Trying to make OTC trimethylsilyl chloride

[megalomania]

I have been researching as of late a way to make some trimethylsilyl chloride from OTC ingredients to use as a protecting group in other OTC needs. I have been having trouble finding any information regarding the synthesis of trimethylsilyl chloride itself. It seems to ubiquitous to be found in the available literature, but not enough to be in some industrial literature. I praise the powers that be for Rhadon’s recent upload of the Ullman’s Encyclopedia which may help a bit.

I would just like to know if anyone has any references handy about this chemical. I really hope I will be able to make it from tetrachlorosilane. One can make magnesium silicide from magnesium metal and silicon dioxide (fine powder), and react that with HCl to form silane gas. This gas can be directly combined with chlorine gas to make tetrachlorosilane. Alternatively one can pass chlorine gas over a mix of silicon dioxide and carbon heated to a red heat to make tetrachlorosilane. Tetrachlorosilane will react with methyl zinc (itself made by reacting methyl iodide and zinc I believe) to form tetramethylsilane. I can only speculate at this point that one can form trimethylsilyl chloride by incomplete reaction of methyl zinc, perhaps by limiting the zinc compound.

Knowing how they do this industrially may lead me to find a better route.

[megalomania]

Horray, I think I have found a route today. More specifics as i work them out, but it involves tetramethylsilane and chlorine with a catalyst at a modest pressure and temperature, all seemingly OTC'able.

[John Ashcroft]

I don't see the point in going to the trouble to prepare SiH4 when SiCl4 can be prepared by passing dry chlorine over heated SiCl2.

How about preparing trimethylsilyl chloride by adding a stoichemitric quantity of CH3MgCl to anhydrous SiCl4 (with the appropriate solvents, of course)?

[megalomania]

I really dislike the high temperature reactions myself; this is just a personal prefeance as I find running them to be a bit difficult and unreliable. I know one can run the reaction with silicon and chlorine gas, I did not know about SiCl₂. Of course, where does one get the SiCl₂?

I would love to try the Grignard route, however I have found no references for it. I have read many allusions to the process, and I have seen the general outline, but the specifics are missing. The gold is in the details.

I have decided to go with a nifty circuitous route involving methyl aluminum dichloride (MAD) and silica gel (or any basic silicon containing compound excepting sand). In this all OTC route I can make the MAD from aluminum foil, methyl chloride, and aluminum trichloride (see my website, it is made from Al and Cl). The MAD reacts with silica gel to form tetramethylsilane (TMS) quite readily. The TMS is reacted with antimony trichloride (hence my recent post asking about it) to form trimethylchlorosilane in a nifty pressurized setup along with chlorine gas. The good thing is this route is all OTC.

My goal is to use the stuff as a protecting group on ethylene bromohydrin or chlorohydrin in which to run a Grignard reaction with ethylene oxide to extend the carbon chain and make, after deprotection, 1,4-butanediol. From here it is all OTC GHB or THF depending on what you want to do. I am sure my friends over at the Hive will enjoy this.

Having OTC trimethylchlorosilane will likely come in handy in many ways. If someone would like to suggest other handy protecting groups please do so. The above process of making MAD can be easily adapted to make other alkyl aluminum chlorides, which in turn can make other alkyl silanes. TMCS is just easier to add and remove than other alkyl silanes.

About that, I could use some help narrowing down a good acid scavenger for the silation reaction. When trimethylchlorosilane is added to an alcohol forming an ether it produces HCl as a byproduct. The silyl ether is quite reactive to acids (one of the reasons it makes a good protecting group is the ease of removal, especially in an OTC setting; add a little HCl and it breaks off) which is not a good thing as it will form an equilbrium that does not favor the silyl ether. In fact I think acid converts the silyl portion into a silyl alcohol (please correct me if I am wrong I would like to know). If true that means our trimethylchlorosilane will end up as trimethylsilyl alcohol, a complete waste :( A scavenger is needed to react with the acid as it is formed instead of it deprotecting the target molecule.

