About this Author
DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

Chemistry and Drug Data: Drugbank
Chempedia Lab
Synthetic Pages
Organic Chemistry Portal
Not Voodoo

Chemistry and Pharma Blogs:
Org Prep Daily
The Haystack
A New Merck, Reviewed
Liberal Arts Chemistry
Electron Pusher
All Things Metathesis
C&E News Blogs
Chemiotics II
Chemical Space
Noel O'Blog
In Vivo Blog
Terra Sigilatta
BBSRC/Douglas Kell
Realizations in Biostatistics
ChemSpider Blog
Organic Chem - Education & Industry
Pharma Strategy Blog
No Name No Slogan
Practical Fragments
The Curious Wavefunction
Natural Product Man
Fragment Literature
Chemistry World Blog
Synthetic Nature
Chemistry Blog
Synthesizing Ideas
Eye on FDA
Chemical Forums
Symyx Blog
Sceptical Chymist
Lamentations on Chemistry
Computational Organic Chemistry
Mining Drugs
Henry Rzepa

Science Blogs and News:
Bad Science
The Loom
Uncertain Principles
Fierce Biotech
Blogs for Industry
Omics! Omics!
Young Female Scientist
Notional Slurry
Nobel Intent
SciTech Daily
Science Blog
Gene Expression (I)
Gene Expression (II)
Adventures in Ethics and Science
Transterrestrial Musings
Slashdot Science
Cosmic Variance
Biology News Net

Medical Blogs
DB's Medical Rants
Science-Based Medicine
Respectful Insolence
Diabetes Mine

Economics and Business
Marginal Revolution
The Volokh Conspiracy
Knowledge Problem

Politics / Current Events
Virginia Postrel
Belmont Club
Mickey Kaus

Belles Lettres
Uncouth Reflections
Arts and Letters Daily
In the Pipeline: Don't miss Derek Lowe's excellent commentary on drug discovery and the pharma industry in general at In the Pipeline

In the Pipeline

« Naked Synthesis | Main | Vectibix Lurches A Bit »

March 25, 2007

Wandering Through the Hydrides

Email This Entry

Posted by Derek

If you want to get a feel for chemistry, one way might be to wander through the periodic table, picking one particular type of compound and seeing how things change as you go from element to element. (That's a good part of how Mendeleev figured the whole thing out, actually). But you'll want to pick carefully. Chlorides, for example, are rabble, as Primo Levi put it memorably. He was right: one chloride is often very much like another, even when the elements involved are very different - it's as if they've been pulled down to a lowest common denominator. I make some exception for the beautiful green of nickel (II) chloride, or the startling metallic purple of the anhydrous chromium (III) salt, but really, if you can't get something neat looking from the nickel or chromium compounds, you're really in a bad way. Most other chlorides are nondescript white powders. Boring!

Pick hydride instead. Hydrides are, if anything, a bit too exciting sometimes, since they tend to be rather reactive. With water, the usual reaction of a metal hydride is to strip off a proton immediately, giving you the hydroxide of the metal and plenty of lively hydrogen gas bubbling off. Sometimes the whole process is joyful enough for the whole mess to burst into flame.

That'll happen to you with the alkali metal hydrides, over on the left-hand side of the table. Organic chemists the world over know sodium hydride the best. It's a fine strong base - kinetically rather slow, but it deprotonates and spares not. By contrast, you hardly ever see much lithium hydride around. Potassium hydride makes an appearance every so often, though, to muttered curses, since it's usually stored as a slurried suspension in mineral oil and is correspondingly painful to weigh and dispense. It's lively stuff, too, and will set things on fire for you with great thoroughness. The higher alkali hydrides are things I've never seen, and I have no desire to, if their ferocity steps up like potassium does versus sodium.

The next row over (the alkaline earths) feature a compound that gets used every so often in the lab, calcium hydride. It's a good drying agent, because of that water reactivity, and solvents are distilled from a spoonful or two of it to make them anhydrous. But has anyone ever seen or handled magnesium hydride? I sure haven't. It's one of the things that the hydrogen-storage people mess around with, apparently, but you just don't come across it in an organic chemistry lab. Ditto for the other alkaline earths: barium hydride? Never seen it or even thought about it. I don't have access to Scifinder for the time being, since I have no desire for a second mortgage on my house just now, but I see from the web that apparently some people are using the stuff. Maybe it has a great future in organic synthesis, but it sure has no past.

This same pattern holds as you go across the elements. You come across some things that are used all the time (boron hydride, better known as borane), and some that are encountered once in a while (aluminum hydride, copper hydride). There are some well-studied chemicals that are just too reactive and nasty for most people, like phosphine or stannane, and some that are too reactive and nasty for any sane person at all, like mercuric hydride. Some of the nasty ones that are used much more outside of organic chemistry. People who do semiconductor work, for example, know all about the arsenic and germanium hydrides, for example, while few organic chemists have ever touched them.

