(Stranger)
05-16-00 10:45
No 5065
(Rated as: excellent)
Okay this synthesis involves the decarboxylation and methylation of phenylalanine in one step. The basic equation is:
C6H5-CH2-CHNH3-COOH + CH3COONa --{electroysis @ Pt anode}--> C6H5-CH2-CHNH2-CH3 + H2 + CO2
The problem that I find with this is the solublity of phenylalanine... What does phenylalanine, or it's salt dissolve in? Where could I find that...
________
From "Synthetic Organic Electrochemistry", by Albert J. Fry, yr 1972
Library of Congress # QD273.F78, page 273
"8 OXIDATION PROCESS
...
8.1 CARBOXYLIC ACIDS
It has been known for conciderably more than a century that
electrochemical oxidation of salts of carboxylic acids results in
dimeric products [6]:
2 RCO2(-) --{O}--> 2 CO2 + RR
This reaction is known as the Kolbe reaction after the early
investator who, though not it's discoverer, studied it in sufficent
detail to outline its scope. Perhaps no other organic reaction has
been studied as intensively as has the Kolbe reactioon; indeed,
investigation into its sublter aspects have continued right up to the
present day. While some mechanistics details still remain unclear,
the preparative methodology and mechanism are sufficently well
established that synthetic applications are straight forward. ...
8.1.1 The Kolbe and Related Reactions
Mechanism
Weedon has discussed optimal experimental procedures for the Kolbe
reaction [1]. ... Apparently, a film of absorbed intermeditates
inhibits oxidation of the solvent and permits a potential to be
attained where the Kolbe reaction can then occur. This feature is of
interest synthetically because it results in considerable experimental
simplifications. Since anodic potential control (to avoid oxidation
of the solvent) is rendered unnecessary by this absorption process,
one may use constant-current, rather than controlled-potential,
electrolysis. As Weedon has pointed out, the experimental apparatus
for the Kolbe reaction can be quite simple, merely a beaker
containing both the solution and a pair of platinium electrodes
connected to a source of direct current (see Chapter 9) [1].
...
Synthetic Scope and Limitations
Kolbe dimers are formed in 50-90% yeild when the intermeditate radical
is either primary [1] or is substituted by electron-withdrawing groups
[15], that is,
RC*H2 or RC*HX or RC*X2_____________(X = COO2R', CONR2', etc.)
When the [alpha] position of the acid containsa substituent capable of
stablizing a carbonium ion (X = alkyl, alkoxyl, halogen, aryl, etc.),
yields of the Kolbe dimer are very low ( 0-10% ). In such cases, the
intitially formed radical is oxidized further to a carbonium ion:
RCO2(-) - e(-) --{ -CO2}--> R* --{ - e(-)}--> R(+) --> products
... There are a few other other cases where the Kolbe yields are low.
Aryl [16] and [alpha], [beta]-unsaturated acids [17] afford little or
no dimer, for example. The isolation of benzene from the oxidation of
benzonic acid [16], ...
Other than these, there are really very few restrictions on the nature
of the R group in a carboxylic acid (RCO2H) that is to be submitted to
the Kolbe reaction. ...
...
A valuble extension of the Kolbe reaction was first reported by Wurtz
[23]. He found that oxidation of a mixture of two different
carboxylic acids results in a mixture of three possible coupling
products:
RCO2H + R'CO2H --{ -e(-)/ -CO2}--> RR + RR' + R'R'
The fact that the three are formed in more or less statistical ratio
need not be a detterent, for the proper choice of the molecular size
of R and R' the products can be made to differ substantially in
physical properties, thus making separation easy, and use of a large
excess of the cheaper acid increases the relative yield of the desired
mixed product RR'. ...
(One common application of this crossed Kolbe coupling is the oxidation
of a carboxylic acid in the presense of a large excess of acetate ion,
thus resulting in efficent conversion of the acid RCO2H to the alkane
RCH3 in one step [10-12]. This reaction would be useful for the
introduction of a labeled methyl group.)
