Tin-free systems

Aminostannanes. Aminostannanes react with aryl and alkenyl bromides to give the corresponding amino compounds.But recently, tin-free systems have been developed,... 

Due to the high reactivity of the prepolymer, extremely high curing rates (tack-lree times < 1 min) can be achieved. Tin-free systems are possible, too (catalyst (e.g.) tertiary amines). 

Materials used for various pharmaceutical drug-delivery systems include tin-plated steel, mild steel, stainless steel, tin-free steel, and aluminum and its various alloys. 

Metals—tinplate, tin free steel, aluminium, aluminium alloy, etc., and even stainless steel (vessels for bulk storage must also have effective closure systems). 

The toxicity of organotin derivatives and the difficulty in removing tin residues has spurred considerable eflforts to devise catalytic systems or, preferably, completely tin-free processes for conducting radical reactions. The use of poly(methylhydrosiloxane) in conjunction with a small amount of hexabutylditin oxide, a combination of reagents initially proposed by Grady and Kuivila [21a], has recently been applied to Barton-McCombie type deoxygenations [21b]. Several silanes have been examined... 

Osomio Yazmin M, Cruz-Afrnanza R, Jimenez-Montano V, Miranda Luis D (2003) Efficient, intermolecular, oxidative radical alkylation of heteroaromatic systems under tin-free conditions. Chem Commun (Cambridge, UK) 2316—2317... 

Menes-Arzate M, Martinez R, Cruz-Almanza R, Muchowski Joseph M, Osomio Yazmin M, Miranda Luis D (2004) Efficient, tin-free radical cyclization to aromatic systems. Synthesis of 5,6,8,9,10,ll-hexahydroindolo[2,l-a]isoquinolines. J Org Chem 69 4001-4004... 

The systems are color-stable, weather resistant, flexible, and also adhere well to tin-free and low-tin sheet metals, as used in the manufacture of beverage and aerosol cans. Although arene-ferrocenium complexes even allow the cure of bisphenol A epoxy resins, provided postcuring takes place, these systems have not yet become important in surface protection applications. The reasons for this are inadequate color stability and weather resistance as well as the intense color of these films. 

Coatings for Sheet-Metal Cans and Containers. By far the most important area of use is the coating of sheet-metal containers and cans for the storage and preservation of food and other products. Thin sheets of galvanised steel (tin plate), nickel-plated steel (tin-free steel), or aluminum alloys are generally used as substrate. Untreated steel sheet may, however, also be used (e.g., to produce containers and drums for chemicals), and are usually coated with pigmented or nonpigmented paint systems (varnishes). 

The formal synthesis of racemic pancracine (73) via radical cyclization of a A -(2-cyclohexenyl)-a-phenylthioacetamide has been reported 266). Racemic monta-nine (98), coccinine, and pancracine (73) have been prepared using a phenyl-thiotetrahydroisoquinoline derivative as the radical precursor (267). Recently, Zard has described the construction of the carbon skeleton of kirkine (19). In these model studies, thiosemicarbazide proradicals interact with lauroyl peroxide (a tin-free initiator) to trigger a reaction cascade that ultimately yields the desired tetracyclic system of kirkine (19) (268). 

Joseph Storey has introduced a zinc hydroxystannate flame retardant, which it found to be the closest non-toxic alternative to antimony trioxide in halogenated systems. The new material also has excellent smoke suppression properties. In halogen-free systems, tin char formation occurs, leading to reductions in filler loadings and improved physical properties. 

A key driver of change and new product development in the plastics additives markets is a host of environmental concerns. This is seen most dramatically in PVC where concerns over the use of heavy-metal heat stabilizers based on lead have led to a widespread conversion to tin-based materials and even to nonmetallic stabilizers. The widely used phthalate-based Plasticizers for flexible PVC have come under fire because of concerns over their potential adverse effects on the human reproductive systems. Concerns over the potential for brominated FRs to form dioxins are fueling the development of new halogen-free systems. 

The rarely investigated tin(II) halide-free systems have been generated from (P ligand)2Pt(0113)3 8(06115)3, BFg, or BPh3 [20]. Heterobimetallic... 

Figure 1.10 Tin(ll) halide-free systems used in Pt-catalyzed hydroformylation.

Phosphine platinum complexes give active hydroformylation catalysts and both terminal and internal alkenes can be hydroformylated by selectively employing platinum-diphosphine complexes, often activated by an excess of tin chloride as the cocatalyst [25,26]. The combination of platinum chloride andtin(II) chloride leads to the formation of the trichlorostannate anion, which presumably acts as a weak coordinating anion, as tin-free catalyst systems have also been reported [27]. The group of Vogt found that the preformation of the catalyst also proved to be effective with only one equivalent of the tin source [28]. 

Apart from acrylate-based systems, which are cured by a free-radical mechanism, epoxide-based systems that are cured cationically are also used. Epoxide-based formulations yield excellent overprint varnishes on tin-free steel and aluminum for rigid packaging, especially when producing steel food cans and aluminum beer and... 

Water is very poor at displacing this oil which can form very thin films, even down to mono-molecular layers, on the surface of the steel (ETP - electro-tinplate or TFS- tin free steel, sometimes referred to as ECCS) or aluminium. This is in direct contrast to solvent based systems which readily displace any oil present. Thus, the wetting of the substrate is a major problem with water based systems. The fact that water based systems are run successfully day in, day out, on DWI lines producing 1500-2000 cans per minute, per line, illustrates that these wetting problems can be overcome. 

Although the new tin-free conditions represented a major advance, the scope of the A-arylation reactimis was still quite limited with the original Pd/P(o-tol)3 catalyst system. Over the next several years, a series of experiments illustrated that the nature of the phosphine ligand played a key role in reactivity and selectivity. Thus, a number of ligands were subsequently employed that allowed for efficient coupling of a broad... 

Sepro Conta.iner, The Sepro container consists of a collapsible plastic bag fitted into a standard three-piece, tin-plated container such as a 202 X 214, 202 x 406, or 202 x 509 can. The product is placed within the bag, and the propellant is added through the bottom of the container, which is fitted with a one-way valve. There is no limitation on the viscosity of the product but compatibiUty with the plastic bag must be considered. A free-dowing hquid can be dispensed either as a stream or a fine spray, depending on the type of valve employed. A viscous material is often dispensed as a stream. This system has been used for caulking compounds, postfoaming gels, and depilatories. 

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

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