The kinetics of aquation and racemization of some cis- chloro-, hydroxo-, and aquabis(ethylenediamine)(amine)cobalt(III) complexes

Aquation rates forcis-CoCl(en)₂(A)²⁺ (A = 3,5-lutidine, imidazole, N-methylimidazole, benzimidazole) have been determined by halide release titration in 1.0 M HNO₃ at 50–80°C. Kinetic parameters are (in the above order of A) 10⁷k₂₉₈ (sec^?1), 7.4, 5.7, 1.3, 9.7; E_a (kJ/mole), 103, 101, 130, 112; log PZ (sec^?1), 11.89, 11.53, 16.04, 13.58; ΔS₂₉₈^? (J/°K· mole),?26, ?32, +54,+7. Rates of racemization for active cis-Co(en)₂(A)-(OH₂)³⁺ were measured spectropolarimetrically in 0.1 M HClO₄, 0.02 M Hg²⁺ for A = ammonia, cyclohexylamine, 3,5-lutidine, N-methylimidazole. Kinetic parameters are (units as above) 10⁹k₂₉₈ = 1.8, 38.0, 7.7, 1.7; E_a = 150, 135, 152, 157; log PZ = 17.49, 16.18, 18.56, 18.87; ΔS₂₉₈^? = +82, +57, +102,+108. Rates of racemization of the active hydroxo complexes cis-Co(en)₂(A)(OH)²⁺ (A = NH₃, CH₃NH₂, 3,5-lutidine, imidazole) were measured similarly at pH = 8 (π = 2.0, NaClO₄). The racemization of the hydroxo is ca. (3–4) × 10³ faster than for the corresponding aqua complex. Kinetic parameters are 10⁶k₂₉₈ = 2.55, 7.2, 30.1, 7.0; E_a = 138, 123, 122, 128; log PZ = 18.58, 16.39, 16.85, 17.18; ΔS₂₉₈^? = +102,+60, +69,+76. Racemization rates for aquahydroxo mixtures (A = CH₃NH₂, 3,5-lutidine, imidazole) were also determined in the pH range of 4–8 (θ = 2.0, NaClO₄) at 50.6°C, and pK_a data calculated from the pH versus k plot are 5.50, 5.65, and 6.40, respectively, for A.     

Ammonia free partial reduction of aromatic compounds using lithium di-tert-butylbiphenyl (LiDBB)

The reduction of a series of hetero- and carbocyclic aromatic compounds under ammonia free conditions is described. By using LiDBB as a source of electrons, bis(methoxyethyl)amine (BMEA) as a protonating agent, and THF as a solvent, we were able to accomplish reductions more usually performed under Birch type conditions. Moreover, the use of these conditions was further enhanced by the tolerance of the reducing system toward reactive electrophiles that cannot be used successfully in ammonia.     

Examining the Types,Features, and Use of Instructional Materials in Afterschool Science

Afterschool programs have garnered much attention as promising environments for learning where children can engage in rich science activities. Yet, little is known about the kinds of instructional materials used in typical, large‐scale afterschool programs that implement science with diverse populations of children. In this study, we investigated the types, features, and use of science instructional materials at more than 150 public afterschool program sites across California. Using afterschool site survey data, we categorized the types and the range of materials used at the sites. We then collected a subsample of the instructional materials for in‐depth analysis of their support features for enabling staff and children to enact science. We also interviewed afterschool site staff to better understand how they selected and used materials. Results from our analysis of survey and interview data show that afterschool staff primarily used stand‐alone lessons and activities found on the Internet or in activity books as resources for planning and enacting science. Our analysis of the subsample of instructional materials indicate that curricular materials, while used less frequently by afterschool staff, have on average more of the support features that would help them implement high‐quality science experiences with children.     

Die Adsorption von inerten Gasen an NaCl. II. Eine Virialanalyse gasf?rmig-fest von Argon, das an NaCl adsorbiert ist

Ohne Zusammenfassung     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Decomposition of cis-and trans- potassium diaquobis(oxalato)chromate(III)

The decomposition of cis- and trans-K[Cr(C₂O₄)₂](H₂O)₂] has been studied using differential scanning calorimetry. Dehydration occurs as the first step with activation energies being 27.5 and 13.9 mol^?1, respectively, for the cis and trans complexes. After dehydration, continued heating results in loss of CO amd CO₂. For the trans complex, an additional endothermic peak is seen and the mass loss indicated that CO has been lost in a single step. In both cases, the final product indicated by mass loss data is KCrO₂.     

Kinetic studies on the deamination of [Co(en)3](NCS)3

The loss of ethylenediamine from [Co(en)₃](NCS)₃ has been studied using isothermal weight loss methods. The reaction has been found to be catalyzed by NH₄SCN and piperidine hydrothiocyanate, and the reaction appears first order in catalyst. However, the reaction proceeds so slowly without a catalyst present that a reliable activation energy could not be obtained. For the catalyzed process, the activation energy appears to decrease slightly as the amount of catalyst used is increased, although the results are inconclusive when NH₄SCN is the catalyst. When piperidine hydrothiocyanate is the catalyst, the activation energy appears to decrease from 37.7 kcal mole^?1 to 29.4 kcal mole^?1 as the amount of catalyst increases from 0.5 to 8.0 mole percent. In all cases, the product turned dark after a few hours indicating some reduction as a complicating feature.