The crossed Kolbe coupling reaction has the dual advantage of being
able to accommodate a wide variety of functional groups and of
enabling quick assembly of molecular subunits whose coupling by other
routes might be lengthy. ..."
[1] B. C. L. Weedon, Advan. Org. Chem., 1, 1 (1960)
[6] H. Kolbe, Ann., 69, 257, (1849)
[10] W. J. Koehl, Jr., J. Org. Chem. 32, 614 (19670.
[11] W. A. Bonner and F. D. Mango, J. Org. Chem., 29, 430 (1964).
[12] H. Breederveld and E.C. Kooyman, Rec. Trav. Chim., 76, 297 (1957).
[13] G. W. Kenner, M.A. Murray, and C. M. B. Tylor, Tetraherdon, 1,
259 (1957)
[15] L. Eberson, Acta Chem. Scand., 17, 1196 (1963); L. Eberson and
B. Sandberg, Acta Chem. Scand., 20, 739 (1966); but see L. Eberson
and S. Nilsson, Acta Chem. Scand., 22, 2453 (1968).
[16] F. Ficher and R. E. Myer, Helv. Chim. Acta, 17, 535 (1934); F.
Ficher and H. Stenzl, Helv. Chim. Acta, 22, 970 (1939).
[17] J. Petersen, Z. EleKtrochem., 18, 710 (1912); P. Karrer and M.
Stoll, Helv. Chim. Acta, 14, 1189 (1931).
[23] A. Wurtz, Ann. Chim. et Phys., 44, 291 (1855); A. Wurtz,
Jahresberichte, 575 (1855).
++++++++++++++++++++++++++++++++++++++++
From "The Journal of Organic Chemistry", Vol. 29, yr 1964, page 430
Title "Kolbe Electrolyses of 3-Phenyl- and 3,3-Diphenylpropanonic
Acids"
"EXPERIMENTAL
...
... The electrode unit consisted of two platinium foil electrodes
(1.25 X 1.25 cm.) spaced approximately 2 mm. apart and joined to
wires sealed into a tapered glass head (...) equipped with a gas exit
tube. The cell compartment (30 mL), fitted to recieve the electrode
unit, was equuipped with a water jacket for thermosating. The
electrolysis appartus was energized by a 12-V Heathkit battery
eliminator.
...
Electrolysis of 3-Phenylpropanonic Acid in Acetic Acid.- A solution of
3-phenylpropanonic acid (2.89 gr.) [0.01927 mol], and sodium acetate
(1.43 g.) [0.0174 mol], in acetic acid (25 mL) [assume Glacial acetic
acid- .425 mol @ 17 mol/L] was electrolyzed as above for 21 hr. (0.2
amp., 8 f./mol). ... The observed retention times showed that
n-propylbenzene and 2-phenylethyl acetate were present..."
========================================
This post is for informational purposes only an is not intended to facilate illegal activity.
(Newbee)
05-18-00 01:32
No 6051
H20 10-50mg/ml
is your best bet
(Moderator)
05-18-00 03:26
No 6068
It should be much more soluble in acidic or basic solutions, like the ones used in that synthesis.
(Hive Bee)
05-21-00 08:53
No 7376
I thought of this idea before. I also found a book in the library that said that carboxylic acids that are branched at the alpha position produce little or no yield of hydrocarbon product (Kolbe reaction). Also, the amino group might be a problem, ie. note the free radical intermediates.
(Newbee)
05-22-00 13:02
No 7941
I have read a couple articles that the alpha-amino carboxyl acids do produce Kolbe dimers, but not in perfect yields. Even if the yield is low it still is easy...
This post is for informational purposes only an is not intended to facilitate illegal activity.
(Hive Bee)
05-22-00 18:39
No 8045
Looks interesting CHEM_GUY. Can you list any references where they talk about alpha amino acids?
(Newbee)
05-23-00 09:52
No 8335
I'll try but I don't think I ever notated them. For now here's a good reference with a lot more information, hell it probably has the references for the the alpha-substituted compounds sited:
Topics in Current Chemistry, Vol 152, Electrochemistry IV, edited by E. Stekhon, Library of C # QD1 F58 V.152
This post is for informational purposes only an is not intended to facilitate illegal activity.
