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Author: Subject: The short questions thread (2)
ketel-one
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[*] posted on 8-9-2009 at 17:08


Short question, I know it's very beginnerish

When you cleave an ether R1-O-R2 with boiling HI, you get R1-OH and R2-I, right? If you got R1-OH and R2-OH it probably would just be called hydrolysis. And can you use HI3 instead of HI?
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kclo4
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[*] posted on 8-9-2009 at 17:36


I assume HI3 is a mix of HI and I2, and is used to increase the solubility of I2 in solution?
I don't think it would be wise to use..




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ketel-one
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[*] posted on 8-9-2009 at 17:57


Alright I suppose I'd bubble some hydrogen through it to make more HI, I don't exactly have any H2S

And forget about the first question I've figured out already you do get R1-OH + R2-I
http://www.brainmass.com/homework-help/chemistry/organic-che...
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[*] posted on 8-9-2009 at 20:36


Quote: Originally posted by ketel-one  
Alright I suppose I'd bubble some hydrogen through it to make more HI, I don't exactly have any H2S


That will give you hydrogen gas containing a bit of elemental iodine, the reaction is very slow without a catalyst.

You can use iodine, water, and H2S, which give aqueous HI and elemental sulfur; iodine, water, and SO2, which gives you aqueous HI and H2SO4; or I2, H2O, and red phosphorous, the favorite of meth makers.
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kclo4
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[*] posted on 8-9-2009 at 20:44


Sulfur is easy to get, and you can make H2S easily from it by heating it with wax.
SO2 can obviously be made by burning the sulfur.




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ketel-one
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[*] posted on 8-9-2009 at 20:55


Oh right I just remembered a good way to get sulfur... Lots of matches in HCl, i believe last time I tried it it also made Cl2O or something... I forget it was a couple years ago.
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dann2
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[*] posted on 9-9-2009 at 02:29


Hello,

Quote: Originally posted by kclo4  
Sulfur is easy to get, and you can make H2S easily from it by heating it with wax.


How do you do that. Simply heat Sulphur and candle wax together?
Dann2
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[*] posted on 9-9-2009 at 04:12


Yes, simply heat a mix of sulphur and paraffin. Use excess paraffin. If you buy white candles, then try to find the paraffin ones. There also are stearin-based candles and these may react in a different way. Paraffin can also be purchased from eBay as a pure chemical, it just is an alkane with many C-atoms in a chain (IIRC numbers of C atoms is more than 20).

When the mix of sulphur and paraffin is heated, then the paraffin melts, the sulphur also melts, but somewhat later. On stronger heating the mix starts fuming and bubbling. The fume is due to evaporation and recondensation of paraffin, the bubbles you obtain consist of H2S gas. Purification can be achieved by bubbling through paraffin oil (which also is a mix of alkanes, but with somewhat lower number of C-atoms). The paraffin fumes dissolve in the paraffin oil, the H2S bubbles through the oil. Try to pass large bubbles of gas through a tall column, otherwise you will suffer from excessive foaming.

Be warned though, that this procedure is very messy. Your reaction vessel is covered by a gummy very hard to remove material which has a terrible smell. I once did the experiment in a large and wide test tube. I decided to discard that tube, it simply appeared impossible to make it clean again. Also keep in mind that H2S is very toxic, one of the members of this forum almost passed out after inhaling too much H2S. The sense of smell is deadened by high concentrations of H2S, this introduces an additional safety risk.

[Edited on 9-9-09 by woelen]




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Klute
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[*] posted on 9-9-2009 at 04:40


I really advise against using H2S, even in a sealed apparatus. The event of a leak is just too dangerous. I was thinking I could handle it with a good scrubber, but didn't realize that even after gas generation has finished the sludge still contains enough H2S to kill someone. I had a very bad and frightening experience with it. Certainly not something for newbees or even intermediates..



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ketel-one
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[*] posted on 9-9-2009 at 11:32


Quote: Originally posted by Klute  
Certainly not something for newbees or even intermediates..


