Butyltin halides determination

The determination of the Concentrations in pyridine [N] which cause the coalescence of the signals of the diastereotopic groups of a 0.262 M solution methylneophyl-t-butyltin bromide (6) and of 0.332 M solution methylneophylphenyltin chloride (3) at 22 °C at respectively 60, 100 and 270 MHz shows12) that the k2 term is much smaller than the k3[N] term. From these results, it is clear that the inversion of the configuration of the metal atom of triorganotin halides is second-order in the nucleophile pyridine. An analogous rate equation has been found for the racemiza-tion of triorganosilicon halides 29), for which the activation entropy AS is about —50 e.u. Several mechanisms with increase of coordination number 30) can be proposed to account for this second order in the nucleophile 31) ... 

In a similar attempt to determine the nature of the rate-determining step in the reaction of aryl halides with magnesium, the kinetics of the reaction of substituted aryl bromides with magnesium and with tri-/i-butyltin hydride in ethereal solvents were examined [81c], using competitive kinetics techniques, and were correlated with the substituent effect using Hammett cr parameters. A Hammett plot log iK/K)=f(( x) then provided the value of the Hammett constant p for the reactions of aryl halides with magnesium and with tri-u-butyltin hydride in various solvents (Fig. 4 and Table 11). 

Similarly, known mixtures of the component halides, e.g. butyltin tribromide, dibutyltin dibromide and tributyltin monobromide, were made up, and plots were constructed of peak heights and areas against weight concentrations in the mixture. These calibration curves were sufficient to enable each component of the mixture to be determined quantitatively. Peak areas were measured as the products of peak height and width at half peak height (Scott and Grant ). 

Steinmeyer et al applied gas chromatography to the analysis of butyltin bromides. They showed that the butyltin bromides may be quantitatively converted to their more volatile butylmethyltin analog with methyl Grignard reagent and then determined by gas liquid chromatography with an estimated accuracy of about - 2%. Direct chromatography of the alkyltin bromides appeared to produce severe sample decomposition. The method is stated to be applicable to a number of tetralkyl and/or tetraryltins and alkyl or aryltin halides. 

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