(Stranger)
05-31-00 15:47
No 11959
This looks very interesting ... I will check with the lokal library and report ASAP.
(Phukin' lurkin' around for two years ....)
Promethium, burnin' yar beard!
(Hive Bee)
07-01-00 10:36
No 23649
Here's some more shit on this synthesis. Have fun!
Phenylalanine Properties:
Phenylalanine, dl- CAS# 150-0-1
Phenylalanine, l- CAS# 63-91-2
From- http://ntp-server.niehs.nih.gov/htdocs/C
Radian63-91-2.html
[for l-phenylalanine]
*SOLUBILITIES:
WATER : 10-50 mg/mL @ 25 C (RAD)
DMSO : <1 mg/mL @ 25 C (RAD)
95% ETHANOL : <1 mg/mL @ 25 C (RAD)
METHANOL : Very slightly soluble [031,295]
ACETONE : <1 mg/mL @ 25 C (RAD)
TOLUENE : Not available
OTHER SOLVENTS:
Ether: Very slightly soluble Post 043 (not existing)
Alcohol: Very slightly soluble [043,295]
Dilute mineral acids: Very slightly soluble Post 295 (not existing)
From- www.chemfinder.com
[for L-phenylalanine]
water solutblity: 1-5 g/100 mL at 25 C
@ http://esc.syrres.com/interkow/webprop.e
[for L-Phenylalanine]
Water Solubility:
Value : 2.69E+004 mg/L
Temp : 25 deg C
Type : EXP
Ref : YALKOWSKY,SH & DANNENFELSER,RM (1992)
End of Properties-
==================
From "Topics in Currnet Chemistry" Volume 152, Electrochemistry IV,
edited by E. Stekhan, LoC# QD1. F58 v.152
page 93
"The yield and selectivity of the Kolbe electrolysis is determined by
the reaction conditions and structure of the carboxylate. ...
Experimental factors that influence the the outcome of the Kolbe
electrolysis are the current density, the temperature, the pH,
additives, the solvent, and the electrode material.
High current densities and high carboxylate concentrations favor the
formation of dimers. This is due to a high radical concentration at
the elctrode surface that promotes dimerization. Furthemore, at high
current densities the so called critical potential of about 2.4
(vs NHE) is reached [28] above which the Kolbe dimerization proceeds
smoothly. ... There is, however, no need for potential control in
Kolbe electrolysis as the critical potential is already exceeded at 1
to 10 mA/cm^2. This is much below the usually applied current density,
which should be as high as possible, normally equal to or greater than
250 mA/cm^2. ...
...
A nuetral, or even better a weakly acidic medium seems to be
prefferable for the Kolbe reaction. This is achieved by nuetralizing
the carboxylic acid to an extent of 2 to 5%, in some cases up to 30%,
by an alkali metal hydroxide or alkoxide. ... The endpoint of the
electrolysis is indicated by a change of the electrolyte to an alkaine
pH. ...
In aqueous solution an elevated pressure favors the Kolbe-coupling
against non-Kolbe products [37]. ...
Temperature has some effect on Kolbe electrolysis. Higher temperatures
seem to support disproportionation against the coupling reaction and
intramolecular additions to double bonds against a competing inter-
molecular coupling (Chap. 6). ...
Additives can strongly influence the Kolbe-reaction. Foreign anions
should be definitively excluded, because they seem to disturb the
formation of the necessary carboxylate layer at the anode. Their
negative effect increases with the charge of the anion. ...
Foreign cations can increasingly lower the yield in the order of
Fe(+2), Co(+2) < Ca(+2) < Mn(+2) < Pb(+2) [22]. Alkali and alkaline
earth metal ions, alkylammonium ions and also zinc or nickel cations do
not effect the Kolbe reaction [40] and are therefore counter ions of
choice in preparative applications. Methanol is the best sutied
solvent for Kolbe electrolysis [7, 43]. ... The following
electrolytes with methanol as a solvent have been used: MeOH-sodium
carboxylate [44], MeOH-MeONa [45, 46], MeOH-NaOH [47],
MeOH-Et3N-pyridine [48]. The yield of the Kolbe dimer decreases in
media that contains more than 4% water.
