88 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a) • -------- ' ---•---e --. Prevan Prevan-Bronopol Prevan-Germall 11 5 7 14 21 28 35 Days Bronopol Preyan b) t = 0 t = 5 weeks • Bronopol - -- Prevan interaction product Prevan ------- • Germall ll5 •E' Prevan Germall 11 5 •1 ----------- interaction product Figure 1. a) Trend of DHA.Na concentrations vs. time. b) HPLC runs of binary mixtures DHA.Na- Bronopol © (see method la) and DHA.Na-Germall 115 © (see method lb). with an integral three times each of the two mentioned above. The appearance of the spectrum is very dissimilar to that of DHA (Figure 5): a one-proton singlet at 8 16.60, a one-proton quartet at 8 5.93 with coupling constant of 0.7 Hz, a singlet at 8 2.67, and a doublet at 8 2.29, both with a three-proton integral. Noticeable is the disappear- ance in the spectrum of compound 1 of the acetyl group at 8 2.67, and the mainte- nance of the methyl group and that of the corresponding coupled (J = 0.7 Hz) proton at 8 2.26 and 8 5.88, respectively. The other noticeable feature is the great variation of chemical shift from 8 16.60 to 8 3.29 for the remaining peak. In the first case it can be due to a very deshielded proton, attributable to the acidic hydrogen atom in the 3-posi- tion, while in the second it could originate from a slightly deshielded aliphatic proton(s). According to the molecular weight, the molecule should have a symmetry plane, and therefore the latter peak must be attributable to a methylene moiety. From
REACTION OF DEHYDROACETIC ACID AND FORMALDEHYDE 89 I. 280 1.02o 0.768 0.512 0.256 4 8 min. O. 16 O. 32 O. 48 O. 64 O. 80 Formaldehyde mg/ml Figure 2. Chromatographic pattern of a DHA.Na/formaldehyde water solution five weeks after storage and DHA.Na behavior in dependence on formaldehyde concentration. the above-reported data and from comparison with simple calculations of chemical shift, based on the usual additivity rules, we suggest the structure 3,7-dimethyl- 1H, 9H, 10H-dipyrano[4,3-b: 3 ', 4'-e]pyran- 1,9-dione (7). The 70 eV E1 mass spectrum of compound 1 is shown in Figure 3, while the related 1 OO- 246 Rel. Ab. 80- 60- 40- 20- 149 I 175 69 85 J 161 I ß J,,IL,,i,,,J .... , ..... I,,...,,, ..... ,,, ........ ,,, .... .•.,. ,...•L .... ,,i .... I, I i I 50 100 150 203 217 ,, ,, • ,, I,,i • Ii 200 250 m/z Figure 3. 70 eV EI mass spectrum of compound 1.
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REACTION OF DEHYDROACETIC ACID AND FORMALDEHYDE 87 following procedure: frequency 80 MHz mode FT lock internal from CDC13 tempera- ture 3 iøC solvent CDC13 with 1% v/v TMS as internal standard concentration about 0.1 M tube size 5 mm O.D. pulse width 58 }xs: acquisition time 1 sec spectral width 1500 Hz no. of transients 100 no. of data points 4K (16K with zero filling before FT). Coupling constants are given in Hz the relative peak areas, the decoupling experi- ments, and calculations of the chemical shifts using additivity rules were in agreement with all assignments. Mass Spectrometry. All measurements were performed on a VG ZAB 2F mass spectrom- eter operating in Electron Impact (EI) conditions (70 eV, 200 }xA). Samples were intro- duced via direct inlet system with an ion source temperature of 200øC. Metastable transitions were obtained by B/E linked scans (6). Exact mass measurements were per- formed by the peak matching technique at 10,000 resolution (10% valley definition). RESULTS AND DISCUSSION Our observation that some formulations could not prevent the development of molds over a long period of time suggested the possible degradation of the preservative system. Hence we undertook a study of the kinetics of disappearance of DHA.Na vs time, either alone or in a mixture with formaldehyde releasers (Bronopol © or Germall 115 ©) via HPLC. The results, reported in Figure la, showed that there is a strong decrease in the concen- tration of DHA.Na in the presence of Bronopol © or Germall 115 © in comparison with control samples of DHA.Na alone. It was postulated that this decrease was due to an interaction between DHA.Na and the released formaldehyde, giving rise to the forma- tion of a new product. In fact, the HPLC runs of binary mixtures showed a third product, whose concentration is time-dependent (see Figure lb). To confirm the involvement of formaldehyde in the reaction, we carried out a series of tests on aqueous solutions of DHA.Na and formaldehyde in different molar ratios. The results, reported in Figure 2, fully support our hypothesis. The observed peak due to the interaction product was confirmed by various HPLC methods to be a unique product (4) whose structure must be determined as a first necessary step for further toxicological studies. The unknown product (compound 1) is obtained as a precipitate in significant amount (1.4 g) with a 25% yield by long-time (4 weeks) reaction of aqueous equimolecular (0.08 M) solutions of DHA. Na and formaldehyde at room tem- perature. The product, recrystallized from chloroform, does not melt up to 340øC. The elemental analysis gave: C, 63.44% H, 3.99%, which is in accordance with a molec- ular formula: C13HloO 5 (Calculated: C, 63.41% H, 4.09%). The corresponding mo- lecular weight was confirmed by mass spectrometry. In fact, the 70 eV electron impact mass spectrum (Figure 3) shows the most abundant peak at m/z 246, in agreement with a molecular ion [C13HloO5] +o. Furthermore, accurate mass measurements gave a value of 246.0534 (_+0.002), in agreement with the molecular formula C•3HloO 5 (246.0525). The •H-NMR spectrum (Figure 4) shows a quartet at 8 5.88 with a coupling constant of 0.8 Hz, a broad singlet at 8 3.29 with the same unit integral, and a doublet at 8 2.26
88 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a) • -------- ' ---•---e --. Prevan Prevan-Bronopol Prevan-Germall 11 5 7 14 21 28 35 Days Bronopol Preyan b) t = 0 t = 5 weeks • Bronopol - -- Prevan interaction product Prevan ------- • Germall ll5 •E' Prevan Germall 11 5 •1 ----------- interaction product Figure 1. a) Trend of DHA.Na concentrations vs. time. b) HPLC runs of binary mixtures DHA.Na- Bronopol © (see method la) and DHA.Na-Germall 115 © (see method lb). with an integral three times each of the two mentioned above. The appearance of the spectrum is very dissimilar to that of DHA (Figure 5): a one-proton singlet at 8 16.60, a one-proton quartet at 8 5.93 with coupling constant of 0.7 Hz, a singlet at 8 2.67, and a doublet at 8 2.29, both with a three-proton integral. Noticeable is the disappear- ance in the spectrum of compound 1 of the acetyl group at 8 2.67, and the mainte- nance of the methyl group and that of the corresponding coupled (J = 0.7 Hz) proton at 8 2.26 and 8 5.88, respectively. The other noticeable feature is the great variation of chemical shift from 8 16.60 to 8 3.29 for the remaining peak. In the first case it can be due to a very deshielded proton, attributable to the acidic hydrogen atom in the 3-posi- tion, while in the second it could originate from a slightly deshielded aliphatic proton(s). According to the molecular weight, the molecule should have a symmetry plane, and therefore the latter peak must be attributable to a methylene moiety. From

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