Material hazards

Explosive chemicals.  Ahhh yes. <maniacal facial expression with insane
laughter>  Well, first of all Karen, I sent in a short note about picric
acid. Didn't you read it?? (Obviously I'm terribly hurt. :-) )

Apart from that.... 

1)  Hydrogen peroxide is normally stabilized with tin chloride (I tend
to prefer this one), tetrasodium pyrophosphate (aka TSPP, pyro, sodium
pyrophosphate or tetrasodium dipolyphosphate), acetanilide (aka
N-phenylacetamide) or other similar organics.  Yes, it, like many strong
oxidizers can cause combustible materials to "spontaneously" burn. The
interesting thing is that in spite of the fact that if you want 30%
H2O2, it is reactive enough (and unstable enough) that it is hard to
store.  On the other hand, it tends to form a death grip on some
materials like cellulose. I remember after talking with Bob McComb about
the peroxide fuming test we (Kodak and IPI) were working on for ANSI, I
tested a piece of chromatography paper more than 48 hours after it had
been used (a small volume of 2% H2O2 had been applied and evaporated.)
Even after more than two days I could easily detect peroxides in the
paper.

As a consequence of the reactivity of hydrogen peroxide, we buy it in
100 mL bottles and store them in the refrigerator.  In this way, "fresh"
bottles are "opened" (since the bottles are vented, "opened" is not
quite the right word) fairly often.  It is also very important to
minimize contamination of the bottle so follow good lab practice -- pour
H2O2 into a beaker and then measure out the quantity needed.  Do not
pour excess H2O2 back into the bottle.  Some contaminants may cause
hydrogen peroxide to decompose with explosive force. I have only seen
100 mL bottles produced by EM Science (available through places like VWR
Scientific).  Note also that the vented bottles tend to leak especially
if the bottles have not been stored or shipped up-right.  Wear gloves
when handling the outer bags and the bottle.  One last precaution: 90%
hydrogen peroxide is used in rockets (!!)

2) All ethers autoxidize (via a free radical mechanism).  In this
regard, isopropyl ether (aka diisopropyl ether, 2-isopropoxypropane or
2,2'-oxybis[propane]) is probably the most dangerous.  However, ethyl
ether (what we commonly call "ether" or diethyl ether) and
tetrahydrofuran (aka THF, diethylene oxide or tetramethylene oxide) are
also quite dangerous. About 10 years ago I had the "pleasure" of seeing
the aftermath of an ether explosion (I was visiting my old high school
when it happened.)  There were four - 1 pt cans of ethyl ether stored in
an "explosion proof" lab freezer. Fortunately only 1 can exploded.  The
location was a prep. room/office between two large science classrooms
(enough lab benches in each for 40 to 50 students).  There was about a 4
foot aisle between the front of the fridge/freezer and a huge (!) cinder
block "book" shelf 15 X 10 X 4 ft. The explosion tore off the
fridge/freezer door (naturally).  A steel door leading out into the
school hall was folded (top and bottom hinges destroyed; crease line
between the doorknob latch (where it fits into the steel door frame) and
the center hinge.)  The book shelf was pushed about 2 feet (the junior
and senior football teams were called in a couldn't move it back. It had
to be disassembled.)  Most of the ceiling tiles in both classrooms were
on the floor and all of the wooden window frames (not just the glass) in
both classrooms were blown out.  Fortunately, no one is hurt (or killed)
in the blast.  All that action from just one can (in an explosion proof
lab freezer no less!)  In another case, a 2 liter container of THF being
purified exploded demolishing the lab, moving the walls several inches
(!) and knocking over the bookshelves in the adjacent office. (No, I
didn't get to see this one.)

Often THF and ethyl ether are stabilized (with BHA, p-cresol,
hydroquinone or 4,4'-thiobis(6-tert-butyl-m-cresol)), but they still
should be handles carefully.  In particular, watch for strong oxidants
such as H2O2 above. Often nitric acid is forgotten as a strong oxidizer
(since it is more widely known as a strong acid), but dry nitric acid
will cause ether to explode rather violently.

Peroxides in ethers may be tested for using a standard test. (For
convenience I have taken this from Laboratory Text for Organic Chemistry
by Daniel J. Pasto and Carl R. Johnson and published by Prentice-Hall
Inc. 1979.)

"Place 10 mL of the ether in a test tube and add 1 mL of a freshly
prepared 10% aqueous potassium iodide solution.  Acidify with several
drops of dilute sulfuric acid.  Add a drop of starch indicator.  A blue
color is indicative of the presence of peroxides. (Starch-iodide paper
is not reliable for this test.)"

Peroxides may be removed using solutions of ferrous sulfate or cuprous
chloride. Dry (anhydrous) ether may be purified by refluxing 12 to 24
hours with lithium aluminum hydride (LiAlH4).  ETHER MUST BE DRY! LiAlH4
reacts violently with water!!  The refluxed ether may then be distilled
(but not to dryness).  The remaining LiAlH4 residues should be destroyed
by the slow, cautious addition of ethyl acetate or 10% sodium hydroxide.
(DO NOT USE LiAlH4 refluxing with THF! Exothermic cleavage of THF by
metal halides may cause explosions!)

The safest method of getting rid of peroxides in ethers is to call
campus safety to dispose of the whole can (or bottle.)  :-)

Organic labs often store dry ethers over molecular sieves (to absorb
water) and under a nitrogen atmosphere (to prevent autoxidation.)

Chemical substitutions should only be done after considering what you
want to use the chemical for.   Many substitutions are only useful in
some situations while being totally useless in other cases.  Also
consider the degree of gain. Often xylenes or toluene are substituted
for the more dangerous benzene, but personally, I'm not exactly thrilled
about using the substituted solvents either.  Similarly, chloroform for
carbon tetrachloride was a great substitute until there were so many
questions about the safety of chloroform. On the other hand, guano makes
a reasonably safe (though not too pleasant) substitute for ammonium
phosphate.  (The dangers of guano are mainly found in collecting it, but
may be reduced by remembering to wear a hat and not to look up.) Looking
forward to seeing what campus safety recommends to you.

Best regards,

-Doug
dwnpph [at] ritvax__bitnet

                                  ***
                  Conservation DistList Instance 5:14
                  Distributed: Friday, August 9, 1991
                        Message Id: cdl-5-14-002
                                  ***