And then there are some that I'm not sure anyone ever messes with at all. They don't seem to be particularly worse than their neighbors; they just sort of seem to be overlooked. Chemists in the audience - ever thought about titanium hydride? Me neither. Chromium hydride? Never once, until this evening (I wonder what color it is?) These are simple compounds, but even among the simple ones you keep finding all these streets that no one ever walks down. . .

Comments (23) + TrackBacks (0) | Category:


1. Jose on March 25, 2007 10:06 PM writes...

Several years ago, I had similar thoughts. CsH and RbH have never been prepared, or reported other than computational/theoretical studies.... I feel pretty certain it was tried with rather frightening results!

Permalink to Comment

2. Jal-Frezi on March 26, 2007 5:30 AM writes...

The only lab fire I've ever had was down to that hideous potassium hydride sludge (mixed with my own naivety and a sink with traces of waste acetone), but there was a JOC note last year about an air-stable, solid 1:1 mix of KH and paraffin that might make the sludge a thing of the past.

The ref is JOC(2006),71(23), 8973

Has anyone tried this stuff and more importantly I wonder if anyone sells it...

Permalink to Comment

3. schinderhannes on March 26, 2007 8:35 AM writes...

Hi Derek,

you forgot to mention carbon hydride, a very dangerous highly flammable gas (some also call it methane or natural gas :-)
Plus all ist higher hómologues, the hydro-carbons.

Permalink to Comment

4. Wavefunction on March 26, 2007 8:50 AM writes...

Nitrogen hydride is also not entirely uninteresting

Permalink to Comment

5. eugene on March 26, 2007 10:44 AM writes...

Yeah, I know what you mean Jal-Frezi, my potassium hydride came as a sludge too, so I washed off all the stupid mineral oil with hexanes several times to get that pure white and dry powder that I can now easily weigh out and add to my mixtures. In the glove box of course. I prefer my organolithiums as white solids too. A little pyrophoric though... But (more) air stable KH would be great to have of course.

Permalink to Comment

6. aa on March 26, 2007 11:29 AM writes...

lets not forget the hideous chalcogen hydrides... H2Se must have a disgusting odor if it is anything like MeSeH... Has anyone ever used this or H2Te?

Permalink to Comment

7. Hap on March 26, 2007 12:49 PM writes...

Has anyone made KH-impregnated silica gel? Someone had reported (and patented, I think), BuLi on silica gel as a relatively stable and manipulable compound, and I would think that you could do KH on silica as well.

Taber reported paraffin-suspended compounds as well - I repmember because silver carbonate suspended in paraffin was reported in the LaClair synthesis(?) of hexacyclinol/whatevertheycalleditol.

Permalink to Comment

8. Wavefunction on March 26, 2007 1:05 PM writes...

I doubt if anyone who has smelt H2Te has lived to tell the tale.
Consider the following charming conversation between Linus Pauling and Matthew Meselson:

LP: Well, Matt, you know about tellurium, the group VI element below selenium in the periodic chart of the elements?

MM: Uh, yes. Sulfur, selenium, tellurium ...

LP: I know that you know how bad hydrogen sulfide smells. Have you ever smelled hydrogen selenide?

MM: No, I never have.

LP: Well, it smells much worse than hydrogen sulfide.

MM: I see.

LP: Now, Matt, Hydrogen telluride smells as much worse than hydrogen selenide as hydrogen selenide does compared to hydrogen sulfide.

MM: Ahh ...

LP: In fact, Matt, some chemists were not careful when working with tellurium compounds, and they acquired a condition known as "tellurium breath." As a result, they have become isolated from society. Some have even committed suicide.

MM: Oh.

LP: But Matt, I'm sure that you would be careful. Why don't you think it over and let me know if you would like to work on the structure of some tellurium compounds?

I would love to smell some H2Po if it exists.

Permalink to Comment

9. DRogers on March 26, 2007 3:26 PM writes...

And let's not forget the infamous dihydride of oxygen...

"Dihydrogen Monoxide (DHMO) is a colorless and odorless chemical compound, also referred to by some as Dihydrogen Oxide, Hydrogen Hydroxide, Hydronium Hydroxide, or simply Hydric acid. Its basis is the unstable radical Hydroxide, the components of which are found in a number of caustic, explosive and poisonous compounds such as Sulfuric Acid, Nitroglycerine and Ethyl Alcohol."

Permalink to Comment

10. Stephen on March 26, 2007 4:50 PM writes...

Alkali metal rxns w/water are a fun trend to watch.

Permalink to Comment

11. kiwi on March 26, 2007 6:27 PM writes...

KH is a bit of an unpredictable beast, sometimes the dry powder is fine, sometimes its rather angry. its pretty easy to just strip it off in the flask with 2x pentane washes, vac it down and weigh. probably could make the solid paraffin dispersion by that method quite quickly/cheaply

Permalink to Comment

12. Spiro on March 26, 2007 7:46 PM writes...

To Jal-Frezi about KH in paraffin

>Has anyone tried this stuff and more importantly I wonder if anyone sells it...

