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Author: Subject: The short questions thread (1)
Nicodem
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[*] posted on 16-2-2009 at 00:59


Only few imines of the most electrophylic carbonyl compounds (formaldehyde, some benzaldehydes, etc.), or the ones that are additionally stabilized by hydrogen bonds, or endocyclic imines, or certain groups at the amine part, are stable enough for isolations involving extractions from aq. phases. Others hydrolyse very rapidly even in neutral pH, and about immediately in acidic aq. media.

PS1: I don't want to see any more drug cooks acronyms like P2P, MDP2P or similar! This is a forum for amateur science, so use chemical names.

PS2: The condensation Intergalactic_Captain was inquiring was the Knoevenagel condensation between substituted benzaldehydes and nitromethane. He is not asking about any Henry reaction, just about the applicability of that method at Org. Synth. for substituted benzaldehydes.




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hector2000
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[*] posted on 16-2-2009 at 04:20


what is d-tartaric acid?
(L-(+)-tartaric acid) or(D-( − )-tartaric acid)?

[Edited on 16-2-2009 by hector2000]




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Nicodem
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[*] posted on 16-2-2009 at 04:51


http://en.wikipedia.org/wiki/Tartaric_acid
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hector2000
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[*] posted on 16-2-2009 at 05:54


yes before i read it but i am confused
always d isomer is + and l isomer is - but tartaric acid has diffrent
d is - and l is +
d-tartaric acd is dextro tartaric acid or is d(-)tartarc acid?




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sparkgap
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[*] posted on 16-2-2009 at 07:07


The Small-type Capitalized D and L and the small d and l are two different things. See this.

Another reason to be careful with capitalization!

sparky (~_~)




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hector2000
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[*] posted on 16-2-2009 at 11:02


yes you say true
my question is this:
d-tartaric acd is dextro tartaric acid or is D(-)tartarc acid?
i want to Resolution of Racemates




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Nicodem
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[*] posted on 17-2-2009 at 00:09


The prefix (+)- means dextrorotatory, (-)- is levorotatory. Read the wikipedia entry I linked above and the one Sparkgap provided to figure out which configuration of tartaric acid corresponds to which optical activity. Nobody here can answer your question but yourself since you do not use the prefixes correctly. For example, your name "d(-)tartarc acid" makes no sense whatsoever since "d-" is the prefix for dextrorotatory while "(-)-" is the prefix for levorotatory (you can not have a "dextrolevorotatory" compound :o ). Make up your mind or correct your capitalisation. It is quite probable you confused D- with d- and L- with l-, two things that have nothing in common.
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[*] posted on 17-2-2009 at 03:02


I think he just got the dash '-' mixed up with the negative sign '-'

Indeed on some keyboards these are even the same key :D




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[*] posted on 17-2-2009 at 05:38


@nicodem i know that and also i am confused about that
for example see these componet:
L(+)-tartaric acid merck number:100804
D(-)-tartaric acid merck number:800799
really which one is d-tartaric acid(dextrotartaric acid)




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sparkgap
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[*] posted on 17-2-2009 at 05:40


The "+" in L(+)-tartaric acid would imply that that is the dextrorotatory enantiomer.

sparky (~_~)




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[*] posted on 17-2-2009 at 19:52


Extra short and easy question for you:

If you monomethylate (say with MeOH/H2SO4) an alkyl hydroquinone, will it methylate the OH ortho to the alkyl group or meta to the alkyl group? For example, would it form 2-ethyl-4-methoxyphenol or 3-ethyl-4-methoxyphenol or, god forbid, a mixture of the two?

Thanks.

[Edited on 17-2-2009 by 497]
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[*] posted on 17-2-2009 at 22:33


alkyl are o,p directing so I would say the major product would be ortho but you'd get 3-5% of the meta as well



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[*] posted on 17-2-2009 at 23:22


But it's not actually methylating on the ring, so does that still apply?
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[*] posted on 18-2-2009 at 00:22


You'll get a mix, more para than ortho if the alkyl group crowds the ortho HO- enough. You may find you get some C-methylation as well, primarily at the C-O positions but possibly at the C-alkyl as well; for most substrates this happens to only a small degree if at all.
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[*] posted on 18-2-2009 at 00:24


Quote:
Originally posted by chemrox
alkyl are o,p directing so I would say the major product would be ortho but you'd get 3-5% of the meta as well

497 is asking about O-methylation, I guess with dimethyl sulfate or methyl hydrogensulfate, because "MeOH/H2SO4" does not makes much sense, unless he is talking about the benzoquinone catalysed monoalkylation of hydroquinones with alcohols which is however a different thing altogether... In any case electrophilic aromatic substitution has nothing to do with this.
Quote:
Originally posted by 497
But it's not actually methylating on the ring, so does that still apply?

