Author Topic: Short Questions Thread  (Read 10820 times)

Waggledance

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Re: Short Questions Thread
« Reply #960 on: August 08, 2011, 01:51:26 PM »
What are some reactions that will replace an existing group with a carbonyl group? I've been reading pdfs and searching for almost 12 hours straight and I'm starting to think it's just not possible.

What kind of group are you talking about? Alcohols can be easily oxidized to their corresponding aldehydes or carboxylic acids (primary) or ketones (secondary) using many reagents, for example acidified dichromate. 

reDEEMed

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Re: Short Questions Thread
« Reply #961 on: August 08, 2011, 02:12:29 PM »
I wondered if a methyl group could be replaced by a carbonyl. I know about oxidizing alcohols to aldehydes/ketones>carboxylic acids.

Edit: Maybe I should add that I would not want the carbonyl on the end of the chain, but rather more inline with where it would be located for a ketone.
« Last Edit: August 08, 2011, 02:14:03 PM by reDEEMed »
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akcom

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Re: Short Questions Thread
« Reply #962 on: August 08, 2011, 06:01:00 PM »
You're being a bit obtuse here.  C-H/C-C activation is usually hard to accomplish in a controlled manner with transition metal chemistry.  Show us the reaction you want (substrate, product)

reDEEMed

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Re: Short Questions Thread
« Reply #963 on: August 08, 2011, 07:39:42 PM »
Okay, sorry. How about this- The only difference between an aldehyde and a ketone is the position of the carbonyl. Obviously one just can't pluck it off the end of an aldehyde and stick it in the middle of the next methyl down the chain, but maybe you could add one there then remove the one from the end thereby making your aldehyde a ketone. If ever the words experimental applied, they do here. I'm just curious as to how possible it is. I'm in no means gearing up to try this.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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Methyl Man

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Re: Short Questions Thread
« Reply #964 on: August 10, 2011, 02:26:00 PM »
Urgent:  Is it okay/possible to use a 1000 ml RB flask for a vac distillation where a 500 ml RB is the proper flask size? Would the extra headroom be a problem?

He's getting ready to do some work, thought he had every last piece of needed gear, then suddenly wakes up bolt upright in bed early this morning realizing he doesn't have the 500 which is what he always used to distill the ketone at the end of a wacker. Now he's anxious, trying to figure out whether he absolutely has to make a nearly 100-mile round trip to go buy one.
There's a methyl to my madness...
==+==+==+==+==+==+==+==+==+==

java

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Re: Short Questions Thread
« Reply #965 on: August 10, 2011, 02:34:01 PM »
.....in my experience it works ...it takes longer, but it works fine.......java
¡Prefiero morir de pie que vivir siempre arrodillado!.Emiliano ZapataIt is better to die on your feet than to live on your knees!.......

java

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Re: Short Questions Thread
« Reply #966 on: August 10, 2011, 02:34:13 PM »
Okay, sorry. How about this- The only difference between an aldehyde and a ketone is the position of the carbonyl. Obviously one just can't pluck it off the end of an aldehyde and stick it in the middle of the next methyl down the chain, but maybe you could add one there then remove the one from the end thereby making your aldehyde a ketone. If ever the words experimental applied, they do here. I'm just curious as to how possible it is. I'm in no means gearing up to try this.

...if I was interested in finding out i would ask google " converting an aldehyde to a ketone " which can give you quite a few leads....

....here is one,

Unfortunately, Let's reason.......

Ketones can not be directly converted into aldehydes.

A ketone, has a carbonyl group (C=O) with two R groups attached on either side (R can not be hydrogen).

An aldehyde, has a carbonyl group, with only ONE R group attached. The other atom attached to the carbonyl carbon is a hydrogen atom.

A ketone can be reduced - it will give you a secondary alcohol.

The ketone can not be oxidized.

In order to get an aldehyde, you could oxidize a primary alcohol, RCH2OH.

RCH2OH ---[Ox]----> RCHO (aldehyde) -----[Ox]----> RCOOH (carboxylic acid).

The aldehyde can be oxidized to a carboxylic acid.
Source(s):
my Ph.D. in Chemistry



or....


Chem freak is right. React the aldehyde with a Grignard then oxidize the secondary alcohol to the ketone. The only thing I would do different is not use CrO3 (Jones reagent when H2SO4 is used). Cr is toxic and I have seen reactions run away uncontrollably. Both PCC and CrO3 are difficult to remove from your reaction. A better reagent is DMP (Dess-Martin periodinane). Yields are high. The only drawback is it is expensive and can be explosive. Other oxidants that can be used are TPAP and Swern oxidation.
Source(s):
PhD in organic chemistry
« Last Edit: August 11, 2011, 01:46:33 AM by java »
¡Prefiero morir de pie que vivir siempre arrodillado!.Emiliano ZapataIt is better to die on your feet than to live on your knees!.......

reDEEMed

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Re: Short Questions Thread
« Reply #967 on: August 11, 2011, 03:06:20 PM »
Quote
oxidize the secondary alcohol to the ketone

AHHHA!! That's what I'm talking about.

