THE MUSK ODOUR 427 The propyl ketone (isobutyryl) compound possesses a faint musk odour, but is rather fugitive. The compound 4-acetyl-6-tertiarybutylindane is odourless, but the introduction of one methyl group in the 1 position results in a compound with an odour of medium strength and somewhat like musk ketone with some ambrette sweetness. Although the initial odour is quite strong, it is not long lasting. The introduction of a second methyl group in the 1 position produces quite dramatic results, the new compound possessing a strong, clean intense odour similar to musk ketone. The odour remains on the smelhng slip for a reasonably long period of time. When the sub- stituents in the 1.1 position are methyl and ethyl, the resulting compound is rather similar in odour to the 1.1-methylmethyl compound but has inferior lasting powers. The introduction of an isopropyl group in the 6 position results in a musk compound of medium strength. When the substituent is tertiary butyl the odour is of a strong musk ketone type and long lasting: a secondary butyl group produces only a weak odour similar to musk ketone and which is not long lasting. The introduction of a tertiary amyl group results in a strong smelling musk rather similar to the corresponding tertiary butyl compound. Two outstanding indane musks are, 4-acetyl-l.l-dimethyl-6-tertiary- butylindane (X) and 6-acetyl-l.l.3.3.5-pentamethylindane (XI):-- Compound X possesses a fine strong odour somewhat similar to musk ketone but more intense and with a suggestion of jasmin. Compound XI is a strong musk-like body somewhat sharp and fruity. A large range of indane musks has been described a. THE NITRO MUSKS It will be noticed that the important nitromusks all possess a high degree of substitution. The five commercially available nitro musks are:

428 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS musk xylene (XlI), musk ketone (XlII), musk ambrette (XlV), moskene (XV) and tibetine (XVI). NO: I CH• HaC Ha HaC CHa O•N NO: O.•N•NO• O•N• N kkv//' 0CHa HaC • C • CHa O, I HaC • [ • CHa CHa HaC • C • CHa { CHa (XlI) (XlIl) (XlV} CH: CHa O: 0, •C HaC, Ha CH, O,N"'•'N0• HaC• H:C -- C -- CH• CH: •H: (xv) (xw) Musk xylene Musk ketone Musk ambrette (moskene could also be placed in the category of an indane compound.) The above five compounds possess the following odour characteristics: Full, not intense, "chemically". Cleaner and sweeter than xylene. Intense, rather metallic-blackberry, a little of the ester intensity, sharp. Moskene Somewhat similar in odour to ambrette but rather weaker and lacking the penetrating intensity. Tibetine Has an odour rather similar to musk xylol with a little of the musk ketone effect. THE STEROID MUSKS Quite frankly, the steroid musks are of academic interest only. It appears that only a very small group of steroids possess an appreciable