Right I guess that's my que.
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entropy51
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[*] posted on 9-9-2009 at 12:29


And here you are crapping all over another thread.

They're just BS'ing you man. H2S isn't poisonous. Make all you want.
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[*] posted on 9-9-2009 at 13:05


Quote: Originally posted by entropy51  
(cut)They're just BS'ing you man. H2S isn't poisonous. Make all you want.

Oh yeah? Besides being smelly, the stuff is DEADLY poisonous, being comparable to HCN or (CN)2, HOCN, CO, CH2N2, PH3, and HN3, as gases or vapors, and their salts, which have a similar mode of action entailing preferential bonding to the Fe atom in hemoglobin in place of O2. There are some people here who apparently do not want to see you back, so you could oblige them by making and breathing in a large enough amount of the stuff.
P.S. If your statement was intended as a joke, there are, unfortunately, those naïve enough to take it literally.

[Edited on 9-9-09 by JohnWW]
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[*] posted on 9-9-2009 at 14:10


Thank you, John for ruining my joke.
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[*] posted on 9-9-2009 at 14:37


Quote: Originally posted by Klute  
I really advise against using H2S, even in a sealed apparatus. The event of a leak is just too dangerous.
I'll second this, not from experience, because I don't intend to have any with this. Don't make H2S in a sealed apparatus made out of iron pipe, even. H2S causes sulfide embrittlement in iron and steel, causing cracking from the inside that leads to a sudden rupture visible from the outside. Industrially, when significant quantities of H2S are present, various high-nickel alloys are specified, such as the Hastelloy series, and those are pricey. This is even something to worry about with ordinary sulfur, as moisture + sulfur + heat makes non-trivial amounts of H2S.
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[*] posted on 9-9-2009 at 22:19


Can brominated bicyclic molecules be used as alkylating agents? For example, 2-bromo-1,7,7-trimethylbicyclo[2.2.1]heptane (i.e. borneol [alcohol of camphor] brominated at the OH):


Many thanks!

Formula409.

[Edited on 10-9-2009 by Formula409]

[Edited on 10-9-2009 by Formula409]
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[*] posted on 10-9-2009 at 01:17


What liquid substance will dissolve the most substances at room temperature? Water? DMSO?
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[*] posted on 10-9-2009 at 03:38


Quote: Originally posted by Formula409  
Can brominated bicyclic molecules be used as alkylating agents? For example, 2-bromo-1,7,7-trimethylbicyclo[2.2.1]heptane (i.e. borneol [alcohol of camphor] brominated at the OH):


Many thanks!

Formula409.

In what way ... Friedel-Crafts? I doubt it.
But it should react with a Grignard, and should form a Grignard, and alkylate that way.

This compound can be made, I think, from alpha pinene and dry HBr. Any reason why it wouldn't react as I suggest?
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[*] posted on 10-9-2009 at 03:56


I suspect making the grignard reagent will work oks. Also the alkyllithium, possibly by lithium-bromine exchange with MeLi or the likes. You havent staed as to whether the bromine substituent is endo or exo, and suspect that only the endo-isomer (I hope I've got this right) will react in any form of Sn2 (albeint probably poorly) with nucleophilic reagents as there is too much steric hindrance for the approach of the nucleophile in the exo isomer (and this may be the case with the endo isomer too...)
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[*] posted on 10-9-2009 at 06:35


Yes, a secondary bromide like that one could be made into a Grignard reagent, for introduction of a 2-bromo-1,7,7-trimethylbicyclo[2.2.1]heptanyl group into another alkyl or aryl halide, substituting for the halogen. In addition, that secondary bromide would show some dissociation into a carbocation in a polar aprotic solvent, enabling it to be used for electrophilic addition reactions, e.g. to amines to make substituted amine salts, or to alcohols or ketones or aldehydes to make ethers, or possibly under some conditions to ethers to make oxonium salts.
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[*] posted on 10-9-2009 at 08:32