I searched using the exact term you you did, but I missed that somehow. That sounds like a great strategy for what I'm asking about. Very nice, thanks!

Now tell me how to attach that OH where it needs to be to make my secondary alcohol HAHA, just kidding, I'll look that up myself. In fact I probably already have the perfect text for it. I found an ancient text a few days ago called 'Oxidations In Organic Chemistry' that is plain awesome for info along these lines. It's one of my favorite pdf's I have lol, looks like it's about to be spot on again.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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Tsathoggua

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Re: Short Questions Thread
« Reply #968 on: August 11, 2011, 03:42:51 PM »
Fancy uploading it somewhere and posting it? might just become one of some other wasp's favourite reads if you do. Would bee appreciated. (If you are willing, please do so publicly in the request thread here, so others can read it, and find it, however I haven't yet actually read, and do not currently follow, although I guess I should, those threads, and Toady, he has a medical memory problem, so alerting him if you are willing to share it, and have actually done so, via PM, would bee much appreciated)  Toad face administered multiple IV doses of methoxetamine last night, and insufflated a considerable quantity over the previous few days to this post being written, so the ability of his hippocampus to organize the encoding of memories and consolidate them from short and working to long term memory, via glutamatergic AMPA receptor-dependent hippocampal long term potentiation is impaired. So he may not remember he asked. A PM would bee most appreciated if you can upload that book on oxidations.

Drawback to the Swern oxidation if I remember rightly, is the use of DMSO. Low volatility/high boiling under atmospheric pressure, reduction in this particular reaction to dimethyl sulfide, at least to a degree, which is most certainly volatile, and most certainly foul smelling (and probably not particularly a pleasant substance to come into significant contact with either, certainly though, I don't recall reading it having the same extremely potently lethal, and highly carcinogenic properties of dimethyl sulfATE) and there is to consider, the danger inherent with DMSO in any reaction, of it coming into contact with the skin. It absorbs very quickly transdermally, and is capable of carrying substances with it. It has indeed, been used with multiple compounds (never by myself however) to deliver drugs transdermally.

Not a toxic solvent, particularly, compared to most, and has medical applications, BUT, I do recall reading a journal paper not too long ago, although I can't remember what, or which issue to cite it, search should reveal it, where DMSO used alone was shown to exert a neurotoxic or neurodegenerative effect upon the brains of lab animals. I cannot remember if this neurotoxic and/or neurodegenerative effect was targeted at a specific location/structure within the brain, or was generalised and diffuse in character. (uggh...disgusting, cruel bastard fucks, poisoning animals and torturing them...I HATE it, to see animals treated that way, even though I have to eat them [no, not rats :P])

My guess is that it (DMSO) would also penetrate the blood brain barrier extremely efficiently and quickly once it is either applied to or spilled on the skin, carrying whatever might be dissolved, if anything with it. Weather a transition metal ion that lacks a specific affinity for being deposited in fat would go through the lipid portion of the BBB very well once it gains access to the bloodstream (such as for example the insidious, lethal and altogether cunting scary dimethylmercury, which does so as though it were born for causing that specific effect and goes STRAIGHT to the brain, and once there, stays there tenaciously, killing cells left right and center) is anyone's guess, I do not know.

But I sure as hell wouldn't want to spill DMSO with a load of CrO3 or dichromate in there on me....that would NOT be a good thing to come into contact with and medical consequences if exposed to anything more than a minute quantity, would be unsurprising, and indeed quite probable, and near certain in the case of a large quantity. Hexavalent Cr being particularly nasty, appearing to me to act locally as a carcinogen upon sites of contact (skin contact sans DMSO, being washed off in timely fashion, I consider relatively unlikely to cause harm. Occupational inhalation of chromium hex is known to cause lung cancer, and also kidney cancer, and increases risk likewise of cancer of the lower GI tract. Purely oral exposure I assume will not selectively target lungs but instead concentrate the manifestation of the toxic effects in the GI tract, and kidneys. Presumably also the bladder if it gets absorbed well into the bloodstream and circulates, after being accidentally orally intaken although I am unsure weather this happens to a significant extent after exposure.

Toad features had to replace some furniture after getting chromium hex distributed all over the show once, years back, glass shattered during distillation of a quantity of chromyl chloride, perhaps 150, maybe 200ml or so. It was being synthesized by addition of 98% H2SO4 to an intimate mixture of table salt and he forgets now, but either potassium or sodium dichromate. An excellent way to produce chromyl chloride by the way, analagous iodides, or bromides do not exist, by way of an interesting tidbit of info, nor, he believes, do fluorides.

