This May Be the Last Straw

So I bought this awesome laser pointer/pen/stylus 3-in-1 thingy for $20 from the bookstore, and the douchebag REU student who's too shy to ask to borrow it has both stolen and lost it. That I can deal with; after all, it's just a pen and my mom (via my student ID account) paid for it. But today...I walked into my office to find all my books pushed aside and the REU student's computer (courtesy of UK, the rotten bastards) on my desk.

So essentially, I have no desk. We can't isolate the PCN radical, all the parts for the matrix isolation system are in the machine shop, and now I have no desk.

And I was beginning to think not doing an REU was a good thing. Thanks for proving me wrong UK!

Tag Team, Back Again

So it's been a while since my last post...I've been spending a lot of time learning the laser lab and reorganizing the ol' disiloxane synthesis project. My biggest problem at the moment is getting my hands on a reliable supply of hydrogen iodide, which we use in turn to make silyl iodide using phenylsilane. Matheson TG has stopped selling it, probably because it wasn't economically sound to offer it. During the synthesis I use, which involves red phosphorus, iodine, and water, unwanted byproducts tend to coat the iodine shards and insulate the valuable inner iodine from reacting. Thus, I decided I'm going to beat the hell out of the iodine, grounding it into a powder with a large surface area (and releasing some stored-up anger in the process).

The alternative to perfecting the syntheses of HI and silyl iodide is making a different halosilane from (pre-bought, hooray!) hydrogen bromide or chloride. The strange thing is, most of the halosilane literature I've looked at used silyl chloride or silyl bromide. Where my advisor got the idea for silyl iodide, I have no idea. Perhaps the disiloxane hydrolysis doesn't work quite as well with bromide or chloride. Yet, hexamethyldisiloxane is made using silyl chloride.

Cloush is in Ohio for a conference this week. When the cat is away, the mice will play... :-D

Gems from UK's Inorganic Lab "Lab Safety" Webpage

That's NOT dry ice! I didn't take the picture, but the caption underneath said that these peroxide crystals "autodetonated shortly after this photo was taken." They formed in an old bottle of ispropyl ether.

The page says something about not letting liquid oxygen condense in a trap, which seems odd to me (anything colder than liquid nitrogen seems too expensive to use in an undergrad lab!). It links to a video showing Purdue students lighting a charcoal grill with a lit cigarette and three gallons of liquid oxygen. If we really are going to possess the cooling power to condense oxygen out of the air in CHE 450G, I commend you University of Kentucky.

EDIT: The boiling point of oxygen is higher than that of nitrogen, so liquid oxygen will condense out of a constant stream of air. My bad!
Oh wow, this is a good one. In the spring of 1997 in advanced organic lab (CHE 533), someone dumped methylene chloride into a waste container containing some icky stuff, including nitric acid. He capped the waste bottle, and a couple of minutes later BAM! Shards of glass and chemicals went flying across the room. Miraculously, no one was injured.

PDA for PDIs!

This paper caught my eye because I recalled my one regular commenter (come on dear readers...where are you? :'-( ) working with perylenes in the past. The reactant in the middle is imide-substituted perylene diimide, PDI. DMP PDI, compound 1a, has some interesting solid-state photochemical quirks, so who knows, substituting the perylene core could lead to the next big thing in photonic organics. So the author says.

The first reaction described looks less than impressive: for 1a, 26% came out a mixture of dibrominated isomers (1,6-3a and 1,7-3a), 57% came out monobrominated, and 15% remained unreacted. Restricted rotation of the bulky R groups about the C-N bond meant two isomers for each potentially brominated carbon. The author goes on to describe a reaction using a refluxing solution of bromine that gives exclusively dibrominated product overnight, with a 1,7/1,6 ratio of 3:1. The regioisomers can be separated by recrystallization from a 1:1 solution of dichloromethane and hexane.

Sonogashira coupling of 2a with TMS acetylene works, as does nucleophilic substitution by piperidine.


Bromination causes an interesting "core twist" vibration involving, well, the twisting of the perylene core. Energy barriers associated with the motion were relatively low and thus interconversion between the two "twist states" of the molecule is relatively easy.

Enter the Matrix

My lab's matrix IR apparatus is almost done, and naturally the guy I'm working with just had to have a baby. In the meantime, I get to watch over it and get things ready for our first target molecule, chlorosilylene. It is the silicon analogue of the one, the only chlorocarbene.

Herzberg was the first to investigate this molecule, having produced it in 1964 by flash photolysis of chlorosilane. As research on CVD intermediates picked up steam, a number of research groups obtained varied results on the extent to which chlorosilylene is produced during CVD. The Clouthier group, of which I am a humble member, revived spectroscopic studies of the radical by performing laser-induced fluoresence experiments on it in 1997. They obtained a whole slew of rotational constants, geometric parameters, and most importantly vibrational frequencies exhibited by the molecule. That's right, a whole slew.

Our goal is to observe HSiCl's ground-state vibrational frequencies directly by jolting trichlorosilane in an electric discharge and performing matrix IR.

Pictures of the apparatus to follow soon!

Latest on the Rotaxane Front

Something about rotaxanes intrigues me. If you think about it, the fact that such massive molecules can come together to form ordered, interlocked units is an outright entropic miracle. The field of rotaxane synthesis is particularly suited to what I like to call "miracle reactions," reactions with laughably simple procedures that give complicated molecules in disturbingly high yield. One such reaction can be found in this recent paper by Hirose et al. from Osaka University.

Their idea, stylized in the picture, was to first connect the center of a dumbbell to a ring, then use nucleophilic attack (specifically, aminolysis) by the other half of the dumbbell to form the final rotaxane. Hiratani did something similar to this back in 2002.

The ring is a phenolic crown ether with side groups attached. Why the phenol? Because the first step is an esterification involving the phenolic OH (which points inside the ring) and the half axle, a benzoyl chloride. The resulting "half-rotaxane" is just a benzene-stoppered ester of the crown ether. To form the final rotaxane, an amine with a bulky group attached is added to the half-rotaxane. Nitrogen attacks the carbonyl carbon of the ester group, and voila! The axle becomes an amide and the ring reverts back to a phenolic crown ether. Miraculously, this reaction requires no heat or special treatment of any kind aside from column chromatography. Put the stuff together, stir, wait three days, evaporate the solvent, and voila! Rotaxane city.

Bromosilane go BOOM!

Well ladies and gentlemen, I've reached a milestone...I caused my first explosion in lab yesterday. I was cleaning out a flask after a cold-trap separation of the reaction products of the bromosilane synthesis reaction:

PhSiH3 + HBr --> SiH3Br + C6H6

I believed that no bromosilane (or perhaps a negligibly small amount) remained in said flask. I was wrong. Set the flask inside the hood, put a little heat on it to vaporize things, took a step back to walk away, and BAM! A huge, quick flame burst out of the flask's mouth, accompanied by a horrible noise like a gunshot. Incredibly, the flask was just fine, save for a few brown spots that 48% HF took care of right away. Nothing got burned in the hood either. It was just a really loud, scary noise and a few flames. Doesn't mean it didn't scare the pants off me, of course.

The picture, for your viewing pleasure, is the LUMO of bromosilane.