12-05-03 08:09
No 474827
hi, bees.
here's the catch: i'm in search of a practical otc and large scale
propenylbenzene to benzaldehyde oxidation. with large scale i mean
something like 50-100g per batch. if you think i demand too much,
please note that yields don't need to be high. 50% is perfectly ok,
30% (reproducible) is acceptable. the propenylbenzene at hand is
anethole, but i'm not pissed if it works on other substrates
.i've found the following oxidation methods, but they all suck:
a) old-school KMnO4: this needs huge amounts of solvent, gives
low inconsistent yields, ugly sideproducts and just sucks.
b) KMnO4 on solid support: this can give nice yields, but the amount
of oxidation agent is just ridiculous.
c) electrolysis: the paper i have gives low (but acceptable) yields
due to overoxidation, is slow and needs _lots_ of current. i'm not
going to pump several ampere for several days through my solution.
and the needed equipment is rather expensive/hard to make.
d) dichromate, CrO3 and similar: not otc
e) weird Ru or other complexes: not otc
f) ozonolysis: working with gases sucks. you don't know how much was
produced, how much was taken up, you have to somehow dispose of your
toxic gases, the ozone generator is either expensive or of unknown quality.
in short: a questionable investment
g) CuO (as in Post 293365 (Antoncho: "Double bond ox. cleavage (to aldehyde) with CuO", Chemistry Discourse)):
i guess this won't work, since anethole does not dissolve in water.
i'd be very grateful for any hints/ideas.
otherwise i'm stuck with a) and f), a) sucking ass and f) maybe not
even being a possiblity
patriots are idiots
(Hive Bee)
12-05-03 11:26
No 474845
cub would advise oxidising this chemical to ketone via peracid oxidation,if ketone is needed final product.
(Hive Addict)
12-05-03 14:36
No 474881
(Rated as: excellent)
A phenyl-2-propanone is not what he is after, he wants to oxidise the sidechain to obtain the substituted benzaldehyde.
I was thinking, maybe barium permanganate or cetyl trimethyl ammonium permanganate? They are both used under aprotic and non-aqueous conditions, they are easily made OTC and are milder oxidation agents then KMnO4. I have however no real references to back up these suggestions.
Ba(MnO4)2 :
Post 420462 (Vitus_Verdegast: "Barium permanganate", Chemistry Discourse)
CTAP :
Post 99463 (Cherrie Baby: "Re: Oxidation of Piperic Acid (Pepper to Piperonal)", Chemistry Discourse)
CTAP is perhaps your best bet, as it was suggested for the oxidation of piperine to piperonal instead of KMnO4 :
General Procedure for the Oxidative Cleavage with CTAP
To a stirred solution of the alkene substrate (1 mmol) in DCM (7 mL) was added a solution of CTAP (1 mmol) in DCM (6 mL) at 25°C. After 2-6 h, diethyl ether (50 mL) was added and the reaction mixture was filtered through a pad of Celite and anhydrous MgSO4. The filtrate was concentrated in vacuo and the crude product was purified by chromatography on silica gel to afford the pure carbonyl product. (From: J. Chem. Res. (S), 1986, 459)
Note (mine): CTAP: cetyltrimethylammonium permanganage.
Why do they add diethyl ether and not more DCM? Surely better to stick with just one solvent so that it can be recycled?
Cetyltrimethylammonium Permanganate, CTAP
To a stirred solution of potassium permanganate (3.168 g, 20 mmol) in water (100 mL) at 20°C is added, dropwise over 20 min, a solution of CTAB - Cetyltrimethylammonium Bromide (8.02 g, 22 mmol) in water (100 mL). A fine violet precipitate forms immediately. Stirring is continued for 30 min, the precipitated product is isolated by suction, washed thoroughly with water, and dried in a dessicator over phosphorus pentoxide in vacuo for 3 h at room temperature to give the salt as a fluffy violet solid; yield: 6.5 g (80%). The reagent is stored in a brown bottle in the refrigerator. (From Synthesis 1984, p 431)
Notes: a suitable alternative to CTAB is CTAC aka Cetrimide or Cetrimonium Chloride - found in hair conditioners. [A small cosmetics company would have no difficulty getting hold of mucho supplies of this in mega quantities]
An alternative dessicant to the P2O5 is KOH or NaOH? Why not? Dessication is essential and these quaternary ammonium compound are very hygroscopic.
I can get CTAB easily by the kilogram from my local European pharmacist.
Also, if you can get ahold of THF, you might want to check this ref out:
KMnO4 in THF-H2O: J. Org. Chem. 51, 3213 (1986)
Post 99459 (Cherrie Baby: "Re: Oxidation of Piperic Acid (Pepper to Piperonal)", Chemistry Discourse)
Flight of the Bumble Bee (http://www.geocities.com/eric_vornoff/B
(Hive Addict)
12-05-03 14:52
No 474885
thank you very, very much.
i'll get the THF/H2O/KMnO4 article ASAP.
