Imidates formation

Post-Curing. Whenever production techniques or economics permit, it is recommended that compounds based on terpolymer grades be post-cured. Relatively short press cures can be continued with an oven cure in order to develop full physical properties and maximum resistance to compression set. Various combinations of time and temperature may be used, but a cycle of 4 h at 175°C is the most common. The post-cure increases modulus, gready improves compresson set performance, and stabilizes the initial stress/strain properties, as chemically the polymer goes from an amide formation to a more stable imide formation. Peroxide-cured dipolymer compounds need not be post-cured. 

In the absence of solvents and with suitable catalysts the evolution of carbon dioxide simultaneously with the polycarbodi-imide formation gives rise to a foamed product. These foams are cross-linked because of reactions between carbodi-imide groups and free isocyanate groups. Raw materials for such foams are now available from Bayer (Baymid). 

S)-Camphanyl chloride is expensive and limited in supply. And the dias-tereomeric imide formation required 1.6equiv of the reagent... 

In the early 1990s, FTIR was being evaluated at Merck for the in situ monitoring of reactions. This new technology was expected to provide a powerful means to study a reaction as well as a method for analytical control in production [28]. Both silyl imidate formation and the reaction with DDQ could be conveniently monitored by FTIR, as shown in Figure 3.13. Silyl imidate formation was indicated by the appearance of an absorbance at 1667.5 cm4 with concomitant disappearance of the absorbance corresponding to BSTFA at 1324.0cm-1. A new absorbance... 

Unexpectedly, it was found that a small amount of ammonia was released at 25°C in a reaction much faster than the amide hydrolysis. It was suspected that this was due to imide formation, in analogy with the reported behavior of succinamide (11) ... 

Figure 2. Imide formation and hydrolysis from polyacrylamide (2.2 mg/mL) in 0.22 N NaOH at 25 C as monitored by UV absorption at 235 nm.

Whereas, Goharshadi et al. [16] have synthesized the ZnO nanoparticles of 60 nm (Fig. 8.4.) using a room temperature ionic liquid, l-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide, Formation of ZnO was not observed when the ionic liquid was replaced by water. Also, in the absence of ultrasound, formation of ZnO was not observed which is very similar to the one as proposed in the previous case of ZnO dendritic nanostructures. 

Thus, the best compromises for Boc and Fmoc chemistries seem to be cyclohexyl and 2,4-dimethylpent-3-yl (Dmpn), which is of intermediate stability, and the removal of which by trifluoromethanesulfonic acid with the aid of thioanisole (see Section 6.22) leads to minimal imide formation (see Section 6.13). Points to note are that acidolysis of esters by hydrogen fluoride can lead to fission at the oxy-car-bonyl bond instead of the alkyl-oxy bond, thus generating acylium ions that can react with nucleophiles (see Sections 6.16 and 6.22), and that benzyl esters may undergo transesterification if left in methanol. The side reactions of cyclization (see Section 6.16) and acylation of anisole (see Section 6.22) caused by acylium ion formation do not occur at the side chain of aspartic acid.47-51... 

IMIDE FORMATION FROM SUBSTITUTED DICARBOXYLIC ACID RESIDUES... 

FIGURE 6.15 Imide formation from a dipeptide sequence containing an aspartyl residue with side-chain functional group in various states followed by generation of two peptide chains resulting from cleavage at the bonds indicated by the dashed arrows. The reaction is catalyzed by base52 or acid. [Merrifield, 1967]. The table shows the effect of the nature of the substituent on the extent of this side reaction. Dmpn = 2,4-dimethylpent-3-yl. 

These results can be rationalized as follows. Cyclic imide formation is maximal with a Gly residue because of its minimal steric interference. In contrast, steric bulk (i.e., size and branching) of the C-flanking residue is the major factor decreasing the reactivity of Asn to form a succinimide. Residues with a functionalized side chain, namely serine, threonine, and histidine, behaved as exceptions to this rule (see above). 

Clearly, strong 0-H interaction occurs leading to dissociation of ammonia, formation of OH groups, dehydroxylation, and surface imide formation. The NH(a) species has a characteristic N(ls) value of 398 eV, i.e., 1 eV greater than N(a) and 1 eV less than NH2(a). 

Prior to imide formation, the imide-aryl ether ketimine copolymers were converted to the imide-aryl ether ketone analogue by hydrolysis of the ketimine moiety with para-toluene sulfonic acid hydrate (PTS) according to a literature procedure [51,52,57-59]. The copolymers were dissolved in NMP and heated to 50 °C and subjected to excess PTS for 8 h. The reaction mixtures were isolated in excess water and then rinsed with methanol and dried in a vacuum oven to afford the amic ester-aryl ether ether ketone copolymer, 2e (Scheme 8.)... 

Di-carboxy substituted diazepine 226 results in spiro 228 after Boc-protection, hydrolysis, CDl activation and imide formation (Scheme 48, Section 3.1.1.3 (1993JHC897)). The conjugated ester group of (+ )-anthramycin derivative 197 can be constructed by cross-metathesis of pyrrolo-benzodiazepine 196 (Scheme 40, Section 3.1.1.2 (2004T9649)). 

Excessive activity of the enzyme aldose reductase sometimes accompanies diabetes. The net result is often accumulation of reduced sugars such as galactose in the lens of the eye and ensuing cataract formation. A1 restatin (43), an aldose reductase inhibitor, is one of the first agents found that holds promise of preventing diabetes-induced cataracts. The compound, actually used as its sodium salt, is prepared in straightforward manner by imide formation between 1,8-naphthalic anhydride (41) and glycine. ... 

Deamidation and imide formation can also negatively influence a protein s biological activity. Deamidation refers to the hydrolysis of the side-chain amide group of asparagine and/or... 

An epoxytrichloroacetimidate was used as a key intermediate in the total synthesis of (+)-myiiocin. The intermediate diene 157 was constructed in several steps from 156. Stereospecific epoxidation of 157, followed by imidate formation gave 158. Treatment of 158 with Et2AlCl provided 159 for which the proper stereochemistry of the amino group is now set for the natural product (Scheme 8.46). 

Benzimidazoles substituted with an alkylamine at position 2 have a venerable history as Hi antihistaminic agents. The standard starting material for many benzimidazoles consists of phenylenediamine (40-1), or its derivatives. Reaction of that compound with chloroacetic acid can be rationalized by invoking initial formation of the chloromethyl amide (40-2). Imide formation with the remaining free amino group closes the ring to afford the 2-chloromethyl benzimidazole (40-3). Displacement of... 

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