Tollen's and melons, removing that tricky residual aldehyde
So I have been playing with enamine > ketone. I have done it successfully plenty of times. BUT I pretty much always have residual traces of aldehyde remaining. Sometimes more of a "trace" than other times. This last time has turned into quite the debacle.
I usually get pretty damn close to complete conversion but never 100%. When I distill the ketone I use a column and bring the temp up VERY slowly. Even if there is some isolation, anyone who's done this knows distillation just won't work to separate them.
My next bright idea was DCVC. I can achieve good seperation on a plate so why not run it through a column. And in theory I know I could make this work. I've never done DCVC but it is an opportunity to learn some new skills. And I did try two times on a small sample.
While I failed to get seperation on my 2 test runs I know it is doable and know what my issue was, most likely. My test runs were somewhat proportional to what my big run would be. The issue is overloading which is why I picked DCVC. Supposedly you can run larger samples with this method. Even if done correctly and seperation is achieved perfectly, I am stepping away from this path for one reason that wouldn't change, solvent volume. At my scale, it would require more solvent than I am currently willing to work with at this time.
Which brings me toooo......
Tollen's Reagent
I have seen the discussion of selectively oxidizing the leftover aldehyde. I have a friend who is also working on this.
(Feel free to jump in if you want)
I half-assed tried a couple of times earlier on when I was still learning this technique. Nothing that I expected to work nor did the attempts work.
I dismissed the idea of Tollens back then for reasons I don't fully recall but I feel it was having to use silver that turned me off from it. I have always wanted to do the silver mirror experiment. Probably as long ago as I made my first gallium spoon. Fun for the kids (and me).
Ok, enough fluff. I made a solution of distilled ketone contaminated with helional in DCM at about a 1:7 dilution. Put 4 ml (.5 gram ketone) into a beaker and set to stir with a few ml of Tollens. It quickly turned gray, indicating it was working. Let the biphasic mix stir at RT for an hour. Separated, washed with water then brine. A little MgSO4 then TLC. Nadal!
TLC doesn't show a significant decrease in aldehyde. But the Tollens turned dark grey cloudy which should mean it reacted with something. Also, being that this is the main use of Tollens, I know there is a way to make it work.
I think I'm asking if anyone has any suggestions about parameters or reaction conditions? Drip? Heat? PTC? Different solvent?
Any input, feedback or comments are appreciated.
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