简单的异羟肟酸如acteohydroxamic酸（AHA）已被确定为用于Pu和Np个的在先进分离过程核燃料控制合适的试剂再处理诸如高级PUREX或基于UREX再循环工艺中，由于其剥离四价能力从磷酸盐到硝酸三丁基Pu和Np个的形成。然而，游离和结合金属异羟是已知的在低pH下经历酸催化的水解，其中动力学必须执行PUREX / UREX基于再加工工艺流程的前来表征。为了支持这一实现，它描述的NP（IV）的存在既复杂的形态和AHA的水解全面的热力学和动力学模型已经研制成功。该模型具有两个独特的功能：（ⅰ）在水解反应动力学的情况下，该模型不仅包括游离AHA的水解，而且两者的单和bishydroxamato-Np个（Ⅳ）配合物; （ii）用于关联的形态的计算，该模型明确地不仅包括单 - 的离子强度依赖和bishydroxamato-Np为（IV）配合物，而且单和bisnitrato镎（iv）和monohydroxoneptunium（IV）配合物。对于后者三个品种，ε的各个SIT系数（1，NO3）= -0.13 +/-0.03公斤摩尔（-1），，ε（2，NO 3）= -0.37 +/-0.13公斤摩尔（-1） ，ε（1，OH）= -0.36公斤摩尔（-1）和日志（10）K01，OH = -1.23还测定。从一系列的Np个（ⅳ）-AHA系统上动力学研究的利用实验数据，该模型已被用于确定的水解速率常数单 - 和双 - acetohydroxamatoneptunium（ⅳ）在25℃的第一次。这些被发现是3.5×10（-5）+/- 2.5×10（-5）DM（3）摩尔（-1）S（-1），1.9×10（-3）+/- 1.3×10 （-3）DM（3）摩尔（-1）S（-1），分别。与速率常数的自由AHA的水解这些值的比较表明AHA与Np个该络合（ⅳ）增加异羟肟酸水解的速率 - 的观察，我们将其归因于电子的Np个内撤回金属中心的作用（ⅳ） -AHA复杂增加AHA羰基碳亲核攻击的易感性，在其水解的机制的公认第一步。

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