Octyl tins

Wirth and Andreas [141] studied the effect of octyl-tin chlorides on the thermal stability of PVC. They were found to significantly retard the dehydrochlorination in the following order ... 

Methyltins are less likely than the butyl- and octyl-tins to partition to sediments, soils, and organic carbon. Modelled data for K c suggest much lower capacity for binding to organic carbon than do measured values, often by several orders of magnitude. Measured data have been used in preference to model environmental fate of the compounds. The compounds also bind strongly to clay minerals, montmorillonite in particular. 

This loss of catalyst and contamination of product with benzene caused us to select the more stable tri(n-alkyl)tin iodides. These catalysts are not as active as the triaiyltin iodides but exhibit veiy good stability under normal reaction conditions. They are also readily prepared from industrially-available bulk starting materials. Tri(n-octyl)tin iodide [(n-Oc sSnl, referred to as "TOT"] can be prepared from three different starting materials although the iodide displacement is preferred ... 

Awareness of the problem developed in the mid 1970s when it was found that mineral waters sold in polyvinyl chloride (PVC) bottles contained measurable amounts of vinyl chloride monomer. Vinyl chloride is a known carcinogen. The Codex Alimentarius Committee on Food Additives and Contaminants has set a guideline of 1 ppm for vinyl chloride monomer in PVC packaging and 0.01 ppm of the monomer in food (Institute of Food Technologists 1988). Another additive found in some PVC plastics is octyl tin mer-captoacetate or octyl tin maleate. Specific regulations for these chemicals exist in the Canadian Food and Drugs Act. 

SYNS ACETIC ACID, ((OCTYLSTANNY7JDYNE)-TRITHIO)TRI-, TRIS(2-ETHYLHEXYL) ESTER MONO-n-OCTYL-TIN-TRIS-(2-ETHYLHEXYLMERCAPTO-ACETATE) TIN, OCTYX-, TRIS(ISOOCTYLTHIO GLYCOLLATE)... 

Hydrolysis of monoorganotin compounds can give rise to a wider variety of hydroxides and oxides through a combination of hydrolysis, dehydration, and aggregation reactions,116 but less work has been done in this field. In moist air, ethyl-, butyl- and octyl-tin trichloride are hydrolysed as far as the hydrated hydroxide dichlorides, RSnCl2(OH)... 

The melting temperature, about 212°C, and decomposition temperature of PVC are very close together, rendering unmodified PVC very difficult to process. Decomposition produces HCl, which is highly corrosive, especially in the presence of water. To reduce problems associated with decomposition, stabilizers are added to PVC octyl tins are most often used in rigid PVC for food and pharmaceutical packaging. The first indications that PVC is decomposing occur at temperatures as low as 100°C (212°F). 

Among these heat stabilisers, those containing tin (such as tin mercaptides, and tin carboxylates or maleates) are considered to be the most efficient, and can be used in a wide variety of applications. Metallic tin is harmless but there are suspicions that organotin-compounds can be toxic to the central nervous system and the liver. However, tin stabilisers have a low capacity for migrating, and hence they are still considered to be safe. Tin stabilisers such as methyl and octyl tins are used in food contact applications. For PVC, it is believed that tin stabilisers act as HCl scavengers (generating tin chloride) as well as an antioxidant. Thio-tin compounds (preferred for rigid pipe extrusions and profiles (for window frames) of PVC) may develop an odd odour due to sulfur. 

Poly(vinyl chloride) or a chlorinated pol5rvinyl chloride is stabilized with composition comprising either methyl, butyl or octyl tin mercaptide stabilizer and salt of a polymeric polyacid material in the solid form. The last improves performance of tin stabilizer, especially if the moisture level in composition is higher than 0.52 wt%. 

Acetic acid octyl ester. See Octyl acetate Acetic acid, 2,2, 2"-((octylstannylidyne) tris (thio)) tris-, triisooctyl ester. See (n-Octyl) tin S,S, S" tris (isooctylmercaptoacetate)... 

Dioctyltin bis (isooctylmercaptoacetate) Di-(n-octyl) tin-S,S -bis (isooctyl mercaptoacetate) Dioctyltin S,S -bis (isooctyl mercaptoacetate) Dioctyltin bis (isooctyl thioglycolate) ... 

Octylthiol. Seen-Octyl mercaptan (n-Octyl) tin S,S, S" tris (isooctylmercaptoacetate)... 

Lead carbonate basic Lead 2-ethylhexoate Lead phthalate, dibasic Lead stearate, dibasic Lead sulfate, basic Magnesium/aluminum/hydroxide/carbonate Methyltin tris (isooctylthioglycollate) Methyltin tris (2-mercaptoethyl oleate) p-Nonyl phenol (n-Octyl) tin S,S, S" tris (isooctyl mercaptoacetate) 2-Phenyl indole Thiodiglycol di-P-aminocrotonate Tris (nonyiphenyi) phosphite Tris (tridecyl) phosphite Zinc laurate Zinc stearate... 

Generally toxic, with aromatic amines showing carcinogenic tendencies. Newer types less toxic Considered non-toxic as also used in foods. Recently investigated and found non-carcinogenic Only class of tin compound classified as of low toxicity and used in medical applications e.g. di-(n-octyl)tin maleate polymer... 

Yean et al. reported the use of different diorgano (n-butyl, n-octyl) tin dialkoxides (n-butoxide, n-pentoxide, n-hexoxide, n-heptoxide, n-octox-ide, n-decoxide, phenoxide, substituted phenoxide) for transesterification of palm oil fatty acids (reaction 7.13) which could be attractive in production of biodiesel (fatty acid esters) [62]. 

Organotin stabilisers are very widely used in PVC in North America and in a few European countries, notably France. There are a few associated toxicity issues, because overexposure to methyl tin can affect the nervous system, while butyl and octyl tin could impact on the immune system. The problems associated with organotin antifouling agents in ships are not generally thought to be very relevant to plastics. 

One tin stabihser category consists of thiotin compounds, such as dimethyl tin di(mercaptopropionate) or di(iso-octyl) tin disulfide. One disadvantage is that some of these substances may require extra lubricants and some UV stabilisation. Thio-tin compounds can also suffer from a very strong odom. 

The type of tin compound favoured in PVC stabilisers varies in different parts of the world. In Europe, 60% of the tin stabilisers used are octyl compounds, including those used in potable water pipes, and 30% butyl. In North America, where tin is widely used in pipe, foam and window profiles, 50% of the tin stabilisers are methyl, and most of the rest are butyl. Methyl and octyl compounds are FDA approved in some cases and allowed in food packaging. In Asia, 50% of tin stabilisers are methyl, and 40% octyl. In Japan, octyl tin is preferred for food packaging and potable water pipe, while butyl tin is used in construction applications. 

Di-n-octyl tin maleate Study of degradation products of this compound produced on processing [97]... 

Food packaging film Mercaptides Calendered sheet Methyl/octyl tin mercaptides 0.8-1.4 16-19 8.00-11.00... 

A Di-n-butyl-tin dichloride B Di-n-octyl-tin dichloride C Separation oi A + B D Di-isooctyl-tin dichloride E Separation oi A B D... 

---