With a methylating reagent, a mixture of all mono- and dimethylation products would be obtained, with the ratio depending on the reaction conditions, but never selectively only one product.
With the benzoquinone catalysed alkylation with MeOH you would obtain a mixture of both possible monomethylated products in a ratio approaching 1 : 1, but not exactly such. Electronic effects should in my opinion somewhat favour the formation of 2-ethyl-4-methoxyphenol due to the higher basicity of the carbonyl group distant from the alkyl in the benzoquinoid intermediate. But then again, this is hard to predict unless you use the DFT theory and do some computational chemistry.

To not_important: Concurrent C-alkylation of the phenoxides generally occurs <5% extent in most phenols, with some electrophiles more than others (allyl bromide is one such, but still ~5%), at least in my experience. Yet there are phenols that will give a much larger proportion of C-alkylation, for example resorcinol and some others. This is a topic that interest me quite a lot. If you happen to have a reference or a review paper discussing the topic, I would appreciate if you could share it.

[Edited on 18/2/2009 by Nicodem]
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[*] posted on 18-2-2009 at 00:46


Thank you Nicodem, that was exactly what I wanted to know. Although not the answer I was hoping to hear :P. I think I've found a way around that problem anyhow.
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[*] posted on 18-2-2009 at 23:19


Did any one come accross a picture of JWH-018 binding to the CB receptor(of any kind), or any other 1-alkyl-3-aroylindole binding? I mean, which atoms are relevant for binding, and the alkyl chain disposition while binding. If possible, gei me a link, or tell where can i find a picture(i want just in brief for JWH018, not to study all the cannabinoid family)..

[Edited on 18-2-2009 by Ebao-lu]
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[*] posted on 19-2-2009 at 00:35


If by "picture" you mean crystallographic data then the answer is negative since both CB receptors are transmembrane receptors and thus have not been crystallized (with or without a ligand) yet (I think rhodopsin is the only transmembrane protein ever crystalized up to now and of which the crystallographic data is available).
On the other hand, if by "picture" you mean a hypothetical model of interaction, then you better start looking for review papers on the topic as surely some model was described (if not graphically, at least by describing the interactions of the pharmacophore).
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[*] posted on 19-2-2009 at 04:11


Yes, of course i mean a model of interaction. My main interest is the position of alkyl "tail" there - is it directed to fill the space between N and naphtoyl, or it is directed perpendicularry to the indole ring, or any other way...
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[*] posted on 19-2-2009 at 13:44


Nicodem - Thanks for pointing that out. I should have recognized the confusion earlier on, but I figured the members here with experience in the matter would know what I was asking.

Another unrelated question - I need a small amount of n-pentanol, and it doesn't appear to be a particularly common ingredient in anything. Hydrolysis of amyl acetate first came to mind, but the stuff's expensive and most likely iso-amyl acetate (the more commonly used banana/"juicy fruit" flavoring). Right now I'm thinking this - Baeyer-villiger oxidation of cyclopentanone (from pvc solvents) to caprolactone, hydrolysis to 6-HO-caproic acid, and then decarboxylation to the one-carbon shorter n-pentanol.

Anyone ever tried to decarboxylate an aliphatic substance? Would the hydroxyl group interfere in any way in a simple benzoic acid style carboxylation (add a base and heat)? The reason I ask is related to biodiesel - It seems that if decarboxylation of fatty acids was particularly easy, the market would be flooded with plant-derived gasolines rather than methyl-esters. Once again, maybe I'm not being clear in illustrating my confusion, but that's the parallel that's got me wondering.

...and, completely unrelated once again, anyone have any experience with organocadmium reagents? I found a couple papers on their ketone-forming and other reactions and have been completely fascinated for a few days now.




