2-Acetyl pyrrole

Description

Methyl 2-pyrrolyl ketone is like bread, walnut, licorice. May be prepared from pyrryl magnesium iodide and acetyl chloride; a volatile flavor component in roasted filberts.

Description

Happy Thanksgiving! If you are like many of us, sweet potatoes (aka yams) are one of the highlights of your Turkey Day meal. The aroma of a casserole baking in the oven adds to that comfort-food feeling.
A chemist would naturally ask, “Why do roasting or baking sweet potatoes smell so good?” Ola Lasekan* and Li Shing Teoh at University Putra Malaysia (Serdang), identified 29 aroma compounds in roasting white yam (Dioscorea rotundata)1. Among them, the two that had the highest odor activity factors were 2-acetylfuran (2AF, aka 2-furyl methyl ketone) and 2-acetylpyrrole (2AP, aka 2-pyrrolyl methyl ketone).
According to the authors, 2AF “elicited an almond-like note” whereas 2AP had “a popcorn-like note”. The aromas emitted by the other components, mostly furans, pyrroles, and pyrazines, were given labels such as “toasty”, “caramel”, “chamomile flower–like”, and “smoky”.
The focus of this study was to identify the aroma compounds that contribute to the potatoes’ antioxidant properties. Using an established test based on substances’ ability to inhibit the oxidation of hexanal, the authors found that the pyrrole-containing aroma components were substantially superior antioxidants to the furans and especially the pyrazines.
A glance at the hazard information tables shown here might give you pause. 2AF in particular looks as if it might kill you as you’re enjoying the holiday. But rest assured that these, like many other odorous substances, are detectable in air at very low concentrations.
So, this Thanksgiving Day, while you’re watching the virtual Macy’s parade and NFL football games, take satisfaction that some of the food aromas you’re inhaling add to your antioxidant supply.
1. Full disclosure: Dioscorea spp. are “true yams”, as opposed to the orange-colored sweet potatoes (Convolvulaceae spp.) that some Americans call yams. The baking and roasting aromas of both yam genera contain 2AF and 2AP.

Chemical properties

white to beige crystalline powder

Chemical properties

Methyl-2-pyrrolyl ketone has an odor reminiscent of bread, walnut and licorice

Occurrence

Reported found in essential oils of tobacco leaves, apple, asparagus, onion, baked and fried potato, roasted almonds, wheat bread, cooked chicken, cooked beef and pork, beer, malt whiskey, cocoa, coffee, tea, roasted filberts, and peanuts, peanut butter, potato chips, soybean, coconut, mushrooms, almond, mango, licorice, sweet corn, malt, wort, dried bonito, Bourbon vanilla, chicory root, okra, crab, scallop and clam.

The Uses of 2-Acetyl pyrrole

hepatoprotectant, organoleptic

The Uses of 2-Acetyl pyrrole

2-Acetylpyrrole has been used in the synthesis of 2-acetyl-1-pyrroline.

Definition

ChEBI: A pyrrole carrying an acetyl substituent at the 2-position.

Preparation

From pyrrole magnesium iodide and acetyl chloride; a volatile flavor component in roasted filberts

Synthesis Reference(s)

The Journal of Organic Chemistry, 48, p. 3214, 1983 DOI: 10.1021/jo00167a014
Tetrahedron Letters, 26, p. 4649, 1985 DOI: 10.1016/S0040-4039(00)98776-8

General Description

2-Acetylpyrrole undergoes alkylation reaction with alkyl iodide in benzene/solid KOH system in the presence of 18-crown-6 to yield the corresponding 1-alkyl derivative.