Ester-group decomposition

Thermal decomposition, viz. dehydrochlorination of PVC, unzipping of PMMA or POM, ester-group decomposition, carbonization of lignin, etc. 

PMMA, which in itself is stable on exposure to NO2, enters into reactions after previous irradiation by UV light at 293 K [16]. The photolysis of PMMA induces the formation of double bonds as a result of ester group decomposition. The ESR spectrum observed after exposure of samples to NO2 is shown in Figure 2. The spectrum represents the superposition of the signals of two nitroxyl radicals at low frequencies of rotational mobility (10 s < Tc < 10 s) ... 

Being cross-linked, the resin will not dissolve without decomposition but will be swollen by liquids of similar solubility parameter to the cured resin. The chemical resistance is as much dependent on the hardener as on the resin since these two will determine the nature of the linkages formed. The acidic hardeners form ester groups which will be less resistant to alkalis. 

One heterocyclic subunit which is an excellent donor group is the 2,6-pyrido-sub-stitutent - ". However, when 4-chloro-2,6-dicarboxypyridine was utilized as precursor to the macrocycle, the product apparently was less stable than was the corresponding nonchlorinated ester The decomposition was apparently initiated by complexation of either Sr or Ba " but the mechanism by which this degeneration occurred was not suggested nor is it obvious to the present authors, especially in the absence of any commentary concerning the products of decomposition. The synthesis of the apparently unstable system is illustrated below. 

Hydrazine was first obtained by hydrolytic decomposition of bis-diazoacetic acid . The latter, a tetrazine derivative, is obtained from ethyl diazoacetate in the form of alkali salt by the (catalytic) action of strong alkali. Two molecules of the acid simply unite and, at the same time, the ester group is hydrolysed ... 

A, 1). The thermal stability with respect to retro-Diels-Alder reaction of those derivatives with ester groups at the 2- and 3-positions increases with increasing electron withdrawal by the N-suhstituent. Prinzhach et al made revealing comparisons of the decomposition of the adducts 15-18 at 65° which support this generalization. The diacid (5) decomposed in refluxing aqueous sodium carbonate to regenerate A-benzylpyrrole -7 some of the anhydride (6) was also obtained on acidification of the reaction mixture. 

The industrial production of copolymers of trioxane with ethylene oxide or di-oxolane (1-5%) is conducted as a bulk polymerization in special equipment. The incorporation of small amounts of C-C bonds into the C-0 chain has a remarkable effect on the thermal and chemical stability. In homopolymers the thermal decomposition starts at the semiacetal end groups ( unzipping ) and leads to a complete destruction of the polymer chain, whereas this reaction stops in copolymers already at the first C-C bond. A thermally stable OH end group is thus formed which, in addition, contributes to a much better alkali resistance compared to ester group-terminated homopolymers (see Examples 3-40 and 5-13). 

A new synthesis of cr-substituted and a,a-disubstituted a-amino acid derivatives based on the ammonium ylide formation/[2,3]-sigmatropic rearrangement has been recently reported by Clark s group.Decomposition of a-diazo -keto ester 153 was studied in detail with Rh2(OAc)4, Cu(acac)2, and Cu(hfacac)2 as the catalyst. Cu(acac)2 and Cu(hfacac)2 gave similar results, but Rh2(OAc)4 turned out less effective (Equation (23)). 

Hydrolysis and transesterification of 85a result in the ester acid (85f) and the mixed ester (85b), respectively. The ester group in the 5-position has been shown to be severely hindered and is not coplanar with the ring system. Attempts to remove functional groups by thermolysis of 85c, 85e, and 85f failed, decomposition taking place instead.106,101... 

Desmaroux [73a] followed the decomposition of nitrocotton kept at a temperature of 132°C and established that the reaction types (1) and (3) predominated. Only j-j of the substance broke down by the hydrolysis of ester groups. Desmaroux also determined the loss of weight of the sample so as to compare it with the loss of nitrogen. The weight loss of the nitrocellulose calculated on the basis of the nitrogen lost is 3-12 times smaller than the total weight loss, as seen from the data in Table 66. 

The synthesis of the [2.3.4]cyclazine derivatives (301) and (186) has been described in Section 3.08.6.3.2 (Scheme 24). It has been shown in Section 3.08.6.1.3 that attempts to synthesize 9-aza[2.3.4]cyclazine (302) yielded the 8,9-dihydro derivatives (146), which may have been formed by reduction of the intermediate cyclazine. Attempts to remove the ester groups of (301) and (186) by hydrolysis of the ethyl ester and subsequent thermal decarboxylation or by thermolysis of the f-butyl ester failed. The reaction of (301) with LAH led to decomposition. The preparation of a dihydro[2.3.4]cyclazine derivative (89) has been described in Section 3.08.3.5. It has been pointed out that an attempted elimination of HCN, to give the fully conjugated cyclazine, failed. 

Discussion Catalyst 52 is prepared from Boc-(L)-ter -leucine in five steps, with a 75% overall yield [41]. Details of imine and phosphite preparation are also provided by Jacobsen and co-workers [81]. The hydrophosphonylation reactions as reported by Jacobsen can be carried out without any special precautions, in unpurified commercial diethyl ether (Et20) and under an ambient atmosphere. A reduction in temperature was shown to have a beneficial effect on product enantiopurities, but with a decrease in reaction rates. Unbranched aliphatic aldehydes were incompatible with the reaction conditions as reported, due to their rapid decomposition prior to phosphonylation. Although phosphite ester groups that are more electron-withdrawing than o-nitrobenzyl significantly increase the overall reaction rates, products are obtained with diminished optical purities, possibly due to a retro-addition pathway. 

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