I tried that stuff : it does work very well and is user-friendly. You can scale up safely, and even better, scale down to as little as a 0.1 mmol scale reaction without a dry box. Weigh your 5 mg or 5 kg of KH (in paraffin) in air and put it in your reactor, argon-flush, and add your dry solvent.

Now, I wish I had all my air-sensitive reagents in paraffin....

By the way, it is sold by Wilmington Pharma Tech.

Permalink to Comment

13. Tot. Syn. on March 27, 2007 3:49 AM writes...

Have any of you seen the prep for NaH? I thought about this a few weeks ago, and had a look on Wikipedia, where they describe the process as bubbling hydrogen gas through liquid sodium. Erk!!! I'd presume the procedure for KH is the same, so I can definitely understand why CsH and RbH aren't available from Aldrich...

Permalink to Comment

14. Jonadab the Unsightly One on March 27, 2007 10:35 AM writes...

> they describe the process as bubbling hydrogen gas through liquid sodium

One wonders why they don't have undergrad students do that in lab...

Permalink to Comment

15. Harry on March 27, 2007 11:55 AM writes...

Well, I can talk about my experiences making Sodium Amide in 20 kg batches. Much fun to be had in dropping 2 lb bricks of Sodium metal into a stirred reactor full of liquid ammonia with just a touch of Ferric Nitrate for a catalyst. Wait til the Hydrogen evolution dies down and chuck in another until you've added the required amount. Once thats done you simply heat a bit to drive off the excess ammonia and dump the dry Sodamide into antistatic bags and seal. I guess you might consider Sodamide to be a sort of mixed hydride.

I also made Lithium Amide in the same way, and like the hydrides, Lithamide is tame compared to Sodamide. I'd never ever want to make Potassium Amide.

Ahh... good times... good times.

My $0.02, YMMV.

Permalink to Comment

16. milkshake on March 27, 2007 7:26 PM writes...

I have seen old lab preparation for NaH, it used liquid Na dispersion in hot xylenes and hydrogen.

NaH is made in huge quantities for steel metalurgy use (without the solvent I think). The trick is how to prepare a fluffy NaH powder rather than hard chunky stuff that is difficult to dig out from the reactor. Impure hydrogen obtained from petrochemical precesses supposedly gives nicer NaH product than electrolytically-pure hydrogen.

Permalink to Comment

17. Yogi on March 28, 2007 4:29 PM writes...

This post on hydride is filled with great insights. You're absolutely right about some of the hydride the semi-conductor industry uses for metal-vapor deposition. I found out the other day on Wikipedia that a new agent being used in semiconductor is isobutyl germane (iso-BuGeH3) which appear to be an easy to handle liquid. I was wondering what kind of reducing power this would have and potential selectivity vs something like DIBAL. Has anyone seen any use of this organo-germanium in chemistry? I'm really curious

Permalink to Comment

18. Jose on March 29, 2007 6:32 PM writes...

Yogi- via google, strange little review of organogermanium chemistry.

Permalink to Comment

19. Yogi on March 31, 2007 6:58 AM writes...

Thanks a lot Jose I'm going to have a look at that review. Not to many schemes...

Permalink to Comment

20. Morten on March 31, 2007 11:11 AM writes...

LiD packs quite a punch in the Teller-Ulam configuration. I know lithium deuterium technically isn't a hydride but you organic types rarely seem to care about isotopes.
My only question now is why do they call it an H-bomb when it's mainly deuterium and tritium?

Permalink to Comment

21. ****** on August 24, 2007 9:11 AM writes...

From: High School Chemistry and Math Teacher

Question: Can metal hydrides be used to reduce (no pun intended) or mitigate (or treat) galvanic corrosion in brass -- particularly along solder joints? What hydrides could be delivered to a corroded joint and yield a reduction of oxidized metal species of Ag, Pb, and Zn?

CuH2 + ZnO (etc.)

I am presently treating corrosion with polysiloxanes, I have also considered graphite impregnation.


Permalink to Comment

22. dave weston on July 24, 2008 6:57 AM writes...

I just found this by accident. I made Rb Abnd Cs hydrides for my PhD in about '93. Direct combination. Pretty easy really.

They tend to detonate slightly in air though.

Nopw play with MgH2. Cool.

Permalink to Comment

23. Doug Taber on November 30, 2009 2:06 PM writes...

KH 50% by weight in paraffin is now available from SigmaAldrich, product #708860. As mentioned in a post above, this material is easy to handle both on a small scale and on a large scale.

Permalink to Comment


Remember Me?


Email this entry to:

Your email address:

Message (optional):

Gitcher SF5 Groups Right Here
Changing A Broken Science System
One and Done
The Latest Protein-Protein Compounds
Professor Fukuyama's Solvent Peaks
Novartis Gets Out of RNAi
Total Synthesis in Flow
Sweet Reason Lands On Its Face