I don't know exactly which compound Formula409 is asking about (the structure is ambiguous) since the bromination of borneol can give two compounds, bornyl bromide or isobornyl bromide, or a mixture of two, depending on the method used. The examples in the literature use some pretty hard to obtain reagents. Therefore, I have no idea how Formula409 intents to obtain (iso)bornyl bromide except maybe from HBr addition on pinene like Paddywhacker suggested (described in Journal of Organic Chemistry, 51, 4947-4953).
In any case an SN2 substitution is nearly impossible on the two bornyl bromides, because it is a stericaly hindered, bridged, cyclic and secondary bromide (each of these factors is deactivating for SN2 mechanism). It might be possible with S-nucleophiles or other extremely strong and not too basic nucleophiles. Under basic conditions only an E2 mechanism can result. An SN1 would most likely give a rearrangement product(s) and in any case is only possible in an acidic media so the choice of nucleophiles (which Formula409 failed to specify) is very limited. There are examples of some SET based nucleophilic substitutions on such systems described in the literature (for example the mechanistical study in Tetrahedron Letters, 30, 493-496), but I doubt this is relevant.

JohnWW, aliphatic secondary alkyl bromides do not dissociate to carbocations just like that, certainly not in absence of any acid! There is no way you can get an SN1 substitution with amines on normal secondary alkyl halides and I wish you could provide a reference if you know about any such example. Only tertiary alkyl halides and some alkyls stabilized by resonance can participate in SN1 reactions in neutral or basic media. You would need the presence of a very strong acid, AlBr3 for example, to get something resembling a carbocation, but only transiently resembling. And obviously this is not possible in the presence of such nucleophiles like the amines because they are too basic. I could find no examples for your suggestion of using (iso)bornyl bromide derived Grignards in a Kumada coupling, but there are some examples of Kumada, Suzuki and Stille couplings using Grignard reagents on norbornyl bromides (that is similar, but in the reversed role of reaction partners, from what you proposed).




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[*] posted on 10-9-2009 at 18:57


Quote: Originally posted by Nicodem  
(cut)JohnWW, aliphatic secondary alkyl bromides do not dissociate to carbocations just like that, certainly not in absence of any acid! There is no way you can get an SN1 substitution with amines on normal secondary alkyl halides and I wish you could provide a reference if you know about any such example. Only tertiary alkyl halides and some alkyls stabilized by resonance can participate in SN1 reactions in neutral or basic media. You would need the presence of a very strong acid, AlBr3 for example, to get something resembling a carbocation, but only transiently resembling. And obviously this is not possible in the presence of such nucleophiles like the amines because they are too basic. I could find no examples for your suggestion of using (iso)bornyl bromide derived Grignards in a Kumada coupling, but there are some examples of Kumada, Suzuki and Stille couplings using Grignard reagents on norbornyl bromides (that is similar, but in the reversed role of reaction partners, from what you proposed).

I am sorry to disappoint you, Nicodem, but I must believe the evidence before my eyes, in the form of the authoritative organic textbooks, such as Solomons, McMurry, Morrison & Boyd, Bruice, etc., that I have before me. Aliphatic secondary halides, especially bromides of a fairly large structure like that one in question which provide some steric support for dissociation, DO undergo slight dissociation to form carbocations in aprotic polar solvents in equilibrium with the undissociated form, although of course the degree of dissociation is much less than that of tertiary halides (especially tertiary halides in which the resulting positive charge is delocalized by resonance as in triphenylmethyl(+)). And, moreover, the same textbooks indicate that the degree of dissociation, though small, IS quite sufficient, by shifting the equilibrium, for the resulting carbocations to quantitatively bond by electrophilic addition to the N atoms of amines to form substituted amine halide salts. I simply cannot understand why you should think otherwise. The same would apply to electrophilic addition to oxo-compounds to result in oxonium salts, and similarly sulfonium salts. The equilibria in favor of carbocation formation, and hence reaction rates, can be improved by catalytic use of Lewis acids such as AlBr3 or FeBr3.

