Butyltin bromides 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) ... 

Tri-n-butyltin bromide (TBT), triethyltin bromide (TET), and trimethyltin chloride (TMT) inhibited the cardiac SR Ca uptake (Figure 4.1.2) and Ca +-ATPase (Figure 4.1.3) in vitro in rat heart in a concentration-dependent manner. The order of potency for Ca +-ATPase as determined by IC50, is TBT (2 pM) > TET (63 pM) > TMT (280 pM). For Ca uptake, it followed the same order, i.e., TBT (0.35 pM) > TET (10 pM) > TMT (440 pM). In agreement with them vifro results, both cardiac SR Ca +-ATPase and Ca uptake were significantly inhibited in vivo in rats treated with these organotin compounds... 

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. 

Unger et al. [217] determined butyltins in non saline water by gas chromatography with flame photometric detection and confirmation by mass spectrometry. The sample was extracted with tropalone in //-hexane and organotin compounds derivatised with n-hexyl magnesium bromide to form tetraalkyltins. The n-hexyl derivatives of methyltin and butyltin species were easily separated and quantified relative to an internal standard (triphenyltin chloride) which was not found to be present in environmental samples and did not interfere. 

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). 

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