IR kinetic studies

Hisatsune and co-workers [290—299] have made extensive kinetic studies of the decomposition of various ions in alkali halide discs. Widths and frequencies of IR absorption bands are an indication of the extent to which a reactant ion forms a solid solution with the matrix halide. Sodium acetate was much less soluble in KBr than in KI but the activation energy for acetate breakdown in the latter matrix was the larger [297]. Shifts in frequency, indicating changes in symmetry, have been reported for oxalate [294] and formate [300] ions dispersed in KBr. 

No comparative kinetic study has been made on the same alkyl carbonyl system for two members of a given transition metal triad. Qualitative data show that the middle member is more reactive than the heaviest one e.g., CpMo(CO)jR > CpW(CO)jR (Section VI,B), Rh(III) > Ir(III) (Section VI,E), and Pd(II) > Pt(II) (Section VI,F). However, the extreme unreactivity of CpW(CO)jR and a considerable difference in lability between most alkyls of Rh(III) and Ir(III), as well as those of Pd(II) and Pt(II), have prevented detailed investigations. Surprisingly, no kinetic studies have been conducted on insertion reactions of RRe(CO)5, which would seem readily amenable to such investigations. 

Triphenylformazan can be isolated in two forms the red form is assigned to the tautomeric structure 178 or 179 and the yellow form is assigned to the trans-anti geometry 181.303,304 This assignment is supported by IR, NMR, X-ray diffraction as well as kinetic studies.245,305-315... 

The effect of oxidizing atmospheres on the reduction of NO over rhodium surfaces has been investigated by kinetic and IR characterization studies with NO + CO + 02 mixtures on Rh(lll) [63], Similar kinetics was observed in the absence of oxygen in the gas phase, and the same adsorbed species were detected on the surface as well. This result contrasts with that from the molecular beam work [44], where 02 inhibits the reaction, perhaps because of the different relative adsorption probabilities of the three gas-phase species in the two types of experiments. On the other hand, it was also determined that the consumption of 02 is rate limited by the NO + CO adsorption-desorption... 

These authors have also employed this technique for the study of other metallic inclusions into poly(3-methylthiophene) films, including Ir, Au, and Pt. Thus, this type of arrangement could open up new exciting possibilities in terms of kinetic studies. 

These IR kinetic experiments (75) were the first examples of vibrationally excited metal carbonyls to be observed. More detailed studies on the behavior of hot carbonyls should provide an intriguing insight into the photophysics of these molecules. We now look at metal carbonyl photochemistry in solution. 

After 20 years pharmacological interest in nitrofurans is as strong as ever, and still prompts studies including nucleophilic substitutions. Kinetic studies of the replacement of halogen by dimethylamine in 5-halo-2-nitrofurans yield second order rate constants and disclose spectroscopic (IR, UV, and... 

Some of the first transient infrared data on heterogeneous catalysis were gathered by Heyne and Tomkins in 1966 (16). The method has been advocated and used by Tamaru, who has recently reviewed his work since 1967 in this field (17). Dent and Kokes used the transient method in IR studies in 1970 (18). Since then the method has been applied to kinetic studies in particular by Ueno et al. (19, 20) and most recently by Savatsky and Bell (21). 

Kinetic studies of the hydrogenations of BT to DHBT catalyzed by [Rh(PPh3)2(cod)]PF6 [56] and [Ir(PPh3)2(cod)]PF6 [57] indicated the hydride migration yielding the dihydrobenzothienyl intermediate as the rate-determining step. In contrast, the rate-determining step of the reaction catalyzed by [RuH(tri-phos)]+ was shown to be the reversible dissociation of DHBT from the metal center [59],... 

Kinetic studies of the stoichiometric carbonylation of [Ir(CO)2l3Me] were conducted to model the rate-determining step of the catalytic cycle [73,85]. The reaction can form both fac,cis and mer,trans isomers of [Ir(CO)2l3 (COMe)] (Scheme 13), the product ratio varying with the solvent and temperature used. An X-ray crystal structure was obtained for the fac,cis isomer. Carbonylation of [Ir(CO)2l3Me] is rather slow and requires temperatures > 80 °C in chlorinated solvents (e.g. PhCl). However, the presence of protic solvents (e.g. methanol) has a dramatic accelerating effect. This is interpreted in terms of the protic solvent aiding iodide dissociation by solvation. 

The mby fluorescence method allows us to perform pressure measurements in a short time scale (1-10 s), providing a real-time access for pressure control comparing to the time scale of many solid-state chemical processes. As a matter of fact, real-time pressure measurements are necessary when studying kinetic processes [117], but it is also important to minimize the laser power used for measuring the mby fluorescence in order to avoid undesired photochemical effects on the sample, whenever these are possible. In the case of IR absorption studies, which are commonly used for kinetic purposes, the advantage of using the mby fluorescence method, once photochemical effects are prevented, with respect to the employment of vibrational gauges is that no additional absorption bands are introduced in the IR spectmm. 

Zverev, S.M., Smirov, K.S., and Tsyganenko, A.A. (1988) IR spectroscopic study of low-temperature adsorption of molecular nitrogen on the surface of oxides. Kinet. Katal.,... 

ATR FT-IR spectroscopy allows for analysis of the polymer surface, rather than the bulk of the sample. Whereas the spectra obtained from the FT-IR microscope and BCA are recorded in transmittance mode and are used to analyze the entire bead, an ATR objective can be brought into direct contact with the sample in order to yield information about the chemistry taking place mainly on the periphery of the bead. Some FT-IR microscopes are equipped with an ATR crystal, and ATR analysis can be achieved on a single bead [172], but there have been no reports of automated ATR instruments. This technique has been used in kinetic studies, to prove that the esterification of Wang resin (4) (Scheme 1.4) to give the corre-... 

Crabtree and coworkers proposed a catalytic cycle for the reaction outUned in Equation 6.10. The mechanism is based on labeling and kinetic studies, and is outlined in Scheme 6.4 [25]. Adduct 36 was observed in nuclear magnetic resonance (NMR) spectra and appears to be a catalyst resting state. It should be noted that there is no change in the oxidation state of Ir, and that the key step is thought... 

A logical development of this study will be to consider the microscopic point of view i.e the elementary reactions to build the infinite reverse micelles of the network. Detailed structural information is necessary to undertake a more microscopic approach of the kinetics. The aggregation mechanisif involves hydrogen bonding as clearly demonstrated by an IR spectrocopy study (3 ) and has to be understood. 

Kinetic study of the reaction of cyclopentyl-MgBr + 4-methylmercaptoacetophenone by using stopped-flow UV and IR spectroscopies also showed that the rate constant was in the range of 2-6 s in diethyl ether at 25 °C, and the rate was first order in RMgX at low concentration (ca 0.1 M) and 0th order at high concentrations (0.3-0.8 M). The results were interpreted by the mechanism which involved pre-equilibrium of complex formation and conversion of the complex to the product. 

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