Here's some information from a fellow I hold in high esteem.
He
(Predator) and
Lone Ranger have similar styles; and both are likeable, inventive
rogues who convey valuable information in a humorous
manner.
This may be a bit over the top, as regards the question:
but what the hey...
enjoy.. ":<)
From: "" Subject: Bromine, electrolytic reduction, etc.
Date: 1998/04/23
Hi there a.d.c. dudes... I'd like to relate to you some of my experiences concerning a couple of things close to your fibrillating little hearts, firstly, electrolytic reduction, and secondly, elemental bromine. The irritating requirements some of you have expressed, concerning the reduction of various naughty drug precursors, are only irritating insofar as the authorities don't like you reducing certain molecules, so they have made it tricky to get the required agents... anhydrous THF, Lithium aluminium hydride, or raney nickel, or sodium borohydride, or whatever. I don't know yet... have they banned the aminoborohydrides?
They're quite useful and lack most of the antisocial properties of say, LiAlH4... the aminoborohydrides will not explode if they get wet, and they don't do such amusing things as spontaneously catch fire on exposure to air. However I don't think they reduce C=C bonds, so all you potential nitrostyrene weenies out there should not get your hopes up too much. But I digress.
Reduction is something which can be done more easily and more cheaply with plain ol' DC electrons, as explained in Hudlicks's Organic Reductions. I decided I'd give it a whirl, so I diverted some of my minimal cashflow into building a borosilicate electrolytic reducing unit.
The rig looks like so. Take a 55mm diameter quickfit joint. The bottom half of it will be about 150mm long. Onto the top half of it get your friendly glassblower to fit a 14mm joint socket. Take a 14mm joint with a push-thru thermometer fitting (like you'd have on top of a Claisen or simple distillation head) and into it insert a cylindrical 6mm diameter rod, length about 300mm, of the highest grade carbon rod you can get. Note that carbon rods are black, and brittle. The glassblower will possibly have some of this stuff lying around, since they use ultra-pure carbon to handle hot glass without contaminating it. You gently place the rod in the thermometer holder, screw it down finger tight, and then put the 14mm joint and socket together, so the carbon rod dangles down vertically from the top of the 55mm joint. The carbon rod will be your electron-depleted electrode, at which 2Br-(aq) --> Br2(aq) will occur. If you feel energetic, another port, with, say, a teflon stopcock, can also be fitted to the top half of the joint if there are any gaseous products you might want to make. The product I wanted, in this case elemental Br2, needed no such venting, but if I ever want to make Cl2 gas, (cough cough) then I can use the rig for that too.
Almost, but not quite, at the base of the bottom half of the 55mm joint, fuse-in a Schott No4 sintered glass frit. This separates the oxidising half and the reducing half of the reactions so that the products of each don't simply recombine and waste all the juice you used to make them appear in the first place. A No.4 frit is small enough to catch viruses, and as such will hold a small column of water or other reactants because when you eventually seal the 55mm joints a very slight vacuum will develop when some of the reactants have seeped out. It will also permit some of the reaction mix to seep down thru the porous frit, to permit contact with the other electrode. I had my friendly glassblower mould the bottom of the 55mm joint so that there was a ridge of glass just below the frit so that the electron-rich electrode was pushed up against the bottom if the frit when wiggled into place.
I bought a chinese stainless steel sieve, and cut the mesh out of it, in a circle of just the right size to fit snugly against the underside of the frit, where the seep is. I didnt cut a complete circle, I also left a long tag of the woven stainless steel mesh so that I could connect my -ve battery charger terminal to it without getting hydroxide all over the terminal, which is not stainless :-)
Then I made a saturated solution of potassium bromide from KBr salt obtained from the friendly photography store... I usually have a lot of KBr lying around for density gradient centrifugation but it was cheap at the foto store, and anyway, this was just a protoype run, after all. It takes a while to dissolve, and you know you have a saturated solution when there is salt left over which refuses to dissolve into the distilled water which you use to make up good saturated solutions ;-) So I clamped the bottom half of the Reactor in a retort, with the top half hovering above it, poured in about 200mL of saturated KBr(aq) and then closed it all up. The carbon rod was now dangling in the solution. Some of the solution had dribbled thru the frit, but I wanted that, since there was now electrical contact with the stainless steel mesh. The reactor was then closed, and stood clamped in a vertical orientation with a 500mL beaker under it to catch any further dribble from the frit.
I wrapped the protruding top of the carbon rod in aluminium foil, and clamped the +(red) end of a 2A, 12V car battery charger to it. I clamped the -(black) to the protruding end of the stainless steel mesh tag, and turned it on. Sure enough, the fluid immediately around the carbon rod went yellow, then a dense reddish brown, typical of elemental bromine. A faint fizzing sound was heard adjacent to the stainless steel mesh at the bottom, and a drop of the exudate from the mesh behaved strongly alkaline towards my litmus paper. So I let it run, happy that my imaginings about reduction of halogens were in some sense true. I imagine that since the unit reduced Br- to Br, that it would be suitable for other reductions too. Voltage, current and pH would all need to be regulated, of course, as would photon flux, temperature, nitrogen shielding (etc) for any photo/air sensitive or thermolabile products. After about an hour (I dunno what coulombs had been thru the system) the mother liquor was a deep red, and I turned off the juice, put on my goggles, took a deep breath, and opened the Reactor, and poured my newly made bromine water into a 250mL RB flask where I quickly stoppered it and put it in the fridge to cool (it was moderately warm). I washed the KOH in the beaker down the drain with a lot of water, then took the carbon rod out, washed it, dried it, returned it to its little box, and then I immersed the entire rig in hot water overnight. Bromine smells fairly unpleasant but my lab is well ventilated. Now... so I had this solution sitting in my refrigerator, with water, KBr and aqueous elemental bromine in it. How to separate them? Well given bromine's BP of about 57 degrees, I thought simple distillation would be the go. I set up just such a rig, complete with big anhydrous chunks of MgSO4 in the Claisen head to snarf any stray H2O molecules in the distillate, and ran a condenser with standard tap water, and expected a product to drop out into the 100mL RB, immersed in ice-saline, at the downstream end of the condenser. It was here that I discovered a problem. Bromine really hates to and obstinately refuses to condense. So I persuaded a stack of the brown-red vapour into a 2L 3 neck flask and took the lot of it down to -22C in the freezer. I got a teensie speck of solid Br2 after a week. Sheesh! So... apart from something really ritzy like a dry ice cold trap, has anyone any technical suggestions on how to get bromine to condense?