Stuff went everybloodywhere in the wooden wardrobe his only workspace, as a kid, at the time, had to be in. Oh boy did he ever vacate the room, luckily it stayed localised, what was released being absorbed mostly by the wooden surface, or unfortunately, volatilizing to a degree. HCl fuming everywhere, leaving a slowly spreading pool of conc. H2SO4, dichromate sludge, and chromyl chloride slithering across the work surface. Toady stopping in only to grab his gas mask, put absorbent material down to soak up the escaping tide of shite, close the door, to avoid contaminating the house, and opening all windows possible within the area of effect. The salt being in there, acting like sand would, to a degree, although itself causing release of minor quantities of further halide. Left for a long, long, long walk, and when he had to come home, sleeping in his mask. He had to cut a piece of wood to size, after cleaning up the aftermath, once the shit had stopped hitting the fan and dripping down therefrom, to cover the green stains (looked approximately the color of somewhere between the tetraminecopper complex formed by CuSO4 and aq. ammonia mixed with the green hue of nickel chloride), and then permanently glue it securely over that part of the wardrobe.

That episode, looking back on it was fuck ugly in toady's opinion. Could have got nasty, very nasty in fact.

In the case of exposure via DMSO he imagines it [ Cr(VI) ] would have the tendency to cause cancer in ALL areas of the peripheral body, perhaps not penetrating the BBB if absorbed onto the skin in solution, but given the lipophilic nature and rapid absorption, presumably correspondigly rapid distribution in vivo also, that is likely, in his opinion not to be the case.

So Swern oxidations, whilst sounding and seeming like an excellently useful reaction for preparing aldehydes from the appropriate precursor or intermediate experimental/synthetic substrates in Tsathoggua's opinion have some very significant safety issues associated with them, and in the case of a private lab, should, responsibly, be very well protected from environmental release, and the possibility of Me2S release dealt with.

DMS being of course, the thioether counterpart to dimethyl ether, which is extremely flammable, this one is stinky too, and its the sort of chemical which will get everywhere if not watched.

Quick question for the sake of learning.....do small molecule thioethers tend to peroxidise like their oxygenated counterparts?
Not relevant, I would thought, from my reading on the safe handling of THF, and by extension, other simple ethers, as peroxidation seems, according to my reading, to occur exclusively in the liquid phase, and not in THF vapor. In the liquid underneath it, yes, but not the vapor itself if no liquid THF is present.
« Last Edit: August 11, 2011, 05:55:44 PM by Tsathoggua »
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reDEEMed

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Re: Short Questions Thread
« Reply #969 on: August 11, 2011, 03:53:00 PM »
http://127.0.0.1/talk/index.php/topic,2496.msg25292.html#msg25292

Not the best pdf as it's not searchable, but the table of contents works just fine. I've found info in there that I have been searching for for weeks.
« Last Edit: August 13, 2011, 10:08:14 PM by reDEEMed »
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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Tsathoggua

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Re: Short Questions Thread
« Reply #970 on: August 11, 2011, 05:56:38 PM »
Nice one for that, Shall have to download it and have a look when I have spare time.
Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

reDEEMed

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Re: Short Questions Thread
« Reply #971 on: August 13, 2011, 10:01:32 PM »
Why, even after hours, is the sand in a sand bath 20-30 degrees hotter than the reaction? Seriously, if the fucking sand is 65 degrees and the reaction flask and solution are in the sand for 2-3 hours at this temperature, why the hell is the solution in the flask not reaching that temperature?
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna

akcom

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Re: Short Questions Thread
« Reply #972 on: August 13, 2011, 10:31:26 PM »
Heat transfer isn't perfect.  That seems pretty reasonable to me.  For a smaller flask, mantle -> oil -> rxn you loose probably 20-30 depending on how efficient it is.

reDEEMed

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Re: Short Questions Thread
« Reply #973 on: August 13, 2011, 11:54:33 PM »
Ahh. I wanted the softest finest sand I could find, but the sand I got really sucks. Now that you mention it, I can totally see that. Thanks.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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dingbow

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Re: Short Questions Thread
« Reply #974 on: August 14, 2011, 12:17:32 AM »
I use glycerine as my bath 'oil', easier to clean then non polar oils. Sand is not that great at heat transfer.

reDEEMed

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Re: Short Questions Thread
« Reply #975 on: August 14, 2011, 12:32:35 AM »
I might give that a try. I just like sand because it's not splashable, also if I break something I'd rather it go into sand. I think I will try the glycerin bath at least once, though.
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
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Tsathoggua

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Re: Short Questions Thread
« Reply #976 on: August 14, 2011, 03:08:35 AM »
I would just make sure no reagents that act as dehydrating agents, such as polyphosphoric acid, bisulfate salts, H2SO4 (conc.) can possibly spit from a rxn vessel, and land in the hot glycerine bath. Nice idea though, might just give that a shot myself also.

