392 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS linalool (A) III VIII , (B) . • II V •1 Figure 4. Decomposition of linalool over ultramarine blue and red iron oxide with microcatalytic reactor at 178 ø C. (A) Ultramarine blue. (B) Red iron oxide. black iron oxide or hydrated chromium oxide, only cis-ocimene, trans-ocimene, and myrcene were formed. With those pigments of moderate conversion rates, such as silica and mica, limonene and terpinolene were also formed. With pigments of high conver- sion rates, such as prussian blue and red iron oxide, cis-alloocimene, trans-alloocimene, alpha-terpinene, and p-cymene were also formed. AMOUNT OF THE PIGMENT AND THE DISTRIBUTION OF THE DECOMPOSITION PRODUCTS Figure 5 shows the variation in the yield of the decomposition products from linalool by changing the amount of talc. Myrcene plus ocimene gradually decreased as the amount of talc increased. On the other hand, limonene plus terpinolene and alpha-terpinene showed less change, while alloocimene and p-cymene generally increased, which corre- sponds well with the fact that alloocimene and p-cymene are formed over the pigments at high conversion rates. REACTION OF LIMONENE AND TERPINOLENE Table IV summarizes the reaction of limonene by these cosmetic pigments. Examina- tion of the data of Tables III and IV suggests that those pigments that do not produce

DECOMPOSITION OF LINALOOL BY PIGMENTS 393 Table III Decomposition of Linalool Over Cosmetic Pigments With a Microcatalytic Reactor Linalool Product distribution (%) recovery Pigments (%) I II III IV V VI VII VIII IX Other Zinc oxide 86.5 nd nd Black iron oxide 57.5 75.0 12.5 Hydrated chromium oxide 54.0 73.3 nd Cobalt blue 34.5 64.3 11.9 Silica 23.0 50.0 15.6 Mica 34.5 43.6 12.0 Yellow iron oxide 15.0 43.7 12.5 Talc 25.0 19.4 12.9 Titanium dioxide A 20.5 26.2 12.3 Ultramarine blue 18.5 46.2 14.3 Titanium dioxide R 9.5 24.0 15.6 Titanium dioxide A-R 7.5 20.9 6.8 Ultramarine violet 2.5 25.4 10.9 Prussian blue 1.0 10.0 6.9 Kaolinire 0.5 7.9 1.1 Red iron oxide 1.0 11.3 7.2 nd nd nd nd nd nd nd nd 12.5 nd nd nd nd nd nd nd 26.7 nd nd nd nd nd nd nd 16.7 7.1 nd tr tr nd nd nd 21.9 12.5 tr nd nd nd nd nd 25.6 10.5 2.3 nd nd nd nd 6.10 16.3 22.5 5.0 nd nd nd nd nd 14.4 13.7 10.1 7.2 10.9 9.4 tr 2.0 12.3 18.0 13.1 8.2 9.8 nd nd 0.1 24.4 11.7 1.7 0.8 0.8 nd nd 0.1 13.5 12.5 7.3 5.2 11.4 10.4 nd 0.1 10.5 12.6 7.9 4.2 7.3 5.8 nd 24.0 17.4 12.3 7.2 2.9 4.3 8.0 7.2 4.4 7.7 6.9 3.1 1.5 1.5 6.9 30.8 24.7 9.1 1.1 11.4 5.7 9.1 30.7 11.4 12.5 12.4 13.4 12.9 4.6 6.2 16.5 8.8 6.7 Reaction temp., 178 ø C carrier gas, N 2 50 ml/min pigment amount, 10 mg pulse size, 0.3 }xl nd, no detectable amount of decomposition product found. limonene from linalool do not change limonene. The reaction products of limonene with these pigments are the cyclized terpenoids such as alpha-terpinene, gamma-ter- pinene, terpinolene, p-cymene, etc. Products such as myrcene and ocimene were not detected, as in the case of the reaction of terpinolene with these pigments summarized by Table V. This shows that once a terpenoid cyclizes, the ring does not reopen. Since limonene isomerizes into terpinolene and vice versa, as stated by Wystrach et al., it is likely to occur by addition of a proton and formation of an intermediate (iv) (11). Though decomposition of p-cymene was investigated, it was not changed further over any pigment. Therefore, p-cymene is considered to be the most stable of these com- pounds. DECOMPOSITION MECHANISM OF LINALOOL OVER COSMETIC PIGMENT Figure 3 summarizes a proposed decomposition mechanism for linalool over cosmetic pigments. First of all, linalool forms an oxonium ion (i) by proton addition in the same manner as noted with t-butyl alcohol. The oxonlure ion is then alehydrated to form a carbonium ion intermediate (ii). Then, a proton can be eliminated preferentially from the adjacent carbon atom according to Saytzeff elimination, forming myrcene and 3,7- dimethyt-l,3,6-octatriene. However, due to the presence of the double bonds, two other isomers, cis-ocimene and trans-ocimene, form. When a pigment of low activity is used, only these three compounds will be produced. Under more stringent pigments, an intermediate (iii) is produced by allyl rearrange- ment, which can form a cyclized intermediate (iv), and then limonene and terpinolene are produced by proton elimination. It is known that such allyl rearrangement is liable to proceed when linalool changes into geraniol.