α-Isomethyl ionone, also known as α-cetone, is a synthetically made and naturally occurring organic compound found in Brewer's yeasts or the species known as ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

.'' The compound is an isomer of methyl

ionone The ionones, from greek ἴον ion "violet", are a series of closely related chemical substances that are part of a group of compounds known as rose ketones, which also includes damascones and damascenones. Ionones are aroma compounds found in ...

. Alpha-isomethyl ionone can be colorless or pale-straw coloured liquid. Its primary scent is flowery and secondary scent is violet. It may also have a woody or orris-like scent. and is often used in flavouring and cosmetic industries for example, aftershave lotions, bath products, hair care products, moisturizers, perfumes, shampoos and skin care products. It is also an ingredient used in

Chanel No. 5 Chanel No. 5 is the first perfume launched by French couturier Gabrielle "Coco" Chanel in 1921. The scent formula for the fragrance was compounded by French-Russian chemist and perfumer Ernest Beaux. The design of its bottle has been an imp ...

, and other branded products such as Fidji by Guy Laroche. Perfume fragrances that α-isomethyl ionone is used in are for example,

amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

chypre Chypre () is the name of a family (or ''concept'') of perfumes that are characterised by an accord composed of citrus top note (perfumery), notes, a middle centered on labdanum, cistus labdanum, and a mossy-animalic set of basenotes derived from oa ...

violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Vi ...

mimosa ''Mimosa'' is a genus of about 600 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. Species are native to the Americas, from North Dakota to northern Argentina, and to eastern Africa (Tanzania, Mozambique, and ...

, reseda,

iris Iris most often refers to: *Iris (anatomy), part of the eye * Iris (color), an ambiguous color term *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (given name), a feminine given name, and a list of peopl ...

, orris,

cyclamen ''Cyclamen'' ( or ) is a genus of 23 species of perennial flowering plants in the family Primulaceae. In English, it is known by the common names sowbread or swinebread. ''Cyclamen'' species are native to Europe and the Mediterranean Basin ea ...

berries A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone fruit, stone or pit (fruit), pit although many wikt:pip#Etymology 2, pips or seeds may be p ...

, woody notes,

ylang-ylang ''Cananga odorata'', known as ylang-ylang ( ) or cananga tree, is a tropical tree that is native to the Philippines, Malaysia, Indonesia, New Guinea, the Solomon Islands, and Queensland, Australia. It is also native to parts of Thailand and Vie ...

, leather,

orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower ** Orange juice *Orange (colour), the color of an orange fruit, occurs between red and yellow in the vi ...

nut Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed * Nut (food), a dry and edible fruit or seed, including but not limited to true nuts * Nut (hardware), fastener used with a bolt Nut, NUT or Nuts may also refer to: A ...

pistachio The pistachio (, ; ''Pistacia vera'') is a small to medium-sized tree of the Anacardiaceae, cashew family, originating in Iran. The tree produces nut (fruit)#Culinary definition and uses, seeds that are widely consumed as food. In 2022, world ...

muscatel Muscatel ( ) may refer to any type of wine made from muscat grapes. In the United States, however, “muscatel” normally refers only to fortified wine made from these grapes. Fortified muscatel became popular in the United States at the end of ...

, and

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

Properties

α-Isomethyl ionone would be classified as a norsesquiterpenoid, having 14 carbon atoms (1 less than the 15 of three consecutive

isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common volatile organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. It is produced by many plants and animals (including humans) and its polymers ar ...

units). It is an extremely

weak base A weak base is a base that, upon dissolution in water, does not dissociate completely, so that the resulting aqueous solution contains only a small proportion of hydroxide ions and the concerned basic radical, and a large proportion of undissocia ...

, the calculated p''K''_a values within the molecule being 19.7 (strongest acidic) and −4.8 (strongest basic). The percentage of α-isomethyl ionone used in perfumes is approximately ranging from 0.1% to 11.9%, with an average of 1.1%. For example, it is usually used in conjunction with hydroxycitronellal, woody notes, copaiba, N-methyl ionone, ionone, or Vetiver.

Synthesis

The synthesis of α-isomethyl ionone involves a cross-aldol condensation of

citral Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...

with

methyl ethyl ketone Butanone, also known as methyl ethyl ketone (MEK) or ethyl methyl ketone, is an organic compound with the formula CH3C(O)CH2CH3. This colorless liquid ketone has a sharp, sweet odor reminiscent of acetone. It is produced industrially on a large s ...

A high temperature and strong alkali is used. The ratio between the n-form and iso-form is controlled in order to obtain methyl pseudo-ionone and allow ring formation to occur. Iso-forms is then synthesized consequently.

References

{{reflist Perfume ingredients Flavors Enones Cyclohexenes