90 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 10 8 6 4 2 0 • Figure 4. •H-NMR spectrum of compound 1. fragmentation pattern is reported in Scheme II. Also in this case a good relationship between the proposed structure and the El-induced fragmentation pattern has been found. Most of the total ion current is retained by the molecular ions at m/z 246, which give rise to the base peak of the mass spectrum. This behavior is in agreement with the aromatic-like proposed structure. The primary fragmentation pathway consists in methyl loss, leading to [C12H705] + ions at m/z 231 and to CO and CHO' losses. These last two fragmentation pathways result quite typically in El mass spectrometry of qui- nones and pyranones (8). For the ions at m/z 218, the formation of a substituted furan 2 , +. rearr. ' • H3C-.•.•.•' O • m/z 149 (33) O •• 0 0 0 0 H •C13H1oO• +' • ........ rearrange7t M+',m/z 246 (1OO) m/z 203 (68) •C12H904] + m/z 217 (20) Scheme II • C9H503] + m/z 161 (9) •C 12H705] + m/z 231 (5) II 0 +' +. OCH [C12H1oO4 ] - 3 m/z 218 (10) C oH70 3 m/z 175 (18)

REACTION OF DEHYDROACETIC ACID AND FORMALDEHYDE 91 16.60 10 8 6 4 2 0 • Figure 5. •H-NMR spectrum of DHA. ring can be invoked, due to the higher stability of such a polycyclic structure. Analo- gously, for the ions at m/z 217 the formation of a pyranyl cation can be proposed. Finally, the cleavages 1 and 2 reported in Scheme II, of the polycyclic skeleton lead to ionic species [C9H503] + (m/z 161) and [C8H503] + (m/z 149) respectively, while the primary CH3CO loss leads to [CllH704] + ions. Having determined the structure of the reaction product of DHA.Na and formaldehyde in aqueous solutions, we thought it of interest to test its presence in cosmetic formula- tions containing DHA.Na and Bronopol © or Germall 115 ©. HPLC runs of a standard solution of compound 1 and of cosmetic emulsions (3 months stored at room temperature) preserved with Prevan-Bronopol © and Prevan-Germall 115 © are reported in Figure 6. The cosmetic samples were diluted 1:10 with THF/H20 (9/1) before HPLC analysis (9). In their chromatographic patterns there clearly appears a well-marked peak presenting the same k' = 1.76 of compound 1. In order to confirm its structure we collected the corresponding peak fractions that had undergone mass spectrometry analysis. The spectra, in accordance with the standard, gave unambiguous evidence of the reaction between DHA.Na and CH20 released by preservatives. Other ingredients of the cos- metic formulation did not affect the formation of 3,7-dimethyl-lH,9H,10H-di- pyrano[4,3-b: 3', 4' -e]pyran- 1,9-dione. CONCLUSIONS An interaction product between DHA.Na and formaldehyde released from other preser- vatives has been demonstrated by HPLC methods using aqueous solutions or cosmetic formulations. The structure of this unexpected product appears to be: 3,7-dimethyl- 1H,9H,10H-dipyrano[4,3-b:3',4'-e]pyran-l,9-dione, by elemental analysis, •H- NMR, mass spectrometry and X-ray analysis. In contrast to what has been suggested in the past, the degradation product exhibits a