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[*] posted on 19-2-2009 at 18:22


Question,
when decomposing ammonium dichromate why does it seem like there is way more product than reactant after the reaction has finished?
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[*] posted on 19-2-2009 at 18:35


The chromium (III) oxide is produced is very voluminous compared to the ammonium dichromate.
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[*] posted on 20-2-2009 at 00:57


Quote:
Originally posted by Intergalactic_Captain

Anyone ever tried to decarboxylate an aliphatic substance?

Most don't decarboxylate very well, it takes electron withdrawing groups nearby, preferably alpha. Thus malonic acid, acetoacetic acid, Cl3CCO2H, and so on, all lose CO2 fairly readily.

Quote:
Would the hydroxyl group interfere in any way in a simple benzoic acid style carboxylation (add a base and heat)?

I suggest reading the history of polymer chemistry, in particular the work of Wallace Carothers, and you may wish to reflect on the term polyester.

Quote:
The reason I ask is related to biodiesel - It seems that if decarboxylation of fatty acids was particularly easy, the market would be flooded with plant-derived gasolines rather than methyl-esters.

You got that right, babe. There have been a number of schemes for thermal decomposition of waste biological materials, many of which were to produce significant quantities of alkanes. To date none have been particularly successful, see Wiki on "thermal depolymerization".


Quote:
...and, completely unrelated once again, anyone have any experience with organocadmium reagents? I found a couple papers on their ketone-forming and other reactions and have been completely fascinated for a few days now.

Yes. Sensitive to moisture, oxygen, light, sometimes to the phase of the Moon, and occasionally to the existence of space-time. Toxic, if ignited have the delightful property of forming finely divided CdO smoke which is known to be a human carcinogen and has other interesting effects on health.

To some extent replaced by organocopper compounds, but still interesting chemistry. To get some useful details on the use of organocadmium compounds, you may wish to read this http://pubs.acs.org/doi/abs/10.1021/cr60315a001
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[*] posted on 21-2-2009 at 02:45


Quote:
Originally posted by Ullmann
And about the sodium methoxide : it can easily be done from a methanolic NaOH solution (3 molar) by addition of one equivalent of 3A molecular sieves, which can be obtained OTC for conservation of artcraft... also Na2CO3 in MeOH can be use to form it...


Is this true? I'm skeptical because I've never seen it mentioned anywhere else, always that you have to have Na metal to make NaOMe...
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[*] posted on 21-2-2009 at 03:58


Quote:
Originally posted by Formula409
Actually, I was planning on exploring whether thiourea dioxide (http://www.sciencemadness.org/talk/viewthread.php?tid=11785) is suitable for performing the reduction, naturally I will need some sort of way of quantitatively measuring yield, so the reduction procedures detailed on Rhodium are unsuitable for research.

Formula409.

[Edited on 16-2-2009 by Formula409]


Rhodium has a procedure for the reduction of imines with sodium dithionite. It calls for forming the imine first in DMF by combining the ketone and amine, then adding the dithionite, Na2CO3 and water.

An adaptation using thiourea dioxide should adhere to the same general outline of forming the imine in the usual way and then adding to it the reducer, a base and water. Note the funky cosolvent used, which I think should be replaced with isopropanol or ethanol.

See here:

Quote:
To a solution of the imine (30 mmol), either preformed or prepared in situ from the amine (30 mmol) and the carbonyl compound (30 mmol), in dimethy1formamide (70 ml) at 110ーC under nitrogen was added solid sodium hydrogen carbonate (120 mmol). The mixture was stirred vigorously; solid sodium dithionite (60 mmol) was added, followed immediately by water (30 ml). Gas evolution took place some minutes after the addition of the water. Stirring was continued at 110ーC for 30 min; the reaction-mixture was allowed to cool to room temperature and then poured into water (300 ml). The aqueous solution was extracted with ether (4x75 ml) which was in turn washed with water (4x50 ml) and saturated brine (50 ml). The ethereal extract was dried and evaporated to give the amine. The product was purified by distillation or through the hydrochloride.

The amine hydrochlorides were prepared by adding a slight excess of 5 M hydrochloric acid to the neat amine. The mixture was stirred and the solid product was collected by filtration.

http://www.erowid.org/archive/rhodium/chemistry/redamin.dith...

[Edited on 21-2-2009 by manimal]




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