Cyclic anhydride structures

Scheme 5.19 Synthesis of a bis[3]catenane 19 with two cyclic anhydride structures.

Ortho-xylene may be oxidized directly by air in vapor phase over vanadium pentoxide catalysts under conditions resembling those used in oxidation of naphthalene to phthalic anhydride. The stability of the cyclic anhydride structure of phthalic anhydride at the temperatures required and in the presence of oxidizing conditions is, of course, the distinctive feature. Since the oxidation of o-xylene to phthalic anhydride requires the theoretical interaction of only six atoms of oxygen relative to the nine required by naphthalene, the amount of heat generated per unit of product is less, and the volume of diluent gases in the product stream may be lower. Because of decreased formation of quinones and color bodies, product purification should be easier. Very little is available by way of information relative to commercial operating conditions. Some laboratory results of early work showed a maximum conversion to total acids of 18.2 per cent when commercial xylene was oxidized in vapor phase over unfused vanadium oxide catalyst. Recent work with o-xylene showed a conversion of 42.7 per cent to phthalic anhydride over unfused vanadium oxide catalyst and conversions up to 61.7 per cent to phthalic anhydride plus fi.6 per cent to maleic... 

A mechanism can only be presented with confidence in the case of PIPA and PTBA, for which the nonradical ester decomposition route to alkene and carboxylic acid provides a satisfactory explanation (Scheme 7). There are six and nine P hydrogens respectively in these structures. The initially produced carboxylic acid groups dehydrate to give the six-membered cyclic anhydride structure. Carbon dioxide probably arises either by decarboxylation of some of the CO2H groups or by decomposition involving the cyclic anhydride. 

Pyrrole is one of the most prominent heterocycles, having been known for more than 150 years, and it is the structural skeleton of several natural products, synthetic pharmaceuticals, and electrically conducting materials. A simple access to the pyrrole ring system involves the conversion of cyclic anhydrides into five-membered imides. Mortoni and coworkers have described the conversion of 2-methylquinoline-3,4-dicarboxylic acid anhydride to a quinoline-3,4-dicarboximide library by treatment of the anhydride with a diverse set of primary amines under microwave conditions (Scheme 6.180) [341]. The authors studied a range of different conditions, including dry media protocols (see Section 4.1) whereby the starting materials were adsorbed onto an inorganic support and then irradiated with microwaves. For the transforma-... 

In this short section, cyclic compounds are discussed that are not strictly lactones since they contain an endocyclic structural motif of the type -O-CO-X- or -X-O-CO-. However, these compounds share with lactones the possibility to be hydrolyzed at the endocyclic -CO-O- bond. This is the case for cyclic diesters of carbonic acid (-O-CO-O-), cyclic esters of car-bamic acid (-0-C0-NH-), and cyclic anhydrides (-C0-0-C0-). One example of each class is presented here. 

Succinic anhydride, the structure of which is shown, is a cyclic anhydride often used in Friedel-Crafts acylations. Give the structure of the product obtained when benzene is acylated with succinic anhydride in the presence of aluminum chloride. 

In this paper, we try to review results obtained from anionic copolymerization of cyclic ethers with cyclic anhydrides. For a better understanding data and theoretical views on non-catalyzed copolymerizations are also included. We concentrate mainly on the kinetics and mechanism of copolymerization and the effect of the type and character of the initiator used. The influence of the epoxide and anhydride structure on copolymerization, of proton donors on the rate and course of copolymerization, and on the molecular weight of the resulting polyesters are also discussed. 

However, the experimental data in the literature do not allow to determine the effect of the structure of the amines on the rate of copolymerization of epoxides with cyclic anhydrides, nor to verify the validity of Eq. (36) for this type of reaction. 

The question of initiation, structure and character of the active centre is fundamental for the copolymerization of epoxides with cyclic anhydrides. We therefore analyze arguments supporting individual mechanisms. Since in most mechanisms HA compounds are involved, the question arises whether proton donors are necessary for the formation of an active centre. 

Proton donors may be present or formed at the beginning of copolymerization and are necessary for the formation of primary active centres. In such a case, initiation according to Fischer s mechanism 39,40 (Eq. (37)) does not take place. Although the formation of a zwitterion (betaine-like structure) supports the possibility of the generation of charge-transfer complexes between cyclic anhydrides and amines, which may yield betaine-like structures82), simple anhydrides are much weaker ti acceptors than the often employed tetrachlorophthalic anhydride. 

