Dibenzamide

Restelli de Labriola and Deulofeu have degraded benzoylated nitriles of the hexose series and tetrabenzoyl-L-rhamnononitrile, with ethanolic ammonia. The dibenzamide compounds of the lower sugars were obtained, but in the case of compounds with a benzoylated primary hydroxyl group, such as pentabenzoyl-D-glucono-, D-mannono- and D-galactononitriles (XXXI) the benzoyl group that esterifies the terminal hydroxyl was not removed (XXXII). 

With tetrabenzoyl-L-rhamnononitrile (XXXIII), a normal 5-desoxy-L-arabinose dibenzamide (XXXIV) was obtained. 

Examples of the condensation of amides with aldehydes were also known at this time. Roth and Schuster, working in Strecker s laboratory, had prepared benzylidene diacetamide and anisylidene diacetamide by heating the aldehydes with acetamide. Von Richter in 1872 reported that Tawildarow obtained ethylidene diacetamide by heating acetaldehyde and acetamide, and Nencki obtained ethylidene dibenzamide by carrying out a similar reaction in the presence of hydrochloric acid. 

Evidence that the aldose diacetamides are derived from the union of preformed amides with the aldehydo form of the aldose was obtained many years later. Brigl, Miihlschlegel and Schinle, obtained n-glucose dibenzamide (XXXVIII) by the action of methanolic ammonia on penta-benzoyl-oWe%do-D-glucose (XXXVII). They studied the same reaction... 

In the case of the above mentioned benzoyl-D-glucose derivatives a correlation was found between the formation of D-glucose dibenzamide and the permanent or transitory existence of a free aldehyde group. The same behavior was noted for triacetyl-oZdehydc-L-erythrose (XLI), which by the action of ammonia produces L-erjrthrose diacetamide (XLII). Isbell and Frush have obtained a similar result in the case of tetraacetyl-oWe/it/do-L-arabinose which, when treated with methanolic ammonia, gave L-arabinose diacetamide in 53 % yield. 

Dibenzamides of the aldose series were first prepared by Brigl, Muhlschlegel and Schinle and afterward by Restelli de Labriola and Deulofeu. They were highly insoluble in all solvents tried except pyridine. 

Tetrabenzoyl-L-rhamnononitrile was prepared by Restelli de Labriola and Deulofeu in 91 % yield from the oxime with pyridine and benzoyl chloride, and was degraded to 5-desoxy-L-arabinose dibenzamide in very small yield (13%) by treatment with ammonia in ethanol. 

Hexabenzoyl-D-manno-D-fifaZa-heptononitrile was prepared in 89% yield by benzoylation of the free nitrile and degraded in the same way as above to give a sdeld of 33 % D-mannose dibenzamide. 

Selective debenzoylation has been shown to occur by Restelli de Labriola and Deulofeu160 in the cleavage of penta-O-benzoylhexonic acid nitriles (LXXXIII) to form O-benzoyl-pentose dibenzamides (LXXXIV) with ammonia. Since tetra-O-benzoyl-L-rhamnonic acid nitrile (LXXXV) yields 5-deoxy-L-arabinose dibenzamide (LXXXVI), the benzoyl group in the Wohl degradation products is assumed to be in the 5 positions of the resulting pentoses. 

The latest results on imprinted chiral footprints [154] have shown that enantioselective catalysis (hydrolysis) does occur, and based on kinetic measurement the authors believe that this is due to an enantioselective mechanism. Kaiser and Andersson also chose aluminium doped silica as a polymeric material to obtain phenanthrene imprints and their work has been discussed earlier [52]. No selectivity towards the template was observed when imprinted silica was used as stationary phase. Only relative retention and capacity factors increased. Furthermore, even after careful extraction in a Soxhlet, the polymer still leaked phenanthrene. They also found that diazomethane yields a side reaction forming long alkyl chains. Finally they attempted to rej at the work of Morihara et al. [150-155]. but were not able to detect any selectivity using dibenzamide as the template and instead found that the template decomposes into at least five different products when adsorbed on the silica. Clearly further work is required on these systems. 

Later work by Deulofeu and Deferrari further supports this mechanism they showed that D-glucose dibenzamide results from the respective action of ammonia on the pentabenzoates of a-n-glucopyranose, 8-D-gluco-... 

The PMR spectrum of 179 indicated an A-methyl group with restricted internal rotation, one A -methyl group, one proton adjacent to a hydroxyl, five aromatic protons, and a cyclopropyl methylene an amide was inferred from the IR spectrum. The assumption that 179 might be a benzamide of cyclovirobuxine-D (181) proved to be erroneous since benzoylation of 179 furnished a dibenzamide (182) isomeric to, but not identical with, A,A -dibenzoylcyclovirobuxine-D (183). 

Acylation of amides is naturally much harder to achieve, because of their lower basicity, but it is very greatly facilitated by the presence of pyridine.583 617 618 The reason for this effect is, of course, the intermediate formation of 1-acylpyridinium salts as mentioned above.619 For instance, dibenzamide is formed almost quantitatively from benzoyl chloride and benzamide in pyridine solution even at room temperature, whereas there is no reaction in the absence of pyridine.620 Also, by the action of aromatic acid halides on aliphatic or aromatic amides in the presence of pyridine at temperatures as low as —60° to —70° Thompson617 obtained high yields of triacyl derivatives. 

In order to determine the manner in which sulfuric acid interacts with PPTA we are investigating the structure of PPTA oligomers omplexed with sulfuric acid. We have recently determined the structure of a N,N -(p-phenylene)dibenzamide (PPDB)/sulfuric acid complex using single crystal x-ray methods and similar studies with longer PPTA oligomers are underway now. We expect that the general principles for the interaction of sulfuric acid and PPTA will become apparent from these studies. 

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