Stopped-flow chlorides

Chromyl chloride oxidation of alkenes proceeds via the formation of adducts at a rate necessitating stopped-flow techniques. At 15 °C the formation of 1 1 adduct from styrene and oxidant in CCI4 solution is simple second-order with 2 = 37.0 l.mole .sec . Measurements with substituted styrenes yielded = — 1.99. E = 9.0 kcal.mole and = —23.8eu for styrene itself. Hydrolysis of the styrene adduct yields mostly phenylacetaldehyde (76.5 %)and benzaldehyde (21.1 %). Essentially similar results were obtained with a set of 15 alkenes and... 

Bi(V) in aqueous perchloric acid is very strongly oxidising but kinetic studies have been confined to a few stopped-flow measurements on oxidation of iodide, bromide and chloride ions. The appearance of Bi(III)-halide complexes was first-order with respect to Bi(III) and in all cases the first-order rate coefficient,, was the same, i.e. 161 + 8 sec at 25 °C ([H30 ] = 0.5 M, p. = 2.0 A/), irrespective of the nature or concentration of the halide. A preliminary attack on solvent is compatible with these interesting results, viz. 

A kinetic smdy of the acylation of ethylenediamine with benzoyl chloride (110) in water-dioxane mixtures at pH 5-7 showed that the reaction involves mainly benzoylation of the monoprotonated form of ethylenediamine. Stopped-flow FT-IR spectroscopy has been used to study the amine-catalysed reactions of benzoyl chloride (110) with either butanol or phenol in dichloromethane at 0 °C. A large isotope effect was observed for butanol versus butanol-O-d, which is consistent with a general-base-catalysed mechanism. An overall reaction order of three and a negligible isotope effect for phenol versus phenol- /6 were observed and are consistent with either a base- or nucleophilic-catalysed mechanism. Mechanistic studies of the aminolysis of substituted phenylacetyl chlorides (111) in acetonitrile at —15 °C have revealed that reactions with anilines point to an associative iSN2 pathway. ... 

Electrochemically generated solutions of radical-cations will react with nucleophiles in an inert solvent to generate a radical intemiediate. Under these conditions the intermediate is oxidised to the carboniiim ion by a further radical-cation. Generally, an aromatic system is then reformed by loss of a proton. Reactions of 9,10-diphenylanthracene radical-cation nucleophiles in acetonitrile are conveniently followed either by stop flow techniques or by spectroelectrochemistry. Reaction with chloride ion follows the course shown in Scheme 6.2, where the termination... 

Investigations into the mechanism of hydrolysis and alcoholysis of acyl halides have been largely concerned with acyl chlorides and in particular with benzoyl chloride and the related aromatic acid chlorides. This was a result of the relatively slow rate of hydrolysis of benzoyl chloride compared with acetyl chloride (although their alcoholysis rates are easily measurable) and it is only comparatively recently90 that stop-flow techniques have been used to measure the faster rate of hydrolysis. However, in spite of this limitation, considerable progress has been made towards elucidation of the mechanism or mechanisms of hydrolysis and alcoholysis of these halides. 

Later studies on acetyl chloride hydrolysis were those of Hudson and Moss90, using a stopped-flow apparatus at 27°C and working with dioxan-water mixtures (19.6-75.6 v/v), and Cairns and Prousnitz102 with acetone/water (15.35% v/v) at low temperatures. The value of the Grunwald-Winstein103... 

More recently, rate and equilibrium constants have been determined directly for the nitrosation by nitrosyl chloride of some alcohols in acetic acid using stopped-flow spectrophotometry (Dalcq and Bruylants, 1975). A second order term in [ROH] was noted for the O-nitrosation of methanol (and a corresponding term containing [ROH] for the reverse step), which was not significant for the other alcohols studied, so that the rate eqn(38) represented the kinetics. A mechanism was proposed involving attack by NOCl at the... 

Stopped flow spectrophotometry has also been used to measure the forward and reverse rate constants for the nitrosation of a number of alcohols and carbohydrates in aqueous solution (Aldred and Williams, 1980 Aldred et al., 1982). Both reactions were acid-catalysed and were also catalysed by added chloride and bromide ion. Structural effects were not marked but the sequence MeOH > EtOH > i-PrOH > t-BuOH was established for the forward reaction and was attributed to a steric effect, whilst for the reverse reaction the rate constants were not very dependent on the alcohol structure. The halide ion-catalysed reactions were believed to involve equilibrium concentrations of reactive NOCl and NOBr rate constants for the bimolecular process (39) were determined as 2.1x10 and 2.0 x 10 dm mol s for NOCl and NOBr respectively, for reaction with methanol at 25°C. Thus, as... 

