Degradation solvolytic

This method for the preparation of cyclobutanone via oxaspiropentane is an adaptation of that described by Salaiin and Conia. The previously known large-scale preparations of cyclobutanone consist of the reaction of the hazardous diazomethane with ketene, the oxidative degradation or the ozonization in presence of pjrridine of methylenecyclobutane prepared from pentaerythritol, or the recently reported dithiane method of Corey and Seebach, which has the disadvantage of producing an aqueous solution of the highly water-soluble cyclobutanone. A procedure involving the solvolytic cyclization of 3-butyn-l-yl trifluoro-methanesulfonate is described in Org. Syn., 54, 84 (1974). 

In order to ameliorate the problem of solvolytic degradation, compound 109 was treated with TIPSOTf, to provide silyl ether 113 in 72% yield (Scheme 19). The acetonides were removed with PPTS in warm MeOH to provide a mixture of compounds in which the TBS groups were also partially removed. Exposure of this mixture to HF-pyridine successfully generated filipin III (114), in 39 % overall yield from 113. 

Finally, three examples are reported in which iminoboranes as intermediates do not react with trapping agents but stabilize themselves intramolecularly in the gas phase during a hot tube procedure [Eqs. (17)-(19)]. A prerequisite is the steric availability of side groups with respect to the BN bonds (9, 21). The products are well established either by solvolytic degradation (9) or by X-ray analysis (21). Note that... 

An unusual route to system (113) was found by Paetzold. Starting from the borimide (123) and phenylacetylene, compound (124) was obtained, with (125) as a postulated intermediate (Scheme 20). Solvolytic degradation ruled out any isomeric structure containing a 1,2-azaborete ring (68CB2881). 

Units linked to an adjacent unit by a linkage [23] are present in pinoresinol structures and in analogous structures 24 and 25. The isolation of dilactone 26 from lignins degraded by nitric acid provides proof of the occurrence of structures of the pinoresinol type [70]. Solvolytic [29,71,72] and reductive [22,52,53] degradation studies provide evidence of the occurrence of different types of pinoresinol-related structures [24 and 25] in lignins. 

On the basis of mechanism (4-10), it is likely that nitrosation products of primary amines are also carcinogenic. This is, however, not easy to observe, since nitroso-amines of primary amines very rapidly decompose solvolytically, whereas N-nitroso derivatives of secondary amines may accumulate and degrade over a longer period. Indeed, alkylation products of DNA in vitro have been found in the presence of N-nitroso-alkyl-ureas (summary Wiessler, 1986). With AT-nitroso-butylurea, even rearranged butyl-1- and butyl-2- guanine and thymine adducts were found, i. e., products which are typical for the well-known rearrangement of the 1-butyl into the 2-butyl cation. 

First derivative spectra of levomepromazine (LV) and its sulphoxide were employed for investigation of LV photodegradation [11]. The degradation process of biapenem was monitored by measurement of first-derivative amplitude at 312 nm [12]. The determined rate constants for studied process were in good agreement with those obtained by HPLC method [12]. The second-order derivative spectrophotometric method was used for investigation of solvolytic reaction 2-phenoxypropionate ester of fluocinolone acetonide [45]. The run of process was observed by measurement the second-order amplitude at 274.96 nm corresponded to fluocinolone acetonide. The solvolysis rate constant was calculated using derivative method and compare with those obtained by HPLC methods [45]. 

The increased solubility of coal under these conditions (more specifically, at these temperatures) was first reported in 1916 when subbituminous and bituminous coals were extraaed with benzene at 250°F (480°F) and yields of extracts were approximately 10-20 times greater than those obtainable by Soxhlet extraction at the normal boiling point of benzene. Since the nature and extent of the thermal degradation processes in coal depend on temperature, it must be anticipated that the yield and conposition of soluble matter extracted under solvolytic conditions will also vary with extraction temperatures. However, extract yields are, as in milder forms of solvent extraction, also dependent on the choice of solvent. 

Presence of solvolytic agents, oxygen, or other degradation promoting agents... 

Polyurethanes are susceptible to degradation which can be initiated by several means, including photolytic, thermal, oxidative, and solvolytic. With polyurethane adhesives, photodegradation is typically not a problem, since it is uncommon for the adhesive to be exposed to direct light. The other three forms of degradation, however, do pose problems. The factors affecting degradation and the means by which they may be inhibited have been well documented by a number of authors. ... 

The selective removal of C-5 from 2 -deoxynucleosides via de-carboxylative degradation has been reported . Some N-methyl-pyridi-nium, -quinolinium, and -isoquinolinium iodides have been successfully demethylated by simply refluxing their dimethylformamide solution . The solvolytic cyanogen bromide-degradation of alkaloids has been improved by addition of bases such as MgO . 

The solvolytic reactions of the considered polymers containing heteroatoms in their backbone consist in the cleavage of C-0 or C-N bonds of the chain. The polymer chains are degraded according to Schemes 3 to 5, respectively. 

FVom the point of view of the application of ester, amide, and urethane polymers, hydrolysis, alcoholysis/glycolysis and ammonolysis/aminolysis reactions are the most important. These processes are often used for recycling to feedstocks and offer raw materials, mainly for virgin polymer/resin syntheses. The schemes of the respective reactions with brief comments on the practical importance of the particular processes are presented in Figures 2 to 4. A description of the important solvolytic degradation processes for ester, amide, and urethane polymers is also given in this chapter. 

Another polyester type, i.e., polycarbonate, is rather seldom solvolytically depolymerized because of losing (at least partially) carbonate groups/bonds obtained via phosgene route synthesis. Troev et al. [29] recently described PC chemical degradation with dialkyl phosphonates (dimethyl or diethyl) or triethyl phosphate. The products, oligomeric carbonates containing phosphorus atoms, can be considered as precursors for the modification of various polymers by improving their flame-retardant properties, thermal stability, and adhesion. 

Solvolytic methods, as related to the step-growth copolymers, seem to be of minor significance because of the rather complex mixture of the chemical degradation products. However, these methods have some importance for waste polyurethane elastomers and some polycondensation homopolymers. Incineration for energy recovery seems to be of minor importance as a recycling option for TPEs, as compared to some commodity waste polymers. 

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