Trapped air (oxygen) will be a technical consideration for
aerosols into the foreseeable future, complicating the product
Under certain conditions, both ethyl alcohol and lower dialkyl ethers can slowly react with air (oxygen). A
report suggests that ethyl alcohol and air can produce traces of acetaldehyde in the presence of small catalytic
levels of water and iron. The acetaldehyde altered the fragrance, causing a product recall. With diethyl ether,
and particularly di-isopropyl ether, air contact can produce peroxides and aldehydes. Solid films of these
peroxides can be explosive. They may (or may not) have been associated with the explosion of a Toronto,
Canada aerosol filling plant in about 1970 during its production of a 91% diethyl ether and 9% carbon
dioxide aerosol engine starter.
A number of organic chemicals have been shown to be air (oxygen) sensitive. They include some aldehydes
and some vitamins. Suppliers package them in well filled containers, preferably quite anhydrous and usually
out of contact with iron or aluminum surfaces. Large amounts may be held in plastic or tin-lined metal
drums, with any head-space air replaced with nitrogen or argon. Argon is sometimes preferred because it is
about 38% heavier than air, while nitrogen is only about 97% as dense and may tend to “float” away to some
extent.
Since aldehydes (R-CHO) often have intense odors they are used quite sparingly in formulating essential
oil fragrances. Their oxidation often leads to the corresponding carboxylic acid (R-COOH). Where “R” is
propyl, (C2) propylic acid has a pungent, suffocating, rancid odor. It is not used in perfumery, nor is propionaldehyde.
The same applies to (C3) butric acid, (C4) valeric acid and (C5) caproic acid. However, caproaldehyde
has a eucalyptus odor and is used.
The still higher aldehydes (to C13) are also utilized.
AIR SENSITIVE ORGANIC COMPOUNDS
INGREDIENT FORMULA ODOR
Caproaldehyde CH3-(CH2)4-CHO Eucalyptus
Heptanaldehyde CH3-(CH2)5-CHO Harsh hyacinth
Caprylic aldehyde CH3-(CH2)6-CHO Citrus
Pelargonic aldehyde CH3-(CH2)7-CHO Fatty rose
Capric aldehyde CH3-(CH2)8-CHO Orange
Undecyl aldehyde CH3-(CH2)9-CHO Fatty rose – orange peel
Lauryl aldehyde CH3-(CH2)10-CHO Wood violet
Myristyl aldehyde CH3-(CH2)12-CHO Fatty orris
Hydroxycitronella C10H20 Linden
6-Methylione C14H22 Violet – orris
Dihydrojasmone C11H18O Jasmine
2,6-Dimethyl-1,5- C9H16O Melon
heptenal
Methyl Anisate C9H10O3 New mown hay
Methyl Anthrilate C8H9NO Orange
p-Me Benzaldehyde C8H8O Almond
Tolyl Aldehyde C8H8O Almond
Vitamin A (Retinol) C 20H30O
Vitamin A2
Vitamin D C27H44O
Vitamin D2
Vitamin E (Tocopherol)
Vitamin K5
Other air sensitive organics include phenol (red deepens with air), oil of anise, oil of lemon, oil of tansy
and oleic acid (discolors and racidifies). Anti-oxidants are often added to fragrance blends to stabilize them.
They are chemically changed in contact with air (oxygen). In general, easily oxidized ingredients are at risk.
Typical anti-oxidants are hydroquinone and its monomethyl ether.
Contacts with air (oxygen) produce not only oxidation products, but also resinification, dimerization,
polymerization, trans-esterification and various interactions between functional groups. All of these effects
are seen in the case of terpenes. During fragrance formulation and aerosol product development programs,
it is useful to prepare the final product and test it for stability. The aerosol program should include two week
38 SPRAY March 2018
development and production programs.
continued on page 47