CTAP sounds interesting too. let's hope that 7ml DCM/1mmol substrate is
not a necessity
patriots are idiots
(Moderator)
12-05-03 18:17
No 474916
(Rated as: excellent)
Here's the article, as well as some others of possible interest:
A Novel Procedure for the Cleavage of Olefin Derivatives to Aldehydes Using Potassium Permagnate
JOC 51 3213-4 (1985)
Oxidation of Hydrocarbons-Use of Dimethyl Polyethylene Glycol as a Phase Transfer Agent for the Oxidation of Alkenes by Potassium Permagnate
JOC 43 1522-5 (1978)
Phase-Transfer Catalyzed Permagnate Oxidations using TDA-1
Syn Comm 17 647-55 (1987)
4-Butyl Iodoxybenzene: An Effective Ozone Equivalent
Tet Lett 26 4955-6 (1985)
Chemistry is our Covalent Bond
(Hive Addict)
12-06-03 02:07
No 474977
that's already a _big_ improvement, i'll try with less solvent
and see if it gives acceptable yields.
but what does this (scary) sentence mean:
"Attention: Usage of neat THF or addition of solid KMnO4 may lead
to an explosion and therefore must be avoided"?
neat as in without water or without substrate?
and is possible peroxide formation not a problem, as long as there
is water? must the concentration step be watched closely?
also, when peroxides are formed, wouldn't they be taken up in the
organic phase, giving an explosion hazard when distilling off
the solvent?
thx.
ps: i like the looks of the tBu-iodo thingy, but i fear this is
out of reach
.
patriots are idiots
(Hive Bee)
01-22-04 05:27
No 484002
(Rated as: excellent)
Bearing strong similarity to the method described at ../rhodium /piperon
Taken from: Patent GB774608
A process for the preparation of aromatic carbonyl compounds from aryl ethylenes
Aromatic aldehydes or ketones of the type are prepared by oxidizing aryl ethylenes of the type (i.e. in which the ethylenic linkage is conjugated with the aromatic nucleus) with manganese dioxide or a hydrate thereof in an aqueous medium and in the presence of an acid which is stable under the reaction conditions. One or more other oxidizing agents, such as a dichromate, may be present in addition to the manganese dioxide. Compounds known to inhibit the oxidation of the aldehydes or ketones may also be present. Such compounds may be aromatic aminosulphonic acids such as sulphanilic acid or acid-resisting dispersing agents.
The aryl ethylenes may be mono- or poly-substituted in the side chain and/or the aromatic nucleus by alkyl-, aryl-, aralkyl-, alkoxy-, methylene-dioxy-, aralkyloxy-, aryloxy- or acyloxy-groups or by halogens. The oxidation may be effected by adding dilute mineral acid to a mixture of the compound to be oxidized, the oxidizing agent and water at an elevated temperature. The manganese dioxide may be in the form of pyrolusite, or may be manganese dioxide obtained by reacting a permanganate with a manganese salt, or obtained as a byproduct from a permanganate oxidation in an alkaline medium.
Examples illustrate the oxidation with manganese dioxide and aqueous sulphuric acid of methyl-isoeugenol to veratric aldehyde; and anethol to anisaldehyde, both in the presence of sulphanilic acid; styrene to benzaldehyde and some benzoic acid; a-methylstyrene to acetophenone and some benzoic acid; and b-methyl styrene to benzaldehyde and some benzoic acid; anethol is oxidized to anisaldehyde with pyrolusite in the presence of sulphuric acid and of sulphanilic acid; and methyl-isoeugenol is oxidized to veratric aldehyde by a mixture of manganese dioxide and sodium dichromate in the presence of sulphuric acid and sulphanilic acid.
Yields of 80%+ are achievable using MnO2 alone as the oxidising agent. Yields of 90%+ are achievable using a mixture of MnO2 and sodium dichromate as oxidising agents.
(Stranger)
02-12-04 14:42
No 488194
yes home and lab ozone equip can b pricey. but you have to shop in the right place to find a deal. if you go to the nearest mega mart(the 1 with food and Chinese crap in the same store, on different sides) you may see an example of a good deal. go behind the store to the side that the food is on. there will b a dumpster. there may be a suitcase sized thingy on it. there will be a 110V line to the store and a 2" hose to the dumpster. the machine may b bolted or may b resting on hangers. these machines are quiet, dependable, very useful, and weatherproof. the 2"hose can b modified to a much smaller hole, giving a nice steady bubbly stream into your propenyl cpd, GAA, and Zn. there will be a tag on the machine saying who made it and possibly the distributor. this is your contact. these machines are cheap! and if you dont have a fume hood what are you doing? if you have a long enough hose you can add it to the depleted ozone layer. as for other methods...Pb tetraacetate has been used in a few contexts here. note its usage to convert the allylbenzene croweacin to its subs. phenylacetaldehyde. and on a propenylbenzene? note that none of TFSE refs were on one. a recent post by Rhodium was from a journal where MDP-glycol(1 step b4 hydro to MDP2P) was converted to piperonal w/a periodic acid. on the same page of one of my chemtexts that outlines this, is also Pb(OAc)4 with the statement "the yields are so good that olefins are oft converted to glycols and cleaved w/HIO4 or Pb(OAc)4 rather than being cleaved directly with ozone, dichromate, or KMnO4. it also says MnO2 works. it gives as refs:KMnO4-Synthesis 1987 85-127 *HIO4:Synthetic Reagents vol 4 1981 p147-335, Synthesis 1974 229-272*MnO2-Synthesis 1976 65-104 & 133-167, Synthetic Reagents vol 2 1974 143-174. the cleavage w/ HIO4 is aqueous and the Pb(OAc)4 is in org solv. so looking at the alternatives to performic there is m-chloroperoxybenzoic acid/H2O, and alkaline KMnO4 is an option if you do it right. this is also in the above KMnO4 ref. personally, dichromate is the way to go. heat, add piper er... the cpd of your choice when it is legal to do so and it sublimes as it is oxidized, preventing unfortunate losses. enviromental concerns? if its in contact w/org material it wont stay +6 for long. reduce w/HCHO b4 you let it go.
