Hexahydro-oxadiazines

The antimicrobial efficacy of the amine-formaldehyde reaction products essentially corresponds to the formaldehyde content of these compounds. Known exceptions are HTA, hexahydro-oxadiazines and octahydro-s-tetrazines, which derive from ammonia respectively certain alkylolhydrazines (Paulus, 1980) here the detection of formaldehyde by the Taimenbaum methods gives a negative result, which means that these substances have no significant antimicrobial effect at neutral to alkaline pH they release formaldehyde in acidic media only. This pH dependency is broken off, if, for example, HTA is quatemized (Jacobs et al., 1916). In contrast to HTA the quaternary hexaminium salts release formaldehyde widely independent of pH and therefore may be used as preservatives also for media of neutral to alkaline pH. They are not comparable with the surface active conventional quaternary ammonium compounds (QACs see Section 16.1)... 

Recently, a variable-temperature study of the 13C-NMR of 3,4-dimethyl-hexahydro-l,3,4-oxadiazine and of the trans-fixed derivative 434 have completely clarified the conformational equilibria and allowed a rather complete energy contour to be constructed for the monocyclic oxadiazine (Fig. 17).344 The conformational analysis of other methyl-substituted tetrahydro-1,3,4-oxadiazines345,346 is consonant with these results. 

Differential thermal analysis was conducted for 2-methoxy-7,8,9,10-tetrahydropyrido[2,l-c][l,2,4]benzothiadiazine-5,5-dioxide, and it was found that this compound exists in two polymorphic forms, one of them being remarkably unstable. Detailed conformational analyses for hexahydro[2,l-6][l,3,4]oxadiazines <93AX(C)1786> and hexahydropyrido[2,l-e][l,2,5]oxadiazines <92AP(325)157> were described on the basis of x-ray and NMR studies, respectively. 

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