A hydrolase-type reaction is otherwise rare in homogeneous catalysis, but the opening of prochiral cyclic anhydrides mediated by cinchona alkaloid in the presence of methanol leads to optically active hemiesters (Bolm, 2000). Very structurally di-... 

Because the anhydride is cyclic, its structural units are not incorporated into a ketone and a carboxylic acid as two separate product molecules. Rather, they become part of a four-carbon unit attached to benzene by a ketone carbonyl. The acyl substituent terminates in a carboxylic acid functional group. 

Structure 5.5). Cyclic neopentyl thiophosphoric anhydride (Structure 5.6), a solid additive, is used to flame retard viscose rayon, especially in Europe. In spite of the anhydride structure, it is remarkably stable, surviving addition to the highly alkaline viscose, the acidic coagulating bath, and also resisting the multiple launderings of the rayon fabric. 

The selected example by Seneci et al. [51] reported the use of an IDA-DC [52] (iminoDiacetic acid based double cleavable) linker for structure determination and controlled release of pool libraries based on teicoplanin aglycone (TD) [53] and tested for their antimicrobial activities. The synthesis and the structure of the linker and the structure of teicoplanin aglycone are shown in Figure 9.15. Starting from iminodiacetic acid the linker was prepared in four trivial chemical steps (the cyclic anhydride used in step 4 was prepared in two steps from iminodiacetic acid) its structure was symmetrical with the amide arm bearing the carboxylic handle for the solid support attachment and the identical other arms bearing protected propylamine groups for the library synthesis. 

Although they are more difficult to formulate into epoxy adhesive systems, anhydride cured epoxies have somewhat better thermal stability than amine cured systems. Aromatic and cyclic anhydrides, such as phthalic anhydride, pyromellitic dianhydride, and chlorendic anhydride, provide the most stable structures. 

Curing with anhydride hardeners requires a long curing time and a high temperature. The cured resins are excellent in mechanical and particularly in electrical properties at temperatures above Tg. Anhydride hardeners are extensively used. Many practical studies on mechanical and electrical properties 381 but few systematic studies on the structures of the cured resins and physical properties have been reported 27,39 41). The reasons why such systematic studies are scarce are as follows Most of the acid anhydride hardeners are cyclic anhydrides of dibasic acids. The main structure of the cured resins is such as shown in Fig. 1 b. Differences among the structure of the cured resins with different hardeners are only based on the differences in the R segment and consequently, cured resins with rather different mechanical properties cannot... 

Problem 16.36 Give the structural formula and name for the product formed when 1 mol of succinic anhydride, the cyclic anhydride of succinic acid (Problem 16.22), reacts with (a) 1 mol of CH3OH (b) 2 mol of NH3 and (c) 1 mol of C6H6 with A1C13. M... 

Fig. 18. Schematic tree-like representation of the structures monoepoxide-cyclic anhydride (a), and diepoxide-cyclic anhydride (b)...

The data manipulation capabilities of the FTIR spectrometer can be used to quantitatively resolve the structural features which are superimposed upon the intrinsic absorption. The spectral features which exceed a baseline drawn between 1880 and 880 cm 1 in five independent preparation and measurement experiments are shown in Figure 4. The superposition of these five spectra illustrate both the reproducibility and the quantitative nature of this technique. The "resolved" spectra consist of three broad absorptions centered around 1725,1595 and 1245 cm1 and two superimposed sharp bands at 1135 and 1340 cm1. These latter peaks are characteristic of the particular type of carbon black and are presumably caused by impurities introduced in the manufacturing process. They may reflect the presence of residual sulfur compounds present in the form of sulfones or sulfonic esters in which the symmetric and antisymmetric stretching modes of the S02 vibrational modes occur in the range of 1140-1160 cm1 and 1300-1350 cm 1 [24], Note the absence of discemable bands above 1730 cm 1. This implies that these carbon blacks do not contain the lactone and cyclic anhydride functionalities observed on other carbon surfaces (see Figure 1) [17]. 

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