Vanillin (Wherein I venture into the dangerous world of describing smells again)
26th June 2006
This one is obvious. It smells like, well, vanilla. Exactly like vanilla. Some people claim that it is a simplistic, cloying version of vanilla and you should always buy real vanilla extract instead of synthetic (which is mostly vanillin); I say these people are exaggerating. While you can definitely smell a difference, vanillin gets you 95% of the way there, and it isn’t a one-note wonder. If the smell weren’t so ubiquitous we’d find it much more amazing. Earthy and rich, yet spicy and vibrant, it really is a singular aroma.
Interestingly, the vanillin substructure is found in some other molecules in nature, such as capsaicin, covered here before. I am not sure of the biosynthetic pathway to vanillin, but some commonality between that of vanillin and structures like capsaicin wouldn’t surprise me a bit. My favorite vanillin-related molecule is veratraldehyde:
You can see it is just vanillin, plus a methyl. Fabulous stuff. It melts just a little bit above room temperature. It is no coincidence I remember this; when I was using this I was doing research right around the end of August, I remember it coming in as a lump in the shape of the bottom of the bottle (organic chemicals almost always come as fluffy crystals. if you’re less lucky, it will be little prills/balls or chunks. but never a brick. surely it melted en route and froze upon delivery).
This isn’t the reason why I love it so much, though. As we’ve discussed, the relationship between structure and odor is ill-understood. Fortunately, if you don’t stray too far from familiar ground in structure, you often won’t in odor. This is the case with veratraldehyde. It smells like vanilla too, but not quite like vanillin. I always thought it smelled EXACTLY like waffle cones (which, I’m sure, contain ample vanilla. My favorite quote about vanilla is that it is like “salt to a pastry chef.”).
June 27th, 2006 at 8:22 am
What a small chemical world! We just ordered veratraldehyde and related catechol derivatives as analogues of DOPAL in our synthesis of anti-malarial compounds.
http://usefulchem.blogspot.com/2006/06/dopal-nmr-and-phosphoric-acid.html
Nice to know it will smell like waffles in the lab
In your prior research, do you have a recommendation for demethylation of catechol ethers?
June 27th, 2006 at 7:32 pm
I was actually trying to fold it into a ring system, I had a bunch of benzaldehydes and was trying to tune redox properties with substituents. Never bothered with -OH.
June 27th, 2006 at 8:00 pm
Hmmm, and I just happened to burn all my vanillin tlc indicator today on plates….the lab smells strangely of burnt vanillin!
I previously tried to demethylate similar compounds with boron tribromide…couldn’t separate the product from the inorganic byeproducts, although proton NMR was clean for the product.
June 28th, 2006 at 9:11 am
Propter - do you know if methylenedioxy is harder to remove than the dimethyl ether catechol derivatives?
June 28th, 2006 at 5:43 pm
Cook’s Illustrated did a taste test and found that people liked synthetic vanillin better than real vanilla!
June 28th, 2006 at 8:58 pm
Jean-Claude: I swear I’ve seen milder stuff used for methylenedioxy deprotection, which would stand to reason, since it really is just an acetal. Something like BCl3 in DCM at 0C for a few hours. This was from a reasonably close substrate to whatever you’re using, too, the catechol nucleus having had a fair bit of attention. I can’t seem to find the paper right now, but I remember marveling at how mild the conditions were. Take a look at some of the sketchier, drugs-of-abuse type sites.
I have come across procedures on these sites that actually worked really well (I forget what for, oddly, but it stands to reason that they work OK, since a lot of these are intended for only semi-trained hands). Someone in a synth lab I was working in needed gamma-butyrolactone a few years ago, right when the hysteria was going on. For some reason, we couldn’t even get a hold of it (in a medchem lab at a big uni, maybe it’s scheduled now, I’ve never had cause to get some). So he used some prep from the drug-chef literature. Worked OK, not much of a yield. I think it was the KMnO4 oxidation of THF, or something along those lines. Ugly. Anyway, this probably won’t be much of a help, but my sympathies go out to you, good luck! I like what you’re doing with the blog, etc!
Lauren: Vindicated again. My favorite food writer has railed on vanillin on numerous occasions, but I never got it. I usually trust JS on these matters too. I took out my artificial and natural vanilla extracts (of course I keep both!) and smelled them after I wrote the entry. They are very much different, but I really don’t notice it as much in the cooked dishes. I fear the only way for me to settle my preference once and for all is a side-by-side creme brulee standoff.
June 29th, 2006 at 2:36 pm
JCB - I tried demethylating safrole right before I gave up on this route. BBr3 1M in DCM, -78 warming to 0 over a couple of hours. I always felt this should go easier than the dimethoxy variant, once you get half the molecule off, it should be easy. It was always just the workup - got purple liquid when the product should (according to lit) be a white powder, crude NMR showed it worked perfectly, but the impurity always interfered with the next step.
Motd - I believe gamma-butyrolactone is scheduled now, or at least very restricted. We have a bottle, and make lactone based polymers for bio apps. Always worry about what the breakdown projuct might be…;-)