How does Ambrox smell

The fairy tale of the bitter almond smell

Hydrocyanic acid and its salts, the cyanides, are often used in crime novels as insidious poisons.

Usually the detective or the medical officer bends over the corpse and states: “Typical bitter almond smell; I suspect poisoning with hydrogen cyanide! "

During the autopsy of the half-burned corpse of Adolf Hitler, the Russian doctors noticed the "bitter almond smell" and suspected suicide by hydrogen cyanide.

That smell is a fairy tale.

During my doctoral thesis, I too almost became a victim of hydrogen cyanide: Apparently an apparatus in which I work with HCN had leaked. However, I did not notice the gas escaping (HCN boils at 26 degrees), but waited for the bitter almond smell as an alarm signal. It was only through the courageous intervention of my laboratory colleagues that I jumped the Grim Reaper one more time.

I had read in an ancient chemistry book that smoking a cigar at the same time allows you to smell hydrogen cyanide “better”. When I tried this while continuing to work, I got sick from smoking! But then I preferred to stop working with hydrogen cyanide and take a different - less dangerous - synthesis route.

During my work as a fire brigade officer in a large petrochemical plant, I also dealt with hydrogen cyanide: the synthesis of acrylonitrile from propylene and ammonia produced hydrogen cyanide as a by-product. This was then initially stored in large tanks and transported in 20 t rail tank cars to what was then DEGUSSA in Wessling. There it was mainly processed into cyanides for gold mining. In the event of an accident on the approximately 30 km long railway line, the fire brigade should fire the leaking hydrogen cyanide with a signal pistol. (Hydrocyanic acid then burns with a beautiful blue flame to form harmless CO2 , Water and nitrogen)

Incidentally, the only scenario in my fire service career where the fire service - instead of extinguishing - has to act as an arsonist!

Once a year each of my firefighters in the hydrogen cyanide plant had to sniff a (dilute) hydrogen cyanide solution. So that he doesn't wait in vain for the alleged bitter almond smell in an emergency.

The fact is: Hydrocyanic acid is almost odorless. It smells faintly pungent; a bit like SO2 and (usually) produces a slightly scratchy, furry feeling in the throat. So nothing with "bitter almond"!

How did this false claim come about?

Hydrocyanic acid comes in the plant kingdom as a "glycoside" with the name Amygdalin in front. (Glycosides are compounds of alcohols with grape sugar.) From a chemical point of view, amygdalin is a glycoside of mandelic acid nitrile, which in turn breaks down into hydrogen cyanide plus benzaldehyde.

Amygdalin breaks down into 2 glucose plus mandelic acid nitrile (the cyanohydrin of benzaldehyde):

Mandelic acid nitrile breaks down into benzaldehyde plus hydrogen cyanide

plus HCN (hydrocyanic acid)

Here again the entire disintegration
(from https://www.verwaltung.steiermark.at/cms/dokumente/11712303_75777092/530d90ed/2010-03.pdf):

Even Professor Blume, whom I hold in high esteem (http://www.chemieunterricht.de/dc2/tip/04_06.htm) tries to explain why hydrogen cyanide smells like benzaldehyde (bitter almond-like). Obviously he has never worked with hydrogen cyanide.

How does the misjudgment come about that has dragged itself through all textbooks for 150 years?

In my opinion, through the former representation of hydrogen cyanide from bitter almonds.

It was probably like the "Mars channels" that the Italian astronomer Schapparelli saw in the telescope in 1870. And all the following astronomers observed the ever-changing channels (it was even speculated by the green Martians as builders).
Until the US Mars probes "Mariner" found in 1965 and 1969: No trace of channels. Everything was just an optical illusion!

Probably no chemist has dared to really sniff the bluebell (or many belonged to the 40% of people who have no olfactory sense for hydrogen cyanide?). In any case, the fairy tale of the bitter almond smell persists to this day.

The fermentation of the almond kernels produces glucose, hydrogen cyanide and benzaldehyde. The hydrogen cyanide evaporates when heated and, as I said, boils at 26 degrees. So even lighter than ether! The rest was traded as "bitter almond oil" and used for flavoring.

Amygdalin ===> 2 glucose + HCN + benzaldehyde

Pure benzaldehyde smells intensely of bitter almond. You can buy it under the name "Artificial Bitter Almond Oil" on Ebay and use it for flavoring and perfuming. There we have the culprit.

Because hydrogen cyanide (in addition to the decomposition of Berlin blue; hence the name!) Was obtained as a by-product from almond oil 150 years ago, it was always contaminated with benzaldehyde. And that's why hydrogen cyanide smelled like bitter almond.

Today hydrocyanic acid and its salts, the cyanides, are produced technically (e.g. as described above).

Without bitter almond smell!