uv bond breaking

[embezzler]

does anyone know if it is possible theoretically at least to us uv light of a set wavelength to specifically target the oh bond in ephedrine and allow it to reform with h atoms instead

[stratosphere]

ive wondered about that myself, or what i actually thought about was using uv to split H2 into radicals, but you could take a 2 prong approach, excite the hydroxy carbon bond, and split the H2 , doing it all in the gas phase.

the potential problems i see are side reactions, for instance could the frequency needed also take off the amine group or break c-c bonds or something else sucky?

other potential problems are that in order to work, i would imagine youd have to do it at very low presure, else collisions would de-excite the radicals before they formed. and thirdly reaction rate vs. UV intenisty, would it be fast eneuogh to be practical?
ill try to get some numbers and report back.

[embezzler]

as far as i know the wavelenth should be specific for each bond, in the ir spec this kind of energy absorbance is used to fingeprint molecules by their bonds the absobance in uv i think is based on electronic transitions within molecules.
Is it safe to assume that the intensity of the light would be proportional to the rate of any such reaction, the gas phase may not need to be at low pressure the affiliation of h atoms to shoul allow the rxn to take place once oh has been removed,this may have to be one in excess acidic solution to allow the oh molecules an altenative reaction route.
This could all be wishful thinking of course.
Feel free to pm me any sites or references and i will do the same in the future

[elfspice]

i wonder, if one found this exact uv frequency, if one got a container one could put the freebase pseudo/ephedrine, that had a coating applied to it which created a filter blocking all but the frequency required... then stick it out in the sun

that would be the most economic method of finding a strong enough source of ultraviolet, although the heat may interfere (?)... a mirrored dish could be used to increase the amount of light.... etc...

it would be neat if there were some way to control the chirality of the raction via this method too, maybe by using polarisation?

[livid]

thats a cool thought,what about cracking it with pressure ?

[embezzler]

suppose maybe usin diffraction grating or something but uv lasers are mentioned in the research i have read...
not sure what you mean by pressure cracking

[Nicodem]

UV cannot just exchange an OH group with H. Don't simplify chemistry like that!
UV can homoliticaly split a bond, but this always generates a pair of radicals. So even if it could generate a HO* and a benzylic radical (but to my knowledge it dosn't) they would again recombine in the starting compound.
It can do that with the Br instead of OH (an R-Br) and the pair of radicals can be reduced by (n-Bu)₃SnH into R-H and (n-Bu)₃SnBr. But you don't even need UV for that as (n-Bu)₃SnH works best with a minimal amount of radical initiators like AIBN and similar.

[SQUIDIPPY]

UV,.....doesn't seem feasable.

S/D has many times pondered the use of an ultrasonic cleaner, however.

[embezzler]

i never meant to simplify the process but it is easier to get my meaning across in more straight foward english. i didnt think it would be simple enough for a clandestine laboratory but since my question was on the theory that is not important. I wanted a discussion to build on my undestanding so a negative response is as good as a posative one. my thoughts were that the oh* could be replaced with H* atoms .never said it would be easy

[MnkyBoy78]

SWIM has quite frequently placed the rxn in the sun.  No extra heating is needed and the rxn just chugs away.  Come evening the rxn is complete and all is good.

THis has struck my curiosity as well, and here is the next few days SWIM was going to have a piece from a broken flask scanned for its transmitance of various wavelents (L.IR ->UV).

[embezzler]

it is unlikely that borosilicate glass would even allow the transmission of ultra voilet radiation instead where this is required quartz glass is used.
the uv energy i was referring to was that from a laser and is not straight forward as sunlight it requires the selective exitation of the oh bond from my limited yet growing knowledge of photolysis i=t seems that in ir laser is even used before a uv one to excite the bond .make sure to keep us informed if the yields vary as where swim is from there is not much sun in winter.

the reaction in the sun MAY work better that indoors but this is not due to uv radiation but to longer wavelengths of electromag radiation from the sun and this extra energy would serve the same as heating up the reaction.

[Organikum]

A usual procedure to produce BzCl from toluene is - whilst Cl2 is bubbled in - to place the flask in the sun or to use a strong lamp (500W) if no immersible UV lamp is available.

So there will be some UV light going through the borosilicate glass, yes?
Of course thin glass is preferable here, but the sun is an astonishing strong UV source and on a hot summerday a thickwallet flask makes no problems at all.

MnkyBoy is right IMHO - never forget we talk here about INITIATION of reactions not of the driving force through the whole reaction.....

[embezzler]

that still doesnt answer MY question, i WASNT talking about the initiation of reactions but i was talking about uv as a driving force behind them.

ps i was aware the sun was a source of uv but thanks anyway

[Organikum]

[embezzler]

[embezzler]

regarding photolysis of organic compound using He-Ne laser:

http://www.chem.uic.edu/chem343/Flash-Photolysis.pdf

it may not be an oh group getting attacked but the principle should be the same.