I have heard such things as pyridine or triethylamine could be used. I would prefer something, ehh, OTC. It does not have to be perfect at the OTC level, maybe something simple like sodium hydroxide or zinc oxide would work? What I really need to find is some old literature about using silanes as protecting groups; the new stuff all use fancy chemical reagents. If I can’t find a good OTC scavenger this would hardly be a useful OTC project.

[John Ashcroft]

I take back my suggestion to prepare SnCl4 from SnCl2. I'm worried that heating SnCl2*2H2O (prepared by dissolving tin in HCl) will not yield SnCl2. But, SnCl4 can still be prepared by passing dry chlorine over heated tin. Beware, the reaction can be vigorous.

The silyl ether would probably react with acid to reform the silyl chloride and the alcohol. Keep the reactants dry, and the reaction equilibrium between the silyl chloride and the alcohol should be far to the right.

Amines are easy OTC compounds if you can get ahold of nickel salts (for urishiba nickel - NiO and NiCO3 can be bought from ceramics suppliers) or of mercury (for Al/Hg amalgam - thermometers, switches, etceteras). They're just a reductive amination away from your favorite aldehyde/ketone! See this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=534 for discussion of preparing uber-OTC nickel.

[Mr Cool]

"SiCl4 can be prepared by passing dry chlorine over heated SiCl2."

"I take back my suggestion to prepare SnCl4 from SnCl2. I'm worried that heating SnCl2*2H2O (prepared by dissolving tin in HCl) will not yield SnCl2. But, SnCl4 can still be prepared by passing dry chlorine over heated tin."

Damn that Si <=> Sn equilibrium reaction! The bane of all semiconductor research... ;) :D

(But you are right, heating SnCl2*2H2O --> Sn(OH)2 + 2 HCl, although I believe it can be dessicated over H2SO4 etc. Anhydrous chlorides need to be prepared by passing chlorine gas over the solid elements and condensing/subliming the vapours.)

Edit: "From here it is all OTC GHB or THF depending on what you want to do."

THF is OTC, and Na-GHB can be made from it by oxidising it to -OCH2CH2CH2(CO)- (I have seen NaOCl and HNO3 mentioned for doing this), then breaking the ring with NaOH to form Na-GHB.

[John Ashcroft]

Damn that Si <=> Sn equilibrium reaction! The bane of all semiconductor research...

Oh my. I really shouldn't be posting anything when I'm as ill as I've been. Feel free to jettison me into space. :eek:

[megalomania]

I have seen the posts at the Hive about converting THF to GHB and I don’t think they were conclusive. I gathered the reaction was more of a pipe dream as no one was able to produce the goods. I also know one can get THF from pipe cement, but that seemed like such an expensive way to go about it. Cheap bastard that I am I want something more plentiful.

I would think it may be a bit easier to make triethylamine from ethylbromide and ammonia in alcohol. Actually this would be a three step process because this produces ethylamine hydrobromide, which must be reacted with a base to make ethylamine. In the second part the ethylamine is again reacted with ammonia in alcohol to produce diethylamine hydrobromide, again add base. In the third we react this yet again to get triethylamine.

I would gather ethylamine or diethylamine may be just as good as triethylamine since both are bases and liquid at reasonable temperatures (OK maybe not so much ethylamine). These just need to dissolve the reactants.

I didn't realize it before, but I suppose the HCl can't react as there should be no water in the reaction. This could be why some references recommend using a nitrogen atmosphere. For the life of me I didn't see any chemical that would react to air, so it must be the moisture then.

[John Ashcroft]

If you're looking for an amine simply for its basic properties, I suggest reductive amination on acetone (or MEK, if you're wanting a higher-boiling amine) using Al/Hg amalgam in ammonia/alcohol/water. I've found that it's a *lot* easier than the alkyl halide + ammonia process - largely because alkyl halides (unless the substrate alcohol is tertiary) are a nuisance to prepare OTC.

[Mr Cool]

John, could you please post the reductive amination procedure for acetone?