In aqueous solutions especially, the current yield is distinctly lower;
furthermore, solublity problems can occur when the salt-deficit method
is used. In aqueous solution, alpha-amino- or alpha-phenyl subsituted
carboxylates lead mainly to decomposition products, whilst in dry
methanol or methanol-pyridine, coupling products were obtained with
alpha-phenyl- and alpha-acetylaminocarboxylates [49].
...
As anode material, smooth platinum in the form of a foil or net seems
to be most univerisally applicable [32, 33]. ...
...
The nature of the cathode material is not critical in the Kolbe
reaction. ...
...
In summary the following general experimental conditions should be
applied for a sucussful dimerization of carboxylic acids: An undivided
beaker type cell can be used equipped with a smooth platinum anode and
a platinum, steel or nickel cathode in close ditance; a current
density of 0.25 A/cm^2 or higher should be provided by regulated power
supply, a slightly acidic or nuetral electrolyte, prefferable methanol
as solvent and a cooling device to maintain temperatures between 10 to
45 C should be employed. With this simple procedure and equipment
yields of coupling product as high as 90% can be obtained, provided
the intermediate radical is not easily further oxidized (see Chap. 7)."
Read my Disclaimer. http://chemguy.homestead.com/disclaimer.
(Stranger)
12-15-00 19:05
No 75774
Hi guys,
So what is the verdict on this method?? I am kind of suprised that there hasn't been more interest in this as it would appear to be one of the easiest methods out there.
I just had some thoughts that might be of interest/use.
1. Using 99.9% pure silve would be almost as good as Pt would it not? (just for all those people who don't have solid sheets of platnium hanging around the house)
2. Are there any other chems besides Sodium Acetate that could be used (ie. ones that are a bit easier to procure). This would be useful info for our non-US friends.
Anyway thanks to Chem_guy for finding this method
Cheers
--------------------
Master of Puppets is pulling your strings.....
(Stranger)
12-16-00 17:14
No 75909
You're welcome,...
(Wizard Master)
12-18-00 17:28
No 76419
I've posted this before on the Old Hive BB. The synthesis gives a mixture of products and CH3COONa MUST BE in large excess to minimize this.
(Stranger)
12-20-00 16:48
No 76916
Well SWIM tried out this synth but ran into problems with the current required. For some reason there seemed to be a large amount of resistance in the solution (after putting in almost 18 V there were like 0.07 milliamps being produced). This struck SWIM as being a bit strange, as usually there is too much amperage when the current is run through the solution in the festerlytic method. Hmmmm....out of curiousity the solution was changed several times involving alcohol, water, and then finally some sulphuric acid. It would not appear that there was anything wrong with any of the connects as when the electrodes touched each other in the solution it sent the amps soaring. Does anyone have any ideas about what was happening? Personally I would have thought that acetic acid (plus the sodium acetate and phenylalanine) would have been fairly good conductors (there is certainly no problems with inadequate current in the festerlytic method). Any clues??
The idea about the Ag came from the festerlytic method - it can be substituted for the Pd or Pt in that reaction so I thought that its similar properties to these metals may have helped out in this instance.
--------------------
Master of Puppets is pulling your strings.....
(Stranger)
12-23-00 14:40
No 77490
I say add more sodium acetate and decrease the electrode distance to several millimeters.
This should solve the problem.
(Wizard Master)
12-26-00 04:39
No 77914
Acetic acid and phenylalanine are poor ionic conductors in electrolyte solutions. Sodium acetate is good. Just lookup their acid constants and solution ionization constants.
The high resistance can be minimized by large surface area electrodes.
(Stranger)
12-28-00 20:32
No 78406
Hi,
In regards to SWIM's earlier problems. The acetic acid was essentially saturated with sodium acetate (ie. it wouldn't absorb any more of the stuff) and even when there was a tiny space between electrodes the current was very small.
