The article requested in Post 518070 (https://www.thevespiary.org/talk/index.php?topic=11962.msg51807000#msg51807000)
(moo: "Please", Novel Discourse) and abstracted in Post 512060 (missing)
(moo: "Nickel catalyzed Leuckart reaction.", Methods Discourse)
J. Gen. Chem. U.S.S.R. 25, 1377-81(1955)(Engl. translation)
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)
8)
and everyone else, with this remark:
""My guess would be the second one, as it seems to allow for a smoother temp. control - and after all, this is the purpose behind it, right? ""
While the second one is the one he proposed to do like this :
""2. Such that the formed FD is continuously removed from the rxn, or better said tapping off same amount like FD that distills over - the FD layer gets thicker and thicker, while the amount of water in trap decreases constantly.""
And that is NOT the way it should be done. The FD must flow back in the reaction, nearly exactly as is proposed by him in the first one :
""1. In a way that allows the FD top layer to fall back into rxn flask, i.e. tapping off as much water as is formed, minus the amount of FD that distills too - the FD top layer inside trap stays the same size all the time.
I got a PM where it is explained now, that Armageddon used the prefilled-with-water trap and got zilch (btw the word only Uncle Fester used in this thread) :
""You obviously didn't read Armageddons other posts in this thread: he DID prefill the trap with water, and he DID get the clue that it would have to be tapped off slowly so as to just allow the formyl amphetamine to flow back nto the rxn vessel, while gradually tapping off the water as it is formed...
...over the course of 4-6 hours, until 160°C are reached......followed by 1h boiling at that temp. ......got zilch (40% yield, from P2P)....this Leuckart variation is BULLSHIT!!!!!!!!!!!!""
I did read all Armageddons posts several times in this thread, and have not found any indication there, that he prefilled the trap with water first. This is the only time I am told now, in PM.
So lets presume he did that. Then there are numerous other things which could lead to a low yield.
Zealot described the problems which could arise when you start with an impure ketone (P2P f.ex.):
""The FD is obtained as described earlier for cyclohexanone, w/same nearly quantitative yield. The main factor here is purity: the higher it is, the better yield. If you take an impure ketone, you may get as low as 50% yield; so only a slightly yellow transparent oil should bee used"".
This will mean that if one did not obtain the P2P from a trustable official source which indicates a purity above 98%, then one should double or triple distill ones obviously homebrew P2P, untill sufficient purity is obtained.
And there is much more to read in the first post, which could go wrong if not followed exactly.
A 72% yield with a modified Leuckart with P2P can be obtained, no doubt about that, but I personally have never seen higher yields.
But the proposed addition of a nickel catatalys by Cesium in
Post 303011 (missing)
(cesium: "Catalysed Leucard", Methods Discourse)
""The temperature and reaction time during first step could be lowered to approx. 125-135°C and 45 minutes by using 0,5 % of nickel catatalyst prepared by anaerobic thermal decomposition of Ni formate. Yield of N-formyl-MDA is almost quantitative, however due to the harsh acid hydrolysis the overall yield was lowered to 63% after workup. This procedure was originaly published in russian Zh. Obs. Kchim around 1964.""
sounds damn interesting, and if an alkaline hydrolysis as proposed by Zealot would be adopted, it will have the possibility of heightening the yield in the 90+% ranges.
The preparation of such a nickle catalyst is described in :
Post 512060 (missing)
(moo: "Nickel catalyzed Leuckart reaction.", Methods Discourse)
""It appears that in
Post 326428 (missing)
(zealot: "Äàëüíåéøåå óëó÷øåíèå ðåàêöèè Ëåéêàðòà-zealot’a", Russian HyperLab)
is a procedure for nickel catalyzed Leuckart reaction but the catalyst isn't Raney nickel. The catalyst is prepared by thermal decomposition of nickel formate, using a test tube and a gas flame, and is referred to as pyrophoric nickel. I guess this one from Zealot isn't translated to english yet.
Couln't find anything about using nickel formate in Leuckart, but there is a ref. about Raney nickel.""
in Moo's same post is this Raney nickle one described in the abstract:
""
Abstract
Alk. catalysts in the presence of Raney Ni accelerate the Leuckart reaction and direct the reaction to the formation of predominant formation of secondary amines. It was shown that the Leuckart reaction goes through the step of dissocn. of HCONH2, and the 1st product is not the amine but its formyl deriv. Improved techniques for formation of amines are described below. ""
This technique should be concentrated on, to obtain higher yields as 72%. LT/
PS: this remark of Nicodem should be looked at also:
""Post 529543 (https://www.thevespiary.org/talk/index.php?topic=10369.msg52954300#msg52954300)
(Shane_Warne: "Sodium ethanoate is the same as sodium acetate", Newbee Forum) +
Post 529389 (https://www.thevespiary.org/talk/index.php?topic=10369.msg52938900#msg52938900)
(Nicodem: "Urea hydrolysis and urea pyrolysis", Newbee Forum)
I think most amides get hydrolysed faster with NaOH than HCl, but urea may be an exception, I don't know. You should bee able to notice the end of hydrolysis by the end of CO2 bubbles formation from the boiling stones if you lower the reflux bellow the boiling point for a moment. Usually this is a clear sign in reaction involving CO2 formation (like the Leuckart or decarboxylisations). If I dare making a guess I would say that 6h of reflux would do, but don't forget you need an excess of conc. HCl since it gets neutralised by the forming ammonia (at least a 20% excess). If you will use the 20% HCl put a somewhat larger excess and reflux for a longer time.""
And this one, about never exposing your ketones to extreme pH values:
Post 338541 (https://www.thevespiary.org/talk/index.php?topic=6969.msg33854100#msg33854100)
(lab_bitch: "The chemistry of ketone polymerization", Chemistry Discourse)
""The moral of the story is NEVER, NEVER, NEVER expose ketone to extreme pH, ESPECIALLY if you plan to heat it up (i.e. distillation). Simple distilled water and sodium bicarb washes are sufficient. ""
And there is a lot more info in that post which should be taken to heart.
This post is also highly interesting:
Post 61613 (https://www.thevespiary.org/talk/index.php?topic=9510.msg6161300#msg6161300)
(psyloxy: "Re: Leukard scaleable ?", Methods Discourse)
""a variation of the Leuckart, that doesn't even use formic acid and has yields reported as high as 70%.""
I think Rhodiums answer was dedicated to Armageddon, not me...
And, by the way:
"although he tried it numerous times, with highest purity reagents, exactly same amounts, appropriately sized glassware and the utmost care to do good lab work - 55% yield!"
Post 528023 (https://www.thevespiary.org/talk/index.php?topic=9628.msg52802300#msg52802300)
(armageddon: "92% are impossible to achieve..", Methods Discourse)
The road is open for new explorers in this field! ;)
indole_amine