Stannous Halides

The halostannanes can also be generated in situ by reactions of allylic halides with tin metal or stannous halides. 

Mukaiyama, T. Harada, T. Shoda, S. (1980) An efficient method for the preparation of homo allylic alcohol derivatives by the reaction of allyl iodide with carbonyl compounds in the presence of stannous halide, Chem. Lett., 1507-10. 

Halides. The tin haUdes of the greatest commercial importance are stannous chloride, stannic chloride, and stannous fluoride. Tin hahdes of less commercial importance are stannic bromide [7789-67-5], stannic iodide [7790-47-8], stannous bromide [10031-24-0], and stannous iodide [10294-70-9] ( ) ... 

Owens C, Pytlewski LL, Mikulski CM, et al. 1979. X-ray crystallographic, morphological and thermal-decomposition studies of 2-1 adduces of diisopropyl methylphosphonate with stannous and stannic halides. Journal of Inorganic Nuclear Chemistry 41(9) 1261-1268. 

Cyanoethylidene derivatives can be prepared from the corresponding glycosyl halides by the treatment with KCN and n-Bu4NBr in CH3CN or from the corresponding peracetates and TMSCN in the presence of stannous chloride (Scheme 5.9). 

Two different mechanisms have been proposed for the ROP of (di)lactones depending on the nature of the organometalhc derivatives. Metal halides, oxides, and carboxylates would act as Lewis acid catalysts in an ROP actually initiated with a hydroxyl-containing compound, such as water, alcohol, or co-hydroxy acid the later would result more hkely from the in-situ hydrolysis of the (di)lac-tone [11]. Polymerization is assumed to proceed through an insertion mechanism, the details of which depends on the metal compound (Scheme la). The most frequently encountered Lewis acid catalyst is undoubtedly the stannous 2-ethylhexanoate, currently referred to as stannous octoate (Sn(Oct)2). On the other hand, when metal alkoxides containing free p-, d-, or f- orbitals of a favo-... 

A variation of the above tests is that devised by Lenher.1Ms which depends on tho low solubility of certain metal ions in alkaline solution. Treatment of an epoxide with concentrator aqueous man ganoua chloride, for example, causes the gradual appearance of a manganous hydroxide precipitate as OH ions are liberated (Eq. SS i). Other halides examined by Lenher but found to he less effective wore nine chloride, ferrous chloride, and stannous chloride. 

Tin forms dihahdes and tetrahahdes with all of the common halogens. These compounds may be prepared by direct combination of the elements, the tetrahalides being favored. Like the halides of tile lower main group 4 elements, all are essentially covalent. Their hydrolysis requires, therefore, an initial step consisting of the coordinative addition of Iwo molecules of water, followed by the loss of one molecule of HX. the process being repeated until the end product ft S111 Oil c is obtained. The most significant commercial tin halides are stannous chloride, stannic chloride, and stannous fluoride. 

The oxidative addition of aliphatic organic halides to stannous chloride has long been of interest for the preparation of monoorganotin trihalides ... 

A significant advance in the synthesis of monoorganotin trihalides was the preparation of p-substituted ethyltin trihalides in good yield from the reaction of stannous chloride, hydrogen halides, and CC, 3-unsaturated carbonyl compounds, eg, acrylic esters, in common solvents at room temperature and atmospheric pressure (153,154). The reaction is believed to proceed through a solvated trichlorostannane intermediate (155) ... 

The elements Si, Ge, Sn, and Pb all exhibit the oxidation states of +2 and +4. However, the +2 state for Si is rare. One reason is that SiO is not stable and the halides SiF2 and SiCl2 are polymeric solids. A few Ge(II) compounds are known (e.g., GeO, GeS, and Gel2). The +2 and +4 oxidation states are about equally common for Sn and Pb. For example, Sn02 is the most common ore of Sn, and numerous compounds contain Sn(II) (stannous compounds). As we will see later, there are also numerous common compounds of both Pb(II) and Pb(IV). 

The tin(II) halides are much less volatile than the corresponding tin(IV) compounds in fact, they are probably ionic, containing Sn2+ and X- ions. Tin(II) chloride in aqueous solution is commonly used as a reducing agent. Tin(II) fluoride (stannous fluoride) was for many years added to toothpaste to help prevent tooth decay. It has since been replaced by sodium fluoride. 

The yield of the more active RRR-a-tocopherol can be improved by selective methylation of the other tocopherol isomers or by hydrogenation of a-tocotrienol (25,26). Methylation can be accomplished by several processes, such as simultaneous haloalkylation and reduction with an aldehyde and a hydrogen halide in the presence of stannous chloride (27), aminoalkjdation with ammonia or amines and an aldehyde such as paraformaldehyde followed by catalytic reduction (28), or via formylation with formaldehyde followed by catalytic reduction (29). 

Compounds of divalent Ge are well known. There is no evidence that GeO is a stable phase at temperatures below 1000°K (compare SiO), but compounds stable at ordinary temperatures include GeS, all four dihalides, and complex halides such as MGeCla. The Ge ion is not stable in water, and its crystal structure shows that GeF2 is not a simple ionic crystal (p. 929). There seem to be no simple ionic crystalline stannous compounds. In solution Sn presumably exists as complexes its easy conversion into Sn" gives stannous compounds their reducing properties. Lead presents a quite different picture. The stable ion is Pb . This has no reducing properties, and there is no evidence that Pb can exist in aqueous solution, but it certainly exists in crystalline compounds such as Pb02 (rutile structure). 

Reactivity follows the sequence RI > RBr > RC1, and SnL > SnBr2 > SnCl2. The uncatalysed reaction of methyl iodide with stannous iodide at 160 °C has been reported,72 but usually a catalyst is necessary. These catalysts are similar to those which are used for the direct reactions, and include dialkyl sulphides, amines, ammonium and phosphonium salts, and copper(II). The trialkylstibines appear to be particularly effective and the compounds RSnX3, R = Ci to Cis, have been prepared by this method. A similar reaction with the a,co-dihalides, X(CH2) X, n = 4-5, provides access to functionally substituted tetraorganotin compounds, but the aryl halides are unreactive. 

For most commercial applications, it is necessary to add some form of accelerator to the formulation to speed the rate of cure. Both acidic and basic accelerators can be used. Consequently, several latent accelerators have appeared on the commercial scene in recent years. Included among these are quaternary ammonium halides such as benzyltrimethylammonium chloride (9 ), stannous octoate ( ), zinc stearate (1 ), extra-coordinate siliconate salts(11), triethanolamine borate (12), triethanolamine titanate (13), and various other metal chelates (14). However, all of these materials have been rejected for one reason or another and... 

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