Is there anything that can be done to reduce the resistance of the solution?
Also although it is suggested that platnium is used for the electrodes (and one or two people have stated that silver couldn't be used) I don't really understand why this is so. Could someone please explain why silver, palladium etc can't be substituted for the platnium - although my chem experience is pretty inadequate I can't find any references that would suggest that these other metals wouldn't work (although not quiet as well).
Finally does anyone have any ideas about how many amp seconds have to pass through the solution per gram of phenylanaline for maximum yeilds??
Thanks again for all your help
--------------------
Master of Puppets is pulling your strings.....
(Hive Bee)
01-08-01 18:14
No 80998
Try putting in some water to reduce the resistance. I noticed also that glacial acetic acid doesn't react too quickly with NaHCO3 and found that some water had to be added to get it going (indicated by faster effervesence). The acetic acid probably needs water to be ionized. The same thing might be true with the sodium acetate, ie. it needs some water to ionize in solution. I think you need the ionization to get an electrolytic cell to work.
(Moderator)
01-09-01 02:49
No 81141
Maybe the power supply has a current regulation (or a short circuit detector) which was triggered by a too high current through your solution.
(Hive Addict)
01-10-01 01:36
No 81415
"In summary the following general experimental conditions should be
applied for a sucussful dimerization of carboxylic acids: An undivided
beaker type cell can be used equipped with a smooth platinum anode and
a platinum, steel or nickel cathode in close ditance; a current
density of 0.25 A/cm^2 or higher should be provided by regulated power
supply, a slightly acidic or nuetral electrolyte, prefferable methanol
as solvent and a cooling device to maintain temperatures between 10 to
45 C should be employed. With this simple procedure and equipment
yields of coupling product as high as 90% can be obtained, provided
the intermediate radical is not easily further oxidized (see Chap. 7)."
Happy New Year
(Hive Bee)
02-24-01 05:49
No 175248
http://www.ticalc.org/archives/files/fil
solubilities
BISD: Built-in shit detector
(Newbee)
03-15-01 17:06
No 178820
I think that weter is the best solvent for this reaction - it is just too hard to get any significant amount of phenylalanine disolved in methanol.
Does anyone know how much current needs to pass through the solution for the conversion of a gram of phenylalanine (ie. how many coloumbs)?
Everyone repeat after me - "I am an individual, just like everybody else"
(Wizard Master)
04-20-01 17:48
No 185570
After seening the trouble MasterofPuppets is having, I thought its time to put this too rest.
The Kolbe Electrolysis.
The process is the dimerization (joining together) of generated organic free radicals.
The basic mechanism is:
R-COONa ==solvent==>> R-COO(-) + Na(+)
R-COO(-) + e ==>> R. + CO2 R. represents the organic free radical
2R. ==>> R-R R-R is the dimerization
Cross dimerization of two different organic free radical to make Meth is not easy and many by-products result due to many highly unstable 1st (primary) organic free radical combinations.
The perfect dimerization mechamism is:
C6H5-CH2-CH.-(NH2) + CH3. ==>> C6H5-CH2-CH-(NH2)-CH3
-CH.- is the primary organic free radical carbon atom.
From hereon PE. means C6H5-CH2-CH.-(NH2) the phenylethylamine radical.
A large excess of CH3. is need too force the chemical equilibium to the right and thus form more C6H5-CH2-CH-(NH2)-CH3 dimerization. Since CH3. & PE. are highly unstable 1st (primary) radicals, many combinations of products result through the rapid dimerization.
By-products are:
PE-PE that is C6H5-CH2-CH-(NH2)-(NH2)-CH-CH2-H5C6
H3C-CH3 Ethane
C6H5-CH2-CH-(NH2)-CO-O-CH3 Phenylalanine acetate
C6H5-CH2-CH-(NH2)-CH2-OH Phenylalanine alcohol
C6H5-CH2-CH-(NH2)-CH2-O-CH3 Phenylalanine methyl ether
... and may more.