Perhaps I should put it in another solvent which is low boiling and distill it out of that? Or maybe I should freeze dry out the water, or dessicate it for a _long_ time? Hmmm.
Only people with actual real-world experience in water-from-bromine separation need comment here. Useful references would also be appreciated if anyone has some. Caution: Do not do any reactions which might earn you the attention of your local depredational legal system. God will smack your bottie for all eternity if you do. Blah blah blah. Happy trails-
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And anudder one from Predator:
(In response to a question from our old buddy,
ReadyEddie)
Subject: Re: electrocatalytic-hydrogenation
Date: 1999/06/13
To: readyeddie@my-deja.com
readyeddie@my-deja.com wrote: > Does anyone know anything about this method. 
[[[[[[[[[[[[[[[[]]]]]]]]]]]]]]]]]]]]]]
Yeah. There's an expensive book called synthetic electro-organic chemistry by a guy called Fry. $igma AldRICH sells it. Hudlicky also has some chapters about it in his book on organic reductions. I imagine these tomes have been banned by now in order to boost sales on LiAlH4. 8-)
My take on it is this. You've got some stuff which if you were to fully reduce it, would become a useful drug. Of course, because lithium aluminum hydride has been identified as a precursor chemical and is a nuisance to work with anyway (need dry ether, catches fire in air, etc), and because Raney nickel is a nuisance too, and the much user-friendlier aminoborohydrides do not seem to reduce those pesky double bonds (in, say, nitrostyrenes) the only remaining simple way to do the chemistry is to use electrons. These are provided by the national power grid and are unlikely to be illegalized anytime soon. This was done extensively in the 1920s and 1930s. It works like so.
You have a cell (glass dish), a power source (12V battery charger, it has to be DC), a solvent to dissolve the reaction in and a soluble proton source to provide you with hydrogens where the molecule to be reduced needs them. You have a pile of something you want to reduce. You know the molecular formula of the stuff you wanna reduce and can figure out how many electrons you're gonna need to add to each molecule to do things like reduce C=C to C-C (two electrons), and -NO2 to-NH2 (four electrons). It follows that you're gonna need to add protons to these sites too. You can calculate how much juice to pass through the cell... if I have half a mole of whatever to reduce, and each molecule needs 6 electrons to reduce it down, then I have to supply three moles of electrons to the system, plus a little bit more to account for the reduction of some of the solvent, if that occurs (depends on the solvent).
You'll also need to look at supplying the same number of protons with a soluble acid. So then you divide your dish in two with a porous frit or use a salt bridge and two dishes, which will permit current to go through but not permit the compartments of each cell to mix. Into each half goes a carbon electrode (glassblowers have these, high purity, a bit expensive but work well).
Then on each side you add solvent. The old literature tends to use ethanol &HCl. Ethanol is cheap, available everywhere, and easy to purify, and also if you happen to notice, if you oxidise it, it becomes acetic acid, if you reduce it, it becomes ethane, both these byproducts are not very problematic - the ethane goes to atmosphere (no smoking nearby!) and acetic acid just floats around in the cell, trying weakly to donate a proton to something. The electrolyte is HCl.
The reaction will prolly produce some elemental Chlorine which will react immediately with the ethanol. Ethanol doesn't carry much current. Add a little HCl to both sides of the cell to facilitate this. In one side of the cell you now add your known quantity of thing-to-reduce. Adding an appropriate amount of HCl to supply enough protons to enable the reduction of thing-to-reduce can be worked out. HCl(aq) dissolves in ethanol. Probably your thing-to-reduce will too. Now, you need to add the electrickery. You want to pump electrons into the thing-to-reduce side of the system. So clamp the negative end of the battery charger to the electrode which is sitting in the same side of the cell as the stuff-to-reduce.
Switcheron. It will get warm, and the subsequent convection currents stir the cell for you. It helps a lot to have an ammeter so you can figure out how many moles of electrons you have pumped through so you know when to stop. For something like a nitrostyrene, which is orange, the colour change is diagnostic : a nitrostyrene will reduce fully down to a phenylethylamine, which is not orange, so the solution will become clarified.
The other reason there is HCl in the rig is to react with the product. Extraction by the usual methods... you pull the solvent off under vacuum, and the precursor is separated from the product with a solvent extraction in acidified water and say, diethyl ether.
Yeah, it's a good method.
I posted previously about a related experience concerning the manufacture of elemental bromine and KOH from KBr and water. Dejanews has it. Enjoy.
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He has some nifty stuff he sent me on electro-mescaline: I think Esteemed Leader Rhodium has it up already..
out