Flammable gas. Very dangerous fire hazard when exposed to heat, flame, or powerful oxidizers. Moderate explosion hazard when exposed to flame and sparks. Explodes on contact with interhalogens (e.g., bromine trifluoride, bromine pentafluoride), magnesium and alloys, potassium and alloys, sodium and alloys, zinc, Potentially explosive reaction with aluminum when heated to 152° in a sealed container. Mixtures with aluminum chloride + ethylene react exothermically and then explode when pressurized to above 30 bar. May ignite on contact with aluminum chloride or powdered aluminum. To fight fire, stop flow of gas and use CO2, dry chemical, or water spray. When heated to decomposition it emits highly toxic fumes of cr. See also CHLORINATED HYDROCARBONS, ALIPHATIC. 

Lorimer and Pepper have recently reported a study of the polymerisation of styrene by perchloric acid in methylene chloride at low temperature. Althou the stop-flow apparatus they used was not very fast, some rough ideas on the kinetics of initiation could be obtained. Assuming that the initial increase in absorption at 340 nm was due to the protonation of styrene, unhampered by side reactions (esterification), the approximate rate law observed at —80 °C,... 

Sawamoto and Higadiimura have continued their investigation of the stop-flow spectroscopic behaviour of the polymerisation of p-methoxystyrene and added triflic acid to the series of catalysts previously tried. Again, they observed the typical absorption around 380 nm, attributed to the protonated monomer and calculated an initiaticm rate constant at 30 °C in ethylene chloride (assuming a bimolecular interaction orders not determined) kj = 5 x 10 s . This value is expectedly much... 

Trimethylstyrene has also been studied at —80 °C and evidence for the presence of the corresponding carbenium ions obtained by ultravicdet ctroscopy Both a-methylstyrene and p-methoxystyrene were studied at —80 °C by stop-flow spectrophotometry. They were ftwnd to polymerise so rapidly that the spectra taken were in fact those of species present at the end of the polymerisaticm . The polymerisation of p-methoxystyrene by perchloric acid in methylene chloride at room... 

Rooney has recently revived work on this monomer in an investigation of its polymerisation by trityl hexafluoroantimonate - He used a spectroscopic stop-flow apparatus to follow initiation and an adiabatic calorimeter to measure rates of polymerisation. Propagation was shown to compete effectively with initiation to the point that some initiator was often present at the end of the polymerisations. These observations cast some doubts on the assumption made in the paper by the Liverpool school discussed above. A kinetic analysis of the initiation reaction showed it to be bimolecular, with a rate constant of about 130 sec at 20°C. The determination of the propagation rate constant was less strai tforward despite the fact that further monomer-addition experiments seemed to rule out any appreciable termination. The kp values fluctuated considerably as the initial catalyst concentration was varied, a fact which induced Rooney to propose that the empirical constant was a composite function of kp and kp. Experiments with a common-anion salt supported this proposal and their kinetic treatment led to the individual values of kp = 6 x 10 sec and kp = 5 x 10 sec. It is difficult to assess the reliability of these values in view of the following statement by the author the reaction at a 5 x 10 M concentration of initiator, thought to proceed exclusively through paired ions. .. . This statement is certainly incorrect as far as the initiator is concerned for which the proportion of ion pairs for a concentration 5 x 10 M at 20°C is only about 20% in methylene chloride However, the experiments... 

Sawamoto et al. studied the spectroscopic stop-flow behaviour of the polymerisation of styrene and some of its derivatives by triflic acid In ethylene chloride at 30°C. They obtained overall values of the propagation rate constant of about 1 x 10 M s for styrene, p-chlorostyrene and p-methylstyrene. As previously in the same laboratory with p-methoxystyrene, invisible species were held responsible for some or most of the propagation, particularly in media of low dielectric constant, i.e. pseudocationic polymerisation occurs in all these systems and predominates when the polarity of the solvent does not favour ion formation. 

The measuring cell which serves as a basis of the CFMIO method [3] can also be used in a stopped-flow mode by positioning of one or more observation channels perpendicular to the flow tube. This combined stopped-flow, continuous-flow method [5] was used to determine the effect of surface-active substances (sodium dodecyl sulfate or dodecyltrimethylammonium chloride) on electron-transfer reactions between metal complexes. 

EQCM studies in Co(II)-En chloride solution of different pH carried out under stopped-flow (Figure 19.10A) and wall-jet conditions (Figure 19.10B) show increase in Co(II) oxidation rate... 

Methyl Chloride <32 8.1 17.2 Dry chemical or carbon dioxide. Stop flow of gas Not pertinent Containers may explode 1170 No ... 

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