BTW the C atom to which the Br atom is bonded in 2-bromo-1,7,7-trimethylbicyclo[2.2.1]heptane is, as in borneol, asymmetric (chiral) and optically active; and it is not clear from the illustration provided which enantiomer is the one in question. The one in which the dimethylated bridge is closer to the Br atom would undergo the greater degree of dissociation, and thereby react faster.

[Edited on 11-9-09 by JohnWW]
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[*] posted on 11-9-2009 at 04:08


Quote: Originally posted by JohnWW  

And, moreover, the same textbooks indicate that the degree of dissociation, though small, IS quite sufficient, by shifting the equilibrium, for the resulting carbocations to quantitatively bond by electrophilic addition to the N atoms of amines to form substituted amine halide salts. I simply cannot understand why you should think otherwise. The same would apply to electrophilic addition to oxo-compounds to result in oxonium salts, and similarly sulfonium salts. The equilibria in favor of carbocation formation, and hence reaction rates, can be improved by catalytic use of Lewis acids such as AlBr3 or FeBr3.

I'm not saying that SN1 based reactions on bornyl bromide is not possible. Like I already said, they could (and actually should) be possible but only under acidic conditions. It is true that the bornyl carbocation is somewhat more stabilized than a normal secondary carbocation (due to hyperconjugation over the ring structure), but still not as much as tert-carbocations are. I searched CA and Beilstein and could find no reactions of bornyl halides&alcohols&esters with amines. The only SN1 based reactions with N-nucleophiles found, were several examples of the Ritter reaction on bornyl alcohols (which are often acompanied by rearrangement to camphene system) and the reactions of bornyl alchols&chlorides with a mixture of aniline&aniline salts. Both are reactions in acidic media. The reaction or bornyl alcohols and bornyl chlorides with anilines is low yielding and also gives a large amount of camphene and tricyclene as side product, thus indisputibly indicating an SN1 mechanism (ref: Journal fuer Praktische Chemie, 322, 423-428; Chemische Berichte, 43, 3204; DE205850). However, I could find absolutely no examples of SN1 based reactions in basic media. So I still say that the reaction of bornyl bromides with amines can not give bornyl amines because the SN2 mechanism is practicaly unavailable due to deactivating factors, while the SN1 mechanism requires acidic media in which aliphatic amines are not nucleophilic any more (and is thus limited to anilines and perhaps some other amines of low basicity, the salts of which are acidic enough to catalyse the reaction). The topic of SN1 based reactions in neutral and basic media trully interests me and my request for an example of a reaction of the type you describe is still valid. I searched for almost an hour and could find none.




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[*] posted on 11-9-2009 at 12:02


Can anyone suggest a method of deploymerizing PVC or CPVC to yeild Vinylchloride or much better yet 1-2-Dichloroethane since that will be the target compound anyway. I have been reading up but as of yet all I have found it methods that require supercritical water and/or strange conditions of high heats and pressure.




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[*] posted on 11-9-2009 at 13:36


Depolymerization - in general, this is difficult, if not impossible, given that most polymerization reactions are exothermic and probably also involve an increase in entropy. However, those that involve acid or alkaline hydrolysis of polyesters (including polycarbonates) or polyamides (including nylons and proteins), in which strongly polar groups provide the linkages, are quite feasible. But such methods would generally not apply to other types of polymers formed in different types of reactions such as condensations of unsaturated monomers or free-radical reactions, e.g. polyethylene, or related polymers of other monomers derived from ethylene or acetylene, such as those of propylene, vinyl chloride or fluoride or acetate, or tetrafluoroethylene.

The methods described for the latter types of polymers in http://en.wikipedia.org/wiki/Thermal_depolymerization generally involve hydrous anaerobic pyrolysis; and the products are not the original monomers but instead simply substances of lower molecular weight - oligomers, like light crude oil.

[Edited on 12-9-09 by JohnWW]
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[*] posted on 11-9-2009 at 14:30


Polystyrene and Polymethylmethacrylate can be decomposed by pyrolysis and the monomer distilled out.



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