Dehydration of glycerine mind you, like I mention, can result in formation of acrolein. this is very very NASTY stuff. The fumes of acrolein are a powerful lachrymator, even a low concentration in air will I imagine, blind at least temporarily until it wears off if you are exposed and cannot leave the lab. Pouring a few mililiters, a small quantity, from a test tube down the sink, and getting close enough over the plug-hole, head several feet away in terms of height, within a minute or two after pouring it away, gave Toady a taste of its lachrymatory properties. Acrolein makes chloroacetones saturated with HCl(g) explosively distributed as a vapor in a small garage thanks to an exotherm induced flashboil look like getting a whiff of moderately conc. acetic or formic acid from some distance away.

Never had the unpleasant experience himself of getting hit in the eyes with CS spray, PAVA, mace etc. but he doubts it would be a vast amount worse than a significant exposure to acrolein vapor. Bloody vicious stuff. From what I gather, fairly toxic too.

Never handled gallium personally, but what about a gallium bath? or one of the gallium alloys that liquify even when held in a human palm? thermal expansion and contraction could I imagine, crush a flask if it were ever allowed to set around it, and contract if its hot enough to experience significant contraction. It would surround the flask just like a fluid such as water, oil, glycerine just the same, and the thermal conductivity, if its anything like aluminium (which certainly couldn't be used thanks to its melting point of course) I imagine, be pretty bloody good. Al chunks/pipe/bar will conduct heat very damn fast if one holds it and heats the other end one will feel it quickly.

Not sure what the vapor pressure of Ga is like, AFAIK it has vastly less toxicity than the notorious Hg, but breathing the fumes is unlikely to be a great idea.
« Last Edit: August 14, 2011, 03:13:25 AM by Tsathoggua »
Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

Adrenaline

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Re: Short Questions Thread
« Reply #977 on: August 14, 2011, 09:42:35 AM »
I wondered if a methyl group could be replaced by a carbonyl. I know about oxidizing alcohols to aldehydes/ketones>carboxylic acids.

Replacing methyl groups by carbonyl groups is rather difficult, because under such conditions carbonyl groups will be oxidized as soon as they`re formed.
There`s one method which uses chromic acid in acetic anhydride as an oxidizer. As soon as the aldehyde is formed it reacts with the acetic anhydride. The resulting Diacetate will not be further oxidized by the chromic acid. hydrolysis of the diacetate will yield your aldehyde.

Another method is selective oxidation with ceric ammonium nitrate.

reDEEMed

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Re: Short Questions Thread
« Reply #978 on: August 14, 2011, 01:03:07 PM »
But, if further oxidation were your goal, say to the ketone, you'd be gold. Especially if this were happening to a secondary alcohol as it would more readily stop at the ketone.

I'm just happy to hear its possible. Everything for me is difficult, except maybe mixing vinegar and baking soda, I can do that pretty good. If I were 1337 I would grignard the aldehyde to give a secondary alcohol, then do something to the carbonyl on the end to neuter it, then oxidize the newly formed alcohol to the ketone then go back and remove my neutered carbonyl on the end. I suppose what ever I did to neuter it would make it easy it to remove at the end. I dunno, it's fun to not have a clue as to was is and is not possible. Maybe I can make gold!

Thanks for the new names to read about!
« Last Edit: August 14, 2011, 03:27:24 PM by reDEEMed »
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna

reDEEMed

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Re: Short Questions Thread
« Reply #979 on: August 15, 2011, 04:17:53 PM »
What's the proper Ph for titration solution that you would keep pre-made to salt out various bases? Ultimately I would like to have HCl, tartaric and citric acid solutions prepared and in the fridge for salting out. The HCl I have been using is Ph 2, but that doesn't give me much of an aqueous layer by the time my solution is at Ph 5-7. I know I'm not doing it right.

Any help?

Edit: Another, more important question- Depending on where you look, ie rhodium versus wikipedia versus where ever, the structure of MDA is different. Sometimes the amine portion is on the very end of the chain while other times there is a methyl on the end and the amine part is between that and the rest of the chain. Is it that it makes no difference, or is one wrong? It seems to me that moving a group's position would affect it somehow. Maybe the fact that it's the position on the chain and not the ring that changes it doesn't matter as much? If that's the case then why the big difference between ketone and aldehyde? This is very confusing to me.
« Last Edit: August 15, 2011, 04:53:55 PM by reDEEMed »
"Ego is a structure that is erected by a neurotic individual who is a member of a neurotic culture against the facts of the matter. And culture, which we put on like an overcoat, is the collectivized consensus about what sort of neurotic behaviors are acceptable."
— Terence McKenna