Using monoalkyl tins

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

If the reaction temperature is controlled through the use of a low boiling solvent or other means, it is possible to isolate equimolar quantities of monoalkyl tin trichloride and tri alkyl tin chloride using a 1 1 ratio of tetraorganotin and tin tetrachloride ... 

Applications of organotin compounds have been progressively restricted by environmental considerations the major use continues to be in PVC stabilization, and the monoalkyl tin compounds are being increasingly used for coating glass with Sn02. 

It had been customary to use loadings of 2 to 3% in the case of the first generation dialkyltin/long-chain mercaptan stabilisers, which meant putting as much as 5400 ppm tin into the PVC. Since then there has been a substantial reduction in tin content. The amount of tin in PVC stabilised with third generation monoalkyl tin combined with short chain or functionalised mercaptides or sulfides is only about 172 to 1800 ppm, depending on the tin content of the stabiliser used. This assumes low loadings of 0.04 to 0.75 %. 

The reaction of diols with alkylating agents can also be performed such that approximately the theoretical amount of monoalkylated product is obtained. Some substrates can even be monoalkylated [36, 41, 42] or monoarylated [43] with substantially higher yields than statistics would predict what must be due to the slowness of the second alkylation. This behavior, however, is not usually observed, and other strategies must usually be used to achieve clean monoalkylations. Use of excess diol will often furnish pure monoalkylated diol, but a suitable means of removal of excess diol will be required. In the examples sketched in Scheme 10.10 the products were purified by column chromatography, recrystallization, or distillation. As with acylations, the formation of monoalkylated diols can also be promoted by Ag20 [44] or by transient protection with boron [45] or tin [46] derivatives. 

Kinetic TBDMS enol ethers were isomerized to the thermodynamic ethers in the presence of catalytic amounts of the coordinate complexes of tin tetrachloride and the monoalkyl ethers of BINOL or biphenol, whereas the use of the coordinate complexes with biphenol and other monoaryl alcohols predominantly afforded the corre-... 

Tin stabihzers are commonly used. There are many types in use but generally they are monoalkyl or dialkyl tin esters or mercaptides. Common alkyl groups are methyl, butyl, and octyl. Alkyl tin thioglycolates are effective heat stabilizers and are commonly used. 

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