(Hive Addict)
02-12-04 21:43
No 488284
WTF is up with the varying purities of MnO2?? Are they adding some kind of buffer to affect each product differently?
Any idea as to the impurity in this? I'm assuming pure MnO2 from a chem supply or made electrolytically would require a readjustment of the ammount to be used?
Like they state that 709g of 74% MnO2 at first and 83% pyrolucite later and again a 66%...??
(Stranger)
02-13-04 04:06
No 488343
they are using the cheap mined MnO2 which is used as is, with impurities. the chemistry of MnO2 itself is a bit complex, unless someone has figured it out since then. the mined form is oft used because it is reactive. other forms are not so reactive. the kind in batteries is one of the reactive forms. the kind from reduction of KMnO4 is not.
the less reactive forms can be made more active by heating @ 600-800C (or 300C w/coal dust), dissoving that form of Mn203 in hot H2SO4, and adding more H2SO4. some Mn precips as an active MnO2, rest stays in sol. as MnSO4. of course the "unreactive" types do react. impurities in the mined pyrolusite are mostly Fe cpds.
(Hive Bee)
02-13-04 09:45
No 488391
There is much discussion about creating an Ozone generator, and some discussion about ozone as an oxidizer here:
http://www.sciencemadness.org/talk/viewt
http://wps.prenhall.com/wps/media/object
I would love to know more about ozone's use as an oxidizer, such as what can it oxidize and how much does it oxidize it? Does it give the same results as more conventional oxidizers such as KMnO4, CrO3, and peroxy-acids? What concentration of O3 is needed?
Here is my attempt at answering my own questions: http://www.fin-tek.com/ozone/whatisozone
COMPARATIVE OXIDIZING POTENTIALS, 25°C
COMPOUND Volts
Flourine (F2) 2.87
Ozone (O3) 2.07
Hydrogen Peroxide (H2O2) 1.78
Potassium Permanganate (KMnO4) 1.70
Hypobromous Acid (HOBr) 1.59
Hypochlorous Acid (HOCl) 1.49
Chlorine (Cl2) 1.36
Chlorine Dioxide (ClO2) 1.27
Oxygen (O2) 1.23
Chromic Acid (H2Cr2O4) 1.21
Bromine (Br2) 1.09
Nitric Acid (HNO3) 0.94
Iodine (I2) 0.54
http://www.towson.edu/~ryzhkov/handouts/
What waste gasses can it break down? Is it capable of destroying NO and NO2 rapidly?
Ok, this doesn't have much to do with chemistry, but apparently this site reccomends that AIDS patients insufflate O3 with their butt. http://www.keephope.net/ozone.html I include this link because it provides an interesting perspective on O3's toxicity (safe at low concentrations).
(Hive Bee)
04-02-04 06:14
No 498669
192 grams of water and 53 grams (0.2 mols) of isodillapiole were introduced into a reaction flask.
56 grams of manganese dioxide (0.65 moles) and 6.5 grams of sulphanilic acid were added.
The whole was heated to 85C with vigorous stirring. During ¼ hour, 224 grams of water and 112 grams of sulphuric acid cooled to room temperature were added whilst maintaining the reaction temperature at 87C to 93C.
After having been stirred for another ¼ hour at the same temperature, the reaction mixture was cooled.
Result: a big lump of black tar and a very dark brown aqueous layer.
During the course of the reaction a definite change in smell was noticed from that of Isodillapiole to something more akin to benzaldehyde smell. In addition there was another component to the odor which was somewhat like caramelized sugar.
Is it likely that due to the increased ring substitution, this molecule is significantly more sensitive to oxidations?
Do you think there is a workaround here (e.g. run at lower temperature?
(Wonderful Personality)
04-02-04 07:11
No 498673
(Rated as: excellent)
From the Journal of Chemical Education
Vol.76, Nr.12, Dez.1999, p.1712/1713
A simple and efficient ozone generator
