The decomposition products of 3-hydroxy-5-phenyl-2, 4(3H, 5H-frandione (FH
2), dihydro-4-hydroxy-5-imino-2-phenyl-3(2H)-furanone (IFH
2), 5-phenyl-2, 3, 4(5H)-furantrione (F), and 3-phenylhydrazone of F, which have an enediol group in their molecules and are partly similar to L-ascorbic acid (AAH
2) and dehydroascrobic acid (DHA) in their structure, were investigated in connection with their browning activities. The reaction of these reductones with 7-tolylamine (pT) was carried out in ethanol solution as described in the previous paper
3) of this series. The browning activities of FH
2 and F were much stronger than those of AAH
2 and DHA. The browning reaction of FH
2 required air and its decomposition did not progress in N
2, while that of F did in N
2 as smoothly as in air. Oxalo-p-tolylamine (I), oxamoyl-p-tolylamine (IIa), mesoxamoyl-p-tolylamine hydrate (IIIa), N, N'-di-p-tolylurea (IV), p-tolylmandelamide (V), p-tolylbenzamide (VI), and p, p'-azotoluene (VII) were separated and identified as the decomposition products in the reaction of IFH
2 with pT. N, N'-Di-p-tolyloxamide (IIb) and N, N'-di-p-tolylmesoxamide hydrate (IIIb) were obtained in addition to I, IV, V, VI and VII in the reaction of pT with either FH
2 or F. Formation of these products suggests that the decomposition of these reductones with PT proceeds through a radical cleavage of one to three carbon fragments in the lactone ring of FH
2 and F ; IIa and IIb are originated from C
1-C
2, IIIa and IIIb from C
1-C
2-C
3, V from C
3-C
4, VI from C
4, and the formation of I and IV may be attributed to the secondary decomposition of IIIa or IIIb. It is also assumed that the formation of VII is attributable to the condensation of two p-tolylaminyl groups which may be formed by the elimination of p-tolylamino group from the condensation products between pT and FH
2 or F. These facts indirectly indicate that the browning reaction proceeds by autoxidation.
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