Modified Organotins

In contrast with the important amount of work done to solve the purification problems caused by organotin side products in tin-hydride chemistry, very little attention has been paid to the allyl transfer process. Nevertheless, as most of the radical reactions are conducted with an excess of the allyltin, new allyltin reagents were proposed to optimize the purification process. 

---

Some selected applications (chemical class, mobile phase, stationary phase, column, detector) are as follows fatty acids, C02, PEG or CN-PS, OTC, FID organotin, C02, PhMe-PS, OTC, FPD [305], ThepSFC-ICP system is an effective tool for speciation of metal-containing compounds [362], even in the presence of modifiers to control the retention of components. 

TABLE 6. Annual consumption of tin metal as organotin chemicals in the USA, Europe and Japan (modified from Reference 32)... 

TABLE 9. Tin(IV) and organotin compounds0 in some environmental waters (modified from Reference 42)... 

TABLE 12. 96-h-ECso and relative toxicity of organotin compounds for growth of S. obliquus (modified from Reference 81) ... 

TABLE 20. Concentration factor of organotin compounds (modified from Reference 115)... 

Modified from Laughlin, R.B., Jr., R.B. Johannesen, W. French, H. Guard, and F.E. Brinckman. 1985. Structure-activity relationships for organotin compounds. Environ. Toxicol. Chem. 4 343-351. 

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

In the present work, some promising results obtained with this kind of asymmetric heterogeneous catalyst, based on silica-supported Ni, Rh and Pt, chemically modified with chiral organotin compounds, are presented. The systems were tested in the enantioselective hydrogenation of ethyl pymvate, acetophenone and 3,4-dimethoxyacetophenone. The stabiUty of these catalysts was also studied to check if they could be reused. 

The enantioselective hydrogenation of acetophenone afforded an excess of the (S)-phenylethanol isomer. An enantiomeric excess (e.e.) of around 20% was obtained with all the chiral organotin compounds tested, which is a good result for acetophenone, a non-activated ketone, and especially because of the high selectivity to PE (over 97%). Previously published results with the classical Pt/cinchoni-dine system showed an e.e. of 17%, corresponding to a yield of 4.7% [133]. The similar e.e.s obtained for the three rather different modifiers employed in this work seems to indicate that chiral induction must be assigned to the presence of at least one menthyl group attached to the surface. 

To improve the thermal stability of PVC, it is common to add stabilizers, generally metalloorganic compounds, in concentrations of 1-5 parts per 100 parts of PVC. Although the cis-1,4-polybutadiene grafted PVC, in the absence of an added stabilizer, yielded essentially colorless or only faintly discolored films, completely colorless films were obtained when the conventional stabilizers were added in concentrations of 0.1-0.3 parts per 100 parts of modified PVC. Organotin stabilizers were not necessary and, in some cases, actually resulted in greater color development than when they were absent. 

Oudsema, J.W. and Poole, C.F. (1992) On-line supercritical fluid extraction and chromatography of organotins with packed microbore columns and formic acid modified carbon dioxide. Fresenius J. Anal. Chem., 344, 426-434. 

Thomaidis, N.S., A.S. Stasinakis, and T.D. Lekkas. 2007. A screening method for the determination of toluene extractable organotins in water samples by electrothermal atomic absorption spectrometry and rhenium as chemical modifier. Appl. Organometal. Chem. 21 425-433. 

---