Some studies of the reactions of amines with aldehydes and with aromatic nitro-compounds in acetonitrile
Kinetic and equilibrium studies of the reactions between three trinitroaromatic species, 1,3,5-trinitrobenzene, ethyl 2,4,6-trmitrophenyl ether and phenyl 2,4,6- trinitrophenyl ether and the ahphatic amines n-butylamine, pyrrolidine and piperidine, in acetonitrile were undertaken. It was found that the reactions between 1,3,5-trinitrobenzene and each amine were too fast to measure. However kinetic information was gamed from the decomposition of the c-adducts formed from1.3.5- trinitrobenzene and both pyrrolidine and piperidme. Both the 3-adduct and the 1-adduct are observed as intermediates m the reaction of the ethyl ether with each amine, though formation of the 3-adduct was too fast to measure by stopped flow spectrometry. Formation of the picramides is subject to general acid catalysis due to the poor leaving group ability of the ethoxide ion. Only the 3-adduct intermediate was observed in the formation of each picramide from the phenyl ether. The fact that the 1-adduct is not seen is attributed to the phenoxide ion being a weaker base and hence a much superior leaving group to the ethoxide ion. The equilibrium constants K(_c,3)º and K(_c,1)º are a factor of ca. 10(^4) smaller in acetonitrile than dimethyl sulphoxide. This is due to acetonitrile being inferior to dimethyl sulphoxide in its ability to solvate charged species. The value of k(AM) for reaction at an unsubstituted position approaches the diffusion controlled Unit of acetonitrile. The reactions of propanal, 2-chloroethanal, 2,2-dichloroethanal and 2,2,2- trichloroethanal (chloral) with ammonia and several primary amines were studied. Only the reactions of ammonia with propanal and 2-chloroethanal produced the corresponding 2,4,6-trisubstituted-l,3,5-hexahydrotriazme.Reactions of the aldehydes with primary ammes yield propylidene imines as relatively stable species. Trimerisation was not observed however the imine may undergo dimerisation together with elimination of amine. Kinetic and equilibrium studies are reported on the formation in acetonitrile of2.4.6- triethyl-l,3,5-hexahydrotriazine, (TEHT), from propanal and ammonia, and also the corresponding decomposition reaction. The equilibrium constant was found to decrease with increasing water content in the acetonitrile which can be attributed to stabilisation of ammonia by the water. Good correlation was achieved for values of the equilibrium constant calculated directly from absorbance measurements and from combination of rate constants obtained from the formation and decomposition reactions.