Do almonds smell like they do because of cyanide?

Question

I am guessing so otherwise it is quite a coincidence that cyanide smells of bitter almonds. And if so, are large quantities of almonds over a long period safe?

Answer 1

Almonds smell like they do mostly due to the presence of benzaldehyde:

This colorless liquid has a characteristic almond-like odor. Benzaldehyde is the primary component of bitter almond oil and can be extracted from a number of other natural sources.

Hydrogen cyanide also has an almond-like odor, but it is not as pronounced as that of benzaldehyde. From CDC|Facts About Cyanide:

Cyanide sometimes is described as having a “bitter almond” smell, but it does not always give off an odor, and not everyone can detect this odor.

Benzaldehyde and hydrogen cyanide are both byproducts of the enzymatic catalysis of amygdalin, which is present in almonds (and other foods). Have a look at this abstract (Toomey VM, Nickum EA, Flurer CL. Cyanide and amygdalin as indicators of the presence of bitter almonds in imported raw almonds. J Forensic Sci. 2012 Sep 57 (5): 1313-7) for more about the cyanide-amygdalin-almond connection.

In terms of safety:

For a 70-kg human, the lethal dose is estimated at 50 mL. Benzaldehyde has been classified as a hazardous substance by the United States Environmental Protection Agency.

and

Benzaldehyde does not accumulate in any specific tissues. It is metabolized and then excreted in urine.

Safety issues from benzaldehyde consumption $\it{via}$ the almond consumption route appear to be minimal.

From our sister SE site Skeptics in re: "How many almonds does it take to get cyanide poisoning?":

With bitter almonds, 8 - 32 almonds will give you the lethal dosage of cyanide. Bitter almonds yield about 6.2 mg of cyanide per almond and the LD50 for cyanide is 50 mg - 200 mg.

This applies only to bitter wild almonds: considering that you're not dead, you most likely ate domesticated sweet almonds, which apparently do not have this problem. The sale of wild almonds may be illegal, in fact, though I can only find blogs and internet comments alluding to this.

From wikipedia

Wild almonds are bitter, the kernel produces deadly cyanide upon mechanical handling, and eating even a few dozen at one sitting can be fatal. ...

While wild almond species are toxic, domesticated almonds are not

Given the evidence and the expectation that you won't ingest several kilograms of almonds in a day or so, I'm comfortable in endorsing the almond as safe for consumption.

Answer 2

As someone who has smelled a lot of HCN during experiments I can tell you that the smell of HCN is nothing like the smell of Benzaldehyde or any almond oils you can buy as flavors. I never really smelled real fresh almonds and if you look a bit further into literature it says it may smell like really fresh almonds (not the ones you buy) so I cannot really compare but its nothing like benzaldehyde at least. It is very characteristic though. I could easily tell if something is HCN or not, it's like with vanilla for example. You don't confuse that smell with any other like you would do for various solvents. Also what literature also does not mention that often is that this characteristic smell of HCN only applies for low conc. you should not forget that it is still a Pseudohalogen and it has the same property as for example HCl. If you get a higher conc. at once it will burn in your nose without any characteristic smell at all, just like when smelling on a bottle of HCl. I once had the unfortunate accident to get a small cloud of higher HCN conc. into my nose when the pressure in my setup became to big.

Also to the original question, I doubt almonds smell like cyanide or vice versa. A friend of mine is working with really big molecules and sometimes he has to attach small reactive groups so he can link them. He was working with two very big aromatic compounds and added an -SH group to both of them. One then started to smell incredibly intense while the other one didn't change at all. Sometimes this is just how we attach a smell to something. So perhaps there is a small relationship that they bind to similar receptors, or the people who extracted HCN from almonds for example didn't fully clean it and the smell of the almonds somehow contaminated the experiment?