Photolytic degradation, methods

Table 4.24 summarises the main features of solid-state photolysis-GC for polymer/additive analysis. Photolytic degradation products obtained from PE/1 % DLTDP and PE/1 % DSTDP, PMMA/9 % DNP and PVC/19 % DOP were examined [189]. The method has found little follow-up. 

Hamlin WE, Chulski T, Johnson RH, Wagner JG. A note on the photolytic degradation of antiinflammatory steroids. J Am Pharm Assoc (Sci Ed) 1960 49(4) 253-255. Pawelczyk E, Knitter B, Knitter K. Kinetics of drug decomposition. Part 50 graphic method for calculation of zero-order rate constants of indomethacin photodegradation. Pharmazie 1977 32(8-9) 483 85. 

Pharmaceutical preparations containing riboflavin have been analyzed by TLC using concentrated ethanolic extracts on silica gel plates developed in butanol-benzene-acetic acid-water (8 7 S 3) or butanol-acetic acid-water (9 4 5) (7). Foods, tissue samples and urine each require particular methods of sample preparation and these, together with a number of solvent systems have been reviewed (8). A darkroom is required for sample preparation and chromatography of flavins to prevent photolytic degradation. The fluorescent property of flavins provides a convenient means of detection and spots have been located under radiation at 254 and 366nm (4). HPTLC followed by fiberoptic fluorimetry has been used to quantitate riboflavin in vitamin mixtures and can detect 48-320 ng (6). Recently, a method has been described using mixed-layer plates of GDX-102 and silica gel G (1 1) precoated with hexadecyl-trimethylammonium bromide developed in 60-70% ethanol (9). 

Juvet et showed that characteristic reaction products occur during photolytic degradation and polymer additives may on this basis be identified without separation from the polymer samples. The excellent reproducibility reported for photolytic degradation of liquid samples indicated the possibility of quantitative determination of polymer additives (Method 102). They developed equations to predict the shape of calibration curves expected for both trace level additives and those present at higher concentration. Photolytic degradation has been shown to yield simple and more reproducible decomposition patterns due to greater control of input energy and the more predictable manner in which compounds decompose photolytically. 

METHOD 102 - IDENTIFICATION AND DETERMINATION OF ADDITIVES IN POLYMERS. PHOTOLYTIC DEGRADATION-GAS CHROMATOGRAPHIC METHOD."... 

Both silene isomers 278 and 279 are ideal precursors for the generation of silylene 284, since their interconversion to 284 is spontaneous (in the case of 278) or can be easily induced by irradiation (in the case of 279). There are numerous well-established methods to prepare transient silylenes 279. Three important examples are shown in equation 69, namely the photolytic generation from a trisilane 280153, thermolytic or photolytic decomposition of cyclic silanes 28114,154,155 and degradation of diazidosilanes 282153,156. The photolysis of the diazido silane 282 is an especially clean reaction which has been used in several spectroscopic studies157. The photolysis of w-diazo compounds 283 is the only frequently used reaction path to silenes 284 via a carbene-silene rearrangement8. 

The Hunsdiecker Reaction. The classical Hunsdiecker reaction is somewhat restricted due to the relatively harsh conditions required. In the Barton version, alkyl radicals generated from O-acyl thiohydroxamates, under either thermal or photolytic conditions, are efficiently trapped either by CI3C-X (X=C1 or Br CbC is the chain carrier) or by IodoformThe method is applicable to sensitive substrates for which the classical methods are unsuitable. thus allowing the preparation of a wide range of alkyl chlorides, bromides, and iodides by the one-carbon degradation of a carboxylic acid. Similar reactions of aromatic acid derivatives tend to require an additional radical initiator (e.g. Azo-bisisobutyronitrile), if high yields (55-85%) are to be obtained. ... 

---