A varying degree of ethers, alcohols, olefins, parafins and acetates form.
The radicals are too unstable and unpredicable.
The methanol and acetic acid used as a solvent interacts with the radicals forming many combinations of products. The methanol is absolute methanol (ie dryed methanol), and sodium methoxide NaOCH3.
The sodium carboxylate salts can be first prepared:
C6H5-CH2-CH-(NH2)-COOH + NaOH ==>> C6H5-CH2-CH-(NH2)-COONa + H2O
The C6H5-CH2-CH-(NH2)-COONa must be anhydrous and in absolute methanol with anhydrous sodium acetate, 1:2 mole ratio.
The secondary organic free radicals generated are more stable than the primary radicals, but the CH3. radical is still highly unstable and dimerization with the C6H5-CH2-C.-(NH2)-(CH3) is STILL poor.
Now if secondary organic free radicals are generated by starting with:
C6H5-CH2-C-(NH2)-(CH3)-COO(-) + e ==>> C6H5-CH2-C.-(NH2)-(CH3)
C6H5-CH2-C.-(NH2)-(CH3) + CH3. ==>> C6H5-CH2-C-(NH2)-(CH3)-CH3 Phentermine
EXPERIMENTAL
Voltages 100-130 at approx 0.4 Amps (+ or - 10%) for 17 hours. Experiment 1.
Voltages 130-170 at approx 0.5 Amps (+ or - 10%) for 10 hours. Experiment 2.
Electrodes are two 2cm X 3cm, spaced 1cm apart, immersed completely in 100 mls of dimethylformamide solvent, in a 150 mls tall walled beaker. Externally ice water cooled and magnetically stirred.
Experiment 1: The anhydrous sodium carboxylate salts of Phenylalanine (0.1 mole) and acetic acid (0.2 mole) were used in a 1:2 ratio. Approx 19% yield.
Experiment 2: Anhydrous Phenylalanine (0.1 mole) and glacial acetic acid (0.2 mole) were used in a 1:2 ratio with 3 mls of triethylamine. Poor yield.
The use of a non-reacting, highly polar dimethylformamide solvent medium, helped diminished the by-products only slightly. The yield is less than 24%, between 19-24% with dimethylformamide.
The use of dimethylformamide solvent + diphenylacetic acid, (C6H5)2-CH2COOH, ONLY formed 24% of tetraphenylethane, (C6H5)2-CH2-CH2-(H5C6)2 Ref 2.
References:
(1) Vogel 5th Edition Pg 115, 484.
(2) The Kolbe Electrolysis in Dimethylformamide, JOC, Vol 25, Pg 136.
JOC means Journal of Organic Chemistry.
(Hive Bee)
04-23-01 11:34
No 186241
Wizard X,
So this is from JOC? Or did you perform this? Either way, BRAVO! I have been looking for something like this for a long time, but unable to find any reference to phenylalanine specifically.
Given the molar ratios of the phenylalanine to the acetate ion, 1 to 2 respectively, the theorical yield would have been only 66%, which means that the actual yeild is just under 1/3 of the theory in this set up. Therefore if one increases the acetate ions in relation to phenylalanine one can approach a theorical 100% yeild which translates into an actual yield of roughly 26%.
Although this is not a wonderful yield it still proves that it works!
As an improvement I would increase the Amps/cm^2 used.
Maybe someone should try using methanol, or DMF/methanol, or even a DMSO variation....
Thjanks a million Wizard X... I will look up that JOC articel right now
(Wizard Master)
04-23-01 18:58
No 186347
I used the JOC procedure with the diagram and info from Vogel. Remember, that generating MORE CH3. primary radicals would give higher yeilds in respect to the "collision law", BUT would also generate MORE BY-PRODUCTS.
(Hive Bee)
04-24-01 13:21
No 186517
By-Products? The decomposition products?
I don't know about that, however i think that pH control is a huge factor in this experiment as well, come to think of it. The acetate and the phenylalanine ionize in different ways: The phenylalanine is a zwitteron afterall.
I am not sure what a good pH would be, or how to go about that however...
