Lactone chemistry

During oxidation of a polymer, carbon-centred free radicals are generated that react rapidly with oxygen to form peroxy radicals, which may further react with the polymer chains, leading to formation of hydroperoxides. These decompose, yielding highly active alkoxy and hydroxy radicals - which in turn produce new 

For special applications synergistic combinations of hindered amines and dialkylhydroxylamine can be used, in which the latter acts as a radical trap. The accepted system has been binary blends of selected sterically hindered phenolics (primary) and phosphites (secondary), but none of these is a carbon-centred radical scavenger. 

The addition of HP-136 to the classic binary phenol/phosphite systems significantly improves performance both in melt flow and colour, enabling a producer and converter to tailor the formulation to meet specific cost targets. In some cases it is possible to reduce the concentration of the classic binary system by more than 50%, In combination with high-performance phosphites there is also a dramatic improvement, with significant reductions in overall concentration of stabilizer without loss of performance. 

In polypropylene tape applications. HP-136 is very effective when used with a classic phenolic or in a ternary blend and. compared with a traditional binary blend, data indicate that there is potential for a 50% reduction in total stabilizer concentration, with comparable melt flow stability, improvement in colour, and an improvement in water carry-over, again providing a significant margin for optimization of formulation. In polypropylene fibre applications, a combination of HP-136 with a hindered amine and a phosphite shows melt flow and colour comparable with a traditional binary system, but superior gas-fade resistance and UV stability in phenol-free blends. This improvement is seen at 40% less concentration. 

Irganox HP makes it possible to process at higher temperatures (above 300°C) than is possible with conventional anti-oxidant systems. It also permits as much as 50% reduction in overall additive loading, giving an attractive cost/ performance profile and potential for improved additive compatibility. 

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The sesquiterpene lactone chemistry was reinvestigated in greater detail by Porter and Mabry (1972), who used plant material from 20 populations of A. psilostachya... 

Lactone chemistry Improved melt processing, colour improvers... 

New developments are hydroxylamines and lactones (for processing stability), which operate at an earlier stage during stabilisation. Lactone (benzofuranone) chemistry has been identified as commercially viable, and marks a revolutionary advance in comparison to hindered phenols and phosphites [18]. New lactone chemistry (Figure 10.1) provides enhanced additive compatibility, reduced taste and odour (organoleptics), resistance to irradiation-induced oxidation, and inhibition of gas fade discoloration. The commercial introduction of fundamentally new types of stabilisers for commodity and engineering polymers is not expected in the near future. 

Finally, as already noted, simple and elegant lactone chemistry [115, 116] starting from the readily available 1,4-galactonolactone (11) and HBr/HOAc yields crystalline... 

Bourguignon, J. J. and Wermuth, C. Cj., Lactone chemistry synthesis of p-substituted, f functionali/.ed butanolides and butenolides and succinaldehydic acids from glyoxylic acid, J. Orfi. Chen, 46, 4889. 1981. 

Spring, O. Buschmann, H. Vogler, B. Schilling, E.E. Spraul, M. Hoffmann, M. Sesquiterpene Lactone Chemistry of Zaluzania grayana from Online LC-NMR Measurements, Phytochemistry 39(3), 609-612 (1995). 

Recent advances in (3-lactone chemistry , Pommur, A. and Pons, J.-M., Synthesis, 1993, 441. 

Another aspect of the 8-lactone chemistry is the interconversion between 8-lac-tone and 5-hydroxy fatty acid. Under basic aqueous conditions, the equilibrium favors the formation of the 5-hydroxy fatty acids. In contrast, catalytic amounts of acid will cause rapid cyclization/dehydration of the 5-hydroxy fatty acid into the 8-lactone. By utilizing the equilibrium between these two species, 5-hydroxy fatty acids were synthesized directly from meadowfoam oil (Scheme 13). 

Populations of Ambrosia confertifloray a ragweed disttib-uted widely through Texas and Mexico, reveal complex sesquiterpene lactone chemistry. Most populations from south-central Texas are characterized by a chromosome number n = 66 and the pseudoguaianolides confertiflorin (95) and desacetylconfertiflorin (99), whereas plants from northeastern Mexico yield germacranolides and a few eudesmanol-ides. All of those studied have chromosome number n = 54. A dilactone race (with both = 54 and n = 66) occurs further west in Texas and in Mexico along the western slopes of the Sierra Madre into the area where Ambrosia cumanensis occurs. A fourth race characterized by the presence of germacranolides occurs in northwestern Mexico (Mabry, 1972). 

Iron acyl and Tt-allyltricarbonyliron lactone chemistry Protocol 2. 

Extrapolating from Ester Chemistry to Lactone Chemistry... 

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