What do you think?
I do think that given that the catalysis takes place at the anodes surface that given a larger quantity of carboxylate ions at the anode's surface the yield of dimers should go up. I think that since most people are not going to use pressure, the next best thing is a higher current density.
(Stranger)
05-23-01 16:25
No 196550
And what kind of electrodec should be used ???
(surely Pt or Pd -not easy to obtain- but what about the 'second' electrode - katode??? ---thinking on carbon ...but lead (plumbum) maybe too ?????)
(Stranger)
05-23-01 16:47
No 196553
maybe little offtopic, but what about this ???
At the first place I¨d like to say, that I am very comprehent that on the Hive there is several (nearly hundred :) ) of threads on pheny, but in no of these there is no complete steps .This thread is to be something such as racemate version of all those pheny threads :)
I would like to ask the huge scientists on Hive, if is possible this "substitution":
- according master KRZ and his catalytic hydrogenation (via Rylander) of l-phenylalanine into dextroamph. via Pt/C 5% catalyst, glacial acetic acid and anhydride Ethanol (as a solvent for reaction) in hydrogenator at 6 atmospheres (90 psi) - if is possible to make this reaction without using pressurized hydrogen vessel , but , as a substitude use some kind of hydrogen donor (i dont know what king exactly)??? is possibility to use some of these hydrogen donors - ammonium formate , cyclohexane , hydrazine (not much good) , formic acid , cyclohexadiene , phosphinic acid , sodium hypophosphite , LiAlH4 , NaBH4 or LiBH4 (i dont know which are basis or acidy) ??? I suppose also that , if this way is possible , the best hydrogen donor should be formic acid ,
cause it reacts via this: H(C=O)OH (catalyst)--> O=(C=O) + nascent hydrogen (H2) (gives hydrogen and produces CO2).
- the second "main" question I have to all math-profesors and math-scientist on Hive is this:
is possible to provide the reaction (again) via KRZ (l-pheny to dextroamph.) with using stronger catalyst than Pt/C 5% - something for ex. as Pd/C 10 %
(maybe for the prize of little lowered 'ring reduction' - and lowered yield) ?
if yes, so there is my (very apprentice) idea to make reaction in MW oven (under reflux) on low irradiation (and maybe on modulated irradiation - but this thing is another big question) and as a hydrogen source use some kind of Gas Hydrogen generator (for example by Mr. Drone #342) and bubble the hydrogen through the
'reacting' solution (same as use KRZ) under very good stirring and under MW irradiation (as above). The temperature sholdnt rise above 45 - 50 C degrees ,
so the MW irradiation is to be very low (defrosting stage ? - it is about 30% and is modulated) and so there will be no evaporation of ethanol (solvent) or rather no evap. at all.
Is this pioneer idea possible ? How much time should the reaction take ? Or is the better way to use some kind of hydrogen donor (if some exist for this
type of reaction) ? Or this thread is bullshit (excuse for this word) and the only way is to use pressure vessel ???
thank you for your reply
Perpeetuum (goes forever and forever and forever and ....)
P.S: Please, don't blame me for all these words above, I'm just appretice in chemia.
(Hive Addict)
05-24-01 18:09
No 196788
catalytic hydrogenation (via Rylander) of l-phenylalanine into dextroamph
It is generally accepted that this doesn't work.
(Stranger)
05-25-01 15:00
No 197107
In fist place, sorry to cros-post this article. I promise, I will never cros-post again !
I understand, that this quazi-mw-bubling method won't work (or there will be no or very tiny yield).
But the pressure method of Mr. KRZ works. Or not ? (when not , will You give some reason why the Catalyst will not change the esterificated pheny- (uder pressure) into dextro ???, please.)
Perpeetuum
(Hive Addict)
05-25-01 17:25
No 197129
when not , will You give some reason why the Catalyst will not change the esterificated pheny- (uder pressure) into dextro ???,
Don't know why, that is just the way things are. I do not know of any examples of catalytic hydrogenation being used to convert a carboxylic acid or its ester to a methyl.